Portable Assay Research Articles

Trans-dimensional nanocoral gold foam interfaces affords ultrasensitive detection of influenza virus.

Development of sensitive and cost-effective strategies for detecting influenza viruses is crucial to combat the spread of infectious diseases. In this study, a novel trans-dimensional nanocoral gold foam (NCGF) was fabricated on screen-printed carbon electrodes using hydrogen template electrodeposition method. This unique structure, with interconnected large and small pores, significantly increased the specific surface area and stability of the sensor. Based on this nanostructure, the antibodies were further modified and used for influenza A viruses (IAVs) detection by enzyme-linked immunoelectrochemical method. The combination of the large specific surface area of NCGF and the catalytic reaction of alkaline phosphatase led to a dual amplification of electrochemical signals, enabling ultra-sensitive detection of IAVs. The NCGF-based biosensor demonstrated exceptional stability, sensitivity, and achieved a reliable limit of detection as low as 13.14fg/mL, which is several orders of magnitude improvement in sensitivity over conventional electrochemical immunosensor. Furthermore, 72 clinical samples were analyzed using a portable detection device that could directly read signals from a mobile phone, and the results correlated well with gold standard PCR method. Overall, this rapid, sensitive, and portable assay provides a valuable option for early viral infection diagnosis.

P-2112. Development and Validation of a Cheap, Portable Assay to Rapidly Profile Bacterial Infections of the Bloodstream

Abstract Background Antimicrobial resistant (AMR) bacterial infections pose a significant and growing health threat worldwide, and their burden is most severe in lower income areas where diagnostic infrastructure is lacking. The development of cost-effective and accessible diagnostic tools for the rapid identification of resistant infections in low-resource settings is crucial. Specific High-sensitivity Enzymatic Reporter Unlocking, or SHERLOCK, is a promising CRISPR-based system that can aid in the diagnosis of infections and support clinical decision making. Here, we present an assay termed BADLOCK (Bacteria and AMR Detection by SHERLOCK) that uses this technology to rapidly identify bacterial species and AMR genes on blood cultures. BADLOCK workflow demonstrating simplicity of approach and rapid turnaround. Methods We combine isothermal amplification of targets with CRISPR/Cas13-based detection into a single step, allowing for a streamlined workflow and a total time-to-identification of less than two hours from positive cultures using lateral flow strips (Fig. 1). The assay primarily targets topA for species identification, a highly conserved gene within species with sufficient variability between them to enable species-level typing. A panel of clinically important AMR genes, including the ESBL blaCTX-M-15, three major carbapenemases, and the GPC resistance genes mecA and vanA, is also included. Pilot study assessing assay performance. A) each column represents a different isolate while each row represents a different CRISPR gene target, which are enumerated at the bottom. Each species name refers to the topA gene sequence unique to that species. The top box shows the expected gene content based on prior sequencing, while the bottom box shows the results of each assay. The blue shading shows relative fluorescence intensity of the generated signal. B) Basic test characteristics for each target gene. Results In addition to the AMR resistance genes, we have validated a panel of 9 gram-negative rods, 6 staphylococci, 2 enterococci, and 2 streptococcal species with further targets being developed, and have performed a laboratory pilot study on a subset of these (Fig. 2). We have additionally collected over 600 sequential positive blood cultures and are in the process of performing a large clinical validation study on patient samples, thereby elucidating the precise test characteristics of our assay. Conclusion We have developed an assay capable of rapidly detecting bacterial species causing bloodstream infections and their major epidemic AMR genes on low-cost paper strips. Our work has the potential to improve the diagnostic landscape for resistant infections in low-and-middle-income countries and serve as an adjunctive diagnostic to traditional approaches in highly resourced setting, which would represent a major step forward in infectious disease diagnostics. Disclosures All Authors: No reported disclosures

Surface-Enhanced Raman Spectroscopy for Nitrite Detection.

Nitrite is an important chemical intermediate in the nitrogen cycle and is ubiquitously present in environmental and biological systems as a metabolite or additive in the agricultural and food industries. However, nitrite can also be toxic in excessive concentrations. As such, the development of quick, sensitive, and portable assays for its measurement is desirable. In this review, we summarize the working principles and applications of surface-enhanced Raman spectroscopy (SERS) as a rapid, portable, and ultrasensitive method for nitrite detection and showcase its applicability in various water, food, and biological samples. The challenges and opportunities for future developments are also discussed.

Fully Integrated Microfluidic Digital Chip for Simple and Highly Quantitative Detection of Norovirus.

