A label-free aptamer-based assay for the highly sensitive and specific detection of Ochratoxin A (OTA) was developed using a cationic polymer and gold nanoparticles (AuNPs). The OTA aptamer was used as a recognition element for the colorimetric detection of OTA based on the aggregation of AuNPs by the cationic polymer. By spectroscopic quantitative analysis, the colorimetric assay could detect OTA down to 0.009 ng/mL with high selectivity in the presence of other interfering toxins. This study offers a new alternative in visual detection methods that is rapid and sensitive for OTA detection.
A novel adsorbent is described for magnetic solid-phase extraction (MSPE) of the aflatoxins AFB and AFB (AFBs). Magnetic agarose microspheres (MAMs) were functionalized with an aptamer to bind the AFBs which then were quantified by HPLC and on-line post-column photochemical derivatization with fluorescence detection. Streptavidin-conjugated MAMs were synthesized first by a highly reproducible strategy. They possess strong magnetism and high surface area. The MAMs were characterized by transmission electron microscopy, scanning electron microscopy, optical microscopy, laser diffraction particle size analyzer, Fourier transform infrared spectrometry, vibrating sample magnetometry and laser scanning confocal microscopy. Then, the AFB-aptamers were immobilized on MAMs through biotin-streptavidin interaction. Finally, the MSPE is performed by suspending the aptamer-modified MAMs in the sample. They are then collected by an external magnetic field and the AFBs are eluted with methanol/buffer (20:80). Several parameters affecting the coupling, capturing and eluting efficiency were optimized. Under the optimized conditions, the method is fast, has good linearity, high selectivity, and sensitivity. The LODs are 25 pg·mL for AFB and 10 pg·mL for AFB. The binding capacity is 350 ± 8 ng·g for AFB and 384 ± 8 ng·g for AFB, and the precision of the assay is <8%. The method was successfully applied to the analysis of AFBs in spiked maize samples. Graphical abstract Schematic of novel aptamer functionalized magnetic agarose microspheres (Apt-MAM) as magnetic adsorbents for simultaneous and specific affinity capture of aflatoxins B and B (AFBs).
The selective detection of ultra trace amounts of aflatoxin B1 (AF1) is extremely important for food safety, since it is the most toxic mycotoxin class that is allowed to be present in edible food and agricultural products with strictly Maximum Residue Limit (MRL). Sensitive detection of AFB1 residues requires time-consuming techniques and expensive instruments. An aptasensor for AFB1 detection, using unmodified gold nanoparticles (AuNPs) indicator, was developed in the present study, based on the salt-induced AuNPs aggregation phenomenon. Its linear dynamic range and detection sensitivity were found to be 0.025 ng/mL-100 ng/mL and 0.025 ng/mL of AFB1 respectively, which were lower than the maximum residue limit (MRL) in edible food, as set by China and the European Commission. Our study provides a simple, fast, and visible method for AFB1 analysis, with high sensitivity, which can be applied in future on-site detection for food and agricultural products.
Selective detection of ultratrace amounts of cadmium (Cd 2+ ) is extremely important for food safety and environmental monitoring because of its toxicity and widespread use. In this work, we developed a facile, rapid, sensitive, and highly selective method for the detection of Cd 2+ based on a label-free aptasensor using an unmodified double-stranded deoxyribonucleic acid-specific dye (PicoGreen). The linear range was 0.10-100 µg/mL, and the detection limit (0.038 ng/mL) was lower than the guideline from the World Health Organization for Cd 2+ in drinking water (3 ng/mL). The sensor exhibited excellent selectivity towards Cd 2+ ions. We tested the aptasensor in application to a series of real water samples spiked with different concentrations of Cd 2+ . Compared with atomic absorption spectrometry, the results showed good tolerance to the matrix effect. The developed approach shows great potential for on-site and high-throughput analysis in routine monitoring.
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