Novel diffusion gradient in thin-films based on antibiofouling Ag/polydopamine membranes for measurement of antibiotics in natural waters

Abstract

Background

The diffusion gradient in thin-films (DGT) device is widely used for in situ measurement of pollutants in aquatic environments, offering high enrichment efficiency and robustness to environmental variations such as temperature and hydrodynamics. These characteristics make DGT particularly suitable for monitoring a diverse array of trace organic contaminants in waters. However, long-term deployment is often compromised by biofilm formation on the sampling outer membrane, which can obstruct analyte diffusion and lead to underestimation of analyte concentrations. This study addresses the need for a biofouling-resistant DGT device that maintains accuracy during extended field applications.

Results

A novel DGT device incorporating an antifouling Ag/polydopamine-modified polyethersulfone (Ag/PDA-PES) membrane was developed. The modified membrane demonstrated dual functional improvements: a 40 % reduction in water contact angle, indicating enhanced hydrophilicity, and strong antimicrobial efficacy, evidenced by an inhibition zone of 1165 μm ± 110 μm against Escherichia coli, while maintaining diffusion characteristics comparable to the original PES membrane. In extended deployment in both simulated and natural waters, the Ag/PDA-PES membrane effectively inhibited biofilm formation and maintained stable analyte diffusion coefficients over time compared to the unmodified membrane. The DGT devices showed constant sampling performance across varying pH (5.0–9.0), ionic strength (0–200 mM NaCl), and dissolved organic matter levels (0–20 mg/L). Field validation confirmed the device reliability, with measured total antibiotic concentrations (692–1062 ng/L) consistent with grab sampling.

Significance

This work signifies a step forward in DGT passive sampling technology by integrating antifouling properties directly into the membrane, thereby enabling accurate long-term monitoring of pollutants in biofilm-prone waters. Moreover, this study provides a promising strategy for improving the reliability of long-term DGT sampling, with meaningful implications for the precise monitoring and ecological risk assessment of other emerging pollutants.