Changrui Xing

Rapid and Highly Sensitive Detection of Lead Ions in Drinking Water Based on a Strip Immunosensor

In this study, we have first developed a rapid and sensitive strip immunosensor based on two heterogeneously-sized gold nanoparticles (Au NPs) probes for the detection of trace lead ions in drinking water. The sensitivity was 4-fold higher than that of the conventional LFA under the optimized conditions. The visual limit of detection (LOD) of the amplified method for qualitative detection lead ions was 2 ng/mL and the LOD for semi-quantitative detection could go down to 0.19 ng/mL using a scanning reader. The method suffered from no interference from other metal ions and could be used to detect trace lead ions in drinking water without sample enrichment. The recovery of the test samples ranged from 96% to 103%. As the detection method could be accomplished within 15 min, this method could be used as a potential tool for preliminary monitoring of lead contamination in drinking water.

Ultrasensitive immunochromatographic assay for the simultaneous detection of five chemicals in drinking water.

In this paper, we describe the development of a multicomponent lateral-flow assay based on an antibody-antigen reaction for the rapid and simultaneous detection of trace contaminants in water, including a heavy metal, algal toxin, antibiotic, hormone, and pesticide. The representative analytes chosen for the study were lead (Pb(II), microcystin-leucine-arginine (MC-LR), chloramphenicol (CAP), testosterone (T), and chlorothalonil (CTN). Five different antigens were immobilized separately in five test lines on a nitrocellulose membrane. The monoclonal antibodies specifically recognized the corresponding antigens, and there was no cross-reactivity between the antibodies in the detection assay. Samples or standards containing the five analytes were preincubated with the freeze-dried colloidal-gold-labeled monoclonal antibody conjugates to improve the sensitivity of the assay. The results were obtained within 20min with a paper-based sensor. The cut-off values for the strip test were 4ng/mL for Pb(II), 1ng/mL for MC-LR, 0.1ng/mL for CAP, 5ng/mL for T, and 5ng/mL for CTN. The assay was evaluated using spiked water samples, and the accuracy and reproducibility of the results were good. In summary, this lateral-flow device provides an effective and rapid method for the onsite detection of multiple contaminants in water samples, with no treatment or devices required.

Development of an ELISA and Immunochromatographic Strip for Highly Sensitive Detection of Microcystin-LR

A monoclonal antibody for microcystin–leucine–arginine (MC-LR) was produced by cell fusion. The immunogen was synthesized in two steps. First, ovalbumin/ bovine serum albumin was conjugated with 6-acetylthiohexanoic acid using a carbodiimide EDC (1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride)/ NHS (N-hydroxysulfosuccinimide) reaction. After dialysis, the protein was reacted with MC-LR based on a free radical reaction under basic solution conditions. The protein conjugate was used for immunization based on low volume. The antibodies were identified by indirect competitive (ic)ELISA and were subjected to tap water and lake water analysis. The concentration causing 50% inhibition of binding of MC-LR (IC50) by the competitive indirect ELISA was 0.27 ng/mL. Cross-reactivity to the MC-RR, MC-YR and MC-WR was good. The tap water and lake water matrices had no effect on the detection limit. The analytical recovery of MC-LR in the water samples in the icELISA was 94%–110%. Based on this antibody, an immunochromatographic biosensor was developed with a cut-off value of 1 ng/mL, which could satisfy the requirement of the World Health Organization for MC-LR detection in drinking water. This biosensor could be therefore be used as a fast screening tool in the field detection of MC-LR.

Development of a monoclonal antibody-based immunochromatographic strip for cephalexin

An anti-cephalexin (CEX) monoclonal antibody was prepared by the immunogen of CEX-keyhole limpet hemocyanin connected by disuccinimidyl suberate, which was used for the establishment of a rapid immunochromatographic test strip. With this semi-quantitative detection method, a low limit of deduction of 10 ng mL−1 was obtained with the naked eyes and 1.3 ± 0.1 ng mL−1 by a strip reader in unprocessed milk within 5 min, which was much lower than the European Union Maximum Residue Limit of 100 µg kg−1 in milk. The recovery in the range of 87–120% was measured in another milk sample. In conclusion, this method with high sensitivity and satisfactory recovery shows significant potential for CEX residue detection in milk.

Paper supported immunosensor for detection of antibiotics.

