Label-free gold nanoclusters as quenchable fluorescent probes for sensing olaquindox assisted by glucose oxidase-triggered Fenton reaction

Four birds with one stone: Aggregation-induced emission-type zeolitic imidazolate framework-8 based bionic nanoreactor for portable detection of olaquindox in environmental water and swine urine by smartphone

The abuse of olaquindox (OLA) as both an antimicrobial agent and a growth promoter poses significant threats to the environment and human health. While nanoreactors have proven effective in hazard detection, their widespread adoption has been hindered by tedious chemical processes and limited functionality. In this study, we introduce a novel green self-assembly strategy utilizing invertase, horseradish peroxidase, antibodies, and gold nanoclusters to form an aggregation-induced emission-type zeolitic imidazolate framework-8 nanoreactor. The results demonstrate that the lateral flow immunoassay not only allows for qualitative naked eye detection but also enables optical analysis through the fluorescence generated by aggregated gold nanoclusters and enzyme-catalyzed enhancement of visible colorimetric signals. To accommodate more detection scenarios, the photothermal effects and redox reactions of the nanoreactor can fulfill the requirements of thermal sensing and electrochemical analysis for smartphone applications. Remarkably, the proposed approach achieves a detection limit 17 times lower than conventional methods. Besides, the maximum linear range spans from 0.25 to 5 μg/L with high specificity, and the recovery is 85.2-112.9% in environmental water and swine urine. The application of this high-performance nanoreactor opens up avenues for the construction of multifunctional biosensors with great potential in monitoring hazardous materials.

Recent advances in the biomolecules mediated synthesis of nanoclusters for food safety analysis

The development of nanoclusters based on incorporating biomolecules like proteins, lipids, enzymes, DNA, surfactants, and chemical stabilizers creates a stable and high fluorescence bio-sensors promising future due to their high sensitivity, high level of detection and better selectivity. This review addresses a comprehensive and systematic overview of the recent development in synthesizing metal nanocluster by various strategized synthesis techniques. Significantly, the application of nanometal clusters for the detection of various food contaminants such as microorganisms, antibodies, drugs, pesticides, metal contaminants, amino acids, and other food flavors have been discussed briefly concerning the detection techniques, sensitivity, selectivity, and lower limit of detection. The review further gives a brief account on the future prospects in the synthesis of novel metal nanocluster-based biosensors, and their advantages, shortcomings, and potential perspectives toward their application in the field of food safety analysis.

A fluorescent lateral flow immunoassay based on CdSe/CdS/ZnS quantum dots for sensitive detection of olaquindox in feedstuff

A portable fluorescence immunosensor based on the CdSe/CdS/ZnS quantum dots (QDs) with multiple-shell structure was fabricated for the precise quantification of olaquindox (OLA). The QDs labeled anti-OLA antibody used as bioprobe played an important role in the design and preparation of a lateral flow test strip. Due to the strong fluorescent intensity of QDs, the sensitivity is greatly improved. The quantitative results were obtained using a fluorescent strip scan reader within 8 min, and the calculated limit of detection for OLA at 0.12 µg/kg, which was 2.7 times more sensitive than that of the conventional colloidal gold-based strips method. Acceptable recovery of 85.0%-95.5% was obtained by the spiked samples. This newly established QDs-based strip immunoassay method is suitable for the on-site detection and rapid initial screening of OLA in swine feedstuff, and is potentially applied for the detection of other veterinary drugs to ensure food safety.

A simple and sensitive sensor for lactose based on cascade reactions in Au nanoclusters and enzymes co-encapsulated metal-organic frameworks

In this work, one kind of zeolite imidazole frameworks containing bovine serum albumin stabilized Au nanoclusters (AuNCs), β-galactosidase (β-Gal) and glucose oxidase (GOx) (AuNCs/β-Gal/GOx@ZIF-8) were obtained to detect lactose. Compared with other fluorescent nano-materials, AuNCs show distinct advantages as a guest species in ZIF-8, specifically their extremely small size (<1 nm), simple synthesis, excellent biocompatibility and high stability. Furthermore, the bovine serum albumin on their surfaces can promote the formation of ZIF-8 coating; thus, AuNCs were co-encapsulated in ZIF-8 with the enzymes together. X-ray diffraction (XRD) analysis indicates the composite possesses the similar crystalline structure with pure ZIF-8. Fluorescence microscope images, Fourier transform infrared spectra and energy dispersive X-ray spectroscopy indicate the presence of AuNCs in the composite. Owing to the high local concentrations of the fluorescent probe and the quenching agent in AuNCs/β-Gal/GOx@ZIF-8, the quenching rate was enhanced 3.4-fold that of free AuNCs and enzymes in solution.

Dual-mode immunoassay system based on glucose oxidase-triggered Fenton reaction for qualitative and quantitative detection of danofloxacin in milk

In this study, a novel colorimetric and fluorescent dual-mode ELISA based on glucose oxidase (GOx)-triggered Fenton reaction was developed for the qualitative and quantitative detection of danofloxacin (DAN). In this system, streptavidin-linked biotinylated anti-DAN-monoclonal antibody (SA-Bio-mAb) and biotinylated GOx (Bio-GOx) form the immune complex mAb-Bio-SA-Bio-GOx. In the absence of DAN, the mAb-Bio-SA-Bio-GOx would be immobilized by combining with coated DAN-BSA and catalyzed glucose to generate H₂O₂. The Fenton reaction between H₂O₂ and Fe²⁺ generated hydroxyl radicals, which oxidized the o-phenylenediamine to 2,3-diamino-phenazine. A dual-signal immunoassay with colorimetry and fluorescence as the signal readout was established. In the presence of DAN, DAN and DAN-BSA competed with Bio-mAb, decreasing the connection between immune complexes and DAN-BSA and finally resulting in lower signal of colorimetry and fluorescence. Under optimal conditions, the limit of detection of the fluorescence immunoassay was 0.337 ng/mL and was 5.24-fold lower than that of traditional ELISA. The colorimetric immunoassay cut-off value was 30 ng/mL in milk. The average recoveries of the method for milk samples that are spiked with different concentrations of DAN were 91.1 to 128.3%, with a coefficient of variation of 0.7 to 8.2%. These results of the method exhibited good agreement with those of liquid chromatography-tandem mass spectrometry system (LC-MS/MS) method. In brief, this work provides an improved screening strategy with high sensitivity and accuracy for the qualitative or quantitative detection of DAN in milk monitoring.

Colloidal Gold Immunochromatographic Assay for Rapid Detection of Carbadox and Cyadox in Chicken Breast

Abused or misused carbadox (CBX) and cyadox (CYA) in animal feed may cause food safety concerns, threatening human health. Here, we describe the design of a novel hapten for preparation of a monoclonal antibody against CBX and CYA simultaneously. Using this antibody, colloidal gold immunochromatographic assay (GICA) was developed for screening of CBX and CYA residues in chicken breast. Under optimal conditions, semiquantitative analysis results were visible by eye, with a visual limit of detection of 8 μg/kg for CBX and CYA, and cut-off values of 20 μg/kg for CBX and 40 μg/kg for CYA in chicken breast. Quantitative analysis could be performed using a hand-held strip scanner, with a calculated limit of detection of 2.92 μg/kg for CBX and 2.68 μg/kg for CYA in chicken breast. Validated by liquid chromatography-MS/MS, the developed GICA provides a useful tool for rapid on-site CBX and CYA residue screening in chicken breast.