An immunochromatographic strip sensor for marbofloxacin residues.

Marbofloxacin (MBF) was once widely used as a veterinary drug to control diseases in animals. MBF residues in animal food endanger human health. In the present study, an immunochromatographic strip assay (ICSA) utilizing a competitive principle was developed to rapidly detect MBF in beef samples. The 50% inhibitory concentration (IC50) and the limit of detection (LOD) of the ICSAs were 2.5 ng/mL and 0.5 ng/mL, respectively. The cross-reactivity (CR) of the MBF ICSAs to Ofloxacin (OFL), enrofloxacin (ENR), norfloxacin (NOR), and Ciprofloxacin (CIP) were 60.98%, 32.05%, 22.94%, and 23.58%, respectively. The CR for difloxacin (DIF) and sarafloxacin (SAR) was less than 0.1%. The recovery rates of MBF in spiked beef samples ranged from 82.0% to 90.4%. The intra-assay and interassay coefficients of variation (CVs) were below 10%. In addition, when the same authentic beef samples were detected in a side-by-side comparison between the ICSAs and HPLC‒MS, no statistically significant difference was observed. Therefore, the proposed ICSAs can be a useful tool for monitoring MBF residues in beef samples in a qualitative and quantitative manner.

Colloidal gold-based immunochromatographic strip assay for the rapid detection of diminazene in milk.

Diminazene (DIM) is widely used to treat trypanosomiasis in livestock, but its residues in animal products can cause food safety problems. Thus, a rapid colloidal gold-based immunochromatographic strip assay was established to analyse DIM residue in milk samples. A highly sensitive and specific monoclonal antibody (mAb) against DIM was produced with a new synthetic immunogen by the active ester method. The titre of the prepared antibody was up to 1:1.0 × 106, the affinity constant was 2.2 × 108 L mol-1 and the half-maximal inhibitory concentration (IC50) was 0.4 ng mL-1 based on enzyme-linked immunosorbent assay (ELISA). Then, the colloidal gold-labelled mAb probe was successfully prepared and used for preparing the immunochromatographic strip. The strip showed high sensitivity and specificity, the IC50 for DIM was 5.2 ng mL-1, the limit of detection was 1.2 ng mL-1 and the linear range of detection was 1.8-15.4 ng mL-1. The average recoveries ranged from 89.5% to 91.7%, and coefficients of variation were 6.6-7.2%. The immunochromatographic strip assay can be employed in the rapid detection of DIM residue in milk samples.

Colloidal gold-based immunochromatographic strip assay for the rapid detection of bacitracin zinc in milk.

In this study, a murine monoclonal antibody (mAb) of 6D2-G10 against bacitracin zinc (BAC) was produced and applied to an immunochromatographic strip (ICS) for the initial detection of BAC in milk. The ICS with a cut-off value of 25 ng/mL could be perceived by the naked eye within 10 min. With the assist of the strip reader, the limit of detection (LOD) was measured as 0.82 ng/mL, the half-maximal inhibitory concentration (IC50) was recorded as 3.16 ng/mL, and the linear detection range was from 0.97 to 10.30 ng/mL. The recoveries ranged from 87.7% to 96.0% with the highest coefficient of variation (CV) of 9.1% in the intra-assay and from 84.3% to 90.2% with the highest CV of 10.7% in the inter-assay. In short, the established ICS provided a serviceable analytical tool for qualitatively and quantitatively monitoring BAC in milk.

A highly sensitive monoclonal antibody-based paper sensor for simultaneously detecting valnemulin and tiamulin in porcine liver.

