Acetone gas in exhaled breath and skin gas is produced when fatty acids are used as an energy source in the body. The selective and sensitive continuous measurement of acetone gas would be useful for the early screening of diabetes mellitus, a condition characterized by increased fatty acid metabolism. In particular, there is a growing need for acetone gas sensors that enable the wearable measurement of trace concentrations of acetone gas emitted through the skin. In this study, we improved the sensor's sensitivity by optimizing the fluorescence measurement system and flow cell of a previously developed biofluorometric acetone gas sensor (bio-sniffer) using secondary alcohol dehydrogenase. To evaluate the performance of the improved acetone bio-sniffer, we constructed a dilution system to prepare acetone gas at subparts per billion by volume (ppbv) levels and verified its accuracy using gas chromatography-mass spectrometry. As a result, the dilution system was able to prepare 0.1 ppbv of acetone gas with a coefficient of variation of 5%. The improved acetone bio-sniffer demonstrated quantitative characteristics in the concentration range of 0.5-1000 ppbv, with a lower limit of quantification that was 40 times better than that of the conventional acetone bio-sniffer. In the future, this system is expected to be used for continuous measurement of acetone gas released through the skin.