Microwave electromagnetic properties of single bacterial cells measured for the first time

Image: how scanning microwave microscopy measures the electric permittivity of a biological object at the nanoscale

Having measured the low frequency (kHz) electric polarizability of DNA and of single bacterial cells in 2014 and of the main components of the cell membrane earlier this year, the Nanoscale Bioelectrical Characterization group has achieved this novel breakthrough by using a technique referred to as scanning microwave microscopy. With this technique a single cell or microorganism, in this case a bacterial cell, can be imaged by using microwaves similar to those used in mobile phone telecommunications or in the microwave ovens, from where the microwave electromagnetic properties can be quantified at the nanoscale with high accuracy and reproducibility.

“New advances in non-invasive medical imaging techniques for cancer diagnostics, therapeutic ablation techniques for cancer treatment and novel electrosurgical techniques are under development based on the use of microwaves and on the knowledge of the high frequency electromagnetic properties – the complex permittivity – of biological tissues,” explains Gabriel Gomila, who led the research. “Now, we have demonstrated the possibility to measure this key physical property also at the level of a single cell, thus providing a better understanding of the interaction of microwaves with biological entities and paving the way for novel medical applications of microwaves.”

The researchers quantified the electric permittivity of single Escherichia coli cells, showing too that their technique could detect the presence of small-scale structures even inside the microorganisms, providing endless applications in the label-free imaging of single bacterial cells at high spatial resolution, and more generally, in eukaryotic cells.

“Revealing the complex permittivity of single cells can provide unique information about their internal structure and biochemical composition, and of their state and phase,” says Gabriel. “It can also be used to design and implement label-free electrical techniques for counting, sizing, separating and identifying cells, thus opening even more avenues towards new and improved biological and medical applications.”

Maria Chiara Biagi, René Fábregas, Georg Gramse, Marc Van Der Hofstadt, Antonio Juárez, Ferry Kienberger, Laura Fumagalli and Gabriel Gomila (2015). “Nanoscale electric permittivity of single bacterial cells at GHz frequencies by scanning microwave microscopy”. ACS Nano, 10 (1), pp 280–288