Hollow nitrogen-doped carbon microspheres pyrolyzed from self-polymerized dopamine and its application in simultaneous electrochemical determination of uric acid, ascorbic acid and dopamine.

Hollow nitrogen-doped carbon microspheres (HNCMS) as a novel carbon material have been prepared and the catalytic activities of HNCMS-modified glassy carbon (GC) electrode towards the electro-oxidation of uric acid (UA), ascorbic acid (AA) and dopamine (DA) have also been investigated. Comparing with the bare GC and carbon nanotubes (CNTs) modified GC (CNTs/GC) electrodes, the HNCMS modified GC (HNCMS/GC) electrode has higher catalytic activities towards the oxidation of UA, AA and DA. Moreover, the peak separations between AA and DA, and DA and UA at the HNCMS/GC electrode are up to 212 and 136 mV, respectively, which are superior to those at the CNTs/GC electrode (168 and 114 mV). Thus the simultaneous determination of UA, AA and DA was carried out successfully. In the co-existence system of UA, AA and DA, the linear response range for UA, AA and DA are 5-30 µM, 100-1000 µM and 3-75 µM, respectively and the detection limits (S/N = 3) are 0.04 µM, 0.91 µM and 0.02 µM, respectively. Meanwhile, the HNCMS/GC electrode can be applied to measure uric acid in human urine, and may be useful for measuring abnormally high concentration of AA or DA. The attractive features of HNCMS provide potential applications in the simultaneous determination of UA, AA and DA.

Sensitive and selective electrochemical sensing of L-cysteine based on a caterpillar-like manganese dioxide-carbon nanocomposite.

A novel one-dimensional (1-D) caterpillar-like manganese dioxide-carbon (MnO(2)-C) nanocomposite has been synthesized by a direct redox reaction between carbon nanotubes (CNTs) and permanganate ions for the first time. The as-prepared nanostructured MnO(2)-C composite mainly consisting of ε-MnO(2) nanoflakes had a unique microstructure, high specific surface area (200 m(2) g(-1)) and favourable conductivity. The nanostructured MnO(2)-C composite, added as a modification to the glassy carbon (GC) electrode via a direct electrochemical co-deposition process with a chitosan hydrogel, was found to exhibit excellent catalytic activity toward L-cysteine electro-oxidation because the specific interaction between the -SH group of L-cysteine and solid MnO(2) occurred to form surface complexes. A determination of L-cysteine at the MnO(2)-C/chitosan/GC (MnO(2)-C/chit/GC) electrode was carried out by amperometric measurement. Under the optimum experimental conditions, the detection response for L-cysteine was fast (within 7 s). The logarithm of catalytic currents shows a good linear relationship with that of the L-cysteine concentration in the range of 0.5-680 µM (R = 0.9986), with a low detection limit of 22 nM. The MnO(2)-C/Chit/GC electrode exhibited excellent stability (without any decrease of the response signal after 1 month) and admirable resistance against interference like glutathione and other oxidizable amino acids (tryptophan, tyrosine, L-lysine and methionine).

Polymerized ionic liquid-wrapped carbon nanotubes: the promising composites for direct electrochemistry and biosensing of redox protein.

Polymerized ionic liquid-wrapped carbon nanotubes (PIL-CNTs) were firstly designed for direct electrochemistry and biosensing of redox proteins. The CNTs were coated successfully with polymerized ionic liquid (PIL) layer, as verified by transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. The PIL-CNTs were dispersed better in water and showed superior electrocatalysis toward O(2) and H(2)O(2) comparing to pristine CNTs and the mixture of IL monomer and CNTs. With glucose oxidase (GOD) as a protein model, the direct electrochemistry of the redox protein was investigated on the PIL-CNTs modified glassy carbon (GC) electrode and excellent direct electrochemical performance of GOD molecules was observed. The proposed biosensor (GOD/PIL-CNTs/GC electrode) displayed good analytical performance for glucose with linear response up to 6mM, response sensitivity of 0.853 microA mM(-1), good stability and selectivity.

Impedimetric aptasensor with femtomolar sensitivity based on the enlargement of surface-charged gold nanoparticles.

A simple and ultrasensitive label-free electrochemical impedimetric aptasensor for thrombin based on the cascaded signal amplification was reported. The sandwich system of aptamer/thrombin/aptamer-functionalized Au nanoparticles (Apt-AuNPs) was fabricated as the sensing platform. The change of the interfacial feature of the electrode was characterized by electrochemical impedance analysis with the redox probe [Fe(CN)(6)](3-/4-). For improving detection sensitivity, the three-level cascaded impedimetric signal amplification was developed: (1) Apt-AuNPs as the first-level signal enhancer; (2) the steric-hindrance between the enlarged Apt-AuNPs as the second-level signal amplification; (3) the electrostatic-repulsion between sodium dodecylsulfate (SDS) stabilized Apt-AuNPs and the redox probe [Fe(CN)(6)](3-/4-) as the third-level signal amplification. Enlargement of Apt-AuNPs integrated with negatively charged surfactant (SDS) capping could not only improve the detection sensitivity of the impedimetric aptasensor for thrombin but also present a simple and general signal-amplification model for impedimetric sensor. The aptasensor based on the enlargement of negatively charged Apt-AuNPs showed an increased response of the electron-transfer resistance to the increase of thrombin concentration through a wide detection range from 100 fM to 100 nM. The linear detection range was 0.05-35 nM, and thrombin was easily detectable to a concentration of 100 fM. The aptasensor also has good selectivity and reproducibility.