This work was supported by the Project of Shanghai Science and Technology Committee (STCSM) (22S31902000) and the Clinical Research Incubation Program of Shanghai Skin Disease Hospital (NO. lcfy2021-10).

The study was approved by the Institutional Review Board of Shanghai Skin Disease Hospital (No. 2020-15). All experimental procedures involving human blood samples were conducted in a Biosafety Level II laboratory. The details of the reagents and equipment used in this study are listed in the Table of Materials.
1. Preparation of QDs nanobeads
NOTE: For QD nanobead synthesis, an emulsion-solvent evaporation technique was used to synth...

Quantum Dot Nanobeads for Enhanced Sensitivity in Biomarker Detection

<ol>
	<li>de Puig, H., Bosch, I., Gehrke, L., Hamad-Schifferli, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Challenges+of+the+nano-bio+interface+in+lateral+flow+and+dipstick+immunoassays.">Challenges of the nano-bio interface in lateral flow and dipstick immunoassays.</a> Trends Biotechnol. 35 (12), 1169-1180 (2017).</li><li>Miller, B. S., 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=Spin-enhanced+nanodiamond+biosensing+for+ultrasensitive+diagnostics.">Spin-enhanced nanodiamond biosensing for ultrasensitive diagnostics.</a> Nature. 587 (7835), 588-593 (2020).</li><li>Gao, 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=Platinum-decorated+gold+nanoparticles+with+dual+functionalities+for+ultrasensitive+colorimetric+in+vitro+diagnostics.">Platinum-decorated gold nanoparticles with dual functionalities for ultrasensitive colorimetric in vitro diagnostics.</a> Nano Lett. 17 (9), 5572-5579 (2017).</li><li>Fan, 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=Deeply-dyed+nanobead+system+for+rapid+lateral+flow+assay+testing+of+drugs+at+point-of-care.">Deeply-dyed nanobead system for rapid lateral flow assay testing of drugs at point-of-care.</a> Sensors Actuators B Chem. 362, 131829 (2022).</li><li>Garcia, V. S., Guerrero, S. A., Gugliotta, L. M., Gonzalez, V. D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+lateral+flow+immunoassay+based+on+colored+latex+particles+for+detection+of+canine+visceral+leishmaniasis.">A lateral flow immunoassay based on colored latex particles for detection of canine visceral leishmaniasis.</a> Acta Trop. 212, 105643 (2020).</li><li>You, M., 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=Household+fluorescent+lateral+flow+strip+platform+for+sensitive+and+quantitative+prognosis+of+heart+failure+using+dual-color+upconversion+nanoparticles.">Household fluorescent lateral flow strip platform for sensitive and quantitative prognosis of heart failure using dual-color upconversion nanoparticles.</a> ACS Nano. 11 (6), 6261-6270 (2017).</li><li>Ye, Z., Tan, M., Wang, G., Yuan, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+fluorescent+europium+chelate-doped+silica+nanoparticles:+preparation,+characterization+and+time-resolved+fluorometric+application.">Novel fluorescent europium chelate-doped silica nanoparticles: preparation, characterization and time-resolved fluorometric application.</a> J Mater Chem. 14 (5), 851 (2004).</li><li>Xu, Y., Li, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+fluorescent+labeling+of+silica+nanoparticles+with+lanthanide+chelates+for+highly+sensitive+time-resolved+immunofluorometric+assays.">Multiple fluorescent labeling of silica nanoparticles with lanthanide chelates for highly sensitive time-resolved immunofluorometric assays.</a> Clin Chem. 53 (8), 1503-1510 (2007).