Photoelectrochemical (PEC) sensor is an important type of biosensor widely used in glutathione (GSH) sensing. The PEC properties of the photoanode present in the sensor are critical to its sensing performance. Zinc oxide (ZnO) is an excellent semiconductor with a suitable band gap and light absorption ability for photoanode applications. Meanwhile, the interfacial layer is also important in the separation and transportation process of the excitons. In this work, high-quality ZnO nanorods were grown on the indium tin oxide (ITO) substrates. An interfacial layer consisting of reduced graphene oxide (RGO) or MXene (a two-dimensional transition metal carbide)-derived TiO₂ was introduced. Our results show that the introduction of the RGO/TiO₂ hybrid interfacial layer can promote both the high-quality growth of ZnO nanorods and also provides suitable band gap grading for efficient excitons separation and transportation. The GSH sensing performance of the PEC sensor based on the ZnO nanorods grown on the RGO/TiO₂ hybrid layer-coated ITO photoanode can dramatically improve the photocurrent strength and linearity.

We proposed an active differential intensity (DI) fiber coupled plasmon waveguide resonance (CPWR) sensor based on the mode competition effect in the C-band, aiming to enhance the sensitivity. The sensing head is a fiber probe with a sensing layer of ITO/Au/ITO/TiO₂ film, enabling the excitation of CPWR in the C-band. The narrow CPWR spectrum allows DI interrogation by tracking the intensity of light at two wavelengths. The fiber probe is inserted into a dual-wavelength fiber laser to adjust the intra-cavity loss at the two lasing wavelengths. By using the differential modulation of the reflectivity from the refractive index variations, the mode competition effect is triggered. The powers at two lasing wavelengths change oppositely, enlarging the power difference and then resulting in enhanced sensitivity. The average sensitivity is up to 5702 dB/RIUs, which is 10 times higher than that of conventional DI interrogation. The sensitivity enhancement mechanism based on the mode competition effect provides a new technical approach for enhancing the sensitivity of DI SPR sensors.