This thesis consists of two topics. We proposed a low power half-run RC5 cipher for portable biomedical devices in the first part of this thesis. The second topic is to realize a frequency-shift readout system for FPW-based biosensors. In the first topic, a half-round low-power RC5 encryption structure is proposed. To reduce hardware cost as well as power consumption, the proposed RC5 cipher adopts a resource-sharing approach, where only one adder/subtractor, one bi-directional barrel shifter, and one XOR with 32-bit bus width are used to carry out the entire design. Two data paths are switched through the combination of four multiplexers in the encryption/decryption procedure. For the sake of power reduction, the clock in the key expansion can be turned off when all subkeys are generated. In the second topic, an IgE antigen concentration measurement system using a frequency-shift readout method for a two-port FPW (flexural plate-wave) allergy biosensor is presented. The proposed frequency-shift readout method adopts a peak detecting scheme to detect the resonant frequency. A linear frequency generator, a pair of peak detectors, two registers, and an subtractor are only needed in our system. According to the characteristics of the FPW allergy biosensor, the frequency sweep range is limited in a range of 2 MHz to 4 MHz. The precision of the measured frequency is proved to the 4.2 kHz/mV, which is for better than that of existing designs.