Abstract

We describe a novel microfluorometric technique, based on the temperature-dependent fluorescence emission from single dye-labeled phospholipid vesicles, for the determination of localized heating effects. An increase in sample temperature results in a red shifting of the probe fluorescence spectrum. As individually calibrated microthermometers, fluorescent liposomes exhibit a temperature sensitivity of ∼0.1°C in the vicinity of the bilayer phase transition temperature. Through modification of the bilayer components, both the sensitivity and operating temperature range of these microthermometers can be controlled. Micron spatial resolution is achieved at a signal-to-noise ratio in excess of 103:1. We use the above technique, for the first time, to determine localized heating effects induced by a laser beam focused to its near-diffraction limited spot size. At the laser wavelength of λ=1.064 μm, a temperature change of 1.1°C/100mW in 10-μm-diam organic liposomes is reported. Implications for the real-time optical monitoring of temperature in biological systems are discussed.