</li><li>Zhang, 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=Improving+detection+sensitivity+by+oriented+bioconjugation+of+antibodies+to+quantum+dots+with+a+flexible+spacer+arm+for+immunoassay.">Improving detection sensitivity by oriented bioconjugation of antibodies to quantum dots with a flexible spacer arm for immunoassay.</a> RSC Adv. 6 (55), 50119-50127 (2016).</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=Rapid+and+sensitive+detection+of+protein+biomarker+using+a+portable+fluorescence+biosensor+based+on+quantum+dots+and+a+lateral+flow+test+strip.">Rapid and sensitive detection of protein biomarker using a portable fluorescence biosensor based on quantum dots and a lateral flow test strip.</a> Anal Chem. 82 (16), 7008-7014 (2010).</li><li>Wang, 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=Fluorescent+strip+sensor+for+rapid+determination+of+toxins.">Fluorescent strip sensor for rapid determination of toxins.</a> Chem Commun. 47 (5), 1574-1576 (2011).</li><li>Medintz, I. L., Uyeda, H. T., Goldman, E. R., Mattoussi, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+dot+bioconjugates+for+imaging,+labeling+and+sensing.">Quantum dot bioconjugates for imaging, labeling and sensing.</a> Nat Mater. 4 (6), 435-446 (2005).</li><li>Smith, A. M., Nie, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compact+quantum+dots+for+single-molecule+imaging.">Compact quantum dots for single-molecule imaging.</a> J Vis Exp. 68, e4236 (2012).</li><li>Wang, 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=Layer-by-layer+assembly+of+magnetic-core+dual+quantum+dot-shell+nanocomposites+for+fluorescence+lateral+flow+detection+of+bacteria.">Layer-by-layer assembly of magnetic-core dual quantum dot-shell nanocomposites for fluorescence lateral flow detection of bacteria.</a> Nanoscale. 12 (2), 795-807 (2020).</li><li>Hu, J., Tang, F., Jiang, Y. Z., Liu, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+screening+and+quantitative+detection+of+Salmonella+using+a+quantum+dot+nanobead-based+biosensor.">Rapid screening and quantitative detection of Salmonella using a quantum dot nanobead-based biosensor.</a> Analyst. 145 (6), 2184-2190 (2020).</li><li>Wang, 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=Introduction+of+graphene+oxide-supported+multilayer-quantum+dots+nanofilm+into+multiplex+lateral+flow+immunoassay:+A+rapid+and+ultrasensitive+point-of-care+testing+technique+for+multiple+respiratory+viruses.">Introduction of graphene oxide-supported multilayer-quantum dots nanofilm into multiplex lateral flow immunoassay: A rapid and ultrasensitive point-of-care testing technique for multiple respiratory viruses.</a> Nano Res. 16 (2), 3063-3073 (2023).</li><li>Wang, 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=Colorimetric-fluorescent+dual-signal+enhancement+immunochromatographic+assay+based+on+molybdenum+disulfide-supported+quantum+dot+nanosheets+for+the+point-of-care+testing+of+monkeypox+virus.">Colorimetric-fluorescent dual-signal enhancement immunochromatographic assay based on molybdenum disulfide-supported quantum dot nanosheets for the point-of-care testing of monkeypox virus.</a> Chem Eng J. 472, 144889 (2023).</li><li>Zheng, S., 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=Dual-color+MoS2@QD+nanosheets+mediated+dual-mode+lateral+flow+immunoassay+for+flexible+and+ultrasensitive+detection+of+multiple+drug+residues.">Dual-color MoS2@QD nanosheets mediated dual-mode lateral flow immunoassay for flexible and ultrasensitive detection of multiple drug residues.</a> Sensors Actuators B Chem. 403, 135142 (2024).</li><li>Wang, G., 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=Efficient+incorporation+of+quantum+dots+into+porous+microspheres+through+a+solvent-evaporation+approach.">Efficient incorporation of quantum dots into porous microspheres through a solvent-evaporation approach.