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In JoVE (1)
Other Publications (5)
Articles by Yassin A. Hassan in JoVE
JoVE General
Rapid PCR Thermocycling using Microscale Thermal Convection
1Department of Mechanical Engineering, Texas A&M University, 2Department of Mechanical Engineering and Department of Nuclear Engineering, Texas A&M University, 3Department of Chemical Engineering, Texas A&M University
We describe a novel method to perform DNA replication via the polymerase chain reaction (PCR). Thermal convection is harnessed to continuously shuttle reagents between denaturing, annealing, and extension conditions by maintaining opposing surfaces of the reactor at constant temperature. This inherently simple design promises to make rapid PCR more accessible.
Other articles by Yassin A. Hassan on PubMed
Multiphase Bubbly Flow Visualization Using Particle Image Velocimetry
This article describes advances made in using particle image velocimetry (PIV) techniques in the study of multiphase bubbly flow. One of the fundamental issues in bubbly flow is the prediction of the velocity field. A methodology that allows for velocity field measurements of both components of a two-phase bubbly flow is presented. The bubble shape is also constructed via a shadow imaging technique combined with PIV.
Interfacial Complexation Explains Anomalous Diffusion in Nanofluids
A recent report describing dramatic anomalous enhancement in mass transport properties of nanofluids (>1000% increase in tracer dye diffusivity) has excited intense interest, but the findings have yet to be conclusively confirmed or explained. Here we investigate these phenomena using a microfluidic approach to directly probe tracer diffusion so that interactions between the suspension's principle components (nanoparticles, surfactant, and dye) can be clearly identified. Under conditions matching previously reported studies, we unexpectedly observe spontaneous formation of highly focused and intensely fluorescent plumes at the interface between fluid streams, suggesting strong complexation interactions between the dye and nanoparticles. These phenomena, driven by competition between the rates at which free tracer molecules are transported into the interfacial zone subsequently consumed by dye-nanoparticle complexation, have likely been incorrectly interpreted as anomalous diffusion enhancement. These interactions are important to consider when devising tracer-based studies of nanoparticle suspensions and may lay a foundation for new adsorption-based analytical methods.
Experimental Characterization of Temperature Sensitive Dyes for Laser Induced Fluorescence Thermometry
Laser induced fluorescence (LIF) is a non-intrusive optical technique that uses fluorescent dyes to measure whole-field fluid scalars such as temperature, concentration, pH, etc. LIF measurements' accuracy is strongly influenced by the fluorescent dye's behavior under different experimental conditions. In particular, ratiometric LIF thermometry accuracy depends on the correct selection of fluorescent dyes mixtures. Therefore, a thorough characterizations of fluorescent dyes is needed to obtain optimal mixtures and suitable optical configurations for given experimental conditions. This work presents the experimental characterization of fluorescein-27 (FL27) and rhodamine-B (RhB) mixtures to determine suitable aqueous solutions for ratiometric LIF thermometry. The mixtures' fluorescence emission intensity was measured with a spectrofluorometer, and the influence of concentration ratio (C(RhB)/C(FL27)), temperature, excitation wavelength (λ(ext)), and pH were analyzed. The results show that the temperature dependence of FL27 emission intensity changed from a negative to a positive value as the excitation wavelength increased. The temperature sensitivity (4.0% per °C) of RhB and FL27 mixture under 532 nm excitation wavelength was found to be higher than that of the commonly used mixture of RhB and Rh110 (2.0% per °C) at the same excitation wavelength. While the emission intensities of the dyes are sensitive to pH value, the temperature dependence is unaffected. The influence of concentration ratio on temperature sensitivity depends on both the detected bands of the emitted spectrum and the temperature; the concentration ratio should be selected based on the measured temperature scope. A new multicolor method or advanced two color method with high temperature sensitivity (6.0% or 10.0% per °C) is presented. This technique was specially developed to improve whole-field temperature measurements.
