Name: preparation of silicon nanowire field-effect transistor for chemical and biosensing applications
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Description: Watch this Scientific Journal Video about Preparation of Silicon Nanowire Field-effect Transistor for Chemical and Biosensing Applications at JoVE.com

This research was financially supported by Ministry of Science and Technology, Taiwan (104-2514-S-009 -001, 104-2627-M-009-001 and 102-2311-B-009-004-MY3). We thank the National Nano Device Laboratories (NDL) for its valuable assistance during device fabrication and analysis.

1. Fabrication and Preservation of pSNWFET Devices
<ol>
	<li>Device Fabrication 
	Note: The pSNWFET was fabricated using a sidewall spacer technique as previously reported23,24.
	<ol>
		<li>Prepare the gate dielectric layer.
		<ol>
			<li>Cap a 100-nm-thick thermal oxide (SiO2) layer on a Si substrate by using the wet oxidation process25 (O2 and H2 process gas at 980 &#176;C for 4 hr).</li>
			<li>Deposit a 50-nm-thick nitride (Si3N...

<ol>
	<li>Lin, C. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+composition+and+interactions+of+mobile+charges+with+immobilized+molecules+on+polycrystalline+silicon+nanowires.">Surface composition and interactions of mobile charges with immobilized molecules on polycrystalline silicon nanowires.</a> Sensor Actuat B-Chem 211. 211, 7-16 (2015).</li><li>Patolsky, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+detection+of+single+viruses.">Electrical detection of single viruses.</a> P Natl Acad Sci USA. 101, 14017-14022 (2004).</li><li>Wang, W. U., Chen, C., Lin, K. H., Fang, Y., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+detection+of+small-molecule-protein+interactions+by+using+nanowire+nanosensors.">Label-free detection of small-molecule-protein interactions by using nanowire nanosensors.</a> P Natl Acad Sci USA. 102, 3208-3212 (2005).</li><li>Patolsky, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection,+stimulation,+and+inhibition+of+neuronal+signals+with+high-density+nanowire+transistor+arrays.">Detection, stimulation, and inhibition of neuronal signals with high-density nanowire transistor arrays.</a> Science. 313, 1100-1104 (2006).</li><li>Bi, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+electrochemical+calcium+sensors+by+using+silicon+nanowires+modified+with+phosphotyrosine.">Development of electrochemical calcium sensors by using silicon nanowires modified with phosphotyrosine.</a> Biosens Bioelectron. 23, 1442-1448 (2008).</li><li>Lin, T. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+detection+of+protein-protein+interactions+using+a+calmodulin-modified+nanowire+transistor.">Label-free detection of protein-protein interactions using a calmodulin-modified nanowire transistor.</a> P Natl Acad Sci USA. 107, 1047-1052 (2010).</li><li>Mishra, N. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultra-sensitive+detection+of+bacterial+toxin+with+silicon+nanowire+transistor.">Ultra-sensitive detection of bacterial toxin with silicon nanowire transistor.</a> Lab on a chip. 8, 868-871 (2008).</li><li>Lin, C. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasensitive+detection+of+dopamine+using+a+polysilicon+nanowire+field-effect+transistor.">Ultrasensitive detection of dopamine using a polysilicon nanowire field-effect transistor.</a> Chem Commun. , 5749-5751 (2008).</li><li>Hahm, J., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+ultrasensitive+electrical+detection+of+DNA+and+DNA+sequence+variations+using+nanowire+nanosensors.">Direct ultrasensitive electrical detection of DNA and DNA sequence variations using nanowire nanosensors.</a> Nano Lett. 4, 51-54 (2004).</li><li>Lin, C. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly-silicon+nanowire+field-effect+transistor+for+ultrasensitive+and+label-free+detection+of+pathogenic+avian+influenza+DNA.">Poly-silicon nanowire field-effect transistor for ultrasensitive and label-free detection of pathogenic avian influenza DNA.</a> Biosens Bioelectron. 24, 3019-3024 (2009).</li><li>Wu, C. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+biosensing+of+a+gene+mutation+using+a+silicon+nanowire+field-effect+transistor.">Label-free biosensing of a gene mutation using a silicon nanowire field-effect transistor.</a> Biosens Bioelectron. 25, 820-825 (2009).</li><li>Zhang, G. -. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silicon+nanowire+biosensor+for+highly+sensitive+and+rapid+detection+of+Dengue+virus.">Silicon nanowire biosensor for highly sensitive and rapid detection of Dengue virus.</a> Sensor Actuat B-Chem. 146, 138-144 (2010).</li><li>Lu, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CMOS-compatible+silicon+nanowire+field-effect+transistors+for+ultrasensitive+and+label-free+microRNAs+sensing.">CMOS-compatible silicon nanowire field-effect transistors for ultrasensitive and label-free microRNAs sensing.</a> Small. 10, 2022-2028 (2014).</li><li>Zheng, G., Patolsky, F., Cui, Y., Wang, W. U., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiplexed+electrical+detection+of+cancer+markers+with+nanowire+sensor+arrays.">Multiplexed electrical detection of cancer markers with nanowire sensor arrays.</a> Nat Biotechnol. 23, 1294-1301 (2005).</li><li>Choi, J. H., Kim, H., Choi, J. H., Choi, J. W., Oh, B. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Signal+enhancement+of+silicon+nanowire-based+biosensor+for+detection+of+matrix+metalloproteinase-2+using+DNA-Au+nanoparticle+complexes.">Signal enhancement of silicon nanowire-based biosensor for detection of matrix metalloproteinase-2 using DNA-Au nanoparticle complexes.</a> ACS Appl Mater Interfaces. 5, 12023-12028 (2013).</li><li>Lin, T. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+silicon+nanowire+field-effect+transistors+for+fast+protein-protein+interaction+screening.">Improved silicon nanowire field-effect transistors for fast protein-protein interaction screening.</a> Lab Chip. 13, 676-684 (2013).</li><li>Chen, H. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+sensitive+and+selective+magnetic+graphene+composite-modified+polycrystalline-silicon+nanowire+field-effect+transistor+for+bladder+cancer+diagnosis.">A sensitive and selective magnetic graphene composite-modified polycrystalline-silicon nanowire field-effect transistor for bladder cancer diagnosis.