Review—Surface-Enhanced Raman Scattering Sensors for Food Safety and Environmental Monitoring

Abstract

This article gives a review of surface-enhanced Raman scattering (SERS) sensors for food safety and environmental pollution monitoring. It introduces the basic concepts of SERS substrates, SERS enhancement factors and mechanisms, SERS probes/labels, molecular recognition elements as well as optofluidic SERS devices (SERS sensors integrated with microfluidics). This article places an emphasis on the design strategies of various SERS sensors by utilizing fingerprinting SERS spectra or by using SERS probes. It highlights the applications of SERS sensors in detection of heavy metals (such as Hg 2+ , Pb 2+ , Cd 2+ and As 3+ ), inorganic anions (nitrite, nitrate, perchlorate and fluoride), toxic small molecules (polycyclic aromatic hydrocarbon, polychlorinated biphenyls, herbicides, pesticides, antibiotics and food additives), as well as pathogens (bacteria and viruses Food safety and environment pollution are among great challenges in the human society. There are some common pollutants in the environment and food, such as heavy metals, nitrites, phosphates, pesticides, herbicides, antibiotics, hormone, pathogens and other additives. Some pollutants initially are released into the environment, and then accumulate in the food chain, and enter human bodies. Uptake of pollutants by human poses a threat to human health to different extents. 1,2Hence it is essential to monitor pollutants in the environment and food. Currently pollutants are typically measured with various laboratorybased techniques, such as atomic absorption spectroscopy, atomic fluorescence spectrometry, X-ray fluorescence spectrum, inductively coupled plasma and ion-coupled plasma-mass spectroscopy, mass spectrometry, chromatography, capillary electrophoresis, analytical profile index (API), polymerase chain reaction (PCR), and enzymelinked immunosorbent assay (ELISA).3-7 Although these techniques have high sensitivity and accuracy, they rely on expensive instruments and require professional to treat samples and operate instruments in centralized laboratories. Additionally, analysis generally takes several hours to days. For example, 0.024 ppb of Hg 2+ and 0.023 ppb of As 3+ in drinking water can be detected using atomic absorption spectroscopy with a two-step electrothermal atomizer and hydride generation atomic fluorescence spectrometry, respectively. 8,9 However, they need multiple sample preconcentration processing and expensive instruments. PCR can improve the number of the target while ELISA can produce amplified recognition signal, which could both improve the detection sensitivity to pathogens. For example, oligonucleotide microarray with combination of CdSe/ZnS quantum dots as fluorescent labels shown high specificity and sensitivity of 10 colony forming units (CFU)/mL. 10 However, the complicated procedures are very time-consuming, and the method is also vulnerable to contamination. These laboratory-based techniques cannot meet the critical need of rapid on-site measurement of pollutants. Therefore, it is essential to develop portable sensors f...

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