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A double signal enhanced surface plasmon resonance (SPR) biosensor system was developed, which involved graphene-based magnetic dispersion solid-phase extraction (MDSPE) and carboxylated graphene oxide (GO-COOH) materials as amplifying elements in order to achieve real-time determinations of estradiol (E2), diethylstilboestrol (DES), and bisphenol A (BPA) via an indirect competition method. In this work, the graphene-based MDSPE materials were synthesized using the chemical co-precipitation method, with a maximum enrichment efficiency of 500 times. To improve the detection sensitivity, the complete antigen (E2-BSA, DES-BSA, and BPA-BSA) was conjugated on the GO-COOH-modified gold chips for signal amplification. Furthermore, the GO-COOH materials could also significantly improve the performance and stability of the immobilized E2-BSA, DES-BSA, or BPA-BSA conjugations. Real-time SPR signals were obtained while mixing the targets (E2, DES, BPA) with anti-target monoclonal antibodies (E2-mAb, DES-mAb, BPA-mAb) at a 1:1 volume ratio. After optimizing the experimental conditions, the minimum detection limits (LOD) of E2, DES, and BPA were 3.605 × 10−6 ng/mL, 2.901 × 10−6 ng/mL, and 5.169 × 10−5 ng/mL, respectively. This simple, accurate, and stable method combined the advantages of two types of graphene materials to simplify the complicated pre-treatment and detection procedures. This study demonstrates a presumable and general method for detecting estrogen-like small molecules in the environment and in food.

Isothermal amplification, such as hybridization chain reaction (HCR), is a simple and reliable method for detecting signal amplification. However, the hairpin in HCR will not fully participate in the reaction. And after the hairpin is opened, the distance between the fluorophore and the quencher does not change much. Therefore, the signal magnification is limited. Here, we designed a new isothermal amplification method named hybridization assemble nicked displacement amplification (HANDA), combining HCR and strand displacement amplification (SDA) ingeniously. HANDA first triggers HCR through the target sequence to form long double-strand DNA (dsDNA) with gaps. Then SDA is performed from the gap to obtain a large amount of single-stranded DNA (ssDNA), so as to achieve the purpose of double signal amplification. The base sequence of DNA hairpin had also been optimized. The best sequence design rule was found and had universal applicability. We have demonstrated that HANDA combined with DNA barcodes can be used for trace detection of ricin. This new isothermal amplification method provides an effective and universal platform for the trace detection of various toxic substances.

Antibiotic compounds in natural waters are normally present at low concentrations. In this paper, an easy and highly sensitive screening method using graphene oxide–functionalized magnetic composites (GO@NH2@Fe3O4) combined with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was established for twelve quinolone antibiotics. GO@NH2@Fe3O4 composites were utilized as adsorbents for magnetic solid-phase extraction. This method combines the advantages of magnetic solid-phase extraction and MALDI-TOF MS, which allows for fast detection of quinolones at low concentrations. To improve absorption efficiency, the following parameters were individually optimized: sample acidity, extraction time, amount of adsorbent used, eluent used, and desorption time. Under the optimum conditions, the established method gave a low detection limit of 0.010 mg/L and allowed the high-throughput screening of twelve quinolone antibiotics (enoxacin, norfloxacin, ciprofloxacin, pefloxacin, fleroxacin, gatifloxacin, enrofloxacin, levofloxacin, sparfloxacin, danofloxacin, difloxacin, and lomefloxacin). The proposed method, having an easily prepared sorbent with a high affinity for quinolones and a convenient, high-throughput detection step, has been shown to have merit for the detection of antibiotics in water samples.

Surface siloxane (3-aminopropyl triethoxysilane hydrolyzates)-modified silica materials were used as "initiators", which resulted in the release and desorption of intact molecules adsorbed on the surface of a matrix. A covalently cross-linked MIL-53(Al) material was used to enhance the ionization of analytes. Herein, we have provided an efficient matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) matrix strategy, which responded to both ion and laser irradiation with low background interference in the low-molecular-weight (MW) region. The matrixes MIL-53(Al), SBA-15@APTES, SiO2@APTES, SBA-15@APTES@MOF, and SiO2@APTES@MOF were synthetized and used for the analysis of a series of low-MW compounds to verify the effectiveness of the strategies. Compared to conventional matrixes, the surface-modified SBA-15@APTES@MOF and SiO2@APTES@MOF had low background, high sensitivity, extensive applicability, good stability, and ultrahigh tolerance of salt concentrations. The detection limits of standard analytes were determined to range from 0.1 to 1 × 10-5 mg/mL for 16 amino acids as well as citric acid, reserpine, tetraethylammonium chloride, melamine, bisphenol A, and malachite green. These results could help in designing more efficient nanostructure-initiator materials and further promote the application of MALDI-TOF MS.