The prevalence of foodborne illnesses is a significant global concern, resulting in numerous illnesses, deaths, and substantial economic losses annually. Traditional detection methods for foodborne pathogens are often slow, limited, and impractical for field use, underscoring the need for rapid, sensitive, and portable assays. Microfluidic technology has emerged as a promising solution for sample preparation, reaction, and detection on a small scale. Our study introduces a novel microfluidic digital loop-mediated isothermal amplification (LAMP) assay platform, which employs digital microfluidic chips for absolute quantitative analysis of nucleic acids. This portable chip utilizes LAMP technology to achieve ultrasensitive detection of target nucleic acids within 30 min and reduces the detection limit to 1 fM without the need for complex instrumentation. By digitizing amplification signals directly from the target sample, our platform offers simplicity, affordability, portability, and quantitative molecular readouts. This innovation represents a crucial step toward the on-site detection of foodborne pathogens, thereby enhancing food safety and mitigating disease outbreaks.

A novel dialdehyde cellulose-based colorimetric and turn-on fluorescent probe for H2S detection and its application in red wine

Hydrogen sulfide (H2S) is considered one of the most important gaseous transmitters in the metabolic system, and the abnormal concentration of H2S is associated with a variety of diseases. Up to now, it is still a challenge to develop a portable assay for H2S even though the research about the detection of H2S is booming. Herein, a novel bifunctional dialdehyde-cellulose fluorescent probe DAC-DPD was prepared with high selectivity and sensitivity to H2S with colorimetric and fluorescent “turn-on” characteristics, and the limit of detection (LOD) of DAC-DPD for H2S was 0.831 μM. The sensing mechanism of DAC-DPD's to H2S was a Michael addition reaction confirmed by HRMS, 1H NMR and density-functional theory (DFT) calculations. DAC-DPD can be used to detect H2S in red wine samples. In Addition, the prepared DAC-DPD embedded fluorescent membrane can be used as a reliable sensing platform for rapid detection of H2S. It provided a convenient and rapid detection material, simplifying the detection process of H2S, which is of great significance for the development of cellulose-based fluorescent smart material.

DNA‐encoded plasmonic bubbles aggregating dual‐microRNA SERS signals for cancer diagnosis

AbstractSolid bubbles have expanded the SERS assay toolbox, but their detection performance in biofluids is still hampered by the irrational design of the plasmonic sensing interface. A plasmonic bubble aggregate‐driven DNA‐encoded SERS assay is reported here that enables simultaneous, ultrasensitive, and specific detection of multiple miRNAs in blood samples for accurate cancer diagnosis. In this assay, the buoyancy of plasmonic bubbles allows them to self‐aggregate at a droplet apex for SERS reconfiguration, form single‐layer bubble aggregates with plasmonic nanogaps, and prevent the coffee ring effect during evaporation assembly. Furthermore, DNA‐encoded plasmonic bubbles seamlessly couple with dual‐color catalytic hybridization assembly to amplify the specific miRNA‐responsive Raman signal, and function as both an analyte concentrator and a Raman signal aggregator without external forces. Using these merits, this magnet‐free, portable assay achieves femtomolar dual‐miRNA quantitation with single‐base resolution, simultaneous miRNA detection across four cell lines, and accurate cancer diagnosis (AUC = 1) via analyzing 40 blood samples with machine learning, thus providing a promising tool for clinical diagnosis.

Dual-mode photothermal/chemiluminescence vertical flow assay for sensitive point-of-care detection of carcinoembryonic antigen using Cu2-xAgxS@liposome on a filter membrane

Conventional lateral flow assays based on colorimetry and fluorescence still have shortages in sensitivity and selectivity due to the severe background interference from complex human fluid sample matrices. In this work, Cu2-xAgxS nanocrystals with high photothermal conversion efficiency and good peroxidase-like activity were synthesized and applied in the construction of a dual-mode near-infrared-photothermal/chemiluminescence (CL) vertical flow assay of carcinoembryonic antigen (CEA). These two-mode principles showed nearly zero background and the synthesized Cu2-xAgxS exhibited a high photothermal conversion efficiency of 75.23%, enabling the luminol-H2O2 CL system to have over 4 min of chemiluminescence. By combining filter membrane enrichment, Cu2-xAgxS@liposome encapsulation amplification, and nanozyme catalysis, a dual-mode photothermal/CL portable assay was constructed for sensitive and accurate detection of CEA in serum, with linear ranges of 0.02–40 and 0.001–30 ng mL−1, and detection limits of 0.0023 and 0.00029 ng mL−1, respectively. Furthermore, a smartphone application and a 3D printing device were combined for point-of-care testing. This assay can be completed within 20 min, with simple operation and no need for large instruments. It exhibited good sensitivity, selectivity, and stability, and is expected to be used in early diagnosis and prevention of relevant diseases in resource-limited areas.

