SERS-Active Substrate with Collective Amplification Design for Trace Analysis of Pesticides

Abstract

Health risks posed by the exposure to trace amounts of pesticide residue in agricultural products have gained a lot of concerns, due to their neurotoxic nature. The applications of surface-enhanced Raman Scattering (SERS) as a detection technique have consistently shown its potential as a rapid and sensitive means with minimal sample preparation. In this study, gold nanoparticles (Au NPs) in elliptical shapes were collected into a layer of ordered zirconia concave pores. The porous zirconia layer (pZrO2) was then deposited with Au NPs, denoted as Au NPs (x)/pZrO2, where x indicates the deposition thickness of Au NPs in nm. In the concave structure of pZrO2, Au-ZrO2 and Au-Au interactions provide a synergistic and physical mechanism of SERS, which is anticipated to collect and amplify SERS signals and thereafter improve the enhancement factor (EF) of Au NPs/pZrO2. By taking Rhodamine 6G (R6G) as the test molecule, EF of Au NPs/pZrO2 might reach to 7.0 × 107. Au NPs (3.0)/pZrO2 was then optimized and competent to detect pesticides, e.g., phosmet and carbaryl at very low concentrations, corresponding to the maximum residue limits of each, i.e., 0.3 ppm and 0.2 ppm, respectively. Au NPs (3.0)/pZrO2 also showed the effectiveness of distinguishing between phosmet and carbaryl under mixed conditions. Due to the strong affinities of the phosphoric groups and sulfur in phosmet to the Au NPs (3.0)/pZrO2, the substrate exhibited selective detection to this particular pesticide. In this study, Au NPs (3.0)/pZrO2 has thus demonstrated trace detection of residual pesticides, due to the substrate design that intended to provide collective amplification of SERS.

Ag Nanostructures with Spikes on Adhesive Tape as a Flexible Sers-Active Substrate for In Situ Trace Detection of Pesticides on Fruit Skin

“…With varying concentrations of R6G, a trend was observed wherein the logarithmic values of R6G concentrations and the intensities of the peak at 1361 cm −1 appeared to be a linear calibration plot as shown in Figure 3d. This indicates that the substrate holds a potential in quantitative determination of analyte even with only SERS peak intensity is given, as also observed in some studies [15,16].…”

“…While it is highly preferred that NSPs agglomerate to some degree, heavy agglomeration may not always provide an optimized SERS-active effect coming from a particular NSP. As compared with the case of a study utilizing Au NPs, a decrease in the peak intensities was observed when Au NPs were observed to be heavily clustered [15]. shown in Figure 2e, showing randomly-oriented Ag NSPs featuring blunt-tipped spikes, and a single Ag NSP could be distinguished in Figure 2f.…”

Dielectric Nanoparticles Coated upon Silver Hollow Nanosphere as an Integrated Design to Reinforce SERS Detection of Trace Ampicillin in Milk Solution

“…Based on the equations (2.1), (2.2), and (2.3), I SERS is the Raman signal intensity at 1361 cm −1 for each substrate, I Bulk is 25 after Raman spectral analysis, N Bulk is estimated around 3.9 × 10 10 molecules, and N SERS is estimated as a value of 2.6 × 10 6 . The results indicate that (1) the EF of Ag HNS shows slightly higher as the size and dimension of cavity is smaller [16]; (2) all the Di NPs/Ag HNS_130 have EFs significantly higher than Ag HNSs and greater than 10 7 ; (3) Al 2 O 3 /Ag HNS_130 has the largest EF with a value of 6.2 × 10 7 , which also shows that Ag HNS with the attachment of lower dielectric constant NPs results in a high EF [44]. Note that the values of dielectric constant for Al 2 O 3 , HfO 2 , and TiO 2 / are 9-10, 20-30, and 10-85, respectively [46,47].…”

“…A lipid-removal procedure, as described in Experimental section, was thus necessarily prior to the sample into the detection [50,51]. The peak found at 1035 cm −1 presumably resulted from the surface of Al2O3 NPs/Ag HNS, which is likely the background thar contributed by the core shell structure of Ag HNS [52,53] and Al2O3 NPs upon Ag HNS, in the case of ampicillin in milk solution [44]. In Figure 6b, by taking these three peaks and low concentration (i.e., 0.01 ppm) of ampicillin in water and milk solution for a comparison, the results show the influence of ampicillin in different solutions.…”

“…Fabrications of PS, Ag HNS, and Di NPs/Ag HNS Uniform polystyrene beads (PS_Bs), with a diameter of 130, 240, and 260 nm that were synthesized through surfactant-free emulsion polymerization, were first deposited onto clean 2 × 2 cm 2 Si substrates, by drawing out the Si substrates that were briefly immersed in PS_Bs suspended in water, as illustrated in Figure 1a(i-v). The PS-coated Si was then subjected to slight annealing at 50 • C for 10 min [44], ensuring that all the solvents have evaporated and that the PS_Bs are fixed onto the surface of the Si. As shown in Figure 1a(vi), Ag thin film was then deposited onto PS_Bs/Si by an e-beam evaporator (VT1-10CE, ULVAC, Chigasaki, Japan), followed by annealing at 400 • C for 45 min to remove the PS_Bs.…”