Valnemulin (VAL) and tiamulin (TIA) are pleuromutilin antibiotics used primarily for treating bacterial infections in swine or other food animals. Furthermore, VAL and TIA are also employed as feed additives to promote animal growth. However, the illegal use of VAL and TIA could cause a series of hazards to consumers. Here, VAL was designed to be conjugated with bovine serum protein to prepare immunogen. A highly sensitive monoclonal antibody that recognized both VAL and TIA has been successfully produced. Moreover, an immunochromatographic strip assay for rapidly screening VAL and TIA in porcine liver was established with visual detection limits (cutoff values) of 50 and 25 ng/g, respectively. The IC50 values calculated from the equation of the standard curve were 6.06 and 3.45 ng/g and the limits of detection were 0.96 and 0.29 ng/g for VAL and TIA. According to the recovery experiment results, the test strip exhibited acceptable accuracy and precision. Generally, the proposed strip provided a practical tool for the detection of VAL and TIA. PRACTICAL APPLICATION: We produced a highly sensitive monoclonal antibody and developed an immunoassay strip for simultaneously monitoring TIA and VAL. Additionally it was preliminarily confirmed that the rapid detection tool was suitable for screening TIA and VAL in porcine liver.

Gold Nanoparticle Aggregation-Induced Quantitative Photothermal Biosensing Using a Thermometer: A Simple and Universal Biosensing Platform.

A simple, low-cost, and universal gold nanoparticle (AuNP) aggregation-induced photothermal biosensing platform has been developed for the first time and applied for the visual quantitative genetic detection using a common thermometer. By exploiting the photothermal effect of target-induced gold nanoparticle aggregation, visual quantitative biochemical analysis can be achieved by simply recording temperature signals using a common thermometer. Compared to conventional genetic testing methods, it is label- and amplification-free and can be completed in 40 min without the aid of any advanced analytical instruments. Mycobacterium tuberculosis (MTB) DNA was used as a model target to demonstrate the application of this photothermal biosensing platform. Although no costly instrument was used, high sensitivity and specificity were achieved with the limit of detection (LOD) of 0.28 nM, which was nearly 10-fold lower than that of the colorimetric method using a spectrometer. This AuNP aggregation-induced photothermal biosensing strategy provides a simple, low-cost, and universal platform for broad application of visual quantitative detection of nucleic acids and many other biomolecules, particularly in point-of-care (POC) biosensing applications.

Multiphysics Modeling of Plasmonic Photothermal Heating Effects in Gold Nanoparticles and Nanoparticle Arrays.

Induced hyperthermia has been demonstrated as an effective oncological treatment due to the reduced heat tolerance of most malignant tissues; however, most techniques for heat generation within a target volume are insufficiently selective, inducing heating and unintended damage to surrounding healthy tissues. Plasmonic photothermal therapy (PPTT) utilizes light in the near-infrared (NIR) region to induce highly localized heating in gold nanoparticles, acting as exogenous chromophores, while minimizing heat generation in nearby tissues. However, optimization of treatment parameters requires extensive in vitro and in vivo studies for each new type of pathology and tissue targeted for treatment, a process that can be substantially reduced by implementing computational modeling. Herein, we describe the development of an innovative model based on the finite element method (FEM) that unites photothermal heating physics at the nanoscale with the micron scale to predict the heat generation of both single and arrays of gold nanoparticles. Plasmonic heating from laser illumination is computed for gold nanoparticles with three different morphologies: nanobipyramids, nanorods, and nanospheres. Model predictions based on laser illumination of nanorods at a visible wavelength (655 nm) are validated through experiments, which demonstrate a temperature increase of 5 °C in the viscinity of the nanorod array when illuminated by a 150 mW red laser. We also present a predictive model of the heating effect induced at 810 nm, wherein the heating efficiencies of the various morphologies sharing this excitation peak are compared. Our model shows that the nanorod is the most effective at heat generation in the isolated scenario, and arrays of 91 nm long nanorods reached hyperthermic levels (an increase of at least 5 °C) within a volume of over 20 µm3.

A rapid colloidal gold-based immunochromatographic strip assay for monitoring nitroxynil in milk.

