Researcher:
Ayaz, Rana Muhammed Armaghan

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PhD Student

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Rana Muhammed Armaghan

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Ayaz

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Ayaz, Rana Muhammed Armaghan

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2016 - 201912020 - 20225

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Now showing 1 - 6 of 6
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    Enhanced dissolution of liquid microdroplets in the extensional creeping flow of a hydrodynamic trap
    (Amer Chemical Soc, 2016) Tanyeri, Melikhan; N/A; Department of Physics; N/A; N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Department of Physics; Mustafa, Adil; Erten, Ahmet Can; Ayaz, Rana Muhammed Armaghan; Kayıllıoğlu, Oğuz; Eser, Ayşenur; Eryürek, Mustafa; Irfan, Muhammad; Muradoğlu, Metin; Kiraz, Alper; PhD Student; Teaching Faculty; PhD Student; PhD Student; Master Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; 233923; N/A; N/A; N/A; N/A; N/A; 46561; 22542
    A novel noncontact technique based on hydrodynamic trapping is presented to study the dissolution of freely suspended 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) the Epstein-Plesset (EP) model which considers only diffusive mass transfer, and (ii) the Zhang-Yang-Mao (ZYM) model which considers both diffusive and convective mass transfer 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 microdroplet liquid (c(s)) is used as the only fitting parameter. Experiments with BB microdroplets at low surfactant concentration (10 mu M) reveal c(s) values very similar to that reported in the literature. In contrast, experiments with BB and n-decanol microdroplets at 10 mM surfactant concentration, higher than the critical micelle concentration (CMC) of 5 mM, show further enhancements in microdroplet dissolution rates due to micellar solubilization. The presented method accurately tests the dissolution of single microdroplets into a second immiscible phase in extensional creeping flow and has potential for applications such as separation processes, food dispersion, and drug development/design.
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    Amplified phase shift - fiber cavity ring down spectroscopy for biosensing applications at 1550nm
    (Spie-Int Soc Optical Engineering, 2020) Cheema, Muhammed Imran; Ullah, Ubaid; Ghauri, M. Daniyal; N/A; N/A; N/A; Department of Physics; Ayaz, Rana Muhammed Armaghan; Uysallı, Yiğit; Morova, Berna; Kiraz, Alper; PhD Student; PhD Student; Researcher; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 22542
    We present a novel active fiber cavity platform for biosensing applications at 1550nm. We employed the phase shift-cavity ring down spectroscopy to the amplified fiber cavity and demonstrate sensing of sugar solutions with sensitivity and detection limit of 2659 degrees/RIU and 1.11 x 10(-5) RIU, respectively.
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    Linear cavity tapered fiber sensor using amplified phase-shift cavity ring-down spectroscopy
    (Optical Society of America (OSA), 2021) N/A; N/A; N/A; Department of Physics; Ayaz, Rana Muhammed Armaghan; Uysallı, Yiğit; Morova, Berna; Kiraz, Alper; PhD Student; PhD Student; Researcher; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 22542
    Phase-shift cavity ring-down spectroscopy (PS-CRDS) enables the measurement of minute fluctuations in optical loss encountered by an intensity modulated laser beam via lock-in demodulation of the accumulated signal phase as the laser beam propagates through the cavity. A linear fiber cavity containing two highly reflective fiber Bragg gratings (FBGs) and a tapered fiber is a favorable cavity geometry for sensor applications due to its compact nature and wide availability of its components at telecom wavelengths. However, due to the optical absorption of water, usage of telecom wavelengths for sensing of aqueous solutions degrades the sensitivity. This problem can be worked around via an optical amplifier placed inside the fiber cavity, compensating for intrinsic cavity losses. In this work, we demonstrate amplified PS-CRDS using such a linear cavity tapered fiber sensor utilizing an optical amplifier that enables the use of thinner tapered fibers, thus achieving higher sensitivities. We also employ continuous laser wavelength sweeps and analyze peak-to-peak PSs of individual cavity modes instead of using laser-cavity mode locking with the Pound-Drever-Hall technique. This enables further simplification of the experimental arrangement without compromising sensor performance. To test the performance of the reported sensor, solutions of varying sucrose concentrations in deionized water were measured systematically by tracking the average peak-to-peak PS of the cavity modes. Tapered fibers with waist diameters (D-taper) around 2.2 mu m were used during the experiment and limit of detection (LOD) values were measured down to 2.7 mu M, corresponding to 1.01 x 10(-7) RIU. The reported LOD values can be further improved by mechanical stabilization and thermal control of the device by the use of FBGs with higher reflectivity, by applying automatic optical gain control, and by spectral filtering to remove errors caused by amplified spontaneous emission. The presented concentration sensing device can be suitable for developing compact and highly sensitive, label-free optofluidic sensors.
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    Refractive index sensing by phase shift cavity ringdown spectroscopy