Rapid and Sensitive Detection of Shiga Toxin-Producing Escherichia coli (STEC) from Food Matrices Using the CANARY Biosensor Assay.

Shiga toxin-producing Escherichia coli (STEC) causes a wide spectrum of diseases including hemorrhagic colitis and hemolytic uremic syndrome (HUS). Previously, we developed a rapid, sensitive, and potentially portable assay that identified STEC by detecting Shiga toxin (Stx) using a B-cell based biosensor platform. We applied this assay to detect Stx2 present in food samples that have been implicated in previous STEC foodborne outbreaks (milk, lettuce, and beef). The STEC enrichment medium, modified Tryptone Soy Broth (mTSB), inhibited the biosensor assay, but dilution with the assay buffer relieved this effect. Results with Stx2a toxoid-spiked food samples indicated an estimated limit of detection (LOD) of ≈4 ng/mL. When this assay was applied to food samples inoculated with STEC, it was able to detect 0.4 CFU/g or 0.4 CFU/mL of STEC at 16 h post incubation (hpi) in an enrichment medium containing mitomycin C. Importantly, this assay was even able to detect STEC strains that were high expressors of Stx2 at 8 hpi. These results indicate that the STEC CANARY biosensor assay is a rapid and sensitive assay applicable for detection of STEC contamination in food with minimal sample processing that can complement the current Food Safety Inspection Service (US) methodologies for STEC.

Endotoxin, a novel biomarker for the rapid risk assessment of faecal contamination of coastal and transitional waters

ABSTRACT Contaminated water has been responsible for the spread of disease for centuries. Current methods for testing water for faecal contamination rely on the culture of faecal indicator bacteria (FIB; Escherichia coli and Enterococci) that take 24–48 h, which leads to delays in taking proactive measures and poses a risk to public health. More rapid methods are therefore required. Here, we have tested a rapid, portable assay (Bacterisk) that detects the bacterial biomarker endotoxin in 30 min to quantify the bacterial biomass present, to evaluate 159 coastal water samples and to compare the results with the traditional culture of FIB. There was a significant correlation between the Bacterisk data given in endotoxin risk (ER) units and FIB culture that could accurately distinguish between poor and sufficient or good quality bathing water using the EU bathing directive values. Receiver operating characteristic analysis was used to determine the optimal ER threshold for coastal water samples, and the area under the curve was 0.9176 with a p-value of <0.0001. The optimal threshold was 7,300 ER units with a sensitivity of 95.45% and a specificity of 83.48%. In conclusion, we have shown that the Bacterisk assay provides a rapid and easy-to-use in situ method to assess bathing water quality.

An ionic liquid-modified PEDOT/Ti3C2TX based molecularly imprinted electrochemical sensor for pico-molar sensitive detection of L-Tryptophan in milk

L-Tryptophan (L-Trp) is essential for the human body and can only be obtained externally. It is important to develop a method to efficiently detect L-Trp in food. In this work, ionic liquid (IL) modified poly(3,4-ethylendioxythiophene)/ Titanium carbide (PEDOT/Ti3C2TX) was used as a substrate material to improve detection sensitivity. Molecular imprinted polymers (MIP) film for specific recognition of L-Trp was fabricated on the surface of modified electrodes using electrochemical polymerization. The monitoring results showed that the molecularly imprinted electrochemical sensors (MIECS) exhibited good linearity ranges (10−6 - 0.1 μM and 0.1–100 μM) with a low detection limit (LOD) of 2.09 × 10−7 μM. In addition, the MIECS exhibited remarkable stability, reproducibility, and immunity to interference. A good recovery (93.54–99.59%) was demonstrated in the detection of milk. The sensor was expected to be developed as a highly selective and sensitive portable assay, and applied to the detection of L-Trp in food.

Development of a Rapid and Sensitive CANARY Biosensor Assay for the Detection of Shiga Toxin 2 from Escherichia coli.

