A fluorometric assay for staphylococcal enterotoxin B by making use of platinum coated gold nanorods and of upconversion nanoparticles

A Comprehensive Review on Upconversion Nanomaterials-Based Fluorescent Sensor for Environment, Biology, Food and Medicine Applications

Near-infrared-excited upconversion nanoparticles (UCNPs) have multicolor emissions, a low auto-fluorescence background, a high chemical stability, and a long fluorescence lifetime. The fluorescent probes based on UCNPs have achieved great success in the analysis of different samples. Here, we presented the research results of UCNPs probes utilized in analytical applications including environment, biology, food and medicine in the last five years; we also introduced the design and construction of upconversion optical sensing platforms. Future trends and challenges of the UCNPs used in the analytical field have also been discussed with particular emphasis.

SERS-Active Composites with Au-Ag Janus Nanoparticles/Perovskite in Immunoassays for Staphylococcus aureus Enterotoxins

The accurate detection of Staphylococcus aureus enterotoxins (SEs) is vital for food safety owing to their high pathogenicity, which may be performed with surface-enhanced Raman scattering (SERS) if SERS-active nanostructures are used. Herein, a Au-Ag Janus nanoparticle (NPs)/perovskite composite-engineered SERS immunoassay was developed for SEC detection. Plasmonic Au-Ag Janus NPs demonstrated inherent SERS activity from the 2-mercaptobenzoimidazole-5-carboxylic acid ligands. CsPbBr₃@mesoporous silica nanomaterials (MSNs) were prepared and transformed into CsPb₂Br₅@MSNs in the aqueous phase. Paired SEC antibody-antigen-driven plasmonic Au-Ag Janus NP-CsPb₂Br₅@MSN composites were prepared. They showed amplified SERS activity, attributed to the depressed plasmonic decay due to electromagnetic field enhancement and the electron transfer mechanism. A positive relationship was established between SERS signals of composites and the SEC concentration. An additive-free SERS immunoassay was developed for simple, sensitive, and reproducible SEC detection. This study will be extended to develop multiple additive-free SERS-active plasmonic NP/perovskite composites that will open up the possibility of exploring more SERS detection probes for food safety monitoring.

Rapid point-of-need detection of bacteria and their toxins in food using gold nanoparticles

Biosensors need to meet the rising food industry demand for sensitive, selective, safe, and fast food safety quality control. Disposable colorimetric sensors based on gold nanoparticles (AuNPs) and localized surface plasmon resonance are low-cost and easy-to-perform devices intended for rapid point-of-need measurements. Recent studies demonstrate various facile and versatile AuNPs-based analytical platforms for the detection of bacteria and their toxins in milk, meat, and other foods. In this review, we introduce the general characteristics and mechanisms of AuNPs calorimetric biosensors, and highlight optimizations needed to strengthen and improve the quality of devices for their application in food matrices.

Lanthanide ion (Ln3+ )-based upconversion sensor for quantification of food contaminants: A review

The food safety issue has gradually become the focus of attention in modern society. The presence of food contaminants poses a threat to human health and there are a number of interesting researches on the detection of food contaminants. Upconversion nanoparticles (UCNPs) are superior to other fluorescence materials, considering the benefits of large anti-Stokes shifts, high chemical stability, non-autofluorescence, good light penetration ability, and low toxicity. These properties render UCNPs promising candidates as luminescent labels in biodetection, which provides opportunities as a sensitive, accurate, and rapid detection method. This paper intended to review the research progress of food contaminants detection by UCNPs-based sensors. We have proposed the key criteria for UCNPs in the detection of food contaminants. Additionally, it highlighted the construction process of the UCNPs-based sensors, which includes the synthesis and modification of UCNPs, selection of the recognition elements, and consideration of the detection principle. Moreover, six kinds of food contaminants detected by UCNPs technology in the past 5 years have been summarized and discussed fairly. Last but not least, it is outlined that UCNPs have great potential to be applied in food safety detection and threw new insight into the challenges ahead.

