Browsing by Author "Tefek, Uzay"

Now showing 1 - 13 of 13

Restricted
Ankara Model Uçak Kurumu Derneği tarihi
(Bilkent University, 2018) Altun, Aslı; Keskin, Büşra Gizem; Çetiner, Merve Ayşe; Tefek, Uzay; Coşkun, Yağmur Buğu
Open Access
Classification of dielectric microparticles by microwave impedance cytometry
(Cold Spring Harbor Laboratory, 2022-09-28) Hanay, M. Selim; Sarı, Burak; Tefek, Uzay
AbstractCoulter counters and impedance cytometry are commonly used for counting microscopic objects, such as cells and microparticles flowing in a liquid, as well as to obtain their size distribution. However, the ability of these techniques to provide simultaneous material information — via dielectric permittivity measurements — has been limited so far. The challenge stems from the fact that the signals generated by microparticles of identical size, but different material composition, are close to each other. The similarity in impedance signals arises because the material-dependent factor is determined mainly by the volume of aqueous solution displaced by the microparticles, rather than the microparticles themselves. To differentiate between materially distinct particles with similar geometry and size, another measurement mode needs to be implemented. Here, we describe a new microfluidics-based sensor that provides material classification between microparticles with similar sizes by integrating impedance cytometry with microwave resonator sensors on the same chip. While low-frequency impedance cytometry provides the geometric size of particles, the microwave sensor operating at three orders-of-magnitude higher frequency provides their electrical size. By combining these two measurements, the Clausius-Mossotti factors of microparticles can be calculated to serve as a differentiation parameter. In addition to distinguishing dielectric materials from cells and metals, we classified two different dielectric microparticles with similar sizes and electrical characteristics: polystyrene and soda lime glass, with 94% identification accuracy. The proposed technique can serve as an automated monitoring system for quality control of manufactured microparticles and facilitate environmental microplastic screening.
Open Access
Dielectric detection of single nanoparticles using a microwave resonator integrated with a nanopore
(American Chemical Society, 2024-02-08) Seçme, Arda; Küçükoğlu, Berk; Pisheh, Hadi S.; Alataş, Yağmur Ceren; Tefek, Uzay; Uslu, Hatice Dilara; Kaynak, Batuhan E.; Alhmoud, Hashim; Hanay, M. Selim
The characterization of individual nanoparticles in a liquid constitutes a critical challenge for the environmental, material, and biological sciences. To detect nanoparticles, electronic approaches are especially desirable owing to their compactness and lower costs. While electronic detection in the form of resistive-pulse sensing has enabled the acquisition of geometric properties of various analytes, impedimetric measurements to obtain dielectric signatures of nanoparticles have scarcely been reported. To explore this orthogonal sensing modality, we developed an impedimetric sensor based on a microwave resonator with a nanoscale sensing gap surrounding a nanopore built on a 220 nm silicon nitride membrane. The microwave resonator has a coplanar waveguide configuration with a resonance frequency of approximately 6.6 GHz. The approach of single nanoparticles near the sensing region and their translocation through the nanopores induced sudden changes in the impedance of the structure. The impedance changes, in turn, were picked up by the phase response of the microwave resonator. We worked with 100 and 50 nm polystyrene nanoparticles to observe single-particle events. Our current implementation was limited by the nonuniform electric field at the sensing region. This work provides a complementary sensing modality for nanoparticle characterization, where the dielectric response, rather than ionic current, determines the signal.
