Liquid polymer nanosensors for intracellular applications: Fibers and PEBBLEs.

Abstract

Live cells exhibit a complex chemistry, which literally determines life, disease and death. Liquid polymer fiber based nano-optodes with tip dimensions in the 100 nm size range and optimized tip shape were applied effectively for monitoring potassium or sodium in single cells. Even with tips in nm dimensions the penetration volume of the optode as well as the required breach of the cell membrane limited the cell lifetime. A new class of liquid polymer PEBBLE (Probes Encapsulated By Biologically Localized Embedding) nanosensors was developed to enable monitoring of potassium, sodium and chloride with less perturbation than pulled fiber optodes. The PEBBLE nanosensors are self-contained spherical optodes that require no connecting fibers. Liquid polymer PEBBLE sensors have been developed here as a means of utilizing the highly selective commercial ionophores that were synthesized for use in ion selective electrodes (ISEs). Liquid polymer PVC PEBBLEs did not give the desired results, thus a cross-linked decyl methacrylate (DMA) process was developed for lipophilic PEBBLE fabrication. The decyl methacrylate was polymerized using an oil in water emulsion with polyethylene glycol (PEG) 5'000 monomethyl ether as a steric stabilizer for particle formation. The polymer spheres were 600 nm in diameter, which represents one ppm of the volume of a single 100 mum mouse oocyte. The resulting nanosphere sensors obey bulk optode thermodynamic relations for calibration, with the associated dynamic range, selectivity and reversibility. They have been successfully applied to the fabrication of highly selective nano-sensors for K<super>+</super>, Na<super>+</super>, and Cl<super>- </super>, utilizing the ionophores BME-44, monensin decyl ester and Chloride Ionophore III, respectively. The response time of the sensors is less than a second. Potassium and sodium PEBBLEs were applied successfully for the real time monitoring of ion flux in viable rat C6 glioma cells during kainic acid stimulation.