PDMS biofunctionalization study for the development of a microfluidic device: Application to salivary cortisol

This paper presents the study of the PDMS (poly(dimethylsiloxane)) surface functionalization for the development of a microfluidic immunosensor that quantitatively analyss salivary cortisol by optical detection. The functionalization was performed using different antibodies immobilization methods on PDMS surface: (a) immobilization by passive adsorption on pristine PDMS; (b) silanization of PDMS surface with (3-aminopropyl)-triethoxysilane (APTES) to generate amino groups and posterior covalent immobilization of antibodies on APTES-PDMS using cross-linker glutaraldehyde (GA); (c) coating the PDMS surface with BSA to block nonspecific protein adsorption, and then covalent bond of the protein A via GA. In this last approach, the antibodies were covalently immobilized to protein A due to its high affinity with the constant fraction (Fc) region of the antibodies. Atomic force microscope (AFM) and spectrophotometric analysis demonstrated that the immobilization method using protein A is more efficient since a higher roughness and uniformity on the PDMS surface and higher absorbance signals were obtained.