The experiments were conducted at West Virginia University. We acknowledge the Shared Research Facilities at West Virginia University for device fabrication and material characterization. This work was supported by the US National Science Foundation under Grant No. NSF1916894.

1. Transferring chemical vapor deposition of graphene
<ol>
	<li>Cut the graphene sheet on a copper substrate in half (2.5 cm x 5 cm) using scissors. Apply heat resistive tape to fix the four corners of the graphene square on a spinner gasket (see Table of Materials). 
	NOTE: The purchased graphene has a dimension of 5 cm x 5 cm (see Table of Materials).</li>
	<li>Spin-coat the sheet of the graphene with a thin layer (100-200 nm) of PMMA 495K A4 spinning at 500 rpm for 10 s and then 2000 rpm for 50 s. Then bake the sample at 150 &#176;C for 5 min.</li>
	<li>Remove the backside of the graphene with oxygen plasma (see Table of Materials) at 30 W, 15 sccm for 5 min.</li>
	<li>Cut the plasma-treated graphene square into smaller dimensions (1 cm x 2 cm) for device fabrication.</li>
	<li>Cut the pre-cleaned substrate (SiO2) into small pieces with an approximate dimension of 2.5 cm x 2 cm.</li>
	<li>Etch the copper off using the graphene commercial etchant (Ferric chloride) (see Table of Materials). Do not dilute the etchant. Float the sample with the copper side down and the PMMA side up on the liquid etchant.</li>
	<li>After copper etching, lift the graphene film slowly using the plasma-treated substrate.</li>
	<li>Air-dry the transferred graphene for 2 h and then bake at 80 &#176;C for 15 min.</li>
	<li>Remove the PMMA following the steps below.
	<ol>
		<li>Warm up the sample with acetone vapor at 70 &#176;C. Keep the sample at ~2 cm above acetone vapor for 4 min with the PMMA side facing down. Then immerse the sample in acetone for 5 min.</li>
		<li>Wash the sample with DI water cautiously and observe the transferred graphene under a microscope. Finally, gently blow-dry the sample with N2.</li>
		<li>Perform Atomic force microscopy (AFM) observation to ensure PMMA residue-free graphene. If PMMA residue is visible in the image, perform the acetone vapor cleaning and immersion once again.</li>
	</ol>
	</li>
	<li>Perform Raman and AFM characterization to confirm the monolayer of graphene transferring and observe the surface properties (Figure 1A,B).</li>
</ol>
2. Fabrication of Graphene Field Effect Transistor (GFET)
<ol>
	<li>Wash the substrate with the transferred graphene using acetone, IPA, and DI water; then bake the substrate on a hot plate at 75 &#176;C for 30 min (Figure 2A).</li>
	<li>Using the E-beam evaporator30 (see Table of Materials), deposit 5 nm nickel and 45 nm gold on the graphene sample (Figure 2B).</li>
	<li>Apply the first photolithography30 process using mask A (Supplementary Figure 1) for the patterning of the electrodes (Figure 2C).</li>
	<li>Spin a positive photoresist (AZ 5214E, see Table of Materials) on the sample (2000 rpm for 45 s) and cure the sample at 120 &#176;C for 1 min.</li>
	<li>Place the sample in the UV flood exposure system and expose it for ~10 s under 200 mJ/cm2.</li>
	<li>Develop the sample with a photoresist developer (AZ300 MIF, see Table of Materials) for ~2 min, and then rinse with DI water.</li>
	<li>Immerse the sample in a gold etchant to etch the gold layer for 10 s; rinse with DI water and remove the remaining photoresist layer by immersing in acetone for 10 min (Figure 2C).</li>
	<li>Using acetone, IPA, and DI water, wash the sample; bake on a hot plate at 75 &#176;C for 30 min. Then apply the second photolithography process using mask B (Supplementary Figure 1) to pattern the graphene channels. 
