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Rapid and high-sensitive detection of mycotoxins is believed to be of vital importance in assuring food safety. In this study, we developed a novel fluorescence immunochromatographic sensor (ICS) for the mycotoxin of zearalenone (ZEN) in cereals. This was done by using a black phosphorus-Au nanocomposite (BP-Au) as the 2D quenching platform. Herein, gold nanoparticles (AuNPs) were directly reduced on the surface of BP nanosheets (BPNSs) to form BP-Au nanocomposites, showing higher fluorescence (quantum dots, λEm = 525 nm) quenching efficiency compared to the BPNSs and AuNPs. The fluorescence quenching efficiency of the prepared BP-Au nanocomposite reached 73.8%, which was 1.73-fold and 1.44-fold higher than AuNPs and BPNSs, respectively. The density functional theory was also successfully used to explore the formation mechanism of the BP-Au nanocomposite. By introducing the quantum dots/BP-Au signal/quencher pair, a high-sensitive fluorescence quenching ICS (B-FICS) was developed for the detection and discrimination of ZEN with the limit of detection of 0.1 μg/l in pure working buffer. This was 2.5-fold more sensitive than AuNPs-based FICS (A-FICS). The B-FICS was successfully applied in real cereals detection with the sample limit of detection of 2 μg/kg. The successful construction of B-FICS offers a novel method for a rapid and high-sensitive detection of ZEN in cereals. It also provides a new practical application of 2D BPNSs in food safety sensing. [ABSTRACT FROM AUTHOR]

This work demonstrates rapid sensing of kaempferol using active sensing material synthesized using the one-pot surface-imprinting synthesis method. This sensor consisted of molecularly imprinted polymer (MIP) consisting of mesoporous molecular sieves (SBA-15) loaded with carbon dots (CDs). Fourier transform infrared (FT-IR) spectroscopy confirmed successful incorporation of CDs onto the surface of imprinted mesoporous molecular sieves. Ordered hexagonal arrays of CDs@SBA-15@MIP mesopore structure were confirmed with transmission electron microscopy. Fluorescence intensity of CDs@SBA-15@MIP composites linearly correlated with kaempferol content in the 0.05–2 mg/L range. Detection limit was 14 μg/L. MIPs were used for efficient detection of kaempferol in fruit and vegetable samples with recovery values from 80% to 112%. The method has high sensitivity, low cost, good selectivity, and many application potentials useful for research and development of flavonoid monomer presence in food. [ABSTRACT FROM AUTHOR]

In this study, a novel fluorescent "turn-on" aptasensor was developed for sensitive and rapid detection of tetracycline (TC) in animal-derived food. It is based on aptamer-functionalized nitrogen-doped graphene quantum dots (N-GQDs-aptamer) coupled with cobalt oxyhydroxide (CoOOH) nanoflakes. The CoOOH nanoflakes are efficient fluorescence quenchers in homogeneous solutions, and this is due to their advantages of excellent optical properties, superior flexibility, and water dispersibility. The proposed method's mechanism is driven by quenching based on the fluorescence resonance energy transfer (FRET) between the donor (N-GQDs) and the acceptor (CoOOH nanoflakes). On the other hand, fluorescence recovery is caused by the structure switching behavior of the aptamer. Compared with previous methods, our developed method exhibits better behavior in terms of being easy to fabricate and being simple in detection procedure and maintains the detection limit low enough in TC determination: a linear range from 1 to 100 ng mL−1 and a detection limit of 0.95 ng mL−1 (S/N = 3). Furthermore, the proposed method was applied to five animal-derived food samples (milk, honey, fish, eggs, and chicken muscle) and demonstrated practical applicability. As well, the method has the advantages of simplicity in pre-treatment and convenience in instruments, saves times, and is cost-effective. Finally, the proposed method demonstrates significant potential for sensitive and rapid detection of specific components in real samples. [ABSTRACT FROM AUTHOR]

A colorimetric microplate assay for determination of Staphylococcus aureus DNA is described. Linear padlock probes were designed to recognize target sequences. After DNA binding, the linear padlock probes were circularized by ligation and then hybridize with biotin-labeled capture probes. Biotin-labeled capture probes act as primers to initiate the RCA. The biotin-labeled RCA products hybridize with digoxin-labeled signal probes fixed on streptavidin-functionalized wells of a 96-well plate. To enhance sensitivity, an AuNP-anti-digoxigenin-POx-HRP conjugate was added to the wells and then bound to digoxin-labeled signalling probes. The oxidation of tetramethylbenzidine (TMB) by H2O2 produces a color change from colorless to blue via HRP catalysis. After the reaction was terminated, absorbance is measured at 450 nm. For target sequences of Staphylococcus aureus, the detection limit is 1.2 pM. For genomic DNA, the detection limit is 7.4 pg.μL−1. The potential application of the method was verified by analyzing spiked food samples. [ABSTRACT FROM AUTHOR]