</a> Langmuir. 28 (14), 6141-6150 (2012).</li><li>Li, 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=Fluorescent+lateral+flow+immunoassay+for+highly+sensitive+detection+of+eight+anticoagulant+rodenticides+based+on+cadmium-free+quantum+dot-encapsulated+nanospheres.">Fluorescent lateral flow immunoassay for highly sensitive detection of eight anticoagulant rodenticides based on cadmium-free quantum dot-encapsulated nanospheres.</a> Sensors Actuators B Chem. 324, 128771 (2020).</li><li>Gao, 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=Rational+design+of+dendritic+mesoporous+silica+nanoparticles'+surface+chemistry+for+quantum+dot+enrichment+and+an+ultrasensitive+lateral+flow+immunoassay.">Rational design of dendritic mesoporous silica nanoparticles' surface chemistry for quantum dot enrichment and an ultrasensitive lateral flow immunoassay.</a> ACS Appl Mater Interfaces. 13 (18), 21507-21515 (2021).</li><li>Xu, L. D., Zhu, J., Ding, S. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunoassay+of+SARS-CoV-2+nucleocapsid+proteins+using+novel+red+emission-enhanced+carbon+dot-based+silica+spheres.">Immunoassay of SARS-CoV-2 nucleocapsid proteins using novel red emission-enhanced carbon dot-based silica spheres.</a> Analyst. 146 (16), 5055-5060 (2021).</li><li>Tao, S., 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=SARS-Cov-2+Spike-S1+antigen+test+strip+with+high+sensitivity+endowed+by+high-affinity+antibodies+and+brightly+fluorescent+QDs/silica+nanospheres.">SARS-Cov-2 Spike-S1 antigen test strip with high sensitivity endowed by high-affinity antibodies and brightly fluorescent QDs/silica nanospheres.</a> ACS Appl Mater Interfaces. 15 (23), 27612-27623 (2023).</li><li>Wang, 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=Development+of+an+ultrasensitive+fluorescent+immunochromatographic+assay+based+on+multilayer+quantum+dot+nanobead+for+simultaneous+detection+of+SARS-CoV-2+antigen+and+influenza+A+virus.">Development of an ultrasensitive fluorescent immunochromatographic assay based on multilayer quantum dot nanobead for simultaneous detection of SARS-CoV-2 antigen and influenza A virus.</a> Sensors Actuators B Chem. 345, 130372 (2021).</li><li>Chen, L., Chen, C., Li, R., Li, Y., Liu, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CdTe+quantum+dot+functionalized+silica+nanosphere+labels+for+ultrasensitive+detection+of+biomarker.">CdTe quantum dot functionalized silica nanosphere labels for ultrasensitive detection of biomarker.</a> Chem Commun. 19, 2670-2672 (2009).</li><li>Chu, M., 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+novel+method+for+preparing+quantum+dot+nanospheres+with+narrow+size+distribution.">A novel method for preparing quantum dot nanospheres with narrow size distribution.</a> Nanoscale. 2 (4), 542-547 (2010).</li><li>Zhang, P., Lu, H., Chen, J., Han, H., Ma, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+and+sensitive+detection+of+HBsAg+by+using+a+quantum+dots+nanobeads+based+dot-blot+immunoassay.">Simple and sensitive detection of HBsAg by using a quantum dots nanobeads based dot-blot immunoassay.</a> Theranostics. 4 (3), 307-315 (2014).</li><li>Ouyang, S., 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=An+on-site,+ultra-sensitive,+quantitative+sensing+method+for+the+determination+of+total+aflatoxin+in+peanut+and+rice+based+on+quantum+dot+nanobeads+strip.">An on-site, ultra-sensitive, quantitative sensing method for the determination of total aflatoxin in peanut and rice based on quantum dot nanobeads strip.</a> Toxins. 9 (4), 137 (2017).