Microsensors are used in many different applications such as the detection of poisonous gases. They are also integrated into miniaturized transmitter/receiver systems such as RFID chips. Since the sensors often contain precious metals that are harmful to both the environment and human health, they are not suitable for medical applications involving direct contact with the human body, or for inclusion in food products. There is a need for microsensors made from non-toxic materials that are also biodegradable.
Such biocompatible microsensors were developed by encapsulating a superfine, tightly wound electrical filament made of magnesium, silicon dioxide, and nitride in a compostable polymer. Magnesium is an important component of the human diet, while silicon dioxide and nitride are biocompatible and dissolvable in water. The polymer is produced from corn and potato starch, and its composition complies with EU and US food legislation.
The sensor is 16 micrometers thick, a few millimeters in length, and weighs less than a fraction of a milligram. In its current form, the sensor dissolves completely in a one-percent saline solution over the course of 67 days. At present, the sensor continues to function for one day when completely submersed in water. This time would be sufficient to monitor a shipment of fish from Japan to Europe. The operating life could be extended by adjusting the thickness of the polymer; however, a thicker sensor would be less flexible. The current sensor is so thin that it continues to function even if it is completely crumpled or folded. Even when stretched by 10% of its original size, the sensor remains intact.
For the power supply, the sensor is connected to an external micro-battery using ultra-thin biodegradable zinc cables. On the same (non-biodegradable) chip, there is a microprocessor and a transmitter that send the temperature data via Bluetooth to an external computer. This makes it possible to monitor the temperature of a product over a range of 10 to 20 meters.
Uses for the sensors would not be limited to temperature measurement. Similar microsensors could be deployed to monitor pressure, gas build-up, and UV exposure.