Folic acid (FA) is an essential vitamin in humans, and thus, rapid, accurate, and sensitive methods for its quantification in different biological samples are needed. This work describes a novel, simple, and effective dual-emission fluorescence nanoprobe for FA detection and quantification. The probe was covalently linked to amino-modified orange quantum dots (QDs) and carboxyl-modified blue graphene quantum dots (GQDs). The resulting material exhibited two emission peaks at 401 and 605 nm upon excitation at 310 nm. The probe had good selectivity and sensitivity toward FA with an exceptionally low detection limit (LOD = 0.09 nM). This probe was effectively used to quantify FA in animal serum samples. The method has potential utility for FA analysis in different types of biological samples. [ABSTRACT FROM AUTHOR]

• A dicyanoisophorone-based fluorescent probe was developed for sensing H 2 S with a large Stokes shift (155 nm). • The probe showed faster time response and high sensitivity for H 2 S. • The probe can be used to detect exdogenous and endogenous H 2 S in living HeLa cells. Due to the importance of hydrogen sulfide (H 2 S) in physiology and pathology, the development of fluorescence probes for the detection of H 2 S has attracted extensive attention of researchers. We developed a H 2 S fluorescence probe (DCN-S) based on dicyanoisopentanone using dithioether and ester groups as the reaction sites. Under the nucleophilic substitution of H 2 S, disulfide bond of DCN-S was broken. Then the probe changed into dicyanoisophorone derivative and emitted an orange fluorescence band from 530 nm to 700 nm (centred 580 nm). Upon response for H 2 S, DCN-S exhibited high sensitivity (88 nM detection limit) and large stokes shift (155 nm). Importantly, the probe also was successfully used for endogenous and exogenous imaging of living cells. [ABSTRACT FROM AUTHOR]

A fluorometric aptamer-based method is described for the determination of aflatoxin B1 (AFB1). The fluorescent dye thioflavin T (ThT) forms a complex with the aptamer against AFB1 (aptamer/ThT), and the fluorescence of the complex is strongly enhanced. On addition of AFB1, it will bind to the aptamer and release ThT. The fluorescence of free ThT is much weaker. The fluorescence of the system, best measured at excitation/emission wavelengths of 440/487 nm, drops gradually in the AFB1 concentration range from 0.2 to 200 ng·mL−1, exhibiting good linearity. The detection limits are 0.2 ng·mL−1 in buffer solution, and 1 ng·mL−1 when applied to plant-derived food. The recovery of AFB1 from spiked foodstuff ranges from 74.7% to 121%. The assay can be performed within 20 min. Graphical abstract Schematic presentation of label-free thioflavin T (ThT)-based fluorescence aptasensor using aflatoxin B1(AFB1) aptamer/ThT G-quadruplex complex and the AFB1 aptamer/AFB1 complex fluorescent signal system for the rapid and sensitive detection of AFB1 in soy sauce, spirits, rice, corn and peanuts. [ABSTRACT FROM AUTHOR]

In view of the importance of hydrogen sulfide (H 2 S) in the organism, a fast, noninvasive method for the detection of H 2 S in situ is needed. Fluorescent probes based on disulfide-bond nucleophilic substitution-addition can selectively detect H 2 S in vivo, which is very popular because it allows quick response for H 2 S, thus it will be a useful tool for monitoring H 2 S in the vivo. We developed a dicyanoisopentanone-based H 2 S fluorescent probe (EW-H) that used a disulfide group as a self-destructive linker reaction site. Under the nucleophilic substitution of H 2 S, the disulfide bond of EW-H was cleaved, and then nucleophilic addition took place intramolecularly to release the fluorophore (at 580 nm). The response to H 2 S, EW-H had high sensitivity (86 nM of the detection limit), large Stokes shift (155 nm) and a fast response time. More importantly, the probe was also applied for bioimaging in HepG2 cells, indicating its potential applications in biological organism. Unlabelled Image • Based on disulfide-bond nucleophilic substitution-addition probe for H 2 S was obtained. • The probe showed fast time response and high sensitivity for H 2 S. • The probe with large Stokes shift (155 nm) was used for bioimaging successfully. [ABSTRACT FROM AUTHOR]