	NOTE: Use the same process parameters as the first one (step 2.4-2.6), except the UV exposure system in the mask aligner (Figure 2D).</li>
	<li>Immerse the sample in nickel etchant at 60 &#176;C to etch the nickel layer for 10 s; rinse with DI water; blow dry using N2&#160;(Figure 2D).</li>
	<li>Place the sample in the plasma asher and remove the exposed graphene using oxygen plasma (100 W for 90 s with oxygen flow at 49 sccm); after that, remove the photoresist layer by immersing in acetone for 10 min (Figure 2E).</li>
	<li>Wash the sample using acetone, IPA, and DI water; bake on a hot plate at 75 &#176;C for 30 min and apply the third photolithography process using mask C (Supplementary Figure 1) for the patterning of the passivation photoresist layer to protect the underlying graphene on the substrate. Use the same process parameters as the first one (step 2.4-2.6), except the UV exposure system in the mask aligner (Figure 2F).</li>
	<li>After the third photolithography process, immerse the sample in nickel etchant at 60 &#176;C for 10 s to remove the remaining nickel layer; then rinse with DI water and blow dry using N2 (Figure 2G). Finally, bake the sample on a hotplate at 120 &#176;C for 30 min (Figure 2H).</li>
</ol>
3. Functionalization of GFET for IgG Detection
<ol>
	<li>Assemble the sample-delivery channel.
	<ol>
		<li>Fabricate the sample-delivery channel in PDMS using soft lithography techniques31.</li>
		<li>Immerse the graphene device in 0.1 M of NaOH solution for 30 s; rinse with DI water and leave a thin water layer on the device surface to assist PDMS well&#39;s alignment and bonding. Then activate the PDMS well&#39;s surface using oxygen plasma.</li>
		<li>Align the sample delivery channel and the graphene device under a microscope; place the aligned device in a 60 &#176;C oven for 3 h to allow the bonding. The assembled device is shown in Figure 3A.</li>
	</ol>
	</li>
	<li>Functionalize the GFET.
	<ol>
		<li>Functionalize the graphene surface with IgG aptamer (see Table of Materials). Use pipettes to load and remove each reagent or buffer from the PDMS well. The schematic process is shown in Figure 4. 
		NOTE: The following steps were operated at room temperature.</li>
		<li>After rinsing the graphene surface with DMSO three times, apply 1-pyrene butyric acid N-hydroxysuccinimide ester (PBASE, 10 mM dissolved in DMSO, see Table of Materials) and keep for 2 h.</li>
		<li>After rinsing with DMSO, apply 5&#39;amino-modified IgG aptamer (20 &#181;M in 1x PBS), incubate for 3 h, and rinse with 1x PBS three times.</li>
		<li>Apply bovine serum albumin (BSA, 10% w/v in 1x PBS) on graphene for 1 h and rinse with 1x PBS three times.</li>
	</ol>
	</li>
</ol>
4. IgG detection
<ol>
	<li>Rinse the device with 0.01x PBS three times. Fill the PDMS well with 0.01x PBS (detection buffer) (Figure 3A,B).</li>
	<li>Connect the electrodes with a high-performance parameter analyzer (see Table of Materials). Connect the source electrode to the ground, the drain, and the gate electrodes to Source Measurement Units (SMU 1 and SMU 2) equipped with the parameter analyzer, respectively (Figure 3C).</li>
	<li>Set up the measurement parameters and turn on the sampling process.</li>
	<li>Test the response of the EGGFET to IgG by continuously monitoring the drain current. Dissolve IgG in 0.01x PBS with different concentrations, add the solution into the detection chamber, and monitor the drain current continuously. Save the data.</li>
</ol>

