FAQ
Contents
- What is the difference between RESI-technology and other surface analysis measurements like SPR and QCM-D?
- What is the difference between RESI-technology and traditional impedance measurements like cyclic voltametry and impedance spectroscopy?
- What effects the surface start capacitance and resistance?
- Why is it so important to measure the sensor surface impedance response?
- Can mass be determined as an indirect value for some applications?
- What are the benefits of measuring at several low frequencies simultaneously?
- What is the sensitivity of the z-LAB instrument?
- What is the time resolution?
- What is the frequency range of the z-LAB instrument?
- What coatings/surfaces can be used?
- What is the detection range from the surface?
- What is the temperature range of the z-LAB instruments?
- How many times can the sensor surface be reused?
- What sample volumes are needed?
- What fluids can I use?
What is the difference between RESI-technology and other surface analysis measurements like SPR and QCM-D ?
The z-LAB instruments is sensitive for changes in the sensor surface electrochemical properties, which can differ regardless of the amount of adsorbed mass. Both the acoustic QCM-D and optical SPR system measure the amount of adsorbed mass on the surface. SPR systems are favoured for compact and dense layers while QCM-D provides parameters for both adsorbed mass as viscous properties. However, for changes in i.e., surface charge, structural changes or molecular interaction the RESI-technology can provide new insights beyond mass determination data.
What is the difference between RESI-technology and traditional impedance measurements like cyclic voltametry and impedance spectroscopy?
The RESI-technology provides real-time monitoring of impedance changes as described as the change in Capacitance and Resistance over the sensor surface. An integrated fluidic system allows for low target consumption and the potentiostatic system allows for control of the surface potential. Furthermore, all data can be modelled in e.g. Microsoft Excel.
What effects the surface start capacitance and resistance?
The insulating properties of the surface chemistry applied to the z-LAB Sensor will have an great impact on the start values, which it renders it to become a qualitative control of the applied chemistry. A sensor surface coated with an organized thiol will start of at a low capacitance, thus the overall response to changes will be smaller than for a more transparent surface chemistry. Although the ”noise to signal ratio is minimized on surfaces with lower capacitance.
Which surface chemistry to use and depend on the focus of your experiment and has to be considered in regard to what kind of sensor surface are being used in the set-up.
Why is it so important to measure the sensor surface impedance response?
The result alone that something adsorb or not, or to a certain degree does not cover the whole ”truth” about surface science procedures. The same amount of adsorbed mass can take on widely different structural properties, that is detectable using the RESI-technology. Detection of small and charged molecules is also difficult to monitor using traditional mass sensitive techniques, but they have a great influence on the surface impedance response.
Can mass be determined as an indirect value for some applications?
The build-up of highly controlled gold nanoparticle structured surfaces and sequential adsorption to adsorption of protein to the surface allows for modelling where the number of proteins adsorb to each particle can be estimated.
What are the benefits of measuring at several low frequencies simultaneously?
The band-pass filter used for RESI-technology allows for the monitoring of a resonance top, and the predicted change in positioning allows for a very fast sample rate and optimization to reduce signal-to-noise disturbances.
What is the sensitivity of the z-LAB instrument?
The sensitivity is very dependent on the choice of sensor surface and the insulating properties of the surface chemistry. For well organized surfaces changes down to 1 pF/cm2 has been detected.
What is the time resolution?
The time between measurements can be regulated dependent on the quality of the resonance top. A decreased polygram and number of measurement points increase the time resolution, but simultaneously increases the signal-to-noise ratio. For a ”perfect” top about 15 measurement points/min is recommended.
What is the frequency range of the z-LAB instrument?
The frequency range is 300 – 10000 Hz for the current set-up.
What coatings/surfaces can be used?
The sensor crystal can be coated with material which can be applied as a thin homogeneous layer firmly attached to the underlying surface. Layer thickness is depending on the insulating properties. Layerlab offers precoated sensor surfaces with for example hydroxyapatite and gold nanoparticle structured surfaces.
What is the detection range from the surface?
The detection range varies from nanometers to micrometers, depending on the dielectric properties of the applied film and ionic strength of the buffer.
What is the temperature range of the z-LAB instruments?
Proper temperature stabilization and function of the chamber can be obtained at temperatures between 20-40ºC in normal room temperature. Buffers should be well degassed to prevent air bubbles.
How many times can the sensor surface be reused?
Repeated use of sensor surfaces is depending on application and possibility to clean. For certain applications a standard surface can be used only once.
What sample volumes are needed?
Minimal injection volume is recommended to be at least half of the loop volume. In the Start Kit for the z-LAB instrument a 200 ul Loop is included, but loops with other volumes is sold via Layerlab on request.
What fluids can I use?
Impedance measurement with the z-LAB instrument is focused on changes in the double layer capacitance and hence the measurement fluid must contain some salt.