Electrochemical Detection of Antibiotics in Environmental Matrices Using Functionalized Boron-Doped Diamond Electrodes

Ciprofloxacin (CIP) is a widely prescribed fluoroquinolone antibiotic used in health care and agricultural industries to treat against human and animal bacterial diseases. Due to the fact that only a portion of the antibiotic is metabolized during administration to humans and livestock, large loads of CIP are delivered to watersheds via agricultural runoff or wastewater discharge. The presence of antibiotics in the environment may cause the proliferation of bacterial drug resistance. For this reason the development of sensitive and selective sensors to monitor antibiotics in the environment is an active area of research. In this work, we discuss the development of selective electrochemical sensors through the functionalization of boron-doped diamond (BDD) film electrodes. Sensors are developed by functionalizing the BDD surface with a layer of multi-walled carbon nanotubes (MWCNTs) and a templated-Nafion film. Experiments show that the CIP templated-Nafion film enabled CIP detection at the BDD surface by modifying the polymer pore size and electrostatically excluding anionic species. This templating procedure was shown to be effective for selectively detecting CIP in the presence of other fluoroquinolones (i.e., amoxicillin) and other non-target water constituents (i.e., Cl^-, Ca²⁺, salicylic acid). Additionally, the addition of MWCNTs significantly lowered the detection limit by increasing the specific surface area of the sensor and by promoting specific adsorptive interactions between CIP and surface functional groups of the MWCNTs. Differential pulse voltammetry scans showed that a detection limit as low as 5 nM could be achieved at a pH of 4.5. Linear current response with respect to CIP concentration was achieved up to concentrations of 15 μM, and the peak current response was on the order of 2.8 μA/μM. This sensor platform was extended to other fluoroquinolone antibiotics in order to develop sensor arrays for the simultaneous detection of a number of antibiotics in environmental matrices.