Hello from Hanna:
"In the spirit of "Do no harm" we decided on wire sensors instead of screen printed electrodes (SPE). The SPE has an impractical shape for measurements done in tissue, it's not biocompatible and so it does not fulfill our criteria "stay inside the fish and don't kill it".
The first generation of wire sensors (red and black wire) would have caused inflammation in surrounding tissue if it were to be implanted, but it is flexible and thus a better fit for the inside of a fish. It's not made of biocompatible materials, which is why we had to develop a 2nd generation wire sensor.
Nothing has taught me how to solder like the making of wire sensors has. I have soldered a lot of them. So have a lot of our other engineers at ZP. But apart from developing a relationship with our soldering station: I have been taught how to make wires and enzymes into something that can detect bits of chemicals within a given sample, and that is so cool!"
When we started the FishTag project, we already had two types of functioning glucose sensors: Wire sensor and SPE. We already knew they could measure glucose up to our standard in a lab, but we needed to test their long-term stability and temperature sensitivity as well. It would be both waste- and harmful to operate a sensor into a fish if the sensor were to malfunction or have too much drift within its lifetime (3 months). Therefore we did a long-term test, which you can read more about here.
The main issue with the earliest sensor is its biocompatability: Neither the wires, isolating layers or the ink used is biocompatible. They deliver great results, but it will harm a fish if stored inside for an extended amount of time. As our goal is to improve the fishes' health and not to kill it slowly from the inside, we had to make some changes to the materials. The team have done research and have developed a more fish-friendly wire sensor: Generation 2 wire sensors.
While we were at it: we reduced its size and weight too. A small and light system will be less stressful for the fish. One of our top priorities is to have our system effect the fish as little as possible. Animal welfare is important to us at ZP: We do not want our fishtag to do the fish more harm than good. The idea of FishTag is to have a monitoring system implanted in the fish. That way the fish will only be removed from the water once (to insert the system), instead of the fish being regularly removed from its tank to draw blood. Pulling a fish out of a tank will stress the fish and even though we want to measure stress, we do not want to be the cause of it.
The first thing one notice is the change of wires. The red and black wires have been changed to pink and gold medical grade wires. The diameter of the medical wires are 0.19mm OD, making it smaller and lighter than the previous wire sensor. The red/black wire sensor is 1.7mm OD after twisting.
The dielectric layer and the heat shrink have also been changed to biocompatible ones.
The connector have been changed from a pin-connector to a connector housing, but it is not biocompatible. The connector is for our own sake, as we are still developing, testing and improving. In the current version of our system the sensors are soldered onto the PCB.
In the first tests on the new wire sensor we had some trouble with noise. A troubleshoot led us to believe it was due to loose a connector on the cable side, which was an easy fix. We now have a functioning biocompatible wire sensor!
Until next time,
Hanna T. Bråthen
Engineer at ZP
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