Fabrication of multifunctional g-C3N4-modified Au/Ag NRs arrays for ultrasensitive and recyclable SERS detection of bisphenol A residues.

Monolayer g-C3N4-modified Au/Ag nanorods (g-C3N4/Au/Ag NRs) array is fabricated as a dual-function platform with high surface-enhanced Raman scattering (SERS) response and excellent photocatalytic degradation ability for bisphenol A (BPA) residues. FDTD simulation results of Au/Ag NRs proves that the electromagnetic field intensity is significantly enhanced at the gap of Ag NRs and Au NPs and the protrusion of Au NPs, which endows the arrays with excellent SERS activity. The arrays exhibit high sensitivity for rhodamine 6G (R6G) (LOD = 1.1 × 10-11 mol/L) and high SERS enhancement (EF = 9.2 × 107). In addition, the g-C3N4/Au/Ag NRs could degrade ˃90% of BPA adsorbed on the substrate surface within 140 min under visible light irradiation, and maintains its SERS activity after repeated use for 4 times. The dual-function platform with high SERS response and excellent recycling capability is proved to be reliable and is very promising for monitoring of BPA residues in food.

Highly sensitive gold nanoparticles-modified silver nanorod arrays for determination of methyl viologen.

Gold nanoparticles-modified silver nanorod (AuNPs@AgNR) arrays were fabricated as surface-enhanced Raman spectroscopy (SERS) substrates. The coffee ring effect of the AuNPs@AgNR was explored as a preconcentration method for enriching the target analytes and increasing the "hot spots." Furthermore, methyl viologen (MV) as a toxic herbicide used in agricultural production was successfully determined to investigate the application of the coffee ring effect on AuNPs@AgNR arrays and density functional theory (DFT) was employed to calculate its vibrational modes of corresponding characteristic peaks. Good linearity was obtained in the range 0.10-100 mg/L, and the limit of detection (LOD) of MV was estimated to be 0.01 mg/L, which was lower than the US maximum residue limits (MRLs). This method was also applied to practical detection of MV in river water and apple peel with LODs of 0.10 mg/L and 0.05 mg/L, respectively. SERS results suggest that the coffee ring on AuNPs@AgNR arrays provides a promising way for monitoring environmental pollution and food safety caused by pesticides.

Highly sensitive SERS substrates with multi-hot spots for on-site detection of pesticide residues.

Pesticide residues will be a huge threat to food security and ecological environment; therefore, there is an urgent need to achieve rapid and on-site detection of pesticide residues. Herein, a plasmonic substrate with multiple "hot spots" was fabricated by transferring three-dimensional (3D) Au nanoparticles (NPs) onto the polydimethylsiloxane (PDMS) membrane for highly sensitive surface-enhanced Raman scattering (SERS) detection of pesticide residues. In combination with 3D-FDTD simulations, high SERS enhancement (EF = 1.2 × 108) and high detection sensitivity (LOD = 6.3 × 10-10 M) were achieved, mainly due to the enhanced electromagnetic fields around the "hot spots". Additionally, the PDMS-based SERS substrate held good transparency and flexibility, enabling conformal contact with non-planar surfaces and allowing the laser to penetrate the back of the analytes. Combined with a portable Raman spectrometer, the substrates holds great potential for rapid, high-sensitive, and on-site detection of contaminants in food, especially for the analyte on the nonplanar surfaces.

Preparation of a silver nano-tripod structure by a tilting angle deposition technique and its SERS application.

A silver nano-tripod (AgNT) structure with a high-density "hot spots" distribution was fabricated by a tilting angle deposition technique. The electric field simulation distribution showed that the electric field enhancement of the AgNT structures is optimal when the tilting angle is 72°. Such AgNT substrates were successfully obtained experimentally when the included angle between the silver vapor and the normal of the sample platform was set to 86°. R6G and CV were used as probe molecules to investigate the SERS activity of AgNT, which revealed that the detection limits of AgNT for R6G and CV were 2.24×10-8 M and 4.01×10-8 M, the relative standard deviations (RSDs) were 4.26% and 4.44%, and the enhancement factors (EFs) were 9.58×106 and 1.16×107, respectively. The AgNT substrates with simple preparation and high distribution density of "hot spots" illustrate a good application prospect in environmental monitoring.