Identification and classification of ATS in oral fluid based on Ag nanoassemblies on Si surface doped with Au nanobipyramids

Abstract

Herein, a novel Ag NP substrate doped with Au nanobipyramids was designed and fabricated via a convenient procedure of galvanic reaction for the identification and classification of amphetamine-type stimulants (ATS) in oral fluids in combination with surface enhanced Raman scattering (SERS). The substrate was shown to have a three-dimensional nanostructure, high SERS activity, and good stability. In combination with SERS, the Ag NP substrate doped with Au nanobipyramids was able to detect ultra-low traces of ATS, including amphetamine, methylamphetamine (MA), 3,4-methylenedioxyamphetamine (MDA), and 3,4-methylenedioxymethylamphetamine (MDMA) in oral fluid with limit of detection (LOD) and limit of determination quantitation (LOQ) as low as 10^-9 mg/mL, which is much better than the current spectroscopic techniques. The equations between concentration and peaks intensity for quantitative analysis displied good doublelogarithmic linear relations and reliability figures of merit at nanogram concentration level in compartion with GC-MS method. The approach can be broadly applied to the ultra-low trace detection of ATS in oral fluid and would be particularly useful for the analyses of nitrogenous organic compounds.

Figure 1

SEM images of obtained Ag NPs. (a) ‘rough’ surface of Si substrate at a micro-level (10 μm), (b) ‘rough’ surface of Si substrate at a nano-level (1 μm), (c) ‘rough’ surface of Si substrate at a nano-level (500 nm), (d) spectra of SEM/EDS of nanoparticles (map scanning, scanning region 2 μm × 2 μm).

Figure 2

SERS of MA (1.0 × 10⁻⁶ mol/L) on the Ag NPs substrates prepared at different reaction times.

Figure 3

The effect of pH of aqueous solutions on surface-enhanced Raman signal of ATS with same concentrations. (a) Amphetamine, (b) MA, (c) MDA, (d) MDMA.

Figure 4

SERS spectra of aqueous solutions of ATS at the same concentration. (a) Amphetamine, (b) MA, (c) MDA, (d) MDMA. Each data point were obtained from 5 repeated experiments.

Figure 5

SERS spectra of aqueous solutions of ATS. (a) amphetamine (1.0 × 10^–12 mg/mL), (b) MA (1.0 × 10^–14 mg/mL), (c) MDA (1.0 × 10^–8 mg/mL), (d) MDMA (1.0 × 10^–14 mg/mL). Each data point were obtained from 5 repeated experiments.

Figure 6

Linear regression equation of peak intensity at 997, 755, 970 and 1442 cm^–1 versus the concentrations of amphetamine, MA, MDA, and MDMA, respectively at the nanogram (10^–9 mg/mL) concentration range. (a) amphetamine, (b) MA, (c) MDA, (d) MDMA. R is correlation coefficient.