Browsing by Author "Chen, CH"

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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
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    A scanning photoemission microprobe study of the adsorption of cysteine on Pt{1 1 1}
    (Elsevier B. V., 2005-02-12) Stampfl, APJ; Chen, CH; Wang, SC; Huang, ML; Klauser, R
    High resolution photoemission spectroscopy using sub-micron beams of soft X-rays is used to probe in situ prepared cysteine/Pt{1 1 1} surfaces. Cysteine is found to adsorb intact in its zwitterionic form and only its thiol group is observed to bond with surface Pt. The bright beams of light used in these experiments eventually reduce the sulphur-bonded cysteine molecule to a sulphur-bonded CxHy type-molecule. In order to minimise local damage fast scanning is required when imaging using the scanning photoemission microprobe. © 2005 Elsevier