</li><li>Liu, 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=Quantitative+ciprofloxacin+on-site+rapid+detections+using+quantum+dot+microsphere+based+immunochromatographic+test+strips.">Quantitative ciprofloxacin on-site rapid detections using quantum dot microsphere based immunochromatographic test strips.</a> Food Chem. 335, 127596 (2021).</li><li>Chen, Y., Fu, Q., Xie, J., Wang, H., Tang, Y. <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+a+high+sensitivity+quantum+dot-based+fluorescent+quenching+lateral+flow+assay+for+the+detection+of+zearalenone.">Development of a high sensitivity quantum dot-based fluorescent quenching lateral flow assay for the detection of zearalenone.</a> Anal Bioanal Chem. 411 (10), 2169-2175 (2019).</li><li>Zhang, Q., 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=SARS-CoV-2+detection+using+quantum+dot+fluorescence+immunochromatography+combined+with+isothermal+amplification+and+CRISPR/Cas13a.">SARS-CoV-2 detection using quantum dot fluorescence immunochromatography combined with isothermal amplification and CRISPR/Cas13a.</a> Biosens Bioelectron. 202, 113978 (2022).</li><li>Zhong, 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=CRISPR-based+quantum+dot+nanobead+lateral+flow+assay+for+facile+detection+of+varicella-zoster+virus.">CRISPR-based quantum dot nanobead lateral flow assay for facile detection of varicella-zoster virus.</a> Appl Microbiol Biotechnol. 107 (10), 3319-3328 (2023).</li><li>Liu, Y., Xiao, M., Xu, N., Yang, M., Yi, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Point-of-need+quantitation+of+2,4-dichlorophenoxyacetic+acid+using+a+ratiometric+fluorescent+nanoprobe+and+a+smartphone-based+sensing+system.">Point-of-need quantitation of 2,4-dichlorophenoxyacetic acid using a ratiometric fluorescent nanoprobe and a smartphone-based sensing system.</a> Sensors Actuators B Chem. 367, 132083 (2022).</li><li>McCafferty, 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=Blood+collection+processing+and+handling+for+plasma+and+serum+proteomics+BT+-+Serum/plasma+proteomics.">Blood collection processing and handling for plasma and serum proteomics BT - Serum/plasma proteomics.</a> Methods Mol Biol. 2628, 33-40 (2023).</li><li>Zhang, P., 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=Rapid+and+quantitative+detection+of+C-reactive+protein+based+on+quantum+dots+and+immunofiltration+assay.">Rapid and quantitative detection of C-reactive protein based on quantum dots and immunofiltration assay.</a> Int J Nanomedicine. 10, 6161-6173 (2015).</li><li>Hu, 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=Sensitive+and+quantitative+detection+of+C-reaction+protein+based+on+immunofluorescent+nanospheres+coupled+with+lateral+flow+test+strip.">Sensitive and quantitative detection of C-reaction protein based on immunofluorescent nanospheres coupled with lateral flow test strip.</a> Anal Chem. 88 (12), 6577-6584 (2016).</li><li>Fan, 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=One-component+dual-readout+aggregation-induced+emission+nanobeads+for+qualitative+and+quantitative+detection+of+c-reactive+protein+at+the+point+of+care.">One-component dual-readout aggregation-induced emission nanobeads for qualitative and quantitative detection of c-reactive protein at the point of care.</a> Anal Chem. 96 (1), 401-408 (2024).</li><li>Gui, 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=Colorimetric+and+reverse+fluorescence+dual-signal+readout+immunochromatographic+assay+for+the+sensitive+determination+of+sibutramine.">Colorimetric and reverse fluorescence dual-signal readout immunochromatographic assay for the sensitive determination of sibutramine.</a> ACS Omega. 9 (6), 7075-7084 (2024).</li></ol>

