Highly sensitive bio-field-effect transistor (bioFET) molecular sensors require optimized gate dielectrics for an efficient surface charge modulation of the semiconductor channel. Hafnium oxide has a dielectric constant at least four times greater than conventional SiO2 gate dielectrics, increasing the potential bioFET sensitivity and permitting the use of a thicker dielectric layer to better protect the semiconductor surface. In this study, we demonstrate the stability of the capacitance response of atomic-layer-deposited HfO2 dielectrics in aqueous electrolytes. We also verify the possibility of biotin functionalization of HfO2 using photoelectron spectroscopy, capacitance-voltage analysis, and molecular atomic force microscopy imaging methods.