Stability of self-assembled monolayers on titanium and gold.
Methyl- and hydroxyl-terminated phosphonic acid self-assembled monolayers (SAMs) were coated on Ti from aqueous solution. Dodecyl phosphate and dodecyltrichlorosilane SAMs were also coated on Ti using solution-phase deposition. The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au, and its stability was also investigated under similar conditions. In TBS, a significant proportion of phosphonic acid or phosphate molecules were desorbed from the Ti surface within 1 day, while the trichlorosilane SAM on Ti or thiol SAM on Au was stable for up to 7 days under similar conditions. The stability of hydroxyl-terminated phosphonic acid SAM coated Ti and thiol SAM coated Au was investigated in ambient air and ultraviolet (UV) light. In ambient air, the phosphonic acid SAM on Ti was stable for up to 14 days, while the thiol SAM on Au was not stable for 1 day. Under UV-radiation exposure, the alkyl chains of the phosphonic acid SAM were decomposed, leaving only the phosphonate groups on the Ti surface after 12 h. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied by oxidation of thiolates.
Mani
Gopinath
G
Department of Biomedical Engineering, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA.
Johnson
Dave M
DM
Marton
Denes
D
Dougherty
Victoria L
VL
Feldman
Marc D
MD
Patel
Devang
D
Ayon
Arturo A
AA
Agrawal
C Mauli
CM
D002021:Buffers; D006046:Gold / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D013057:Spectrum Analysis; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D002021:Buffers; D014867:Water; D006046:Gold; D014025:Titanium