The principle and the characteristics of the bias-scanning based tunable localized surface plasmon resonance (LSPR) sensors for environmental refractive index have been theoretically and numerically investigated in detail. The sensors exhibit linear negative-shifts in the scattering-bias spectral position when the refractive index of the surrounding medium increases. By bias-scanning, a single-wavelength measurement for sensing the environmental refractive index can be realized effectively. In addition, we demonstrate that the sensing performance of the designed sensor can be adjusted by nano-scale manipulations of metal nanoparticles' sizes and shapes. The proposed devices may pave the way for the development of electrochemical sensors that can convert spectrum scanning into bias scanning.