Here, we describe a protocol for the preparation of quantum dot nanobeads (QDNB)27 and the use of QDNB for the preparation of fluorescent lateral flow immunoassays (LFIA). The qualitative and quantitative measurement of CRP in samples is demonstrated. This QDNB-based LFIA can also be applied to other disease biomarkers25,32, food toxins29,30, viruses16,...

Lateral flow immunoassay (LFIA) strips serve as crucial rapid detection tools at point-of-care1,2, particularly in disease screening during epidemics. However, traditional colloidal gold-based LFIA test strips exhibit low detection sensitivity and only provide qualitative results3. To enhance the detection sensitivity of LFIA, various new nanoparticles have emerged, including colored latex4,5, upconversion fluorescent nanoparticles6, time-resolved fluorescent microspheres7,8, and quantum dots9,10,11. Quantum dots (QDs)12,13, also known as semiconductor nanocrystals, offer tunable emission wavelengths, a wide excitation range, and high luminescence efficiency, making them ideal labels for biological imaging.
However, the fluorescence signal emitted by individual quantum dots remains weak, resulting in relatively low detection sensitivity in immunoassays. Encapsulation of numerous quantum dots within microspheres can amplify signals and improve the sensitivity of quantum dot-based immunoassays. Various methods, such as layer-by-layer self-assembly14,15,16,17,18, the swelling method19,20, and silica microsphere21,22,23,24 encapsulation, have been employed to encapsulate quantum dots inside microspheres. For example, quantum dot-functionalized silica nanosphere labels can be achieved by increasing QD loading per sandwiched immunoreaction25. A spray dryer equipped with an ultrasonic atomizer has also been used to prepare nanoscale QD-BSA nanospheres26. However, the aforementioned methods suffer from complex multi-steps, fluorescence quenching, and low productivity.
In our previous work27, an emulsion-solvent evaporation method for encapsulating quantum dots inside polymer nanobeads was reported. This preparation technique is simple, maintains the fluorescent efficiency of QDs, ensures high encapsulation efficiency, and allows for easy scalable production. Several research groups have successfully developed LFIA strips using QDNBs prepared through this method for applications, including food toxin detection28,29,30, infectious disease biomarker detection31,32, and environmental monitoring33.
This protocol presents specific preparation steps for quantum dot nanobeads (QDNB), QDNB and antibody conjugation, preparation of QDNB-based LFIA, and measurement of C-reactive protein (CRP) in human plasma samples.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>(dimethylamino)propyl)-N&#8217;-ethylcarbodiimide hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>03450</td>
			<td></td>
		</tr>
		<tr>
			<td>Absorbance paper&#160;</td>
			<td>Kinbio Biotech</td>
			<td>CH37K</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine serum albumin</td>
			<td>Sigma-Aldrich</td>
			<td>B2064</td>
			<td></td>
		</tr>
		<tr>
			<td>Casein</td>
			<td>Sigma-Aldrich</td>
			<td>C8654</td>
			<td></td>
		</tr>
		<tr>
			<td>CdSe/ZnS quantum dot</td>
			<td>Suzhou Mesolight Inc.</td>
			<td>CdSe/ZnS-625</td>
			<td></td>
		</tr>
		<tr>
			<td>Choloroform</td>
			<td>Sino Pharm</td>
			<td>10006818</td>
			<td></td>
		</tr>
		<tr>
			<td>CRP antibody</td>
			<td>Hytest Biotech</td>
			<td>4C28</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescent lateral flow assay reader</td>
			<td>Suzhou Helmence Precision Instrument</td>
			<td>FIC-H1</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass fiber pad</td>
			<td>Kinbio Biotech</td>
			<td>SB06</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-rabbit IgG</td>
			<td>Sangon Biotech</td>
			<td>D111018</td>
			<td></td>
		</tr>
		<tr>
			<td>Nitrocellulose membrane&#160;</td>
			<td>Satorious</td>
			<td>CN140</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(styrene-maleic anhydride) copolymer&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>S458066</td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit IgG</td>
			<td>Sangon Biotech</td>
			<td>D110502</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulfate</td>
			<td>Sino Pharm</td>
			<td>30166428</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Sino Pharm</td>
			<td>10019718</td>
			<td></td>
		</tr>
	</tbody>
</table>

