Many biosensor applications are based on
streptavidin (SA) binding to partially biotinylated self-assembled
thiol monolayers (
SAMs). In our study, binary
SAMs on
gold were prepared from solutions containing 16-mercapto-1-hexadecanol (
thiol I) and N-(8-biotinyl-3,6-dioxa-octanamidyl)-16-mercaptohexadecanamide (
thiol II) in varying component ratios. Either
chloroform or
ethanol was used as
solvent. After 24 h
thiol incubation, SA was immobilized on the resulting
SAMs using the strong SA-
biotin interaction. The SA binding process was monitored by QCM-D (
quartz crystal microbalance monitoring dissipation factor). It is shown that the Sauerbrey equation is valid to calculate the mass quantities of the immobilized SA layers. Under the chosen incubation conditions, marginal fractions of the biotinylated component II in
chloroform ((n(I)/n(II))(
solution) approximately = 1000) lead to
SAMs which ensure a maximal SA binding quantity of m(Sauerbrey SA) approximately = 400 ng x cm(-2), being equivalent to a SA single-layer arrangement on the SAM surface. In case of incubations from ethanolic solutions, a complete SA layer formation needs significantly higher amounts of the biotinylated component II during SAM preparation ((n(I)/n(II))(
solution) approximately = 50). X-ray photoelectron spectroscopy data show that the fraction of biotinylated
thiol II in the SAM determines the amount of surface-bound SA. The SAM
thiol ratio ((n(I)/n(II))(SAM)) not only depends on the corresponding component ratio in the incubation
solution, but is also strongly influenced by the
solvent. Using
chloroform as
solvent during SAM preparation significantly increased the fraction of biotinylated
thiol II in the
SAMs compared to
ethanol.