RESI
Resonance Enhanced Surface Impedance (RESI)
The core of Layerlab RESI-technology based instrument z-LAB is the micro-fabricated dual electrode z-LAB Sensors. An electrical field is exited by applying an AC voltage over the electrodes giving rise to a current and the impedance is measured as the ratio between the AC voltage and the AC current. The electrode array with a total area about one square millimetre is situated in a micro fluidic
channel. A computer controlled fluidic system ensures a precise and steady flow of sample to the active site. The small size of the electrodes and channels, and the flow control enable measurements using small sample volumes.
Illustration of z-LAB Sensor (ZC-ID-10) with interdigitated electrodes and enclosed micro fluidic channel
Instrument output
The instrument records and presents in real-time the impedance as the interfacial capacitance, CI and interfacial resistance, RI reflecting the charging of and the charge-transfer across the electrode-electrolyte interface respectively. Also the solution resistance RS contributes to the impedance, however this contribution is usually weak.
The electrode surfaces may be prepared with different surface chemistries
depending on the assay by injections directly into the integrated fluidic system.
What is detected?
Upon binding of proteins or other bio-
molecules to the electrode interface water molecules and electrolyte ions become displaced from the surface leading to a change in capacitance and resistance. The more biomolecules that bind, the more water molecules and ions are displaced and a larger impedance response can be seen. The response is also dependent on the structural state of the bound molecules. Dense proteins and films induce larger responses than loosely packed structures.