Langmuir : the ACS journal of surfaces and colloids, Sep 29, 2016
A novel non-contact technique based on hydrodynamic trapping is presented to study the dissolutio... more A novel non-contact technique based on hydrodynamic trapping is presented to study the dissolution of liquid microdroplets into a second immiscible phase in a simple extensional creeping flow. Benzyl benzoate (BB) and n-decanol microdroplets are individually trapped at the stagnation point of a planar extensional flow, and dissolution of single microdroplets into an aqueous solution containing surfactant is characterized at different flow rates. The experimental dissolution curves are compared to two models: (i) Epstein-Plesset (EP) model which considers only diffusive mass transfer, and (ii) Zhang-Yang-Mao (ZYM) model which considers both diffusive and convective mass transfers in the presence of extensional creeping flow. The EP model significantly underpredicts the experimentally determined dissolution rates for all experiments. In contrast, very good agreement is observed between the experimental dissolution curves and the ZYM model when the saturation concentration of the micro...
ABSTRACT We report an integrated optical sensor of hydrogen (H2) gas employing an SU-8 polymer mi... more ABSTRACT We report an integrated optical sensor of hydrogen (H2) gas employing an SU-8 polymer microdisk resonator coated with a palladium (Pd) layer and coupled to a single-mode optical waveguide. The sensing mechanism relies on the expansion in the Pd lattice due to palladium hydride formation in the presence of H2. Strain induced in the microresonator then causes a red shift of the spectral positions of the resonator whispering gallery modes (WGMs) which is monitored using a tunable laser coupled to the waveguide. H2 concentrations below the flammable limit (4%) down to 0.3% could be detected in nitrogen atmosphere at room temperature. For H2 concentrations between 0.3− 1 %, WGM spectral positions shifted linearly with H2 concentration at a rate of 32pm/% H2. Average response time of the devices was measured to be 50 s for 1%H2. The proposed device concept can also be used to detect different chemical gases by using appropriate sensing layers.
A self-stabilization mechanism locking the size of single inorganic salt (NaCl)–water microdrople... more A self-stabilization mechanism locking the size of single inorganic salt (NaCl)–water microdroplets that are standing on a superhydrophobic surface and kept in a humidity-controlled chamber is demonstrated. The effect is based on the hysteretic behavior of a photothermal tuning cycle caused by the whispering gallery mode (WGM) absorption resonances that are observed when scanning the power of an infrared laser focused at the rim of a microdroplet. When locked, the microdroplet size and WGM spectrum are resilient to environmental perturbations and can be maintained for hours as the mechanism does not rely on a photobleachable dye. The bistable nature of the system is also demonstrated, enabling reversible switching between two sizes. A rate equation-based thermodynamical model of the hysteretic behavior is provided, giving good agreement with the experimental results. Our results may be used to establish stable experimental conditions for ultrahigh resolution spectroscopy of microdro...
We report lasing in airborne, rhodamine B-doped glycerol-water droplets with diameters ranging be... more We report lasing in airborne, rhodamine B-doped glycerol-water droplets with diameters ranging between 7.7 and 11.0 μm, which were localized using optical tweezers. While being trapped near the focal point of an infrared laser, the droplets were pumped with a Q-switched green laser. Our experiments revealed nonlinear dependence of the intensity of the droplet whispering gallery modes (WGMs) on the pump laser fluence, indicating dye lasing. The average wavelength of the lasing WGMs could be tuned between 600 and 630 nm by changing the droplet size. These results may lead to new ways of probing airborne particles, exploiting the high sensitivity of stimulated emission to small perturbations in the droplet laser cavity and the gain medium.
Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 2002
Abstract Summary form only given. Recent photon correlation measurements performed on single quan... more Abstract Summary form only given. Recent photon correlation measurements performed on single quantum dots provide evidence for non-classical emission from these structures. We show here how this technique can be used to study multi-charged lines in quantum dots (QDs). We studied a sample of InAs/GaAs MBE grown quantum dots. Single QDs are isolated in 2 microdisks containing at most one QD. The sample is studied at 4 K in a microphotoluminescence setup for which a cw diode laser emitting at 785 nm is used. The ...
The development of non-toxic theranostic nanoparticles capable of delivering a therapeutic cargo ... more The development of non-toxic theranostic nanoparticles capable of delivering a therapeutic cargo and providing a means for diagnosis is one of the most challenging tasks in nano-biotechnology. Gene therapy is a very important mode of therapy and polyethyleneimine (PEI) is one of the most successful vehicles for gene transfection, yet poses significant toxicity. Optical imaging utilizing quantum dots is one of the newer but fast growing diagnostic modalities, which requires non-toxic, highly luminescent materials, preferentially active in the near infrared region. Ag 2 S NIRQDs fit to this profile perfectly. Here, we demonstrate the aqueous synthesis of cationic Ag 2 S NIRQDs with a mixed coating of 2-mercapto-propionic acid (2MPA) and PEI (branched, 25 kDa), which are highly luminescent in the NIR-I window (λ em = 810–840 nm) as new theranostic nanoparticles. Synergistic stabilization of the QD surface via the simultaneous use of a small molecule and a polymeric material provided the highest quantum yield, 150% (with respect to LDS 798 at pH 7.4), reported in the literature for Ag 2 S. These cationic particles show a dramatic improvement in cytocompatibility even without PEGylation, a strong optical signal easily detected by confocal laser microscopy and effective conjugation and transfection of the green fluo-rescence protein plasmid (pGFP) to HeLa and MCF-7 cell lines (40% efficiency). Overall, these Ag 2 S NIRQDs show great potential as new theranostics.
