Herein, a novel turn-off fluorescent aptasensor was developed for selective detection of ampicillin (AMP) at picomolar level based on 3,4,9,10-perylenetetracarboxylic acid diimide (PTCDI) as an affordable and low-cost fluorophore. This aptasensor was designed using aptamer, its complementary strand (CS) and gold nanoparticles (AuNPs). The principle of the sensing method is a decrease in the fluorescence intensity of PTCDI in the presence of free CS. Following the addition of AMP, Aptamer/CS-modified AuNPs releases CS and so, the fluorescence intensity of PTCDI is reduced. The designed analytical method indicated a good linear range from 100 pM to 1000 pM and a limit of detection (LOD) of 29.2 pM was obtained. Furthermore, the sensing strategy indicated satisfactory results for the detection of AMP in the spiked human serum samples. By changing the sequences of aptamer and its CS, the presented analytical approach can be easily applied for detection of other antibiotics.

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