A dichromatic label-free aptasensor for sulfadimethoxine detection in fish and water based on AuNPs color and fluorescent dyeing of double-stranded DNA with SYBR Green I

A dichromatic label-free aptasensor was described for sulfadimethoxine (SDM) detection. Compared with the binding of SDM-aptamer to SDM, the higher affinity of aptamer to cDNA may result in the hybridization of dsDNA. In the presence of SDM, the aptamer specifically binds to SDM, leading to a blue color of AuNPs in deposit and fluorescence at 530 nm in supernatant after adding cDNA and SGI. With no target of SDM, AuNPs protected with the aptamer re-disperse in PBS with a red color, and no fluorescence occurs in supernatant. Based on the principle, SDM can be quantitatively detected through both fluorescent emission and AuNPs color changes with recoveries ranging from 99.2% to 102.0% for fish and from 99.5% to 100.5% for water samples. An analytical linear range of 2–300 ng mL −1 was achieved with the detection limits of 3.41 ng mL −1 for water and 4.41 ng g −1 for fish samples (3 σ , n  = 9).