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The authors have no competing interests or conflicting interests to disclose.

The purchased CVD graphene on copper film needs to be trimmed to the right size for the following fabrication steps. Cutting of the films can cause wrinkling, which needs to be prevented. The parameters provided in the fabrication step can be referred to for plasma etching of graphene, and these numbers could be varied when using different instruments. The etched sample must be closely monitored and inspected to ensure complete graphene etching. Multiple pre-cleaning methods can be applied to clean the substrates, such a...

Graphene and its derivatives have been investigated and used for many applications, including electronics1,2, sensing3,4,5, energy storage6,7, and photocatalysis1,6,8. Synthesis and fabrication of high quality, good uniformity, and low defects graphene are critical for high-performance and highly sensitive devices. Since the development of Chemical vapor deposition (CVD) in 2009, it has shown colossal promise and set its place as an essential member of the graphene family9,10,11,12,13. It is grown on a metal substrate and, later for practical uses, is transferred onto insulating substrates14. Several transferring methods have been used to transfer CVD graphene recently. The poly (methyl methacrylate) (PMMA) assisted method is the most used among the different techniques. This method is particularly well-suited for industrial usage because of its large-scale capability, lower cost, and high quality of the transferred graphene14,15. The critical aspect of this method is getting rid of the PMMA residue for CVD graphene&#39;s applications because the residues can cause declination of the electronic properties of graphene14,15,16, cause an effect on biosensors&#39; sensitivity and performance17,18, and create significant device-to-device variations19.
Nanomaterials-based biosensors have been significantly investigated over the past decades, including silicon nanowire (SiNW), carbon nanotube (CNT), and graphene20. Because of its single-atom-layer structure and distinctive properties, graphene demonstrates superior electronic characteristics, good biocompatibility, and facile functionalization, making it an attractive material for developing biosensors14,21,22,23. Due to field-effect transistors (FET) characteristics such as high sensitivity, standard configuration, and cost-effective mass producibility21,24, FET is more preferred in portable and point-of-care implementations than other electronics-based biosensing devices. The electrolyte-gated graphene field-effect transistor (EGGFET) biosensors are examples of the stated FETs21,24. EGGFET can detect various targeting analytes such as nucleic acids25, proteins24,26, metabolites27, and other biologically relevant analytes28. The technique mentioned here ensures the implementation of CVD graphene in a label-free biosensing nanoelectronics device which offers higher sensitivity and accurate time detection over other biosensing devices29.
In this work, an overall process for developing an EGGFET biosensor and functionalizing it for biomarker detection, including transferring CVD graphene onto an insulating substrate, Raman, and AFM characterizations of the transferred graphene, are demonstrated. Furthermore, fabrication of EGGFET and integration with a polydimethylsiloxane (PDMS) sample delivery well, bioreceptor functionalization, and successful detection of human immunoglobulin G (IgG) from serum by spike-and-recovery experiments are also discussed here.