• Nanobody-based sandwich ELISA (sELISA) was constructed for detecting β-LG with the LOD of 0.24 ng/mL. • sELISA achieved effectively discrimination of pasteurized milk and UHT milk. • sELISA achieved the assessment of milk or β-LG content in milk-containing and milk-free beverages. The problems of inaccurate detection values of thermal-processed β-lactoglobulin (β-LG) content seriously affect the screening of allergens. A monoclonal antibody (mAb) against β-LG was successfully prepared and a highly sensitive sandwich ELISA (sELISA) was constructed with specific nanobody (Nb) as the capture antibody with detection limit of 0.24 ng/mL. Based on this sELISA, the ability of Nb and mAb to recognize β-LG and β-LG interacting with milk components was explored. Combined with protein structure analysis to elaborate the mechanism of shielding β-LG antigen epitopes during thermal-processing, thus enabling the differentiation between pasteurized and ultra-high temperature sterilized milk, the detection of milk content in milk-containing beverages, and the highly sensitive detection and analysis of β-LG allergens in dairy-free products. The method provides methodological support for identifying the quality of dairy products and reducing the risk of β-LG contamination in dairy-free products. [ABSTRACT FROM AUTHOR]

[Display omitted] • AuNPs and PANI were modified to the electrode by electropolymerization. • The AuNPs acted as luminophore and also made antibodies immobilizing. • PANI with porous structure synergically amplify AuNPs luminophore signal. • The fabricated ECL sensor exhibited good selectivity and sensitivity towards 3-NT. As an appropriate biomarker for oxidative stress, 3-nitrotyrosine (3-NT) in biological samples is associated with many neurodegenerative disorders and inflammatory diseases. Herein, a novel and rapid electrochemiluminescence (ECL) immunosensor was successfully fabricated for ultrasensitive detection of 3-NT. Electrodeposited gold nanoparticles (AuNPs) being used as the luminophore and polyaniline being electropolymerized to promote the luminescence of AuNPs, a stable and efficient ECL system was obtained with an ECL intensity 28 times higher than that of bare electrodes. Taking advantage of the good biocompatibility and large specific surface area of AuNPs, the antibody was effectively immobilized on the electrode, achieving high selectivity for 3-NT detection. Under the optimal conditions, the immunosensor exhibited good analytical performance for 3-NT with a wide linear detection in the range of 1 × 10−11–1 × 10−8 mol/L and a low detection limit of 2.57 × 10−12 mol/L. Furthermore, the established sensor had a high recovery rate (85.29%–103.94%) in practical sample applications. The sensor had simple preparation method, high sensitivity and good stability, providing a promising sensing platform for the detection of 3-NT. [ABSTRACT FROM AUTHOR]

[Display omitted] • A label-free Immune-co-Chemical ECL-sensor based on poly(DVB-Co-PBA) and high luminous-efficiency Ti,Mg@N-CDs was developed. • The Ti,Mg@N-CDs-based ECL-reagent enhanced biosensor signal and provide binding sites of antibody for capturing target. • The dual-recognition Immune-co-Chemical ternary-system exhibits good selectivity and sensitivity towards AFP. • By changing AFP recognition unit, this method can be extended to determination of other disease biomarkers. In this paper, a high-efficiency electrochemiluminescence (ECL) ternary immune-system was firstly constructed for ultrasensitive assay of alpha-fetoprotein (AFP) based on the Ti, N/Mg co-doped carbon dots (Ti,Mg@N-CDs) as brand-new nanocomposite emitter, Poly(DVB-Co-PBA) as novel AFP-signal reporter and coreaction accelerator. A fluorescent microspheres Poly(DVB-Co-PBA), synthesizing based on 4-vinylphenylboronic acid (4-MPBA) and divinylbenzene (DVB), was used as a signal indicator-probe via the specific carbohydrate-AFP interaction to fabricate a dual-recognition label-free immune-co-chemical biosensor. The as-prepared Ti,Mg@N-CDs exhibited high ECL emission of 3.7-folds compared with CDs. Moreover, the large surface area, promising biocompatibility and nitrogen-rich functional group bearing on the nanohybrid was helpful for the antibody adsorption immobilization of Anti AFP /Ti,Mg@N-CDs/GCE. The successful synthesis and enhancement mechanism of the nanomaterials were also characterized through a serious of techniques including HR-TEM, SEM, EDS, FT-IR, UV–vis, PL and CV. With an immune-co-chemical ECL-assay format, target and signal reporter-probe (Poly(DVB-Co-PBA)) were introduced in sequence via specific reaction. Based on multiple signal amplification and dual recognition strategy, a largely linear detection ranges from 2.25 × 10−6 to 2250 ng mL-1 with a low detection limit (1.55 × 10-7 ng mL-1) were obtained via the resultant ECL ternary (Poly(DVB-Co-PBA)-AFP/Anti AFP /Ti,Mg@N-CDs/GCE) system. This proposed new method was applied to detect human serum samples with satisfactory results and acceptable recovery (96.04 % ∼ 111.22 %), indicating a potential application in clinical monitoring of disease biomarkers. [ABSTRACT FROM AUTHOR]