In this Letter, a sensitive light-induced thermoelastic spectroscopy (LITES)-based trace gas sensor by exploiting a super tiny quartz tuning fork (QTF) was demonstrated. The prong length and width of this QTF are 3500 µm and 90 µm, respectively, which determines a resonant frequency of 6.5 kHz. The low resonant frequency is beneficial to increase the energy accumulation time in a LITES sensor. The geometric dimension of QTF on the micrometer scale is advantageous to obtain a great thermal expansion and thus can produce a strong piezoelectric signal. The temperature gradient distribution of the super tiny QTF was simulated based on the finite element analysis and is higher than that of the commercial QTF with 32.768 kHz. Acetylene (C2H2) was used as the analyte. Under the same conditions, the use of the super tiny QTF achieved a 1.64-times signal improvement compared with the commercial QTF. The system shows excellent long-term stability according to the Allan deviation analysis, and a minimum detection limit (MDL) would reach 190 ppb with an integration time of 220 s.

With the rapid development of laser technology, information technology, and materials, the detection of trace gas has been taken to a new level. Advanced analytical methods were invented, for example, gas chromatography, mass spectrometry, chemical sensors, absorption spectrum, and so forth. With the detailed data gathered from new high-tech equipment, we can predict and diagnose diseases such as diabetic ketoacidosis, irritable bowel syndrome, lung cancer and so on. However, there is still a large amount of exhaled gas that has not been discovered, which means that breath analysis of exhaled gas is a very promising field in the future. Non-invasive breath diagnosis and monitoring technology have attracted huge attention from all over the world. Using exhaled gas to diagnose and monitor human disease has numerous advantages for being non-invasive, convenient and environment friendly.