Graphene oxide-enhanced FRET aptasensor: Precision detection of ertapenem residues in milk

Abstract

Ertapenem (ER), a β-lactam antibiotic categorized as a carbapenem, is recognized for its broad-spectrum antibacterial efficacy against both Gram-negative and Gram-positive bacteria, making it an important therapeutic agent for treating various bacterial infections. Recent studies have reported carbapenem-resistant bacteria and their corresponding resistance genes in raw milk samples. In this study, graphene oxide (GO)-SELEX was employed to rapidly elute target-bound sequences and identify high affinity aptamers specific to ER from an ssDNA library. The 81 nucleotides (81-mer) aptamer ER-3 was selected for its highest affinity, with a Kd value of 77.69 ± 4.16 nM, as determined by the carboxyfluorescein (FAM) labeled fluorescence method. The original aptamer was truncated to ER3-T2, which enhanced both its affinity and selectivity, with a K_d value of 1.84 ± 0.07 nM. A Förster Resonance Energy Transfer (FRET)-based aptasensor was developed by incorporating both the original and the truncated aptamer to establish an accurate calibration plot. The aptasensor demonstrated a significant linear relationship between fluorescence intensity (FI) and ER concentration, ranging from 1 to 100 nM, with a limit of detection (LOD) of 1.72 nM for the aptamer ER3-T2. These results highlight the FRET-based aptasensor as a promising, sensitive, and efficient analytical platform for the rapid detection of ER in milk samples.