Rapid Analysis of Multiple Sudan Dyes in Chili Flakes Using Surface-Enhanced Raman Spectroscopy Coupled with Au–Ag Core-Shell Nanospheres

Trace analysis of organic compounds in foods with surface‐enhanced Raman spectroscopy: Methodology, progress, and challenges

“…SERS has been applied to analyze trace chemicals in various foods, mainly hazardous compounds that may pose health risks. These typically include residual pesticides, herbicides, or insecticides in plant source foods (Fan et al., , ; Kang, Wu, Chen, Li, & Du, ; Liou, Nayigiziki, Kong, Mustapha, & Lin, ; Sun, Yu, & Lin, ; Zhao, Huang, Fan, & Lai, ), banned and restricted drugs (such as growth hormones and antibiotics) in muscle foods such as fish and chicken (Li et al., ; Xu et al., ), naturally occurred toxicants such as aflatoxins in grains (Lee, Herrman, Bisrat, & Murray, ) and histamine in fish (Janči et al., ), as well as prohibited or restricted additives such as melamine in processed foods (Lin et al., ; Zhao et al., ), formaldehyde in shrimp and squid (Zhang, Zhao, Ma, & Li, ), Sudan dyes in chili flakes (Ou et al., ), Sunset Yellow and Allura Red in beverages (Ou et al., ), and tert‐butylhydroquinone (TBHQ) in vegetable oils (Pan et al., ).…”

“…Similarly, Ou et al. () replaced n‐hexane with acetonitrile to extract four Sudan dyes from chili powder and greatly improved the sensitivity of an SERS method for two out of the four tested dyes.…”

“…When metallic nanoparticle colloid is involved, similar to that for the substrate with a nanostructured surface, the colloid could be deposited onto a glass slide or other sample holder and dried first; next, the analyte is dropped on top of the assembled nanoparticles (Pei et al., ; Y. Zhang et al., ). However, most often, colloidal nanoparticles and the analyte solution or sample extract is mixed, and then a drop of this mixture is deposited on a sample holder; following this, SERS spectra are collected from multiple spots of the dried droplet (Figure 3b) (Luo et al., ; Ou et al., ; Pei et al., ; Wijaya et al., ; Y. Zhang et al., ). This “dried colloid” method is simple and widely applied in analyzing food or other samples, but the distribution of the target compound and nanoparticles on the surface of a sample holder could be very complicated, depending on the surface properties (for example, charge) of both nanoparticles and the target molecules (Culha, ).…”

“…Since gold substrates are generally more stable and often result in more reproducible spectra compared to silver substrates, gold substrates have been employed much more frequently for analyzing complex foods including muscle foods, fruits, and vegetables. Silver and gold bimetallic substrates, such as gold coated by silver (Au-Ag) nanospheres and multilayer nanoparticles (e.g., Au-Ag-Au) that provide the capability for a tunable resonance frequency by adjusting the thickness of the gold and silver layers, have been applied to achieve combined advantages of Ag and Au substrates (Alexander, Skinner, Zhang, Wei, & Lopez, 2010;Liao et al, 2013;Ou et al, 2017;Pei et al, 2014;Rodríguez-González, Burrows, Watanabe, Kiely, & Liz-Marzán, 2005;Wang, Sun, Pu, & Wei, 2019;Xu, Lai, Fan, Rasco, & Huang, 2019). Although not quite common, copper and aluminum along with some transition metals (Pt, Ru, and Fe) have also been used as SERS substrates.…”

“…The modified extraction method led to much more intensive characteristic peaks and less interferences from nontarget compounds. Similarly, Ou et al (2017) replaced n-hexane with acetonitrile to extract four Sudan dyes from chili powder and greatly improved the sensitivity of an SERS method for two out of the four tested dyes.…”