Sub-picomole level photoelectrochemical sensing of l-cysteine based on plasmonic silver nanoparticles modified hierarchically structured zinc oxide

• A novel “on–off” plasmonic nano-Ag/ZnO-based PEC sensor of l-cysteine.
• In situ synthesis of plasmonic silver nanoparticles for enhancement of photocurrent.
• Hierarchically structured ZnO is favorable to enhance incident light capture.
• Plasmonic nano-silver can efficiently promote the separation of carriers of ZnO.
• The fabricated PEC sensor exhibited good performances for l-cysteine detection.

A novel photoelectrochemical (PEC) sensor for l-cysteine was fabricated using in situ plasmonic silver nanoparticles modified hierarchically structured zinc oxide. The fabricated PEC sensor was based on Ag–S coordination chemistry and the collective oscillatory motion of electrons resulting from the coherent excitation of the “free” electrons in the conduction band of silver nanoparticles. The energetic electrons from the surface plasmon of the silver nanoparticles may be injected into the conduction band of the hierarchically structured zinc oxide and then fast transferred to the ITO electrode. However, the enhanced photocurrent produced by the plasmonic silver nanoparticles can be efficiently inhibited due to the bonding of Ag–S upon the simulated sunlight irradiation and at the bias voltage of 0.2 V. Under the optimized condition, the fabricated PEC sensor was linear with the concentration of l-cysteine in the range from 0.67 to 34.77 pmol L−1 with the detection limit of 0.21 pmol L−1. The presence of definite concentration of conventional species did not interfere in the detection of l-cysteine and the results agreed well with those obtained by HPLC. This novel plasmonic PEC sensor has good performances in high sensitivity, good selectivity, easy operation, economy, short detection time, and portability. The strategy of localized surface plasmon resonance by in situ generation of silver nanoparticles provides an alternative way to construct a PEC sensor of l-cysteine.

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