DEVELOPMENT OF A FIBER OPTIC MICRO-OPTRODE FOR INTRACELLULAR PH MEASUREMENTS

The authors describe the production and experimental evaluation of a m iniaturised fibre optic micro-optrode which has been designed for intr acellular measurements. The fabrication process initially involves the controlled tapering of a single-mode optical fibre to yield micron- a nd submicron-diameter tips. By selectively coating the fibre tips with a thin metal film, it is possible to form a light-transmissive optica l aperture at the tip. Such tapered and coated fibres are similar to t he probes used in near-field optical microscopy. The probes here are c onverted to micron and submicron pH sensors by immobilising a fluoresc ent pH sensitive reagent within a glass film which is deposited on the surface of the fibre tip using a sol-gel process. When appropriate pu mp radiation is guided to the tip of the sensor, the fluorescence yiel d of the pi-I-sensitive reagent is indicative of the pH of the environ ment of the sensor. The authors have successfully used these sensors t o monitor the pH of buffer solutions inside micron-size holes in a pol ycarbonate membrane and to probe the intracellular environment of mous e embryonic fibroblast cells. It was found that the sensors were rever sible in the pH range 3-10.