Dandan Song

Stripping voltammetric detection of mercury(II) based on a bimetallic Au-Pt inorganic-organic hybrid nanocomposite modified glassy carbon electrode.

A new, highly sensitive and selective sensor for the electrochemical assay of Hg(II) by anodic stripping voltammetry has been developed, whereby a glassy carbon electrode is modified with a novel inorganic-organic hybrid nanocomposite, namely, bimetallic Au-Pt nanoparticles/organic nanofibers (labeled as Au-PtNPs/NFs). The sensor possesses a three-dimensional (3D) porous network nanoarchitecture, in which the bimetallic Au-Pt NPs serving as metal NP-based microelectrode ensembles are homogenously distributed in the matrix of interlaced organic NFs. The surface structure and composition of the sensor were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Its electrochemical performance was systematically investigated. Our results show that such a newly designed, Au-PtNPs/NF nanohybrid modified electrode provides remarkably improved sensitivity and selectivity for the stripping assay of Hg(II). The detection limit is found to be as low as 0.008 ppb (S/N = 3) that is much below the guideline value from the World Health Organization (WHO). Interferences from other heavy metal ions such as Cu(II), Cr(III), Co(II), Fe(II), Zn(II), and Mn(II) ions associated with mercury analysis are effectively inhibited. Toward the goal for practical applications, the sensor was further evaluated by monitoring Hg(II) in tap and river water specimens.

Development of acetylcholinesterase biosensor based on CdTe quantum dots/gold nanoparticles modified chitosan microspheres interface

In this paper, a novel acetylcholinesterase (AChE) biosensor was constructed by modifying glassy carbon electrode with CdTe quantum dots (QDs) and excellent conductive gold nanoparticles (GNPs) though chitosan microspheres to immobilize AChE. Since GNPs have shown widespread use particularly for constructing electrochemical biosensors through their high electron-transfer ability, the combined AChE exhibited high affinity to its substrate and thus a sensitive, fast and cheap method for determination of monocrotophos. The combination of CdTe QDs and GNPs promoted electron transfer and catalyzed the electro-oxidation of thiocholine, thus amplifying the detection sensitivity. This novel biosensing platform based on CdTe QDs-GNPs composite responded even more sensitively than that on CdTe QDs or GNPs alone because of the presence of synergistic effects in CdTe-GNPs film. The inhibition of monocrotophos was proportional to its concentration in two ranges, from 1 to 1000 ng mL(-1) and from 2 to 15 microg mL(-1), with a detection limit of 0.3 ng mL(-1). The proposed biosensor showed good precision and reproducibility, acceptable stability and accuracy in garlic samples analysis.

Signal-on electrochemiluminescence of biofunctional CdTe quantum dots for biosensing of organophosphate pesticides.

A new, highly sensitive and selective ECL assay biosensor based on target induced signal on has been developed for the detection of organophosphate pesticides (OPs), whereby the smart integration of graphene nanosheets (GNs), CdTe quantum dots (CdTe QDs), and acetylcholinesterase (AChE) enzymatic reaction yields a biofunctional AChE-GNs-QDs hybrid as cathodic ECL emitters for OPs sensing. The electrochemically synthesized GNs were selected as a supporting material to anchor CdTe QDs, exhibiting a significantly amplified ECL signal of QDs. On the basis of the effect of OPs on the ECL signal of AChE-QDs-GNs modified glassy carbon electrode (GCE), a highly sensitive GNs-anchored-QDs-based signal-on ECL biosensor was developed for sensing OPs, combined with the enzymatic reactions and the dissolved oxygen as coreactant. The conditions for OPs detection were optimized by using methyl parathion (MP) as a model OP compound. Under the optimized experimental conditions, such a newly designed system shows remarkably improved sensitivity and selectivity for the sensing of OPs. The detection limit was found to be as low as about 0.06 ng mL(-1) (S/N=3). Toward the goal for practical applications, the resulting sensor was further evaluated by monitoring MP in spiked vegetable samples, showing fine applicability for the detection of MP in real samples.

An Electrochemical Immunosensor Based on Chemical Assembly of Vertically Aligned Carbon Nanotubes on Carbon Substrates for Direct Detection of the Pesticide Endosulfan in Environmental Water

A glassy carbon substrate was covalently modified with a mixed layer of 4-aminophenyl and phenyl via in situ electrografting of their aryldiazonium salts in acidic solutions. Single-walled carbon nanotubes (SWNTs) were covalently and vertically anchored on the electrode surface via the formation of amide bonds from the reaction between the amines located on the modified substrate and the carboxylic groups at the ends of the nanotubes. Ferrocenedimethylamine (FDMA) was subsequently attached to the ends of SWNTs through amide bonding followed by the attachment of an epitope, i.e., endosulfan hapten to which an antibody would bind. Association or dissociation of the antibody with the sensing interface causes a modulation of the ferrocene electrochemistry. Antibody-complexed electrodes were exposed to samples containing spiked endosulfan (unbound target analyte) in environment water and interrogated using the square wave voltammetry (SWV) technique. The modified sensing surfaces were characterized by atomic force microscopy, XPS, and electrochemistry. The fabricated electrochemical immunosensor can be successfully used for the detection of endosulfan over the range of 0.01-20 ppb by a displacement assay. The lowest detection limit of this immunosensor is 0.01 ppb endosulfan in 50 mM phosphate buffer at pH 7.0.

