A simple method for safely preparing Au nanoparticles of a few to 20 nm in diameter has been developed on the basis of chemical reduction of HAuCl 4 with glucose and fructose produced by the acidic hydrolysis of sucrose. The method includes seeding formation in the solid mixture of HAuCl 4 and sucrose via heat treatment at 70-100 °C and seeding growth after dissolving the heated mixture in water at room temperature. The X-ray photoelectron spectroscopic analyses of the HAuCl 4 -sucrose mixture heated at 80 °C for 15 min confirmed the presence of Au(0) and Au(I) in the sample. Both the X-ray diffraction and UV-vis spectroscopic measurements of the heated mixture suggest the very small sizes of gold clusters in the sample. The particle growth in the aqueous solution was followed by in-situ monitoring of the surface plasmon band with a timeresolved UV-vis spectrometer. The size and size distribution of the resulting nanoparticles were measured by both dynamic light scattering and transmission electron microscopy. Electrophoresis combined with visible spectroscopy confirmed that gold nanoparticles in the aqueous solution carried negative charges that resulted from carboxylic acid groups bound to the particles, based on the infrared spectroscopic measurement.

No abstract

We describe the electrochemical detection of DNA methylation through the direct oxidation of both 5-methylcytosine (mC) and cytosine (C) in 5'-CG-3' sequence (CpG) oligonucleotides using a sputtered nanocarbon film electrode after digesting a longer CpG oligonucleotide with endonuclease P1. Direct electrochemistry of the longer CpG oligonucleotides was insufficient for obtaining the oxidation currents of these bases because the CG rich sequence inhibited the direct oxidation of each base in the longer CpG oligonucleotides, owing to the conformational structure and its very low diffusion coefficient. To detect C methylation with better quantitativity and sensitivity in the relatively long CpG oligonucleotides, we successfully used an endonuclease P1 to digest the target CpG oligonucleotide and yield an identical mononucleotide 2'-deoxyribonucleoside 5'-monophosphate (5'-dNMP). Compared with results obtained without P1 treatment, we achieved 4.4 times higher sensitivity and a wider concentration range for mC detection with a resolution capable of detecting a subtle methylated cytosine difference in the CpG oligonucleotides (60mer).

Highly efficient single-cell elemental analysis of microbial cells was achieved using a developed ICP-MS system with approximately 100% cell introduction efficiency and high time resolution.

No abstract