Saif Abdul Kadir Khan
Email Address
chesakk@nus.edu.sg
Organizational Units
ENGINEERING
faculty
COLLEGE OF DESIGN & ENG
faculty
47 results
Publication Search Results
Now showing 1 - 10 of 47
Publication Exploring optical properties of liquid crystals for developing label-free and high-throughput microfluidic immunoassays(2009-01-12) Xue, C.-Y.; Khan, S.A.; Yang, K.-L.; CHEMICAL & BIOMOLECULAR ENGINEERINGA liquid crystals (LC)-based detecting method suitable for microfluidic immunoassays was successfully demonstrated in the study. The microfluidic device comprised three serpentine channels supported on an immunoglobulin (IgG)-coated glass slides and sealed with poly(dimethylsiloxane) (PDMS) with embedded microfluidic channels. Two fluorescence-labeled antibody solutions, fluorescein-isothiocyanate-conjugated anti-human IgG (FITC-anti0IgG) and FITC-conjugated anti-biotin IgG (FITC-anti-biotin), were then piped into the inlet reservoirs of two separate channels, allowing both solutions to enter the microfluidic channels by capillary actions. After 30 minutes, the slides were rinsed with PBS buffer with 1% SDS and deionized water. It was demonstrated that LC-based detection and microfluidic immunoassays provide a label-free, multiplexed and high-throughput diagnostic platform, which can be used to detect multiple samples of anti-IgG, anti-biotin and mixture of both.Publication Passively triggering asymmetric digital flows at symmetric microfluidic junctions(2011) Parthiban, P.; Khan, S.A.; CHEMICAL & BIOMOLECULAR ENGINEERINGThe diverse and often complex dynamics of digital flows in microfluidic networks is of much current interest to the microfluidic community due to the wide range of applications facilitated by such flows. In this paper, we highlight a counterintuitive phenomenon in the traffic of bubble trains. We show how all bubbles of a train can be sorted exclusively into one of the arms of a symmetric loop by the simply increasing its speed beyond a threshold value. We find that this filter regime is accessed when bubbles lower the hydrodynamic resistance of microchannels, an interesting phenomenon in itself. Copyright © (2011) by the Chemical and Biological Microsystems Society.Publication Microreactor engineering for metallic nanoparticles synthesis(2008) Khan, S.A.; CHEMICAL & BIOMOLECULAR ENGINEERINGPublication UV-Defined flat PDMS stamps suitable for microcontact printing(2010-03-02) Xue, C.-Y.; Chin, S.Y.; Khan, S.A.; Yang, K.-L.; CHEMICAL & BIOMOLECULAR ENGINEERINGWe report a simple method of creating well-defined micropatterns on the surface of a flat PDMS stamp, making it suitable for microcontact printing of proteins. This method only requires a UV lamp (254 nm) and a TEM grid (as a photomask) to modify the surface of PDMS for creating desired micropatterns. By using the UV-modified stamp, a printed protein micropattem that resembles the original TEM. grid can be obtained. Surprisingly, unlike the oxygenplasma-treated. PDMS, the UV-modified flat stamp is also long-lasting ( > 1 week). The method reported herein is very economical for microcontact printing applications because expensive silicon masters and microstructured PDMS are no longer required. © 2009 American Chemical Society.Publication Filtering microfluidic bubble trains at a symmetric junction(2012-02-07) Parthiban, P.; Khan, S.A.; CHEMICAL & BIOMOLECULAR ENGINEERINGWe report how a nominally symmetric microfluidic junction can be used to sort all bubbles of an incoming train exclusively into one of its arms. The existence of this "filter" regime is unexpected, given that the junction is symmetric. We analyze this behavior by quantifying how bubbles modulate the hydrodynamic resistance in microchannels and show how speeding up a bubble train whilst preserving its spatial periodicity can lead to filtering at a nominally symmetric junction. We further show how such an asymmetric traffic of bubble trains can be triggered in symmetric geometries by identifying conditions wherein the resistance to flow decreases with an increase in the number of bubbles in the microchannel and derive an exact criterion to predict the same. © 2012 The Royal Society of Chemistry.Publication Two-step machine learning enables optimized nanoparticle synthesis(Nature Research, 2021-04-20) Mekki-Berrada, Flore; Ren, Zekun; Huang, Tan; Wong, Wai Kuan; Zheng, Fang; Xie, Jiaxun; Tian, Isaac Parker Siyu; Jayavelu, Senthilnath; Mahfoud, Zackaria; Bash, Daniil; Hippalgaonkar, Kedar; Khan, Saif; Buonassisi, Tonio; Li, Qianxiao; Wang, Xiaonan; MATHEMATICS; COLLEGE OF DESIGN AND ENGINEERING; CHEMICAL & BIOMOLECULAR ENGINEERINGIn materials science, the discovery of recipes that yield nanomaterials with defined optical properties is costly and time-consuming. In this study, we present a two-step framework for a machine learning-driven high-throughput microfluidic platform to rapidly produce silver nanoparticles with the desired absorbance spectrum. Combining a Gaussian process-based Bayesian optimization (BO) with a deep