Open Access
High resolution dielectric characterization of single cells and microparticles using integrated microfluidic microwave sensors
(Institute of Electrical and Electronics Engineers, 2023-03-01) Seçme, Arda; Tefek, Uzay; Sarı, Burak; Pisheh, Hadi Sedaghat; Uslu, H. Dilara; Akbulut, Özge; Küçükoğlu, Berk; Erdoğan, R. Tufan; Alhmoud, Hashim; Şahin, Özgür; Hanay, M. Selim
Microwave sensors can probe intrinsic material properties of analytes in a microfluidic channel at physiologically relevant ion concentrations. While microwave sensors have been used to detect single cells and microparticles in earlier studies, the synergistic use and comparative analysis of microwave sensors with optical microscopy for material classification and size tracking applications have been scarcely investigated so far. Here we combined microwave and optical sensing to differentiate microscale objects based on their dielectric properties. We designed and fabricated two types of planar sensor: a Coplanar Waveguide Resonator (CPW) and a Split-Ring Resonator (SRR). Both sensors possessed sensing electrodes with a narrow gap to detect single cells passing through a microfluidic channel integrated on the same chip. We also show that standalone microwave sensors can track the relative changes in cellular size in real-time. In sensing single 20-micron diameter polystyrene particles, Signal-to-Noise ratio values of approximately 100 for CPW and 70 for SRR sensors were obtained. These findings demonstrate that microwave sensing technology can serve as a complementary technique for single-cell biophysical experiments and microscale pollutant screening.
Open Access
High resolution dielectric characterization of single cells and microparticles using integrated microfluidic microwave sensors
(Institute of Electrical and Electronics Engineers, 2023-03-01) Seçme, Arda; Tefek, Uzay; Sarı, Burak; Pisheh, Hadi Sedaghat; Uslu, H. Dilara; Akbulut, Özge; Küçükoğlu, Berk; Erdogan, R. Tufan; Alhmoud, Hashim; Şahin, Özgür; Hanay, M. Selim
Microwave sensors can probe intrinsic material properties of analytes in a microfluidic channel at physiologically relevant ion concentrations. While microwave sensors have been used to detect single cells and microparticles in earlier studies, the synergistic use and comparative analysis of microwave sensors with optical microscopy for material classification and size tracking applications have been scarcely investigated so far. Here we combined microwave and optical sensing to differentiate microscale objects based on their dielectric properties. We designed and fabricated two types of planar sensor: a Coplanar Waveguide Resonator (CPW) and a Split-Ring Resonator (SRR). Both sensors possessed sensing electrodes with a narrow gap to detect single cells passing through a microfluidic channel integrated on the same chip. We also show that standalone microwave sensors can track the relative changes in cellular size in real-time. In sensing single 20-micron diameter polystyrene particles, Signal-to-Noise ratio values of approximately 100 for CPW and 70 for SRR sensors were obtained. These findings demonstrate that microwave sensing technology can serve as a complementary technique for single-cell biophysical experiments and microscale pollutant screening.
Embargo
Microwave resonant sensor integration with impedance cytometry in microfluidic platform for probing micro-scale dielectric permittivity
(2023-09) Tefek, Uzay
This thesis presents a novel multiphysical sensor that integrates low-frequency impedance cytometry with high-frequency microwave capacitance sensing. The characterization of microscale objects, including microparticles and cells, is essential in various scientific disciplines, such as biology, materials science, and environmental science. Accurate identification and classification of these microscale entities are critical for applications ranging from drug delivery optimization to environmental impact assessment, however, the current techniques fall short in terms of the rapidity and cost-effectiveness necessary for analyzing extensive populations. To address this challenge, our hybrid sensor combines low-frequency impedance cytometry and high-frequency microwave capacitance sensing for material characterization based on dielectric permittivity. This integration offers a rapid, cost-effective, and highly accurate method for identifying and characterizing microscale particles and cells. Experimental studies demonstrate the sensor’s efficacy, achieving remarkable signal-to-noise ratios. The sensor’s versatility ex-tends monitoring permittivity changes in single cells exposed to fixing agents offering valuable insights into cellular properties. In summary, this thesis introduces an innovative multiphysical sensor that advances microscale entity analysis, enabling rapid and precise identification and characterization.
Open Access
Microwave resonators enhanced with 3D liquid-metal electrodes for microparticle sensing in microfluidic applications
(Institute of Electrical and Electronics Engineers , 2023-11-22) Alataş, Yağmur Ceren; Tefek, Uzay; Sari, B.; Hanay, Mehmet Selim
In electrical sensing applications, achieving a uniform electric field at the sensing region is required to eliminate the compounding effect of particle location on the signal magnitude. To generate a uniform electric field in a microfluidic platform, 3D electrodes based on conductive electrolyte liquids have been developed before, where the ionic conductivity of the electrolyte was sufficient for impedance measurements at low frequencies (typically lower than 50 MHz). However, electrolyte liquids cannot be used as electrodes at microwave frequencies (>1 GHz) due to the low mobility of ions. Here, we used Galinstan, a room-temperature liquid metal, to microfabricate 3D liquid electrodes connected to a microwave resonator — and all integrated within a microfluidic system. By generating a highly uniform electric field, a mixture of 20 μm and 30 μm diameter polystyrene particles were measured and analyzed without any calibration for particle position. The results demonstrate the utility of liquid electrodes in enhancing the electrical characteristics of microwave resonant sensors.