Langmuir : the ACS journal of surfaces and colloids, Sep 29, 2016
A novel non-contact technique based on hydrodynamic trapping is presented to study the dissolutio... more A novel non-contact technique based on hydrodynamic trapping is presented to study the dissolution of liquid microdroplets into a second immiscible phase in a simple extensional creeping flow. Benzyl benzoate (BB) and n-decanol microdroplets are individually trapped at the stagnation point of a planar extensional flow, and dissolution of single microdroplets into an aqueous solution containing surfactant is characterized at different flow rates. The experimental dissolution curves are compared to two models: (i) Epstein-Plesset (EP) model which considers only diffusive mass transfer, and (ii) Zhang-Yang-Mao (ZYM) model which considers both diffusive and convective mass transfers in the presence of extensional creeping flow. The EP model significantly underpredicts the experimentally determined dissolution rates for all experiments. In contrast, very good agreement is observed between the experimental dissolution curves and the ZYM model when the saturation concentration of the micro...
ABSTRACT We report an integrated optical sensor of hydrogen (H2) gas employing an SU-8 polymer mi... more ABSTRACT We report an integrated optical sensor of hydrogen (H2) gas employing an SU-8 polymer microdisk resonator coated with a palladium (Pd) layer and coupled to a single-mode optical waveguide. The sensing mechanism relies on the expansion in the Pd lattice due to palladium hydride formation in the presence of H2. Strain induced in the microresonator then causes a red shift of the spectral positions of the resonator whispering gallery modes (WGMs) which is monitored using a tunable laser coupled to the waveguide. H2 concentrations below the flammable limit (4%) down to 0.3% could be detected in nitrogen atmosphere at room temperature. For H2 concentrations between 0.3− 1 %, WGM spectral positions shifted linearly with H2 concentration at a rate of 32pm/% H2. Average response time of the devices was measured to be 50 s for 1%H2. The proposed device concept can also be used to detect different chemical gases by using appropriate sensing layers.
A self-stabilization mechanism locking the size of single inorganic salt (NaCl)–water microdrople... more A self-stabilization mechanism locking the size of single inorganic salt (NaCl)–water microdroplets that are standing on a superhydrophobic surface and kept in a humidity-controlled chamber is demonstrated. The effect is based on the hysteretic behavior of a photothermal tuning cycle caused by the whispering gallery mode (WGM) absorption resonances that are observed when scanning the power of an infrared laser focused at the rim of a microdroplet. When locked, the microdroplet size and WGM spectrum are resilient to environmental perturbations and can be maintained for hours as the mechanism does not rely on a photobleachable dye. The bistable nature of the system is also demonstrated, enabling reversible switching between two sizes. A rate equation-based thermodynamical model of the hysteretic behavior is provided, giving good agreement with the experimental results. Our results may be used to establish stable experimental conditions for ultrahigh resolution spectroscopy of microdro...
We report lasing in airborne, rhodamine B-doped glycerol-water droplets with diameters ranging be... more We report lasing in airborne, rhodamine B-doped glycerol-water droplets with diameters ranging between 7.7 and 11.0 μm, which were localized using optical tweezers. While being trapped near the focal point of an infrared laser, the droplets were pumped with a Q-switched green laser. Our experiments revealed nonlinear dependence of the intensity of the droplet whispering gallery modes (WGMs) on the pump laser fluence, indicating dye lasing. The average wavelength of the lasing WGMs could be tuned between 600 and 630 nm by changing the droplet size. These results may lead to new ways of probing airborne particles, exploiting the high sensitivity of stimulated emission to small perturbations in the droplet laser cavity and the gain medium.
Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 2002
Abstract Summary form only given. Recent photon correlation measurements performed on single quan... more Abstract Summary form only given. Recent photon correlation measurements performed on single quantum dots provide evidence for non-classical emission from these structures. We show here how this technique can be used to study multi-charged lines in quantum dots (QDs). We studied a sample of InAs/GaAs MBE grown quantum dots. Single QDs are isolated in 2 microdisks containing at most one QD. The sample is studied at 4 K in a microphotoluminescence setup for which a cw diode laser emitting at 785 nm is used. The ...
The development of non-toxic theranostic nanoparticles capable of delivering a therapeutic cargo ... more The development of non-toxic theranostic nanoparticles capable of delivering a therapeutic cargo and providing a means for diagnosis is one of the most challenging tasks in nano-biotechnology. Gene therapy is a very important mode of therapy and polyethyleneimine (PEI) is one of the most successful vehicles for gene transfection, yet poses significant toxicity. Optical imaging utilizing quantum dots is one of the newer but fast growing diagnostic modalities, which requires non-toxic, highly luminescent materials, preferentially active in the near infrared region. Ag 2 S NIRQDs fit to this profile perfectly. Here, we demonstrate the aqueous synthesis of cationic Ag 2 S NIRQDs with a mixed coating of 2-mercapto-propionic acid (2MPA) and PEI (branched, 25 kDa), which are highly luminescent in the NIR-I window (λ em = 810–840 nm) as new theranostic nanoparticles. Synergistic stabilization of the QD surface via the simultaneous use of a small molecule and a polymeric material provided the highest quantum yield, 150% (with respect to LDS 798 at pH 7.4), reported in the literature for Ag 2 S. These cationic particles show a dramatic improvement in cytocompatibility even without PEGylation, a strong optical signal easily detected by confocal laser microscopy and effective conjugation and transfection of the green fluo-rescence protein plasmid (pGFP) to HeLa and MCF-7 cell lines (40% efficiency). Overall, these Ag 2 S NIRQDs show great potential as new theranostics.
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Papers by Alper Kiraz