Rapid One-Pot Microwave Assisted Green Synthesis Nitrogen Doped Carbon Quantum Dots as Fluorescent Precursor for Estimation of Modafinil as Post-Covid Neurological Drug in Human Plasma with Greenness Assessments.

The neuro-stimulant anti-narcoleptic drug as modafinil (MOD) is used to treatment neurological conditions caused by COVID-19. MOD was used to treatment narcolepsy, shift-work sleep disorder, and obstructive sleep apnea-related sleepiness. So, an innovative, quick, economical, selective, and ecologically friendly procedure was carried out. A highly sensitive N@CQDs technique was created from green Eruca sativa leaves in about 4 min using microwave synthesis at 700 w. The quantum yield of the synthesized N@CQDs was found to be 41.39%. By increasing the concentration of MOD, the quantum dots' fluorescence intensity was gradually quenched. After being excited at 445 nm, the fluorescence reading was recorded at 515 nm. The linear range was found to be in the range 50 - 700 ng mL-1 with lower limit of quantitation (LOQ) equal to 45.00 ng mL-1. The current method was fully validated and bio analytically according to (US-FDA and ICH) guidelines. Full characterization of the N@CQDs has been conducted by high resolution transmission electron microscope (HRTEM), Zeta potential measurement, fluorescence, UV-VIS, and FTIR spectroscopy. Various experimental variables including pH, QDs concentration and the reaction time were optimized. The proposed study is simply implemented for the therapeutic drug monitoring system (TDMS) and various clinical laboratories for further pharmacokinetic research.

A Novel Strategy for Rapid Fluorescence Detection of FluB and SARS-CoV-2.

Undoubtedly, SARS-CoV-2 has caused an outbreak of pneumonia that evolved into a worldwide pandemic. The confusion of early symptoms of the SARS-CoV-2 infection with other respiratory virus infections made it very difficult to block its spread, leading to the expansion of the outbreak and an unreasonable demand for medical resource allocation. The traditional immunochromatographic test strip (ICTS) can detect one analyte with one sample. Herein, this study presents a novel strategy for the simultaneous rapid detection of FluB/SARS-CoV-2, including quantum dot fluorescent microspheres (QDFM) ICTS and a supporting device. The ICTS could be applied to realize simultaneous detection of FluB and SARS-CoV-2 with one test in a short time. A device supporting FluB/SARS-CoV-2 QDFM ICTS was designed and had the characteristics of being safe, portable, low-cost, relatively stable, and easy to use, ensuring the device could replace the immunofluorescence analyzer in cases where there is no need for quantification. This device does not need to be operated by professional and technical personnel and has commercial application potential.

Three birds, one stone: Disinfecting and turning waste medical masks into valuable carbon dots for sodium hydrosulfite and Fe3+ detection enabled by a simple hydrothermal treatment.

Disposable medical masks are widely used to prevent respiratory infections due to their ability to block virus particles from entering the human body. The coronavirus disease 2019 (COVID-19) pandemic highlighted the importance of medical masks, leading to their widespread use around the world. However, a large number of disposable medical masks have been discarded, some carrying viruses, which have posed a grave threat to the environment and people's health, as well as wasting resources. In this study, a simple hydrothermal method was used for the disinfection of waste medical masks under high-temperature conditions as well as for their transformation into high-value-added carbon dots (CDs, a new type of carbon nanomaterial) with blue-emissive fluorescence, without high energy consumption or environmental pollution. Moreover, the mask-derived CDs (m-CDs) could not only be used as fluorescent probes for sensing sodium hydrosulfite (Na2S2O4), which is widely used in the food and textile industries but is seriously harmful to human health, but also be used for detecting Fe3+ which is harmful to the environment and human health due to its wide use in industries.

Flexible Amperometric Immunosensor Based on Colloidal Quantum Dots for Detecting the Myeloperoxidase (MPO) Systemic Inflammation Biomarker.