    (Springer Science and Business Media B.V., 2022) Cheema, M. Imran; N/A; N/A; N/A; N/A; Department of Physics; Ayaz, Rana Muhammed Armaghan; Uysallı, Yiğit; Bavili, Nima; Morova, Berna; Kiraz, Alper; PhD Student; PhD Student; Researcher; Researcher; Faculty Member; Department of Physics; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; N/A; College of Sciences; N/A; N/A; N/A; N/A; 22542
    Cavity ring down spectroscopy is a sensitive optical detection technique but it makes use of expensive electronics and data fitting algorithm. Both of these factors put a limitation on its performance for sensing applications. In this study cost effective and easy to use phase shift cavity ring down spectroscopy (PS-CRDS) technique, has been demonstrated for refractive index sensing. A refractive index sensor consisting of a tapered single mode optical fiber and two fiber Bragg gratings (FBGs) is proposed. In this sensing methodology, an intensity modulated laser beam centered at 1550 nm from a DFB laser is scanned at a narrow wavelength range and cavity modes are excited. Later the phase shift corresponding to these cavity modes is measured using a lock-in amplifier. Sucrose solutions of various concentrations are used for performance analysis of the refractive index sensing device. The resultant limit of detection (LOD) came out to be ~6.4 × 10−6 refractive index units (RIUs), which can be improved further by using thinner fiber tapers or fiber Bragg gratings with higher reflectivity. © 2022, Springer Nature B.V.
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    Linear cavity tapered fiber sensor using mode-tracking phase-shift cavity ring-down spectroscopy
    (Optical Society of America (OSA), 2020) Ullah, Ubaid; Ghauri, M. Daniyal; Cheema, M. Imran; N/A; N/A; N/A; N/A; Department of Physics; Ayaz, Rana Muhammed Armaghan; Uysallı, Yiğit; Morova, Berna; Bavili, Nima; Kiraz, Alper; PhD Student; PhD Student; Researcher; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 22542
    Phase-shift cavity ring-down spectroscopy (PS-CRDS) is an alternative CRDS approach that allows the detection of minute changes in cavity losses by measurement of the phase shift experienced by a modulated laser as it propagates through a high-quality factor cavity. Fiber loop resonators and microresonators have been employed in previous PS-CRDS demonstrations for liquid phase applications. Here we employ a tapered fiber-based linear fiber cavity for the demonstration of a highly sensitive sensor for sucrose concentration in water using PS-CRDS. Our linear fiber cavity has a small cavity length (similar to 1.25 m) that enables the observation and tracking of individual cavity modes in transmission and phase spectra recorded during laser sweeps. Hence, we eliminate the need for Pound-Drever-Hall locking of the laser source to the cavity resonance and thus provide a simpler experimental scheme. We analyze the recorded data sets to track the changes in phase shifts observed only when the laser wavelength is in resonance with the cavity modes. Such a mode-tracking PS-CRDS approach reveals limit of detection values less than around 400 mu M better than the performance of previously demonstrated PS-CRDS sucrose concentration sensors employing fiber loop resonators. The sensitivity of our sensor critically depends on the fiber taper diameter and can reach up to around 6 degrees/1 mM Suc. for 3.2 mu m taper diameter at 6 MHz modulation frequency using fiber Bragg gratings (FBGs) with reflectivities around 86%. This value can be further increased by employing FBGs with higher reflectivities or fiber tapers with smaller diameters provided that the cavity loss due to water absorption is compensated with an amplifier.
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    PublicationOpen Access
    Detection of aflatoxin M1 by fiber cavity attenuated phase shift spectroscopy
    (Optical Society of America (OSA), 2021) Ghauri, M. Daniyal; Hussain, Syed Zajif; Ullah, Ubaid; Saleem, Rahman Shah Zaib; Cheema, M. Imran; N/A; Department of Physics; Ayaz, Rana Muhammed Armaghan; Kiraz, Alper; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 22542
    Aflatoxin M1 (AFM1) is a carcinogenic compound commonly found in milk in excess of the WHO permissible limit, especially in developing countries. Currently, state-of-the-art tests for detecting AFM1 in milk include chromatographic systems and enzyme-linked-immunosorbent assays. Although these tests provide fair accuracy and sensitivity, they require trained laboratory personnel, expensive infrastructure, and many hours to produce final results. Optical sensors leveraging spectroscopy have a tremendous potential of providing an accurate, real-time, and specialist-free AFM1 detector. Despite this, AFM1 sensing demonstrations using optical spectroscopy are still immature. Here, we demonstrate an optical sensor that employs the principle of cavity attenuated phase shift spectroscopy in optical fiber cavities for rapid AFM1 detection in aqueous solutions at 1550 nm. The sensor constitutes a cavity built by two fiber Bragg gratings. We splice a tapered fiber of < 10 μm waist inside the cavity as a sensing head. For ensuring specific binding of AFM1 in a solution, the tapered fiber is functionalized with DNA aptamers followed by validation of the conjugation via FTIR, TGA, and EDX analyses. We then detect AFM1 in a solution by measuring the phase shift between a sinusoidally modulated laser input and the sensor output at resonant frequencies of the cavity. Our results show that the sensor has the detection limit of 20 ng/L (20 ppt), which is well below both the U.S. and the European safety regulations. We anticipate that the present work will lead towards a rapid and accurate AFM1 sensor, especially for low-resource settings.