Carbon dots and covalent organic frameworks based FRET immunosensor for sensitive detection of Escherichia coli O157:H7.

The combination of carbon dots (CDs) with covalent organic frameworks (COFs) was used to design an innovative sensor based on fluorescence resonance energy transfer (FRET) for the detection of Escherichia coli O157:H7 (E. coli O157:H7) in food samples. Carbon dots were used as fluorescence donors, covalent organic frameworks as fluorescence acceptors. The antibody (Ab) specific to E. coli O157:H7 was used to form a CD-Ab-COF immunosensor by linking CDs and COFs. The antibody was specifically bound with E. coli O157:H7, which caused the connection between CDs and COFs to be interrupted, and the carbon dots exhibited fluorescence restoration. The sensor exhibited a linear detection range spanning from 0 to 106 CFU/mL, with the limit of detection (LOD) of 7 CFU/mL. The analytical performance of the developed immunosensor was evaluated using spiked food samples with different concentrations of E. coli O157:H7, validating the capability of assessing risks in food testing.

A DNA tetrahedral scaffolds-based electrochemical biosensor for simultaneous detection of AFB1 and OTA.

Herein, a bifunctional electrochemical biosensor based on the DNA tetrahedral scaffolds (TDNs) was proposed, OTA@TDNs and AFB1@TDNs were adopted for electrochemical signal output in response to OTA and AFB1 concentration, simultaneously. In order to increase the conductivity of the biosensor, highly porous gold (HPG) was loaded on electrode surface by pulse electrodeposition. Under optimal conditions, the PFc displayed a linear range with AFB1 concentration between 0.05 âˆ¼ 360 ng·mL-1 with the LOD of 3.5 pg·mL-1. And the PMB selective and sensitive responses to OTA are achieved with a linear range of 0.05 âˆ¼ 420 ng·mL-1 and a LOD of 2.4 pg·mL-1. This biosensor has high sensitivity, selectivity and stability for OTA and AFB1 detection in peanut samples. The approach streamlines the experimental procedure, leading to significantly improve the detection efficiency of mycotoxins. Collectively, this method suggest a novel approach for the detection and monitoring of OTA and AFB1 in food sample.

A dual-modal biosensor coupling cooperative catalysis strategy for sensitive detection of AFB1 in agri-products.

Herein, the cooperative catalysis effect between nanocomposite (AgPd NPs/POD-M/PEI-rGO) and horseradish peroxidase (HRP) was applied for the fast and sensitive detection of aflatoxin B1 (AFB1). Upon specific and competitive binding of HRP@DNA and AFB1 to cDNA, the working electrode presented different catalytic capacities for supporting electrolytes (TMB and H2O2). In the redox mechanism of TMB and H2O2, HRP and nanocomposite effectively catalyzed the oxidization of TMB to form the one-electron oxidation intermediate TMB+, and contributed the electrical signals and absorbance signals. Electrochemistry and colorimetric analyses were successfully realized for AFB1 detection with 0.2 pg/mL and 8 pg/mL of detection limits, respectively, which is much lower than that of traditional HPLC methods. Overall, this method had significant reliability and sensitivity, offering a promising potential for conveniently evaluating the quality of agri-products polluted with AFB1. Moreover, this approach provides a new idea for fast and accurate detection of mycotoxin.

Modulating hydrophilic properties of ß-cyclodextrin/carboxymethyl cellulose colloid particles to stabilize Pickering emulsions for food 3D printing.

This research investigated edible Pickering emulsions stabilized by polysaccharide complexes as inks for food 3D printing. The interface membrane structure in the Pickering emulsion system was formed using complexes consisting of ß-cyclodextrin (ß-CD) and carboxymethyl cellulose (CMC). Except for provide sufficient steric barrier and electrostatic repulsion to increase the stability of the Pickering emulsions, the interface membrane constructs also can demonstrate good biphasic wettability and lower oil/water interfacial tension. The hydrophilicity of complexes (ß-CD/CMC) was mainly adjusted by the ratio of ß-CD/CMC (Rß/C) and the substitution degree (DS) of CMC, which further adjusted the physical and chemical properties of Pickering emulsion to make it correspond to the rheological behavior applied to 3D printing. The stable Pickering emulsion (Rß/C = 2:2, DS = 1.2, weight ratio of oil phase (φ) = 65 %) displayed excellent printing potential by characterizations analysis of Pickering emulsions. The smoothness, viscosity, and self-supporting ability of the Pickering emulsion under the optimized conditions were further analyzed using a filling density printing experiment of a cuboid model. The emulsifying properties of ß-CD were adjusted by hydrophilic CMC to achieve the required amphipathic properties of the complexes to develop Pickering emulsions for food 3D printing.