Myeloperoxidase (MPO) has been demonstrated to be a biomarker of neutrophilic inflammation in various diseases. Rapid detection and quantitative analysis of MPO are of great significance for human health. Herein, an MPO protein flexible amperometric immunosensor based on a colloidal quantum dot (CQD)-modified electrode was demonstrated. The remarkable surface activity of CQDs allows them to bind directly and stably to the surface of proteins and to convert antigen-antibody specific binding reactions into significant currents. The flexible amperometric immunosensor provides quantitative analysis of MPO protein with an ultra-low limit of detection (LOD) (31.6 fg mL-1), as well as good reproducibility and stability. The detection method is expected to be applied in clinical examination, POCT (bedside test), community physical examination, home self-examination and other practical scenarios.

Polyvinylpyrrolidone-passivated fluorescent iron oxide quantum dots for turn-off detection of tetracycline in biological fluids.

Tetracycline is an antibiotic that has been prescribed for COVID-19 treatment, raising concerns about antibiotic resistance after long-term use. This study reported fluorescent polyvinylpyrrolidone-passivated iron oxide quantum dots (IO QDs) for detecting tetracycline in biological fluids for the first time. The as-prepared IO QDs have an average size of 2.84 nm and exist a good stability under different conditions. The IO QDs' tetracycline detection performance could be attributed to a combination of static quenching and inner filter effect. The IO QDs displayed high sensitivity and selectivity toward tetracycline and achieved a good linear relationship with the corresponding detection limit being 91.6 nM.

Employing functionalized graphene quantum dots to combat coronavirus and enterovirus.

The ongoing COVID-19 (i.e., coronavirus) pandemic continues to adversely affect the human life, economy, and the world's ecosystem. Although significant progress has been made in developing antiviral materials for the coronavirus, much more work is still needed. In this work, N-functionalized graphene quantum dots (GQDs) were designed and synthesized as the antiviral nanomaterial for Feline Coronavirus NTU156 (FCoV NTU156) and Enterovirus 71 (EV71)) with ultra-high inhibition (>99.9%). To prepare the GQD samples, a unique solid-phase microwave-assisted technique was developed and the cell toxicity was established on the H171 and H184 cell lines after 72 h incubation, indicating superior biocompatibility. The surface functionality of GQDs (i.e., the phenolic and amino groups) plays a vital role in interacting with the receptor-binding-domain of the spike protein. It was also found that the addition of polyethylene glycol is advantageous for the dispersion and the adsorption of functionalized GQDs onto the virus surface, leading to an enhanced virus inhibition. The functionality of as-prepared GQD nanomaterials was further confirmed where a functionalized GQD-coated glass was shown to be extremely effective in hindering the virus spread for a relatively long period (>20 h).

CdTe QDs-sensitized TiO2 nanocomposite for magnetic-assisted photoelectrochemical immunoassay of SARS-CoV-2 nucleocapsid protein.

A sensitive, reliable, and cost-effective detection for SARS-CoV-2 was urgently needed due to the rapid spread of COVID-19. Here, a "signal-on" magnetic-assisted PEC immunosensor was constructed for the quantitative detection of SARS-CoV-2 nucleocapsid (N) protein based on Z-scheme heterojunction. Fe3O4@SiO2@Au was used to connect the capture antibody to act as a capture probe (Fe3O4@SiO2@Au/Ab1). It can extract target analytes selectively in complex samples and multiple electrode rinsing and assembly steps were avoided effectively. CdTe QDs sensitized TiO2 coated on the surface of SiO2 spheres to form Z-scheme heterojunction (SiO2@TiO2@CdTe QDs), which broadened the optical absorption range and inhibited the quick recombination of photogenerated electron/hole of the composite. With fascinating photoelectric conversion performance, SiO2@TiO2@CdTe QDs were utilized as a signal label, thus further realizing signal amplification. The migration mechanism of photogenerated electrons was further deduced by active material quenching experiment and electron spin resonance (ESR) measurement. The elaborated immunosensor can detect SARS-CoV-2 N protein in the linear range of 0.005-50 ng mL-1 with a low detection limit of 1.8 pg mL-1 (S/N = 3). The immunosensor displays extraordinary sensitivity, strong anti-interference, and high reproducibility in detecting SARS-CoV-2 N protein, which envisages its potential application in the clinical diagnosis of COVID-19.

