In this research, the broadband light (from 365-940 nm) and room temperature gas (NO, CO) sensing can be achieved by using nano-heterojunction (Ge and SnO₂ nanowire) device; the detail analysis can be measured by in-situ spectrum and electrical measurement system. The in-situ spectrum and electrical measurement can provide the response immediately to investigate the interface defect, band bending and Joule-heating effect through the response of the devices. For broadband light detection experiment, the visible light (532 nm) beam was illuminated at different parts of the nano-heterjunction device (p-type semiconductor, n-type semiconductor, and interface). The broadband light responses only happen at interface part, not at both nanowires. For gas detection experiment, the Raman spectrum and electrical signal can be used for studying gas molecule and nano-heterjunction dynamics. Base on the abovementioned experiment, we can find the parameters to create and design new nano-device in smart way.