chemical electronics

Glucose Fuel Cell for Medical Implants

Professor Rahul Sarpeshkar and colleagues at MIT have created an implantable fuel cell which relies on glucose as its fuel. The device could potentially be used as a power source for the computers needed to decode brain signals and manipulate prosthetic or perhaps paralyzed limbs. The article was published in PLos ONE.

There are many layers of cool in this story. Implantable glucose fuel cells have been invented before – back in the 70s – but contained enzyme-based anodes which degraded over time and needed to be replaced. Because of this, implants like pacemakers rely on lithium ion batteries – which also drain over time, but have a much longer lifespan. This design utilizes a platinum anode to oxidize glucose ultimately to gluconic acid, liberating 2 electrons. The cathode is a matrix of single-walled carbon nanotubes which reduce dissolved oxygen to water.

What strikes me as the coolest part of this story, the fuel cell is fabricated on a silicon chip and would be placed in the cerebralspinal fluid next to the brain. Platinum is already known for being fairly biocompatable, but placing the chip in the cerebrospinal fluid is beneficial as there are very few white blood cells in the CSF to trigger an immune response and potential rejection. The CSF contains roughly the same concentration of glucose as plasma, and is not predicted to consume enough glucose fuel so as to impair brain function.

via DOI:10.1371/journal.pone.0038436

To avoid short circuiting the fuel cell, the platinum anode is enclosed in a ring of the carbon nanotube cathode. The cathode sequesters the dissolved oxygen for the reduction reaction, creating a concentration gradient across the cathode such that dissolved oxygen does not penetrate past the cathode. The nanotubes do not oxidize glucose, but are permeable to glucose, so the glucose passes through the cathode unreacted. The cathode is separated from the anode by a strip of nafion, a biocompatable perfluorniated polymer similar to teflon, but with branched sulfonate groups throughout. The sulfonate groups allow protons to flow through the nafion from the anode to the cathode, and nafion is permeable to glucose as well. The anode is at the center and can be as large as 2.5cm x 2.5cm.

The oxidation reaction at the anode is considerably less efficient than other implantable glucose fuel cells, but the biocompatability and long lifespan of the fuel cell makes this a really nice step forward in the treatment of paralysis and spinal cord injuries.

Android Spectroscopy

I was jealous when I saw Joel write about his boss using his iPhone’s light source for experiments (finally, a really useful science iphone app). I knew I had to one-up him for no other reason then I am a Google Android user. Below is a video of an app I made; the app will scroll through the visible spectrum. In the video the glass contains red wine.

During the video you can see the wine absorbing blue light when the camera pans over the glass for the first time. Next time it pans over the red wine the light is green and still not transparent, but as the light was turning yellow the solution became more transparent. By the end, the light was red and it transmitted through the wine just fine.

If I had an other Android phone on hand I probably could have made a quick and dirty visible spectrometer.


By February 15, 2010 3 comments chemical electronics, fun

Stepper Motors for Chemistry

My research is truly a multidisciplinary adventure. I don’t mean a pseudo-multidisciplinary project, like a Chemist who cracks open E. coli and says they are probing the frontiers of Biology and Chemistry. I mean, you could put a list of science departments on a dart board and throw darts at it and it would make more rational sense than the fields I trudge through to get my research executed. For instance last month I wrote a materials science paper about metal oxide films with some of my fellow lab mates. The month before that we were tweaking polymers. This month we’ve been doing nuclear reactions, and this past week we’ve been doing some hardcore electronics.

To that end, we’ve successfully wired a stepper motor to actually step. This may sound trivial, but as you can see from the circuit board it was rather involved. The video is shown below.

That was yesterday. Today we got the stepper motor to take steps by making my computer pretend it was sending signals to a printer but it was actually talking to the motor. This was programmed through Excel! So, if you ever think your research is tough or that you have no idea what you are doing. Don’t worry, there is an other soul doing something radically different every month. I’m not sure where and when my Ph.D. will end, but it never ceases to provide a truly different set of problems every week!

If stepper motors don’t crank your shaft here is a video of puppy versus kitten action.


Notes: The motor is from one of the syringe pumps. shhhhh…..

By August 17, 2007 0 comments chemical electronics

Pimp My Spin Coater

My research has recently involved the process of spin coating, and being in a nuclear chemistry group we of course don’t have a spin-coater lying around. So, I’ve been hiking up the hill to use the Somorjai group‘s spin-coater. This past week I decided I wanted my own spin-coater and so I set about making my own. The working model is shown below.

Spin-Coater in the Dark: Lights are turned off for more dramatic effect.

If you’re going to start making your own lab equipment you might as well trick out the new hardware. In that spirit, my spin coater has 3 light emitting diodes: a green one, a red one, and a blue one. I can vary the revolution per minute from ~500rpm to ~2500rpm by varying the voltage I supply to the spin coater. The sample is mounted in the center and is stuck to the spin coater by Velcro, this can be more easily seen in the next photo.

Spin Coater Close Up

As can also be seen in the photo, my spin coater is just a regular pc fan I bought at CompUSA this past Wednesday. I monitor the speed of the spin coater with a laser mounted above the spin-coater that shines through the fan’s blades and strikes one of our group’s alpha detectors. The nice thing about the alpha detector is that I don’t even have to supply any power to it. There is enough current generated, I presume by the photoelectric effect, to carry a signal to an oscilloscope which I can use to monitor the fan’s speed. A picture of the laser, which is my boss’s laser pointer he uses for talks, is seen in the next photo at the top of our group’s only non-radioactive chemistry hood.

Spin-Coater in the Hood

It took me 2 days to build my spin coater, Wednesday and Thursday, and one more day to make sure it calibrates properly, Friday. The total amount in extra costs was $20 for the spin-coater(pc fan) all the rest of the equipment we had lying around.

Now what other lab equipment could use some LEDs? Hmmm….

Note 1: Paper that first got me interested in using a pc fan: Spin-Coating of Polystyrene Thin Films as an Advanced Undergraduate Experiment

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