Zhi-Min Liu

Amperometric tyrosinase biosensor using enzyme-labeled au colloids immobilized on cystamine/chitosan modified gold surface

Abstract An amperometric tyrosinase biosensor for phenolic compounds was developed via a simple and effective immobilization method. Tyrosinase‐labeled nano‐Au colloids were immobilized on chitosan layer, which was fixed on cystamine‐modified gold electrode through the glutaraldehyde crosslinking. The tyrosinase retained its bioactivity well in such an immobilization matrix. Phenolic compounds were determined by the direct reduction of biocatalytically generated quinone species at −100 mV vs. SCE. The parameters of the fabrication process and the variables of the experimental conditions for the enzyme electrode were optimized. The resulting sensor exhibited excellent reproducibility, stability and sensitive response. The detection limit of 0.32 µmol L−1 catechol, 0.60 µmol L−1 phenol, and 0.18 µmol L−1 p‐cresol were obtained and 75% of the activity was maintained after 2 weeks.

Optical sensor for berberine utilizing its intrinsic fluorescence enhanced by the formation of inclusion complex with butylated-β-cyclodextrin

Abstract An optical sensor for berberine, the basic ingredient of the widely used traditional Chinese medicine Coptis Chinensis, based on its intrinsic fluorescence enhanced by butylated-β-cyclodextrin (HDB-β-CD) immobilized in plasticized poly(vinyl chloride) (PVC) membrane has been developed. The drastic enhancement of fluorescence intensity of berberine was attributed to the formation of an inclusion complex between HDB-β-CD and berberine, which has been utilized as the basis of the fabrication of a berberine-sensitive fluorescence sensor. The proposed sensor was quite distinct from those fluorescent sensors for berberine reported so far which relied upon quenching the fluorescence of the sensing reagent immobilized on membrane by berberine. The response mechanism of optode membrane was discussed in detail from the view of molecular dynamics and the optimum steric configuration of the inclusion complex was presented by molecular dynamics simulation. The analytical performance characteristics of the proposed berberine-sensitive sensor were investigated. The sensor can be applied to the quantification of berberine with a linear range covering from 4.0×10−7 to 2.0×10−5 moll−1 with a detection limit of 8.0×10−8 moll−1. The sensor exhibits excellent reproducibility, reversibility and selectivity. The recommended method was successfully used for the determination of berberine in pharmaceutical preparations.

Highly Selective Dopamine Determination by Using Carboxymethylated β‐Cyclodextrin Polymer Film Modified Electrode

Abstract A highly selective and sensitive electrochemical sensor modified with carboxymethylated β‐cyclodextrin (CM‐β‐CDP) polymer film was fabricated for the determination of dopamine (DA) in the presence of ascorbic acid (AA). The electrochemical behavior of DA and AA at the chemically modified electrode was investigated by cyclic voltammetry (CV) and differential pulse voltammetry. The response mechanism of CM‐β‐CDP film for DA was based on the combination of electrostatic and inclusion interaction of CM‐β‐CDP for DA, which was distinguished from the response mechanism of the charged polymer film modified electrode that only relied upon the electrostatic interaction between charged polymer film and DA (or AA) to realize the separation of overlapping peak potential of DA and AA. The CM‐β‐CDP film showed preferable analytical performance characteristics in catalytic oxidation of DA compared with the β‐CDP polymer film. Under optimized conditions, it was feasible for the electrode modified with the CM‐β‐CDP film to selectively determine DA in the presence of a large excess of AA. A linear calibration plot was obtained over the range 0.8–60 µM with a sensitivity of 65 nA/µM and a detection limit (signal/noise (S/N) = 3) of 0.2 µM in the presence of 1.0 mM AA. This electrochemical sensor showed excellent sensitivity, repeatability, stability, and recovery for the determination of DA. The interference of AA with the determination of DA could be efficiently eliminated.