Browsing by Author "Yayebjee, M"

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    High resolution synchrotron XPS study of L-cysteine and S-benzyl-L-cysteine on platinum: adhesion mechanisms and radiation damage
    (Australian Institute of Physics, 2006-12-07) Wong, L; Yayebjee, M; Stampfl, APJ; Chen, CH; Wang, SC; Huang, ML; Klauser, R
    Key to the development of functional biomaterials and innovative technologies behind medical implants and biosensors is a deep understanding of the interaction between inorganic surfaces and biological systems at the molecular level. Amino acids adhered onto inorganic substrates are model systems which may be analysed at a fundamental level using x-ray photoelectron spectroscopy (XPS) [1]. L-cysteine has been proposed as a potential anchor for larger molecules, e.g. proteins, to adhere onto metals such as Au, due to cysteine’s reactive thiol group [2]. This paper presents a related but unexplored system: in-situ prepared L-cysteine on Pt{111}. Pt{111} is an atomically flat surface and is a relevant material, used in biosensors and medical implants. To compare the adhesion characteristics of small and large molecules, S-benzyl-L-cysteine on Pt{111} is also analysed. Core level binding energies are examined using high resolution XPS at the National Synchrotron Radiation Research Centre (NSRRC) in Taiwan. Analysis of S 2p binding energies indicates cysteine adsorption via the thiol group. Two N 1s peaks in the spectra suggest that cysteine is present in both neutral and zwitterionic forms. Analysis of S-Benzyl-L-Cysteine core level shifts demonstrates similar adhesion characteristics. An important consideration in the application of biosurfaces is the impact of x-ray irradiation. XPS, using an excitation energy of 480eV, is used to examine the damage to each surface, due to exposure from the x-ray beam. The dramatic evolution of the N 1s spectra from both molecules suggests cleavage of the amine group. In addition, C 1s spectra from L-cysteine and S-benzyl-L-cysteine show cleavage of the carboxyl group due to prolonged irradiation. [1] B. Kasemo, Surf. Sci., 500, 2002, 656. [2] O.Cavalleri, L. Oliveri, A. Daccà, R. Parodi and R. Rolandi, App. Surf. Sci., 175, 2001, 357