| A micro droplet acts as an optical cavity that supports Morphology Dependent Resonances (MDRs) at wavelengths where the droplet circumference is an integer multiple of the emission wavelength. An experimental setup is built consisting of a home-built droplet generator modified from a piezo inkjet printhead, a function generator, a delay generator, a laser, a spectrometer and collection optics. Through this setup, it is possible to probe single droplets for chemical and biological detection. By utilizing a secondary laser/photodiode droplet detection system to the setup, the shot-to-shot differences in signal intensity are reduced resulting in improved signal stability and reproducibility.; By utilizing the developed setup, single bacterial cell detection is accomplished by observing suppression of optical resonances inside microdroplets. The effect of cell morphology and viability on lasing peaks was investigated.; In addition, a FRET-based immunoassay in microdroplets is demonstrated. Optical resonances in microdroplets increased the sensitivity of the detection through enhanced radiative energy transfer occurring at the droplet rim. An emulsion based technique is developed to localize the immunoassay reaction at the rim of a pendant droplet, increasing the coupling efficiency of the optical resonances.; Finally, lasing from spherical microdroplets ejected into a liquid medium with lower refractive index is observed in a microchannel. A microfabricated device that combines the droplet production and excitation/detection has been designed and fabricated. Droplet images show intense lasing emission around the droplet rim. Spectra from the droplets exhibit morphology dependent resonances (MDRs) which are red shifted relative to the bulk fluorescence emission from the dyes. The dependence of resonant peak intensities on the pump beam power is nonlinear. |
