Xuejia Zhan

A mini-review on functional nucleic acids-based heavy metal ion detection.

Recent years have witnessed great progress in developing functional nucleic acids (FNAs)-based sensors for the detection of heavy metal ion. In this review, four types of the FNAs that most widely-used in heavy metal ions detection were briefly introduced and a dozen of recently published review articles which summarized those FNAs-based sensors were introduced. Particularly, according to the degree of automation and system integration, those FNAs-based sensors which belong to the lab-on-a-chip (LOC) category were reviewed in more detail by classifying them into six types such as microfluidic LOC system, microchip, lateral flow dipstick, personal glucose meter, microfluidic paper-based analytical devices (μPADs) and disc-based analytical platform. After gave a brief description of the sensing strategies, properties, advantages or disadvantages of these FNAs-based sensors, existing problems and future perspectives were also discussed.

A simple fluorescent assay for lead(II) detection based on lead(II)-stabilized G-quadruplex formation

A fluorescence quenching result was obtained when an FAM-labelled G-rich oligonucleotide T30695 was treated with Pb2+, owing to the formation of a lead(II)-stabilized G-quadruplex. Based on this phenomenon a selective fluorescent assay for lead(II) detection with a limit of detection of 0.77 ppb and a detection range from 0 to 200 ppb was constructed.

A silver-specific DNA-based bio-assay for Ag(I) detection via the aggregation of unmodified gold nanoparticles in aqueous solution coupled with resonance Rayleigh scattering

We report a label-free, silver-specific DNA-based bio-assay for the detection of silver ion (Ag+) in aqueous solution. The bio-assay relies on the structural change of cytosine (C)-rich silver-specific DNA and the status transition of gold nanoparticles (AuNPs). In the absence of Ag+, unfolded silver-specific DNA stabilizes the dispersed AuNPs at high salt concentrations, which induces low resonance Rayleigh scattering (RRS) intensity. However, in the presence of Ag+, silver-specific DNA folds into a hairpin conformation through C–Ag+–C mismatches, and cannot coat on the surface of AuNPs. Thus, the uncoated AuNPs aggregate at high salt concentrations and cause a significant increase in RRS intensity, which reflects the amount of Ag+ in the system. Under the optimized conditions, the RRS intensity at 550 nm increased linearly with the concentration of Ag+ ranging from 0.20 μM to 1.00 μM, and the limit of detection for Ag+ was determined as 0.202 μM. The bio-assay also shows high selectivity against coexisting cations.

Fluorescent detection of Hg2+ and Pb2+ using GeneFinder™ and an integrated functional nucleic acid.

This paper reports a simple fluorescent assay for the determination of Hg(2+) and Pb(2+) by using a DNA intercalator GeneFinder™ (GF) and an integrated functional nucleic acid (FNA). In the absence of Hg(2+) and Pb(2+), GF intercalated with the FNA and released moderate strong fluorescence. While in the presence of Hg(2+) or Pb(2+), the FNA would be induced to form T-Hg(2+)-T or G-quadruplex structure, interacted with which the GF would exhibit extremely strong or very weak fluorescence. By monitoring the fluorescence changes upon addition of these two ions, the Hg(2+) and Pb(2+) could be selectively detected as low as 3.23 ppb and 2.62 ppb. As the main advantage of this assay is simplicity and the feasibility was demonstrated by detecting Hg(2+) and Pb(2+) in spiked water samples, this assay holds great potential for the development of a cost effective and useful tool for environmental monitoring.

Sensitive fluorescent assay for copper (II) determination in aqueous solution using copper-specific ssDNA and Sybr Green I.

This paper reports a fluorescent turn-off assay for sensitive detection of Cu(2+) in an aqueous solution by using a copper-specific ssDNA Cu100 and Sybr Green I. By monitoring the fluorescence changes arose from different interactions of Sybr Green I with Cu100 and Cu100/Cu(2+) complex, the Cu(2+) could be linearly detected from 5.57 to 250 ppb, with a detection limit of 5.57 ppb. The feasibility of this assay was demonstrated by detecting Cu(2+) in certified reference materials and spiked water samples with satisfactory results.

