Browsing by Subject "Impedance spectroscopy"

Now showing 1 - 4 of 4

Open Access
Focusing-free impedimetric differentiation of red blood cells and leukemia cells: a system optimization
(Elsevier, 2020) Bilican, İ.; Güler, M. T.; Serhatlıoğlu, Murat; Kırındı, T.; Elbüken, Çağlar
A 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.
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.
Open Access
Temperature-dependent electrochemical impedance spectroscopy (EIS) of lithium thionyl chloride and Li-ion batteries
(2024-05) Katırcı, Gökberk
Batteries are one of the most researched and developed energy storage systems in recent years due to their utilization in portable and mobile devices. Therefore, operando and in-situ characterization of batteries should be properly performed to understand the electrochemical processes. For this purpose, Electrochemical impedance spectroscopy (EIS) and its complementary techniques have been utilized in this thesis to investigate various electrochemical systems. This thesis starts with a detailed electrochemistry review, which is necessary for understanding the discussions. Then, experimental and technical details regarding the measurement practices are presented. The initial transient occurrence with a simplified Randles cell and using both experimental and simulation data eventually shows that the initial transients are observed in every measurement and simulation scenario. Even with the real-life dummy cells made of resistors and capacitors, the initial transients are present and cannot be eliminated completely. Thereafter, the temperature-dependent EIS studies are presented, including the temperature-dependent EIS of symmetric and complete cells as well as the spiral/bobbin architectures of Lithium Thionyl Chloride (Li/SOCl2) batteries. The evaluation and comparison of the impedance response of different cell geometries and architectures with the consideration of Arrhenius relations. The Arrhenius relations are utilized for the determination of the activation energies of electro-chemical processes detected by EIS. Thus, the result concludes that the activation energies are dependent on the SoC of the battery, temperature, and chemistry, and these parameters are investigated in detail. Following, another study with similar chemistry, Li/SOCl2/SO2Cl2 batteries, is investigated in terms of EIS and Non-linear Harmonic Analysis (NHA), which shows the relation between the Kramers Kronig (KK) compatibility and NHA based on this cell chemistry. The proper way of measuring this chemistry is also presented with experimental de-tails, which necessitates changing the impedance parameters to acquire linear and reproducible results. Lastly, in the appendix, my personal interest in electric guitar pickups is investigated, and the single-coil and humbucker structures are compared in terms of their impedance responses.
Open Access
Using nanogap in label-free impedance based electrical biosensors to overcome electrical double layer effect
(Springer Verlag, 2017) Okyay, Ali Kemal; Hanoglu, O.; Yuksel, M.; Acar, H.; Sülek, S.; Tekcan, B.; Agan, S.; Bıyıklı, Necmi; Güler, Mustafa O.
Point-of-care biosensor applications require low-cost and low-power solutions. They offer being easily accessible at home site. They are usable without any complex sample handling or any kind of special expertise. Impedance spectroscopy has been utilized for point-of-care biosensor applications; however, electrical double layer formed due to ions in the solution of interest has been a challenge, due to shielding of the electric field used for sensing the target molecules. Here in this study, we demonstrate a nanogap based biosensor structure with a relatively low frequency (1–100 kHz) measurement technique, which not only eliminates the undesired shielding effect of electrical double layer but also helps in minimizing the measurement volume and enabling low concentration (µ molar level) detection of target molecules (streptavidin). Repeatability and sensitivity tests proved stable and reliable operation of the sensors. These biosensors might offer attributes such as low-cost label-free detection, fast measurement and monolithic chip integrability.