A rapid and ultrasensitive method for colourimetric/photothermal dual-readout detection was developed using an 808 nm NIR laser and a thermal imaging app on mobile phone. Norfloxacin was used as a model contaminant to demonstrate this universal rapid detection method. It is innovatively, to use the advanced two-dimensional material black phosphorus as a colourimetric/photothermal reagent for the first time. The samples were added to the strip, and the analytes were selectively captured on the conjugate pad by monoclonal antibody-modified magnetic/upconversion nanocomposites. The samples flowed through the strips by capillary action until reaching the control line, where immune complex formation occurred due to the presence of secondary antibody. The added black phosphorus could be captured by the the antigens which were directly exposed to the test line and a brown band could be observed by naked eye. Upon illumination by NIR light for 1 min, the real-time temperature is obtained for quantitative analysis through the thermal imaging performed by mobile phone camera. This method can achieve the detection of norfloxacin in water samples within 20 min, and the detection limits of colorimetric and photothermal readout can reach 45 pg mL-1. Compared with conventional strips, this method provided an increased sensitivity by about two orders of magnitude, with a integrated portable laser and a mobile phone. It is a valuable method for rapid detection and can be applied to other environmental contaminants as well.

A highly sensitive flow injection analysis (FIA)-based thermal enzyme-linked immunoassay, TELISA, was developed for the rapid detection of atrazine (ATZ) in tap water. ATZ and β-lactamase-labeled ATZ were employed in a competitive immunoassay using a monoclonal antibody (mAb). After the off-column liquid-phase competition, the mAb was captured on the Protein G Sepharose™ 4 Fast Flow (PGSFF) column support material. Injected β-lactamase substrate ampicillin was degraded by the column-bound ATZ-β-lactamase, generating a detectable heat signal. Several assay parameters were optimized, including substrate concentration, flow rates and regeneration conditions, as well as the mAb and ATZ-β dilution ratios and concentrations. The assay linear range was 0.73-4.83 ng mL(-1) with a detection limit of 0.66 ng mL(-1). An entire heat signal requires 10 min for generation, and the cycle time is less than 40 min. The results were reproducible and stable. ATZ-spiked tap water samples exhibited a recovery rate of 103%-116%, which correlated with the UHPLC-MS/MS measurements. We attributed this significant increase in sensitivity over our previously published work to the following factors: (i) the capture of already-formed immune complexes on the column via immobilized Protein G, which eliminated chemical immobilization of the antibody; (ii) off-column preincubation allows the formation of immune complexes under nearly ideal conditions; and (iii) multiple buffers can be used to, in one case, enhance immune-complex formation and in the other to maximize enzymatic activity. Furthermore, the scheme creates a universal assay platform in which sensing is performed in the off-column incubation and detection after capture in the enzyme thermistor (ET) detector, which opens up the possibility of detecting any antigen for which antibodies were available.

A simple and sensitive method was developed for preconcentration and determination of bisphenol A (BPA) in environmental samples by high performance liquid chromatography (HPLC). The hydrophilic silicon-dioxide- and nylon66-functionalised magnetic material (Fe3O4@SiO2@nylon66) was used as a sorbent for magnetic solid-phase extraction (MSPE). With the anhydrous microemulsion reaction, the Fe3O4@SiO2@nylon66 had shown great characteristics such as good magnetic responsivity, water dispersibility and stability. Based on the materials, various extraction parameters including pH, extraction time, elution time, the number of sorbents, sample volume and elution times were optimised. The whole extraction procedure could be accomplished within 20 min and the materials could be used more than 10 times after regeneration. Under the optimised conditions, different types of water samples (Tap water, river water, sea water and underground water) were successfully analysed to verify the applicability of the proposed method. The recoveries of different samples ranged from 88.54% to 104.46%. An enrichment factor of 250 was achieved with 0.05 μg/L detection limit. Thus, the developed MSPE is a potential technique that can be used for water samples preconcentration or combined with other analytical methods for determination of BPA.

A highly selective and sensitive method for Cd(II) detection was developed based on aptamer and gold nanoparticles (AuNPs) combined with a colorimetric smartphone readout. The experimental conditions such as reaction time of polydiene dimethyl ammonium chloride (PDDA) and AuNPs, PDDA dose, time of aptamer and PDDA incubation, and aptamer concentration were optimized. Under the optimized conditions, the color and red(R) value of the solution was concentration-dependent on Cd(II). The proposed method exhibited a linear range of 1&ndash, 400 ng/mL (r2 = 0.9794) with a limit of detection (LOD) of 1 ng/mL. This method had been successfully applied to test and quantify Cd(II) in water and rice samples, and the results were in full agreement with those from the atomic absorption spectrometer. Therefore, low-cost colorimetry demonstrated its potential for practical application in visual or quantitative detection with a smartphone. This approach can be readily applied to other analytes.

Matrix-assisted laser-desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) works inefficiently on small molecules because of the interference of matrix-related peaks in low m/z regions. A modified SBA-15 matrix, ([CHC−] [NH3+-Si-SBA-15-Si-NH3+] [CHC−]), was synthesized by covalently attaching SBA-15 to an ionic liquid formed by α-cyano-4-hydroxy cinnamic acid (CHCA) and 3-APTES. Compared with CHCA and ([SBA-15-Si-NH3+] [CHC−]), [CHC−] [NH3+-Si-SBA-15-Si-NH3+] [CHC−] demonstrated several advantages in melamine analysis, such as minimal background interference ions, high homogeneity, and improved sensitivity and reproducibility. Using the new matrix, we developed a high-throughput screening method for the detection of melamine in milk samples by MALDI-TOF MS. The influence of various parameters, such as solvent, concentration of the matrix suspension, the ratio between matrix and sample, deposition strategy, drying methods, and sample preparation method, were also investigated. Under optimized conditions for melamine determination in milk samples, a low detection limit (0.10 mg/kg) and high reproducibility (RSD ≤ 14%) were obtained.