We fabricated highly sensitive and selective ammonia gas sensors based on quartz crystal microbalance (QCM) platforms that were functionalized with electrospun polyvinyl acetate (PVAc) nanofibers and doped with various organic acids (i.e., oxalic, tartaric, and citric acids). The structural and chemical surface conditions of the nanofiber-based active layers on top of the QCMs were confirmed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared (FTIR) spectroscopy. The sensitivity of the PVAc nanofiber-based QCM sensor doped with citric acid was found to be the highest (2.95 Hz/ppm) among others with a limit of detection (LOD) of down to the subppm level (550 ppb). It also exhibited good selectivity, rapid response, short recovery time, and decent repeatability. This simple yet low-cost alternative solution based on chemical modification of nanofibers could improve the performance of QCM-based ammonia gas sensors in many areas including for smart electronic nose applications.

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The quartz crystal microbalance (QCM) modified by chitosan/α-pinene, prepared by spin-coating technique has been successfully developed with molecular imprinting polymer (MIP) concept. To remove the template, we carried out two treatments namely heating and vacuum in a desiccator. To find out selectivity of the sensor, the QCM modified with polymer chitosan has been tested with another analyte such as acetone, ethanol, N-amyl alcohol, iso-amyl alcohol. The result shows that chitosan/α-pinene coated QCM sensor can provide a good response as good as sensitivity. The best QCM at heating treatment in a furnace with the decline of frequency is 32 Hz, then the QCM vacuum pumping treatment with decline frequency is 27 Hz.