Shihui Si

A sensitive and stable biosensor based on the direct electrochemistry of glucose oxidase assembled layer-by-layer at the multiwall carbon nanotube-modified electrode

A novel strategy for fabricating the sensitive and stable biosensor was present by layer-by-layer (LBL) self-assembling glucose oxidase (GOD) on multiwall carbon nanotube (CNT)-modified glassy carbon (GC) electrode. GOD was immobilized on the negatively charged CNT surface by alternatively assembling a cationic poly(ethylenimine) (PEI) layer and a GOD layer. And the direct electrochemistry of GOD in the self-assembled {GOD/PEI}(n) film was investigated. CNT as an excellent nanomaterial greatly improved the direct electron transfer between GOD in {GOD/PEI}(n) film and the electrode. And the ultrathin {GOD/PEI}(n) film on the CNT surface provided a favorable microenvironment to keep the bioactivity of GOD. Moreover, PEI used as an out-layer was adsorbed on the top of the {GOD/PEI}(n) film to form the sandwich-like structure (PEI/{GOD/PEI}(n)), improving the stability of the enzyme electrode. On basis of these, the developed PEI/{GOD/PEI}(n)/CNT/GC biosensor has a high sensitivity of 106.57 μA mM(-1) cm(-2), and can measure as low as 0.05 mM glucose. In addition, the biosensor has excellent operational stability with no decrease in the activity of enzyme over a 1-week period. Therefore, the developed strategy making use of the advantages of CNT and LBL assembly is ideal for the direct electrochemistry of the redox enzymes and the construction of the sensitive and stable enzyme biosensor.

Electrochemical oxidation of purine and pyrimidine bases based on the boron-doped nanotubes modified electrode.

Based on the excellent physicochemical properties of boron-doped carbon nanotubes (BCNTs), the electrochemical analysis of four free DNA bases at the BCNTs modified glassy carbon (GC) electrode was investigated. Herein, the BCNTs/GC electrode exhibited remarkable electrocatalytic activity towards the oxidation of purine bases (guanine (G), adenine (A)). More significantly, the direct oxidation of pyrimidine bases (thymine (T), cytosine (C)) was realized. It may be due to that BCNTs have the advantages of high electron transfer kinetics, large surface area, prominent antifouling ability and electrode activity. On basis of this, a novel and simple strategy for the determination of G, A, T and C was proposed. The BCNTs/GC electrode showed high sensitivity, wide linear range and capability of detection for the electrochemical determination of G, A, T, and C. On the other hand, the electrochemical oxidation of quaternary mixture of G, A, T, and C at the BCNTs/GC electrode was investigated. It was obtained that the peak separation between G and A, A and T, T and C were large enough for their potential recognition in mixture without any separation or pretreatment. The BCNTs/GC electrode also displayed good stability, reproducibility and excellent anti-interferent ability. Therefore, it can be believed that the BCNTs/GC electrode would provide a potential application for the electrochemical detection of DNA in the field of genetic-disease diagnosis.

A highly selective photoelectrochemical biosensor for uric acid based on core-shell Fe3O4@C nanoparticle and molecularly imprinted TiO2.

Combining the surface modification and molecular imprinting technique, a novel photoelectrochemical sensing platform with excellent photochemical catalysis and molecular recognition capabilities was established for the detection of uric acid based on the magnetic immobilization of Fe3O4@C nanoparticles onto magnetic glassy carbon electrode (MGCE) and modification of molecularly imprinted TiO2 film on Fe3O4@C. The developed biosensor was highly sensitive to uric acid in solutions, with a linear range from 0.3 to 34µM and a limit of detection of 0.02μM. Furthermore, the biosensor exhibited outstanding selectivity while used in coexisting systems containing various interferents with high concentration. The practical application of the biosensor was also realized for the selective detection of uric acid in spiked samples. The study made a successful attempt in the development of highly selective and sensitive photoelectrochemical biosensor for urine monitoring.

Simple and sensitive aptasensor based on quantum dot-coated silica nanospheres and the gold screen-printed electrode.

A novel electrochemical aptasensor involving quantum dots-coated silica nanospheres (QDs/Si) and the screen-printed gold electrodes (SPGE) was developed for the detection of thrombin. The screen-printed electrodes with several advantages, including low cost, versatility, miniaturization, and mechanical regeneration after each measurement cycle, were employed. On the other hand, the gold nanoparticles (AuNPs) were electrodeposited on the surface of SPGE to obtain AuNPs/SPGE. And this sandwich format (Apt/thrombin/Apt-QDs/Si) was fixed on the AuNPs/SPGE to fabricate the electrochemical aptasensor. The bound CdTe QDs were dissolved in an acid-dissolution step and were detected by electrochemical stripping analysis. The proposed aptasensor has excellent performance such as high sensitivity, good selectivity and analytical application in real samples. The combination of nanoparticles with the screen-printed electrode is favorable for amplifying electrochemical signals, and useful for large-scale fabrication of the electrochemical aptasensors, which would lay a potential foundation for the development of the electrochemical aptasensor.

A disposable expanded graphite paper electrode with self-doped sulfonated polyaniline/antimony for stripping voltammetric determination of trace Cd and Pb

A conducting graphite electrode was fabricated by using expanded graphite (EG) paper by a screen-printing technique, onto which self-doped sulfonated polyaniline (SPAN) was electropolymerized via aniline and m-aminobenzenesulfonic acid monomers, and the Sb/SPAN/EG electrode was obtained by electrodepositing Sb onto the copolymer modified EG electrode. The sensitivity of the disposable EG electrode was improved by using a two-step ex situ fabrication procedure, in which the anodic doping of SbCl4− for the SPAN film was kept at +0.3 V for 300 s and then reduced at −0.5 V for 100 s in solution containing 10 mg L−1 Sb(III) and 0.5 M hydrochloric acid. The disposable Sb/SPAN/EG electrodes were used for the simultaneous determination of trace lead and cadmium by differential pulse anodic stripping voltammetry. The stripping currents increased linearly when the metal concentration was in a range of 2–70 μg L−1, and the limits of detection were 0.20 μg L−1 for Pb(II) and 0.41 μg L−1 for Cd(II) at a preconcentration time of 180 s, respectively. The proposed disposable working electrode, as a new style of “mercury-free” electrodes for heavy metal measurements, exhibits encouraging properties for practical use, such as low cost, and good reproducibility.

Study of erythrocyte sedimentation behavior by piezoelectric crystal impedance sensor.

Based on the impedance characteristic of erythrocytes at high frequency, the response of piezoelectric crystal impedance (PCI) sensor in the erythrocyte suspension was derived and verified experimentally. A method of using PCI sensor to investigate erythrocyte aggregation-sedimentation phenomenon was proposed. From the frequency response of the PCI sensor, the erythrocyte aggregation time and sedimentation rate could be obtained during erythrocyte aggregation and sedimentation. With the present method, the effects of the erythrocyte deformability, the osmotic pressure and the coexisting macromolecules on the erythrocyte sedimentation rate were studied. The results show that the PCI sensor possesses some advantages, such as good sensitivity, simplicity of use and no thermal effect for the impedance study of erythrocyte aggregation and sedimentation.