pH Sensitivity of SiC Linked Organic Monolayers on Crystalline Silicon Surfaces

Abstract

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.

Exclusive recognition of sarcosine in water and urine by a cavitand-functionalized silicon surface

“…Below pH 1, the XPS Br 3D signal retains a comparable intensity before and after water dipping, proving the Tiiii-Si•1 stability at that pH. The need to acidify the solution at very low pH to avoid guest decomplexation can be rationalized by recalling two surface effects: (i) the apparent pK a of surface groups (22), and in particular of surface bound amines (pK a ∼ 4) (23) are much lower than their intrinsic value in solution (pK a ∼ 10); (ii) guest deprotonation, decomplexation, and diffusion into the bulk solution are not balanced by the reverse reaction because the guest concentration in the solution resulting from surface decomplexation is negligible.…”

Controlled Oxidation, Biofunctionalization, and Patterning of Alkyl Monolayers on Silicon and Silicon Nitride Surfaces using Plasma Treatment

“…These high-quality alkyl monolayers, prepared by thermal or photochemical reaction of alkenes with hydrogen-terminated silicon surfaces, [23][24][25][26][27][28][29][30][31][32][33][34] have been studied for their high potential in sensing and nanotechnology *E-mail: Han.Zuilhof@wur.nl. applications, [35][36][37][38][39][40] due to the possibility to attach biomolecules directly onto the semiconductor surfaces. [41][42][43][44][45][46][47][48][49] Importantly, these densely packed monolayers possess a much higher stability than thiol monolayers on gold or alkylsiloxane monolayers on oxide surfaces, because of the formation of strong Si-C bonds, 24,26,50 which makes them more robust for applications in aqueous solutions.…”

Construction of Mono- and Multimolecular Layers with Electron Transfer Mediation Function and Catalytic Activity for Hydrogen Evolution on a Hydrogen-Terminated Si(111) Surface via Si−C Bond

“…For example, a monolayer with electron transfer function on Si is very important as far as the application for molecular devices, 10 sensors, 11 photoelectrochemistry, [12][13][14][15] bioelectrochemistry, 16 and electrocatalysis [13][14][15] are concerned. Organic monolayer can be formed on Si surface via direct Si-C bond utilizing thermal, [17][18][19][20][21][22][23] photochemical, 24,25 electrochemical, [26][27][28] or catalytic reaction 28,29 or reaction with radical initiators.…”