Multiplex Aptamer-Based Fluorescence Assay Using Magnetism-Encoded Nanoparticles for Simultaneous Detection of Multiple Pathogenic Bacteria.

Multiplex assay has emerged as a robust and versatile method for the simultaneous detection of multiple analytes in a single test. However, challenges in terms of poor accuracy and complexity remained. In this work, we developed a multiplex aptamer-based fluorescence assay using magnetism-encoded nanoparticles for the simultaneous detection of multiple pathogenic bacteria. The encapsulation of different amounts of Fe3O4 nanoparticles in zeolitic imidazolate framework-90 (ZIF-90) leads to the formation of Fe3O4@ZIF-90 (FZ) composites with distinct magnetism strengths. By functionalizing a specific aptamer on the surface of the FZ composites, target bacteria can be specifically and precisely separated from a mixed sample in a sequential manner. This property allows for the simultaneous quantitative analysis of multiple target bacteria by using a single-color fluorescence label, thereby resulting in minimal spectral crosstalk interference and improved accuracy. The successful determination of multiple bacteria in contaminated milk samples demonstrates the applicability of this multiplex assay in complex biological matrices. Compared to conventional multiplex fluorescence assays, this approach offers distinct advantages of simplicity, efficiency, and implementation. We believe that this study can provide valuable insights into the development of the multiplex assay while introducing a new method for the simultaneous detection of multiple bacteria.

A hybrid composed of MoS2, reduced graphene oxide and gold nanoparticles for voltammetric determination of hydroquinone, catechol, and resorcinol.

A ternary hybrid composed of molybdenum disulfide (MoS2), reduced graphene oxide (rGO) and gold nanoparticles (AuNPs@MoS2-rGO) was prepared and used for voltammetric detection of hydroquinone (HQ), catechol (CC) or resorcinol (RC). The composition and structure of the hybrid were characterized in detail. The electrochemical behaviors of a glassy carbon electrode (GCE) modified with the hybrid towards the oxidation of HQ, CC, and RC were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results revealed 3D MoS2 is active for the catalytic oxidation of these isomers. Additional integration with rGO and AuNPs further improves catalysis due to their synergistic interaction. The enhanced catalysis leads to oxidation of HQ, CC and RC at 0.074 V, 0.178 V, and 0.527 V (vs. Ag/AgCl; by CV) with reduced overpotential (20-100 mV) and 8-fold or 3-fold increased peak current compared to those obtained on MoS2/GCE, or MoS2-rGO/GCE, respectively. Selective detection of one isomer in the presence of the other two was realized by DPV. The linear ranges are 0.1-950 µM, 3-560 µM, and 40-960 µM for HQ, CC, and RC, and the detection limits are 0.04 µM, 0.95 µM, and 14.6 µM, respectively. The sensor also shows good selectivity and displays satisfactory recovery for real sample analysis. Graphical abstract Schematic illustration of the preparation of AuNPs@MoS2-rGO hybrid by hydrothermal growth of MoS2-rGO and subsequent electrodeposition of gold nanoparticles (AuNPs), and its application for selective detection of hydroquinone, catechol and resorcinol by voltammetry.

Time-resolved fluorescence immunoassay based on glucose oxidase-encapsulated metal-organic framework for amplified detection of foodborne pathogen.

BACKGROUND: Fluorescence immunoassays are commonly employed for the detection of pathogenic bacteria as a means of ensuring food safety and preserving public health. However, the challenges such as poor photostability and background interference have limited their sensitivity and accuracy. The emergence of metal-organic frameworks (MOFs) as a label probe offers a promising solution for advancing fluorescence immunoassays owing to their tunable nature. Nonetheless, the low fluorescence efficiency of MOFs and the potential risk of dye leakage pose obstacles to achieving high detection sensitivity. Therefore, there exists a pressing need to fully utilize the potential of MOF composites in fluorescence immunoassays. RESULTS: We explored the potential of glucose oxidase-encapsulated zeolitic imidazole framework-90 (GOx@ZIF-90) as a label probe to construct a time-resolved fluorescence immunoassay with amplified detection signal. This immunoassay involved functionalizing Fe3O4 nanoparticle with porcine antibody to specifically capture and separate the target bacteria, Staphylococcus aureus (S. aureus). The captured S. aureus was then bound by GOx@ZIF-90 modified with vancomycin, resulting in a fluorescence response in the europium tetracycline (EuTc). The encapsulation of GOx in ZIF-90 provided a confinement effect that significantly enhanced the catalytic activity and stability of GOx. This led to a highly efficient conversion of glucose to H2O2, amplifying the fluorescence signal of EuTc. The immunoassay demonstrated a high sensitivity in detecting S. aureus, with a detection limit of 2 CFU/mL. We also obtained satisfactory results in milk samples. Attractively, the time-resolved detection mode of EuTc allowed the immunoassay to eliminate background fluorescence and enhance accuracy. SIGNIFICANCE: This study not only presented a new method for detecting foodborne pathogens but also highlighted the potential of enzyme-encapsulated MOF composites as label probes in immunoassays, providing valuable insights for the design and fabrication of MOF composites for various applications.

pH Meter-Assisted Biosensor Based on Glucose Oxidase-Conjugated Magnetic Metal-Organic Framework for On-Site Evaluation of Bacterial Contamination.

