CAN Spectroscopy – the physics behind it
Venneos' CAN (Cell Adhesion Noise) Spectroscopy brings cell-based assays to the next level: Label-free and non-invasive readout, analysis on a single cell level and a broad spectrum of detectable and distinguishable cellular effects. Venneos' silicon-chip-based imaging-system CAN-Q detects electrical cell properties. The acquired information is then converted into an intuitive microscopy-like image. Let's have a more detailed look at the physics behind the measurement principle.
If a cell attaches to any kind of surface, a tiny gap in the range of 10 to 100 nanometers remains between substrate and cell membrane due to repulsive forces between membrane polymers and substrate surface. Venneos makes use of this natural effect: If a cell attaches to the Venneos chip, the mentioned gap remains filled with the surrounding culture media, which has an electrically conductive property. As the gap is very thin, it is characterized by a high electric resistance. According to Nyquist or - more general - to the fluctuation-dissipation-theorem, every resistor is an intrinsic source for voltage fluctuations.
The core of the Venneos' system is a silicon-chip, on which cells are cultivated for measurement. On the chip's sensitive area, nearly 100,000 electrolyte-oxide-metal-oxide-semiconductor field-effect transistors ('EO-MOSFETs' or 'measuring pixels') are integrated. Each measuring pixel is 6.5 µm in size and sensitive to changes in the local electrical field on the chips surface, thus it detects the mentioned voltage fluctuations. So, if a cell covers a measuring pixel, the pixel detects these voltage fluctuations. Thus the mere adhesion of a cell leads to a detectable signal, and even a partial coverage of a measuring pixel leads to a weaker, yet detectable signal. Consequently, the strength of the voltage fluctuations can be used as the initial measurement readout.
For visualization, the strength of the voltage fluctuations is calculated for each measuring pixel and then translated into the color code. When all measuring pixels of the chip are read out and the color-translation is applied, a microscopy-like image is generated. The figure below compares conventional fluorescence microcopy (right) to CAN Spectroscopy (left): human dermal fibroblasts were cultured on the silicon-chip, stained with a cytosolic dye (calcein) and imaged with a fluorescence microscope. An electrical image with CAN Spectroscopy was simultaneously acquired. Both images – the optical and electrical – correlate.
Several electrical, CAN Spectroscopy-based images can be acquired within minutes on the Venneos system. Measurements can be performed continuously over days and up to weeks. Stacking single images to a video, phenotypic cellular behavior such as migration, proliferation, cell death and others can be monitored. Thereby the analysis can be performed on a single cell level, providing new insights into cellular heterogeneity. CAN Spectroscopy detects every cell attached to the sensitive area, thus the minimum required cell count is low compared to other technologies.
Moreover, cell parameters such as the distance between cell and chip surface, membrane properties such as membrane capacity and membrane resistance; and cytosolic changes, can be extracted from the characteristics of the readout. All these parameters are equally detected on single cell level and can be correlated with phenotypic cellular behavior to open up a large spectrum of new cell-based assays.
This information-rich readout, in combination with the minimal required cell count, makes CAN Spectroscopy the perfect tool for investigating highly valuable cells such as primary cells or stem cells.