fluorescent lateral flow immunoassay based on quantum dots nanobeads

Quantum dots, also known as semiconductor nanocrystals, are novel fluorescent labels for biological imaging and sensing. However, quantum dot-antibody conjugates with small dimensions (~10 nm), prepared through laborious purification procedures, exhibit limited sensitivity in detecting certain trace disease markers using lateral flow immunoassay strips. Herein, we present a method for the preparation of quantum dot nanobeads (QDNB) using a one-step emulsion evaporation method. Using the as-prepared QDNB, a fluorescent lateral flow immunoassay was fabricated to detect disease biomarkers using C-reactive protein (CRP) as an example. Unlike single quantum dot nanoparticles, quantum dot nanobead-antibody conjugates are more sensitive as immunoassay labels due to signal amplification by encapsulating hundreds of quantum dots in one polymer composite nanobead. Moreover, the larger size of QDNBs facilitates easier centrifugation separation when conjugating QDNBs with antibodies. The fluorescent lateral flow immunoassay based on QDNBs was fabricated, and the CRP concentration in the sample was measured in 15 min. The test results can be qualitatively assessed under UV light illumination and quantitatively measured using a fluorescent reader within 15 min.

Author Spotlight: High-Quality Quantum Dot Nanobeads for Sensitive Fluorescent Lateral Flow Immunoassays

Fluorescent Lateral Flow Immunoassay Based on Quantum Dots Nanobeads

Our research interests currently focus on constructing high-quality multifunctional nanomaterials and their application in the development of ultrasensitive point-of-care diagnostics. Lateral flow immunoassay strips serve as critical rapid detection tools at the point-of-care, particularly in disease screening during epidemics to enhance the detection sensitivity to lateral flow immunoassay. Various new nanoparticle has emerged, including colored latex, upcoercion fluorescent nanoparticles, timed-result fluorescent microspheres, and quantum dots.We presented a one-step emulsion evaporation method for preparing quantum dot nanobeads and other applications in sensitivity, for instance, lateral fluoro-immunoassays. Common to other methods of preparing quantum dot nanobeads, this protocol offers the advantage of simplicities of operation and high productivity. Additionally, the polymer composite nanobeads are biocompatible, unlike silica nanobeads, which generally need additional surface modification with polymers.Sensitive fluorescent lateral flow immunoassay strips have been developed using prepared quantum dot nanobeads. These strips can be used to qualitatively and quantitatively detect disease biomarkers at point-of-care. This new assay could help medical professionals diagnose diseases quickly and accurately.

The QDNB preparation procedures are schematically illustrated in Figure 1A. The oil phase containing QDs and polymer in chloroform was mixed with the water phase, and a mini-emulsion was obtained by sonication. The emulsion was solidified by gradual evaporation of chloroform. The transmission electron micrograph (TEM) of QDNB is presented in Figure 2A. The QDNBs have a spherical morphology, with average diameters of 96 nm, measured over 50 QDNBs in TEM images. Q...

Here, we describe a protocol for the preparation of quantum dot nanobeads (QDNB) and the detection of disease biomarkers using QDNB-based lateral flow immunoassay strips. The test results can be qualitatively assessed under UV light illumination and quantitatively measured using a fluorescent strip reader within 15 min.

Quantum dots, also known as semiconductor nanocrystals, are novel fluorescent labels for biological imaging and sensing. However, quantum dot-antibody ...

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Research

JoVE Journal

Biochemistry

Preparation of Quantum Dots (QDs) Nanobeads for QDNB-Based Lateral Flow Immunoassay

To begin, mix 0.4 milliliters of polystyrene co-maleic anhydride solution and 0.1 milliliters of QD solution to prepare 1 milliliter of the oil phase. Then fill the rest with chloroform until the volume reaches 1 milliliter. Next, prepare the aqueous phase using sodium dodecyl sulfate solution.Combine 1 milliliter of the oil phase and 5 milliliters of the aqueous phase in a vial. Place the vial on a magnetic stir and turn it on. Once the oil and aqueous phases are thoroughly mixed, immediately transfer the vial to the programmed ultrasonication device and turn on the power.Then place the vial back on the magnetic stir at room temperature and stir continuously overnight. After solvent evaporation, add 0.1 milliliters of 0.1 millimolar sodium hydroxide to the nanobead suspension, and allow it to react for one hour.

