An On-Site, Ultra-Sensitive, Quantitative Sensing Method for the Determination of Total Aflatoxin in Peanut and Rice Based on Quantum Dot Nanobeads Strip

One-Component Dual-Readout Aggregation-Induced Emission Nanobeads for Qualitative and Quantitative Detection of C-Reactive Protein at the Point of Care

Fluorescent lateral flow immunoassay (LFA) systems are versatile tools for sensitive and quantitative detection of disease markers at the point of care. However, traditional fluorescent nanoparticle-based lateral flow immunoassays are not visible under room light, necessitate an additional fluorescent reader, and lack flexibility for different application scenarios. Herein, we report a dual-readout LFA system for the rapid and sensitive detection of C-reactive protein (CRP) in clinical samples. The system relied on the aggregation-induced emission nanobeads (AIENBs) encapsulated with red AIE luminogen, which possesses both highly fluorescent and colorimetric properties. The AIENB-based LFA in the naked-eye mode was able to qualitatively detect CRP levels as low as 8.0 mg/L, while in the fluorescent mode, it was able to quantitatively measure high-sensitivity CRP (hs-CRP) with a limit of detection of 0.16 mg/L. The AIENB-based LFA system also showed a good correlation with the clinically used immunoturbidimetric method for CRP and hs-CRP detection in human plasma. This dual-modal AIENB-based LFA system offers the convenience of colorimetric testing and highly sensitive and quantitative detection of disease biomarkers and medical diagnostics in various scenarios.

A universal CRISPR/Cas12a-powered intelligent point-of-care testing platform for multiple small molecules in the healthcare, environment, and food

Growing studies focusing on nuclear acid detection via the emerging CRISPR technique demonstrate its promising application. However, limited works solve the identification of non-nucleic acid targets, especially multiple small molecules. To address challenges for point-of-care testing (POCT) in complex matrices for healthcare, environment, and food safety, we developed CRISPR Cas12a-powered highly sensitive, high throughput, intelligent POCT (iPOCT) for multiple small molecules based on a smartphone-controlled reader. As a proof of concept, aflatoxin B1 (AFB1), benzo[a]pyrene (BaP), and capsaicin (CAP) were chosen as multiple targets. First, three antigens were preloaded in independent microwells. Then, the antibody/antigen-induced fluorescent signals were consecutively transferred from the biotin-streptavidin to CRISPR/Cas12a system. Third, the fluorescent signals were recorded by a smartphone-controlled handheld dark-box readout. Under optimization, detection limits in AFB1, BaP, and CAP were 0.00257, 4.971, and 794.6 fg/mL with wide linear ranges up to four orders of magnitude. Using urine, water, soybean oil, wheat, and peanuts as the complex matrix, we recorded high selectivity, considerable recovery, repeatability, and high consistency comparison to HPLC-MS/MS methods. This work promises a practical intelligent POCT platform for multiple targets in lipid-soluble and water-soluble matrices and could be extensively applied for healthcare, environment, and food safety.

Paper-microfluidic signal-enhanced immunoassays

Over the past decade, paper-based microfluidic devices have become popular for their simplicity and ability to conduct diagnostic tests at a low cost. An important class of diagnostic assays that paper-based analytical devices have been used for is immunoassays. The lateral flow immunoassay (LFIA), of which the home pregnancy test is the most prominent example, has been one of the most commercially successful membrane-based diagnostic tests. Yet, the analytical sensitivity of LFIAs is lower than the corresponding laboratory technique called ELISA (enzyme-linked immunoassay). As a consequence, traditional LFIAs fail to deliver on the promise of bedside diagnostic testing for many applications. Recognizing this shortcoming, several new developments have been made by researchers to enhance the sensitivity of membrane-based immunoassays. In this chapter, we present the various strategies that have been employed to this end. In the end, we present a brief SWOT analysis to guide future work in this area.

Evaluating the Performance of Lateral Flow Devices for Total Aflatoxins with Special Emphasis on Their Robustness under Sub-Saharan Conditions

As aflatoxins are a global risk for humans and animals, testing methods for rapid on-site screening are increasingly needed alongside the standard analytical laboratory tools. In the presented study, lateral flow devices (LFDs) for rapid total aflatoxin screening were thoroughly investigated with respect to their matrix effects, cross-reactivity, their performance under harsh conditions in Sub-Saharan Africa (SSA), and their stability, as well as when compared with liquid chromatography-tandem mass spectrometry (LC-MS/MS). To analyze the matrix effects, qualitative test kits offering a certain cutoff level were used to screen different nut samples. In addition, these tests were challenged on their cross-reactivity with 230 fungal toxins and metabolites. Furthermore, the resulting measurements performed under harsh tropical conditions (up to 38.4 °C and 91% relative humidity) in SSA, specifically Burkina Faso and Mozambique, were compared with the results from a well-established and validated LC-MS/MS-based reference method. The comparison of the on-site LFD results with the reference method showed a good agreement: 86.4% agreement, 11.8% non-agreement, and 1.8% invalid test results. To test the robustness of the cutoff tests, short- and long-term stability testing was carried out in Mozambique and Nigeria. For both experiments, no loss of test performance could be determined. Finally, a subset of African corn samples was shipped to Austria and analyzed under laboratory conditions using semiquantitative aflatoxin tests. A good correlation was found between the rapid strip tests and the LC-MS/MS reference method. Overall, the evaluated LFDs showed satisfying results regarding their cross-reactivity, matrix effects, stability, and robustness.

