A label-free, versatile and low-background chemiluminescence (CL) sensing strategy based on gold nanocluster catalysis combined with the separation of magnetic beads (MBs) was developed. Kanamycin was selected as the target analyte to exhibit the analytical performance of this platform. Two single-stranded DNA (named DNA1 and DNA2) are ingeniously designed. DNA1, containing an aptamer sequence of the targets, was firstly immobilized on the MBs which were modified with many amino groups by amidation reaction. DNA2 consists of 30 repeat adenosine bases (A) at the 5' terminal which were used to prepare AuNCs by a UV-light-assisted method and a 12 nucleotide sequence at the 3' terminal which can easily hybridize with DNA1 to form a partly complementary double-stranded structure. In the presence of targets, the aptamer modified on MBs would combine with targets and lead to release the prepared DNA-templated AuNCs. After the magnetic separation, enrichment AuNCs in the supernatant can catalyze the CL substrate to produce a strong CL signal. The well-designed CL sensing strategy exhibited a low detection limit of 0.035 nM for kanamycin, and it also showed good selectivity and stability. Most importantly, different targets can be analyzed only by changing the aptamer sequence that is immobilized on the MBs. Therefore, the strategy we proposed here has provided a versatile sensing platform for sensitively detecting various biomolecules at low levels.
Due to the concern over food safety, it is important to detect the pesticides residues in agricultural products. Here, a highly sensitive and low background fluorescent strategy for the detection of pesticides residues has been developed. The fluorescence intensity of N-methyl mesoporphyrin IX (NMM) binding G-quadruplex could be turn off because of inhibiting effect of the pesticides on the acetylcholinesterase (AChE) activity. For that, four single-stranded DNAs (named linker, trigger, H1 and H2, respectively) are rational designed and T-Hg-T mismatches duplex DNAs as a recognizer combined with the separation of magnetic beads. The design of hybridization chain reaction (HCR) amplification strategy assisted by magnetic separation has been adopted to improve the detection sensitivity. In the presence of pesticides, the amount of the thiol group generated by hydrolysis reaction of acetylcholine (ACh) is reduced, lead to release of less trigger DNA. Therefor subsequent HCR process is retarded with decreased fluorescence intensity. The reduced fluorescence intensity has a quantitative relationship with the pesticide concentration. The limit of detection of chlorpyrifos was estimated to be 2.0 ng ml−1. It has been applied to detect the pesticides residues in real samples.
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