QDNB-Antibody Conjugates Preparation Using One-Step Emulsion Evaporation Method

To begin, add 100 microliters of prepared QD nanobeads to 200 microliters of phosphate buffer. Then add six microliters of EDC. After that, incubate the mixture for 30 minutes at room temperature on a rotary mixer.Centrifuge the mixture at 13, 523 g for 10 minutes at room temperature and discard the supernatant. Next, add 100 microliters of phosphate buffer to the precipitate. Cover the tube with its lid and immerse it in the operational ultrasonic water bath until the precipitate is fully dispersed.Disperse 100 micrograms of antibody in 200 microliters of phosphate buffer, and add the activated QD nanobead suspension to the antibody solution. Incubate the mixture at room temperature for 30 minutes with continuous rotation. Then remove excess antibodies by centrifugation at 6, 010 g for five minutes at room temperature, and carefully discard the supernatant.To block the nanobeads, add 200 microliters of 1%casein solution to the residue. Cover the tube with its lid and immerse it into the operational ultrasonic water bath until the residue is fully dispersed. Incubate the mixture at room temperature for two hours with continuous rotation.Add 100 microliters of preservative solution to the mixture and store at four degrees Celsius for subsequent use.

Lateral Flow Immunoassay Strips Preparation, Assay Operation and its Quantitative Evaluation

To begin, prepare the test line, and control line coating solution. Dilute the C-reactive protein capture antibody, and Goat anti-rabbit immunoglobulin G with phosphate buffer. Next, place the polyvinyl chloride board properly and remove the protective paper located 25 millimeters from the edge of the board.Align and adhere the nitrocellulose membrane along the lower edge of the remaining protective paper to the polyvinyl chloride board. Dispense the test line, and control line coating solutions onto the nitrocellulose membrane, ensuring it is placed 20 millimeters apart from the upper edge, forming a test line. For drying, place the nitrocellulose membrane in conditions with a humidity of less than 30%and a temperature range of 18 to 26 degrees Celsius.To prepare the conjugate pad, submerge the conjugate pad into the conjugate pad treatment solution, then place the soaked conjugate pad in a drying oven for overnight drying treatment. Dilute the prepared QD nano bead antibody conjugate solution with the preservative solution, and dispense it onto the conjugate pad. For sample pad preparation.Submerge the sample pad into the sample pad treatment solution. Then place the soaked sample pad into a drying oven set at 45 degrees Celsius, and dry for 24 hours. Successively, place the absorbent paper, conjugate pad and sample pad on the polyvinyl chloride board with the nitrocellulose membrane.Pipette 10 microliters of plasma sample or calibrator solution into one milliliter of A PBS buffer containing 0.1%tween 20. Then transfer 100 microliters of the prepared diluted sample onto the sample pad of the test strip. After a 15 minute run, observe the fluorescent signals of the test line and control line under ultraviolet light exposure to obtain qualitative results.Insert the strip card into a fluorescent lateral flow assay reader to obtain the fluorescence intensities for quantitative analysis.

379 Views.  Tongji University.  Here, we describe a protocol for the preparation of quantum dot nanobeads (QDNB) and the detection of disease biomarkers using QDNB-based lateral flow immunoassay strips. The test results can be qualitatively assessed under UV light illumination and quantitatively measured using a fluorescent strip reader within 15 min.

Quantum Dot Nanobeads for Enhanced Sensitivity in Biomarker Detection

Summary