</a> Biosens Bioelectron. 66, 198-207 (2015).</li><li>Lee, H. S., Kim, K. S., Kim, C. J., Hahn, S. K., Jo, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+detection+of+VEGFs+for+cancer+diagnoses+using+anti-vascular+endotherial+growth+factor+aptamer-modified+Si+nanowire+FETs.">Electrical detection of VEGFs for cancer diagnoses using anti-vascular endotherial growth factor aptamer-modified Si nanowire FETs.</a> Biosens Bioelectron. 24, 1801-1805 (2009).</li><li>Chua, J. H., Chee, R. E., Agarwal, A., Wong, S. M., Zhang, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+electrical+detection+of+cardiac+biomarker+with+complementary+metal-oxide+semiconductor-compatible+silicon+nanowire+sensor+arrays.">Label-free electrical detection of cardiac biomarker with complementary metal-oxide semiconductor-compatible silicon nanowire sensor arrays.</a> Anal Chem. 81, 6266-6271 (2009).</li><li>Lu, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+and+rapid+electrical+detection+of+hTSH+with+CMOS-compatible+silicon+nanowire+transistor+arrays.">Label-free and rapid electrical detection of hTSH with CMOS-compatible silicon nanowire transistor arrays.</a> ACS Appl Mater Interfaces. 6, 20378-20384 (2014).</li><li>Chen, H. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetic-composite-modified+polycrystalline+silicon+nanowire+field-effect+transistor+for+vascular+endothelial+growth+factor+detection+and+cancer+diagnosis.">Magnetic-composite-modified polycrystalline silicon nanowire field-effect transistor for vascular endothelial growth factor detection and cancer diagnosis.</a> Anal Chem. 86, 9443-9450 (2014).</li><li>Zhang, Y. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silicon+Nanowire+Biosensor+for+Highly+Sensitive+and+Multiplexed+Detection+of+Oral+Squamous+Cell+Carcinoma+Biomarkers+in+Saliva.">Silicon Nanowire Biosensor for Highly Sensitive and Multiplexed Detection of Oral Squamous Cell Carcinoma Biomarkers in Saliva.</a> Anal Sci. 31, 73-78 (2015).</li><li>Lin, H. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+and+low-cost+method+to+fabricate+TFTs+with+poly-Si+nanowire+channel.">A simple and low-cost method to fabricate TFTs with poly-Si nanowire channel.</a> Ieee Electr Device L. 26, 643-645 (2005).</li><li>Lin, H. C., Lee, M. H., Su, C. J., Shen, S. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+and+characterization+of+nanowire+transistors+with+solid-phase+crystallized+poly-Si+channels.">Fabrication and characterization of nanowire transistors with solid-phase crystallized poly-Si channels.</a> Ieee T Electron Dev. 53, 2471-2477 (2006).</li><li>Doering, R., Nishi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Handbook of semiconductor manufacturing technology. , (2008).</li><li>Lu, M. P., Hsiao, C. Y., Lai, W. T., Yang, Y. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Probing+the+sensitivity+of+nanowire-based+biosensors+using+liquid-gating.">Probing the sensitivity of nanowire-based biosensors using liquid-gating.</a> Nanotechnology. 21 (425505), (2010).</li><li>Gaspar, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Digital+lock+in+amplifier:+study,+design+and+development+with+a+digital+signal+processor.">Digital lock in amplifier: study, design and development with a digital signal processor.</a> Microprocess Microsy. 28, 157-162 (2004).</li><li>Vezenov, D. V., Noy, A., Rozsnyai, L. F., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Force+titrations+and+ionization+state+sensitive+imaging+of+functional+groups+in+aqueous+solutions+by+chemical+force+microscopy.">Force titrations and ionization state sensitive imaging of functional groups in aqueous solutions by chemical force microscopy.</a> J Am Chem Soc. 119, 2006-2015 (1997).</li><li>Townsend, M. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+evaluation+of+the+FluChip+diagnostic+microarray+for+influenza+virus+surveillance.">Experimental evaluation of the FluChip diagnostic microarray for influenza virus surveillance.</a> J Clin Microbiol. 44, 2863-2871 (2006).</li><li>Wang, L. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+detection+and+differentiation+of+Newcastle+disease+and+avian+influenza+viruses+using+oligonucleotide+microarrays.">Simultaneous detection and differentiation of Newcastle disease and avian influenza viruses using oligonucleotide microarrays.</a> Vet Microbiol. 127, 217-226 (2008).</li><li>Lin, C. -. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recovery+Based+Nanowire+Field-Effect+Transistor+Detection+of+Pathogenic+Avian+Influenza+DNA.">Recovery Based Nanowire Field-Effect Transistor Detection of Pathogenic Avian Influenza DNA.</a> Jpn J Appl Phys. 51 (02BL02), (2012).</li><li>Lee, K. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Well+controlled+assembly+of+silicon+nanowires+by+nanowire+transfer+method.">Well controlled assembly of silicon nanowires by nanowire transfer method.</a> Nanotechnology. 18 (445302), (2007).</li><li>Li, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sequence-specific+label-free+DNA+sensors+based+on+silicon+nanowires.">Sequence-specific label-free DNA sensors based on silicon nanowires.</a> Nano Lett. 4, 245-247 (2004).</li><li>McAlpine, M. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-performance+nanowire+electronics+and+photonics+on+glass+and+plastic+substrates.">High-performance nanowire electronics and photonics on glass and plastic substrates.</a> Nano Lett. 3, 1531-1535 (2003).</li><li>Cui, Y., Wei, Q., Park, H., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanowire+nanosensors+for+highly+sensitive+and+selective+detection+of+biological+and+chemical+species.">Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species.</a> Science. 293, 1289-1292 (2001).</li><li>Patolsky, F., Zheng, G., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanowire-based+biosensors.">Nanowire-based biosensors.</a> Anal Chem. 78, 4260-4269 (2006).</li><li>Hsiao, C. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+poly-silicon+nanowire+field+effect+transistor+for+biosensing+application.">Novel poly-silicon nanowire field effect transistor for biosensing application.</a> Biosens Bioelectron. 24, 1223-1229 (2009).</li></ol>