<table><tbody><tr><td>1-pyreneutyric acid N- hydroxysuccinimide ester</td><td>Sigma Aldrich</td><td>457078-1G</td><td>functionalization</td></tr><tr><td>Asylum MFP-3D Atomic Force Microscope</td><td>Oxford Instruments</td><td></td><td>graphene characterization</td></tr><tr><td>AZ 300 MIF</td><td>MicroChemicals</td><td>AZ 300 MIF</td><td>photoresist developer</td></tr><tr><td>AZ 300 MIF</td><td>MicroChemicals</td><td>AZ 300 MIF</td><td>photoresist</td></tr><tr><td>Bovine Serum Albumin</td><td>Sigma Aldrich</td><td>810014</td><td>blocking</td></tr><tr><td>Branson 1210 Sonicator</td><td>SONITEK</td><td></td><td>sample cleaning</td></tr><tr><td>Copper Etchant</td><td>Sigma Aldrich</td><td>667528-500ML</td><td>removing copper film to release graphene</td></tr><tr><td>Dimethyl Sulfoxide (DMSO)</td><td>VWR</td><td>97063-136</td><td>functionalization</td></tr><tr><td>Disposable Biopsy Punches, Integra Miltex</td><td>VWR</td><td>21909-144</td><td>create well in PDMS</td></tr><tr><td>Gold etchant</td><td>Gold Etch, TFA, Transene</td><td>658148</td><td>enchant</td></tr><tr><td>Graphene</td><td>Graphene supermarket</td><td>2&quot; x 2&quot; sheet</td><td>biosensing element of the device</td></tr><tr><td>IgG aptamer</td><td>Base Pair Biotechnologies</td><td>customized</td><td>bioreceptor</td></tr><tr><td>Keithley 4200A-SCS Parameter Analyzer</td><td>Tektronix</td><td></td><td>measurement and detection</td></tr><tr><td>KMG CR-6</td><td>KMG chemicals</td><td>64216</td><td>Chromium etchant</td></tr><tr><td>Kurt J. Lesker E-beam Evaporator</td><td>Kurt J. Lesker</td><td></td><td>metal deposition</td></tr><tr><td>Laurell Technologies 400 Spinners</td><td>Laurell Technologies</td><td>WS-400BZ-6NPP/LITE</td><td>thin film coating</td></tr><tr><td>March PX-250 Plasma Asher</td><td>March Instruments</td><td></td><td>sample cleaning</td></tr><tr><td>Nickel etchant</td><td>Nickel Etchant, TFB, Transene</td><td>600016000</td><td>etchant</td></tr><tr><td>OAI Flood Exposure</td><td>OAI</td><td></td><td>photolithography</td></tr><tr><td>Phosphate Buffered Saline (PBS)</td><td>Sigma Aldrich</td><td>806552-500ML</td><td>buffer</td></tr><tr><td>PMMA 495K A4</td><td>MicroChemicals</td><td>PMMA 495K A4</td><td>Photoresist for assisting graphene transferring</td></tr><tr><td>Polydimethylsiloxane (PDMS)</td><td>Sigma Aldrich</td><td>Sylgard 184</td><td>sample delivery well</td></tr><tr><td>Renishaw InVia Raman Microscope</td><td>Renishaw</td><td></td><td>graphene characterization</td></tr><tr><td>Sodium Hydroxide (NaOH)</td><td>Sigma Aldrich</td><td>221465-25G</td><td>functionalization</td></tr><tr><td>Suss Microtech MA6 Mask Aligner</td><td>Suss MicroTec</td><td></td><td>photolithography</td></tr><tr><td>Thermo Scientific Cimarec Hotplate</td><td>Thermo Scientific</td><td>SP131635</td><td>sample and device Baking</td></tr></tbody></table>

development and functionalization of electrolyte-gated graphene field-effect transistor for biomarker detection

In the current study, graphene and its derivatives have been investigated and used for many applications, including electronics, sensing, energy storage, and photocatalysis. Synthesis and fabrication of high quality, good uniformity, and low defects graphene are critical for high-performance and highly sensitive devices. Among many synthesis methods, chemical vapor deposition (CVD), considered a leading approach to manufacture graphene, can control the number of graphene layers and yield high-quality graphene. CVD graphene needs to be transferred from the metal substrates on which it is grown onto&#160;insulating substrates for practical applications. However, separation and transferring of graphene onto new substrates are challenging for a uniform layer without damaging or affecting graphene&#39;s structures and properties. Additionally, electrolyte-gated graphene field-effect transistor (EGGFET) has been demonstrated for its wide applications in various biomolecular detections because of its high sensitivity and standard device configuration. In this article, poly (methyl methacrylate) (PMMA)-assisted graphene transferring approach, fabrication of graphene field-effect transistor (GFET), and biomarker immunoglobulin G (IgG) detection are demonstrated. Raman spectroscopy and atomic force microscopy were applied to characterize the transferred graphene. The method is shown to be a practical approach for transferring clean and residue-free graphene while preserving the underlying graphene lattice onto an insulating substrate for electronics or biosensing applications.

The representative results show the transferred CVD graphene characterized by Raman and AFM, respectively. The G peak and the 2D peaks of the Raman image give comprehensive information regarding the existence and the quality of the transferred monolayer graphene32 (Figure 1). Standard lithography processes30,31 were applied for fabricating the GFET device, as shown in Figure 2. <s...

