Ratiometric fluorescence immunoassay based on FAM-DNA–functionalized CdSe/ZnS QDs for the sensitive detection of tetrabromobisphenol A in foodstuff and the environment

Rapid, on-site quantitative determination of mycotoxins in grains using a multiple time-resolved fluorescent microsphere immunochromatographic test strip

The label probe plays a crucial role in enhancing the sensitivity of lateral flow immunoassays. However, conventional fluorescent microspheres (FMs) have limitations due to their short fluorescence lifetime, susceptibility to background fluorescence interference, and inability to facilitate multi-component detection. In this study, carboxylate-modified Eu(III)-chelate-doped polystyrene nanobeads were employed as label probes to construct a multiple time-resolved fluorescent microsphere-based immunochromatographic test strip (TRFM-ICTS). This novel TRFM-ICTS facilitated rapid on-site quantitative detection of three mycotoxins in grains: Aflatoxin B1 (AFB1), Zearalenone (ZEN), and Deoxynivalenol (DON). The limit of detection (LOD) for AFB1, ZEN, and DON were found to be 0.03 ng/g, 0.11 ng/g, and 0.81 ng/g, respectively. Furthermore, the TRFM-ICTS demonstrated a wide detection range for AFB1 (0.05-8.1 ng/g), ZEN (0.125-25 ng/g), and DON (1.0-234 ng/g), while maintaining excellent selectivity. Notably, the test strip exhibited remarkable stability, retaining its detection capability even after storage at 4 °C for over one year. Importantly, the detection of these mycotoxins relied solely on simple manual operations, and with a portable reader, on-site detection could be accomplished within 20 min. This TRFM-ICTS presents a promising solution for sensitive on-site mycotoxin detection, suitable for practical application in various settings due to its sensitivity, accuracy, simplicity, and portability.

Ratiometric Fluorescence Immunoassay Based on MnO2 Nanoflakes for Sensitive and Accurate Detection of Tricaine

Tricaine is a common anesthetic used in the long-distance transport of live fish. Recently, its negative impact on human health has aroused extensive concern. Thus, rapid and reliable techniques for tricaine residue analysis are essential to ensuring the quality of aquatic products. Herein, a specific anti-tricaine monoclonal antibody (Mab) was prepared. Then, a sensitive and robust ratiometric fluorescence ELISA (RF-ELISA) was constructed for detecting tricaine based on two MnO₂ nanoflake-mediated (MnO₂ NFs) fluorogenic reactions. In the RF-ELISA protocol, MnO₂ NFs with oxidase-like activity can trigger the formation of fluorescent 2,3-diaminophenazine (oxOPD) with an emissive peak at 570 nm from non-fluorescent o-phenylenediamine (OPD), while ascorbic acid (AA) can decompose MnO₂ NFs to lose their oxidase-mimicking activity, which is accompanied by the oxidation of AA into dehydroascorbic acid (DHAA). The subsequent reaction between the generated DHAA and OPD will result in the production of 3-(1,2-dihydroxy ethyl)furo[3,4-b]quinoxalin-1(3H)-on (DFQ), which has a potent emission peak at 445 nm. By virtue of the alkaline phosphatase (ALP) labeled on the antibody, which can catalyze the production of AA from ascorbic acid 2-phosphate (AAP), the concentration of tricaine can be linked to the variation of the RF signal (F₄₄₅/F₅₇₀) via a competitive immunoreaction. After optimization, RF-ELISA displayed a detection limit (LOD) of 0.28 ng/mL toward tricaine (in buffer solution), which was 376-fold lower than that of the traditional colorimetric ELISA. For practical application, the LODs of RF-ELISA for tricaine detection in shrimp and tilapia samples were determined to be 2.8 and 5.6 ng/g, respectively. Recoveries for spiked shrimp and tilapia samples, as well as the validation data from LC-MS/MS, showed that RF-ELISA exhibited good accuracy, precision, and reliability. This RF-ELISA protocol opened up new ways for tricaine and other-target analyses in food safety detection.