Commercializing the top-down and bottom-up fabrication approaches for sSNWFETs is considered difficult because of its cost32,33, SNW position control34,35, and its low production scale36. By contrast, fabricating pSNWFETs is simple and low cost37. Through the top-down approach and combination with the sidewall spacer formation technique (Figure 1), the size of the SNW can be controlled by adjusting the duration of reactive plasma etching. The procedures for pre...

Silicon nanowire field-effect transistors (SNWFETs) have the advantages of ultra-high sensitivity and direct electrical responses to environmental charge variation. In n-type SNWFETs for example, when a negatively (or positively) charged molecule approaches the silicon nanowire (SNW), the carriers in the SNW are depleted (or accumulate). Consequently, the conductivity of the SNWFET decreases (or increases)1. Therefore, any charged molecule near the SNW surface of the SNWFET device can be detected. Vital biomolecules including enzymes, proteins, nucleotides, and many molecules on the cell surface are charge carriers and can be monitored using SNWFETs. With suitable modifications, particularly immobilizing a biomolecular probe on the SNW, a SNWFET can be developed into a label-free biosensor.
Surveillance using biomarkers is critical for diagnosing diseases. As shown in Table 1, several studies have used NWFET-based biosensors for label-free, ultra-high-sensitivity, and real-time detection of various biological targets, including a single virus2, adenosine triphosphate and kinase binding3, neuronal signals4, metal ions5,6, bacterial toxins7, dopamine8, DNA9-11, RNA12,13, enzyme and cancer biomarkers14-19, human hormones20, and cytokines21,22. These studies have demonstrated that NWFET-based biosensors represent a powerful detection platform for a broad range of biological and chemical species in a solution.
In SNWFET-based biosensors, the probe immobilized on the SNW surface of the device recognizes a specific biotarget. Immobilizing a bioprobe usually involves a series of steps, and it is critical that every step is properly performed to ensure the proper functioning of the biosensor. Various techniques have been developed for analyzing the surface composition, including X-ray photoelectron spectroscopy (XPS), ellipsometry, contact angle measurement, atomic force microscopy (AFM), and scanning electron microscopy (SEM). Methods such as AFM and SEM provide direct evidence of bioprobe immobilization on the nanowire device, whereas methods such as XPS, ellipsometry, and contact angle measurement are dependent on parallel experiments performed on other similar materials. In this report, we describe the confirmation of each modification step by using two independent methods. XPS is used to examine the concentrations of specific atoms on polysilicon wafers, and variations in the electric properties of the device are measured directly to confirm the charge variation on the SNW surface. We employ DNA biosensing by using polycrystalline SNWFETs (pSNWFETs) as an example to illustrate this protocol. Immobilizing a DNA probe on the SNW surface involves three steps: amine group modification on the native hydroxyl surface of the SNW, aldehyde group modification, and 5&#39;-aminomodified DNA probe immobilization. At each modification step, the device can directly detect the variation in the charge of the functional group immobilized on the SNW surface, because the surface charges cause local interfacial potential changes over the gate dielectric that alter the channel current and conductance1. Charges surrounding the SNW surface can electrically modulate the electric properties of the pSNWFET device; therefore, the surface properties of the SNW play a crucial role in determining the electrical characteristics of pSNWFET devices. In the reported procedures, the immobilization of a bioprobe on the SNW surface can be directly determined and confirmed through electric measurement, and the device is prepared for biosensing applications.

<table border="0" cellpadding="0" cellspacing="0" width="862">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:327px;">Acetone</td>
			<td style="width:191px;">ECHO</td>
			<td style="width:179px;">AH-3102</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:327px;">(3-Amonopropyl)triethoxysilane (APTES), &#8805;98%</td>
			<td style="width:191px;">Sigma-Aldrich</td>
			<td style="width:179px;">A3648</td>
			<td>Danger</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:327px;">Ethanol, anhydrous, 99.5%</td>
			<td style="width:191px;">ECHO</td>
			<td style="width:179px;">484000203108A-72EC</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:327px;">Glutaraldehyde solution (GA), 50%</td>
			<td style="width:191px;">Sigma-Aldrich</td>
			<td style="width:179px;">G7651</td>
			<td>Avoid light</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:327px;">Sodium cyanoborohydride, &#8805;95.0%&#160;</td>
			<td style="width:191px;">Fluka</td>
			<td style="width:179px;">71435</td>
			<td>Danger and deliquescent</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:327px;">Sodium phosphate tribasic dodecahydrate, &#8805;98%</td>
			<td style="width:191px;">Sigma</td>
			<td style="width:179px;">04277</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:327px;">Phosphoric acid, &#8805;99.0%</td>
			<td style="width:191px;">Fluka</td>
			<td style="width:179px;">79622</td>
			<td>Deliquescent</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Photoresist (iP3650)</td>
			<td style="width:191px;">Tokyo Ohka Kogyo Co., LTD</td>
			<td style="width:179px;">THMR-iP3650 HP</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:327px;">Synthetic oligonucleotides, HPLC purified</td>
			<td style="width:191px;">Protech Technology</td>
			<td style="width:179px;"></td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:327px;">Tris(hydroxymethyl)aminomethane (Tris), &#8805;99.8%</td>
			<td style="width:191px;">USB</td>
			<td style="width:179px;">75825</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:327px;">Keithley 2636 System SourceMeter</td>
			<td style="width:191px;">Keithley</td>
			<td style="width:179px;"></td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:327px;">SR830 DSP Lock-In Amplifier</td>
			<td style="width:191px;">Stanford Research Systems</td>
			<td style="width:179px;"></td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:327px;">SR570 Low-noise Current Preamplifier</td>
			<td style="width:191px;">Stanford Research Systems</td>
			<td style="width:179px;"></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:327px;">Ni PXI Express</td>
			<td style="width:191px;">National Instruments</td>
			<td style="width:179px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

preparation of silicon nanowire field-effect transistor for chemical and biosensing applications

