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Surface plasmon resonance (SPR) sensors provide a useful means to study the interactions of biological molecules and the reaction of living cells on a sensor chip. However, conventional SPR sensors are bulky, expensive and complicated to use as common diagnostic equipment. In this study, we developed a relatively small and simple SPR system, using optical fibers of 250 microm diameter to detect the activation of living cells attached to the fiber tip. For this system, the core of 200 microm diameter with 1cm length of an optical fiber was coated by gold film with 50 nm thickness to cause plasmon resonance. The light provided by a white LED and attenuated due to a SPR phenomenon in the sensor part was detected and analyzed using a spectrum detector. The difference in solvents with various refractive indexes and protein-bindings to the sensor tip was detected with sufficient sensitivity. Moreover, it detected a sustained increase of AR in a real-time manner, when RBL-2H3 mast cells were fixed onto the fiber tip and stimulated by an antigen. This small fiber SPR system might serve as a useful tool for various clinical examinations either within or outside the body.

Living cell reactions are detected as changes of the angle of resonance (AR) for surface plasmon resonance (SPR). Since SPR reflects the events in the field of evanescence, cells need to be fixed on the sensor chip. In this study, we developed methods to fix living cells on a gold surface and to recover adherent cells from the culture dish, preserving their functions to be analyzed by SPR. Human basophils and B cells were fixed to the sensor chip by a biocompatible anchor for cell membranes (alpha-succinimidyloxysuccinyl omega-oleyloxy polyoxyethylene), aminoalkanethiol (cyteamine, 8-amino octanethiol) or an amino-reactive cross-linker (dithiobis [succinimidylpropionate]). They showed an increase of AR in response to various stimuli. RBL-2H3 cells, which firmly adhered to the culture dish, were cultured/recovered with HydroCell/simple pipetting, with RepCell/pipetting at 4 degrees C, or on normal plastic culture dishes with trypsinization or by scraping at 4 degrees C, respectively. The exocytosis of RBL-2H3 cells was largely impaired by scraping, but only slightly by the treatment with pipetting on HydroCell, on RepCell, or with trypsin. The membrane ruffling of the cells prepared by the last three treatments induced by antigens appeared the same. However, the change of AR with cells prepared by trypsin and those by scraping at 4 degrees C were lower than those by HydroCell or RepCell, suggesting that trypsin may harm molecules involved in cellular reactions. Thus, the methods of cell fixation and removal with HydroCell or RepCell should enable us to analyze various reactions in either adherent or non-adherent cells by SPR.

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