Wujian Miao received his undergraduate diploma in chemistry from Nantong University (Nantong, China) in 1982, his M.Sc. degree in analytical chemistry from Zhongshan University (Guangzhou, China, with Jinyuan Mo) in 1991, and his Ph.D. degree in electrochemistry from Monash University (Melbourne, Australia, with Alan M. Bond) in 2000. He then served as a Research Scientist in CSIRO (Melbourne, Australia), followed by a postdoctoral fellowship at the University of Texas at Austin with Allen J. Bard in 2001. Since 2004 he has served as an assistant professor of chemistry at the University of Southern Mississippi.

The reaction occurring on electrooxidation of Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) and tri-n-propylamine (TPrA) leads to the production of Ru(bpy)(3)(2+) and light emission. The accepted mechanism of this widely used reaction involves the reaction of Ru(bpy)(3)(3+) and a reduced species derived from the free radical of the TPrA. However, this mechanism does not account for many of the observed features of this reaction. A new route involving the intermediacy of TPrA cation radicals (TPrA(*+)) in the generation of Ru(bpy)(3)(2+) was established, based on results of scanning electrochemical microscopy (SECM)-electrogenerated chemiluminescence (ECL) experiments, as well as cyclic voltammetry simulations. A half-life of approximately 0.2 ms was estimated for TPrA(*+) in neutral aqueous solution. Direct evidence for TPrA(*+) in this medium was obtained via flow cell electron spin resonance (ESR) experiments at approximately 20 degrees C. The ESR spectra of the TPrA(*+) species consisted of a relatively intense and sharp septet with a splitting of approximately 20 G and a g value of 2.0038.

An ultrasensitive DNA hybridization detection method based on electrogenerated chemiluminescence (ECL) using polystyrene microspheres/beads (PSB) as the carrier of the ECL labels, namely, tris(2,2'-bipyridyl)ruthenium(II) tetrakis(pentafluorophenyl)borate (Ru(bpy)3[B(C6F5)4]2), is reported. Probe single-stranded DNA (p-ssDNA) was attached to the surface of magnetic beads (MB) and hybridized with target-ssDNA (t-ssDNA) with immobilized PSB containing a large number of water insoluble Ru(bpy)3[B(C6F5)4]2 species (approximately 7.5 x 10(9) molecules/bead). With this approach a large amplification factor of Ru(bpy)3[B(C6F5)4]2 molecules for each t-ssDNA can be achieved, when each PSB is attached to a limited number of t-ssDNA. The p-ssDNA-MB <--> t-ssDNA-PSB/Ru(bpy)3(2+) conjugates formed were magnetically separated from the reaction media and dissolved in MeCN containing tri-n-propylamine (TPrA) as an ECL coreactant. ECL was produced with a potential scan from 0 to 3.0 V versus Ag/Ag+, and the integrated ECL intensity was found to be linearly proportional to the t-ssDNA concentration in a range of 1.0 fM to 10 nM under optimized conditions. ECL signals associated with two base pair mismatched ssDNA and noncomplementary ssDNA can be distinguished well from the ECL signal related to the complementary DNA hybridization. A Poisson distribution is followed when a large number of MB reacts with PSB, and the minimum number of 1.0- and 2.8-microm diameter MB required to bind and magnetically separate a single 10-microm diameter PSB from the reaction solution was estimated to be three and one, respectively. The principle described in this paper could be also applied to many other ECL analyses, such as immunoassays.

Anodic electrogenerated chemiluminescence (ECL) with tri-n-propylamine (TPrA) as a coreactant was used to determine DNA and C-reactive protein (CRP) by immobilizations on Au(111) electrodes using tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) labels. A 23-mer synthetic single-stranded (ss) DNA derived from the Bacillus anthracis with an amino-modified group at the 5' end position was covalently attached to the Au(111) substrate precoated with a self-assembled thiol monolayer of 3-mercaptopropanoic acid (3-MPA) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC) and then hybridized with a target ssDNA tagged with Ru(bpy)(3)(2+) ECL labels. Similarly, biotinylated anti-CRP species were immobilized effectively onto the Au(111) substrate precovered with a layer of avidin linked covalently via the reaction between avidin and a mixed thiol monolayer of 3-MPA and 16-mercaptohexadecanoic acid on Au(111) in the presence of EDAC and N-hydroxysuccinimide. CRP and anti-CRP tagged with Ru(bpy)(3)(2+) labels were then conjugated to the surface layer. ECL responses were generated from the modified electrodes described above by immersing them in a TPrA-containing electrolyte solution. A series of electrode treatments, including blocking free -COOH groups with ethanol amine, pinhole blocking with bovine serum albumin, washing with EDTA/NaCl/Tris buffer, and spraying with inert gases, were used to reduce the nonspecific adsorption of the labeled species. The ECL peak intensity was linearly proportional to the analyte CRP concentration over the range 1-24 microg/mL. CRP concentrations of two unknown human plasma/serum specimens were measured by the standard addition method based on this technique.

The electrochemical kinetics for the oxidation of ferrocenemethanol (FcCH 2 OH) over the whole composition range of dimethyl sulfoxide (DMSO)-water solutions of different viscosities (η) containing 50.0 mM (CH 3 ) 4 NClO 4 (TMAP) at a Pt microelectrode was studied using scanning electrochemical microscopy (SECM). The measured diffusion coefficient, D FcCH 2 OH , as well as the standard rate constant of the heterogeneous electron transfer, k 0 , as a function of solution composition, showed a minimum at about a DMSO molar fraction (x DMSO ) of 0.33, corresponding to the mixture with the maximum solution viscosity. The largest k 0 value found, 2.06 ( 0.31 cm s -1 in pure water (electrolyte) medium, was about 15 times larger than that obtained in the solution of x DMSO ) 0.33 (0.14 ( 0.02 cm s -1 ). A good linear correlation between ln k 0 and ln η was observed within the solution composition range of 0.10 e x DMSO e 0.60. An excellent linear correlation between ln k 0 and ln τ L , the longitudinal relaxation time, was also obtained with a slope equal to 1.0 when x DMSO ) 0-0.60. Unusually small rate constants found in the solutions of x DMSO g 0.70 were attributed to adsorption effects at the tip and the substrate electrode. The k 0 obtained for the present system was generally found to be inversely proportional to the viscosity of the solution and directly proportional to the diffusion coefficient of the electroactive species.