Ratiometric Sensing for Ultratrace Tetracycline Using Electrochemically Active Metal-Organic Frameworks as Response Signals.

A novel ratiometric sensor using an electrochemically active metal-organic framework of Mo@MOF-808 and NH2-UiO-66 as response signals was developed to detect tetracycline (TET) in ultratrace quantities. To achieve the dual-response strategy, Mo@MOF-808, with a reduction peak at -1.06 V, and NH2-UiO-66, with an oxidation peak at 0.724 V, were used as signal probes directly. Concretely, Mo@MOF-808, single-stranded DNA (ssDNA), and complex system (Apt@NH2-UiO-66) of aptamer (Apt) and NH2-UiO-66 were sequentially immobilized on the electrode. With the addition of TET, Apt was hybridized with TET and Apt@NH2-UiO-66 was detached from the electrode, resulting in an increase in the current at -1.06 V and a decrease in the current at 0.724 V. Through this strategy, the sensor achieved a wide linear range (0.1-10000 nM) and a low limit of detection (0.009792 nM) for TET. Moreover, the ratiometric sensor exhibited better sensitivity, reproducibility, and stability than a single-signal sensor. Furthermore, the constructed sensor was successfully applied to detect TET in milk samples, suggesting excellent application prospects.

An intrinsic dual-emitting fluorescence sensing toward tetracycline with self-calibration model based on luminescent lanthanide-functionalized metal-organic frameworks.

A novel ratiometric fluorescence sensor based on lanthanide-functionalized metal-organic frameworks (Ag+/Eu3+@UiO-66(COOH)2, AEUC) with intrinsic dual-emitting bands was fabricated to determine tetracycline (TC) residues by exploiting (UiO-66-(COOH)2, UC) as reference units, Eu3+as recognition units and Ag+ as fluorescence enhancer. Benefiting from specific binding sites and functional adsorbent channels of AEUC, efficient capture and specific recognize toward TC could be achieved, remarkably enhancing the reliability. The synergistic effect of inner filter effect (IFE) and photoinduced electron transfer (PET) process between TC and AEUC was verified, enabling the detection limit and quantification limit of established strategy reaching as 12.8 nmol/L and 38.6 nmol/L and conspicuous fluorescence color gradation from red to blue. Given its portability, point-of-care sensing platform and nanoprobe-immobilized test-paper-based measurement allowing for on-site qualitative identification and semi-quantitative assay of TC was devised for sensing visualization and has been successfully applied in foodstuff samples, providing prospect in the field of smart devices for visual monitoring of TC.

Dual modes of fluorescence sensing and smartphone readout for sensitive and visual detection of mercury ions in Porphyra.

A convenient and intuitive method for detecting trace heavy metal ions is vital for food safety and quality monitoring. Herein, a dual-emission ratiometric fluorescence probe based on Zr-based metal-organic frameworks (Zr-MOF) and silver nanoclusters (AgNCs) was assembled to sensitive and visual detect mercury ions (Hg2+). The sensor exhibits good sensitivity from 0.010 to 0.5 µg mL-1 with a low detection limit of 1.8 µg L-1 (corresponding to 0.72 µg kg-1 by weight). The proposed method was finally applied to determine Hg2+ in the Porphyra matrix with satisfactory outcomes, the analytical recoveries were in the range of 94.74%-101.1%, indicating the practicability of the developed method. Meanwhile, the smartphone-based colorimetric method was established by capturing the changes in fluorescence colors of the probes exposed to different Hg2+ concentrations, with a quick sample-to-answer monitoring time of 10 min. The fluorescence probe, with these merits of simplicity, rapid response, and high sensitivity, offered a promising means for evaluating the safety of food polluted with Hg2+.

Simple Design Concept for Dual-Channel Detection of Ochratoxin A Based on Bifunctional Metal-Organic Framework.

