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Most aptasensors are designed based on aptamers' conformational change or structural transformation upon interaction with their targets. A limitation of these strategies is the unpredictability of such structural alterations that may yield false-positive or nonspecific signals. In bioanalysis, a dominant strategy for protein determination is the sandwich assay because of its high specificity and sensitivity resulting from the dual recognition mechanism. However, the approach is poorly suited to detection of low molecular weight targets, which unlikely bind to two aptamers simultaneously due to steric hindrance. To circumvent this drawback, a split aptamer strategy was recently developed, in which nucleic acid aptamers were split into two fragments that could specifically form a ternary assembly in the presence of ligand. This elegant approach has been extensively adopted for detection of various targets, especially small molecular weight targets, with different transduction methods including colorimetric, fluorescence, and electrochemical techniques. This review first introduced split aptamers and how to obtain split aptamers, and then summarized recent advances in the development of sandwich-format biosensing assays based on split aptamer fragments, aiming at providing a general guide for the design of split-aptamer-based sandwich assays. Furthermore, we discussed possible challenges in the development of split-aptamer-based sandwich assay regarding stability, sensitivity and multiplicity, so as to offer future opportunities of this assay. [ABSTRACT FROM AUTHOR]

Fast immunoassay-based screening methods are unavailable for most small-molecule pesticides because of a lack of immunogenicity and the difficulty in obtaining antibodies by animal immunization. Aptamers are single-stranded DNA molecules selected through an in vitro process, which can bind to any target including nonimmunogenic small molecules with high affinity and specificity. Although various aptamer-based sensing methods have been developed for antibiotics, microorganisms, heavy metal ions, and biotoxins, there are few reports on aptamer-based methods for quick detection of organophosphorous pesticides. The gold (Au) nanoparticle (AuNP) colorimetric assay is a widely utilized rapid detection method because of properties such as easy operation and visualized results. In the present study, organophosphorous pesticide aptamers were adsorbed on the surface of AuNPs to stabilize the AuNP solution against high concentrations of salt to prevent AuNP aggregation. After the addition of targets, the aptamers binding to the targets are detached from the AuNPs, resulting in aggregation of AuNPs and a color change from red to purple-blue. The proposed method can detect 6 organophosphorous pesticides with good recoveries from 72% to 135% in environmental river water samples. The present study provides a new way for simple, rapid, and multiplex detection of organophosphorous pesticides. Environ Toxicol Chem 2015;34:2244-2249. © 2015 SETAC [ABSTRACT FROM AUTHOR]