Ultrasensitive FRET-based aptasensor for interleukin-6 as a biomarker for COVID-19 progression using nitrogen-doped carbon quantum dots and gold nanoparticles.

A label-free and specific FRET-based interleukin-6 (IL-6) aptasensor was developed using a DNA aptamer modified with nitrogen-doped carbon quantum dots (NCDs) and gold nanoparticles (AuNPs) as a donor-quencher pair. The assayed target was capable of disrupting the donor-acceptor assemblies yielding a concentration-related fluorescence recovery of NCDs (λem = 445 nm and λex = 350 nm). By designing two different probes, the interaction of DNA aptamers with IL-6 protein was studied using FRET efficiency. It appeared that the sensing probes showed slightly different sensing profiles. One of the aptasensors showed a linear response of 1.5-5.9 pg/mL for IL-6 with a coefficient of determination of R2 ≥ 0.99 and the a detection limit of 0.82 pg/mL (at S/N = 3). The experimental results indicated that the biosensor can be applied to determine IL-6 in human serum (with recovery of 95.7-102.9%). Due to the high sensitivity, excellent selectivity, and simplicity of the procedure, this strategy represents a promising alternative for IL-6 sensing in clinical applications.

Novel approach based on GQD-PHB as anchoring platform for the development of SARS-CoV-2 electrochemical immunosensor.

In the present work, we report an innovative approach for immunosensors construction. The experimental strategy is based on the anchoring of biological material at screen-printed carbon electrode (SPE) modified with electrodeposited Graphene Quantum Dots (GQD) and polyhydroxybutyric acid (PHB). It was used as functional substract basis for the recognition site receptor-binding domain (RBD) from coronavirus spike protein (SARS-CoV-2), for the detection of Anti-S antibodies (AbS). SEM images and EDS spectra suggest an interaction of the protein with GQD-PHB sites at the electrode surface. Differential pulse voltametric (DPV) measurements were performed before and after incubation, in presence of the target, shown a decrease in voltametric signal of an electrochemical probe ([Fe(CN)6]3/4-). Using the optimal experimental conditions, analytical curves were performed in PBS and human serum spiked with AbS showing a slight matrix effect and a relationship between voltametric signal and AbS concentration in the range of 100 ng mL-1 and 10 µg mL-1. The selectivity of the proposed sensor was tested against yellow fever antibodies (YF) and the selective layer on the electrode surface did not interact with these unspecific antibodies. Eight samples of blood serum were analyzed and 87.5% of these total investigated provided adequate results. In addition, the present approach showed better results against traditional EDC/NHS reaction with enhancements in time and the possibility to develop an immunosensor in a single drop, since the proteins can be anchored prior to the electrode modification step.

Amine-Functionalized Quantum Dots as a Universal Fluorescent Nanoprobe for a One-Step Loop-Mediated Isothermal Amplification Assay with Single-Copy Sensitivity.

