Sensing of Oligopeptides Using Alternatively-Deposited Gold Nanorods for Surface-Assisted Laser Desorption/Ionization Ti
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Sensing of Oligopeptides Using Alternatively-Deposited Gold Nanorods for SurfaceAssisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Masanori Fujii1, Naotoshi Nakashima1,2,3 and Yasuro Niidome1,2 1 Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 2 World Premier International (WPI) Research Center, International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 3 JST-CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan ABSTRACT Gold nanorods (NRs) were fixed on an ITO plate and used for the Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SALDI-MS) of oligopeptides (angiotensin I). The SALDI-MS measurements had a high sensitivity to the angiotensin on the ITO plate on which isolated NRs were deposited. Angiotensin molecules in a very diluted solution (1 × 10-11 M) could be detected at m/z = 1297 with a good signal/noise ratio (S/N = 18). In contrast, alternatively deposited NR an ITO plate, which present broad surface plasmon bands, was found to be inactive for SALDI measurements. INTRODUCTION Time-of-flight (TOF) mass spectrometry (MS) using metal particles was first demonstrated by Tanaka et al. in 1988 [1]. In modern SALDI-MS measurements, nanostructured surfaces or nanoparticles absorb photons and assist in desorption and ionization of target molecules [2,3]. Some research groups have recently demonstrated SALDI-MS measurements using various nanoparticles. Gold and silver nanoparticles [4-6], nanostructured gold surfaces [7,8], diamond [9], Fe3O4/TiO2 core/shell [10], silicon surfaces [11], and platinum nanostructures [12] have been applied in SALDI-MS measurements. Castellana et al. proposed combining SP-based sensing and SALDI-MS measurements [6]. They used gold nanorods (NR) modified using 4aminothiophenol and demonstrated the detection of angiotensin II using SALDI-MS measurements. In that work, the target molecules were added in a solution of colloidal NRs. They were then cast on a plate for MS measurements. This procedure was the same as that for matrix molecules in the MALDI method and effective to analyze trace amount of target molecules. The surface modification of an electroconductive plate using nanomaterials is a potential method for preparing a functional substrate for SALDI-MS measurements. The fabrication of metal-coated porous alumina (platinum/alumina), TiO2 printed aluminum foil, silver-coated porous silicone, and the layer-by-layer deposition of silicate, and gold nanoparticles have been reported. The advantages of using surface-modified substrates for SALDI-MS are easy sample preparation, low-noise background, high salt tolerance, and fast data collection without the need for a mixed solution of target molecules and nanoparticles. Previously, we reported SALDI-MS measurements using ITO plates on which NR were deposited. The NR-deposited indium-thin oxide (ITO) plates were highly sensitive for th
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