Prosthetic Monitors - and May Control - Blood Sugar Levels Without Breaking the Skin
Another variant on skin-implanted biosensors for diabetics has been created. This one is a product of the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg, Germany. It consists of a tiny, wire thin biosensor that is placed under the eye.
Since the body's glucose levels are the same in many fluids other than blood, blood glucose levels are not the only option when determining the exact levels circulating round the body. Other fluids, such as tears produced by the eye, or sweat produced by glands all around the body, work just as well, and report the same glucose levels. Since these fluids naturally flow over the skin, there is no need to prick into a vein or artery several times a day to get results.
It is an electrochemically activated biosensor, much smaller than previous attempts, and continually measures the fluids as they pass over it. Glucose oxidase present inside the chip converts glucose into hydrogen peroxide (H2O2) and other chemicals whose concentration can be measured with a potentiostat. As the chip is just inside the dermal layer, it can be refilled by droplets or swab. Again, no need to break the skin.
Perhaps the greatest breakthrough is that, even given the needle-like chip's small size just 0.5 x 2.0 millimetres there is more room than is required for the nanopotentiostat and glucose oxidase storage channels. By creating a customised architecture, the research team have been able to fit an entire diagnostic processor into the remaining space.
It even has an integrated analogue digital converter that converts the electrochemical signals into digital data, explains Tom Zimmermann, business unit manager at IMS. The biosensor transmits the data via a wireless interface, for example to a mobile receiver. Thus, the patient can keep a steady eye on his or her glucose level. In the past, you used to need a circuit board the size of a half-sheet of paper, says Zimmermann. And you also had to have a driver. But even these things are no longer necessary with our new sensor.
Earlier systems required about 500 microamperes at five volts; now, it is less than 100 microamperes. That increases the durability of the system allowing the patient to wear the sensor for weeks, or even months. The use of a passive system makes this durability possible. It uses the exact same technology as passive RFID, meaning that a radio wave of sufficient power at the right frequency will supply power through inductance. You hold the transmitter over the device, (or up to a couple of meters away) and it works.
Whilst the sensor works continuously through enzyme processes when not powered up, it has to receive power in order to transmit its findings wirelessly to a readout device such as a smartphone running a compatible app.
It is cheap to manufacture, and Noviosens, a Dutch medical technology firm have expressed considerable interest in mass producing it.
The eventual hope is to tie it in with an insulin pump implanted deeper in the body, and activate and deactivate that pump automatically based on the glucose levels it records in real-time. A true form of personalised healthcare, and an end to insulin injections, too.
It offers the first real hope of a treatment for diabetes in which needles are never necessary, and the body's blood sugar levels are monitored and corrected in real-time.