Loop-mediated isothermal amplification (LAMP) has received considerable attention for decentralized (point-of-care and on-site) nucleic acid testing in view of its simple temperature control (60-65 °C) and short assay time (15-60 min). There remains a challenge in its wide adoption and acceptance due to the limitations of the existing amplification result reporter probes, e.g., photobleaching of organic fluorophore and reduced sensitivity of the pH-sensitive colorimetric dye. Herein, we demonstrate CdSeS/ZnS quantum dots (semiconductor fluorescent nanocrystals with superior photostability than organic fluorophore) with surface modification of cysteamine (amine-QDs) as a new reporter probe for LAMP that enabled single-copy sensitivity (limit of detection of 83 zM; 20 µL reaction volume). For a negative LAMP sample (absence of target sequence), positively charged amine-QDs remained dispersed due to interparticle electrostatic repulsion. While for a positive LAMP sample (presence of target sequence), amine-QDs became precipitated. The characterization data showed that amine-QDs were embedded in magnesium pyrophosphate crystals (generated during positive LAMP), thus leading to their coprecipitation. This amine-QD-based one-step LAMP assay advances the field of QD-based nucleic acid amplification assays in two aspects: (1) compatibility─one-step amplification and detection (versus separation of amplification and detection steps); and (2) universality─the same amine-QDs for different target sequences (versus different oligonucleotide-modified QDs for different target sequences).

A fluorescence digital image-based method using carbon quantum dots to evaluate the compliance of a biocidal agent.

In this work, a simple, low-cost and easy-to-handle analytical procedure based on carbon quantum dots (CQDs) is proposed to check commercially available formulated microbicides that are used to mitigate the transmission of viruses, such as SARS-COV-2, or bacterial diseases. For this purpose, CQDs were synthesized via pyrolysis using citric acid and ethylenediamine as precursors to produce an intense fluorescence that is used to measure the concentration of hypochlorite, an important biocidal agent present in sanitizing mats, by quenching mechanisms. The characterization of the CQDs was performed using IR spectrophotometry, UV-Vis spectrophotometry, spectrofluorometry, thermogravimetric analysis, scanning electron microscopy, dynamic light scattering, X-ray diffraction, energy-dispersive spectroscopy, and zeta potential measurements. For analytical purposes, fluorescence was measured in a UV chamber irradiated using an LED with the maximum emission at 350 nm. A smartphone was coupled to the UV chamber to measure the fluorescence quenching due to the presence of hypochlorite, and further the digital images were decomposed by RGB data using free software. Tests of pH, CQD concentration and stability of the fluorescence emitted were performed. The stability study of the fluorescence emitted by the CQD solution showed a relative standard deviation lower than 5.0%. The fluorescence digital image-based (FDIB) method resulted in a linear range from 17.44 µmol L-1 to 90.0 µmol L-1 with an LOD of 3.30 µmol L-1 for the determination of hypochlorite using a microplate made of PLA (polylactic acid) customized using a 3D printer. Furthermore, the hypochlorite concentration was tested in situ for its compliance in a sanitizing mat, in a real use situation (daily, a group of four people, each one kept their feet on the mat for 30 s). After 2.5 h, the monitored concentration of hypochlorite was 0.04953% (w/v) or 7.63 mmol L-1, and therefore, it was inefficient to act as a sanitizing agent. Thus, for the first time in the literature, an FDIB method with CQDs is used to verify in situ microbicide practices with a fast and low-cost analytical procedure.

Differential diagnosis of the infection caused by wild-type or CD2v-deleted ASFV strains by quantum dots-based immunochromatographic assay.

African swine fever (ASF), a highly contagious and lethal disease, poses a tremendous threat and burden to the swine industry worldwide. Lack of available vaccines or treatments leaves rapid diagnosis as the key tool to control the disease. Quantum dots (QDs) are unique fluorescent semiconductor nanoparticles, highly versatile for biological applications. In this study, we developed a quantum dots-based fluorescent immunochromatographic assay (QDs-FICA) using CD2v as the diagnosis antigen to detect ASFV antibodies. The titre of the test strip was 1 : 5·12 × 105 . In addition, the strip was highly specific to anti-ASFV serum and had no cross-reaction with CSFV, PPV, PRRSV, PCV-2, PRV and FMDV. Moreover, a comparative test of 71 clinical samples showed that the coincidence rate was 85·92% between the test strip and the commercial ELISA kit (coated with p30, p62 and p72). The QDs-FICA can be used to detect ASFV antibodies, which is meaningful for the surveillance, control and purification of ASF.

