ZnO Nanorod/Ag Nanoparticle─Functionalized Paper Substrate for Sensitive SERS Detection of Environmental Contaminants

In this work, we functionalize Whatman no 1 paper (WP) substrates with zinc oxide nanorods (ZnO NRs) decorated with silver nanoparticles (AgNPs) for detecting environmental contaminants. ZnO NRs were grown by hydrothermal synthesis assisted by microwave irradiation on WP substrate and subsequently decorated with AgNPs using the dewetting deposition method. WP substrates functionalized with ZnO NRs/AgNPs were used as a SERS platform for detecting rhodamine 6G (R6G) dye and the thiabendazole (TBZ) pesticide, widely used in modern agriculture for fungal disease protection in fruits and vegetables. Additionally, a mixture of TBZ and carbendazim (CBZ) was used to evaluate the selectivity of the substrates. WP substrates with ZnO NRs/AgNPs demonstrated superior SERS performance than those with only AgNPs. The set of substrates analyzed also demonstrated high reproducibility and stability for detecting environmental contaminants. The enhanced detection with ZnO NRs is attributed to their large surface area, facilitating target molecule adsorption and increasing interactions with incident light, thus improving sensitivity. For R6G, the enhancement factors (EF) obtained using AgNPs and ZnO NRs/AgNPs were 9.3 × 10³ and 2.1 × 10⁵, respectively, while the limits of detection (LOD) were approximately 4.8 × 10^-8 and 4.3 × 10^-9 mol/L. For the pesticide TBZ, the EF values using AgNPs and ZnO NRs/AgNPs were 2.0 × 10⁵ and 9.8 × 10⁶, with corresponding LODs of 4.0 × 10^-8 and 5.0 × 10^-10 mol/L, respectively. ZnO NRs/AgNPs substrates also demonstrated long-term stability and selectivity for detecting pesticide mixtures, reinforcing the potential of paper-based SERS platforms for environmental monitoring. The paper substrate offers several advantages, including ease of handling, flexibility, sustainability, and low cost. Moreover, its ease of chemical functionalization enables the integration of various nanomaterials, thereby expanding its potential for a wide range of applications, including environmental and biological monitoring, food safety, and beyond.