Mikrodamla lazerlerin olası opto-akışkan biyoalgılama uygulamaları

Dye-doped microdroplets can host lasing whispering gallery modes (WGMs). The sensitivity of laser emission wavelength, lasing threshold, lasing differential efficiency or even lasing beam spatial profile to the physical properties of microdroplets such as size, shape, relative refractive index of the droplet with respect to its surrounding medium, cavity Q-factor, or molecular binding/unbinding inside their constructive material can be used in sensing applications. To this end the necessity of control and manipulation of lasing microdroplets with minimum perturbation in their performance during the study suggests the utilization of advantages of optical forces as non-contact remote manipulation tools. In this thesis firstly we demonstrate lasing from optically manipulated dye-doped emulsion and aerosol droplets. We study their lasing properties such as lasing stability in time and dependence of the lasing WGMs on the physical properties of the microdroplets such as size, refractive index and dye concentration. Moreover, we use optical forces as deforming tools to stretch the microdroplet lasers for tuning their lasing emission. To do this a dual-beam trap is used to stretch the optically pumped dye-doped droplets of oil dispersed in water. Subsequently, resonant path lengths of WGMs propagating in the droplet are modified, leading to shifts in the microlaser emission wavelengths. Using this technique, we present all-optical, almost reversible spectral tuning of the lasing WGMs and show that the direction of tuning depends on the position of the pump beam focus on the droplet. In addition, we study the effects of temperature changes on the spectral position of lasing WGMs and demonstrate that droplet heating leads to red-tuning of the droplet lasing wavelength. In the biosensing side of this thesis, we study microdroplet biolasers that exploit active liquid optical resonators formed by surface-supported aqueous microdroplets containing purified yellow fluorescent protein or a suspension of live E. coli bacterial cells expressing the fluorescent protein. We first demonstrate lasing in fluorescent protein solutions at concentrations as low as 49 µM. Subsequently, we show that a single fluorescent bacterial cell of micrometre size confined in a droplet-based cavity can serve as a laser gain medium. Aqueous droplet microcavities allow the maintenance of the bacterial cells under conditions compatible with unimpeded growth. Therefore, our results also suggest a direct route to microscopic sources of laser light with self-regenerating gain media. Fluorescence resonance energy transfer (FRET) from a donor to an acceptor chromophore is used as an atomic scale ruler to measure the conformational changes in biomolecules. Incorporating FRET into a laser cavity can increase the sensitivity of FRET-based biochemical sensors due to the nonlinear dependence of the lasing output on the FRET parameters. In order to obtain a fundamental understanding of the sensing capabilities by FRET lasing in microdroplets we carry out a comprehensive theoretical analysis of optofluidic FRET lasers on a simpler counterparts of microdroplet lasers called Fabry-Perot microcavity using a rate equation model. We compare conceptually distinct cases of donor and acceptor molecules diffusing freely in bulk solution versus molecules connected by a fixed-length linker and show that the latter arrangement is especially well-suited for sensing of low-concentration analytes. By comparing FRET lasing-based sensors with conventional FRET sensors, we show that for optimal pump fluence and FRET-pair concentration, FRET lasing can lead to more than 100-fold enhancement in detection sensitivities of conformational changes in the Forster radius range. We study the dependence of the sensitivity enhancement on the cavity Q-factor. We show that the highest enhancements can be obtained for Q-factors between 10^4-10^6, and enhancement values decrease for Q-factors above 10^6 due to the radiative energy transfer in the cavity. Finally, we demonstrate FRET lasing from self-assembled tetrahedral DNA complexes labeled with Cy3 and Cy5 dyes and suspended as a gain medium in aqueous microdroplet cavities deposited on a superhydrophobic surface. Threshold fluence and differential efficiency are characterized for DNA complexes containing 1Cy3-3Cy5 and 3Cy3-1Cy5. We demonstrate that at a constant Cy5 concentration, average threshold fluence is reduced 3 to 8 times and average differential efficiency is enhanced 6 to 30 times for 3Cy3-1Cy5 as compared to 1Cy3-3Cy5. Using 3Cy3-1Cy5 nanostructures, FRET lasing is observed at very low concentrations down to 1 µM. This work shows that optofluidic microlasers based on droplet resonators can be combined with DNA nanotechnology to explore applications in biochemical sensing and novel photonic devices.