A Universal Fluorescent Immunochromatography Assay Based on Quantum Dot Nanoparticles for the Rapid Detection of Specific Antibodies against SARS-CoV-2 Nucleocapsid Protein.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is the pathogenic agent leading to COVID-19. Due to high speed of transmission and mutation rates, universal diagnosis and appropriate prevention are still urgently needed. The nucleocapsid protein of SARS-CoV-2 is considered more conserved than spike proteins and is abundant during the virus' life cycle, making it suitable for diagnostic applications. Here, we designed and developed a fluorescent immunochromatography assay (FICA) for the rapid detection of SARS-CoV-2-specific antibodies using ZnCdSe/ZnS QDs-conjugated nucleocapsid (N) proteins as probes. The nucleocapsid protein was expressed in E.coli and purified via Ni-NTA affinity chromatography with considerable concentration (0.762 mg/mL) and a purity of more than 90%, which could bind to specific antibodies and the complex could be captured by Staphylococcal protein A (SPA) with fluorescence displayed. After the optimization of coupling and detecting conditions, the limit of detection was determined to be 1:1.024 × 105 with an IgG concentration of 48.84 ng/mL with good specificity shown to antibodies against other zoonotic coronaviruses and respiratory infection-related viruses (n = 5). The universal fluorescent immunochromatography assay simplified operation processes in one step, which could be used for the point of care detection of SARS-CoV-2-specific antibodies. Moreover, it was also considered as an efficient tool for the serological screening of potential susceptible animals and for monitoring the expansion of virus host ranges.

B-Cell-Epitope-Based Fluorescent Quantum Dot Biosensors for SARS-CoV-2 Enable Highly Sensitive COVID-19 Antibody Detection.

A new antibody diagnostic assay with more rapid and robust properties is demanded to quantitatively evaluate anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunity in a large population. Here, we developed a nanometer-scale fluorescent biosensor system consisting of CdSe-ZnS quantum dots (QDs) coupled with the highly sensitive B-cell epitopes of SARS-CoV-2 that could remarkably identify the corresponding antibody with a detection limit of 100 pM. Intriguingly, we found that fluorescence quenching of QDs was stimulated more obviously when coupled with peptides than the corresponding proteins, indicating that the energy transfer between QDs and peptides was more effective. Compared to the traditional enzyme-linked immunosorbent assay (ELISA), the B-cell-epitope-based QD-biosensor could robustly distinguish coronavirus disease 2019 (COVID-19) antibody-positive patients from uninfected individuals with a higher sensitivity (92.3-98.1% positive rates by QD-biosensor vs. 78.3-83.1% positive rates by ELISAs in 207 COVID-19 patients' sera) in a more rapid (5 min) and labor-saving manner. Taken together, the 'QD-peptides' biosensor provided a novel real-time, quantitative, and high-throughput method for clinical diagnosis and home-use tests.

Sensitive and specific clinically diagnosis of SARS-CoV-2 employing a novel biosensor based on boron nitride quantum dots/flower-like gold nanostructures signal amplification.