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Development and Functionalization of Electrolyte-Gated Graphene Field-Effect Transistor for Biomarker Detection

The present protocol demonstrates the development of electrolyte-gated graphene field-effect transistor (EGGFET) biosensor and its application in biomarker immunoglobulin G (IgG) detection.

In the current study, graphene and its derivatives have been investigated and used for many applications, including electronics, sensing, energy storage, ...

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3.2K Views.  West Virginia University. De methode verwijdert effectief PMMA-residu met behoud van het onderliggende grafeenrooster. Het functionele apparaat toont consistente resultaten bij het detecteren van IgG-antilichamen in bloedserum. Ook zorgt het protocol voor de implementatie van CVD grafeen in een realtime, labelvrij biosensing apparaat.De stappen zijn vrij eenvoudig en kunnen worden gedaan met minimale training. Het apparaat biedt een hoge selectiviteit, hoge gevoeligheid en realtime detectie ten opzichte van and...

Video: Development and Functionalization of Electrolyte-Gated Graphene Field-Effect Transistor for Biomarker Detection

Development of a 3D Graphene Electrode Dielectrophoretic Device

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The protocol details the procedures to construct a versatile, reusable, multiple layer, laminated dielectrophoresis chamber. Specifically, six layers of 50 &#181;m x&#160;0.7 cm x&#160;2 cm graphene paper and five layers of double sided tape were alternately stacked together, then clamped to a glass slide. Then a 700 &#956;m diameter micro-well was drilled through the laminated structure using a computer-controlled micro drilling machine. Insulating properties of the tape layer between adjacent graphene layers were assured by resistance tests. Silver conductive epoxy connected alternate layers of graphene paper and formed stable connections between the graphene paper and external copper wire electrodes. The finished device was then clamped and sealed to a glass slide. The electric field gradient was modeled within the multi-layer device. Dielectrophoretic behaviors of 6 &#956;m polystyrene beads were demonstrated in the 1 mm deep micro-well, with medium conductivities ranging from 0.0001 S/m to 1.3 S/m, and applied signal frequencies from 100 Hz to 10 MHz. Negative dielectrophoretic responses were observed in three dimensions over most of the conductivity-frequency space and cross-over frequency values are consistent with previously reported literature values. The device did not prevent AC electroosmosis and electrothermal flows, which occurred in the low and high frequency regions, respectively. The graphene paper utilized in this device is versatile and could subsequently function as a biosensor after dielectrophoretic characterizations are complete.

A microdevice with high throughput potential is used to demonstrate three-dimensional (3D) dielectrophoresis (DEP) with novel materials. Graphene nanoplatelet paper and double sided tape were alternately stacked; a 700 &#956;m micro-well was drilled transverse to the layers. DEP behavior of polystyrene beads was demonstrated in the micro-well.

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The ...

