A novel scanning microwave microscope for investigating living cells at the nanometric scale.

We present a novel near-field scanning microwave microscope (SMM) capable of providing surface impedance measurements of samples with nanometric resolution. The instrument is the integration of a microwave Vector Network Analyzer (VNA) and a scanning probe microscope (AFM/STM). A key point is that our software, controlling and synchronizing both the instruments, creates simultaneously images of the sample at several frequency points. This can be used to extract several features of the sample depending on the frequency. Moreover, close frequencies show the same features, added to random noise. Exploiting this redundancy of information, we have achieved remarkable results. We have been working on the optimization of this system for biological applications, to detect functional characteristics of cells generating a variation of their dielectric properties. This instrument offers the possibility of performing local impedance measurements on a single live cell and, if correctly calibrated, it provides also quantitative information (e.g. absolute measurements of membrane permittivity). The system was demonstrated to work on Saccharomyces Cerevisiae. A better model for a full test of the potentialities of the new technique is given by excitable cells, characterized by a greater variability of dielectric properties. A challenging objective could be directly imaging ion channels.