The sudden increase of the COVID-19 outbreak and its continued growth with mutations in various forms has created a global health crisis as well as devastating social and economic effects over the past two years. In this study, a screen-printed carbon electrode reinforced with boron nitride quantum dots/flower-like gold nanostructures (BNQDs/FGNs/SPCE) and functionalized by highly specific antisense DNA oligonucleotide presents an alternative and promising solution for targeting SARS-CoV-2 RNA without nucleic acid amplification. The platform was tested on 120 SARS-CoV-2 RNA isolated from real clinical samples (60 positive and 60 negative confirmed by conventional RT-PCR method). Based on obtained quantitative results and statistical analysis (box-diagram, cutoff value, receiver operating characteristic curve, and t-test), the biosensor revealed a significant difference between the two positive and negative groups with 100% sensitivity and 100% specificity. To evaluate the quantitation capacity and detection limit of the biosensor for clinical trials, the detection performance of the biosensor for continuously diluted RNA isolated from SARS-CoV-2-confirmed patients was compared to those obtained by RT-PCR, demonstrating that the detection limit of the biosensor is lower than or comparable to that of RT-PCR. The ssDNA/BNQDs/FGNs/SPCE showed negligible cross-reactivity with RNA fragments isolated from Influenza A (IAV) clinical samples and also remained stable for up to 14 days. In conclusion, the fabricated biosensor may serve as a promising tool for point-of-care applications.

High-throughput Confocal Imaging of Quantum Dot-Conjugated SARS-CoV-2 Spike Trimers to Track Binding and Endocytosis in HEK293T Cells.

The development of new technologies for cellular fluorescence microscopy has facilitated high-throughput screening methods for drug discovery. Quantum dots are fluorescent nanoparticles with excellent photophysical properties imbued with bright and stable photoluminescence as well as narrow emission bands. Quantum dots are spherical in shape, and with the proper modification of the surface chemistry, can be used to conjugate biomolecules for cellular applications. These optical properties, combined with the ability to functionalize them with biomolecules, make them an excellent tool for investigating receptor-ligand interactions and cellular trafficking. Here, we present a method that uses quantum dots to track the binding and endocytosis of SARS-CoV-2 spike protein. This protocol can be used as a guide for experimentalists looking to utilize quantum dots to study protein-protein interactions and trafficking in the context of cellular physiology.

Development of a smartphone-based quantum dot lateral flow immunoassay strip for ultrasensitive detection of anti-SARS-CoV-2 IgG and neutralizing antibodies.

BACKGROUND: As several vaccines for SARS-CoV-2 have been developed, a large proportion of individuals have been vaccinated worldwide so far. The rapid and accurate immunoassays are urgently needed for detecting the specific virus-neutralizing antibody (NAb), which reflect the protective effect of the vaccines among different populations. METHODS: In this study, we designed a quantum dot lateral flow immunoassay strip (QD-LFIA) for smartphones for the detection of specific IgG or neutralizing antibodies in SARS-CoV-2 in human serum or whole blood samples. The recombinant receptor binding domain of the SARS-CoV-2 spike protein was used as the antigen to combine with NAb or angiotensin-converting enzyme 2. RESULTS: Among 81 patients who recovered from COVID-19 who were diagnosed using the nucleic acid test initially, 98.8% (80/81) were positive for IgG and 88.9% (72/81) were positive for NAb by QD-LFIA. Among 64 individuals inoculated with inactivated vaccines and six subunit vaccines, 90% (63/70) were positive for IgG and 82.9% (58/70) were positive for NAb by QD-LFIA, whereas no cross-reaction was found in 150 healthy blood donors, two patients with influenza B, and three patients with common cold. CONCLUSION: The established platform could achieve a rapid and accurate detection of NAb specific to SARS-CoV-2, which could be used for detecting the protective effect of the vaccines in areas of world that currently affected by the pandemic.

Fluorescent-based nanosensors for selective detection of a wide range of biological macromolecules: A comprehensive review.

