A simple approach for the fabrication of 3D microelectrodes for impedimetric sensing

GULER, MUSTAFA TAHSIN/0000-0002-0478-3183; Elbuken, Caglar/0000-0001-8359-6871WOS: 000365167700026In this paper, we present a very simple method to fabricate three-dimensional (3D) microelectrodes integrated with microfluidic devices. We form the electrodes by etching a microwire placed across a microchannel. For precise control of the electrode spacing, we employ a hydrodynamic focusing microfluidic device and control the width of the etching solution stream. The focused widths of the etchant solution and the etching time determine the gap formed between the electrodes. Using the same microfluidic device, we can fabricate integrated 3D electrodes with different electrode gaps. We have demonstrated the functionality of these electrodes using an impedimetric particle counting setup. Using 3D microelectrodes with a diameter of 25 mu m, we have detected 6 mu m-diameter polystyrene beads in a buffer solution as well as erythrocytes in a PBS solution. We study the effect of electrode spacing on the signal-to-noise ratio of the impedance signal and we demonstrate that the smaller the electrode spacing the higher the signal obtained from a single microparticle. The sample stream is introduced to the system using the same hydrodynamic focusing device, which ensures the alignment of the sample in between the electrodes. Utilising a 3D hydrodynamic focusing approach, we force all the particles to go through the sensing region of the electrodes. This fabrication scheme not only provides a very low-cost and easy method for rapid prototyping, but which can also be used for applications requiring 3D electric field focused through a narrow section of the microchannel.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112M944]; European UnionEuropean Union (EU) [322019]This project was supported by The Scientific and Technological Research Council of Turkey (TUBITAK project no. 112M944) and European Union FP7 Marie Curie Career Integration Grant (no. 322019). The authors also thank Dr Aykutlu Dana, Dr Gokhan Bakan and Amir Ghobadi for their help in the measurement setup and their comments on the manuscript

Impedance-based viscoelastic flow cytometry

2nd International Conference of Microfluidics, Nanofluidics and Lab-on-a-Chip -- JUN 08-10, 2018 -- Beijing, PEOPLES R CHINASerhatlioglu, Murat/0000-0003-2083-6756; Elbuken, Caglar/0000-0001-8359-6871; GULER, MUSTAFA TAHSIN/0000-0002-0478-3183WOS: 000461091000010PubMed: 30632175Elastic nature of the viscoelastic fluids induces lateral migration of particles into a single streamline and can be used by microfluidic based flow cytometry devices. In this study, we investigated focusing efficiency of polyethylene oxide based viscoelastic solutions at varying ionic concentration to demonstrate their use in impedimetric particle characterization systems. Rheological properties of the viscoelastic fluid and particle focusing performance are not affected by ionic concentration. We investigated the viscoelastic focusing dynamics using polystyrene (PS) beads and human red blood cells (RBCs) suspended in the viscoelastic fluid. Elasto-inertial focusing of PS beads was achieved with the combination of inertial and viscoelastic effects. RBCs were aligned along the channel centerline in parachute shape which yielded consistent impedimetric signals. We compared our impedance-based microfluidic flow cytometry results for RBCs and PS beads by analyzing particle transit time and peak amplitude at varying viscoelastic focusing conditions obtained at different flow rates. We showed that single orientation, single train focusing of nonspherical RBCs can be achieved with polyethylene oxide based viscoelastic solution that has been shown to be a good candidate as a carrier fluid for impedance cytometry.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [215E086]The authors thank to Zeynep Erdogan, Ziya Isiksacan for contributions during rheometer measurements and preparation of the manuscript. The authors acknowledge support from Kutay Icoz, Urartu S. Seker, Recep Ahan and Elif D. Ergul for biological experiments. The detection system was acquired by financial support from the Scientific and Technological Research Council of Turkey (TUBITAK, Project No. 215E086)

Self-powered disposable prothrombin time measurement device with an integrated effervescent pump

