Fluorescent microspheres lateral flow assay for sensitive detection of the milk allergen casein

A rapid immunomagnetic beads-based sELISA method for the detection of bovine αs1-casein based on specific epitopes

Although αs1-casein poses significant health risks to individuals with milk allergies, the availability of quantification methods for this allergen remains limited. In this study, we developed an immunomagnetic beads-based immunoassay (IMBs-ELISA) for the precise quantitative detection of bovine αs1-CN, specifically targeting epitope AA173-194. No cross-reactivity was observed with the other 7 food allergens including milk allergen. The linear detection range of the established IMBs-ELISA method was 0.125 μg/mL-2.000 μg/mL, with a limit of detection of 0.099 μg/mL. The accuracy of this method was 1.048 %, and the intra-plate and inter-plate precision achieved 4.100 % and 6.777 %, respectively. Notably, the entire IMBs-ELISA process could be completed within 75 min, representing a substantial time-saving advantage over traditional ELISA methods. These results proved the reliability and rapidity of the IMBs-ELISA method for detecting αs1-CN in real food.

Direct count of fluorescent microspheres in a microfluidic chip based on the capillary electrophoresis method

Fluorescent microspheres (FMs) are tiny particles with special functions that are widely employed in biological research. Counting of microscale FMs is a great challenge by capillary electrophoresis. Herein we developed a method to count 2 μm FMs based on a microfluidic chip with a gradual change in inner size. Such a microfluidic chip can inhibit sample blocking at the inlet of the capillary. The results showed that FMs migrated in the wide part of the microchannel side by side, and then passed through the narrow part one by one. There was a linear relationship between the number of peaks in the electropherogram and concentration of FMs if they were running in the microchannel for more than 20 min. A high separation voltage may lead to aggregation of FMs in the microchannels, and about 2 × 10⁴ FMs can be counted within 30 min by this microfluidic chip.

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.

Halo-A Universal Fluorescence Reader Based Threat Agent Detection Platform-A Proof of Concept Study Using SARS-CoV-2 Assays

Polymerase chain reaction (PCR) remains the gold standard in disease diagnostics due to its extreme sensitivity and specificity. However, PCR tests are expensive and complex, require skilled personnel and specialized equipment to conduct the tests, and have long turnaround times. On the other hand, lateral flow immunoassay-based antigen tests are rapid, relatively inexpensive, and can be performed by untrained personnel at the point of care or even in the home. However, rapid antigen tests are less sensitive than PCR since they lack the inherent target amplification of PCR. It has been argued that rapid antigen tests are better indicators of infection in public health decision-making processes to test, trace, and isolate infected people to curtail further transmission. Hence, there is a critical need to increase the sensitivity of rapid antigen tests and create innovative solutions to achieve that goal. Herein, we report the development of a low-cost diagnostic platform, enabling rapid detection of SARS-CoV-2 under field or at-home conditions. This platform (Halo™) is a small, highly accurate, consumer-friendly diagnostic reader paired with fluorescently labeled lateral flow assays and custom software for collection and reporting of results. The focus of this study is to compare the analytical performance of Halo^TM against comparable tests that use either colloidal gold nanoparticles or fluorescence-based reporters in simulated nasal matrix and not in clinical samples. Live virus data has demonstrated limit of detection performance of 1.9 TCID₅₀/test in simulated nasal matrix for the delta variant, suggesting that single-assay detection of asymptomatic SARS-CoV-2 infections may be feasible. Performance of the system against all tested SARS CoV-2 virus variants showed comparable sensitivities indicating mutations in SARS-CoV-2 variants do not negatively impact the assay.

Rapid Detection of Anti-SARS-CoV-2 Antibody Using a Selenium Nanoparticle-Based Lateral Flow Immunoassay

Coronavirus disease 2019 is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 is highly transmissible. Early and rapid testing is necessary to effectively prevent and control the outbreak. Detection of SARS-CoV-2 antibodies with lateral flow immunoassay can achieve this goal. In this study, SARS-CoV-2 nucleoprotein (NP) was expressed and purified. We used the selenium nanoparticle as the labeling probe coupled with the NP to prepare an antibody (IgM and IgG) detection kit. The detection limit, cross reaction, sensitivity and specificity of the kit is verified. Separate detection of IgM and IgG, such as in this assay, was performed in order to reduce mutual interference and improve the accuracy of the test results.The final purity of NP was 91.83%. Selenium nanoparticle and NP successfully combined with stable effect. The LOD of the kit was 20 ng/mL for anti-NP IgG and 60 ng/mL for anti-NP IgM, respectively. The kit does not cross reaction with RF. The sensitivity of the kit was 94.74% and the specificity was 96.23%. The assay kit does not require any special device for reading the results and the readout is a simple color change that can be evaluated with the naked eye. This kit is suitable for rapid and real-time detection of the SARS-CoV-2 antibody IgG and IgM.