Surveillance using biomarkers is critical for the early detection, rapid intervention, and reduction in the incidence of diseases. In this study, we describe the preparation of polycrystalline silicon nanowire field-effect transistors (pSNWFETs) that serve as biosensing devices for biomarker detection. A protocol for chemical and biomolecular sensing by using pSNWFETs is presented. The pSNWFET device was demonstrated to be a promising transducer for real-time, label-free, and ultra-high-sensitivity biosensing applications. The source/drain channel conductivity of a pSNWFET is sensitive to changes in the environment around its silicon nanowire (SNW) surface. Thus, by immobilizing probes on the SNW surface, the pSNWFET can be used to detect various biotargets ranging from small molecules (dopamine) to macromolecules (DNA and proteins). Immobilizing a bioprobe on the SNW surface, which is a multistep procedure, is vital for determining the specificity of the biosensor. It is essential that every step of the immobilization procedure is correctly performed. We verified surface modifications by directly observing the shift in the electric properties of the pSNWFET following each modification step. Additionally, X-ray photoelectron spectroscopy was used to examine the surface composition following each modification. Finally, we demonstrated DNA sensing on the pSNWFET. This protocol provides step-by-step procedures for verifying bioprobe immobilization and subsequent DNA biosensing application.

Various SNWFETs have been reported to serve as transducers of biosensors (Table 1). Single-crystalline SNWFETs (sSNWFETs) and pSNWFETs show comparable electric properties as transducers in aqueous solutions, and both have been reported to have many biosensing applications. An advantageous feature of the pSNWFET device used in this study is its simple and low-cost fabrication procedure. Figure 1a shows the key steps involved in fabricating the pSNWFET. An ...

Watch this Scientific Journal Video about Preparation of Silicon Nanowire Field-effect Transistor for Chemical and Biosensing Applications at JoVE.com

Preparation of Silicon Nanowire Field-effect Transistor for Chemical and Biosensing Applications

We describe key steps for biosensing by using polysilicon nanowire field-effect transistors, including the preparation of the device and the immobilization and confirmation of a DNA molecular probe on the nanowire surface, as well as conditions for DNA sensing.

Surveillance using biomarkers is critical for the early detection, rapid intervention, and reduction in the incidence of diseases. In this study, we ...

