MALDI-TOF MS (Matrix Assisted Laser Desorption Ionization-Time Of Flight Mass Spectrometry) is a method widely used in mass spectrometry of biological macromolecules and the like. MALDI is a method for ionizing a test sample by mixing the test sample with a matrix (a compound which absorbs laser light) and by irradiating the test sample with a laser beam for a time as short as several nanoseconds. MALDI is characterized in that it ionizes a wide variety of biological substances under mild conditions under which the biological substances are not substantially decomposed. TOF MS is a method for calculating the mass of the sample wherein the sample is accelerated between electrodes across which a high voltage is applied, the accelerated sample is introduced into a tube called flight tube containing high vacuum, electric field-free region to make the sample fly at a uniform velocity, and wherein the time required for flying a prescribed distance is measured. In theory, since even if the mass is large, only the measurement time is prolonged and there is no theoretical measurement limit, it is a mass spectrometry suited for macromolecules.
Conventionally, as the plates for MALDI-TOF MS, aluminum plates having a coating film made of gold or a self-assembled monolayer have been used. However, the mass spectrometry of a protein or DNA using the conventional plate for MALDI-TOF MS has a problem in that the reproducibility is poor and a spectrum is hardly obtained for a test substance having a large molecular weight. This tendency is prominent for DNAs, so that the number of cases where MALDI-TOF MS was effectively used for the analysis of DNA is small.    Patent Literature 1: JP-A-2001-13110    Patent Literature 2: JP-A-2004-266100    Patent Literature 3: U.S. Pat. No. 6,743,607    Patent Literature 4: U.S. Pat. No. 6,693,187    Patent Literature 5: US-A-2003/0220254    Non-patent Literature 1: Koomen, J. et al., Anal. Chem., 72: 3860 (2000)    Non-patent Literature 2: Vorm, O. et al., Anal. Chem., 66: 3287 (1994)    Non-patent Literature 3: Berggren, W. T., et al., Anal. Chem., 74: 1745 (2002)    Non-patent Literature 4: Papac, D. I. et al., Anal. Chem., 68: 3215 (1996)    Non-patent Literature 5: Hung, K. C. et al., Anal. Chem., 70: 3088 (1998)