Self-Sterilizing Polymeric Membrane Sensors Based on 6-Chloroindole Release for Prevention of Marine Biofouling

A self-sterilizing strategy based on antimicrobial organic agent release is proposed for polymeric membrane sensors to prevent marine biofouling. A solid-contact polymeric membrane calcium ion-selective electrode (Ca²⁺-ISE) is selected as a model sensor. 6-Cholorindole (6-Cl indole) is utilized as the biocidal agent due to its potential antimicrobial activity and environmental friendliness. The plasticized polymeric membrane doped with 6-Cl indole shows a markedly improved antimicrobial activity against the bacterial cells collected from seawater and effectively prevents the formation of a biofilm on the sensor surface, while displaying response properties (i.e., linear range, selectivity, and response time) similar to those of the undoped membrane. Importantly, the present sensor can preserve an improved antimicrobial activity when kept in the artificial seawater for 45 days, indicating highly stable antibacterial properties of the membrane electrode. Additionally, the 6-Cl indole-doped Ca²⁺-ISE exhibits no significant loss of analytical performance after exposure to a rather concentrated bacterial suspension (∼10⁹ colony-forming units per mL (CFU mL^-1)) for 7 days. The proposed antimicrobial agent release methodology can be extended to develop polymeric membrane-based marine sensors with stable biofouling resistances against bacterial colonization.