QPatch II – Temperature control
QPatch II temperature control is designed to allow for accurate and rapid control of temperature within a range from 10-42°C with a precision of ±0.5°C.
Below read more about the design, accuracy, precision, software and data storage.
If you are more interested in the biological application, go to the product site here.
Concept and design
Temperature measurement and feedback are taken directly from the bed-of-nails (BON) beneath measurement sites.
Temperature regulation is performed using circulating water in the BON. It has not been an easy engineering task to integrate liquid flow in the BON; however, a lot of testing has proven that temperature control must be performed very close to the measurement sites to ensure precise control with minimum fluctuations. If not, laboratory and cabinet temperature will influence the accuracy significantly.
For example, controlling cabinet temperature did not meet our user requirements of ±0.5°C precision.
To decrease time to equilibrium, the manifold base plate is also thermostated with water from the same reservoir ensuring that the manifold has the same temperature as the BON.
Data is registered and stored in the Oracle database together with electrophysiology data. Temperature data is thus readily available for analysis after a run.
Heat transfer and insulation
To design an efficient temperature control, heat must be efficiently transported from BON to QPlate, but at the same time, influence from the surroundings must be avoided. Therefore the design is a sandwich construction of different materials.
In the upper part of the BON, aluminium, with high heat capacity, ensures efficient heat transfer from the liquid through BON to QPlate.
PVC, with a low heat capacity, in the lower part of the BON to insolate from heat generated by amplifiers and the internal part of the QPatch.
Water and electronics
“Why have you decided using water?”, is a question we have received several times, and yes, electronics is, in general, sensitive to water, so why not choose another solution.
Water is an efficient heat conductor, and the method has been proven a solid solution on the Qube 384 temperature control for the past 3 years. The liquid flow gives us the best possible solution to regulate temperature very close to the measurement sites, which must control the temperature with reasonable accuracy.
The solution is ISO-certified for electrical safety by the way.
Accuracy and precision
The design allows for a very stable BON temperature with a temperature span of as little as ±0.1°C and uniformity across the QPlate of ±0.2°C (at 10-30°C) and ±0.4°C at temperatures above 30°C.
Accuracy is ±0.5°C from the target temperature for all sites. This is due to an excellent heat coupling between BON and QPlate, with a coupling efficiency of 0.93.
The QPlate stabilizes temperature within 2 min and is thus well equilibrated after priming has been done.
When QPlate has equilibrated, variation in temperature over time is low. The feedback loop on the Julabo has been adjusted, so the QPlate temperature fluctuations over time are ±0.1°C and thus negligible.
We have tested instrument-to-instrument variation, which can be key when having multiple instruments on the same or several sites. The largest difference we could find between instruments (QPatch II 16 and QPatch II 48) was ±0.25°C which is within user requirement specifications and does not affect pharmacology data as seen in the figure below.
Compounds and equilibration
What happens when a compound, which is currently not temperature-equilibrated, enters the QPlate?
First of all, the compound volume is very low on QPatch II. Normally 5-10 μL is transferred, so even if compound trays were equilibrated, the heating from the pipettes would affect compounds during transfer. To ensure full equilibrium, we would have to control the full liquid transfer chain’s temperature, including pipettes. At this point, we have chosen not to, since compounds obtain equilibrium within 20 seconds after addition.
This was tested using open-hole plates and resistance to measure temperature (since resistance is lower at higher temperatures).
For high and low temperatures (15 and 35°C) it took 15-25 seconds for “compounds” (in this case EC solution) to equilibrate. At 25°C, no effect was seen since the cabinet temperature of the QPatch is approximately 25°C and thus also the compounds (or EC solution).
For voltage-gated channels, compound temperature equilibrium is not a concern. You can just set up the assay to wait 20 seconds. However, when interested in the initial response for ligand-gated channels, you should bear this in mind.
If requested, we will introduce a thermostated compound plate holder. Let us know it this is something you would want.
Software and usability
The QPatch II software is designed to support an efficient laboratory workflow.
The small thing that makes life easier. When starting an assay, the software will tell you when the system has reached the target temperature. If the temperature has not reached the target when hitting ‘start’, you can choose between:
- Start immediately
- Start when the temperature is reached.
By selecting “start when target temperature has been reached” you can save time by not having to return to your QPatch again to check whether target temperature has been reached.
A brief overview of other functionalities:
- Select the default start of temperature control at QPatch startup
- Select default temperature
- Toggle between °C and °F
- View current temperature
- View target temperature
- View time to target temperature has been reached.