Detection of refractive index changes in individual living cells by means of surface plasmon resonance imaging.

Real time imaging of living cell activation is an increasing demand in disciplines of life science and medicine. We previously reported that surface plasmon resonance (SPR) sensors detect large changes of refractive index with living cells, such as mast cells, keratinocyte, human basophils and B-cells activated by biological stimuli. However, conventional SPR sensors detect only an average change of refractive index with thousands of cells at detectable area on a sensor chip. In this study, we developed an SPR imaging (SPRI) sensor with a CMOS camera and an objective lens in order to analyze refractive index of individual living cells and their changes upon stimuli. The SPRI sensor could detect reactions of individual rat basophilic leukemia (RBL-2H3) cells, mouse keratinocyte (PAM212) cells, and human epidermal carcinoma (A431) cells in response to either specific or non-specific stimuli, such as antigen, phorbol ester or epidermal growth factor, with or without their inhibitors, resembling signals obtained by a conventional SPR sensor. Moreover, we distinguished reactions of different type cells, co-cultured on a sensor chip, and revealed that the increase of refractive index around nuclei is rapid and potent as compared to that in peripheries in the reaction of RBL-2H3 cells against antigen. This system may be a useful tool to investigate the mechanism of refractive index-changes evoked in near-membrane fields of living cells, and to develop a system of high-throughput screening for clinical diagnosis.