Gold-Coated Optical Fiber Electrode for <i>In Situ</i> Monitoring of Hydrogen Peroxide Released from Living Cells via Transmitted Electrogenerated Chemiluminescence

The development of a sensitive method for <i>in situ</i> monitoring of hydrogen peroxide (H₂O₂) released from living cells is crucial for disease diagnosis. In this work, we have fabricated a gold-coated optical fiber electrode (GOFE) for <i>in situ</i> monitoring of H₂O₂ released from living cells via transmitted electrogenerated chemiluminescence (ECL). The cylinder GOFE was fabricated by sputtering a conductive Au layer (∼100 nm) on the surface of the cylinder and the cross-section (one proximal end) of the plastic optical fiber, which was 2.4 cm in length and 2.0 mm in diameter. The prepared GOFE was further modified with luminol-conjugated gold nanoparticles (Luminol-AuNPs) on the proximal end as a transmitted sensing platform (abbreviated as Luminol-AuNPs/GOFE). Its proximal end was taken as the venue for sensing and ECL generation, while its distal end was taken as the readout spot for the ECL emission. Two detection modes, including transmission mode and nontransmission mode, were developed for ECL detection. The transmitted ECL intensity at the distal end via transmission mode was directly proportional to the concentration of H₂O₂ in the range from 50 μM to 1.0 mM with a limit of detection of 12.5 μM. Moreover, the developed Luminol-AuNPs/GOFE-based transmitted ECL method was successfully employed to monitor the release of H₂O₂ from living A549 cells <i>in situ</i> under lipopolysaccharide stimulation. This work presents a promising method for fabricating optical electrodes with favorable electroactive and transmittance properties for <i>in situ</i> and sensitive monitoring of biomolecules in different analytical applications.