The modification of glassy carbon and gold electrodes with DNA by adsorption or covalent immobilization in a mono-or submonolayer has been investigated using the couple Co(bpy)3+/2+ as an indicator. It has been found that when the solution containing double stranded or single stranded DNA is evaporated to dryness, dehydrated DNA molecules can be irreversibly adsorbed on the surfaces of glassy carbon electrodes, in an amount close to that of the saturated adsorptive monolayer. The DNA-adsorbed layer on glassy carbon electrodes is unstable to bases, but stable to 1 M HCl solution. The adsorption of DNA on the electrodes can be evaluated from the increase in the peak current, the decrease in the value of △Ep, and the negative shift in the value of E for the Co(bpy)3+/2+ couple. DNA is very strongly adsorbed on the oxidized surfaces of glassy carbon electrodes, and the adsorptive layer is very stable towards heating. The covalent immobilization of DNA directly onto the electrode surfaces is impossible due to considerable steric hindrance; but if the active groups (sites) on the electrode surfaces are elongated with other suitable molecules, the covalent immobilization of DNA becomes possible on the electrode surfaces. The quantity of covalently immobilized DNA at the electrodes reported in the paper is about 31% of the saturated monolayer.

A visual gene-detecting technique using nanoparticle-supported gene probes is described. With the aid of gold nanoparticle-supported 30-end-mercapto-derivatized oligonucleotide serving as detection probe, and 50-end-amino-derivatized oligonucleotide immobilized on glass surface acting as capturing probe, target DNA was detected visually by sandwich hybridization based on highly sensitive "nano-amplification" and silver staining. Different genotypes of Hepatitis B and C viruses in the serum samples from infected patients were detected using homemade HBV, HCV, and HBV/HCV gene chips by the gold/silver nanoparticle staining amplification method. The present visual gene-detecting technique may avoid limitations with the reported methods, for its high sensitivity, good specificity, simplicity, speed, and cheapness. This technique has potential applications in many fields, especially in multi-gene detection gene chips coupled with the detection will find applications in clinic. Additionally, resonance Rayleigh light scattering (RLS) spectroscopy is used, for the first time, to judge and monitor the immobilization of gene probes on gold nanoparticle surfaces.

When illuminated by near-UV light, titanium dioxide (TiO2) exhibits excellent bactericidal activity. However, there exist some different mechanisms for cell killing via photocatalysis. In the present study, the photocatalytically bactericidal mechanism of TiO2 thin films was investigated by atomic force microscopy (AFM) in conjugation with some other techniques. The decomposition process of the cell wall and the cell membrane was directly observed by AFM for the first time. The resultant change in cell permeability was confirmed by potassium ion (K+) leakage. Quantum dots (QDs) were designed originally as a probe to examine the cell permeability for macromolecules. The corresponding bactericidal activity of TiO2 thin films was examined by cell viability assay. These results suggested that the cell death was caused by the decomposition of the cell wall and the cell membrane and the resultant leakage of intracellular molecules.

Double-stranded DNA(poly(dA)30?poly(dT)30)-modified gold electrodes, prepared by air-drying/adsorption method, have been investigated by various techniques, including cyclic voltammetry (CV), quartz crystal microbalance (QCM), electrochemical scanning tunneling microscopy (EC-STM), and surface-enhanced Raman scattering spectroscopy (SERS). CV and QCM results show that an average surface coverage of (7.5 (0.2)

A novel microscale and surface-based method for the study of the interactions of DNA with other redox-active molecules using DNA-modified electrodes is described. The method is simple, convenient, reliable, reagentsaving, and applicable for DNA studies, especially those involving microsamples. Information such as binding site size (s, in base pairs), binding constant (K), ratio (KOx/KRed) of the binding constants for the oxidized and reduced forms of a bound species, binding free energy (△Gb), and interaction mode, including changes in the mode of interaction, and "limiting" ratio KOx°/KRed° at zero ionic strength can be obtained using only 3-15μg of DNA samples. The method was developed using [Co(Phen)3]3+/2+ (Phen) 1,10-phenanthroline)/doublestranded DNA (dsDNA)-modified gold electrodes and [Co(bpy)3]3+/2+ (2,2'-bipyridyl)/dsDNA-modified gold electrodes as model systems. For the [Co(Phen)3]3+/2+/dsDNA-modified gold electrode system, a K2+ of (2.5(0.3)×105M-1 and an s of 5bp were obtained in 5mM pH 7.1 Tris-HCl buffer solution containing 50mM NaCl. For [Co(bpy)3]3+/2+/dsDNA-modified gold electrodes, K3+ and s values of (1.3(0.3)×105M-1 and 3bp, respectively, were obtained. While the s values are consistent with those reported in the literature obtained by solution methods, the K values are almost an order of magnitude larger. A transition in the nature of the interaction between dsDNA and [Co(Phen)3]3+/2+, from electrostatic to intercalative with increasing ionic strength, was found in our studies. Negative values of △E°' for [Co(bpy)3]3+/2+ bound to dsDNA suggest that its interaction with dsDNA is predominantly electrostatic over the ionic strength range of 5-105mM. The "limiting" ratio K3+°/K2+° of 22 obtained for [Co(Phen)3]3+/2+ bound to dsDNA at zero ionic strength suggests that electrostatic interactions are predominant over intercalative ones under these limiting conditions. The ratio for [Co(bpy)3]3+/2+ of 16 also indicates that the 3+ form binds to dsDNA more strongly than the 2+ form at zero ionic strength. For [Co(Phen)3]3+/2+/single-stranded DNA (ssDNA)-modified gold electrodes, the nonuniformity of the surface structure of ssDNA-modified gold electrodes greatly complicates the analysis. A system consisting of a dsDNA-modified gold electrode and [Co(tppz)2]3+/2+ (tppz) tetra-2-pyridyl-1,4-pyrazine) was studied by this method, with a K2+ value of (5(1)×105M-1 and an s value of 7bp being obtained.