Improved charge-transfer resonance in graphene oxide/ZrO2 substrates for plasmonic-free SERS determination of methyl parathion

This work reports a sensitive SERS substrate based on graphene oxide (GO) and quantum-sized ZrO2 nano -particles (GO/ZrO2) for label-free determination of the organophosphate pesticide methyl parathion (MP). The enhanced light-matter interactions and the consequent SERS effect in these substrates resulted from the effective charge transfer (CT) mechanism attributed to synergistic contributions of three main factors: i) the strong mo-lecular adherence of the MP molecules and the ZrO2 surface which allows the first layer-effect, ii) the relatively abundant surface defects in low dimensional ZrO2 semiconductor NPs, which act as intermediate electronic states that reduce the large bandgap barrier, and iii) the hindered charge recombination derived from the transference of the photoinduced holes to the GO layer. This mechanism allowed an enhancement factor of 8.78 x 104 for GO/ ZrO2-based substrates, which is more than 5-fold higher than the enhancement observed for platforms without GO. A detection limit of 0.12 mu M was achieved with an outstanding repeatability (variation <= 4.5%) and a linear range up to 10 mu M, which is sensitive enough to determine the maximal MP concentration permissible in drinking water according to international regulations. Furthermore, recovery rates between 97.4 and 102.1% were determined in irrigation water runoffs, strawberry and black tea extracts, demonstrating the reliability of the hybrid GO/ZrO2 substrate for the organophosphate pesticides quantification in samples related to agri-food sectors and environmental monitoring.

Automated summary

This work reports the development of a sensitive SERS substrate based on graphene oxide (GO) and quantum-sized ZrO2 nanoparticles (GO/ZrO2) for label-free determination of methyl parathion (MP). The substrate exhibited enhanced light-matter interactions and strong SERS effects due to the effective charge transfer mechanism. The GO/ZrO2-based substrates showed an enhancement factor over 5 times higher than platforms without GO, with a detection limit of 0.12 μM and excellent repeatability.