The overall goal of this protocol is to verify bioprobe immobilization and subsequent DNA biosensing on polysilicon nanowire field-effect transistors. This method can help answer important questions in the bioelectric sensing field, such as bioprobe immobilization and nucleic acid detection. Our biosensing device is a promising transistor for real-time, labor-free, and also high-sensitivity biosensing application.The implications of these biosensors extend toward clinical diagnosis of emerging infectious disease, because it can readily, sensitively, and accurately detect the specific bio-target. Though this method can provide insight into nucleic acid detection, it can also be applied to detection of other molecules, such as cytokines, hormones, proteins, and viruses. Generally, individuals new to this method will struggle because it requires interdisciplinary collaboration between biology and the electrical engineering fields.The preparation of the polycrystalline silicon nanowire field-effect transistor is covered by the text protocol. The device is formed from a six-inch wafer. The silicon nanowires on the device are about 100 nanometers wide and 1.6 microns long.To pre-treat the device, first remove it from storage in an electronically dry cabinet and open the sealed vacuum bag that contains it. Clean the biosensor in a Sonicator loaded with pure acetone for 10 minutes. Then, change the bath to pure ethanol and repeat the sonication for another five minutes.After this second bath, use a stream of nitrogen gas to dry the device. Next, treat the device with oxygen plasma at 18 watts for 30 seconds. Now take AC conductance measurements and measure the drain current electric properties on the device, as explained in the next section.Then, proceed with immobilizing DNA on the device surface while taking additional measurements, both AC conductance and drain current, after each modification. First, prepare for the pH profiling. Make 10 millimolar sodium phosphate tribasic dodecahydrate in deionized water, which has a pH of 11.6.Then, make a 10 millimolar phosphoric acid solution in deionized water, which has a pH of 2.35. Now make seven 10 millimolar buffer solutions with pH values ranging from three to nine by mixing the two stock solutions. With the test solutions and microfluidic channel prepared, measure real-time conductance using a lock-in technique.Place two needle probes on each of the source and drain pads. Convert the AC current signal into an AC voltage signal using a low-noise current preamplifier. Then set the optimal liquid gate voltage and proceed with delivering each buffer solution while measuring conductance at a drain voltage of 10 millivolts.Next, measure the drain current with neutral buffer. Flow pH 7 buffer onto the device from a syringe pump at five milliliters per hour. Then, using commercial semiconductor analysis software, measure the drain current in N MOSFET mode.Set the bias voltage to 0.5 volts and sweep the gate potential from negative one to three volts at 0.2-volt intervals. Now run the test and obtain the data. Begin with immersing the biosensor in 2%APTES in ethanol for 30 minutes to covalently link the nanowire surface.Then wash the biosensor three times for 30 seconds with ethanol, and then clean it in a Sonicator loaded with ethanol. Now, to create amine groups on the silicon nanowires, place the biosensor on a 120-degree Celsius surface for 10 minutes. Following the heating step, take measurements on the device as described in the previous section.Next, to create aldehyde groups on the silicon nanowires, immerse the device in 12.5%glutaraldehyde in 10 millimolar sodium phosphate pH 7 for one hour at room temperature. Limit any light exposure during this step. After the glutaraldehyde treatment, wash the device with 10 millimolar sodium phosphate buffer three times for 30 seconds per wash.Then blowdry the biosensor under pure nitrogen gas and take measurements to confirm the surface modification. The next step is to incubate the biosensor in one micromolar of probe solution overnight to thus apply the DNA probe. The following day, block the unreacted aldehyde groups by immersing the device in 10 millimolar Tris with four millimolar sodium cyanoborohydride for half an hour.Then wash the device off with 10 millimolar sodium phosphate buffer at pH 7 three times, followed by blowdrying the device under nitrogen gas, as before. Then take a final set of measurements to confirm the surface modification before proceeding to use it as a biosensor. Begin with taking a baseline measurement.Flow pH neutral sodium phosphate buffer into the device for 10 minutes. During this procedure, the solution flow rate is always five milliliters per hour. Then wait 30 minutes, flow pH neutral buffer over the biosensor for 10 minutes again, and measure the current of the device.Next, load 10 picomoles of DNA, complementary to the probe, onto the silicon nanowire surface by flowing the solution over the device for 10 minutes. Then incubate the biosensor for 30 minutes. As a negative control, apply 100 picomoles of non-complementary DNA to the device.After the incubation, flow pH neutral buffer over the biosensor for 10 minutes to wash off unbound target DNA. Following this step, measure the current of the device as before. Next, load one nanomolar of recovery DNA onto the DNA probe immobilized silicon nanowire surface for 10 minutes.Then incubate the biosensor for 30 minutes, as before. Finally, flow pH neutral buffer over the device for another 10 minutes, and then take current measurements once again. A DNA probe was immobilized on the silicon oxide surface and each modification step was confirmed using X-ray photoelectron spectroscopy.For the unmodified pSNWFET containing the native oxide layer on the SNW surface, the hydroxyl groups were ionized to form charged groups with increasing pH values. Conductance likely varied at different pHs. The shift in the electric properties of the device after different modifications confirms the change in the wire surface.In such experiments, the current voltage curve of the unmodified device was used as the baseline. After the device was immersed in APTES, the current voltage curve of the device shifted to the left because of the positive charge on the wire surface. After conjugating glutaraldehyde to the APTES modified device, the current voltage curve shifted back to the right because of neutrally-charged MI bond formation.Finally, a five prime amine-modified DNA probe was introduced to bind to the APTES glutaraldehyde-modified device. The backbone of the DNA caused the current voltage curve to shift to the far right. After watching this video, you should have a good understanding of how to confirm the bioprobe immobilization and DNA sensing application on polysilicon nanowire field-effect transistors.Once mastered, this technique of the preparation for nucleic acid detection can be done within one hour, if it is performed properly, which can be performed in advance. The final biosensing takes less than 10 minutes. While attempting this procedure, it's important to remember to analyze the electric properties of the device at each step of the bioprobe modification.This technique paved the way for researchers in the field of semiconductor-based sensors to its broader application of biosensing. Following these procedures, other methods like immobilizing cancer biomarker probe, can be performed in order to answer additional questions in fields such as clinical cancer diagnosis.

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Soft Lithographic Functionalization and Patterning Oxide-free Silicon and Germanium

The development of hybrid electronic devices relies in large part on the integration of (bio)organic materials and inorganic semiconductors through a stable interface that permits efficient electron transport and protects underlying substrates from oxidative degradation. Group IV semiconductors can be effectively protected with highly-ordered self-assembled monolayers (SAMs) composed of simple alkyl chains that act as impervious barriers to both organic and aqueous solutions. Simple alkyl SAMs, however, are inert and not amenable to traditional patterning techniques. The motivation for immobilizing organic molecular systems on semiconductors is to impart new functionality to the surface that can provide optical, electronic, and mechanical function, as well as chemical and biological activity. 
Microcontact printing (&mu;CP) is a soft-lithographic technique for patterning SAMs on myriad surfaces.1-9 Despite its simplicity and versatility, the approach has been largely limited to noble metal surfaces and has not been well developed for pattern transfer to technologically important substrates such as oxide-free silicon and germanium. Furthermore, because this technique relies on the ink diffusion to transfer pattern from the elastomer to substrate, the resolution of such traditional printing is essentially limited to near 1 &mu;m.10-16
In contrast to traditional printing, inkless &mu;CP patterning relies on a specific reaction between a surface-immobilized substrate and a stamp-bound catalyst. Because the technique does not rely on diffusive SAM formation, it significantly expands the diversity of patternable surfaces. In addition, the inkless technique obviates the feature size limitations imposed by molecular diffusion, facilitating replication of very small (&lt;200 nm) features.17-23 However, up till now, inkless &mu;CP has been mainly used for patterning relatively disordered molecular systems, which do not protect underlying surfaces from degradation.
Here, we report a simple, reliable high-throughput method for patterning passivated silicon and germanium with reactive organic monolayers and demonstrate selective functionalization of the patterned substrates with both small molecules and proteins. The technique utilizes a preformed NHS-reactive bilayered system on oxide-free silicon and germanium. The NHS moiety is hydrolyzed in a pattern-specific manner with a sulfonic acid-modified acrylate stamp to produce chemically distinct patterns of NHS-activated and free carboxylic acids. A significant limitation to the resolution of many &mu;CP techniques is the use of PDMS material which lacks the mechanical rigidity necessary for high fidelity transfer. To alleviate this limitation we utilized a polyurethane acrylate polymer, a relatively rigid material that can be easily functionalized with different organic moieties. Our patterning approach completely protects both silicon and germanium from chemical oxidation, provides precise control over the shape and size of the patterned features, and gives ready access to chemically discriminated patterns that can be further functionalized with both organic and biological molecules. The approach is general and applicable to other technologically-relevant surfaces.

