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Signal amplification is one of the most effective ways to develop the high-performance electrochemical sensors. However, it can be more complicated for ratiometric detections. Herein, a ratiometric electrochemical aptasensor for aflatoxin B1 (AFB1) was proposed by taking advantage of a dual-amplification strategy by coupling of DNA walker (DW) with hybridization chain reaction (HCR). The special binding of AFB1 with ferrocene (Fc)-labelled aptamer triggers DW on hairpin DNA (hDNA) tracks to produce abundant double-stranded DNA (dsDNA). HCR-based strand amplification occurs on these dsDNA to absorb more methylene blue (MB). Then current ratio of MB (I MB) and Fc (I Fc) is designed as a yardstick to detect AFB1. Our experiments reveal that the interaction between Fc and MB (i.e., steric hindrance, electron mediator) varies. In addition to steric hindrance, the presence of MB also acts as electron mediator, thereby facilitating the electron transfer between Fc and electrode. Such combined effect consequently depresses the efficiency of dual-amplification strategy to improve the detection. The developed ratiometric electrochemical aptasensor allows the accurate detection of AFB1 in the 0.003–3 pg mL−1 range. Our work has shed light on the amplification strategy for ratiometric sensing, and provided a new route in integrating different amplification strategies. • A dual-amplification strategy was proposed by the coupling of DNA walker and hybridization chain reaction. • The developed aptasensor exhibits superior analytical performance for the detection of aflatoxin B1. • The interaction of probes depresses the efficiency of amplification strategy on the improvement of ratiometric sensing. [ABSTRACT FROM AUTHOR]

The development of accurate and reliable sensor for on-site detection of microcystin-LR (MC-LR), one of hazardous environmental pollutants, is highly required. Herein, a laser induced graphene (LIG)-based electrochemical aptasensor for sensitive on-site detection of MC-LR was reported. LIG electrode, the substrate of aptasensor, was prepared via thermal transfer with ethylene-vinyl acetate copolymer, and LIG acted as quasi-reference electrode to replace conventional Ag/AgCl electrode for better operability and robustness. LIG electrode provided large surface area to assemble tetrahedral DNA to absorb methylene blue (MB) for the signal amplification. For detection, the specific recognition of MC-LR with aptamer led to the stripping of tetrahedral DNA complex and further the decreased redox current of MB (I MB). Consequently, the fabricated aptasensor offered high analytical performance for MC-LR detection with a linear range of 1 × 10-2-1 × 105 pM and a detection limit of 3 × 10-3 pM, which was successfully used for water sample analysis with comparable reliability and accuracy of standard method. Furthermore, a portable detection platform by coupling of LIG-based electrochemical aptasensor with electrochemical workstation was constructed for on-site detection of MC-LR. This work offers a novel method for the on-site monitoring of MC-LR, which promotes the investigation of LIG-based electrochemical biosensing in the field of environmental analysis. [ABSTRACT FROM AUTHOR]

Efficient signal amplification using light irradiation in electrochemistry-based sensing attracts growing interest; however, the modulation of electrochemical and photoelectrochemical behaviors of bifunctional probes remains challenging for the better analytical performance. Here, we found that the bifunctional probe methylene blue (MB) under irradiation followed two routes, i.e., photoelectrochemistry (PEC)-driven and electrochemistry (EC)-driven route, while plasmon-modulated competition between PEC-driven and EC-driven routes efficiently enhanced the analytical performance of aptasensor. Ferrocene-labeled aptamer (Fc-apt) was applied to tune the interaction between MB labeled complementary DNA (MB-cDNA) and plasmonic gold nanoparticles (AuNPs). Under visible light illumination, the aptasensor output a weak current of MB (I MB) for the depressed EC-driven redox. The binding of Fc-apt with target led to its stripping from electrode and released MB-cDNA to approach AuNPs, and an increase in I MB was observed due to the synergy of the depressed PEC-driven redox while the restored EC-driven redox. In this way, the amplified response for target could be obtained by depressing background signal while enlarging response signal of I MB under visible light. Consequently, the developed model ratiometric aptasensor offered a higher sensitivity for the determination of aflatoxin B1. Our observation should be favorable to shed light on photo-induced electrochemical mechanism, and the proposed amplification strategy is valuable for the construction of efficient sensors. [ABSTRACT FROM AUTHOR]

Abstract: High-affinity anti-abrin-a monoclonal and polyclonal antibodies were used to develop a sandwich immunochromatographic assay and silver enhancement technology was used to further increase the sensitivity. Using a matrix of double distilled water or soybean milk with added abrin-a, the visual detection limit was found to be 10ngmL−1. The detection limit was 0.1ngmL−1 for abrin-a, an increase in sensitivity of 100-fold when the silver enhancement technology was employed. The assay was portable and very simple to perform and the detection was completed within 20min without complicated handling procedures. There was no significant cross-reactivity with several homologous toxins and associated agglutinin. The assay reagents could be stored for 12weeks at 4°C without significant loss of activity. These characteristics make the strip assay to be an ideal candidate for the development of a rapid toxin detection kit. [Copyright &y& Elsevier]