Electrophoretic-deposited HAP nano-layer as a QCM-D sensor coating: effects of suspension concentration and electric-field strength

This study investigates the fabrication of hydroxyapatite (HAP) nano-coating on a gold–quartz crystal sensor used for quartz crystal microbalance with dissipation (QCM-D) measurement using an electrophoretic deposition technique. Surface morphology and thickness of the HAP coating are examined via scanning electron microscopy and nano-indention testing. Its repeatability is verified via QCM-D testing. Results show that electrophoretic deposition with ultrasonic treatment is feasible and cost-effective for fabricating nano-thick HAP coatings on a QCM-D gold–quartz crystal sensor surface. Both suspension concentration and electric-field strength influence the compactness of HAP coatings. There exists a non-linear relationship between HAP coating compactness and the suspension concentration/electric-field strength. When the HAP suspension concentration is 30 g/l and the applied electric-field strength is 150 V/cm, the HAP coating on the QCM-D gold–quartz crystal sensor surface is uniform and compact with a thickness of 35 nm and is tightly bonded to the sensor surface. The obtained HAP-coated sensor is thus suitable for QCM-D measurement