neural network (DNN), the algorithmic framework is able to converge towards the target spectrum after sampling 120 conditions. Once the dataset is large enough to train the DNN with sufficient accuracy in the region of the target spectrum, the DNN is used to predict the colour palette accessible with the reaction synthesis. While remaining interpretable by humans, the proposed framework efficiently optimizes the nanomaterial synthesis and can extract fundamental knowledge of the relationship between chemical composition and optical properties, such as the role of each reactant on the shape and amplitude of the absorbance spectrum. © 2021, The Author(s).Publication Multi-color lasing in chemically open droplet cavities(Nature Publishing Group, 2018) Zheng, L; Zhi, M; Chan, Y; Khan, S.A; CHEMISTRY; CHEMICAL & BIOMOLECULAR ENGINEERINGIn this paper, we demonstrate FRET-based multicolor lasing within chemically open droplet cavities that allow online modulation of the gain medium composition. To do this, we generated monodisperse microfluidic droplets loaded with coumarin 102 (donor), where the spherical droplets acted as whispering gallery mode (WGM) optical cavities in which coumarin 102 lasing (~ 470 nm) was observed. The lasing color was switched from blue to orange by the introduction of a second dye (acceptor, rhodamine 6 G) into the flowing droplet cavities; subsequent lasing from rhodamine 6 G (~ 590 nm) was observed together with the complete absence of coumarin 102 emission. The ability to control color switching online within the same droplet cavity enables sequential detection of multiple target molecules within or around the cavity. As a demonstration of this concept, we show how the presence of FITC-Dextran and methylene blue (MB) in the medium surrounding the lasing droplets can be sequentially detected by the blue and orange laser respectively. The method is simple and can be extended to a range of water-soluble dyes, thus enabling a wide spectral range for the lasing with the use of a single pump laser source. © 2018, The Author(s).Publication Tunable spatial heterogeneity in structure and composition within aqueous microfluidic droplets(2012-04-26) Hui Sophia Lee, S.; Wang, P.; Kun Yap, S.; Alan Hatton, T.; Khan, S.A.; CHEMICAL & BIOMOLECULAR ENGINEERINGIn this paper, we demonstrate biphasic microfluidic droplets with broadly tunable internal structures, from simple near-equilibrium drop-in-drop morphologies to complex yet uniform non-equilibrium steady-state structures. The droplets contain an aqueous mixture of poly(ethylene glycol) (PEG) and dextran and are dispensed into an immiscible oil in a microfluidic T-junction device. Above a certain well-defined threshold droplet speed, the inner dextran-rich phase is "stirred" within the outer PEG-rich phase. The stirred polymer mixture is observed to exhibit a near continuum of speed and composition-dependent phase morphologies. There is increasing interest in the use of such aqueous two-phase systems in microfluidic devices for biomolecular applications in a variety of contexts. Our work presents a method to go beyond equilibrium phase morphologies in generating microfluidic "multiple" emulsions and at the same time raises the possibility of biochemical experimentation in benign yet complex biomimetic milieus. © 2012 American Institute of Physics.Publication Fireflies-on-a-chip: (Ionic Liquid)-aqueous microdroplets for biphasic chemical analysis(2012-07-23) Barikbin, Z.; Rahman, M.T.; Khan, S.A.; CHEMICAL & BIOMOLECULAR ENGINEERINGInspired by the enchanting bioluminescence of fireflies, herein microfluidic droplet-based 'fireflies' for non-invasive biphasic chemical analysis are demonstrated. Bicompartmental droplets are created where a model analyte is transported from the aqueous compartment to the adjacent ionic liquid segment, yielding a bright fluid firefly structure via a localized catalytic reaction. Analysis of fluorescence emission kinetics and a method to passively decouple the two compartments at a constriction are presented. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Publication Droplet-based microfluidic synthesis of anisotropic metal nanocrystals(2009-12-18) Duraiswamy, S.; Khan, S.A.; CHEMICAL & BIOMOLECULAR ENGINEERINGA droplet-based microfluidic method for the preparation of anisotropic gold nanocrystal dispersions is presented. Gold nanoparticle seeds and growth reagents are dispensed into monodisperse picoliter droplets within a microchannel. Confinement within small droplets prevents contact between the growing nanocrystals and the microchannel walls. The critical factors in translating macroscale flask-based methods to a flow-based microfluidic method are highlighted and approaches are demonstrated to flexibly fine tune nanoparticle shapes into three broad classes: spheres/spheroids, rods, and extended sharp-edged structures, thus varying the optical resonances in the visible-near-infrared (NIR) spectral range. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.