Time-of-flight detection of monoatomic ions generated by femtosecond laser ablation from large molecules Toshiyuki Kato a, * , Tohru Kobayashi b , Mizuki Kurata-Nishimura a , Yuko Okamura-Oho a , Takuma Sano a , Rieko Oyama a , Yonehiro Matsumura a , Hiroshi Yamamoto a , Yoshihide Hayashizaki a,b , Yukari Matsuo c , Jun Kawai a,b a Genomic Science Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi, Yokohama, Kanagawa 230-0045, Japan b Discovery and Research Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan c Nishina Center for Accelerator-Based Science, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan Received 19 November 2007; received in revised form 10 January 2008 Available online 26 January 2008 Abstract Single-shot femtosecond laser ablation (fsLA) was applied to large molecules to analyze elemental composition through out wide range of mass-to-charge ratio. Molecular samples such as Eu-DNA and cosmetic powders were atomized and ionized simultaneously by the single-shot fsLA and positive atomic ions were detected using a reflectron time-of-flight (TOF) mass spectrometer. The ratios among the signal intensity of the detected stable isotopes including 151,153 Eu and 182–184,186 W were consistent with the respective natural abundances of the isotopes. The results demonstrate the feasibility of the fsLA-TOF method as a high-throughput analytical technique for elemental microanalysis of large molecular samples in small quantities. Ó 2008 Elsevier B.V. All rights reserved. PACS: 82.80.Ms; 82.80.Rt; 82.80.Àd Keywords: Femtosecond laser ablation; Time-of-flight mass spectroscopy; Elemental analysis; Stable isotope label; Biological molecule 1. Introduction In order to investigate element distributions on solids including biomaterials at high spatial resolution, it is neces- sary to produce atomic ions from the micro region of solid surfaces and to identify their mass-to-charge ratios all at once. Laser ablation ionization is a suitable method for this purpose and is performed using a compact apparatus com- pared with ion impact ionization. Single-shot femtosecond laser ablation (fsLA) has great potential for rapid and sensitive elemental analyses of large organic molecules. It is particularly useful for stable-iso- tope tracer method and analyses of samples in small quan- tities. This idea is supported by several reports of a femtosecond laser ablation effectively producing atomic ions from materials in the irradiated spot [1–3]. It has also been reported that intensity ratios of the ion species pro- duced in such a manner are precise, reproducible, and accu- rate [4]. However, the performance of fsLA has been studied mainly on bulk materials such as metals and inor- ganic crystals, whereas studies for organic molecules on a substrate are scarce. In a previous study [5], we demon- strated simultaneous atomization and ionization of organic molecules applied on a substrate. Intensity ratios of stable isotope ions produced from organic samples were mea- sured using a quadrupole mass spectrometer (Q-MS), where the possibility of fsLA is denoted for the quantitative analysis of biological samples labeled with stable isotopes. However, mass spectra were acquired by scanning mass-to- charge ratio during successive laser irradiation in this 0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2008.01.030 * Corresponding author. Tel.: +81 45 503 9222; fax: +81 45 503 9216. E-mail address: rgscerg@gsc.riken.go.jp (T. Kato). www.elsevier.com/locate/nimb Available online at www.sciencedirect.com Nuclear Instruments and Methods in Physics Research B 266 (2008) 992–997 NIM B Beam Interactions with Materials & Atoms