Serhatlioglu, Murat/0000-0003-2083-6756; Elbuken, Caglar/0000-0001-8359-6871; GULER, MUSTAFA TAHSIN/0000-0002-0478-3183WOS: 000441519000045Coagulation is an essential physiological activity initiated by the interaction of blood components for clot formation. Prothrombin time (PT) measurement is a clinical test for the assessment of the extrinsic/common pathways of coagulation cascade. Periodic measurement of PT is required under numerous conditions including cardiovascular disorders. We present a self-powered microfluidic device for quantitative PT measurement from 50 mu l whole blood. The entire platform is disposable and does not require any external pumping, power, or readout units. It consists of a 3D-printed effervescent pump for CO2 generation from a chemical reaction, a cartridge for two-channel fluid flow (blood and water), and a grid for the quantification of fluid migration distance. Following the introduction of the fluids to the corresponding channel inlets, marking the coagulation start, an acid-base reaction is triggered for gas generation that drives the fluids within the channels. When the blood coagulates, its flow in the channel is halted. At that point, the distance water has travelled is measured using the grid. This distance correlates with PT as demonstrated through clinical tests with patient samples. This single-unit device has a potential for rapid evaluation and periodic monitoring of PT in the clinical settings and at the point-of-care.ASELSAN Graduate Scholarship for Turkish Academicians; Scientific and Technologic Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [213S127]The authors thank Prof. Ozcan Erel for the clinical tests and Dr. Ismail Bilican for the comments on the manuscript. Ziya Isiksacan is supported by ASELSAN Graduate Scholarship for Turkish Academicians. The authors acknowledge support from The Scientific and Technologic Research Council of Turkey (TUBITAK project no. 213S127)

Focusing-free impedimetric differentiation of red blood cells and leukemia cells: A system optimization

GULER, MUSTAFA TAHSIN/0000-0002-0478-3183WOS:000508110400028A focusing-free microfluidic impedimetric cell detection system is developed. The effect of the channel dimensions, solution conductivity, excitation voltage, and particle size on impedimetric signal outputs were optimized to increase the sensitivity of the system. Conventional microfabrication techniques were adapted to obtain low height, resealable microchannels. The geometry optimization was performed by a combination of analytical, numerical and experimental approaches. The results demonstrate that reliable impedimetric particle differentiation can be achieved without any labeling or particle focusing. The system parameters were studied and rule-of-thumb design criteria were provided. Finally, using the developed system, red blood cells and leukemia cells were experimentally detected and differentiated. Thanks to its simplicity, the focusing-free cell differentiation system may find applications in several cellular diagnostic uses.Kirikkale University (BAP Project)Kirikkale University [2016/077]; TUBITAK Scientific Support Department within the scope of 2211-Domestic PhD scholarship programTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK)This study was financially supported by Kirikkale University (BAP Project No: 2016/077). Ismail Bilican was supported by TUBITAK Scientific Support Department within the scope of 2211-Domestic PhD scholarship program. The authors thank Ziya Isiksacan for proofreading the manuscript

Tape'n roll inertial microfluidics

International Workshop on Piezoelectric Materials and Applications in Actuators (IWPMA) -- SEP 11-14, 2018 -- Kobe Chamber Commerce, Kobe, JAPANGULER, MUSTAFA TAHSIN/0000-0002-0478-3183WOS: 000496341800028Particle focusing and separation in microfluidic devices are critical for biological and medical applications. Inertial microfluidics is used for high throughput bio-particle focusing and separation. Most of the inertial microfluidic systems use planar structures for squeezing the particles in streams. Particle manipulation in 3D structures is often overlooked due to the complexity of the fabrication. In this study, we introduce some novel microchannel designs for inertial microfluidics by using a simple fabrication method that allows construction of both 2D and 3D structures. First, inertial migration of particles in 2D layouts including straight, spiral, and square spiral channels is investigated. Afterward, by applying a "tape'n roll" method, helical and double oriented spiral channels are configured and unexplored inertial migration behaviours are observed. Thanks to the simplicity of the fabrication and the unique characteristics of the new designs, high performance microfluidic inertial migration results can be obtained without any need for complicated microfabrication steps. The design optimization cycle can also be shortened using a computational approach we introduce in this study. (C) 2019 Elsevier B.V. All rights reserved.Japan Soc Precis Engn, Next Generat Sensors & Actuators Com

Assessment of PMMA and polystyrene based microfluidic chips fabricated using CO2 laser machining

Laser machining could be an alternative way for the fabrication of microchannels. In this study, laser machining of polymethylmethacrylate (PMMA) and polystyrene (PS) substrates were characterized in detail. A fabrication method preventing leakage at PS microchannel inlets was developed. The effect of laser parameters (power, speed and frequency) on engraving was analyzed by scanning electron microscopy. Laser ablation mechanism of both materials was explained through thermal analysis and material properties. Defocusing the laser beam was also analyzed as an additional parameter affecting the channel profile. Two parameters affecting the resolution were analyzed which are the minimum channel size that can be achieved by the laser beam and x-y stage of the laser engraver for straight and complex microchannel geometries. The hydrophilicity of the surface before and after laser machining was tested with contact angle measurements. The capabilities/limitations of machining were revealed through some complex channel structures. Finally, a passive micromixer and a droplet generator microfluidic devices were manufactured and tested, and promising results were obtained