Bridging the Bio-Electronic Interface with Biofabrication

Advancements in lab-on-a-chip technology promise to revolutionize both research and medicine through lower costs, better sensitivity, portability, and higher throughput. The incorporation of biological components onto biological microelectromechanical systems (bioMEMS) has shown great potential for achieving these goals. Microfabricated electronic chips allow for micrometer-scale features as well as an electrical connection for sensing and actuation. Functional biological components give the system the capacity for specific detection of analytes, enzymatic functions, and whole-cell capabilities. Standard microfabrication processes and bio-analytical techniques have been successfully utilized for decades in the computer and biological industries, respectively. Their combination and interfacing in a lab-on-a-chip environment, however, brings forth new challenges. There is a call for techniques that can build an interface between the electrode and biological component that is mild and is easy to fabricate and pattern.
Biofabrication, described here, is one such approach that has shown great promise for its easy-to-assemble incorporation of biological components with versatility in the on-chip functions that are enabled. Biofabrication uses biological materials and biological mechanisms (self-assembly, enzymatic assembly) for bottom-up hierarchical assembly. While our labs have demonstrated these concepts in many formats 1,2,3, here we demonstrate the assembly process based on electrodeposition followed by multiple applications of signal-based interactions. The assembly process consists of the electrodeposition of biocompatible stimuli-responsive polymer films on electrodes and their subsequent functionalization with biological components such as DNA, enzymes, or live cells 4,5. Electrodeposition takes advantage of the pH gradient created at the surface of a biased electrode from the electrolysis of water 6,7,. Chitosan and alginate are stimuli-responsive biological polymers that can be triggered to self-assemble into hydrogel films in response to imposed electrical signals 8. The thickness of these hydrogels is determined by the extent to which the pH gradient extends from the electrode. This can be modified using varying current densities and deposition times 6,7. This protocol will describe how chitosan films are deposited and functionalized by covalently attaching biological components to the abundant primary amine groups present on the film through either enzymatic or electrochemical methods 9,10. Alginate films and their entrapment of live cells will also be addressed 11. Finally, the utility of biofabrication is demonstrated through examples of signal-based interaction, including chemical-to-electrical, cell-to-cell, and also enzyme-to-cell signal transmission. 
Both the electrodeposition and functionalization can be performed under near-physiological conditions without the need for reagents and thus spare labile biological components from harsh conditions. Additionally, both chitosan and alginate have long been used for biologically-relevant purposes 12,13. Overall, biofabrication, a rapid technique that can be simply performed on a benchtop, can be used for creating micron scale patterns of functional biological components on electrodes and can be used for a variety of lab-on-a-chip applications.

This article describes a biofabrication approach: deposition of stimuli-responsive polysaccharides in the presence of biased electrodes to create biocompatible films which can be functionalized with cells or proteins. We demonstrate a bench-top strategy for the generation of the films as well as their basic uses for creating interactive biofunctionalized surfaces for lab-on-a-chip applications.

Advancements in lab-on-a-chip technology promise to revolutionize both research and medicine through lower costs, better sensitivity, portability, and ...

Bioengineering

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (&#181;PAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use ...

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them good candidates for high sensitivity biosensors. When a charged molecule binds to such a sensor surface, it alters the carrier density5 in the sensor, resulting in changes in its DC conductance. However, in an ionic solution a charged surface also attracts counter-ions from the solution, forming an electrical double layer (EDL). This EDL effectively screens off the charge, and in physiologically relevant conditions ~100 millimolar (mM), the characteristic charge screening length (Debye length) is less than a nanometer (nm). Thus, in high ionic strength solutions, charge based (DC) detection is fundamentally impeded6-8.
We overcome charge screening effects by detecting molecular dipoles rather than charges at high frequency, by operating carbon nanotube field effect transistors as high frequency mixers9-11. At high frequencies, the AC drive force can no longer overcome the solution drag and the ions in solution do not have sufficient time to form the EDL. Further, frequency mixing technique allows us to operate at frequencies high enough to overcome ionic screening, and yet detect the sensing signals at lower frequencies11-12. Also, the high transconductance of SWNT transistors provides an internal gain for the sensing signal, which obviates the need for external signal amplifier.
Here, we describe the protocol to (a) fabricate SWNT transistors, (b) functionalize biomolecules to the nanotube13, (c) design and stamp a poly-dimethylsiloxane (PDMS) micro-fluidic chamber14 onto the device, and (d) carry out high frequency sensing in different ionic strength solutions11.

We describe the device fabrication and measurement protocol for carbon nanotube based high frequency biosensors. The high frequency sensing technique mitigates the fundamental ionic (Debye) screening effect and allows nanotube biosensor to be operated in high ionic strength solutions where conventional electronic biosensors fail. Our technology provides a unique platform for point-of-care (POC) electronic biosensors operating in physiologically relevant conditions.

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them ...

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 ...

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.

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 ...

