Swelling Effect Observation of the Copper Phthalocyanine Layer on QCM and Its Effect on Surface Roughness and Morphology Changes

Copper Phthalocyanine (CuPc) is one material often used for the active layer on Quartz Crystal Microbalance (QCM) sensor. One important mechanism which can shorten the recovery time in the sensor is the swelling effect. The swelling effect is studied by observing the morphology of the layer and subsequent changes in QCM frequency during surface contact with three kinds of solution. The solutions used in this study were distilled water, phosphate-buffered saline (PBS) and Tris-HCl. The results of frequency measurements indicate a swelling effect which was shown by the decrease of the frequency change after the injection process. The most significant change in frequency occurs in PBS solutions. This change occurs as PBS has a higher molecular weight and ionic strength than distilled water and Tris-HCl. SEM results show that the swelling of the CuPc layer changes the microstructure layer. A decrease in the roughness of the CuPc layer was also observed due to the presence of buffer solution molecules that diffuse through the layer. Upon diffusion of the solution molecules into the CuPc layer, a continuous decrease in the QCM frequency occurs. Further, the diffusion caused the CuPc microstructure to become more tenuous.