Electrochemical Surface Plasmon Resonance Fiber-Optic Sensor: In Situ Detection of Electroactive Biofilms.

Spectroelectrochemistry has been found to be an efficient technique for revealing extracellular electron transfer (EET) mechanism of electroactive biofilms (EABs). Herein, we propose a novel electrochemical surface plasmon resonance (EC-SPR) optical fiber sensor for monitoring EABs in situ. The sensor uses a tilted fiber Bragg grating (TFBG) imprinted in a commercial single-mode fiber and coated with nanoscale gold film for high-efficiency SPR excitation. The wavelength shift of the surface plasmon resonance (SPR) over the fiber surface clearly identifies the electrochemical activity of the surface localized (adjacent to the electrode interface) bacterial cells in EABs, which differs from the "bulk" detections of the conventional electrochemical measurements. A close relationship between the variations of redox state of the EABs and the changes of the SPR under potentiostatic conditions has been achieved, pointing to a new way to study the EET mechanism of the EABs. Benefiting from its compact size, high sensitivity, and ease of use, together with remote operation ability, the proposed sensor opens up a multitude of opportunities for monitoring EABs in various hard-to-reach environments.