The surface-enhanced Raman spectra of aflatoxins: spectral analysis, density functional theory calculation, detection and differentiation

Abstract

High-quality surface-enhanced Raman scattering (SERS) spectra of aflatoxin (AF) B(1), B(2), G(1) and G(2) have been acquired using silver nanorod (AgNR) array substrates fabricated by oblique angle deposition method. Significant vibrational peaks are identified on the argon plasma-cleaned substrates, and those peaks agree very well with the Raman spectra calculated by density function theory (DFT). The concentration-dependent SERS detection is also explored. The relationship between the concentration (C) of different AFs and the SERS intensity (I) of the Raman peak at Δν = 1592 cm(-1) is found to follow the general relationship I = AC(α), with α ranging from 0.32 to 0.46 for the four AFs. The limits of detection (LODs) reach 5 × 10(-5) mol L(-1) for AFB(1), 1 × 10(-4) mol L(-1) for AFB(2), and 5 × 10(-6) mol L(-1) for both AFG(1) and AFG(2) in bulk solution, or 6.17 × 10(-16) mol/1.93 × 10(-4) ng of AFB(1), 1.23 × 10(-15) mol/3.88 × 10(-4) ng for AFB(2), 6.17 × 10(-17) mol/2.03 × 10(-5) ng for AFG(1), and 6.17 × 10(-17) mol/2.04 × 10(-5) ng for AFG(2) per laser spot. Principal component analysis (PCA) is used to successfully differentiate these four different kinds of AFs at different concentrations up to their detection limits. The LODs obtained from PCA agree with the LODs obtained by using peak fitting method. With such a low detection limit and outstanding differentiation ability, we prove the possibility of utilizing the SERS detection system as a platform for highly sensitive mycotoxin detection.

An empirical evaluation of three vibrational spectroscopic methods for detection of aflatoxins in maize

“…Therefore, infrared and Raman spectroscopic techniques with different physical processes may be combined to provide complementary information for better detection of target analyte. In a few previous studies, Raman spectroscopy has been applied and showed some promising results as an analytical method for the detection of aflatoxins, but we found a paucity of study on aflatoxin analysis in contaminated grains and oilseeds where complex and heterogenous samples would make detection more challenging (Golightly, Doering, & Natan, 2009;Grow, Wood, Claycomb, & Thompson, 2003;Lee et al, 2013;Wu et al, 2012).…”

“…The spectral difference was more visible between non-contaminated and contaminated groups than among contaminated groups. The tentative Raman band assignments to particular vibration modes of aflatoxin molecules were made taking into account previous studies (Móricz, Horváth, Ott, & Tyihák, 2008;Séné, McCann, Wilson, & Grinter, 1994;Wu et al, 2012). The skeletal modes of the ring structure in aflatoxin can be found at <700 cm À1 .…”

Characterization of polycyclic aromatic hydrocarbons using Raman and surface‐enhanced Raman spectroscopy

“…The molecular geometries of the PAHs were optimized using the hybrid B3 (exchange) and the LYP (correlation) function (B3LYP) in conjunction with a modest 6-311g** basis set. [27] Fabrication of AgNR substrates SERS-active silver nanorod (AgNR) array substrates were fabricated using oblique angle deposition (OAD) in a custom-built electron beam evaporator as described previously. [28,29] Briefly, glass slides were cleaned with Piranha solution (80% sulfuric acid, 20% hydrogen peroxide), rinsed with deionized water, dried with nitrogen, and loaded into the deposition chamber above the source material.…”

Fundamentals and applications of SERS-based bioanalytical sensing

“…Four major aflatoxins, a type of myotoxin, which appear in food are B 1 , B 2 , G 1 , and G 2 . They can be detected at low concentrations in solution [124] and in ground maize [186] using SERS. Quantitation has been developed for at least B 1 [173].…”

“…Nanoholes and nanovoids show around 10 4 -10 6 SERS enhancement [66][67][68][69]71]. Au and Ag nanodomes were fabricated using nanoreplica molding [124,125]. Depending on the inter-dome spacing, SERS enhancement factor of Ag and Au nanodomes were 8.51 × 10 7 and 1.37 × 10 8 , respectively.…”