In this work a highly sensitive optical technique was used to study the adsorption of thin organic layers onto a gold film from water, in situ and in real-time. Optical excitation of a surface-plasmon resonance (SPR) was used to probe the gold/water interface. The use of an acousto-optic tunable filter then provides a differential technique for monitoring the SPR position in optical wavelength. This allows optical changes at the metal/liquid interface to be measured as the adsorption of thin organic layers occurs. Adsorption of a poly(ethylene glycol) monododecyl ether surfactant (C12E8) and a 30-mer DNA oligonucleotide with a mercaptohexyl group at the 5-phosphate end (DNA-SH) onto gold from water were examined. Conventional, angle-dependent reflectivity measurements taken on the same system provided complementary SPR data, allowing the sensitivity of the two techniques to be compared.

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