Hybrid Quartz Crystal Microbalance (QCM) sensor for the detection of pH

RODRÍGUEZ SEGUÍ, S.A.; TEIXIDOR, F.; CRESPO, L.; SAMITIER, J.; ERRACHID, A.

Agadir

Workshop; International Workshop on Biosensors for Food Safety and Environmental Monitoring; 2005

niversity of Hassan II- Mohammedia

A gravimetric approach to a pH sensor is introduced based on gold quartz crystals functionalized with polypyrrole. We use the cobaltbis (dicarbollide) [3,3?-Co(1,2-C2B9H11)2]-anion as the doping agent for the solid contact PPy layer. The PPy material containing this anion has a number of advantages over that prepared with common dopant anions. The high volume and very low charge density of this anion prevents the dopant-anion exchange observed in alkaline media. Also, the high boron content of the film makes it highly hydrophobic, thus preventing OH- attack on the polymeric chain. The sensibility of the coated crystal to pH variations was analyzed through a wide range of pH values, using a Quartz Crystal Microbalance (QCM). Frequency variations correlated to pH changes were found. The resonant frequency raised while pH is reduced from 9.6, measured at the TRIS solution used, to 1.8, through middle values. pH variation was obtained by means of HCl adding to the TRIS solution. The polypyrrole coating was found to need treatment in order to became pH sensible again, since consecutive experiments with the same sensor coating yielded alterated response.