The implementation of low‐cost and rapid technologies for the on‐site detection of mycotoxin‐contaminated crops is a promising solution to address the growing concerns of the agri‐food industry. Recently, there have been significant developments in surface‐enhanced Raman spectroscopy (SERS) for the direct detection of mycotoxins in food and feed. This review provides an overview of the most recent advancements in the utilization of SERS through the successful fabrication of novel nanostructured materials. Various bottom‐up and top‐down approaches have demonstrated their potential in improving sensitivity, while many applications exploit the immobilization of recognition elements and molecular imprinted polymers (MIPs) to enhance specificity and reproducibility in complex matrices. Therefore, the design and fabrication of nanomaterials is of utmost importance and are presented herein. This paper uncovers that limited studies establish detection limits or conduct validation using naturally contaminated samples. One decade on, SERS is still lacking significant progress and there is a disconnect between the technology, the European regulatory limits, and the intended end‐user. Ongoing challenges and potential solutions are discussed including nanofabrication, molecular binders, and data analytics. Recommendations to assay design, portability, and substrate stability are made to help improve the potential and feasibility of SERS for future on‐site agri‐food applications.

Food fraud, along with many challenges to the integrity and sustainability, threatens the prosperity of businesses and society as a whole. Tea is the second most commonly consumed non-alcoholic beverage globally. Challenges to tea authenticity require the development of highly efficient and rapid solutions to improve supply chain transparency. This study has produced an innovative workflow for black tea geographical indications (GI) discrimination based on non-targeted spectroscopic fingerprinting techniques. A total of 360 samples originating from nine GI regions worldwide were analysed by Fourier Transform Infrared (FTIR) and Near Infrared spectroscopy. Machine learning algorithms (k-nearest neighbours and support vector machine models) applied to the test data greatly improved the GI identification achieving 100% accuracy using FTIR. This workflow will provide a low-cost and user-friendly solution for on-site and real-time determination of black tea geographical origin along supply chains.

Detection of enzyme biomarkers originating from either bio-fluids or contaminating microorganisms is of utmost importance in clinical diagnostics and food safety. Herein, we present a simple, low-cost and easy-to-use sensing approach based on the switchable peroxidase-mimicking activity of plasmonic gold nanoparticles (AuNPs) that can catalyse for the oxidation of 3,3’,5’5-tetramethylbenzidine (TMB) for the determination of protease enzyme. The AuNP surface is modified with casein, showing dual functionalities. The first function of the coating molecule is to suppress the intrinsic peroxidase-mimicking activity of AuNPs by up to 77.1%, due to surface shielding effects. Secondly, casein also functions as recognition sites for the enzyme biomarker. In the presence of protease, the enzyme binds to and catalyses the degradation of the coating layer on the AuNP surface, resulting in the recovery of peroxidase-mimicking activity. This is shown visually in the development of a blue colored product (oxidised TMB) or spectroscopically as an increase in absorbance at 370 and 650 nm. This mechanism allows for the detection of protease at 44 ng·mL⁻¹ in 90 min. The nanosensor circumvents issues associated with current methods of detection in terms of ease of use, compatibility with point-of-care testing, low-cost production and short analysis time. The sensing approach has also been applied for the detection of protease spiked in ultra-heat treated (UHT) milk and synthetic human urine samples at a limit of detection of 490 and 176 ng·mL⁻¹, respectively, showing great potential in clinical diagnostics, food safety and quality control. Open image in new window

Mercury (Hg) is extremely toxic, and continues to cause major threats to aquatic life, human health and the environment. Hg²⁺ mainly derives from seawater as a product of atmospheric deposition, therefore there is great demand for sensing approaches that can detect Hg²⁺ in seawater samples. Herein, we demonstrate that the peroxidase-mimicking activity of gold nanoparticles (AuNPs) or so-called nanozymes, can be exploited for the detection of Hg²⁺ ions in various water samples. In a high electrolyte environment, the catalytic activity for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) was significantly diminished due to poor stability of the bare-AuNPs. This activity was reduced by ∼ 73.7% when the NaCl concentration was higher than 1.168%, which is much lower than that of seawater (∼ 3.5%), thus presenting its unsuitability for detecting Hg²⁺ in harsh water matrices. To overcome this limitation, AuNPs were first functionalized with oligo-ethylene glycol (OEG), of which their colloidal form presented high stability in NaCl concentrations up to 20% and across a wide range of pHs from 1–14. Interestingly, the catalytic activity of OEG-AuNPs for the oxidation of TMB was strongly suppressed by the coating, but enhanced upon formation of Au-Hg amalgamation. This novel finding underlies a straightforward, sensitive, and highly selective detection platform for Hg²⁺ in water samples. The approach could detect the exposure limit level for Hg²⁺ in drinking water (i.e., 2 ppb for tap and bottled water) as set by the United States Environmental Protection Agency (EPA) and the World Health Organization (WHO). When Hg²⁺ was spiked into a 3.5% saline solution and a coastal seawater certified reference material (CRM), the detection limits were found to be 10 and 13 ppb, respectively, which exceed the Hg²⁺ concentrations commonly found within seawater (~ 60–80 ppb). The whole procedure takes less than 45 min to conduct, providing a highly innovative, rapid and low-cost approach for detecting Hg²⁺ in complex water matrices.

Infrared (IR) spectroscopy is increasingly being used to analyze food crops for quality and safety purposes in a rapid, nondestructive, and eco‐friendly manner. The lack of sensitivity and the overlapping absorption characteristics of major sample matrix components, however, often prevent the direct determination of food contaminants at trace levels. By measuring fungal‐induced matrix changes with near IR and mid IR spectroscopy as well as hyperspectral imaging, the indirect determination of mycotoxins in food crops has been realized. Recent studies underline that such IR spectroscopic platforms have great potential for the rapid analysis of mycotoxins along the food and feed supply chain. However, there are no published reports on the validation of IR methods according to official regulations, and those publications that demonstrate their applicability in a routine analytical set‐up are scarce. Therefore, the purpose of this review is to discuss the current state‐of‐the‐art and the potential of IR spectroscopic methods for the rapid determination of mycotoxins in food crops. The study critically reflects on the applicability and limitations of IR spectroscopy in routine analysis and provides guidance to non‐spectroscopists from the food and feed sector considering implementation of IR spectroscopy for rapid mycotoxin screening. Finally, an outlook on trends, possible fields of applications, and different ways of implementation in the food and feed safety area are discussed.

Gold nanostars (AuNSt) amalgamated with mercury ions (Hg²⁺) results in reduced SERS performance whilst their enzyme-mimicking capability is not deteriorated, thus providing a basis for Hg²⁺ detection with inverse sensitivity.