Quantum Dots as Biosensors in the Determination of Biochemical Parameters in Xenobiotic Exposure and Toxins

Quantum dots (QDs) have been exploited for a range of scientific applications where the analytes can be expected to have significant photoluminescent properties. Previously, the applications of QDs as nanosensors for the detection of toxics in biospecimens, especially in cases of poisoning, have been discussed. This review focuses on the applications of QDs as biosensors for the detection of phytotoxins, vertebrate and invertebrate toxins, and microbial toxins present in biospecimens. Further, the role of QDs in the measurement of biochemical parameters of patient/victim as an indirect method of poison detection is also highlighted.

Development of a quantum dot-based lateral flow immunoassay with high reaction consistency to total aflatoxins in botanical materials

Total aflatoxins (AFTs) are an important safety indicator for botanical materials, but at present, rapid detection technology for AFTs is seldom reported. In this study, the monoclonal antibody with similar reactivity to total aflatoxins was produced, and the quantum dot-based lateral flow immunoassay (QD-LFIA) coupled with a portable device was developed to rapidly determine AFT residues in botanical materials. The half maximal inhibitory concentrations (IC50) of the QD-LFIA for AFB1, AFB2, AFG1, AFG2, AFM1, and AFM2 were 10.57, 12.64, 11.34, 12.67, 10.13, and 12.75 μg kg^-1, respectively, which show high reaction consistency to total aflatoxins. For different botanical materials, the sample was simply extracted with methanol-water and diluted with PBS, and the sample solution was directly loaded onto the QD-LFIA strip for determination. To overcome interference from the matrix effects, specific standard curves were established for each kind of botanical material. The detection limit of AFTs in 6 different botanical materials was 0.95~2.03 μg kg^-1 with a linear range of 2~120 μg kg^-1. The spiked recoveries of AFTs in botanical materials of different species and localities of growth were 75~105% with a coefficient of variation below 15%. The test results of the actual samples are consistent with the Chinese national standard test method. This study provides an easy-to-use method to rapidly determine AFTs in different botanical materials. Graphical abstract.

Advantages of Lateral Flow Assays Based on Fluorescent Submicrospheres and Quantum Dots for Clostridium difficile Toxin B Detection

Clostridium difficile colitis is caused by a cytotoxin produced by the anaerobic bacteria C. difficile in the epithelial cells of the large intestine, particularly C. difficile toxin B (TcdB). However, the sensitivity of currently utilized C. difficile endotoxin determination methods has been called into question, and, therefore, more accurate and convenient detection methods are needed. Our study is the first to systematically compare fluorescent submicrosphere-based and quantum-dot nanobead-based lateral fluidity measurement methods (FMs-LFA and QDNBs-LFA) with toxin B quantification in fecal samples via sandwich analysis. The limits of detection (LOD) of FMs-LFA and QDNBs-LFA in the fecal samples were 0.483 and 0.297 ng/mL, respectively. TcdB analyses of the fecal samples indicated that the results of QDNBs-LFA and FMs-LFA were consistent with those of a commercial enzyme-linked immunosorbent assay (ELISA) test kit. The sensitivity of QDNBs-LFA was highly correlated with clinical diagnoses. Therefore, quantum dot nanobeads (QDNBs) are deemed highly suitable for lateral fluidity analyses, which would facilitate the implementation of portable and rapid on-the-spot applications, such as food hygiene and safety tests and onsite medical testing.

A fluorescent nanosphere-based immunochromatography test strip for ultrasensitive and point-of-care detection of tetanus antibody in human serum

Tetanus still possesses a high infection risk and leads a number of human deaths in poor nations. Point-of-care and ultrasensitive detection of tetanus antibody levels in serum is the key to decrease the risk of tetanus infection and improve the health of people. In this work, by using ultra bright fluorescent nanospheres (FNs) and portable lateral flow test strip (LFTS), a point-of-care and ultrasensitive sensing method has been developed for the detection of tetanus antibodies in human serum. This assay works quite well for tetanus antibodies in the concentration range from 0.0002 to 0.0220 IU/mL with a low detection limit of 0.00011 IU/mL, which is 100-fold lower than conventional gold-based LFTSs. The high sensitivity makes this method suitable for use to detect the low-abundant target in real samples. Besides, this cost-effective FN-based LFTS assay possesses good selectivity, high accuracy, and satisfactory reliability, which holds great potential as a robust candidate for routine medical diagnosis and rapid home testing. Graphical abstract.