© 2019 IEEE. This paper describes the development of a filter-free fluorescence sensor that can discriminate light of short wavelengths (400 nm or less). The filter-free fluorescence sensor has a photogate structure, and when excitation light and fluorescence are simultaneously incident, the respective light intensities can be calculated. Up to the present, the conventional filter-free fluorescence sensor has been able to perform cell measurements. However, the filter-free fluorescence sensor used polysilicon for the gate electrode. Polysilicon hardly transmits short wavelength light, hence detection of short wavelength light had been difficult. To solve this problem, using Indium Tin Oxide (ITO) instead of polysilicon. On this new sensor using ITO, 405 nm of wavelength of light was incident and the output current was measured. As a result, a 24.6 times output current was obtained as compared to the conventional sensor. The new device also succeeded in separating 365 and 405 nm of wavelength of light, which was not possible with the conventional sensor.