Open Access
On-chip flow rate sensing via membrane deformation and bistability probed by microwave resonators
(Springer Link, 8-04-2023) Seçme, Arda; Pisheh, Hadi Sedaghat; Tefek, Uzay; Uslu, H. Dilara; Küçükoğlu, Berk; Alataş, Ceren; Kelleci, Mehmet; Hanay, Mehmet Selim
Precise monitoring of fluid flow rates constitutes an integral problem in various lab-on-a-chip applications. While off-chip flow sensors are commonly used, new sensing mechanisms are being investigated to address the needs of increasingly complex lab-on-a-chip platforms which require local and non-intrusive flow rate sensing. In this regard, the deformability of microfluidic components has recently attracted attention as an on-chip sensing mechanism. To develop an on-chip flow rate sensor, here we utilized the mechanical deformations of a 220 nm thick Silicon Nitride membrane integrated with the microfluidic channel. Applied pressure and fluid flow induce different modes of deformations on the membrane, which are electronically probed by an integrated microwave resonator. The flow changes the capacitance, and in turn resonance frequency, of the microwave resonator. By tracking the resonance frequency, liquid flow was probed with the device. In addition to responding to applied pressure by deflection, the membrane also exhibits periodic pulsation motion under fluid flow at a constant rate. The two separate mechanisms, deflection and pulsation, constitute sensing mechanisms for pressure and flow rate. Using the same device architecture, we also detected pressure-induced deformations by a gas to draw further insight into the sensing mechanism of the membrane. Flow rate measurements based on the deformation and instability of thin membranes demonstrate the transduction potential of microwave resonators for fluid–structure interactions at micro- and nanoscales.
Open Access
On-chip liquid and gas flow rate sensing via membrane deformation and bistability probed by microwave resonators
(Springer, 2022-11-15) Seçme, Arda; Pisheh, Hadi Sedaghat; Uslu, H. Dilara; Tefek, Uzay; Küçükoğlu, Berk; Alataş, Ceren; Kelleci, Mehmet; Hanay, M. Selim
Abstract Precise monitoring of fluid flow rates constitutes an integral problem in various lab-on-a-chip applications. While off-chip flow sensors are commonly used, new sensing mechanisms are being investigated to address the needs of increasingly complex lab-on-a-chip platforms which require local and non-intrusive flow rate sensing. In this regard, the deformability of microfluidic components has recently attracted attention as an on-chip sensing mechanism. To develop an on-chip flow rate sensor, here we utilized the mechanical deformations of a 220 nm thick Silicon Nitride membrane integrated with the microfluidic channel. Fluid flow induces deformations on the membrane, which is electronically probed by the changes in the capacitance and resonance frequency of an overlapping microwave resonator. By tracking the resonance frequency, both liquid and gas flows were probed with the same device architecture. For liquid flow experiments, a secondary sensing mechanism emerged when it was observed that steady liquid flow induces periodic deformations on the membrane. Here, the period of membrane deformation depends on the flow rate and can again be measured electronically by the microwave sensor. Flow rate measurements based on the deformation and instability of thin membranes demonstrate the transduction potential of microwave resonators for fluid-structure interactions at micro and nanoscales.
Open Access
Permittivity-based classification by the integration of impedance cytometry and microwave sensing
(IEEE - Institute of Electrical and Electronics Engineers, 2023-11-07) Tefek, Uzay; Sarı, B.; Alhmoud, Hashim; Hanay, Mehmet Selim
The direct determination of the permittivity of individual micro-objects has proven challenging due to the convoluting effect of their geometric size on capacitive signals (i.e., on the electric size of a particle). To overcome this challenge, we have developed a sensing platform to independently obtain both the geometric and electric size of organic and inorganic particles, by combining impedance cytometry and microwave resonant sensing in a microfluidic chip. This way the microwave signal is normalized to yield an intrinsic parameter that depends only on permittivity. The permittivity can then be used for material classification or single-cell interrogation.