Gold Nanomaterials as a Promising Integrated Tool for Diagnosis and Treatment of Pathogenic Infections-A Review

This review summarizes research on functionalized gold nanomaterials as pathogen detection sensors and pathogen elimination integrated tools. After presenting the challenge of current severe threat from pathogenic bacteria and the increasingly serious growth rate of drug resistance, the first section mainly introduces the conspectus of gold nanostructures from synthesis, characterization, physicochemical properties and applications of gold nanomaterials. The next section deals with gold nanomaterials-based pathogen detection sensors such as colorimetric sensors, fluorescence sensors and Surface-Enhanced Raman Scattering sensors. We then discuss strategies based on gold nanomaterials for eliminating pathogenic infections, such as the dual sterilization strategy for grafting gold nanomaterials with antibacterial substances, photothermal antibacterial and photodynamic antibacterial methods. The fourth part briefly introduces the comprehensive strategy for diagnosis and sterilization of pathogen infection based on gold nanomaterials, such as the diagnosis and treatment strategy for pathogen infection using Roman signals real-time monitoring and photothermal sterilization. A concluding section that summarizes the current status and challenges of the novel diagnosis and treatment integrated strategy for pathogenic infections, gives an outlook on potential future perspectives.

Trimer-based aptasensor for simultaneous determination of multiple mycotoxins using SERS and fluorimetry

An aptasensor is reported for the detection of three different kinds of mycotoxins, i.e., zearalenone (ZEN), ochratoxin A (OTA), and fumonisin B1 (FB1). Based on fluorescence resonance energy transfer effect (FRET) and surface-enhanced Raman scattering (SERS), the levels of ZEN, FB1, and OTA can be simultaneously determined. Under 980-nm and 650-nm laser excitation, the logarithmic values of fluorescence signal intensities at 543 nm and 670 nm are slowly increased as the concentrations of ZEN and OTA vary from 0.1 ng mL^-1 and 0.05 ng mL^-1 to 100 ng mL^-1 and 25 ng mL^-1, respectively. For FB1, under 980-nm laser excitation, the logarithmic value of SERS signal intensity at 1567 cm^-1 gradually increases with the concentration of FB1 in the range 0.05-200 pg mL^-1 (R² = 0.996). The detection limits of the proposed assay for ZEN, OTA, and FB1 are 0.03 ng mL^-1, 0.01 ng mL^-1, and 0.02 pg mL^-1, respectively. The selectivity experiment results indicate this assay possesses a high selectivity over other commonly encountered mycotoxins. The average recoveries range from 90 to 107%, revealing satisfactory application potential of the proposed assay. The developed aptasensor will bring bright prospects for research in the field of multiplexed mycotoxine detection. Graphical Abstract Schematic representation of an aptamer-based assay for multiple mycotoxins determination.

Recent Progress in the Identification of Aptamers Against Bacterial Origins and Their Diagnostic Applications

Aptamers have gained an increasing role as the molecular recognition element (MRE) in diagnostic assay development, since their first conception thirty years ago. The process to screen for nucleic acid-based binding elements (aptamers) was first described in 1990 by the Gold Laboratory. In the last three decades, many aptamers have been identified for a wide array of targets. In particular, the number of reports on investigating single-stranded DNA (ssDNA) aptamer applications in biosensing and diagnostic platforms have increased significantly in recent years. This review article summarizes the recent (2015 to 2020) progress of ssDNA aptamer research on bacteria, proteins, and lipids of bacterial origins that have implications for human infections. The basic process of aptamer selection, the principles of aptamer-based biosensors, and future perspectives will also be discussed.

