Optimizing blocking of nonspecific bacterial attachment to impedimetric biosensors

We evaluated the capacity for a variety of commonly used, low and high-molecular weight blocking agents to prevent nonspecific binding of Staphylococcus aureus and Staphylococcus intermedius to impedimetric gold electrodes. The blocking agents tested here were mercaptoundecanol (MCU), polyethylene glycol (PEG, MW≈1kDa or 5kDa), bovine serum albumin (BSA), and chicken serum albumin (CSA). The surfactant Tween 20 was applied additionally in some conditions. BSA and MCU in combination with Tween 20 were found to yield the greatest blocking capacities, whereas 5kPEG was found to actually enhance S. intermedius attachment. Although genetically and physiologically similar, S. intermedius and S. aureus differed significantly in their capacity to attach to the gold substrate. Monitoring of gold functionalization kinetics in real-time via impedance spectroscopy indicated that surface functionalization occurred within a few minutes of gold exposure to a given blocking agent. Higher impedance changes were observed with lower molecular weight blocking agents, likely due to denser molecular packing on the gold substrate. Careful optimization of blocking agent with respect to chemical properties, molecular size and potential interactions is recommended.