Introduction: Objective Heater

In microscopy, it is sometimes necessary to have a stable temperature while taking data. If you are using an oil immersion objective, then the thermal contact of the objective to the oil and the oil to your slide can cause temperature gradients in your sample. This is not a very good scenario for some experiments as is the case for the ones I do. One can stabilize the temperature of a sample by stabilizing the temperature of the objective or, by trying to stabilize the temperature of the room that your microscope is in. While the latter is not very ideal, a stabilized temperature controller that heats up an objective is doable.

As with most things in the world of science, a complete out of the box solution comes at a premium. This Instructable shows how I assembled a temperature controller for our objective with relatively cost effective parts. Another description for how I made this setup can be found in my Open Notebook Science Dissertation.

This build relies heavily on the work done by:

Mahamdeh, M., & Schäffer, E. (2009). Optical tweezers with millikelvin precision of temperature-controlled objectives and base-pair resolution. Optics Express, 17(19), 17190. doi: 10.1364/OE.17.017190.

Update 1-20-11:
As was suggested in the comments below, I'd like to add in this step how my interactions went with using TeTech during this build. As any scientist/researcher will know, companies that sell scientific equipment can be difficult to deal with at times. This was not the case when I was dealing with the customer support with TeTech. They were always informative and responsive and were willing to lend advice when ever I spoke to them or asked questions. They are by far one of my all star companies that I actually enjoy dealing with and would greatly recommend purchasing items from them to anyone.

Update 6-11-2011:
If you would like to site this build in a publication, you can use the following citation

Maloney A, Herskowitz LJ, & Koch SJ (2011) Effects of Surface Passivation on Gliding Motility Assays. PLoS ONE, 6(6): e19522. doi: 10.1371/journal.pone.0019522.

Step 1: Materials & Tools


1x Polyimide Film Heater Kit (Omega KH-KIT-EFH-15001). I personally like the kit version mainly because there is a ton of things you can make with the other heating elements and it is not that much more expensive to get the kit.
1x Copper tape. I used copper tape since it was what I had lying around. However, you can also use aluminum tape as this is what is recommended by TeTech to use with their thermistors.
1x Power supply (TeTech PS-12-8.4). I have never had a problem using MeanWell power supplies and I rather do like their ease of use.
1x Thermal spacer (Bioptechs RMS - 152019R). This part is with out a doubt the most expensive component for this build. Especially since it is nothing more than a piece of ABS plastic with RMS threads on it.
1x Temperature controller (TeTech TC-48-20).
2x 15kΩ thermistors from TeTech (MP-2444 and MP-2996).
1x Bud Industries aluminum box (AC-403) and bottom plate (BPA-1591).
2 LEDs (Yellow and Green). Any will work. I didn't use these exact ones but I wanted to include a link.
2 switches. I used one toggle switch and one rocker switch.
1x Bumpers
2x Black Banana Jack
2x Black Banana Plug
2x Yellow Banana Jack
2x Yellow Banana Plug
2x Orange Banana Jack
2x Orange Banana Plug
2x Blue Banana Jack
2x Blue Banana Plug
1x Green Banana Jack
1x Green Alligator Clip
1x Red Banana Jack
1x Red Alligator Clip


Hand punch
Deburring tool
Soldering iron

Step 2: Enclosing the Power Supply

The Meanwell power supply is shielded but, it does have exposed terminal on it. To prevent anyone from touching the exposed terminals on the power supply, I'd recommend that it always go into some sort of enclosure. I like aluminum boxes since they are easy to work with and one can make holes in them very easily.

I should point out that you will be using power from the wall. This means that you can seriously injure yourself. So, if you don't feel comfortable doing something like this, stop.

Figure 1:
The first thing I did was to lay the power supply on the bottom cover and draw a line around the power supply. This allowed me to mark where the holes needed to be in order to mount the power supply to the plate. I found the hole placements from the spec sheet for the power supply.

Figure 2:
Once I found the hole placements, I used the hole punch to punch slightly larger holes than what are used for #4 screws. The magic of washers fill in the gaps. I suppose if you know for certain that the power supply will not be moving around too much, then you can use double stick tape to attach it to the plate. I'm not that trusting of myself so I made sure to screw it into place. I also added the bumpers to the bottom plate.

Figure 3 - 6:
The wiring is pretty straight forward. The live wire connects to the rocker switch, the neutral to N and the ground to the ground symbol on the power supply. The other end of the rocker switch then gets connected to the L for live on the power supply. I connected a green LED to the COM and +12V to indicate that the power supply is on. If the LED you are using doesn't have a current limiting resistor, make sure to add one. I also grounded the box by attaching the ground of the power supply to the box itself. One should probably also add a fuse to this setup as well.

Figure 7:
The output of the power supply is then connected to a DPST switch. One pole of the switch turns on the LED and the other pole sends current and voltage to the banana connectors.

Step 3: Temperature Controller

The temperature controller comes in two different flavors. One with an on screen LED indicator and on OEM version. I have used both and I do like both.

Figure 1:
The LED version again comes with a hook up panel that leaves exposed wiring. I'm  not a big fan of this so I made a breakout box with banana connectors. Banana connectors in a lab setting are spectacular. They are easy to remove and they are easy to add to existing equipment and make wires for so they are my connector of choice when dealing with wiring things.

Figure 2:
Using the supplied manual, I wired up the RS232, both thermistors, and power in and out of the box.

Step 4: Thermistors

Figure 1:
The first thing I did was add the ABS plastic piece to the objective turret. I then put the larger of the thermistors on the base of the objective and taped it using the copper tape. I then added the flexible heater to the objective by placing it directly above the thermistor. This is the control thermistor and it is used to talk to the temperature controller and tell it if it needs to heat up or not.

Figure 2:
I then mixed up some of the thermal epoxy. I placed the small thermistor on the top of the objective and made sure that its placement would not interfere with microscope slides. This is where the computer reads the temperature of the sample. Since the objective is thermally coupled to the oil used and the oil is thermally coupled to the slide, the top thermistor effectively reads the temperature of the slide. Isolation of the slide from the slide holder is also necessary and can be done with just about any thermally insulating material.

Since there is an increase in height when putting the objective on the ABS spacer, I had to increase the height of the sample stage by adding some spacers.

Step 5: Performance

Figure 1:
The performance of the temperature controller is spectacular. It can hold a stable temperature indefinitely within 0.1 degree Celsius. You can see from the below graph that there is an increase in temperature from room temperature to the set temperature. The system stabilizes the objective nicely until I add oil to the objective of which, the temperature drops and stabilizes quickly.

Figure 2:
For fun, I looked at how long it took for the objective to reach a "stable" temperature and how long it took for it to cool down. I did not put anything on the objective, i.e. no oil and no slide. I did remove the thermal spacer from the objective so that it was in direct contact with the objective turret.

The black line is the temperature of the top thermistor and the blue is an exponential fit to it. The red line is the temperature of the top thermistor after I turned off the mercury lamp. The dark green line is an exponential fit to the red curve.

As you can see, if one wants to take consistent data with no temperature control, you will have to wait about 5 hours till the objective reaches a "stable" temperature. This is unacceptable. Especially since one will have to wait even longer than the 5 hours for the objective to warm up in order for the slide to reach temperature once it is placed on the microscope.

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