Indirect Competitive Immunoassay for Mercury Ion Determination Using Polyclonal Antibody Against the Hg-GSH Complex

Hg is a highly toxic heavy metal in the environment. Detection and quantification of Hg plays an important role in the study of environmental contamination with this metal. A polyclonal antibody that recognizes Hg-ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA) was produced by immunizing the New Zealand white rabbit with Hg conjugated to bovine serum albumin (BSA) via a bifunctional chelator, glutathione (GSH), and the resulting antiserum was screened through indirect noncompetitive enzyme-linked immunosorbent assay (ELISA) using GSH-ovalbumin (OVA) and Hg-GSH-OVA. The polyclonal antibody displayed high levels for the relative Hg-GSH-OVA conjugate. The concentration of Hg2+was quantified based on the ability of its EDTA complexes to inhibit the binding of the goat anti-rabbit IgG conjugated with horseradish peroxidase and, subsequently, color formation in the assay. The indirect competitive ELISA was specific to Hg2+, with the lowest detection limit reaching 9.55 ng/mL. Cross-reactivities with other metals were less than 0.001% except for Cd2+, which showed a slight cross-reactivity in indirect competitive ELISA. The recoveries from deionized water were in the range of 90% to 102%. Results indicated that the ELISA based on polyclonal antibody could be a very promising analytical tool for rapid (3 to 5 hr) and sensitive determination of Hg and other metal ions in the environment. Additionally, the indirect competitive ELISA can potentially be applied in environmental forensics studies, as a sensitive and inexpensive monitoring method for environments polluted with Hg and possibly other metal ions.

A label-free fluorescent sensor for the detection of Pb2+ and Hg2+

A label-free fluorescent DNA-based sensor for the detection of Pb2+ and Hg2+ has been reported in this paper. A single-stranded DNA named modified T30695 was used as a recognition probe and SYBR Green I (SG) was used as a signal reporter. This sensor consisted of two interaction sections: Pb2+ interacts with modified T30695 to form a G-quadruplex and Hg2+ interacts with modified T30695 to form a T–Hg(II)–T hairpin conformation. Circular dichroism confirmed the interactions between modified T30695 and Pb2+ or Hg2+. Based on this, a sensor for the detection of Pb2+ and Hg2+ with limits of detection of 2.09 ppb and 1.14 ppb was constructed.

Preparation of a polyclonal antibody against the cadmium–DTPA complex and its application for determination of cadmium

Cadmium (Cd) is considered one of the most hazardous heavy metals. Therefore, it is important to detect Cd. A polyclonal antibody that recognizes Cd–ethylenediamine-N,N,N′,N′-tetraacetic acid complex was prepared via the injection of BALB/c mice with Cd–2-(4-aminobenzyl)-diethylene triamine pentaacetic acid–keyhole limpet hemocyanin. A simple, inexpensive, and reliable indirect competitive enzyme-linked immunosorbent assay (ELISA) based on the polyclonal antibody was developed for determination of Cd. The assay was specific to Cd with an IC50 value of 2.042 μg mL−1 and the detection limit of 0.0135 μg mL−1. Cross-reactivities (CRs) with Cu2+, Pb2+, Zn2+, Mg2+, Ca2+, Fe2+, and Ni2+ were below 0.001% except for Hg2+ with a CR less than 6%. The recoveries from deionized water were from 92.2% to 116.0%. Results indicated that the ELISA based on the polyclonal antibody would be very promising analytical tools for rapid and sensitive determination of metal ions in the environment.

Synthesis and Characterization of Artificial Antigens for Copper and Application for Development of an Indirect Competitive Enzyme-Linked Immunosorbent Assay

Copper was conjugated to two carrier proteins using penicillin G sodium salt to synthesize artificial antigens for copper. The antigens were identified by ultraviolet spectrometry, circular dichroism, and inductively coupled plasma–optical emission spectrometry. The results of ultraviolet spectrometry showed characteristic absorption peak shifts between haptens and carrier proteins. Circular dichroism showed that the secondary structure of the conjugates was an α-helix. These results suggested that the artificial antigens for copper were synthesized successfully. The polyclonal antibodies of copper were produced by immunizing New Zealand white rabbits with copper antigens. An indirect competitive enzyme-linked immunosorbent assay based on the polyclonal antibodies was developed. The concentration of copper ion was quantified based on the ability of its ethylenediaminetetraacetic acid complexes to inhibit the binding of the goat anti-rabbit immunoglobulin G conjugated with horseradish peroxidase and, subsequently, color formation in the assay. The assay showed an IC50 value of 0.475 microgram per milliliter with a detection limit of 0.007 microgram per milliliter. The antibody showed high affinity with copper and low cross-reactivity with other metals. The recovery of copper from fortified water was between 78.0 and 122 percent. The results indicate that the assay is a convenient supplemental analytical tool for monitoring copper ions in aquatic environments.

A Label-Free Electrochemical Aptasensor for the Rapid Detection of Tetracycline Based on Ordered Mesoporous Carbon–Fe3O4

A novel aptasensor based on a tetracycline (TET) aptamer immobilized by physical adsorption on an ordered mesoporous carbon-Fe3O4 (OMC-Fe3O4)-modified screen-printed electrode surface was successfu ...