BACKGROUND: Nitroxynil (NIT) is a veterinary drug against hepatic fluke disease for food-producing cattle and sheep. NIT has a long half-life time in animals since it is highly bound to plasma protein. Therefore NIT possibly remains in animal edible tissues or milk due to drug abuse. In this study, a specific murine monoclonal antibody (mAb) against NIT was prepared and an immunochromatographic strip assay based on the mAb was developed for screening NIT in milk. RESULTS: The affinity constant of the anti-NIT mAb was 2.93 × 1010 and the anti-NIT mAb had almost no cross-reactivity with other analogs, so that it showed good specificity. The cutoff value of this test strip was considered to be 50 ng mL-1 by the naked eye. When detected by the strip reader, the half maximum inhibition concentration (IC50 ) of the immunoassay strip was calculated to be 5.716 ng mL-1 and the limit of detection (LOD) was 1.146 ng mL-1 . Intra-assay recoveries from 88.80 to 97.13% were obtained, with the highest coefficient of variation (CV) at 9.01%; inter-assay recoveries ranged from 84.60 to 106.87%, with the highest CV at 9.93%. CONCLUSION: The operative procedure of the proposed method can be completed within 10 min. The strip developed in this study was a practical tool for rapid semiquantitative and quantitative detection of NIT in milk. This study suggested great potential for analytically monitoring NIT in other food samples. © 2019 Society of Chemical Industry.

Single Primer Based Multisite Strand Displacement Reaction Amplification Strategy for Rapid Detection of Terminal Deoxynucleotidyl Transferase Activity.

A fluorescence-based multisite strand displacement reaction (MSSDR) amplification strategy is developed for the rapid, sensitive, and selective detection the activity of terminal deoxynucleotidyl transferase (TdT). Oligo dT primer was used for the TdT extension reaction, then the left oligo dT primers were hybridized to the TdT extension reaction product by end to end tiled style and initiated the MSSDR by Klenow polymerase, subsequently, 3' terminals of these single-strand DNA produced by MSSDR are folded back to complement themselves with the adjacent sequences, and Klenow polymerase makes it into double-stranded DNA (dsDNA). The final dsDNA products were analyzed via dsDNA specific fluorescent dye. This method enables rapid (less than 100 min) and sensitive (limit of detection, LOD, 1.35 × 10-5 U) detection and has been demonstrated to work well using a real biosample. Our design would not only serve as a new prototype for high-throughput automated analysis and clinic diagnostic application but also has promising potential for improving the sensitivity of those TDT related biosensing system.

A cucurbit[8]uril sponge.

This paper describes a convenient approach to quantitative removal of the synthetic host cucurbit[8]uril (Q8) from aqueous mixtures using a sepharose resin coated in memantine groups to selectively sequester Q8 in the presence of competing hosts and guests. The "Q8 sponge" can separate Q8 from Q6 and reverse the Q8-mediated dimerization of peptides.

Nanomolar binding of peptides containing noncanonical amino acids by a synthetic receptor.

This paper describes the molecular recognition of phenylalanine derivatives and their peptides by the synthetic receptor cucurbit[7]uril (Q7). The 4-tert-butyl and 4-aminomethyl derivatives of phenylalanine (tBuPhe and AMPhe) were identified from a screen to have 20-30-fold higher affinity than phenylalanine for Q7. Placement of these residues at the N-terminus of model tripeptides (X-Gly-Gly), resulted in no change in affinity for tBuPhe-Gly-Gly, but a remarkable 500-fold increase in affinity for AMPhe-Gly-Gly, which bound to Q7 with an equilibrium dissociation constant (K(d)) value of 0.95 nM in neutral phosphate buffer. Structure-activity studies revealed that three functional groups work in a positively cooperative manner to achieve this extraordinary stability (1) the N-terminal ammonium group, (2) the side chain ammonium group, and (3) the peptide backbone. Addition of the aminomethyl group to Phe substantially improved the selectivity for peptide versus amino acid and for an N-terminal vs nonterminal position. Importantly, Q7 binds to N-terminal AMPhe several orders of magnitude more tightly than any of the canonical amino acid residues. The high affinity, single-site selectivity, and small modification in this system make it attractive for the development of minimal affinity tags.