Here we describe a simple method for patterning oxide-free silicon and germanium with reactive organic monolayers and demonstrate functionalization of the patterned substrates with small molecules and proteins. The approach completely protects surfaces from chemical oxidation, provides precise control over feature morphology, and provides ready access to chemically discriminated patterns.

The development of hybrid electronic devices relies in large part on the integration of (bio)organic materials and inorganic semiconductors through a ...

Preparation of 3D Fibrin Scaffolds for Stem Cell Culture Applications

Stem cells are found in naturally occurring 3D microenvironments in vivo, which are often referred to as the stem cell niche 1. Culturing stem cells inside of 3D biomaterial scaffolds provides a way to accurately mimic these microenvironments, providing an advantage over traditional 2D culture methods using polystyrene as well as a method for engineering replacement tissues 2. While 2D tissue culture polystrene has been used for the majority of cell culture experiments, 3D biomaterial scaffolds can more closely replicate the microenvironments found in vivo by enabling more accurate establishment of cell polarity in the environment and possessing biochemical and mechanical properties similar to soft tissue.3 A variety of naturally derived and synthetic biomaterial scaffolds have been investigated as 3D environments for supporting stem cell growth. While synthetic scaffolds can be synthesized to have a greater range of mechanical and chemical properties and often have greater reproducibility, natural biomaterials are often composed of proteins and polysaccharides found in the extracelluar matrix and as a result contain binding sites for cell adhesion and readily support cell culture. Fibrin scaffolds, produced by polymerizing the protein fibrinogen obtained from plasma, have been widely investigated for a variety of tissue engineering applications both in vitro and in vivo 4. Such scaffolds can be modified using a variety of methods to incorporate controlled release systems for delivering therapeutic factors 5. Previous work has shown that such scaffolds can be used to successfully culture embryonic stem cells and this scaffold-based culture system can be used to screen the effects of various growth factors on the differentiation of the stem cells seeded inside 6,7.
 This protocol details the process of polymerizing fibrin scaffolds from fibrinogen solutions using the enzymatic activity of thrombin. The process takes 2 days to complete, including an overnight dialysis step for the fibrinogen solution to remove citrates that inhibit polymerization. These detailed methods rely on fibrinogen concentrations determined to be optimal for embryonic and induced pluripotent stem cell culture. Other groups have further investigated fibrin scaffolds for a wide range of cell types and applications - demonstrating the versatility of this approach 8-12.

This work details the preparation of 3D fibrin scaffolds for culturing and differentiating plutipotent stem cells. Such scaffolds can be used to screen the effects of various biological compounds on stem cell behavior as well as modified to contain drug delivery systems.

Stem cells are found in naturally occurring 3D microenvironments in vivo, which are often referred to as the stem cell niche 1. Culturing stem cells ...

Sensing of Barrier Tissue Disruption with an Organic Electrochemical Transistor

The gastrointestinal tract is an example of barrier tissue that provides a physical barrier against entry of pathogens and toxins, while allowing the passage of necessary ions and molecules. A breach in this barrier can be caused by a reduction in the extracellular calcium concentration. This reduction in calcium concentration causes a conformational change in proteins involved in the sealing of the barrier, leading to an increase of the paracellular flux. To mimic this effect the calcium chelator ethylene glycol-bis(beta-aminoethyl ether)-N,N,N&#39;,N&#39;-tetra acetic acid (EGTA) was used on a monolayer of cells known to be representative of the gastrointestinal tract. Different methods to detect the disruption of the barrier tissue already exist, such as immunofluorescence and&#160;permeability assays. However, these methods are time-consuming and costly and not suited to dynamic or high-throughput measurements. Electronic methods for measuring barrier tissue integrity also exist for measurement of the transepithelial resistance (TER), however these are often costly and complex. The development of rapid, cheap, and sensitive methods is urgently needed as the integrity of barrier tissue is a key parameter in drug discovery and pathogen/toxin diagnostics. The organic electrochemical transistor (OECT) integrated with barrier tissue forming cells has been shown as a new device capable of dynamically monitoring barrier tissue integrity. The device is able to measure minute variations in ionic flux with unprecedented temporal resolution and sensitivity, in real time, as an indicator of barrier tissue integrity. This new method is based on a simple device that can be compatible with high throughput screening applications and fabricated at low cost.

The Organic Electrochemical Transistor is integrated with live cells and used to monitor ion flux across the gastrointestinal epithelial barrier. In this study, an increase in ion flux, related to disruption of tight junctions, induced by the presence of the calcium chelator EGTA (ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetra acetic acid), is measured.

The gastrointestinal tract is an example of barrier tissue that provides a physical barrier against entry of pathogens and toxins, while allowing the ...

Porous Silicon Microparticles for Delivery of siRNA Therapeutics

Small interfering RNA (siRNA) can be used to suppress gene expression, thereby providing a new avenue for the treatment of various diseases. However, the successful implementation of siRNA therapy requires the use of delivery platforms that can overcome the major challenges of siRNA delivery, such as enzymatic degradation, low intracellular uptake and lysosomal entrapment. Here, a protocol for the preparation and use of a biocompatible and effective siRNA delivery system is presented. This platform consists of polyethylenimine (PEI) and arginine (Arg)-grafted porous silicon microparticles, which can be loaded with siRNA by performing a simple mixing step. The silicon particles are gradually degraded over time, thereby triggering the formation of Arg-PEI/siRNA nanoparticles. This delivery vehicle provides a means for protecting and internalizing siRNA, without causing cytotoxicity. The major steps of polycation functionalization, particle characterization, and siRNA loading are outlined in detail. In addition, the procedures for determining particle uptake, cytotoxicity, and transfection efficacy are also described.