Open Access
Permittivity-based microparticle classification by the integration of impedance cytometry and microwave resonators
(John Wiley and Sons Inc, 2023-11-16) Tefek, Uzay; Sari, B.; Alhmoud, Hashim Ziad; Hanay, Mehmet Selim
Permittivity of microscopic particles can be used as a classification parameter for applications in materials and environmental sciences. However, directly measuring the permittivity of individual microparticles has proven to be challenging due to the convoluting effect of particle size on capacitive signals. To overcome this challenge, a sensing platform is built to independently obtain both the geometric and electric size of a particle, by combining impedance cytometry and microwave resonant sensing in a microfluidic chip. This way the microwave signal, which contains both permittivity and size effects, can be normalized by the size information provided by impedance cytometry to yield an intensive parameter that depends only on permittivity. The technique allows to differentiate between polystyrene and soda lime glass microparticles—below 22 µm in diameter—with more than 94% accuracy, despite their similar sizes and electrical characteristics. Furthermore, it is shown that the same technique can be used to differentiate between normal healthy cells and fixed cells of the same geometric size. The technique offers a potential route for targeted applications such as environmental monitoring of microplastic pollution or quality control in pharmaceutical industry.
Open Access
Position-independent microparticle sensing: microwave sensors integrated with metalized, 3D microelectrodes
(IEEE - Institute of Electrical and Electronics Engineers, 2023-11-07) Alataş, Yağmur Ceren; Tefek, Uzay; Sarı, B.; Hanay, Mehmet Selim
Microfluidics integrated microwave sensors can be used for high throughput and label-free sensing with single particle resolution. For microwave sensors with coplanar electrodes, electric field is nonuniform over the height of microfluidic channel, causing position dependent sensitivity. One way to resolve positional dependency is to place electrodes on the sidewalls of microfluidic channel to obtain uniform electric field. Here, we demonstrate a novel, metal coated 3D SU8 microelectrode integrated with microwave resonator to obtain uniform electric field inside microfluidic channel and mitigate position dependent sensitivity. SU8 electrodes are positioned at the sensing region of the resonator, in contact with the microfluidic channel walls. During microparticle sensing experiments, phase and amplitude of the resonator are tracked using custom built single side band detection circuitry to detect particle induced shifts in these signals. Results of particle sensing, and size classification experiments indicate that with 3D SU8 electrode integrated microwave resonators, position-independent sensitivity can be achieved.
Open Access
Three-dimensional electrode integration with microwave sensors for precise microparticle detection in microfluidics
(IEEE, 2024-05-15) Alataş, Yağmur Ceren; Tefek, Uzay; Küçükoğlu, Berk; Bardakçı, Naz; Salehin, Sayedus; Hanay, M. Selim
Microwave sensors integrated with microfluidic platforms can provide the size and permittivity of single cells and microparticles. Among the microwave sensor topologies, the planar arrangement of electrodes is a popular choice owing to the ease of fabrication. Unfortunately, planar electrodes generate a nonuniform electric field, which causes the responsivity of the sensor to depend on the vertical position of a microparticle in the microfluidic channel. To overcome this problem, we fabricated 3-D electrodes at the coplanar sensing region of an underlying microwave resonator. The 3-D electrodes are based on SU8 polymer, which is then metallized by sputter coating. With this system, we readily characterized a mixture composed of 12- and 20 $\mu \text{m}$ polystyrene particles and demonstrated separation without any position-related calibration. The ratio of the electronic response of the two particle types is approximately equal to the ratio of the particle volumes, which indicates the generation of a uniform electric field at the sensing region. This work obviates the need for using multiple coplanar electrodes and extensive processing of the data for the calibration of particle height in a microfluidic channel: as such, it enables the fabrication of more sophisticated microwave resonators for environmental and biological applications.