Two-dimensional (2D) layered transition-metal dichalcogenides (2DMX 2 ) are materials with unique optoelectronic properties, high surface-tovolume ratio, and high carrier mobility. The combination of noble metal nanoparticles (MNPs) with 2DMX 2 opens new avenues in conceiving more efficient plasmonic sensors, allowing one to optimize both electromagnetic and chemical signal enhancement. Photoinduced enhanced Raman spectroscopy (PIERS) exploits the electron migration from semiconductors to MNPs, upon UV light irradiation, to further boost the chemical enhancement in the surfaceenhanced Raman scattering (SERS) of molecules deposited on hybrid 2DMX 2 − MNP nanostructures. Here, we propose a new PIERS sensor architecture based on tungsten disulfide (WS 2 ) nanosheets produced by liquid-phase exfoliation (LPE) and functionalized with citrate-stabilized Au MPNs. Electron injection from WS 2 to AuNPs is observed when the Au@WS 2 is exposed to ultraviolet light, yielding an increase of the charge carriers' density ≈ 1.8%. The PIERS sensor performances are tested by detecting 4-mercaptobenzoic acid at a concentration of 10 μM. The overall PIERS signal enhancement is ∼10 6 , whereas the photoactivation of WS 2 yields a signal improvement of factor 4 with respect to SERS from Au@WS 2 before UV irradiation. Our sensor is of low cost, easy to fabricate, and has the potential to detect biomolecules and chemical molecules at trace levels.

No abstract

In the present work, a study was carried out with the aim of enhancing the performance of electrochemical biosensors based on Co3O4:Fe2O3 heterojunctions. Specifically, the redox behavior of screen–printed carbon electrodes (SPCEs) modified with Co3O4:Fe2O3 (0.5 wt%:x wt%) nanocomposites, where x ranged from 0.1 to 0.5 wt%, was examined in detail. The hybrid nanocomposites were synthesized using the sol-gel auto-combustion method. Several characterization methods were performed to investigate the morphology, microstructure, and surface area of the pure Co3O4, pure Fe2O3, and the synthesized Co3O4:Fe2O3 nanocomposites. Using cyclic voltammetry (CV) tests, the electrochemical behavior of the modified electrodes toward the dopamine (DA) molecules was investigated. The modified Co3O4:Fe2O3, (0.5 wt%, x = 0.4 wt%)/SPCE resulted in a sensor with the best electrochemical performance toward DA. A high linear relationship between DA concentrations and the faradic current variation (ipa (μA) = 0.0736 + 0.1031 CDA (μA) and R2 = 0.99) was found in the range of 10–100 μM. The sensitivity value was computed to be 0.604 µA µM−1cm−2 and the limit of detection (LOD) 0.24 µM. Based on the characterization and electrochemical results, it can be suggested that the formation of Co3O4:Fe2O3 heterostructures provides a large specific surface area, an increased number of electroactive sites at the metal oxide interface and a p–n heterojunction, thus ensuring a remarkable enhancement in the electrochemical response towards DA.