Shiga-toxin-producing Escherichia coli (STEC) causes a wide spectrum of diseases including hemorrhagic colitis and hemolytic uremic syndrome (HUS). The current Food Safety Inspection Service (FSIS) testing methods for STEC use the Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) protocol, which includes enrichment, cell plating, and genomic sequencing and takes time to complete, thus delaying diagnosis and treatment. We wanted to develop a rapid, sensitive, and potentially portable assay that can identify STEC by detecting Shiga toxin (Stx) using the CANARY (Cellular Analysis and Notification of Antigen Risks and Yields) B-cell based biosensor technology. Five potential biosensor cell lines were evaluated for their ability to detect Stx2. The results using the best biosensor cell line (T5) indicated that this biosensor was stable after reconstitution with assay buffer covered in foil at 4 °C for up to 10 days with an estimated limit of detection (LOD) of ≈0.1-0.2 ng/mL for days up to day 5 and ≈0.4 ng/mL on day 10. The assay detected a broad range of Stx2 subtypes, including Stx2a, Stx2b, Stx2c, Stx2d, and Stx2g but did not cross-react with closely related Stx1, abrin, or ricin. Additionally, this assay was able to detect Stx2 in culture supernatants of STEC grown in media with mitomycin C at 8 and 24 h post-inoculation. These results indicate that the STEC CANARY biosensor developed in this study is sensitive, reproducible, specific, rapid (≈3 min), and may be applicable for surveillance of the environment and food to protect public health.

Arsenic field test kits based on solid-phase fluorescence filter effect induced by silver nanoparticle formation

Millions of people worldwide are affected by naturally occurring arsenic in groundwater. The development of a low-cost, highly sensitive, portable assay for rapid field detection of arsenic in water is important to identify areas for safe wells and to help prioritize testing. Herein, a novel paper-based fluorescence assay was developed for the on-site analysis of arsenic, which was constructed by the solid-phase fluorescence filter effect (SPFFE) of AsH3-induced the generation of silver nanoparticles (AgNPs) toward carbon dots. The proposed SPFFE-based assay achieves a low arsenic detection limit of 0.36 μg/L due to the efficient reduction of Ag+ by AsH3 and the high molar extinction coefficient of AgNPs. In conjunction with a smartphone and an integrated sample processing and sensing platform, field-sensitive detection of arsenic could be achieved. The accuracy of the portable assay was validated by successfully analyzing surface and groundwater samples, with no significant difference from the results obtained through mass spectrometry. Compared to other methods for arsenic analysis, this developed system offers excellent sensitivity, portability, and low cost. It holds promising potential for on-site analysis of arsenic in groundwater to identify safe well locations and quickly obtain output from the global map of groundwater arsenic.

Multifunctional Manganese-Nucleotide Laccase-Mimicking Nanozyme for Degradation of Organic Pollutants and Visual Assay of Epinephrine via Smartphone.

As a natural green catalyst, laccase has extensive application in the fields of environmental monitoring and pollutant degradation. However, susceptibility to environmental influences and poor reusability seriously hinder its application. To address these concerns, for the first time, manganese ion replaced copper ion as the active center to coordinate with guanosine monophosphate (GMP) for synthesizing mimic laccase with high catalytic activity. Compared with natural laccase, the laccase-like nanozyme (Mn-GMPNS) demonstrated superior thermal stability, acid-base resistance, salt tolerance, reusability, and substrate universality. Benefiting from the high catalytic activity of Mn-GMPNS, epinephrine, a significant neurotransmitter and hormone associated with numerous diseases, was visually detected within 10 min and a portable assay by smartphone. More encouragingly, Mn-GMPNS can efficiently degrade dye pollutants, achieving a decolorization rate over 70% within 30 min. Thus, the coordination between manganese ion and nucleotide demonstrated the potential in rational design of nanozymes with high catalytic activity, low cost, good stability, and good biocompatibility.

One-pot synthesized Au@Pt nanostars-based lateral flow immunoassay for colorimetric and photothermal dual-mode detection of SARS-CoV-2 nucleocapsid antibody