A simple fluorescence and electrochemical dual-channel biosensor based on bifunctional Zr(IV)-based metal-organic framework (Zr-MOF) was proposed to detect Ochratoxin A (OTA). The bifunctional Zr-MOF, with photoluminescence properties and enormous electroactive ligands, was exploited to load OTA-specific aptamers for designing signal probes, greatly simplifying the probe-fabrication process and improving sensing reliability. Upon specific recognition of aptamer toward OTA, the anchored probe was released from the sensing interface into the reaction solution. In this circumstance, the increased amount of the signal probe in reaction solution led to an enhanced fluorescence response, while the decreased amount of the signal probe on the sensing interface resulted in a diminished electrochemical response. According to the dual-channel signal change with increasing OTA concentration, the visual fluorescence strategy was established for intuitive OTA detection, and meanwhile, sensitive electrochemical assay with a detection limit of 0.024 pg/mL was also achieved with the help of one-step electrodeposition as a sensing platform. Moreover, the proposed dual-channel assay has been successfully applied to determine OTA levels in corn samples with rapid response, superior accuracy, and high anti-interference capability, providing a promising method for food safety monitoring.

A dual-signal fluorescent sensor based on MoS2 and CdTe quantum dots for tetracycline detection in milk.

A dual-signal fluorescent sensor was developed for tetracycline (TET) detection in milk with excellent reproducibility and stability. In this protocol, molybdenum disulfide quantum dots (MoS2 QDs) with blue fluorescence and cadmium telluride quantum dots (CdTe QDs) with yellow fluorescence were synthesized to establish the MoS2/CdTe-based sensor with two fluorescence emission peaks at 433 nm and 573 nm. With the addition of TET, the fluorescence of MoS2/CdTe were quenched by photoinduced electron transfer (PET), and the fluorescence of CdTe QDs were quenched more obvious than MoS2 QDs. With the strategy, a calibration curve was established between the TET concentration in the range of 0.1-1 µM and the ratio of fluorescence intensity at 573 nm and 433 nm (F573/F433). Furthermore, the dual-signal sensor was applied for TET detection in milk samples with the recovery of 95.53-104.22% and the relative standard deviation (RSD) less than 5%, indicating the strong application potential.

Fluorescence and colorimetric dual-mode sensor for visual detection of malathion in cabbage based on carbon quantum dots and gold nanoparticles.

A dual-mode fluorescence/colorimetric sensor based on carbon quantum dots (CQDs) and gold nanoparticles (GNPs) was developed for visual detection of malathion in cabbage. The CQDs-GNPs nanocomposite exhibited emission wavelength at 527 nm and absorption wavelength at 524 nm. The fluorescence intensity increased and absorption decreased with addition of malathion. Fluorescence and colorimetric calibration curves were established based on fluorescence intensity (R2 = 0.9914) and absorbance (R2 = 0.9608) in the range of 1 × 10-9-1 × 10-2 M, respectively. Furthermore, fluorescence and colorimetric standard arrays were prepared for visual detection of malathion according to the change of fluorescence brightness and color. Finally, the approximate concentrations of malathion in cabbage samples were estimated by the standard arrays and naked eyes. The calibration curves were used for accurate detection in cabbage samples with recoveries of 89.9%-103.4% (fluorescence) and 88.7%-107.6% (colorimetric). The established sensor for visual malathion detection in cabbage was accurate with strong application potential, especially for rapid screening.

Rapid and highly sensitive detection of Salmonella typhimurium in lettuce by using magnetic fluorescent nanoparticles.

The highly efficient detection of Salmonella typhimurium (S. typhimurium), a common foodborne bacterial, is important for the safety assurance of leafy vegetables. In this study, a fluorescent sensor (FMNCs-Apt), based on Fe3O4 magnetic nanoparticles and aptamer-modified carbon quantum dots, was developed for the rapid and highly sensitive detection of S. typhimurium in lettuce. First, carbon quantum dots were covalently bonded to the surface of prepared Fe3O4@chitosan to form magnetic fluorescence composite nanoparticles (FMNCs). Then, the aptamers of S. typhimurium were covalently linked to the surface (and named FMNCs-Apt). Fluorescence intensity of the FMNCs-Apt probes decreased as they aggregated on the surface of the bacteria, and the aggregation was separated using a magnet. Under the optimal conditions, the fluorescence change values of the solution showed a good linear relationship with the concentration of Salmonella (103-106 CFU mL-1). The detection limit of the method is 100 CFU mL-1 and 138 CFU mL-1 in fresh-cut vegetable washing solution and lettuce sample, respectively. Accordingly, this developed fluorescent probe became a highly sensitive and efficient sensor for the rapid detection of S. typhimurium in lettuce.