Lead magnesium niobate-lead titanate piezoelectric immunosensors

Lead magnesium niobate-lead titanate (PMN-PT) single crystals were prepared using a modified Bridgman method and then cut into thin sheets in an [0 0 1] orientation. The sheets have chemical composition of Pb0.995(Mg0.217Nb0.505Ti0.262)O3 and exhibit excellent ferroelectric and piezoelectric properties, in particular a high electromechanical coupling factor, providing a promising potential for the fabrication of thickness vibration mode (TVM) piezoelectric biosensors (PE-sensors). A free standing piezoelectric bio-detection platform was therefore constructed from these oriented sheets by coating gold thin films as electrodes on both sides of the sheet. The resultant platform had a resonance frequency of 4.875 MHz. An equivalent circuit was modelled to further identify the piezoelectric resonant peak. Protein A was immobilized to form a bridge between the gold electrode surface and goat immunoglobulin G (IgG) probe molecules for a PE-immunosensor. The target molecules, anti-goat IgG, were applied onto the electrode of the PE-sensor, leading to a resonance frequency shift due to the added mass. The constructed PE-sensor demonstrates excellent reproducibility, large dynamic range (0.1–10 μg/mL) and good sensitivity (6.72 ng/Hz).