Our modern lives rely on sensors to allow society to run smoothly. Sensors in the road detect cars at traffic lights and adjust the flow through intersections accordingly. Sensors at shopping malls detect your presence and open doors to allow you to enter. Sensors measure the water level in your washing machine and ensure it doesn’t overflow.
Nanosensors work in much the same way but they can detect either minute particles or miniscule quantities of something.
Nanosensors can be chemical sensors or mechanical sensors. Amongst other applications they can be used:
• To detect various chemicals in gases for pollution monitoring
• For medical diagnostic purposes either as blood borne sensors or in lab-on-a-chip type devices
• To monitor physical parameters such as temperature, displacement and flow
• As accelerometers in MEMS devices like airbag sensors
How Chemical Nanosensors Work
Typically nanosensors work by monitoring electrical changes in the sensor materials. Carbon nanotube based sensors work in this way.
For instance when a molecule of nitrogen dioxide (NO2) is present it will strip an electron from the nanotube, which in turn causes the nanotube to be less conductive. If ammonia (NO3) is present it reacts with water vapour and donates an electron to the carbon nanotube, making it more conductive. By treating the nanotubes with various coating materials, they can be made sensitive to certain molecules and immune to others.
How Mechanical Nanosensors Work
Like chemical nanosensors, mechanical nanosensors also tend to measure electrical changes. The nanosensors used in the MEMS systems that car airbags depend upon are monitoring changes in capacitance. These systems have a miniscule weighted shaft attached to a capacitor. The shaft bends with changes in acceleration and this is measured as changes in capacitance.