Junjian Xiang

A novel fluorescence-quenching immunochromatographic sensor for detection of the heavy metal chromium

A novel fluorescence quenching immunochromatographic sensor (ICS) was developed for detecting chromium (Cr(3+)) within 15 min utilizing the fluorescence quenching function of gold nanoparticles (Au-NPs). The sensor performed with a positive readout. When the low concentrations of Cr(3+) samples were applied, detection signals of the test line (T line) were quenched, whereas when higher concentration Cr(3+) samples (1.56 ng/mL) were applied, the detection signal of the T line appeared. The detection signal intensity of the T line increased with increasing concentrations of Cr(3+). The low detection limit of developed fluorescence quenching ICS was 1.56 ng/mL. The fluorescence quenching ICS has a linear range of detection of Cr(3+) comprising between 6.25 ng/mL to 800 ng/mL. The recoveries of the fluorescence quenching ICS to detect Cr(3+) in tap water ranged from 94.7% to 101.7%. This result indicated that the developed sensor gave higher sensitivity and reliable reproducibility. It could provide a general detection method for small analyte in water samples.

A competitive indirect enzyme-linked immunoassay for lead ion measurement using mAbs against the lead-DTPA complex.

Immunoassays for quantitative measurement of environmental heavy metals offer several advantages over other traditional methods. To develop an immunoassay for lead, Balb/c mice were immunized with a lead-chelate-protein conjugate to allow maximum exposure of the metal to the immune system. Three stable hybridoma cell lines were obtained through spleen cells fusion with Sp2/0 cells. One cell line, 2A11D11, produced mAbs with preferential selectivity and sensitivity for Pb-DTPA than DTPA, exhibiting an affinity constant of 3.34 + or - 0.24 x 10(9) M(-1). Cross reactivity (CR) with other metals were below 1%, except for Fe(III) with a CR less than 5%. This quantitative indirect ELISA for the lead ion was used to detect environmental lead content in local water sources; importantly, the results from the immunoassay were in excellent agreement with those from ICP-MS. Development of immunoassays for metal ions may thus facilitate the detection and regulation of environmental pollution.

Colloidal gold probe-based immunochromatographic assay for the rapid detection of lead ions in water samples.

One-step immunochromatographic assay (ICA) has been developed using colloidal gold-labeled monoclonal antibody probe for the rapid detection of lead ions in water samples. The ICA was based on the theory of competitive reactivity, and the results can be easily judged based on the presence or absence of a red colored test line with visual detection. Under optimal conditions, this method shows high detecting sensitivity with a LOD (limit of detection) of 50 ng/ml. Stability test indicates that the immunochromatographic strips are stable for 8 weeks at room temperature. During practical application, nanometer TiO2 is used to enrich the lead ions in water samples. The ICA is successfully applied in the measurement of lead ion concentrations in local water samples, and the results are highly consistent with that of ICP-MS. Detecting lead ions with ICA can be done within 4 min and is very useful for the rapid onsite testing.

Development of a Lateral Flow Immunoassay (LFA) Strip for the Rapid Detection of 1-Aminohydantoin in Meat Samples

UNLABELLED Due to the potential toxic effects of the nitrofuran family of antibiotics, their use in animals in the food industry has raised health concerns. This study was aimed to develop a lateral flow assay (LFA) based on competitive format for the detection of 1-aminohydantoin (AHD) in meat samples. The assay could be completed in 1 min and detected AHDs derivates (CPAHD) at 3 ng/mL, equivalent to 1.40 ng/mL of AHD, which was much lower than that reported in the literature by similar method. The antibody showed no cross-reactivity with a panel of more than 10 nitrofuran analogs except for nitrofurantoin at a high concentration. The test strip was stable at room temperature for up to 8 wk or at 37 °C for 4 wk. Parallel analyses of meat samples with LFA and enzyme-linked immunosorbent assay (ELISA) obtained data in good agreement. This developed gold nanoparticle based LFA had a good specificity, sensitivity, stability, and reliability. It was potentially suitable for on-the-spot large-scale screening of meat samples, and even more other applications. PRACTICAL APPLICATION Nitrofurantoin is one of antibiotics of the nitrofuran family, which has been used not only to prevent and treat diseases, but also to promote growth in animals. However, concerning the carcinogenicity of the metabolite of nitrofurantoin (AHD), a new fast and convenient method for monitoring AHD should be established. We describe the development of a new test assay for rapid screening of meat samples.

Selection and characterization of a human neutralizing antibody to human fibroblast growth factor-2.

Compelling evidences suggest that fibroblast growth factor-2 (FGF-2) plays important roles in tumor growth, angiogenesis and metastasis. Molecules blocking the FGF-2 signaling have been proposed as anticancer agents. Through screening of a human scFv phage display library, we have isolated several human single-chain Fv fragments (scFvs) that bind to human FGF-2. After expression and purification in bacteria, one scFv, named 1A2, binds to FGF-2 with a high affinity and specificity, and completes with FGF-2 binding to its receptor. This 1A2 scFv was then cloned into the pIgG1 vector and expressed in 293T cells. The purified hIgG1-1A2 antibody showed a high binding affinity of 8x10(-9)M to rhFGF-2. In a set of vitro assays, it inhibited various biological activities of FGF-2 such as the proliferation, migration and tube formation of human umbilical vein endothelial cells. More importantly, hIgG1-1A2 antibody also efficiently blocked the growth while inducing apoptosis of glioma cells. For the first time, we generated a human anti-FGF-2 antibody with proven in vitro anti-tumor activity. It may therefore present a new therapeutic candidate for the treatment of cancers that are dependent on FGF-2 signaling for growth and survival.

A sensitive immunosorbent bio-barcode assay combining PCR with icELISA for detection of gonyautoxin 2/3.

In the current study, we developed a nanosphere bio-barcode technology to detect trace gonyautoxin 2/3 (GTX 2/3). GTX 2/3-glucose oxidase (GOX) conjugates were first prepared as the coating antigen in a periodate reaction. Subsequently, gold nanoparticles (NP) dual-labeled with anti-GTX 2/3 monoclonal antibodies (Mab) and DNA oligonucleotides were synthesized via a one-step preparation method. Combining PCR with indirect competitive ELISA (icELISA), a novel immunosorbent bio-barcode assay was established utilizing the Mab-NP-dsDNA complex to convert enzymatic signals to DNA signals. Importantly, the limit of detection of the method was lower than 0.74 microg mL(-1). Thus, the immunosorbent bio-barcode assay is a rapid and high-throughput screening tool to detect GTX 2/3 in aquatic products.