Superparamagnetic Fe₃O₄ Nanoclusters Embedded within Porous TiO₂ Shells for Photoelectrochemical Sensing

Probes are usually required for specific detection using photoelectrochemical (PEC) sensors. However, tedious probe modification and cleaning procedures reduce the efficiency of PEC sensors. To overcome this problem, using the intrinsic properties of the target to develop an elegant and probe-free PEC sensor is an alternative. Herein, yolk–shell-structured Fe3O4@void@TiO2-Na+ was successfully used in the construction of an elegant Ag+ ion PEC sensor using Ag+–Na+ ion exchange and in situ reduction by ethanol. Amorphous TiO2 shells serve as both photoelectric beacons and ion-exchange carriers. The resulting Fe3O4@void@TiO2-Ag+ can be in situ converted to Fe3O4@void@TiO2-Ag by ethanol reduction during magnetic extraction and washing processes. However, other coexisting cations do not have this characteristic, which makes the PEC sensor extremely selective. In particular, the method successfully avoids the complex steps of incubation of biological probes, hybridization, and electrode assembly and effectively improves the accuracy and stability of the PEC sensor. Additionally, the proportional changes of photocurrent result only from the hot electrons of in situ generated plasmonic silver nanoparticles, leading to an ultrasensitive PEC analytical method. In addition to the advantages mentioned above, this elegant PEC sensor has advantages of easy operation, reproducibility, cost-effectiveness, and low time consumption.