The balanced-path scheme of a heterodyne interferometer proposed by Yoon et al. has been applied to the scanning homodyne I/Q-interferometer. This provides an 11-dB improvement on common vibration rejection over the heterodyne scheme and, thereby, allows high sensitivity and high stability phase and amplitude measurements for high-speed scanning interferometer applications. It is shown that our new scanning interferometer scheme is very useful for diagnosing a sample that requires complex analysis. As an example, our new scanning interferometer scheme has been applied for obtaining phase and amplitude images of the protein biochip samples prepared by using the sandwich ELISA. The amplitude images are used for diagnosing homogeneity of the sample, while the phase images are used for measuring the phase difference between samples treated with different concentrations of IL-5.