Dual-mode electrochemical fiber optic surface plasmon resonance sensor (EC-FO-SPR) for real-time and sensitive detection of lipopolysaccharide.

Lipopolysaccharide (LPS), a key component of the outer membrane of Gram-negative bacteria, is the primary trigger of septic shock. The rapid and selective detection of LPS is essential for effective disease prevention and treatment. The conventional prism-based electrochemical surface plasmon resonance (EC-SPR) system is limited by their bulky optical configurations, making it difficult to integrate into portable devices. In this study, we present a compact and implantable electrochemical fiber optic surface plasmon resonance (EC-FO-SPR) sensor to detect LPS. The gold-coated optical fiber serves a dual function as both SPR optical probe and working microelectrode, enabling simultaneous acquisition of optical and electrochemical signals. The sensor ensures high sensitivity by electrochemical detection mode and real-time monitoring molecular adsorption processes by optical SPR mode. The fiber sensing surface is modified with boric acid molecules for highly specific detection of saccharides with cis-diol structures such as glucose and the biomacromolecule LPS, which contains glucose units. The electrochemical signal is collected by detecting changes in the charge distribution of [Fe(CN)6]4-/3- near the electrode surface caused by boronate ester formation, and the optical signal is obtained through refractive index changes near the electrode induced by target molecules. The sensor shows a clear linear relationship between LPS concentration and both SPR wavelength shift and electrochemical peak current. The fiber-based design of EC-FO-SPR is easily integrable into compact, flexible platforms, enabling real-time, in situ monitoring of molecular interactions. It provides a reliable and versatile support for clinical and biomedical applications.