Based on gravimetric detections, the sensor output is directly linear to the amount of adsorbed gas molecule and real-time sorption process can be recorded as well. One class of sensors with the potential to be a candidate for such multi-parameter determinations is the acoustic wave resonators 22, 23. These constants reflect the intrinsic information of VOCs at different gas-solid interface and in principle, can be used as multi-parameter fingerprints with high discriminative power ( Fig. affinities and kinetics constant) of VOCs interaction with functional sensor surface are specific and concentration independent 21. The interfacial chemi(physi)sorption parameters ( e.g. Hence, a concentration-independent discrimination method is urgently needed. Thus, the applied condition of the device is limited ( e.g., an analyte with unknown concentration is difficult to be distinguished with this approach). The fingerprint patterns are built directly from the sensor output which is dependent on the VOC concentrations. Thus, they cannot be fitted directly by the known gas-solid surface adsorption isotherms. The responses from the nanowire sensors are generally caused by the polarity of the gas molecules, which do not show direct correlation with the gas concentrations. Multiple sensor output (voltage threshold, on-current, hole mobility and subthreshold swing) for VOCs detections were recorded to generate multiple fingerprint patterns which largely enhance the discriminative power of such e-nose system 17, 18, 19, 20.
Multiple parameters fingerprints have been recently reported using silicon nanowire field effect transistors functionalized with different self-assemble monolayers (SAMs) 15, 16. Different VOCs may appear similar fingerprint patterns thus, the discrimination capability of the single parameter fingerprints is limited. Conventional fingerprints are based on direct sensor response (single parameter) to a known concentration of the analyte 14. In general, each component of the e-nose array is chemically modified with different gas-sensitive materials, providing a response spectrum, i.e., the “fingerprint” 12, 13. Compared with individual sensor detection, the high-integrated sensor array satisfies the needs of the discrimination of VOCs and determination their concentrations. An alternatively useful method is the electronic nose (e-nose) system that consists of an array of chemical gas sensors 9, 10, 11. However, most commercial potable VOC sensors in the current market ( e.g., photoionization sensors and metal oxide sensors) are dedicated to concentration detections, which leads to a problem of discriminating individual analyte in a vast VOC spectrum.
Accordingly, these applications prefer to have portable sensors which can on-site predict the contents of VOC mixtures and concentration information of each composition. Thus, there is a large demand on the sensitive and selective detection of VOCs in the gas phase for environmental monitoring, process control and medical diagnostics purposes 4, 5, 6, 7, 8. Moreover, some exhaled VOCs are found as effective biomarkers that could be used for the detection of some diseases, including lung cancer. VOCs are believed to have short-term and long-term adverse effects on environment and human health, including the potential cause of cancer 1, 2, 3. furnishings, paints and building materials) which are due to their rather low boiling points. Volatile organic compounds (VOCs) are carbon based chemicals that easily emit from industry productions or indoor environments ( e.g.