In this report, we describe the visible-laser desorption/ionization of biomolecules deposited on gold-coated porous silicon and gold nanorod arrays. The porous silicon made by electrochemical etching was coated with gold using argon ion sputtering. The gold nanorod arrays were fabricated by electrodepositing gold onto a porous alumina template, and the subsequent partial removal of the alumina template. A frequency-doubled/tripled Nd : YAG laser was used to irradiate the gold nanostructured substrate, and the desorbed molecular ions were mass-analyzed by a time-of-flight mass spectrometer. The desorption/ionization of biomolecules for both substrates was favored by the use of the 532-nm visible-laser, which is in the range of the localized surface plasmon resonance of the gold nanostructure. The present technique offers a potential analytical method for low-molecular-weight analytes that are rather difficult to handle in the conventional matrix-assisted laser desorption/ionization (MALDI) mass spectrometry.

The high-sensitive detection of explosives is of great importance for social security and safety. In this work, the ion source for atmospheric pressure chemical ionization/mass spectrometry using alternating current corona discharge was newly designed for the analysis of explosives. An electromolded fine capillary with 115 µm inner diameter and 12 mm long was used for the inlet of the mass spectrometer. The flow rate of air through this capillary was 41 ml/min. Stable corona discharge could be maintained with the position of the discharge needle tip as close as 1 mm to the inlet capillary without causing the arc discharge. Explosives dissolved in 0.5 µl methanol were injected to the ion source. The limits of detection for five explosives with 50 pg or lower were achieved. In the ion/molecule reactions of trinitrotoluene (TNT), the discharge products of NOx (-) (x = 2,3), O3 and HNO3 originating from plasma-excited air were suggested to contribute to the formation of [TNT - H](-) (m/z 226), [TNT - NO](-) (m/z 197) and [TNT - NO + HNO3 ](-) (m/z 260), respectively. Formation processes of these ions were traced by density functional theory calculations. Copyright © 2015 John Wiley & Sons, Ltd.

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