Exploring Biomolecular Interaction Between the Molecular Chaperone Hsp90 and Its Client Protein Kinase Cdc37 using Field-Effect Biosensing Technology

Biomolecular interactions play versatile roles in numerous cellular processes&#160;by regulating and coordinating functionally relevant biological events. Biomolecules such as proteins, carbohydrates, vitamins, fatty acids, nucleic acids, and enzymes are fundamental building blocks of living beings; they assemble into complex networks in biosystems to synchronize a myriad of life events. Proteins typically utilize complex interactome networks to carry out their functions; hence it is mandatory to evaluate such interactions to unravel their importance in cells at both cellular and organism levels. Toward this goal, we introduce a rapidly emerging technology, field-effect biosensing (FEB), to determine specific biomolecular interactions. FEB is a benchtop, label-free, and reliable biomolecular detection technique to determine specific interactions and uses high-quality electronic-based biosensors. The FEB technology can monitor interactions in the nanomolar range due to the biocompatible nanomaterials used on its biosensor surface. As a proof of concept, the protein-protein interaction (PPI) between heat shock protein 90 (Hsp90) and cell division cycle 37 (Cdc37) was elucidated. Hsp90 is an ATP-dependent molecular chaperone that plays an essential role in the folding, stability, maturation, and quality control of many proteins, thereby regulating multiple vital cellular functions. Cdc37 is regarded as a protein kinase-specific molecular chaperone, as it specifically recognizes and recruits protein kinases to Hsp90 to regulate their downstream signal transduction pathways. As such, Cdc37 is considered a co-chaperone of Hsp90. The chaperone-kinase pathway (Hsp90/Cdc37 complex) is hyper-activated in multiple malignancies promoting cellular growth; therefore, it is a potential target for cancer therapy. The present study demonstrates the efficiency of FEB technology using the Hsp90/Cdc37 model system. FEB detected a strong PPI between the two proteins (KD values of 0.014 &#181;M, 0.053 &#181;M, and 0.072 &#181;M in three independent experiments). In summary, FEB is a label-free and cost-effective PPI detection platform, which offers fast and accurate measurements.

Field-effect biosensing (FEB) is a label-free technique for detecting biomolecular interactions. It measures the electric current through the graphene biosensor to which the binding targets are immobilized. The FEB technology was used to evaluate biomolecular interactions between Hsp90 and Cdc37 and a strong interaction between the two proteins was detected.

Biomolecular interactions play versatile roles in numerous cellular processes&#160;by regulating and coordinating functionally relevant biological events. ...

Biochemistry

Dry Film Photoresist-based Electrochemical Microfluidic Biosensor Platform: Device Fabrication, On-chip Assay Preparation, and System Operation

In recent years, biomarker diagnostics became an indispensable tool for the diagnosis of human disease, especially for the point-of-care diagnostics. An easy-to-use and low-cost sensor platform is highly desired to measure various types of analytes (e.g., biomarkers, hormones, and drugs) quantitatively and specifically. For this reason, dry film photoresist technology - enabling cheap, facile, and high-throughput fabrication - was used to manufacture the microfluidic biosensor presented here. Depending on the bioassay used afterwards, the versatile platform is capable of detecting various types of biomolecules. For the fabrication of the device, platinum electrodes are structured on a flexible polyimide (PI) foil in the only clean-room process step. The PI foil serves as a substrate for the electrodes, which are insulated with an epoxy-based photoresist. The microfluidic channel is subsequently generated by the development and lamination of dry film photoresist (DFR) foils onto the PI wafer. By using a hydrophobic stopping barrier in the channel, the channel is separated into two specific areas: an immobilization section for the enzyme-linked assay and an electrochemical measurement cell for the amperometric signal readout.
The on-chip bioassay immobilization is performed by the adsorption of the biomolecules to the channel surface. The glucose oxidase enzyme is used as a transducer for electrochemical signal generation. In the presence of the substrate, glucose, hydrogen peroxide is produced, which is detected at the platinum working electrode. The stop-flow technique is applied to obtain signal amplification along with rapid detection. Different biomolecules can quantitatively be measured by means of the introduced microfluidic system, giving an indication of different types of diseases, or, in regard to therapeutic drug monitoring, facilitating a personalized therapy.

