Weldon School of Biomedical Engineering

2 Articles

Electrochemistry At Home

August 2, 2020 by 11 Comments

A few years ago, I needed a teeny, tiny potentiostat for my biosensor research. I found a ton of cool example projects on Hackaday and on HardwareX, but they didn’t quite fulfill exactly what I needed. As any of you would do in this type of situation, I decided to build my own device.

Now, we’ve talked about potentiostats before. These are the same devices used in commercial glucometers, so they are widely applicable to a number of biosensing applications. In my internet perusing, I stumbled upon a cool chip from Texas Instruments called the LMP91000 that initially appeared to do all the hard work for me. Unfortunately, there were a few features of the LMP91000 that were a bit limiting and didn’t quite give me the range of flexibility I required for my research. You see, electrochemistry works by biasing a set of electrodes at a given potential and subsequently driving a chemical reaction. The electron transfer is measured by the sensing electrode and converted to a voltage using a transimpedance amplifier (TIA). Commercial potentiostats can have voltage bias generators with microVolt resolution, but I only needed about ~1 mV or so. The problem was, the LMP91000 has a resolution of ~66 mV on a 3.3 V supply, mandating that I augment the LMP991000 with an external digital-to-analog converter (DAC) as others had done.

However, changing the internal reference of the LMP91000 with the DAC confounded the voltage measurements from the TIA, since the TIA is also referenced to the same internal zero as the voltage bias generator. This seemed like a problem other DIY solutions I came across should have mentioned, but I didn’t quite find any other papers describing this problem. After punching myself a little, I thought that maybe it was a bit more obvious to everyone else except me. It can be like that sometimes. Oh well, it was a somewhat easy fix that ended up making my little potentiostat even more capable than I had originally imagined.

I could have made a complete custom potentiostat circuit like a few other examples I stumbled upon, but the integrated aspect of the LMP91000 was a bit too much to pass up. My design needed to be as small as possible since I would eventually like to integrate the device into a wearable. I was using a SAMD21 microcontroller with a built-in DAC, therefore remedying the problem was a bit more convenient than I originally thought since I didn’t need an additional chip in my design.

I am definitely pretty happy with the results. My potentiostat, called KickStat, is about the size of a US quarter dollar with a ton of empty space that could be easily trimmed on my next board revision. I imagine this could be used as a subsystem in any number of larger designs like a glucometer, cellphone, or maybe even a smartwatch.

Check out all the open-source files on my research lab’s GitHub page. I hope my experience will be of assistance to the hacker community. Definitely a fun build and I hope you all get as much kick out of it as I did.

Wearable Device For Preventing SUDEP (Sudden Unexpected Death In Epilepsy)

June 22, 2020 by 13 Comments

Epilepsy is a neurological disorder characterized by the occurrence of seizures. Epilepsy can often prevent patients from living a normal life since it’s nearly impossible to predict when a seizure will occur. The unpredictability of the seizures makes performing tasks such as driving extremely dangerous. One of the challenges in treating epilepsy is the condition is still not very well understood.

Neurava, a recent startup company from Purdue University, aims to change this fact. Neurava is developing a neck wearable that “records key biological signals related to epilepsy.” None of the press releases we’ve found so far elaborate on what those biological signals are. Though we have some guesses of our own, we’ll leave it to the Hackaday community to speculate for the time being. One of the major hurdles in using biological signals to treat conditions like epilepsy both lies in the accuracy of the measurement itself in addition to how well the measurement correlates to the underlying condition. From the looks of it, Neurava has been working on this technology for a long time and are certainly more aware of these challenges than we are.

Neurava’s wearable includes a few other functionalities we’ve come to expect in this era of smart devices such as wireless data transmission to both the physician and patient, physician dashboard to monitor the patient’s progress over extended periods of time, and in-time alerts in the event a seizure is detected.

Neurava appears to have garnered a bit of publicity in these last few months and are currently securing seed money to help advance their technology. We’ll check in every so often to see how they’re doing.