pH sensitivity of Si--C linked organic monolayers on crystalline silicon surfaces.
The electrochemical behavior of Si--C linked organic monolayers is studied in electrolyte-insulator-Si devices, under conditions normally encountered in potentiometric biosensors, to gain fundamental knowledge on the behavior of such Si electrodes under practical conditions. This is done via titration experiments, Mott-Schottky data analysis, and data fitting using a site-binding model. The results are compared with those of native SiO(2) layers and native SiO(2) layers modified with hexamethyldisilazane. All samples display pH sensitivity. The number of Si--OH groups on the alkylated samples is calculated to be less than 0.7 % of that of a pure SiO(2) insulator, which still causes a pH sensitivity of approximately 25 mV per pH unit in the pH range: 4-7. The alkylated samples hardly suffer from response changes during up- and down-going titrations, which indicates that very little oxide is additionally formed during the measurements. The pK(a) values of all samples with monolayers (4.0-4.4) are lower than that of native SiO(2) (6.0). The long-term drift (of approximately 1 mV h(-1)) is moderate. The results indicate that biosensors composed of alkylated Si substrates are feasible if a cross-sensitivity towards pH in the sensor signal is taken into account.
Faber
Erik J
EJ
BIOS, Lab-on-a-Chip Group, MESA+ Research Institute, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands.
Sparreboom
Wouter
W
Groeneveld
Wilrike
W
de Smet
Louis C P M
LC
Bomer
Johan
J
Olthuis
Wouter
W
Zuilhof
Han
H
Sudhölter
Ernst J R
EJ
Bergveld
Piet
P
van den Berg
Albert
A