In addition to confirming virus infection, quantitative identification of the antibodies to severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) also evaluates persons immunity to guide personal protection. However, portable assays for fast and accurate quantification of SARS-CoV-2 antibodies remain challenging. In this work, we synthesized Au@Pt star-like nanoparticles (NPs) quickly and easily by a one-pot wet-chemical approach, allowing the stellate Au core to be partially decorated by Pt nanoshells. The nanoparticles were used as probe in a lateral flow immunoassay (LFIA) that operated in both colorimetric and photothermal dual modes, which could detect the antibodies to the SARS-CoV-2 nucleocapsid (N) protein with high sensitivity. Due to the sharp tips on the external region of nanostars and surface plasmon coupling effect between the Au core and Pt shell, the NIR absorption capacity and photothermal performance of these NPs were exceptional. Under optimal conditions, the colorimetric mode's detection limit for SARS-CoV-2 N protein antibody was 1 ng mL−1, which is significantly lower by 2-order of magnitude compared to commercially available colloidal gold strips. And the detection limit for the photothermal mode was as low as 24.91 pg mL−1, which was approximately 40-fold more sensitive than colorimetric detection. Moreover, the method demonstrated favorable specificity, reproducibility and stability. Finally, the approach was employed for the successful identification of actual serum samples. Therefore, the dual-mode LFIA can be applied for screening and tracking the early immunological reaction to SARS-CoV-2, and it has great promise for clinical application.

875. Development of a Cheap, Portable Assay to Rapidly Profile Resistant Bacterial Infections

Abstract Background Antimicrobial resistant (AMR) bacterial infections pose a significant and growing health threat worldwide. The burden of these resistant infections is often most severe in lower income areas, where the medical infrastructure necessary for their diagnosis is lacking. The development of cost-effective and accessible diagnostic tools for the rapid identification of resistant infections in low-resource settings is crucial. Specific High-sensitivity Enzymatic Reporter Unlocking, or SHERLOCK, is a promising CRISPR-based system that can aid in the diagnosis of infections and support clinical decision making. Here, we present an assay termed BADLOCK (Bacteria and AMR Detection by SHERLOCK) that uses SHERLOCK technology to rapidly identify bacterial species and AMR genes on blood cultures. SHERLOCK Schematic Enzymatic activity of the Cas protein is turned on when the target gene is bound, which then activates reporter probes. Methods We combine isothermal amplification of gene targets with SHERLOCK-based detection into a single step, allowing for a streamlined workflow and a total time-to-detection of less than two hours. The assay targets the topA gene for species identification, which is highly conserved within species but has sufficient variability between them to allow for discrimination between even closely related pathogens. A panel of clinically important AMR genes, including CTX-M-15, mecA, and five canonical carbapenemases, is also targeted to provide information on resistance profiles. BADLOCK Targets Gene targets included in the BADLOCK assay. Results BADLOCK has high sensitivity and specificity for both AMR genes and species identification and leverages a lateral-flow platform to provide a simple visual readout. We are currently validating BADLOCK on a library of several hundred clinical isolates with known genetic backgrounds, including a large collection of carbapenem-resistant Enterobacterales, which are major contributors to the global burden of resistant infections. Lateral Flow Assay Results Lateral flow results. Strip 1 is the topA gene specific to K. pneumoniae. Strips 2-4 are AMR genes KPC, CTX-M-15, and MecA. Lane 5 is a positive control; lane 6 is a NTC with bottom banding. “+” and “-” symbols mark representative readouts. Conclusion We have developed an assay for the cheap, rapid detection of bacterial infections of the bloodstream capable of detecting common pathogens as well as a panel of AMR genes. Our work has the potential to improve the diagnostic landscape for resistant infections in low-and-middle-income countries, which would represent a major step forward in infectious disease treatment in these underserved areas. Disclosures All Authors: No reported disclosures

Multiplexed discrimination of SARS-CoV-2 variants via plasmonic-enhanced fluorescence in a portable and automated device.

Portable assays for the rapid identification of lineages of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are needed to aid large-scale efforts in monitoring the evolution of the virus. Here we report a multiplexed assay in a microarray format for the detection, via isothermal amplification and plasmonic-gold-enhanced near-infrared fluorescence, of variants of SARS-CoV-2. The assay, which has single-nucleotide specificity for variant discrimination, single-RNA-copy sensitivity and does not require RNA extraction, discriminated 12 lineages of SARS-CoV-2 (in three mutational hotspots of the Spike protein) and detected the virus in nasopharyngeal swabs from 1,034 individuals at 98.8% sensitivity and 100% specificity, with 97.6% concordance with genome sequencing in variant discrimination. We also report a compact, portable and fully automated device integrating the entire swab-to-result workflow and amenable to the point-of-care detection of SARS-CoV-2 variants. Portable, rapid, accurate and multiplexed assays for the detection of SARS-CoV-2 variants and lineages may facilitate variant-surveillance efforts.

