Selected ssDNA aptamers-graphene oxide-based fluorescent biosensor to detect sulfameter in milk

The abuse of sulfameter (SME) in animal husbandry can cause drug resistance and toxic or allergic reactions in humans. Therefore, it is very important to establish a simple, inexpensive, and efficient method for detecting SME in food. In this work, we propose a single fluorescent aptamer/graphene oxide (GO)-based biosensor to detect SME residues in milk. Aptamers that specifically bind to SME were screened using capture-SELEX and a ssDNA library immobilized on magnetic beads. The 68 active candidate aptamers were chemically synthesized for specificity and affinity characterization. Among the aptamers, the aptamer sulf-1 revealed the highest affinity (K_d  = 77 ± 15 nM) to SME and was selected to construct a GO-based fluorescent biosensor for real milk sample detection. Under optimal conditions, the single fluorescent aptasensor had a wide linear range (R² was 0.997) from 7 to 336 ng/ml and a low detection limit of 3.35 ng/ml that was calculated with a 3SD/slope. The single fluorescent method was also validated using SME-fortified milk samples, showing average recoveries ranging from 99.01% to 104.60% with a relative standard deviation of less than 3.88%. These results demonstrate that this novel aptamer sensor provides an opportunity for sensitive, convenient, and accurate detection of SME residues in milk.