A Review on Tetrabromobisphenol A: Human Biomonitoring, Toxicity, Detection and Treatment in the Environment

Tetrabromobisphenol A (TBBPA) is a known endocrine disruptor employed in a range of consumer products and has been predominantly found in different environments through industrial processes and in human samples. In this review, we aimed to summarize published scientific evidence on human biomonitoring, toxic effects and mode of action of TBBPA in humans. Interestingly, an overview of various pretreatment methods, emerging detection methods, and treatment methods was elucidated. Studies on exposure routes in humans, a combination of detection methods, adsorbent-based treatments and degradation of TBBPA are in the preliminary phase and have several limitations. Therefore, in-depth studies on these subjects should be considered to enhance the accurate body load of non-invasive matrix, external exposure levels, optimal design of combined detection techniques, and degrading technology of TBBPA. Overall, this review will improve the scientific comprehension of TBBPA in humans as well as the environment, and the breakthrough for treating waste products containing TBBPA.

Glutathione-Capped CdTe Quantum Dots Based Sensors for Detection of H2O2 and Enrofloxacin in Foods Samples

Additives and antibiotic abuse during food production and processing are among the key factors affecting food safety. The efficient and rapid detection of hazardous substances in food is of crucial relevance to ensure food safety. In this study, a water-soluble quantum dot with glutathione as a ligand was synthesized as a fluorescent probe by hydrothermal method to achieve the detection and analysis of H₂O₂. The detection limits were 0.61 μM in water and 68 μM in milk. Meanwhile, it was used as a fluorescent donor probe and manganese dioxide nanosheets were used as a fluorescent acceptor probe in combination with an immunoassay platform to achieve the rapid detection and analysis of enrofloxacin (ENR) in a variety of foods with detection limits of 0.05-0.25 ng/mL in foods. The proposed systems provided new ideas for the construction of fluorescence sensors with high sensitivity.

Development of a Highly Specific Fluoroimmunoassay for the Detection of Doxycycline Residues in Water Environmental and Animal Tissue Samples

Doxycycline (DOX) and its metabolite residues in food and the environment pose a serious threat to human health and the ecological environment. In this work, a novel method, termed competitive fluoroimmunoassays (cFIA), based on monoclonal antibody (mAb) bio-conjugated CdSe/ZnS core-shell quantum dots (QDs), was developed for sensitive and rapid bioanalyses of DOX in natural water and commercial meats. After the optimization of the experimental conditions, 1 μg mL^-1 of coating antigen and 0.5 μg mL^-1 of QD-labeled mAb were used for the establishment of the cFIA. With this assay, the 50% inhibition concentration was found to be 0.35 ng mL^-1 of DOX in phosphate-buffered saline samples, and the limit of detection was 0.039 ng mL^-1 with minor cross-reactivity to other tetracycline members. The recoveries from natural water and commercial meats spiked with DOX concentrations of 10-600 ng mL^-1 were 81.3-109.8%, and standard deviation were all below 12%. Levels measured with the QD-cFIA for thirty authentic samples were confirmed by high-performance liquid chromatography with good correlations. These results indicate that QD-cFIA is sultable for the rapid and quantitative detection of DOX residue in environmental and food samples.

Ratiometric fluorescence enzyme-linked immunosorbent assay based on carbon dots@SiO2@CdTe quantum dots with dual functionalities for alpha-fetoprotein

Molecular tags such as fluorophores are increasingly being replaced with nanoparticles thanks to their superior optical properties, substantial chemical stability, and stability against photobleaching. Herein, we innovatively constructed a new ratiometric fluorescence enzyme-linked immunosorbent assay (RF-ELISA) for the screening of alpha-fetoprotein (AFP) in early hepatocellular carcinoma in vitro diagnostics using carbon dots@SiO₂@CdTe quantum dots (CDs@SiO₂@CdTe QDs). Carbon dots with blue fluorescence were initially encapsulated into SiO₂ nanospheres through the typical Stöber method. Thereafter, CdTe QDs with red fluorescence were modified onto the surface of CDs@SiO₂ nanospheres. Dual-emission nanotags with blue and red fluorescent signals were utilized to design a RF-ELISA method for the determination of AFP on the anti-AFP capture antibody-coated microplate using glucose oxidase (GOx)-labeled anti-AFP secondary antibody. After the formation of the sandwiched immunocomplex, GOx catalyzed glucose to generate hydrogen peroxide (H₂O₂), which could quench the red fluorescence of CdTe QDs on the surface of nanotags. Meanwhile, the encapsulated carbon dots in the nanotags could still maintain the initial blue fluorescence intensity. The ratio between red fluorescence intensity and blue-emission intensity could be used for the quantitative monitoring of AFP concentration under optimum conditions. The experimental results indicated that CDs@SiO₂@CdTe QDs-based RF-ELISA could exhibit a good fluorescence signal with a dynamic linear range of 0.05-60 ng mL^-1 at a low detection limit of 8.7 pg mL^-1. Moreover, the fluorescence color of the solution including CDs@SiO₂@CdTe QDs changed from pink to purple to blue with the increasing AFP level when viewed by the naked eye. Good reproducibility, high specificity, and acceptable stability were achieved for the analysis of target AFP. Importantly, the accuracy of ratiometric fluorescence immunoassay was evaluated to determine human serum samples, giving well-matched results relative to commercially usable human AFP ELISA method.

