Objectives. The objective of this study is to develop a sensor that uses the principles of cantilever mechanics and electrochemical impedance spectroscopy (EIS) for detecting a biological analyte, and to subsequently release it through cantilever resonance vibration. The ‘de-binding' technique can be used as a confirmation step, or to regenerate the sensing surface. The model analytes used in this study to demonstrate the principles are: Protein G and E. coli O157:H7.
Methods. Piezoelectrically-excited cantilevers were designed with a sputtered gold electrode to facilitate impedance spectroscopy measurements at the cantilever surface. Impedance spectroscopy was used in tandem with classic dynamic cantilever resonance for detecting target analyte; the measured resistance to charge transfer from the electrode to ferricyanide in solution, and cantilever resonant frequency served as the measured signals of the two techniques, respectively. All resonant frequency and EIS measurements were conducted within a specially-designed flow cell, which incorporated a reference electrode, platinum counter electrode, and the sensor gold surface as a working electrode. After Protein G or E. coli O157:H7 were attached to the sensor surface, the applied excitation potential which induces vibration due to the bonded piezoelectric material to the glass cantilever, was increased until the surface acceleration was sufficient to release the target analytes. Finite element modeling was employed to evaluate the relative surface accelerations for various dynamic modes present in liquid.
Results. The immobilized Protein G or E. coli cells were removed from the sensor electrode when the excitation potential was increased from 100 mV to 10 V, with the assistance of a negative DC potential applied to the electrode. The resistance to charge transfer decreased by ~ 40% when the 10V excitation potential was applied to a sensor saturated with Protein G with the assistance of a -700 mV DC potential applied to the electrode. Little to no removal of analyte was observed with the DC potential alone. The signal returned to its original value when the surface was exposed to fresh Protein G, indicating regeneration of the sensing surface.
Conclusion. . The vibration of the piezoelectric sensor triggered release of the physisorbed Protein G and antibody-bound E. coli with the assistance of electrostatic repulsion. The vibration-induced release approach is useful for repeated sensing requirement applications, and can be used to separate dilute analytes from complex matrix. We show in this study that sensor surface can be regenerated.