Chlorosulfonation of polystyrene substrates for bioanalytical assays: distribution of activated groups at the surface

Abstract

In this work the activation of transparent PS substrates by chlorosulfonation is described and their distribution in the subsurface region is analyzed. For this purpose XPS, FTIR-ATR and colorimetry have been used. It is shown that the electrophilic aromatic substitution of polystyrene in pure chlorosulfonic acid is extremely quick with complete surface coverage by chlorosulfonic groups achieved after only a 10 minute reaction time at -10 °C. It is further demonstrated that the reaction is very surface selective and that even after reaction times as long as 3 hours, the modification is limited to a layer with a thickness of less than one micron. The activated PS substrates can be further functionalized in a second step with carboxylic groups. Due to the excellent optical transparency that the samples maintain upon modification, the modified systems were successfully probed for use in ELISA assays.

Modification of chlorosulfonated polystyrene substrates for bioanalytical applications

“…The absolute density of SO2Cl groups detected in the chlorosulfonated PS plates was 246 nmol cm -2 , which is consistent with previous studies [42][43][44] and corresponds to the number of reactive sites on the surface that can be modified. In the case of aminated surfaces, we compared three diamines with different chain length: ethylenediamine (C2), 1,3-diaminopropane (C3) and hexamethylenediamine (C6).…”

“…PS substrates can be easily chlorosulfonated by immersion of the polymeric material in a cold solution of pure chlorosulfonic acid [43]. The PS substrate is first immersed in a solution of chlorosulfonic acid at -10°C where the polymer suffers an electrophilic aromatic substitution (Scheme 1).…”

“…The substrates are washed afterwards in cold sulfuric acid and then in water. The final substrates are stable and can be stored in ambient conditions for months without losing their reactivity [42][43][44]. Chlorosulfonated PS substrates present high reactivity towards primary aliphatic amines.…”

“…This classical approach is capable of penetrating porous three-dimensional substrates and allows for in situ surface functionalization of microfluidic devices. It has recently been shown that PS substrates can be activated by a simple and economic wet-chemical treatment with chlorosulfonic acid at low temperatures providing surface selectivity with a tunable number of chlorosulfonic groups [42][43][44][45]. The chlorosulfonated species at the surface can be converted in a second step into a different functional group leading to the formation of specifically modified substrates under mild conditions.…”

Quantification of Variable Functional-Group Densities of Mixed-Silane Monolayers on Surfaces via a Dual-Mode Fluorescence and XPS Label

“…Besides a possible development of our system into a reference material, current work in our laboratories addresses other functional groups like epoxy and the integration of other analytical techniques like ToF-SIMS. The potential of the approach however is even more general and can be expanded to supports other than silica (e.g., polymer) and to surfaces other than for microarray applications (e.g., microfluidics). − …”