Thanks to their unique attributes, such as good sensitivity, selectivity, high surface-to-volume ratio, and versatile optical and electronic properties, fluorescent-based bioprobes have been used to create highly sensitive nanobiosensors to detect various biological and chemical agents. These sensors are superior to other analytical instrumentation techniques like gas chromatography, high-performance liquid chromatography, and capillary electrophoresis for being biodegradable, eco-friendly, and more economical, operational, and cost-effective. Moreover, several reports have also highlighted their application in the early detection of biomarkers associated with drug-induced organ damage such as liver, kidney, or lungs. In the present work, we comprehensively overviewed the electrochemical sensors that employ nanomaterials (nanoparticles/colloids or quantum dots, carbon dots, or nanoscaled metal-organic frameworks, etc.) to detect a variety of biological macromolecules based on fluorescent emission spectra. In addition, the most important mechanisms and methods to sense amino acids, protein, peptides, enzymes, carbohydrates, neurotransmitters, nucleic acids, vitamins, ions, metals, and electrolytes, blood gases, drugs (i.e., anti-inflammatory agents and antibiotics), toxins, alkaloids, antioxidants, cancer biomarkers, urinary metabolites (i.e., urea, uric acid, and creatinine), and pathogenic microorganisms were outlined and compared in terms of their selectivity and sensitivity. Altogether, the small dimensions and capability of these nanosensors for sensitive, label-free, real-time sensing of chemical, biological, and pharmaceutical agents could be used in array-based screening and in-vitro or in-vivo diagnostics. Although fluorescent nanoprobes are widely applied in determining biological macromolecules, unfortunately, they present many challenges and limitations. Efforts must be made to minimize such limitations in utilizing such nanobiosensors with an emphasis on their commercial developments. We believe that the current review can foster the wider incorporation of nanomedicine and will be of particular interest to researchers working on fluorescence technology, material chemistry, coordination polymers, and related research areas.

SARS-CoV-2 detection using quantum dot fluorescence immunochromatography combined with isothermal amplification and CRISPR/Cas13a.

The development of reliable, sensitive, and fast devices for the diagnosis of COVID-19 is of great importance in the pandemic of the new coronavirus. Here, we proposed a new principle of analysis based on a combination of reverse transcription and isothermal amplification of a fragment of the gene encoding the S protein of the SARS-CoV-2 and the CRISPR/Cas13a reaction for cleavage of the specific probe. As a result, the destroyed probe cannot be detected on an immunochromatographic strip using quantum fluorescent dots. Besides, the results can be obtained by an available and inexpensive portable device. By detecting SARS-CoV-2 negative (n = 25) and positive (n = 62) clinical samples including throat swabs, sputum and anal swabs, the assay showed good sensitivity and specificity of the method and could be completed within 1 h without complicated operation and expensive equipment. These superiorities showed its potential for fast point-of-care screening of SARS-CoV-2 during the outbreak, especially in remote and underdeveloped areas with limited equipment and resources.

All-solid-state SARS-CoV-2 protein biosensor employing colloidal quantum dots-modified electrode.

Rapid and reliable detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody can provide immunological evidence in addition to nucleic acid test for the early diagnosis and on-site screening of coronavirus disease 2019 (COVID-19). All-solid-state biosensor capable of rapid, quantitative SARS-CoV-2 antibody testing is still lacking. Herein, we propose an electronic labelling strategy of protein molecules and demonstrate SARS-CoV-2 protein biosensor employing colloidal quantum dots (CQDs)-modified electrode. The feature current peak corresponding to the specific binding reaction of SARS-CoV-2 antigen and antibody proteins was observed for the first time. The unique charging and discharging effect depending on the alternating voltage applied was ascribed to the quantum confinement, Coulomb blockade and quantum tunneling effects of quantum dots. CQDs-modified electrode could recognize the specific binding reaction between antigen and antibody and then transduce it into significant electrical current. In the case of serum specimens from COVID-19 patient samples, the all-solid-state protein biosensor provides quantitative analysis of SARS-CoV-2 antibody with correlation coefficient of 93.8% compared to enzyme-linked immunosorbent assay (ELISA) results. It discriminates patient and normal samples with accuracy of about 90%. The results could be read within 1 min by handheld testing system prototype. The sensitive and specific protein biosensor combines the advantages of rapidity, accuracy, and convenience, facilitating the implement of low-cost, high-throughput immunological diagnostic technique for clinical lab, point-of-care testing (POCT) as well as home-use test.