A self-enhanced electrochemiluminescence array chip for portable label-free detection of SARS-CoV-2 nucleocapsid protein with smartphone

SARS-CoV-2 antigen detection plays a key role in the rapid diagnosis of COVID-19. However, current clinically used immunoassays are often limited by assay throughput, sensitivity, accuracy, and field operating conditions. To address these challenges, we constructed a self-enhanced electrochemiluminescence (ECL) array chip (SE2AC) for highly sensitive and label-free detection of SARS-CoV-2 nucleocapsid protein (N protein) with a facile and portable assay setup. Firstly, the self-enhanced ECL nanomaterials with inherent film-forming properties were synthesized by co-doping Ru(bpy)32+ and polyethyleneimine (PEI) in silica nanoparticles (Ru/PEI@SiO2). Secondly, a resistance-induced potential difference-based single-electrode electrochemical system (SEES) was adapted to serve as the electrode array to facilitate one-step assembly without the need for chip alignment. Thirdly, the chip electrode array was functionalized with the synthesized self-enhanced ECL emitters and captured antibodies. In addition, a portable detection box equipped with a smartphone was 3D-printed to serve as the chip holder and “dark room” for imaging acquisition. The SE2AC performance was validated with N protein with a limit of detection (LOD) of 0.47 pg/mL in the range of 1–10,000 pg/mL. Furthermore, the chip successfully detected the viral antigen residue as low as 1.92 pg/mL from diluted rehabilitation patients’ serum samples. This is the first study reporting label-free detection of SARS-Cov-2 N protein based on a self-enhanced ECL immunosensor, which provides a novel facile method for highly sensitive diagnosis of COVID-19 with high throughput, portability, and low cost.

Indolizine-based fluorescent compounds array for noninvasive monitoring of glucose in bio-fluids using on-device machine learning

Monitoring blood sugar level is highly important for managing diabetes and preventing complications. Herein, we describe a paper-based portable assay system for highly accurate monitoring of glucose levels in tears. The system combines enzyme reactions, the perturbation of fluorescence properties, automated image analysis, and pattern recognition powered by a machine-learning algorithms in a single assay without extra manual steps. A small size (20 × 20 mm) assay system was prepared simply by printing black wax crosswise on cellulose paper, melting the wax with heat, and depositing four different fluorescent compounds and glucose oxidase at the test zones. Applying a small drop of sample in the center zone of the system evenly distributes the samples to the test zone via the paper capillary process and eventually induces a generation of unique fluorescence pattern that is specific to glucose. Two models are used to analyze image data collected from the fluorescent compounds array to make accurate estimations on glucose concentration: a random forest model that discretely classifies the concentration with respect to the training data granularity and an SVM regression model that estimates glucose concentration at interpolated finer granularity. These models are combined with feature engineering techniques for efficient sensor data processing on resource limited mobile platforms. As a result, using the random forest approach, glucose concentration in artificial tears can be accurately classified with 96.7% accuracy (0.2 mM intervals) (MSE of 0.060 mM) and the SVM regression model results in an MSE of 0.026 mM.

A Fast and Simple DNA Mini-barcoding and RPA Assay Coupled with Lateral Flow Assay for Fresh and Canned Mackerel Authentication.

The online version contains supplementary material available at 10.1007/s12161-022-02429-6.

Fluorescence Quenching of Graphene Quantum Dots by Chloride Ions: A Potential Optical Biosensor for Cystic Fibrosis

Cystic fibrosis is a genetic disorder caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that encodes an ABC transporter-class ion channel protein, resulting in sticky and thick mucus secretion which clogs the airways and leads to respiratory failure and other complications. It also results in higher chloride ions (Clˉ) in body fluids. Cystic fibrosis is generally detected using the sweat chloride test and ion exchange chromatography, which are lab restricted. Therefore, there is a dire need to develop portable assays to monitor circulatory changes (Clˉ ion detection) to detect CF at the point of care. In this work, fluorescence quenching of graphene quantum dots (GQDs) was used as a property of the optical sensor for chloride ion detection. GQDs were synthesized by varying the carbonizing temperature and time, and then their optical and fluorescence (FL) quenching was investigated upon exposure to chloride ions in comparison with different ionic species. GQDs synthesized at 160°C for 50 min were chosen as they displayed the highest fluorescence. The morphological and optical characterization confirmed the preparation of 12–15 nm GQDs, which were amorphous in nature with the peak emission observed at 462 nm when excited at 370 nm. The fluorescence quenching response of GQDs with Clˉ ions displayed linearity up to 100 mM with a correlation coefficient of 0.98 and the lowest detection limit of approximately 10 mM Clˉ ions.