Fluorescence enhancement of a bleach-resistant solution for use in microfluidic devices

Photo-degradation of organic dyes occasionally causes problems in microoptical devices, e.g., microfluidic or droplet lasers, since a strong optical power is concentrated in a small volume for the enhancement of the operation efficiency. Although lanthanide ions provide bleach-resistant fluorescence emitters, their absorption and emission efficiencies are so poor that they usually require a long optical path. Polyethylene glycol is a useful solvent that enhances both the absorption and emission efficiencies due to its turbid characteristic and its ligand effect. A polyethylene glycol solution of europium ions exhibited an 80-fold stronger fluorescence (613 nm wavelength) than an aqueous solution. In addition, solidification induced twofold enhancement of the fluorescence intensity due to the pump light (396 nm wavelength) confinement in a small volume.