Direct Discrimination of Edible Oil Type, Oxidation, and Adulteration by Liquid Interfacial Surface-Enhanced Raman Spectroscopy

Abstract

The quality and safety of edible oils is a momentous but formidable challenge, especially regarding identification of oil type, oxidation, and adulteration. Most conventional analytical methods have bottlenecks in sensitivity, specificity, accessibility, or reliability. Surface-enhanced Raman spectroscopy (SERS) is promising as an unlabeled and ultrasensitive technique but limited by modification of inducers or surfactants on metal surfaces for oil analysis. Here, we develop a quantitative SERS analyzer on two-liquid interfacial plasmonic arrays for direct quality classification of edible oils by a portable Raman device. The interfacial plasmonic array is self-assembled through mixing the gold nanoparticle (GNP) sols and oil sample dissolved in chloroform without any surfactants or pretreatments. Different kinds of edible oils dissolved in chloroform directly participate in self-assembly of plasmonic arrays that finally localizes onto a three-dimensional (3D) oil/water interface. The 3D plasmonic array is self-healing, shape adaptive, and can be transferred to any glass containers as a substrate-free SERS analyzer for direct Raman measurements. It produces sensitive responses of SERS on different kinds of edible oils. By virtue of principal component analysis (PCA), this analyzer is able to quickly distinguish six edible oils, oxidized oils, and adulterated oils. Moreover, the solvent chloroform generates unique and stable SERS bands that can utilized as an inherent internal standard (IIS) to calibrate SERS fluctuation and greatly improve quantitation accuracy. Compared to conventional lab methods, this analyzer avoids complex and time-consuming preprocessing and provides significant advantages in cost, speed, and utility. Our study illuminates a facile way to determine edible oil quality and promises great potential in food quality and safety analysis.

Self-assembly of colloidal nanoparticles into 2D arrays at water–oil interfaces: rational construction of stable SERS substrates with accessible enhancing surfaces and tailored plasmonic response

“…Moreover, since the chemical composition of the oil is unimportant, as long as it provides a high energy interface with water for self-assembly, a variety of organic solvents can be used as the oil phase, which provides an extremely versatile SERS platform, especially for studying dipolar analyte molecules with low solubility in water. [69][70][71][72][73][74][75] For example, Liu et al showed that six edible oils can be distinguished using SERS and interfacial 2D Au nanoparticle arrays as enhancing substrates (Figure 6c). [72] Moreover, they showed that oxidation and adulteration of the edible oils could also be detected with the assistance of principle component analysis.…”

“…[69][70][71][72][73][74][75] For example, Liu et al showed that six edible oils can be distinguished using SERS and interfacial 2D Au nanoparticle arrays as enhancing substrates (Figure 6c). [72] Moreover, they showed that oxidation and adulteration of the edible oils could also be detected with the assistance of principle component analysis. [66,75] In a separate study from the same research group, it was shown that four different polycyclic aromatic hydrocarbons (PAHs) could be detected with a detection limit of 10 ppb using 2D Au nanoparticle arrays assembled at waterchloroform interfaces as the SERS enhancing substrate.…”

Insights into chemometric algorithms for quality attributes and hazards detection in foodstuffs using Raman/surface enhanced Raman spectroscopy

“…More detailed principle, background, and establishment of the RF algorithm can be summarized elsewhere (Yun et al., 2013). Raman spectroscopy was used for chlorpyrifos at 341 cm −1 on the pear surface to design a quantitative detection model namely RF and others (Du et al., 2019). RF performs better than other models with a correlation coefficient ( R 2 ) of 0.8495 and 0.9003 in the training and prediction test sets.…”

Surface-Enhanced Raman Spectroscopy for Rapid Screening of Cinnamon Essential Oils

“…36 SERS has been used to detect food additives, antibiotics, reference solutions of coumarin, pathogens, and proteins. 36,39–41…”

“…Recently, SERS has been used to detect edible oil samples using a two-liquid interfacial plasmonic array sensor. 41 The sensor requires pretreatment with chloroform to initiate the self-assembly of the plasmonic arrays for SERS detection of edible oils. In the present work, Lee–Meisel colloids are centrifuged to produce a colloid paste substrate.…”