Specific immobilization of electropolymerized polypyrrole thin films onto interdigitated microsensor electrode arrays

Abstract

Electroactive polypyrrole (PPy) thin films were known by potentiostatic electropolymerization at chemically derivatized interdigitated microsensor electrodes (IMEs) of gold on borosilicate glass leading to specific adhesion of the electroconductive polymer film to the device. Films were grown to a constant electropolymerization charge density of 70 mC/cm 2 at 0.65 V us Ag 0 /AgCl, 3 M Cl - from 1.0 M aqueous pyrrole solutions containing 2.5 mM poly(styrenesulfonic acid) (PSSA) and 2.5 mM dodecylbenzynesulfonate with the pH adjusted to 3.0 and the temperature maintained at 20 o C. The interdigit space of the IME devices was chemically derivatized by chemical modification with (3-aminopropyl)trimethoxysilane followed by direct linking of the primary amine to the carboxylic acid of 3-(1-pyrrolyl)propionic acid using the heterobifunctional linker 1,3-diisopropylcarbodiimide enhanced with N-hydroxysulfosuccinimide in aqueous solution. XPS evidence supports the immobilization of ω-(1-pyrrolyl) moieties to the device surface. The 3-(1-pyrrolyl)propionic acid was shown to be electroactive, electropolymerizable, and co-electropolymerizable with pyrrole monomer from aqueous solution. Electroconductive PPy films grown on these ω-(1-pyrrolyl) derivatized IME devices were allowed to bridge the interdigit space and so pyrrole monomer was co-electropolymerized with ω-(1-pyrrolyl) moieties specifically attached to the interdigit space of the device. This leads to specific adhesion of the PPy thin film to the device surface. Films grown in this way were compared to films similarly known on unmodified devices, on IME devices rendered hydrophobic by chemical modification with dodecyltrichlorosilane, and on devices modified with (3-aminopropyl)trimethoxysilane. Cyclic voltammetry revealed no significant difference in the electroactivity of PPy films grown on these various IME surfaces. Films were also characterized by the time to adhesive failure using the adhesive tape test following immersion in PBKCl 7.2 buffer or after being maintained dry under vacuum and over desiccating molecular sieves. The time to adhesive failure in both test environments occurred in the order unmodified < dodecyltrichlorosilane modified « (3-aminopropyl)trimethoxysilane modified « ω-(1-pyrrolyl) derivatized. The failure times were 3 days < 5 days « 27 days « 235+ days for films immersed in aqueous buffer and were 3 days < 36+days « 235+ days « 235+ days for films stored dry under vacuum. The electrochemical and adhesion test evidence suggest that the PPy films are specifically immobilized to the ω-(1-pyrrolyl) derivatized IME devices and that this negates the hydrolytic instability of the PPy/glass interface that leads to poor adhesion under physiologic conditions