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Comparison CAN-Spectroscopy vs. Impedance Spectroscopy

Introduction

Impedance spectroscopy is method to study the activities of cells grown in culture. This technique was invented by Dr. Ivar Giaever (Nobel-Prize in Physics 1973) and Dr. Charles R. Kees.It has been applied to numerous investigations including measurements of the invasive nature of cancer cells, barrier function, toxicity testing and signal transduction.

Technical description

The principle of impedance spectroscopy is the following: Cells are cultured in a culture dish with embedded gold electrodes. When seeded, the cells attach to the electrodes where they act as insulators increasing the impedance. Then, a small alternating current (I) is applied across the electrode pattern, which results in an electric potential (V) across the electrodes which is taken an observable. The impedance of the cell layer is than obtained as Z = V/I.

As cells grow and cover the electrodes, the current is impeded in a manner related to the number of cells covering the electrode, the morphology of the cells, cell-cell contacts and the nature of the cell attachment. Thus, alteration in the cell amount due to proliferation or cell death or even morphological changes like swelling and shrinking for instance as a cellular reaction to a given compound, leads to a change in the obtained impedance. The provided data are impedance over time.

Users confirm four main advantages of impedance spectroscopy: 

  • Label-free: Impedance spectroscopy doesn’t require the usage of a label, thus cells can be analyzed in a very natural way. User don’t have to pick a specific label, but are sensitive to a broad variety of cell changes at the same time.
  • Sensitive to invisible cellular parameters: Impedance spectroscopy allows a measurement of several parameters like para- & transcellular resistance or adhesion potential, that are difficult to capture with other techniques.
  • Real time kinetics: Measurements can be performed continuously from hours up to days and weeks. In comparison to endpoint measurements, this is a big advantage, as kinetics become visible with one single measurement.
  • Direct quantification: The output of most impedance spectroscopic devices is a curve of impedance over time. In comparison to microscopy, there is no error prone and user depended quantification required.

Comparison

CAN-Spectroscopy and impedance spectroscopy have quite some things in common: Both methods are based on electrical cell measurements. CAN-Spectroscopy has all the advantages impedance spectroscopy has, but even goes beyond: 

  • Sensitive & specific: Whereas impedance spectroscopy is sensitive to a broad spectrum of cell changes, it remains a challenge to determine what behavior the cells were showing exactly. E.g. both, proliferation and cell swelling, lead to an increase of the impedance, thus it is difficult to separate between those two. Due to the spatial resolution (simplified, the ‘image’ or CAN-Map), effects like cell swelling and proliferation can easily be distinguished. In conventional impedance spectroscopy, parameters like adhesion potential or para-cellular resistance can only be provided for the whole cell ensemble. However, in many cases it is crucial to obtain those parameters on single cell level to correlate them with other cellular parameters.
  • Awareness for cell heterogeneity: A central challenge of biology is to understand how individual cells process information and respond to perturbations. As much of today’s knowledge is based on ensemble measurements, neglecting cell-to-cell differences within one population. CAN-Spectroscopy allows an analysis on single cell level, thus revealing cell heterogeneity.
  • Low cell consumption: As CAN-Spectroscopic experiments take information of every single cell into account, only a very small number of cells is required per experiment. Depending of the cell type, this might be only a few hundreds of cells.