Highly efficient detection of ciprofloxacin in water using a nitrogen-doped carbon electrode fabricated through plasma modification

Abstract

Ciprofloxacin (CFX) is a widely used second-generation fluoroquinolone, broad-spectrum antibiotic. Increasingly, it has been detected in water supplies and has been shown to be harmful to the environment. Antibiotic contamination in the aquatic environment has adverse effects on non-target organisms, including promoting bacterial resistance, inhibiting algae growth, affecting chloroplast replication, transcription and translation, and disrupting the N cycle involved in microorganisms. Here, a novel electrochemical sensor was developed based on simple nitrogen plasma modification; critically, this sensor effectively detected CFX in water. Collectively, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle (CA) measurements, and electrochemical impedance spectroscopy (EIS) were used to characterize the physical and electrochemical properties of the electrode. The results showed that both the electrochemical activity and the electron transfer of the carbon electrode were significantly enhanced by the nitrogen plasma modification. This was likely due to an increase in nitrogen functional groups (i.e., the nitrogens contained within the pyrrole and graphite groups) and it did not result in damage to the roughness of the electrode s surface. These results also indicated that our sensor selectively detected CFX in the presence of interference antibiotics and/or inorganic ions. Under optimal conditions (pH = 5, plasma power = 140 W, and modification time = 8 min), our sensor showed a broad linear concentration range (2.5 × 10−7–1.0 × 10−4 M) with detection limits as low as 8 nM. The sensor was also successfully applied in the detection of CFX in different types of water sources, namely groundwater and tap water. The recoveries varied from 92.10 to 109.48% with a relative standard deviation (RSD) less than 4.07%. Taken together, these results show a simple and rapid modification method that provides a promising means for rapid, in situ sensor-based monitoring of aquatic environmental pollutants like antibiotics.