Ratiometric fluorescence immunoassay based on MnO2–o-phenylenediamine–fluorescent carbon nanodots for the detection of α-fetoprotein via fluorescence resonance energy transfer

The ratiometric fluorescence immunoassay based on MnO2–o-phenylenediamine–fluorescent carbon nanodots is superior to the traditional single-wavelength-based method.

Detection of Mycobacterium Tuberculosis IS6110 gene fragment by fluorescent biosensor based on FRET between two-dimensional metal-organic framework and quantum dots-labeled DNA probe

Herein, a universal fluorescent biosensor was developed for detecting Mycobacterium Tuberculosis (MTB) specific insertion sequence IS6110 gene fragment based on Förster resonance energy transfer (FRET) strategy. CdTe quantum dots (QDs), with excellent luminous performance, were used to label single-stranded DNA (ssDNA) as fluorescence donor (QDs-DNA), in which the ssDNA was complementary to the IS6110 gene fragment. A new type of two-dimensional metal-organic framework (Cu-TCPP) was served as an acceptor. The Cu-TCPP exhibited a higher affinity towards ssDNA than double-stranded DNA (dsDNA). In the absence of targets, the fluorescence of QDs-DNA was quenched - due to the π-π stacking interactions between Cu-TCPP and ssDNA. Otherwise, QDs-DNA hybridized with the target to form a double helix and the fluorescence maintained in a target-concentration dependent manner. Excess QDs-DNA would be quenched and produced negligible background signal. The fluorescent sensor possessed a linear range from 0.05 nM to 1.0 nM with a low detection limit of 35 pM. Furthermore, we successfully applied this biosensing system to detect clinical sputum samples. This method displayed high sensitivity, specificity and great potentials in the early diagnosis of Tuberculosis.

Indirect competitive-structured electrochemical immunosensor for tetrabromobisphenol A sensing using CTAB-MnO2 nanosheet hybrid as a label for signal amplification

Tetrabromobisphenol A (TBBPA) is a kind of brominated flame retardant that is usually added to products to reduce their flame retardancy. However, its extensive use has resulted in their residues being found in the environment, which is very harmful. Herein, an indirect competitive immunosensor has been established for TBBPA detection based on the signal amplification system. Pd nanospheres in situ reduced on the surface of MnO₂ nanosheet hybrid (MnO₂/Pd) was used as the label for the secondary antibody through the Pd-N bond, and gold-toluidine blue composite was loaded onto MWCNTs (MWCNTs/Au-TB), which functioned as the platform for the immunosensor. The spherical structure of Pd had abundant catalytic active sites, which enhanced the catalytic activity of MnO₂/Pd as the label, hence amplifying the signal response. Besides, MWCNTs/Au-TB improved electron transfer and produced a strong signaling pathway for immobilizing antigens through the Au-NH₂ bond, which can specifically recognize primary antibodies to improve sensitivity. The immunosensor had a linear concentration range of 0-81 ng/mL, a low detection limit of 0.17 ng/mL (S/N = 3), with good stability, selectivity, and reproducibility based on the above advantages. Additionally, the acceptable accuracy and recoveries (recoveries, 92-124%; CV, 3.3-8.8%) in the real water sample analysis indicated that this strategy is promising for emerging pollutant analysis.