Biosensor based on acetylcholinesterase immobilized onto layered double hydroxides for flow injection/amperometric detection of organophosphate pesticides.

We developed a highly sensitive flow injection/amperometric biosensor for the detection of organophosphate pesticides (OPs) using layered double hydroxides (LDHs) as the immobilization matrix of acetylcholinesterase (AChE). LDHs provided a biocompatible microenvironment to keep the bioactivity of AChE, due to the intrinsic properties of LDHs (such as a regular structure, good mechanical, chemical and thermal stabilities, and swelling properties). By integrating the flow injection analysis (FIA) with amperometric detection, the resulting AChE-LDHs modified electrode greatly catalyzed the oxidation of the enzymatically generated thiocholine product, and facilitated the detection automation, thus increasing the detection sensitivity. The analytical conditions for the FIA/amperometric detection of OPs were optimized by using methyl parathion (MP) as a model. The inhibition of MP was proportional to its concentration ranging from 0.005 to 0.3μg mL(-1) and 0.3 to 4.0μg mL(-1) with a detection limit 0.6ng mL(-1) (S/N=3). The developed biosensor exhibited good reproducibility and acceptable stability.

Stripping voltammetric analysis of organophosphate pesticides using Ni/Al layered double hydroxides as solid-phase extraction

A sensitive electrochemical stripping voltammetric biosensor is designed for organophosphate pesticides (OPs) based on solid-phase extraction (SPE) using Ni/Al layered double hydroxides (LDHs) modified glassy carbon electrode (labeled as Ni/Al-LDHs/GCE). The Ni/Al-LDHs as the host are highly efficient to capture OPs, which dramatically facilitates the enrichment of nitroaromatic OPs onto their surface and realizes the stripping voltammetric detection of OPs. The stripping voltammetric performances of methyl parathion (MP) intercalated into LDHs were evaluated by cyclic voltammetric and square-wave voltammetric (SWV) analysis. The combination of the host-guest supramolecular structure, SPE, and stripping voltammetry provides a fast, simple, and sensitive electrochemical method for detecting nitroaromatic OPs by using MP as a model. The stripping analysis is linear over the MP concentration ranges of 0.001-0.1 and 0.2-1.0 microg mL(-1) with a detection limit of 0.6 ng mL(-1) (S/N=3). The developed biosensor exhibits good reproducibility and acceptable stability. This study offers a new promising protocol for OPs analysis.

A multianalyte electrochemical immunosensor based on patterned carbon nanotubes modified substrates for detection of pesticides

A novel multianalyte electrochemical immunosensor based on the assembly of patterned SWNTs on glassy carbon (GC) substrates was developed for simultaneous detection of endosulfan and paraoxon. Based on aryldiazonium salt chemistry, forest of SWNTs can be patterned on GC substrates by C3C bonding using micro contact printing (MCP), which provides an interface showing efficient electron transfer between biomolecules and electrodes. Then redox molecules FDMA and PQQ can be attached to the SWNTs, respectively followed by the attachment of specific epitopes and antibodies. The modified sensing surfaces were characterized by XPS, SEM, AFM and electrochemistry. Based on the current change of specific redox probes, the fabricated immunosensor array can be used for simultaneous detection of endosulfan and paraoxon by a displacement assay. In phosphate buffer solution (50mM, pH 7.0), there is a linear relationship between electrochemical signal of FDMA and the concentration of endosulfan over the range of 0.05-100 ppb with a detection limit of 0.05ppb; the linear range between electrochemical signal of PQQ and the concentration of paraoxon is 2-2500 ppb with a detection limit of 2 ppb. The immunosensor array demonstrates high repeatability, reproducibility, stability and selectivity for the detection of endosulfan and paraoxon.

Towards the fabrication of a label-free amperometric immunosensor using SWNTs for direct detection of paraoxon.

A label-free immunosensor based on SWNTs modified GC electrodes has been developed for the direct detection of paraoxon. Based on aryldiazonium salt chemistry, forest of SWNTs can be vertically aligned on mixed monolayers of aryldiazonium salt modified GC electrodes by C-C bonding, which provides an interface showing efficient electron transfer between biomolecules. PEG molecules were introduced to the interface to resist non-specific protein adsorption. Ferrocenedimethylamine (FDMA) was subsequently attached to the ends of SWNTs through the amide bonding followed by the attachment of epitope i.e., paraoxon hapten to which a paraoxon antibody would bind. This immunosensor shows good selectivity and high specificity to paraoxon, and is functional for the detection of paraoxon in both laboratory and field by a displacement assay. There is a linear relationship between electrochemical signal of FDMA and the concentration of paraoxon over the range of 2-2500 ppb with a lowest detected limit of 2 ppb in 0.1 M phosphate buffer at pH 7.0. The SWNTs based amperometric immunosensor provides an opportunity to develop the sensing system for on-site sensitive detection of a spectrum of insecticides.