The detection of different molecules in the air requires an inexpensive and symple instrument. Currently available systems for such detection are expensive and large-scale and require trained operator, long measurement times, a large amount of material for analysis. In addition, at the end the detection is not reliable. The measurements are difficult because the number of evaporated molecules is very small (in the range 10-9 to 10-14). Molecular detection is based on the adsorption of the target molecules on the receptor layer at the surface of the sensor. The coverage area of the sensor depends on vapor pressure of the material, temperature and interference of other molecules. Target molecules are usually very small the coverage of the sensor is small, therefore the signals from the sensors are very weak; detection is extremely difficult.
We demonstrated recently the possibility of explosives detection in low concentrations with usage of differential COMB capacitive sensor. Realized sensor system is extremely sensitive (sensitivity 0.3aF – is one of the best achieved sensitivities in the world) and uses low noise CMOS circuitry. The system is robust and insensitive to mechanical and thermal influences from the environment and has great potential.
Currently, we are trying to improve the sensitivity for two orders of magnitude, which means that detection of the capacitive change in range 10 zF (10-21 F). We are searching for solutions to enhance chemical selectivity and reliability of detection,using different functionalized sensors; currently measurements are performed with four differently modified sensors. Adsorption of various molecules is different in variously functionalized surfaces so a different “fingerprints” in various responses are expected to be found each type of the target molecules.
Results
We recently published the results of measurements for the sensitivity of the capacitive sensor of the TNT and RDX vapors and achieved the detection level of 3 molecules of TNT and 0.3 molecules of RDX in the 10 + 12 molecules of carrier gas. The article was published in the IEEE Sensors journal . This result is one of the best published for this type of detection. Currently, we would like to increase the sensitivity for about 2 orders of magnitude and improve selectivity.
Fields of application
Medical, security, military, environmental control, food production, science, etc.