There remains a critical need for the detection of bacterial contamination to ensure public health. In this work, we developed a pH meter-assisted biosensor based on glucose oxidase (GOx)-conjugated magnetic zeolitic imidazolate framework-8 (mZIF-8) for on-site evaluation of bacterial contamination. The mZIF-8/GOx conjugate was produced from the electrostatic interaction between GOx and mZIF-8 and was demonstrated to inhibit GOx activity without protein denaturation. However, the presence of bacteria can cause the release of GOx from the mZIF-8 surface through competitive binding with mZIF-8, resulting in the recovery of GOx activity, which converts glucose into gluconic acid and provides an amplified pH signal. This finding allows the mZIF-8/GOx conjugate to be a biosensor for on-site detection of bacterial contamination with a pH meter as a readout. Benefiting from the magnetic separation property of mZIF-8, greatly enhanced sensitivity and precision have been achieved with detection limits of 10 cfu/mL for Escherichia coli and 30 cfu/mL for Staphylococcus aureus. Meanwhile, the flexibility of this biosensor was validated by quantitative analysis of mixed bacteria including Gram-positive and Gram-negative bacteria with desired performances. The accurate bacterial determination in contaminated drinking water samples demonstrates the applicability of this biosensor for reliable home monitoring of water quality.

Layered filter paper-silver nanoparticle-ZIF-8 composite for efficient multi-mode enrichment and sensitive SERS detection of thiram.

A SERS substrate FP/Ag/ZIF-8 composed of filter paper (FP), silver nanoparticles (AgNPs) and zeolitic imidazolate framework (ZIF-8) film arranged in a layered structure was developed for sensitive detection of pesticide thiram in various samples. Roles of these components in analyte adsorption and Raman signal enhancement were studied using a pesticide intermediate 4-Aminothiophenol (4-ATP) as the probe. The substrate showed high adsorption and optimized SERS response with thick metal organic framework (MOF) coating (125 nm), which is different from previous reported plasmonic particle-MOF composite substrate, where thinnest MOF coating produced the strongest SERS signal. Detection limit for 4-ATP improved 1000-fold on FP/Ag/ZIF-8 (3 pM) compared with that on FP/Ag (3 nM). Importantly, the FP/Ag/ZIF-8 with porous and flexible property can efficiently capture pesticide thiram in different real samples using soaking, filtration or swabbing operation. The subsequent SERS detection of thiram showed advantages of low detection limit (soaking, LOD: 0.04 nM in lake water), fast detection (filtration, within 1 min in peach juice) and suitable for curve surface analysis (swabbing, LOD: 0.1 ng/cm2 on apple peel), respectively. The substrate also displayed good reproducibility, high stability and size-selective response for thiram detection. Such a layered plasmonic particle/MOF hybrid may hold great promise for toxicant analysis in environment and food.

Biosensor Based on Covalent Organic Framework Immobilized Acetylcholinesterase for Ratiometric Detection of Carbaryl.

A ratiometric electrochemical biosensor based on a covalent organic framework (COFThi-TFPB) loaded with acetylcholinesterase (AChE) was developed. First, an electroactive COFThi-TFPB with a two-dimensional sheet structure, positive charge and a pair of inert redox peaks was synthesized via a dehydration condensation reaction between positively charged thionine (Thi) and 1,3,5-triformylphenylbenzene (TFPB). The immobilization of AChE on the positively charged electrode surface was beneficial for maintaining its bioactivity and achieving the best catalytic effect; therefore, the positively charged COFThi-TFPB was an appropriate support material for AChE. Furthermore, the COFThi-TFPB provided a stable internal reference signal for the constructed AChE inhibition-based electrochemical biosensor to eliminate various effects which were unrelated to the detection of carbaryl. The sensor had a linear range of 2.2-60 µM with a detection limit of 0.22 µM, and exhibited satisfactory reproducibility, stability and anti-interference ability for the detection of carbaryl. This work offers a possibility for the application of COF-based materials in the detection of low-level pesticide residues.

Multifunctional magnetic sphere-MoS2@Au hybrid for surface-enhanced Raman scattering detection and visible light photo-Fenton degradation of aromatic dyes.

A ternary hybrid, MNPs-MoS2@Au, composed of gold nanoparticles (AuNPs) grown on a magnetic sphere (MNPs)-MoS2 microflower composite (MNPs-MoS2) was proposed for surface-enhanced Raman scattering (SERS) detection and visible-light photo-Fenton degradation of aromatic dyes. The hybrid was prepared by sequential solvothermal growth of MNPs and MoS2, and electroless deposition of AuNPs. A comparison of results revealed that the synergy among these components endowed the hybrid with a much higher SERS enhancement ability than MNPs, or MNPs@MoS2. The dosage of HAuCl4 and MNPs-MoS2 to prepare the hybrid greatly influenced the SERS activity of the hybrid. Under optimized conditions, quantitative SERS analysis of dyes including CV, MG, and MB was performed with a low detection limit (1 pM, 0.15 nM and 1 nM for CV, MG, and MB, respectively) and adequate reproducibility (RSDs were less than 6% and 11% for CV and MG, respectively). The hybrid could also serve as a visible light-active photo-Fenton catalyst for efficient degradation of aromatic dyes, and the decolorization of 20 mg/L RhB was 90% in 40 min in the presence of H2O2 because of a synergy mechanism among components confirmed by comparison experiment and first-order kinetics study. The multifunctional material prepared here possesses great values in SERS analysis, environmental monitoring, and restoration.