Gaiping Li

Electrochemical characters of hymecromone at the graphene modified electrode and its analytical application

In this paper, a modern popular simple voltammetric sensor, graphene modified electrode (GR/GCE), was employed for studying the electrochemical characters of hymecromone. The electrode reaction of hymecromone was investigated systematically for the first time and some kinetic parameters were calculated. The reaction mechanism of hymecromone at the GR/GCE was also discussed. Based on the enhancement sensing of the GR/GCE for hymecromone, a sensitive electroanalytical method was developed with a detection linear range of 8 × 10−8 to 6 × 10−6 mol L−1 and a detection limit of 4 × 10−8 mol L−1, which were obtained under accumulation for only 180 s. For proving the practical applicability of the proposed method, the determination of hymecromone in real samples was carried out with satisfactory results.

Simple and rapid determination of trace iodide by cathodic stripping voltammetry.

This work establishes a highly sensitive and simple stripping voltammetric method for the direct determination of trace iodide. In the presence of abounding bromide and appropriate amount of cetylpyridine bromide (CPB), the iodine was accumulated on the glassy carbon electrode surface as ion association complex (CPBI2Br). After accumulation for a period of time, a linear sweep potential with negative scanning was applied and the I2 in CPBI2Br was reduced again into the solution. Under the optimization conditions, the stripping signals (peak current) were linear relationship with iodide concentration in range of 3.81×10(-3)µg/mL to 0.114 μg/mL and 0.127μg/mL to 2.54μg/mL, with a detection limit of 1.02ng/mL (S/N=3) for a accumulation time of 180s. Determination of trace iodine in pharmaceutical sample, kelp and table salt were performed with high accuracy and satisfactory recovery results.

Sensitive, simultaneous determination of chrysin and baicalein based on Ta2O5-chitosan composite modified carbon paste electrode

Chrysin and baicalein are the major flavonoids found in oroxylum indicum, an essential herb in traditional Chinese medicine (TCM). Owing to their similar characteristics and physiochemical property, it is a great challenge to detect both of them simultaneously. In this work, tantalum oxide (Ta2O5) particles and chitosan modified carbon paste electrode (Ta2O5-CTS-CPE) was prepared and characterized by scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectrum(EIS). Under the optimum conditions, the prepared Ta2O5-CTS-CPE exhibited excellent electrocatalytic activity toward the oxidation of chrysin and baicalein, and it could serve as the sensor for highly sensitive and simultaneous determination both of them. The linear range is 0.08-4.0μM for both of them, and the detection limits were determined to be 0.03 and 0.05μM (S/N=3) for chrysin and baicalein, respectively. Furthermore, the proposed electrochemical sensor displayed high sensitivity, excellent stability and got satisfactory results in oroxylum indicum samples analysis.

A voltammetry sensor platform for baicalein and baicalin simultaneous detection in vivo based on Ta2O5-Nb2O5@CTS composite

Baicalein and baicalin are the major flavonoids found in Scutellariae Radix, an essential herb which has had a presence in traditional Chinese medicine (TCMs) for more than two thousands of years. Owing to their similar characteristics and physiochemical properties, sensitive, it is a great challenge to detect both of them simultaneously. In this work, a novel, facile and sensitive electrochemical method was proposed based on tantalum oxide (Ta2O5), niobium oxide (Nb2O5) particles and antiseptic chitosan modified carbon paste electrode (Ta2O5-Nb2O5@CTS-CPE). Scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) were used to characterize the properties and investigate the electrochemical response of the sensor. The electrochemical behaviors and redox mechanisms of two analytes were investigated at the target electrode. Under the optimum conditions, the highly sensitive and simultaneous determination of baicalein and baicalin was successfully achieved with a linear response range of 0.08-8.0μM for both of them. The obtained detection limits for baicalein and baicalin were of 0.05 and 0.03μM (S/N=3), respectively. Furthermore, the proposed sensor displayed high sensitivity, excellent stability and satisfactory results in Scutellariae Radix samples analysis and hydrolysis process analysis of baicalin in vivo.

A simple and sensitive method for determination of taxifolin on palladium nanoparticles supported poly (diallyldimethylammonium chloride) functionalized graphene modified electrode

Palladium nanoparticles with diameter of around 5-10nm supported on poly (diallyldimethylammonium chloride) (PDDA)-functionalized graphene composites were prepared by a simple chemical method. As-prepared nanocomposites were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), ultraviolet-visible spectrophotometry (UV-vis) and electrochemical techniques, which were clearly demonstrated that palladium nanoparticles were uniformly dispersed on the graphene sheets. Based on the PDDA-Gr-Pd nanocomposites, a new voltammetric sensor was established and exhibited excellent electrocatalytic activity and fast electron transfer rate toward taxifolin. Under the optimal conditions, a lower detection limit of 1×10-9molL-1 (S/N=3) and a wide linear detection range from 4×10-8 to 1×10-6molL-1 were achieved by square wave voltammetry (SWV). The proposed method was successfully applied for determination of taxifolin in fructus polygoni orientalis with well results.