Delivery remains the main challenge for the therapeutic implementation of small interfering RNA (siRNA). This protocol involves the use of a multifunctional and biocompatible siRNA delivery platform, consisting of arginine and polyethylenimine grafted porous silicon microparticles.

Small interfering RNA (siRNA) can be used to suppress gene expression, thereby providing a new avenue for the treatment of various diseases. However, the ...

The Synthesis of RGD-functionalized Hydrogels as a Tool for Therapeutic Applications

The use of polymers as biomaterials has provided significant advantages in therapeutic applications. In particular, the possibility to modify and functionalize polymer chains with compounds that are able to improve biocompatibility, mechanical properties, or cell viability allows the design of novel materials to meet new challenges in the biomedical field. With the polymer functionalization strategies, click chemistry is a powerful tool to improve cell-compatibility and drug delivery properties of polymeric devices. Similarly, the fundamental need of biomedicine to use sterile tools to avoid potential adverse-side effects, such as toxicity or contamination of the biological environment, gives rise to increasing interest in the microwave-assisted strategy.
The combination of click chemistry and the microwave-assisted method is suitable to produce biocompatible hydrogels with desired functionalities and improved performances in biomedical applications. This work aims to synthesize RGD-functionalized hydrogels. RGD (arginylglycylaspartic acid) is a tripeptide that can mimic cell adhesion proteins and bind to cell-surface receptors, creating a hospitable microenvironment for cells within the 3D polymeric network of the hydrogels. RGD functionalization occurs through Huisgen 1,3-dipolar cycloaddition. Some PAA carboxyl groups are modified with an alkyne moiety, whereas RGD is functionalized with azido acid as the terminal residue of the peptide sequence. Finally, both products are used in a copper catalyzed click reaction to permanently link the peptide to PAA. This modified polymer is used with carbomer, agarose and polyethylene glycol (PEG) to synthesize a hydrogel matrix. The 3D structure is formed due to an esterification reaction involving carboxyl groups from PAA and carbomer and hydroxyl groups from agarose and PEG through microwave-assisted polycondensation. The efficiency of the gelation mechanism ensures a high degree of RGD functionalization. In addition, the procedure to load therapeutic compounds or biological tools within this functionalized network is very simple and reproducible.

We present a protocol for the synthesis of RGD-functionalized hydrogels as devices for cell and drug delivery. The procedure involves copper catalyzed alkyne-azide cycloaddition (CuAAC) between alkyne-modified polyacrylic acid (PAA) and a RGD-azide derivative. The hydrogels are formed using microwave-assisted polycondensation and their physicochemical properties are investigated.

The use of polymers as biomaterials has provided significant advantages in therapeutic applications. In particular, the possibility to modify and ...

Light-mediated Formation and Patterning of Hydrogels for Cell Culture Applications

Click chemistries have been investigated for use in numerous biomaterials applications, including drug delivery, tissue engineering, and cell culture. In particular, light-mediated click reactions, such as photoinitiated thiol&#8722;ene and thiol&#8722;yne reactions, afford spatiotemporal control over material properties and allow the design of systems with a high degree of user-directed property control. Fabrication and modification of hydrogel-based biomaterials using the precision afforded by light and the versatility offered by these thiol&#8722;X photoclick chemistries are of growing interest, particularly for the culture of cells within well-defined, biomimetic microenvironments. Here, we describe methods for the photoencapsulation of cells and subsequent photopatterning of biochemical cues within hydrogel matrices using versatile and modular building blocks polymerized by a thiol&#8722;ene photoclick reaction. Specifically, an approach is presented for constructing hydrogels from allyloxycarbonyl (Alloc)-functionalized peptide crosslinks and pendant peptide moieties and thiol-functionalized poly(ethylene glycol) (PEG) that rapidly polymerize in the presence of lithium acylphosphinate photoinitiator and cytocompatible doses of long wavelength ultraviolet (UV) light. Facile techniques to visualize photopatterning and quantify the concentration of peptides added are described. Additionally, methods are established for encapsulating cells, specifically human mesenchymal stem cells, and determining their viability and activity. While the formation and initial patterning of thiol-alloc hydrogels are shown here, these techniques broadly may be applied to a number of other light and radical-initiated material systems (e.g., thiol-norbornene, thiol-acrylate) to generate patterned substrates.

We describe a sequential process for light-mediated formation and subsequent biochemical patterning of synthetic hydrogel matrices for three-dimensional cell culture applications. The construction and modification of hydrogels with cytocompatible photoclick chemistry is demonstrated. Additionally, facile techniques to quantify and observe patterns and determine cell viability within these hydrogels are presented.

Click chemistries have been investigated for use in numerous biomaterials applications, including drug delivery, tissue engineering, and cell culture. In ...

Extraction of Plant-based Capsules for Microencapsulation Applications

Microcapsules derived from plant-based spores or pollen provide a robust platform for a diverse range of microencapsulation applications. Sporopollenin exine capsules (SECs) are obtained when spores or pollen are processed so as to remove the internal sporoplasmic contents. The resulting hollow microcapsules exhibit a high degree of micromeritic uniformity and retain intricate microstructural features related to the particular plant species. Herein, we demonstrate a streamlined process for the production of SECs from Lycopodium clavatum spores and for the loading of hydrophilic compounds into these SECs. The current SEC isolation procedure has been recently optimized to significantly reduce the processing requirements which are conventionally used in SEC isolation, and to ensure the production of intact microcapsules. Natural L. clavatum spores are defatted with acetone, treated with phosphoric acid, and extensively washed to remove sporoplasmic contents. After acetone defatting, a single processing step using 85% phosphoric acid has been shown to remove all sporoplasmic contents. By limiting the acid processing time to 30 hr, it is possible to isolate clean SECs and avoid SEC fracturing, which has been shown to occur with prolonged processing time. Extensive washing with water, dilute acids, dilute bases, and solvents ensures that all sporoplasmic material and chemical residues are adequately removed. The vacuum loading technique is utilized to load a model protein (Bovine Serum Albumin) as a representative hydrophilic compound. Vacuum loading provides a simple technique to load various compounds without the need for harsh solvents or undesirable chemicals which are often required in other microencapsulation protocols. Based on these isolation and loading protocols, SECs provide a promising material for use in a diverse range of microencapsulation applications, such as, therapeutics, foods, cosmetics, and personal care products.

