If you were sitting around worrying that graphene might not be able to live up to its potential in electrochemical bio-sensing (and that has to be at least half of you), then worry no more: All we have to do to make graphene practical for every-day use is mix it with gold! By employing just a tiny amount of the precious metal to offset some of graphene’s least helpful properties, it turns out that we might be able to fully exploit its best ones. A new study published in Nature Nanotechnology uses this hybrid to create a flexible skin patch to monitor blood glucose and, more importantly, automatically administer drugs as needed.
When you’re trying to design a piece of technology to interact with biology, graphene is a natural choice. Not only is it naturally very flexible and strong, but it is physically small enough that it could, for instance, find and act upon small sub-compartments of individual cells, with accurate-enough control. What it could also do is pierce the skin without causing any real irritation, and without opening the body to a significantly increased chance of infection. Graphene is highly conductive, meaning that it can be used to power or zap things — it can even be used as a so-called “spaser” to carry and direct super-small light signals for optogenics and more.
On the other hand, graphene has a number of difficulties, with respect to biotechnology. First, graphene may be inherently toxic to biological material, and it could be less durable than expected in a biological context. But by and large the research says that things shouldn’t be too bad as long as you don’t inhale the stuff.
To create this patch, the researchers had to get around an equally unhelpful characteristic: The cheapest and most reliable method for making graphene makes it too darned perfect. See, to judge blood glucose without piercing the skin, the patch uses the enzyme glucose oxydase to oxidize glucose in the sweat and produce hydrogen peroxide as a marker molecule. Reacting this marker causes easily measurable electrochemical changes in the sweat, which in turn allow good-enough estimates of circulating glucose levels.
The only problem is that to do that electrochemcial measurement we need atomic-scale imperfections in our probe. That’s not usually a tall order for any manufacturing process, but graphene is extremely uniform by nature. What are we to do? Throw some gold in there, of course. The researchers used a “gold doped” version of graphene affixed to a gold mesh, giving it both increased electrochemical properties which in turn makes the glucose reading more accurate. Or, in this case, accurate at all.
But, cool as a non-invasive blood-glucose monitor is, it’s nearly as revolutionary as what comes next: treatment. The patch is studded with “microneedles” that automatically cap themselves with a plug of tridecanoic acid. When high blood-glucose levels are detected, the patch heats a small heater on the needles which deforms the plug and allows the release of metformin, a common drug for treatment of type 2 diabetes. Cooling naturally restores the plug and stops drug release.
Real products using graphene are coming. It’s taken longer than many predicted, and it’s requiring many case-by-case innovations to overcome graphene’s intrinsic properties, but the products are coming. The big question now is how long before they come far enough down in price to be available to the average patient.