The typical core-shell [email protected], 1 mol% Ga doped [email protected] and 2 mol% Ga doped [email protected] nanoparticles were synthesized and utilized in acetone and NO2 sensing. Among those nanoparticles, 1 mol% Ga doped [email protected] based sensor presents excellent acetone sensitive and interesting reversible switching from P-to N-type NO2 sensing. The response of the 1 mol% Ga doped [email protected] based sensor to 50 ppm acetone is as high as 296, and the detecting concentration limit to acetone and NO2 is as low as 10 ppb and 20 ppb. The analogical binary p-n transition phase diagram was established to understand the NO2-sensing reversible switching as a function of operating temperature (T) and NO2 gas concentration (C). The role of Ga doping in enhancing the sensing property and the mechanism of NO2 p-n sensing transition is elaborated. In conclusion, the doping of Ga into core-shell [email protected] was proved to be a feasible method for fabricating acetone and NO2 sensor, with high sensitivity and selectivity.