This protocol/manuscript describes a streamlined process for the production of sporopollenin exine capsules (SECs) from Lycopodium clavatum spores and for the loading of hydrophilic compounds into these SECs.

Microcapsules derived from plant-based spores or pollen provide a robust platform for a diverse range of microencapsulation applications. Sporopollenin ...

Rapid Mix Preparation of Bioinspired Nanoscale Hydroxyapatite for Biomedical Applications

Hydroxyapatite (HA) has been widely used as a medical ceramic due to its good biocompatibility and osteoconductivity. Recently there has been interest regarding the use of bioinspired nanoscale hydroxyapatite (nHA). However, biological apatite is known to be calcium-deficient and carbonate-substituted with a nanoscale platelet-like morphology. Bioinspired nHA has the potential to stimulate optimal bone tissue regeneration due to its similarity to bone and tooth enamel mineral. Many of the methods currently used to fabricate nHA both in the laboratory and commercially, involve lengthy processes and complex equipment. Therefore, the aim of this study was to develop a rapid and reliable method to prepare high quality bioinspired nHA. The rapid mixing method developed was based upon an acid-base reaction involving calcium hydroxide and phosphoric acid. Briefly, a phosphoric acid solution was poured into a calcium hydroxide solution followed by stirring, washing and drying stages. Part of the batch was sintered at 1,000 &#176;C for 2 h in order to investigate the products&#39; high temperature stability. X-ray diffraction analysis showed the successful formation of HA, which showed thermal decomposition to &#946;-tricalcium phosphate after high temperature processing, which is typical for calcium-deficient HA. Fourier transform infrared spectroscopy showed the presence of carbonate groups in the precipitated product. The nHA particles had a low aspect ratio with approximate dimensions of 50 x 30 nm, close to the dimensions of biological apatite. The material was also calcium deficient with a Ca:P molar ratio of 1.63, which like biological apatite is lower than the stoichiometric HA ratio of 1.67. This new method is therefore a reliable and far more convenient process for the manufacture of bioinspired nHA, overcoming the need for lengthy titrations and complex equipment. The resulting bioinspired HA product is suitable for use in a wide variety of medical and consumer health applications.

This paper describes a novel method for the rapid manufacture of high quality bioinspired nanoscale hydroxyapatite. This biomaterial is of great significance in the manufacture of a wide range of innovative medical devices for clinical applications in orthopedics, craniofacial surgery and dentistry.

Hydroxyapatite (HA) has been widely used as a medical ceramic due to its good biocompatibility and osteoconductivity. Recently there has been interest ...

Rapid Fabrication of Custom Microfluidic Devices for Research and Educational Applications

Microfluidic devices allow for the manipulation of fluids, particles, cells, micro-sized organs or organisms in channels ranging from the nano to submillimeter scales. A rapid increase in the use of this technology in the biological sciences has prompted a need for methods that are accessible to a wide range of research groups. Current fabrication standards, such as PDMS bonding, require expensive and time consuming lithographic and bonding techniques. A viable alternative is the use of equipment and materials that are easily affordable, require minimal expertise and allow for the rapid iteration of designs. In this work we describe a protocol for designing and producing PET-laminates (PETLs), microfluidic devices that are inexpensive, easy to fabricate, and consume significantly less time to generate than other approaches to microfluidics technology. They consist of thermally bonded film sheets, in which channels and other features are defined using a craft cutter. PETLs solve field-specific technical challenges while dramatically reducing obstacles to adoption. This approach facilitates the accessibility of microfluidics devices in both research and educational settings, providing a reliable platform for new methods of inquiry.

Here we present a protocol to design and fabricate custom microfluidic devices with minimal financial and time investment. The aim is to facilitate the adoption of microfluidic technologies in biomedical research laboratories and educational settings.

Microfluidic devices allow for the manipulation of fluids, particles, cells, micro-sized organs or organisms in channels ranging from the nano to ...

Synthesis of Near-Infrared Emitting Gold Nanoclusters for Biological Applications

Over the past decade, fluorescent gold nanoclusters (AuNCs) have witnessed growing popularity in biological applications and enormous efforts have been devoted to their development. In this protocol, a recently developed, facile method for preparation of water soluble, biocompatible, and colloidally stable near-infrared emitting AuNCs have been described in detail. This room-temperature, bottom-up chemical synthesis provides easily functionalizable AuNCs capped with thioctic acid and thiol-modified polyethylene glycol in aqueous solution. The synthetic approach requires neither organic solvents or additional ligand exchange nor extensive knowledge of synthetic chemistry to reproduce. The resulting AuNCs offer free surface carboxylic acids, which can be functionalized with various biological molecules bearing a free amine group without adversely affecting the photoluminescent properties of the AuNCs. A quick, reliable procedure for flow cytometric quantification and confocal microscopic imaging of AuNC uptake by HeLa cells also been described. Due to the large Stokes shift, proper setting of filters in flow cytometry and confocal microscopy is necessary for efficient detection of near-infrared photoluminescence of AuNCs.

A reliable and easily reproducible method for preparation of functionalizable, near-infrared emitting photoluminescent gold nanoclusters and their direct detection inside HeLa cells by flow cytometry and confocal laser scanning microscopy is described.

Over the past decade, fluorescent gold nanoclusters (AuNCs) have witnessed growing popularity in biological applications and enormous efforts have been ...