Pyrene-wired antibodies on highly oriented pyrolytic graphite as a label-free impedance biosensor for the sepsis biomarker procalcitonin

An antibody-based, label-free impedance biosensor for the sepsis biomarker procalcitonin (PCT) has been produced using highly oriented pyrolytic graphite (HOPG) as the sensor electrode material and with attachment of the PCT capture antibody via coupling to 1-pyrenebutanoic acid succinimidyl ester (PYSE) pre-immobilised on the electrode by π-π stacking. In an aqueous phosphate-buffered saline (PBS) at pH = 7.4, the charge-transfer resistance for the redox probe Ru(NH₃)₆ ^3+/2+ exhibited a linear dependence on the PCT concentration in the range 10 to 100 ng mL⁻¹ and provided a detection limit for PCT of 3.70 ng mL⁻¹. Also, over the same PCT concentration range, the electrode capacitance showed a steady decrease, offering the prospect of a capacitive sensing mode for the label-free device, possibly removing the need to add a redox species to the sample under test. These results demonstrate the feasibility of using pyrene-modified HOPG as a simple platform for label-free impedance biosensors, here for the important sepsis biomarker PCT.