Integrating TiO2 Nanoparticles within a Catecholic Polymeric Network Enhances the Photoelectrochemical Response of Biosensors

Development of ultrasensitive biosensors for monitoring biologically relevant analytes is the key to achieving point-of-care diagnostics and health-monitoring devices. Photoelectrochemical readout, combining photonic excitation with electrochemical readout, is envisioned to enhance the limit of detection of biosensors by increasing their sensitivity and reducing background currents generated in biological samples. In spite of this, the functionalization of photoelectrochemical transducers with biorecognition elements significantly reduces the baseline current and signal-to-background ratio of these devices. Additionally, the stability of photoactive electrodes created using photoactive nanomaterial assemblies is often insufficient for withstanding multiple washing and potential cycling steps that are involved in biosensing protocols. To overcome these challenges, we created an effective conjugation strategy for integrating TiO2 nanoparticles into photoactive electrodes. This strategy involves two components that work synergistically to increase the photoelectrochemical current of the transducers. The catechol-containing molecule, 3,4-dihydroxybenzaldehyde (DHB), is used to enhance the electronic and optical properties of TiO2 nanoparticles for signal generation. Chitosan (CHIT) is used to enhance the film-forming properties of the DHB-conjugated TiO2 nanoparticles to form uniform and stable films. Together, DHB and CHIT resulted in the formation of an extensive network of TiO2 nanoparticles within the DHB–CHIT matrix and enhanced the generated photocurrent by a factor of 10. We modified the optimized photoelectrode with DNA probes to create a photoelectrochemical DNA detector. The TiO2–DHB–CHIT photoelectrodes offered the required stability and signal magnitude to distinguish between complementary and noncomplementary DNA sequences, paving the route toward photoelectrochemical DNA sensing.