Electrochemical truncated aptasensors for dual detection of enrofloxacin and ofloxacin using in-situ deposited reduced graphene oxide/gold nanoparticle composite

Monitoring fluoroquinolones (FQs), such as enrofloxacin (ENO) and ofloxacin (OFL), commonly used antibiotics, is vital for food and environmental safety. This study presents a novel electrochemical aptasensor for the simultaneous detection of ENO and OFL. Truncated DNA aptamers were designed and tested, showing improved binding affinity ( K d values of 20.6 nM for OFL and 7.9 nM for ENO). First, a composite of in-situ reduced graphene oxide (rGO) and gold nanoparticles (AuNPs) was electrodeposited onto the carbon screen-printed electrodes (rGO/AuNPs/SPE). Morphological and structural analysis of the rGO/AuNPs/SPE was conducted using scanning electron microscopy and X-ray photoelectron microscopy after electrodeposition. The truncated aptamer with the lowest K d was immobilized on the rGO/AuNPs/SPE surface, and the remaining sites were blocked with Mercaptohexanol to enable selective analyte recognition. The constructed multiplexed aptasensor exhibited linear detection ranges from 0.001 to 100 ng/mL for OFL and ENO, with limits of detection of 0.17 pg/mL for OFL and 1.3 pg/mL for ENO, respectively. The dual aptasensor showed excellent selectivity against common interferents, and high recovery rates in spiked milk, tap water, and wastewater samples ranged from 95 to 108 %. This study highlights the truncated aptasensor potential for rapid, on-site detection of fluoroquinolone antibiotics in complex matrices, addressing critical needs in food safety and environmental monitoring. • New truncated aptamers were designed to enhance the binding affinity for OFL and ENO. • A dual electrochemical aptasensor was developed using in-situ electrodeposited rGO/AuNPs. • The aptasensor enabled simultaneous and selective detection of OFL and ENO • The platform demonstrated excellent analytical performance in water and milk samples.