Electrochemical behavior of amaranth and its sensitive determination based on Pd-doped polyelectrolyte functionalized graphene modified electrode

In this work, poly(sodium p-styrenesulfonate) (PSS)-functionalized graphene supported palladium nanoparticles (Pd) composites were fabricated with simple ultrasonic bath method. The morphology and structure of PSS-GR-Pd composites were characterized using UV-vis absorption spectra, X-ray diffraction and Transmission Electron Microscopy. By combining the merits of the PSS-GR and Pd NPs, a new electrochemical sensor was erected to detect amaranth based on the PSS-GR-Pd nanocomposites. The electrochemical behavior of amaranth was investigated systematically in 0.1molL-1 phosphate buffer solution (PBS 2.0). At the optimum parameter, Ipa was found to be linearly dependent on the concentrations of amaranth (1×10-7-9×10-6molL-1). The detection limit was 7nM (S/N=3) and sensitivity was 5.85μAμM-1. Finally, this system was utilized for determining amaranth in soft drink using the standard addition method.

Highly sensitive determination of gallic acid based on a Pt nanoparticle decorated polyelectrolyte-functionalized graphene modified electrode

A sensitive voltammetric sensor for gallic acid was fabricated by using a poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene supported platinum nanoparticle nanocomposite (PDDA–GR–Pt) modified glassy carbon electrode. The nanocomposite was characterized using UV-vis spectra, transmission electron microscopy (TEM) and X-ray diffraction (XRD). This voltammetric sensor exhibited an excellent electrochemical response for gallic acid. The electrode process of gallic acid was investigated in detail and some dynamics parameters were calculated. Under optimum conditions by square wave voltammetry (SWV), a good linear relationship was obtained between peak currents and gallic acid concentrations in the wider range of 3 × 10−8 to 1 × 10−6 mol L−1 with a lower detection limit of 7 × 10−9 mol L−1 (S/N = 3). In addition, the proposed voltammetric method was successfully applied to test gallic acid in real samples with good results.

Electrochemical behavior of tectoridin and its sensitive determination based on l-arginine modified electrode

A simple, inexpensive and highly sensitive voltammetric method for the determination of tectoridin was developed using a poly(L-Arginine) modified electrode. The redox character of tectoridin at proposed electrode was studied systematically and some dynamic parameters were calculated for the first time. A reasonable reaction mechanism of tectoridin on the poly(L-Arginine)/GCE was also dicussed and proposed, which could be a reference for the pharmacological action of tectoridin in clinical study. And the electroanalytical method for determination of tectoridin was established by differential pulse voltammograms (DPV). Under optimum conditions, the response peak currents were linear relationship with tectoridin concentrations in the range of 5.0×10(-8)-2.0×10(-6) mol L(-1) with a detection limit of 4.0×10(-8) mol L(-1). Therefore, the high sensitivity for tectoridin sensing at the proposed electrode was achieved, and the proposed method could also be used to detect tectoridin in the Chinese medicinal herb Blackberrylily with satisfactory results.

Novel electrochemical biosensor based on cationic peptide modified hemin/G-quadruples enhanced peroxidase-like activity

This work designed an artificial substrate peptide to synthesize peptide-hemin/G-quadruplex (peptide-DNAzyme) conjugates. In addition to enhancing catalytic activity of hemin/G-quadruplex, the peptide could also be induced and cleaved by prostate specific antigen (PSA). It was the first report on peptide-DNAzyme conjugates in application of the peptide biosensor. The polyethyleneimine-reduced graphene oxide@hollow platinum nanotubes (PEI-rGO@PtNTs) nanocomposites were cast on the glassy carbon electrode in order to form the interface of biocompatibility and huge surface area for bioprobes immobilization. In absence of PSA, the peptide-DNAzyme conjugates retained intact on the surface of the electrode to produce a strong response signal. But in presence of PSA, the peptide-DNAzyme conjugates were destroyed to release electron mediators, resulting in dramatical decrease of the electrochemicl signal. Therefore, the method had high sensitivity and super selectivity with the limit of detection calculated as 2.0 fg/mL. Furthermore, the strategy would be promising to apply for other proteases by transforming the synthetic peptide module of target.

A novel voltammetric sensor based on poly(l-Citrulline)/SWCNTs composite film modified electrode for sensitive determination of picroside II

A novel voltammetric sensor was constructed by simple dripping single-walled carbon nanotubes (SWCNTs) on to the glass carbon electrode (GCE) firstly and electro-polymerizing L-Citrulline film subsequently. The resulting poly(L-Citrulline)/SWCNTs/GCE showed a significant voltammetric response to picroside II due to the synergistic effect of SWCNTs and poly(L-Citrulline) film. The first electroanalytical method of picroside II was proposed with detection linear range from 8.0 × 10(-8) to 5.0 × 10(-6) mol L(-1) and a detection limit of 3 × 10(-8) mol L(-1). The high sensitivity, selectivity and long-term stability made the sensor suitable for the determination of picroside II. Moreover, based on the systematically investigation and some kinetics parameters calculated in the experimentation, the reaction mechanism of picroside II at the poly(L-Citrulline)/SWCNTs modified GCE was obtained reliably. Lastly, the proposed sensor was used for the determination of picroside II in real sample with satisfactory results. This work promoted the potential applications of amino acid materials and SWCNTs in electro-chemical sensors.