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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3

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Biological lasing in liquid microdroplets deposited on a superhydrophobic surface
(IEEE, 2014) Jonas, A.; McGloin, D.; N/A; N/A; Department of Chemistry; Department of Physics; Department of Physics; Aas, Mehdi; Karadağ, Yasin; Bayraktar, Halil; Anand, Suman; Kiraz, Alper; PhD Student; PhD Student; Faculty Member; Researcher; Faculty Member; Department of Chemistry; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 201764; N/A; 22542
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FRET lasing from self-assembled DNA tetrahedral nanostructures suspended in optofluidic droplet resonators
(Springer, 2014) Jonas, A.; Liu, H.; Fan, C.; Chen, Q.; Fan, X.; Department of Physics; N/A; N/A; Kiraz, Alper; Özelci, Ersan; Aas, Mehdi; Faculty Member; PhD Student; PhD Student; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 22542; N/A; N/A
We demonstrate Förster resonance energy transfer (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 bio/chemical sensing and novel photonic devices.
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Lasing in optofluidic ring resonators with aqueous quantum dots as their gain medium and the prospects of such lasers for biochemical sensing
(IEEE, 2016) Q, Chen; Jonas, A.; Fan, X.; Department of Physics; N/A; Kiraz, Alper; Aas, Mehdi; Faculty Member; PhD Student; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; 22542
We achieved four types of laser emissions with quantum dots (QDs) using the same high-Q-factor optofluidic ring resonator (OFRR) platform. In the first type, 2 μM QDs dissolved in toluene that filled the entire OFRR cavity volume were employed as the gain medium. The lasing threshold was 15-22 μJ/mm 2 . In the second type, 2 μM aqueous QDs were in bulk buffer solution that filled the entire OFRR cavity volume. The lasing threshold was 0.1 μJ/mm 2 , over 3 orders of magnitude lower than the state-of-the-art. In the third type, the aqueous QDs were immobilized as a single layer on the interface between the OFRR inner wall and buffer solution with a surface density as low as 3 × 10 9 - 10 10 cm -2 . The lasing threshold of 60 μJ/mm 2 was achieved. In the fourth type, we achieved optofluidic fluorescence resonance energy transfer (FRET) lasing using aqueous QDs as FRET donors and Cy5 dye molecules as acceptors. We observed lasing from Cy5 emission band in QD-Cy5 pair when excited at QD absorption band, far away from Cy5 absorption maximum. We also report a comprehensive theoretical analysis of optofluidic FRET lasers that was performed based on a Fabry-Perot microcavity using a rate equation model. By comparing FRET lasing based sensors with conventional sensors using FRET signals obtained by spontaneous fluorescence emission, we show that for optimal pump fluence and FRET pair concentration, FRET lasing can lead to more than 20-fold enhancement in detection sensitivities of conformation changes for linker lengths in the Förster radius range. We also 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 106 due to the radiative energy transfer in the cavity.
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Miniature droplet-based FRET lasers stabilized by superhydrophobic surfaces
(IEEE, 2014) Jonas, A.; N/A; N/A; Department of Physics; Özelci, Ersan; Aas, Mehdi; Kiraz, Alper; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 22542
We demonstrate optofluidic microlasers based on liquid microdroplets stabilized by a superhydrophobic surface. Lasing is achieved using highly efficient non-radiative Forster resonance energy transfer between donor and acceptor molecules placed within the droplets.
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Optically transportable optofluidic microlasers with liquid crystal cavities tuned by the electric field
(Amer Chemical Soc, 2021) Jonas, Alexandr; Pilat, Zdenek; Jezek, Jan; Bernatova, Silvie; Jedlicka, Petr; Zemanek, Pavel; Department of Physics; N/A; Kiraz, Alper; Aas, Mehdi; Faculty Member; PhD Student; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; 22542
Liquid crystal microdroplets with readily adjustable optical properties have attracted considerable attention for building reconfigurable optofluidic microsystems for sensing, imaging, and light routing applications. In this quest, development of active optical microcavities serving as versatile integrated sources of coherent light and ultra-sensitive environmental sensors has played a prominent role. Here, we study transportable optofluidic microlasers reversibly tunable by an external electric field, which are based on fluorophore-doped emulsion droplets of radial nematic liquid crystals manipulated by optical tweezers in microfluidic chips with embedded liquid electrodes. Full transparency of the electrodes formed by a concentrated electrolyte solution allows for applying an electric field to the optically trapped droplets without undesired heating caused by light absorption. Taking advantage of independent, precise control over the electric and thermal stimulation of the lasing liquid crystal droplets, we characterize their spectral tuning response at various optical trapping powers and study their relaxation upon a sudden decrease in the trapping power. Finally, we demonstrate that sufficiently strong applied electric fields can induce fully reversible phase transitions in the trapped droplets even below the bulk melting temperature of the used liquid crystal. Our observations indicate viability of creating electrically tunable, optically transported microlasers that can be prepared on-demand and operated within microfluidic chips to implement integrated microphotonic or sensing systems.
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Optofluidic fret lasers and their applications in novel photonic devices and biochemical sensing
(IEEE-Inst Electrical Electronics Engineers Inc, 2016) Chen, Qiushu; Jonas, Alexandr; Fan, Xudong; N/A; Department of Physics; Aas, Mehdi; Kiraz, Alper; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 22542
Incorporating fluorescence resonance energy transfer (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. Here, we carry out a comprehensive theoretical analysis of optofluidic FRET lasers based on a Fabry-Perot microcavity using a rate equation model. We compare conceptually distinct cases of donor and acceptor molecules diffusing freely in a 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 also show that for optimal experimental conditions, donor and acceptor emission intensities become over 20-fold more sensitive to FRET-pair concentration changes in the presence of FRET lasing. 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.
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Optofluidic FRET microlasers based on surfacesupported liquid microdroplets
(Iop Publishing Ltd, 2014) Jonas, A.; N/A; N/A; Department of Physics; Özelci, Ersan; Aas, Mehdi; Kiraz, Alper; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 22542
We demonstrate optofluidic microlasers using highly efficient non-radiative Forster resonance energy transfer (FRET) for pumping of gain medium placed within liquid microdroplets situated on a superhydrophobic surface. Microdroplets generated from a mixture of ethylene glycol, glycerol, and water and stained with the FRET donor-acceptor dye pair Rhodamine 6G-Rhodamine 700 serve as active optical resonant cavities hosting high-quality whispering gallery modes. Upon direct optical pumping of the donor with a pulsed laser, lasing is observed in the emission band of the acceptor as a result of efficient FRET coupling between the acceptor and donor molecules. FRET lasing is characterized for different acceptor and donor concentrations, and threshold pump fluences of acceptor lasing as low as 6.3 mJ cm(-2) are demonstrated. We also verify the dominance of the non-radiative FRET over cavity-assisted radiative energy transfer for the range of parameters studied in the experiments.