Lower yields and poorer quality of biopharmaceutical products result from cell death in bioreactors. Such cell death is commonly associated with programmed cell death or apoptosis. During apoptosis, caspases are activated and cause a cascade of events that eventually lead to cell destruction. We report on an impedance spectroscopy measurement technique for the detection of total caspase-9 in buffer and complex fluids, such as cell culture media. Enhanced sensitivity is achieved by leveraging the physiochemical properties of zinc oxide and copper oxide at the electrode-solution interface. Characterisation of the biosensor surface was performed using scanning electron microscopy and indirectly using an enzyme-linked immunosorbent assay. The characteristic biomolecular interactions between the target analyte and specific capture probe of the biosensor are quantified using non-faradaic electrical impedance spectroscopy (nfEIS). The proof-of-concept biosensor demonstrated a detection limit of 0.07 U/mL (0.032 µM) in buffer. The sensor requires a low sample volume of 50 μL without the need for sample dilution facilitating rapid analysis. Using a luminescence-based assay, the presence of active caspase-9 was detected in the culture media following exposure to a pro-apoptotic agent. We envision that the caspase-9 biosensor will be useful as a cell stress screening device for apoptosis monitoring.
Keywords: Apoptosis; Caspase-9; Copper oxide; Electrical impedance spectroscopy; Immunosensor; Zinc oxide.
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