Formation and Characterization of 2D Closely Packed Arrays of Bare Gold Nanoparticles without Aggregation.

Uniform 2D arrays of metal nanoparticles (NPs) have received significant attention in the field of molecular sensing using localized surface plasmon resonance. Generally, metal NPs bear organic surface-modifying molecules to prevent aggregation and form 2D metal NP arrays. However, surface-modifying molecules negatively affect molecular sensing. Previously, we developed a technique for forming a 2D bare metal NP array, denoted the sandwich (SW) technique. However, the formation mechanism of these 2D metal NP arrays remains unknown and therefore the experimental conditions of the SW technique are not optimized. Here, we observed the formation of a 2D Au NP (d: 60 nm) array using the SW technique with an optical microscope. Moderate drying conditions of the colloidal droplets sandwiched between two parallel substrates were necessary for forming 2D Au NP arrays. We then optimized the drying conditions and obtained a 2D Au NP array. This array was uniform, and the Au NPs were arranged at distances of 4.5 nm with hexagonal periodicity, without aggregation. Further, the 2D Au NP arrays exhibited excellent spot-to-spot reproducibility in surface-enhanced Raman scattering.

Desorption/ionization on carbon mass spectrometry: study of amorphous-carbon property.

In this study, an amorphous carbon was proposed as a new ionization substrate for laser desorption/ionization (LDI) and its efficiency for soft laser ionization without any matrix molecules was focused on the soft laser ionization effect of the amorphous carbon substrate was compared with that of a stainless substrate by LDI and matrix-assisted laser desorption/ionization (MALDI) using a 266-nm irradiation laser. The result of the amorphous carbon substrate was indicated to have a soft ionization effect similar to the result of MALDI. In addition, from the experimental result achieved by soft laser ionization using not only 266-nm-wavelength but also 355-nm-wave length irradiation lasers, the amorphous carbon substrate had a high degree of generality for selecting a sample similarly to soft ionization. The same experimental condition was carried out for other amorphous carbon substrates with different surface roughnesses in order to clarify the ionization mechanism on the amorphous carbon substrates. From the results, it was suggested that factors besides the difference in surface roughness exist for laser ionization efficiency.