We present a complete palm-sized, battery-operated biodetection system based on highly sensitive localized surface plasmon resonance (LSPR). We have replaced the spectrum analyzer by four pulse-powered light-emitting diodes (LED), each with different emission spectra. The reflected light beams from all LEDs were detected by a single photodiode. Its composite output current was demultiplexed by a four-channel lock-in amplifier. Device performance was demonstrated using an LSPR chip covered with a mixture of ethanol/water and 2-propanol/water at different concentrations. The miniaturized system does not require any external power supply or personal computer and it is therefore suitable for point-of-care and field applications.