Advances on the rapid and multiplex detection methods of food allergens

With the gradually increasing prevalence of food allergy in recent years, food allergy has become a major public health problem worldwide. The clinical symptoms caused by food allergy seriously affect people's quality of life; there are unknown allergen components in novel food and hidden allergens caused by cross contamination in food processing, which pose a serious risk to allergy sufferers. Thus, rapid and multiplex detection methods are required to achieve on-site detection or examination of allergic components, so as to identify the risk of allergy in time. This paper reviews the progress of high-efficiency detection of food allergens, including enhanced traditional detection techniques and emerging detection techniques with the ability high-throughput detection or screening potential food allergen, such as xMAP, biosensors, biochips, etc. focusing on their sensitivity, applicability of each method in food, along with their pretreatment, advantages, limitation in the application of food analysis. This paper also introduces the challenges faced by these high-efficiency detection technologies, as well as the potential of customized allergen screening methods and rapid on-site detection technology as future research directions.

Development of a NanoMIPs-SPR-Based Sensor for β-Lactoglobulin Detection

Food manufacturers are aiming to manage the levels of cross-contamination of allergens within food processing plants and ultimately move away from precautionary labelling. Hence, the need for rapid methods to detect allergens cross-contamination. A sensitive and selective label-free nanoMIPs based sensor was developed and tested for the detection of β-lactoglobulin (BLG). NanoMIPs were synthesized using solid-phase synthesis and appeared as spherical nanoparticles with sizes ranging from 264–294 nm, using dynamic light scattering (DLS). The nanoMIPs were functionalized with amine groups and attached to the surface of the SPR gold chip via amine-coupling protocol. The SPR nanoMIPs-based sensor demonstrated a detection limit of 3 ng mL−1 (211 pM) over a linear range of 1–5000 ng mL−1, with binding affinity of 7.0 × 10−8 M and specificity towards BLG. With further testing and final optimization, the developed nanosensor can be integrated on-line or at-line cleaning-in-place (CIP) wash systems, allowing to effectively monitor milk protein allergens as a rapid, point-of-source methodology.

A novel homolateral and dicationic AIEgen for the sensitive detection of casein

The exploitation of highly soluble and responsive AIEgens is essential for further expansion of their practical applications. In this study, dipropyltrimethylammonium bromide-substituted TPE (denoted as o-TPEDTA), a homolateral and dicationic AIEgen, was synthesized and applied for the turn-on detection of casein via hydrophobic interactions. The rapid and sensitive detection of casein was achieved using the designed o-TPEDTA probe with the limit of detection of 0.05 μg mL^-1. The satisfying selectivity of over 1000-fold concentration of other probably existing chemicals, including amino acids, sugars and salts, was achieved due to the strong binding affinity between o-TPEDTA and casein. The evaluation of casein in milk powder samples with small relative standard deviations was realized using the o-TPEDTA probe. The accuracy of the o-TPEDTA probe-based detection method was validated by the consistency of the casein detection results with those obtained via a national standard casein evaluation approach.

A critical review of the specifications and performance of antibody and DNA-based methods for detection and quantification of allergens in foods

Despite the availability of a large number of antibody and DNA based methods for detection and quantification of allergens in food there remain significant difficulties in selecting the optimum technique to employ. Published methods from research groups mostly contain sufficient detail concerning target antigen, calibration procedures and method performance to allow replication by others. However, routine allergen testing by the food industry relies upon commercialised test kits and frequently the suppliers provide disappointingly little specification detail on the grounds that this is proprietary information. In this review we have made a critical assessment of the published literature describing the performance of both commercial and non-commercial test kits for food allergens over the period 2008-2018. Mass spectrometric methods, which have the potential to become reference methods for allergens, are not covered in this review. Available information on the specifications of commercial ELISA and LFD test kits are tabulated for milk, egg and peanut allergens, where possible linking to publications concerning collaborative studies and proficiency testing. For a number of commercial PCR test kits, specifications provided by manufacturers for detection of a small selection of allergen are tabulated. In conclusion we support the views of others of the critical need for allergen reference materials as the way forward to improve the comparability of different testing strategies in foods.

Aptamer-based fluorometric lateral flow assay for creatine kinase MB

A group of aptamers possessing high specificity and affinity for creatine kinase MB (CKMB) was obtained by magnetic systematic evolution of ligands by exponential enrichment. Two aptamers (referred to as C.Apt.21 and C.Apt.30) were found to possess adequately low K_d values. They form a well suited pair for CKMB binding. By using fluorescent microspheres, an aptamer-based lateral flow assay was developed. It is portable, economical, and sensitive. The limit of detection for CKMB is as low as 0.63 ng·mL^-1, and the assay works in the 0.005 - 2 μg·mL^-1 CKMB concentration range. The method is specific for CKMB, and biomarkers for AMI (such as cardiac troponin I and myoglobin) and serum do not interfere. The strip is highly accurate as shown by analysis of spiked serum samples which gave recoveries ranging between 88 and 117%. Graphical Abstract Schematic of the test strip and sandwich aptamer-based fluorometric lateral flow assay for creatine kinease. The detection is based on the specific affinity between CKMB and selected aptamers to form a sandwich structure.