Testing Calorimeters

In order to design and create a working device, I must test a number of different variables that could affect its performance. My first series of tests works with the same template pictured in my previous post. I am currently testing both the reactiveness of the Heraus thermistor ink with the LTCC tape and the effectiveness of different coverings for the thermistor with 32 chips. To test the reactiveness of the thermistor ink, I pre-fired half of the samples before applying the ink to see whether it works better than co-firing the ink with the LTCC. After applying the ink, I applied an additional layer of LTCC tape to four pre-fired and four co-fired chips (Figure 1). In addition, I added an LTCC paste to four of each, and have yet to print layers of two different types of glass on the remaining eight chips of each type. 

Figure 1. LTCC Calorimeter covered with additional tape layer. 

Although this test seems to be relatively straight-forward test of two variables, I have already encountered my share of problems. During the initial electrode screen printing phase, I must have dropped a hair in the screen because a number of my samples have a hairline gap in the printed wires, which renders them useless. I was able to touch-up paint the ones that I didn't already cover, but the majority of the LTCC tape covered sample (Figure 1) are useless. In addition, I had an issue with the furnace over the weekend that ruined at least one chip and required me to re-fire many others. Hopefully by the end of tomorrow I will have at least one working chip for each condition. 

Testing at least one chip for each condition will give me an idea of what techniques work well, but I will have to repeat this experiment to confirm my findings. At the very least, I have a lot more experience working with LTCC and the screen printer and I should be able to avoid any printing or furnace errors next time around. 

Figure 2. New wiring layouts for two chips. Thermistors and
holes are in black. Wires are in gold. LTCC ceramic is blue. 

I am also working on ordering new thermistor and electrode layouts (Figure 2). If all goes well, I will be printing with the new layouts next week. Ideally, I should be able to do all of my testing with these new layouts, which should work very well for my purposes. When I designed these new layouts, I made the wire width thicker to reduce printing errors, I added a third channel so we can have a control and two experimental sensors on each chip, I added three thermistor layouts so we can test and optimize thermistor patterns, and I added circular leads with holes (instead of rectangular as seen in figure 1) for easy soldering. 

After I test the different thermistor coverings and whether pre-firing the ceramic helps prevent the LTCC and thermistors from reacting, I will begin testing wells. Right now, to test the thermistors, I can  drop reactants right onto the ceramic to measure the heat of an exothermic reaction. Once I have established that the thermistors are working properly and I can accurately record temperature, I will build wells on top of thermistors. The bottom of these wells will be coated with a substrate, likely gold, onto which antibodies will be secured. These antibodies are the start of a long chain that will be assembled on the gold surface to catch proteins and initiate a chain polymerization reaction, that gives off a heat profile from which we can determine the concentration of that specific protein. 

I am a long ways off from actually working with the proteins and the chemical reactions to surface coat the wells. I plan on continuing my work with the sensors and then doing some basic experiments with the wells before surface coating them. I definitely have enough to keep me busy for the rest of the summer.