Infrared laser desorption/ionization on silicon

Laser desorption/ionization from a single-crystal silicon surface was performed using a laser operating in the 3-μm region of the mid-infrared. Analyte molecules up to 6 kDa were ionized with no added matrix. As with ultraviolet desorption/ionization from porous silicon (DIOS), IR laser desorption from silicon does not produce matrix ions that can interfere with analysis of low-mass analytes. However, in contrast to UV DIOS, silicon porosity or roughness is not required for ionization using an IR laser. Mass spectra were obtained in the wavelength range between 2.8 and 3.5 μm, which is consistent with energy absorption by a hydrogen-bonded OH group. A mechanism based on desorption of adsorbed solvent molecules is postulated

Infrared laser desorption on transparent targets

Ultraviolet laser desorption ionization from porous silicon (DIOS) was studied. Laser desorbed ions were detected with a dual microchannel plate detector and the resulting signal was acquired with a digital oscilloscope. Mass spectra were obtained from infrared (IR) transparent targets using bradykinin as a test peptide and bovine insulin as a test proteins. The results show that the resistivities and orientation of single crystal silicon between 0.001 and 1500 ωcm