Paper supports were used to develop a simple, inexpensive, fast and sensitive electrochemical immunosensor for the analysis of antibiotic residues in milk samples, where single-walled carbon nanotubes (SWNTs) and a simple dip-dry coating method were employed to prepare the highly sensitive biosensor. Well-dispersed SWNTs were impregnated with an antibody against neomycin to obtain a composite coating solution, followed by dipping the filtration paper in the solution to fabricate the sensitive biosensor which had high electrical conductivity. Based on the impedance change in the entire paper supported biosensor with increased concentrations of neomycin, the limit detection of the optimized method was 0.04 ng mL(-1) and a linear detection range from 0.2 to 125 ng mL(-1), well below the European Union regulations for neomycin in this matrix. This paper supported biosensor was applied to determine neomycin in milk samples after a simple sample treatment, with spiked recoveries which ranged from 93.25 to 110.47%. A variety of antibiotic residues in milk samples could be determined following similar sensor preparation.

A silver enhanced and sensitive strip sensor for Cadmium detection

In this study, an enhanced test strip, based on a monoclonal antibody for the cadmium-ethylenediaminetetraacetic acid (EDTA) complex, but not metal-free EDTA, has been developed. This colorimetric sensor was sensitive and specific for the detection of cadmium in aqueous samples containing excess EDTA. Through a process of silver enhancement, the visual detection limit for Cd(II) was 5 µg/L under optimised conditions and the limit of detection for semi-quantitative detection could be as low as 0.35 µg/L by using a scanning reader. The calibration curve showed that the colour intensity decreased as the Cd(II) concentration increased in the range of 0.5–5 µg/L. The other metal ions did not interfere with the determination of Cd(II). The recoveries of drinking water samples were from 98 to 108%. Consequently, the assay could be employed as a potential on-site screening tool for the detection of Cd(II) in water samples.

Colorimetric detection of mercury based on a strip sensor

Environmental pollution with mercury is a global problem. A fast and accurate detection method is urgently required as an alternative to instrument detection, whose cost is very high. Here we present a sensor for mercury (Hg(II)) detection which has promising analytical applications. The sample treatment process was integrated with the antibody–antigen reaction process. Adequate pre-treatment time before the test resulted in high sensitivity. The strip results showed an excellent linear relationship with the concentration of Hg(II) between 1 and 10 ng mL−1, and the detection limit was 0.23 ng mL−1. Other metals had a negligible effect on the detection of Hg(II). The accuracy of the method was evaluated by adding different concentrations of Hg(II) to tap water samples. The sample recoveries ranged from 103.2% to 108.7%. This immunoassay is simple and portable, which makes it very useful for rapid monitoring of Hg(II) contamination in field analysis.

Wash-free magnetic oligonucleotide probes-based NMR sensor for detecting the Hg ion

An easily applied and sensitive sensor for the detection of heavy metal ion residues based entirely on magnetic nanoparticle and oligonucleotide was developed. The tool is established on the relaxation of magnetic nanoparticles with different dispersion states. The target analyte, Hg ions, induce the aggregation of the MNP oligonucleotide probes. Accordingly, the light produced by the magnetic relaxation image and the transverse relaxation time (T(2)) all change due to the effect of the aggregation. The limit of qualitative detection of the sensor is 0.15 ppt. The recoveries from test samples range between 97.1-101.8%. Using the nuclear resonance instrument, the method is a high throughput and sensitive sensor.

Facile and rapid magnetic relaxation switch immunosensor for endocrine-disrupting chemicals

In order to develop facile, fast and sensitive detection methods for endocrine-disrupting chemicals (EDCs), we described a sensitive biosensing system involving magnetic relaxation switch, based on the assembly of cross-linked superparamagnetic iron oxide (CLIO) nanoparticles induced by the antigen-antibody biorecognition. The design of smart CLIO-based superparamagnetic iron oxide nanoparticles and antigen-OVA was described for the detection of bisphenol A [2,2-bis (4-hydroxyphenol) propane (BPA)]. The addition of BPA to the rapid magnetic relaxation switch immunosensor led to transverse relaxation time (T2) shortening compared to a blank control as shown by NMR relaxometry measurements. This process was also applied to the rapid and facile determination of concentrations of BPA in drinking water (tap water). Good linearity for all calibration curves was obtained, and the limit of detection (LOD) for BPA was 0.4 ng/mL in tap water.

Sensitive and highly specific detection of Cronobacter sakazakii based on monoclonal sandwich ELISA

A sensitive and specific monoclonal antibody-based sandwich enzyme-linked immunosorbent assay (ELISA) was established to detect the Cronobacter sakazakii. A pair of monoclonal antibodies (mAbs) selected from mAbs produced by 11 murine hybridomas was selected for the sandwich ELISA procedure. Targets of two mAbs were 100 kDa and 42 kDa protein extracted from the bacteria, respectively, which were proved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analysis. The limit of detection of this method was established as 1 × 104 cfu/mL, and the linear range from 1 × 105 to 1 × 108 cfu/mL. In the real sample test, 1 cfu/g C. sakazakii was detected in artificially contaminated powdered infant formula with 4 h enrichment.