On-site detection of sub-mg/kg melamine mixed in powdered infant formula and chocolate using sharp-edged gold nanostar substrates

Recent advances in gold nanoparticles-based biosensors for food safety detection

Food safety issue remains a challenge worldwide. Common substances in food can pose a great threat to human health including but not limited to food borne-pathogens, heavy metals, mycotoxins, pesticides, herbicides, veterinary drugs, allergens and illegal additives. To develop rapid, low-cost, portable and on-site detection methods of those contaminants and allergens to ensure food safety, gold nanoparticles (AuNPs) of versatile shapes and morphologies such as nanorods, nanoclusters, nanoflowers, nanostars, nanocages, nanobipyramids and nanowires have been employed as probes because they possess extraordinary properties that can be used to design biosensors enabling detecting various contaminants and allergens. By means of surface modification, AuNPs can directly or indirectly sense specific targets based on different mechanisms, such as hydrogen bonds, nucleic acid hybridization, aptamer-target binding, antigen-antibody recognition, enzyme inhibition, and enzyme-mimicking activity. AuNPs can induce a distinct color change from red to blue when they transform from a monodispersed state to an aggregated state in liquid solution, which can be observed by naked eyes. If Raman molecules are functionalized on AuNPs, their aggregation will alter the interparticle distance and induce the surface-enhanced Raman scattering that can be employed for highly sensitive detection. Ultra-small AuNPs such as Au nanoclusters also feature in fluorescence that enable a fluorescent readout. The formats of AuNPs for food safety detection in real world range broadly including but not limited to films, fibers, liquid solutions, tapes, chips and lateral flow strips. In this review, recent applications of AuNPs-based biosensors for food safety detection will be discussed, mainly in the aspect of different contaminants and allergens encountered in food samples.

Nanostructured Raman substrates for the sensitive detection of submicrometer-sized plastic pollutants in water

We prepared novel Raman substrates for the sensitive detection of submicron-sized plastic spheres in water. Anisotropic nanostar dimer-embedded nanopore substrates were prepared for the efficient identification of submicron-sized plastic spheres by providing internal hot spots of electromagnetic field enhancements at the tips of nanoparticles. Silver-coated gold nanostars (AuNSs@Ag) were inserted into anodized aluminum oxide (AAO) nanopores for enhanced microplastic (MP) detection. We found that surface-enhanced Raman scattering (SERS) substrates of AuNSs@Ag@AAO yielded stronger signals at the same weight percentages for polystyrene MP particles with diameters as small as 0.4 μm, whereas such behaviors could not be observed for larger MPs (diameters of 0.8 μm, 2.3 μm, and 4.8 μm). The detection limit of the submicrometer-sized 0.4 μm in our Raman measurements were estimated to be 0.005% (∼0.05 mg/g =50 ppm) along with a fast detection time of only a few min without any sample pretreatments. Our nano-sized dimensional matching substrates may provide a useful tool for the application of SERS substrates for submicrometer MP pollutants in water.

Review on Nanomaterial-Based Melamine Detection

Illegal adulteration of milk products by melamine and its analogs has become a threat to the world. In 2008, the misuse of melamine with infant formula caused serious effects on babies of China. Thereafter, the government of China and the US Food and Drug Administration (FDA) limited the use of melamine of 1 mg/kg for infant formula and 2.5 mg/kg for other dairy products. Similarly, the World Health Organization (WHO) has also limited the daily intake of melamine of 0.2 mg/kg body weight per day. Many sensory schemes have been proposed by the scientists for carrying out screening on melamine poisoning. Among them, nanomaterial-based sensing techniques are very promising in terms of real-time applicability. These materials uncover and quantify the melamine by means of diverse mechanisms, such as fluorescence resonance energy transfer (FRET), aggregation, inner filter effect, surface-enhanced Raman scattering (SERS), and self-assembly, etc. Nanomaterials used for the melamine determination include carbon dots, quantum dots, nanocomposites, nanocrystals, nanoclusters, nanoparticles, nanorods, nanowires, and nanotubes. In this review, we summarize and comment on the melamine sensing abilities of these nanomaterials for their suitability and future research directions.