Trace level detection of explosives and pesticides using robust, low-cost, free-standing silver nanoparticles decorated porous silicon

Abstract

We report results from our extensive studies on the fabrication of ultra-thin, flexible, and cost-effective Ag nanoparticle (NP) coated free-standing porous silicon (FS-pSi) for superior molecular sensing. The FS-pSi has been prepared by adopting a simple wet-etching method. The deposition time of AgNO3 has been increased to improve the number of hot-spot regions, thereby the sensing abilities are improved efficiently. FESEM images illustrated the morphology of uniformly distributed AgNPs on the pSi surface. Initially, a dye molecule [methylene blue (MB)] was used as a probe to evaluate the sensing capabilities of the substrate using the surface-enhanced Raman scattering (SERS) technique. The detection was later extended towards the sensing of two important explosive molecules [ammonium nitrate (AN), picric acid (PA)], and a pesticide molecule (thiram) clearly demonstrating the versatility of the investigated substrates. The sensitivity was confirmed by estimating the analytical enhancement factor (AEF), which was ∼107 for MB and ∼104 for explosives and pesticides. We have also evaluated the limit of detection (LOD) values in each case, which were found to be 50 nM, 1 µM, 2 µM, and 1 µM, respectively, for MB, PA, AN, and thiram. Undeniably, our detailed SERS results established excellent reproducibility with a low RSD (relative standard deviation). Furthermore, we also demonstrate the reasonable stability of AgNPs decorated pSi by inspecting and studying their SERS performance over a period of 90 days. The overall cost of these substrates is attractive for practical applications on account of the above-mentioned superior qualities.

Picosecond Bessel Beam Fabricated Pure, Gold-Coated Silver Nanostructures for Trace-Level Sensing of Multiple Explosives and Hazardous Molecules

“…In a similar manner, for TH, S-S stretching occurs near 560 cm −1 , whereas CN stretching and symmetric deformation CH 3 are responsible for the appearance of the 1375 cm −1 peak. In case of MB, skeletal deformation of C-N-C can be attributed as the reason for 448 cm −1 Raman peak and ring stretching of C-C is accountable for 1623 cm −1 peak [75,76]. The peak assignments corresponding to different molecular/bond activities is demonstrated for all these molecules and matched well with those presented in the previous reports from our group [75][76][77][78][79][80].…”

“…In case of MB, skeletal deformation of C-N-C can be attributed as the reason for 448 cm −1 Raman peak and ring stretching of C-C is accountable for 1623 cm −1 peak [75,76]. The peak assignments corresponding to different molecular/bond activities is demonstrated for all these molecules and matched well with those presented in the previous reports from our group [75][76][77][78][79][80]. Succeeding the concentration varied study, to produce a survey on the SERS signal homogeneity, an advantageous parameter for real-time detection, relative standard deviation (RSD) of the enhanced Raman signal was estimated by collecting the signal from 30-40 random spots.…”

“…The enhancement factors corresponding to AN, MG, and HEWL molecules were found to be 2.2 × 10 3 , 6.5 × 10 6 , and 1.5 × 10 5, respectively. The limits of detection (LoDs) were also estimated, following the standard 3σ/b method, previously reported in our article [75,77], where 'σ' is the standard deviation of BB structured substrate and 'b' is the slope of the resultant linear plot at lower analyte concentrations. For all the investigated molecules, the linear region at the intensity versus concentration plots corresponding to lower concentrations can be found in the Figure S12, Supplementary material file, page S14.…”

Wafer-scale silver nanodendrites with homogeneous distribution of gold nanoparticles for biomolecules detection

“…The log intensity versus analyte at lower concentrations of the Raman mode at 918 cm −1 was estimated to be linear with an R 2 of 0.99; the data being presented in Figure 11 B. Apart from the SERS activity of substrate, the most prominent factor is to assess the degree of sensitivity by evaluating the analytical enhancement factor (AEF) by the inclusion of adsorption factor η (which is extracted from the intensity versus concentration plot) in the standard formula described in our earlier reports ( Hamad et al., 2014 ; Shaik et al., 2016 ; Vendamani et al., 2021 ). The evaluated AEF for 1 nM CV was ∼3.2×10 7 , which is shown in Table 1 .…”

Real-Time Monitoring of the In Situ Microfluidic Synthesis of Ag Nanoparticles on Solid Substrate for Reliable SERS Detection

“…Among the processes used for the fabrication of effective SERS substrates, the synthesis of noble metal nanostructures on porous silicon (pSi) membranes is an interesting option, thanks to the wide range of achievable morphologies, the high SERS efficiency in a wide range of excitation wavelengths [ 35 , 36 ], and the improved stability of the produced plasmonic nanostructures [ 37 ]. While the spontaneous deposition of metal NPs on pSi from metal salt solutions has been previously studied both on silicon [ 38 , 39 , 40 ] and flexible substrates [ 41 , 42 ], the microfluidic growth of such structures has not been extensively investigated.…”