Real-time measurement of complex refractive indices with surface plasmon resonance

•A novel surface plasmon resonance biosensor is presented.•The real-time measurement of complex refractive indices is demonstrated.•Limits of detection of 1.5e-6 RIU (real) and 3e-6 RIU (imaginary) were achieved.•An experiment with liposomes as a model of biological systems is presented.

Surface plasmon resonance (SPR) is an attractive method for the measurement of refractive indices due to its high accuracy and its broad range of applications. However, the use of this technique for the measurement of complex refractive indices in real-time has not yet been demonstrated. This article discusses and demonstrates how an SPR biosensor can be used to accurately measure both the real and imaginary components of the refractive index of a sample in real-time. The theory of the data analysis method, the calibration of the instrument as well as the application of the new technique to measure the complex refractive index of liposomes are presented.