A fluorometric method for aptamer-based simultaneous determination of two kinds of the fusarium mycotoxins zearalenone and fumonisin B1 making use of gold nanorods and upconversion nanoparticles

An aptamer-based assay for the determination of two different kinds of fusarium mycotoxins, i.e., zearalenone (ZEN) and fumonisin B₁ (FB₁), is presented. Based on the inner filter effect (IFE) strategy, the contents of ZEN and FB₁ can be simultaneously quantified. It is making use of 65-nm gold nanorods (AuNRs), 20-nm upconversion nanoparticles (UCNPs), fluorescence dyes, and DNA sequences. In the absence of ZEN and FB₁, the UCNPs and AuNRs associate through DNA sequences. Due to IFE effect, weak fluorescence signals are collected. In the presence of ZEN or FB₁, UCNPs and AuNRs become unstable and partially separate from each other. This results in the recovery of fluorescence signals. Under 980-nm laser excitation, the logarithmic values of fluorescence signal intensities at 606 nm and 753 nm gradually increase with the concentration of ZEN and FB₁ in the ranges 0.05-100 μg L^-1 (the coefficient of determination is 0.997) and 0.01-100 ng L^-1 (the coefficient of determination is 0.986), respectively. The limits of detection (LOD) of the fabricated assay for ZEN and FB1 are 0.01 μg L^-1 and 0.003 ng L^-1, respectively. The proposed method has a high selectivity over other competitive mycotoxins, including aflatoxin B1, ochratoxin A, patulin and ochratoxin B. The applicability of the assay was evaluated in the determination of ZEN and FB1 contents in spiked corn samples. The average recoveries ranged from 89.9 to 106.6%. This result confirms the practicality of this method. Graphical abstract Schematic representation of an aptamer-based fluorometric method for simultaneous determination of two kinds of the fusarium mycotoxins zearalenone and fumonisin B₁.

Aptamer and gold nanorod-based fumonisin B1 assay using both fluorometry and SERS

An aptamer-based assay is presented for the determination of fumonisin B1 (FB1). It is bimodal in that both surface-enhanced Raman spectroscopy (SERS) and fluorometry are applied for quantitation. It makes use of platinum-coated gold nanorod (AuNR) and DNA sequences. The complementary DNA of aptamer (cDNA) against FB1 is immobilized on the surface of AuNR. The aptamer of FB1 modified with Cy5.5 are complementarily hybridized with cDNA. In the absence of FB1, the aptamer and its cDNA associate. In this situation, strong SERS and weak fluorescence signals are obtained. In the presence of FB1, the aptamer disassociates with its cDNA and binds the target. As the concentration of FB1 increases, the SERS and fluorescence signal intensities of the mixture are gradually decreased and increased, respectively. Under optimized conditions, the SERS signal at 1366 cm^-1 decreases linearly in the 10-500 pg mL^-1 concentration range with the calibration equation of y = 1997lgx-594 (the coefficient of determination is 0.998). The fluorescence signal at 670 nm increases linearly in the 10-250 pg mL^-1 concentration range with the calibration equation of y = 500lgx-383 (the coefficient of determination is 0.991). The assay was applied to the determination of FB1 contents in spiked corn samples. The average recoveries ranged from 92 to 107%, confirming the practicality of this method. The results obtained by this assay are in good agreement with that of LC-MS/MS method. Graphical abstractSchematic illustration of a bimodal aptasensor based on surface enhanced Raman scattering (SERS) and fluorescence change for the detection of fumonisin B1 (FB1).

Noble Metal Nanoparticles Applications: Recent Trends in Food Control

Scientific research in the nanomaterials field is constantly evolving, making it possible to develop new materials and above all to find new applications. Therefore, nanoparticles (NPs) are suitable for different applications: nanomedicine, drug delivery, sensors, optoelectronics and food control. This review explores the recent trend in food control of using noble metallic nanoparticles as determination tools. Two major uses of NPs in food control have been found: the determination of contaminants and bioactive compounds. Applications were found for the determination of mycotoxins, pesticides, drug residues, allergens, probable carcinogenic compounds, bacteria, amino acids, gluten and antioxidants. The new developed methods are competitive for their use in food control, demonstrated by their validation and application to real samples.