Detection of Viruses by Nanoscale Spm-Based Ac Impedance Spectroscopy
Sang-Yup Lee, Robert MacCuspie, and Hiroshi Matsui. Chemistry, City University of New York / Hunter College, 695 Park Ave., New York, NY 10021
Various types of scanning probe microscopies (SPMs) characterized physical properties of various biological molecules, however impedance studies have not been explored extensively yet. Impedance and capacitance are interesting properties for material analysis since they can be correlated with charges and dipoles of biological molecules. In our setup, when dielectric molecules are trapped between SPM tip and electrode, change of electric field and impedance (or capacitance) between the tip and the electrode is detected. For proof-of-principle, we examined gold, silica, and polystyrene nanoparticles and their size effects in impedance and capacitance were analyzed. For the model system for biological macromolecules such as cells, we studied various charged polystyrene nanoparticles to understand the correlation between surface charges on particles and impedances/capacitances. At last, we will present comparison of impedances among three viruses, SV-40, adenovirus-3, and HSV-2 and discuss the potential to apply this SPM-capacitance measurement as a detection/identification tool for viruses, bacteria, and cells. Application of SPM-based AC impedance spectroscopy in biosensing has a few advantages. First of all, high accuracy and reproducibility of measurement are expected because contact between target molecules and electrodes is not issue. Second, this technique can be applied to any conducting or insulating materials. In addition, this AC impedance-based technique is very practical since it can be operated in any environments while conductivity detection- based sensing is only allowed to measure in aqueous solution. Therefore, impedance measurement on biological macromolecules may be utilized to fingerprint the type of those molecules.