Biocompatible pH sensor based on chitosan IPNs and polystyrene colloidal photonic crystal films

Our research involves the fabrication of a pH-sensitive Chitosan-Tetraethyl orthosilicate-Glutaraldehyde Interpenetrating Polymer Network (Chi-TEOS-GA IPN) suitable for combination with polystyrene (PS) colloidal photonic crystal films to produce a device capable of showing a visual color change in response to a change in pH. The pH-sensitive properties of chitosan occur naturally due to its cationic polyelectrolyte structure. Cross-linking chitosan with TEOS and GA increases mechanical strength and PS photonic crystal films provide the means of optical detection. Monodisperse PS particles with various sizes were synthesized by emulsion polymerization of a styrene monomer in the presence of sodium dodecyl sulfate (SDS) as a surfactant. The PS colloid suspension was vertically deposited onto the flexible silicon rubber sheet to make a PS photonic crystal film. The closely packed PS particles were infilled and cured multiple times with polydimethylsiloxane (PDMS) elastomer, which allows for reversible color change by elastic deformation. All Chi-TEOS-GA films were prepared by drop casting with constant experimental conditions such as temperature, substrate, and time. Chi-TEOS-GA films swelling studies show an increase in the size and weight of the films with decreasing pH. The PS photonic crystal films were put on top of the pH-sensitive films and enclosed in a solid frame to prevent swelling in unwanted directions. Investigation of spectrometry measurements shows a shift of the spectra to lower wavelengths with decreasing pH, resulting in a color change of the PS photonic crystal film. These results are discussed in terms of the potential use of this device in biomedical applications, such as wound dressings.