A syringe-aided apta-nanosensing method for colorimetric determination of acetamiprid.

A syringe-aided apta-nanosensing method is reported for the colorimetric determination of acetamiprid. The method employs double-stranded (ds) DNA-conjugated gold nanoparticle@magnetic agarose beads, i.e., dsDNA-AuNP@MABs as peroxidase-mimicking composite probes, in which the aptamer is indirectly attached to the AuNP surface through its hybridization with complementary DNA (cDNA). Upon contact with the acetamiprid target, the probes can give perceptible color change due to the possible conformation switch from dsDNA's brush-like to cDNA's 'pancake' regime. An "air-spaced pumping" procedure using a syringe equipped with ring magnets as the operation platform was proposed to facilitate the magnetic separation of the sensing probes. Therefore, the analytical steps can be easily accomplished in a syringe, including probe loading, acetamiprid capture and magnetic separation from crude samples, chromogenic reagent loading and colorimetric visualization. Acetamiprid concentration down to 3.3 ppb can be easily identified by the naked eye. The final solution also can be transferred for quantitative measurement. Under spectrometer, the ratio of the absorbance at 652 nm in the presence and absence of acetamiprid (A/A) is linearly related to the acetamiprid concentration in the 0.4-4.5 ppb range. The limit of detection is calculated to be 0.24 ppb. Moreover, satisfactory recoveries ranging from 90.90 to 91.82% with relative standard deviations of ≤2.96% were obtained in analyzing real spiked samples.