Non-contact method for measuring solution concentration using surface plasmon resonance apparatus and heterodyne interferometry

A simple non-contact method is proposed for measuring the concentration of solutions. Using the significant phase difference between p- and s-polarizations of the reflected light of a surface plasmon resonance apparatus, the variation in the phase difference, which is caused by a variation in the concentration of a test solution, can be accurately measured by common path heterodyne interferometry. Then, by substituting the corresponding variation in the incident angle of light at the base of the SPR prism in a specially derived equation, the concentration of the test solution can be determined. The validity of this method was demonstrated experimentally. This method is characterized by the advantages of the device having a simple non-contact structure; it being easy to operate; and its high accuracy, stability, and resolution.