A microfluidic biosensor platform was designed and fabricated using low-cost dry film photoresist technology for the rapid and sensitive quantification of various analytes. This single-use system allows for the electrochemical readout of on-chip-immobilized enzyme-linked assays by means of the stop-flow technique.

In recent years, biomarker diagnostics became an indispensable tool for the diagnosis of human disease, especially for the point-of-care diagnostics. An ...

In Vitro Multiparametric Cellular Analysis by Micro Organic Charge-modulated Field-effect Transistor Arrays

Modern electrophysiology has been constantly fueled by the parallel development of increasingly sophisticated tools and materials. In turn, discoveries in this field have driven technological progress in a back-and-forth process that ultimately determined the impressive achievements of the past 50 years. However, the most employed devices used for cellular interfacing (namely, the microelectrode arrays and microelectronic devices based on transistors) still present several limitations such as high cost, the rigidity of the materials, and the presence of an external reference electrode. To partially overcome these issues, there have been developments in a new scientific field called organic bioelectronics, resulting in advantages such as lower cost, more convenient materials, and innovative fabrication techniques.
Several interesting new organic devices have been proposed during the past decade to conveniently interface with cell cultures.&#160;This paper presents the protocol for the fabrication of devices for cellular interfacing based on the organic charge-modulated field-effect transistor (OCMFET). These devices, called micro OCMFET arrays (MOAs), combine the advantages of organic electronics and the peculiar features of the OCMFET to prepare transparent, flexible, and reference-less tools with which it is possible to monitor both the electrical and the metabolic activities of cardiomyocytes and neurons in vitro, thus allowing a multiparametric evaluation of electrogenic cell models.

In Vitro Multiparametric Cellular Analysis by Micro Organic Charge-modulated Field-effect Transistor Arrays

Here, we present the fabrication protocol of an organic charge-modulated field-effect transistor (OCMFET)-based device for in vitro cellular interfacing. The device, called a micro OCMFET array, is a flexible, low-cost, and reference-less device, which will enable the monitoring of the electrical and metabolic activities of electroactive cell cultures.

Modern electrophysiology has been constantly fueled by the parallel development of increasingly sophisticated tools and materials. In turn, discoveries in ...

High-Performance Graphene-Modified Sensing Chip for SARS-CoV-2 Detection

This sensing prototype model involves the development of a reusable, twofold graphene oxide (GrO)-glazed double inter-digitated capacitive (DIDC) detecting chip for detecting severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2) specifically and rapidly. The fabricated DIDC comprises a Ti/Pt-containing glass substrate glazed with graphene oxide (GrO), which is further chemically modified with EDC-NHS to immobilize antibodies (Abs) hostile to SARS-CoV-2 based on the spike (S1) protein of the virus. The results of insightful investigations showed that GrO gave an ideal engineered surface for Ab immobilization and enhanced the capacitance to allow higher sensitivity and low sensing limits. These tunable elements helped accomplish a wide sensing range (1.0 mg/mL to 1.0 fg/mL), a minimum sensing limit of 1 fg/mL, high responsiveness and good linearity of 18.56 nF/g, and a fast reaction time of 3 s. Besides, in terms of developing financially viable point-of-care (POC) testing frameworks, the reusability of the GrO-DIDC biochip in this study is good. Significantly, the biochip is specific against blood-borne antigens and is stable for up to 10 days at 5 &#176;C. Due to its compactness, this scaled-down biosensor has the potential for POC diagnostics of COVID-19 infection. This system can also detect other severe viral diseases, although an approval step utilizing other virus examples is under development.

The present protocol describes the fabrication of low-cost biosensing prototypes based on useful nanosystems for accurately detecting viral proteins (at the Fg level). Such a tiny sensor platform allows for point-of-care applications that can be integrated with the Internet of Medical Things (IoMT) to meet telemedicine objectives.

Development and Functionalization of Electrolyte-Gated Graphene Field-Effect Transistor for Biomarker Detection

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