Electrochemiluminescent sensor based on copper nanosheets for the detection of sulfamethoxazole

Sulfadimethoxine (SDM) is commonly used to inhibit bacterial growth, but its residual presence in food poses a potential risk to public health. Therefore, sensitive and accurate detection of SDM residues is of significant importance. In this study, a highly sensitive "turn-on" electrochemiluminescence (ECL) aptamer sensor was developed for sulfadimidine (SDM) detection using DNA nanosheet-templated copper nanoclusters (DNS-CuNCs) as the luminophores, while carboxylated multi-walled carbon nanotubes modified with 3-glycidoxypropyltrimethoxysilane (MWCNTs-COOH/GPTMS) acted as the electrode functionalization substrate. Additionally, aptamer-modified polydopamine nanospheres (PDAs-APT) were introduced into the system as ECL quenchers to realize target-induced "turn-on" ECL signal activation. A silanization modification strategy was employed to introduce abundant functional groups on the electrode surface, thereby enabling stable immobilization of DNS-CuNCs and enhancing electron transfer efficiency. Hybridization between PDAs-APT and the complementary DNA of DNS-CuNCs quenched the ECL signal, and the specific binding of SDM to PDAs-APT triggered the release of PDAs-APT from the hybrid system, thereby enabling the restoration of the ECL signal. The sensor exhibited a wide linear range from 10 fg mL^-1 to 500 ng mL^-1, with a low detection limit of 4.23 fg mL^-1. The ECL aptamer sensor demonstrated excellent selectivity against interfering antibiotics and showed good reproducibility with a relative standard deviation of 1.09 %. Moreover, the method was successfully applied to SDM detection in milk samples. These results indicate that the proposed ECL aptamer sensor offers advantages of simplicity, high sensitivity, and low cost, making it a promising tool for SDM residue detection in complex food matrices.