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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]

In this study, we propose an interference-free SERS-based aptasensor for trace detection of chlorpyrifos (CPF) in real samples. In the aptasensor, gold nanoparticles coated with Prussian blue (Au@PB NPs) were employed as SERS tags to provide a sole and intense Raman emission at 2160 cm−1, which could avoid overlapping with the Raman spectrum of the real samples in 600–1800 cm−1 to improve the anti-matrix effect ability of the aptasensor. Under the optimum conditions, this aptasensor displayed a linear response for CPF detection in the range of 0.1–316 ng mL−1 with a low detection limit of 0.066 ng mL−1. In addition, the prepared aptasensor shows excellent application to determine CPF in cucumber, pear and river water samples. The recovery rates were highly correlated with high-performance liquid chromatography‒mass spectrometry (HPLC‒MS/MS). This aptasensor shows interference-free, specific and sensitive detection for CPF and offers an effective strategy for other pesticide residue detection. Interference-free SERS-based Aptasensor for Chlorpyrifos Detection. [Display omitted] • An interference-free SERS aptsensor for chlorpyrifos residue detection was firstly developed. • PB containing CN was used as Raman report with a sole Raman emission in Raman-silent region (1800-2800 cm−1). • The aptsensor showed a linear detection range of 0.1–316 ng mL−1 with a LOD of 0.031 ng mL−1. • The aptsensor was successfully appiled to detect chlorpyrifos in real samples. [ABSTRACT FROM AUTHOR]

It is known that gold nanoparticles (AuNPs) possess peroxidase-like activity. They can catalyze the oxidation of 3,3,5,5-tetramethylbenzidine by HO which leads to a color change from red to blue. It is shown here that the peroxidase-like activity of AuNPs can be inhibited by passivating its surface passivation with a ssDNA aptamer against sulfadimethoxine. If, however, the target molecule (sulfadimethoxine) is present, the aptamer is desorbed from the AuNPs surface, and this results in the reactivation of the catalytic property of the AuNPs. The color change of the solution (from purple to blue) is related to the analyte concentration, and this can be judged visually or by UV-visible absorptiometry at 650 nm. The assay, under optimized conditions, has a detection limit of 10 ng·mL of sulfadimethoxine, and the calibration plot is linear over a rather wide concentration range (0.01-1000 μg·mL). The assay can be performed within <15 min, is sensitive, and therefore is well suited for fast screening in food analysis. Conceivably, it can be extended to many other small analytes for which aptamers are available. [ABSTRACT FROM AUTHOR]