Lasing droplets in a microfabricated channel.

Lasing from spherical microdroplets ejected into a liquid medium with a lower refractive index is observed in a microchannel. A microfabricated device that combines droplet production and excitation/detection has been utilized. Droplets of 50 microm diameter containing a fluorescent dye were first detected and then excited through multimode fibers after their production at a T-junction. Images show intense lasing emission around the droplet rim. Spectra from the droplets exhibit morphology-dependent resonances that are redshifted relative to the bulk fluorescence emission from the dyes. The dependence of resonant peak intensities on the pump beam power is nonlinear.

Eu3+-doped Gd2O3 nanoparticles as reporters for optical detection and visualization of antibodies patterned by microcontact printing.

Lanthanide oxide nanoparticles are promising luminescent probes in bioanalysis, because of their unique spectral properties, photostability, and low-cost synthesis. We report for the first time the application of europium-doped gadolinium oxide (Eu:Gd2O3) nanoparticles to the optical imaging of antibody micropatterns. The nanoparticles were synthesized by spray pyrolysis and coated with antibody (IgG) molecules by physical adsorption. Our experiments showed that the Eu:Gd2O3 is a good biocompatible solid support for antibody immobilization. The antibodies (anti-rabbit IgG) immobilized on the nanoparticles had excellent biological activity in the specific recognition reaction with rabbit IgG patterned in line strips (10 micromx10 microm) on a glass substrate by use of a micro-contact printing technique. The specific immunoreaction was confirmed by two independent microscopic techniques-fluorescence and scanning electron microscopy (SEM). Both microscopic images revealed that the nanoparticles were organized into designated structures as defined by the microcontact printing process with negligible non-specific binding. The nanoparticles can be used as fluorescent markers in a variety of immunosensing applications in a microscale format.