Huseyin Kizil

Microfluidic device on a nonwoven fabric: A potential biosensor for lactate detection

In the present study, a novel, wearable textile based microfluidic device was developed that provides a non-invasive, rapid, semi-quantitative detection of the lactate level in simulated sweat solution. The potential application was envisioned to be a biosensor that can monitor an athlete’s physical status during exercise. A photolithography technique was used for the fabrication of hydrophilic micro channels and reservoirs surrounded by hydrophobic barriers made from SU-8 negative photoresist. The reservoirs were functionalized by co-immobilization of lactate oxidase (LOX) and horseradish peroxidase (POX) enzymes. LOX uses L-(+)-Lactic acid as substrate and produces H2O2 which is a POX substrate. Then, POX oxidases H2O2 in the presence of 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) and results in color formation. The studies showed that excess amount of analyte presence resulted in analyte inhibition. It was also shown that analyte pH and temperature were effective on the color formation. For effective results, analyte pH and temperature should be ≥5℃ and 25–30℃, respectively. Lower pH and higher temperature values resulted in a decrease in the enzyme activity. The textile based biosensor system could make a semi-quantitative visual detection to differentiate between the normal (<5 mM) and high (≥5 mM) lactate level: while a high lactate level led to a denser purple color formation, normal levels led to a light purple formation and a green color started to be observed.

SiO2-confined silicon/carbon nanofiber composites as an anode for lithium-ion batteries

Because of its ultra-high theoretical capacity (4200 mA h g−1), Si is considered as the most promising anode material candidate for next-generation high-energy lithium-ion batteries. However, the practical use of Si based anodes is constrained by the high volume change (up to 400%) of the Si active material during cycling. Intensive volume change of Si causes severe pulverization, loss of electrical contact between Si particles and the carbon current collector, and unstable SEI formation on the electrode surface. Herein, we introduce nanoscale silica-coated silicon/carbon (Si@C–SiO2) nanofiber composites that can maintain their structural stability during repeated cycling. Results indicated that nanoscale SiO2 coating of Si@C nanofibers helped preserve the Si particles within the nanofiber structure, resulting in stable solid electrolyte interphase formation and improved cycling performance. Electrochemical performance results showed that the Si@C–SiO2 nanofiber composite anodes had good capacity retention of 89.8% and high coulombic efficiency of 97.2% at the 50th cycle. It is, therefore, demonstrated that nanoscale SiO2 coating is an effective method to improve the electrochemical performance of Si@C nanofiber composite anodes.

NON-METALLIC BRUSH SEALS FOR GAS TURBINE BEARINGS

A non-metallic brush seal has been developed as an oil seal for use in turbomachinary. Traditionally labyrinth-type seals with larger clearances have been used in such applications. Labyrinth seals have higher leakage rates and can undergo excessive wear in case of rotor instability. Brush seals reduce leakage by up to an order of magnitude and provide compliance against rotor instabilities. Brush seals are compact and are much less prone to degradations associated with oil sealing. This paper describes the benefits and development of the non-metallic brush seals for oil sealing application.Copyright

Microfluidic Nonwoven-Based Device as a Potential Biosensor for Sweat Analysis

Monitoring body fluids such as sweat composition can provide useful information about the physiological status. Physiological monitoring of body fluids such as sweat with a textile-based system has the advantage of being non-invasive and easily accessible and such monitoring is beneficial to indicate information about bodys physiological status. In the present study, it is aimed to design a textile-based system with non-invasive methods which can be used to monitor a sportsmans performance. A novel, disposable and wearable biochemical analytical device was designed and fabricated by patterning micro channels and reservoirs using SU-8 photoresist through photolithography technique on an absorbant bicomponent Evolon® nonwoven substrate. It was obtained that hydrophilic reservoirs were well defined and demarcated by hydrophobic barriers. Therefore, no liquid leakage was observed around the reservoirs which was crucial for achieving a proper enzyme immobilization and the successful detection of the color change after the simulated sweat was deposited on the hydrophilic reservoir areas. Analyte optimization studies revealed that color change became more evident with the increasing analyte concentration until 20 mM and started to decrease with further increase due to analyte inhibition. Also, on textile fabrics, color densities started to decrease after 40 mM analyte concentration.

Fabrication and Characterization of Si Nano-Columns by Femtosecond Laser

We fabricated Si Nano-columns by a femtosecond laser with various wavelengths and process parameters, whilst the specimen was submerged in water. The experiments were carried out by three types of wavelengths i.e. 1030 nm, 515nm, 343nm, with 500 fs laser pulses. The scales of these spikes are much smaller than micro spikes that are constructed by laser irradiation of silicon surface in vacuum or gases like SF6, Cl2. The Si nano-columns of 300 nm or less in width were characterized by SEM measurements. The formation of these Si Nano-columns that were revealed by SEM observation, indicates chemical etching with laser ablation occurred when surface exposed by laser beam. We observed 200 nm spikes height at the center of laser beam profile and the ones uniform in height at lateral incident area.

Tekstil Yüzeylerinde Nano ve Mikro Ölçekte Fonksiyonel İnce Film Depolanması:Gelişen Teknolojiler ve Uygulamalar

This paper discusses the emerging technologies to produce uniform films of functional materials on textiles. These include development of nano-coatings and micro-scale coatings using physical vapor deposition, atomic layer deposition, chemical vapor deposition techniques, and layer-by-layer deposition on textile substrates. Functionalities are added by these processes to textiles such as electromagnetic shielding, antibacterial efficacy, heat or UV radiation resistance, electrical conductivity, soil and oil release, self cleaning, chemical resistance and flame retardancy, with minimum effect on the strength, handle or comfort properties.This paper discusses the emerging technologies to produce uniform films of functional materials on textiles. These include development of nano-coatings and micro-scale coatings using physical vapor deposition, atomic layer deposition, chemical vapor deposition techniques, and layer-by-layer deposition on textile substrates. Functionalities are added by these processes to textiles such as electromagnetic shielding, antibacterial efficacy, heat or UV radiation resistance, electrical conductivity, soil and oil release, self cleaning, chemical resistance and flame retardancy, with minimum effect on the strength, handle or comfort properties.

The Effect of Asymmetry on Particle Focusing in Microchannels

We studied the effect of geometry on single focusing of particles in the passive microfluidic channels. There is a quantitative analysis of focusing on non-axisymmetric straight channels with two different unique designs as well as curved channels having symmetrical and asymmetrical radius of curvatures in one turn. We found that there is a clear relationship in existence of single line focusing with the degree of non-symmetry in microchannels. One-degree of asymmetry in straight channels does not induce any formation of single focusing, but single line focusing is pronounced by two-degree of asymmetry in straight channels. On the other hand, single line focusing in the curved channels is enhanced with asymmetrical radius of curvatures in one turn. The single line focusing in curved channels is seen at Rep values higher than 1, which gives us better continuous and high-throughput performance. The position of single focused particles in the microchannels is found to be 50 m with respect to the channel wall in the asymmetrical curved microchannels.

Single Cell Array Impedance Analysis for Cell Detection and Classification in a Microfluidic Device.

Impedance analysis of single cells is presented in this paper. Following the separation of a target cell type by dielectrophoresis in our previous work, this paper focuses on capturing the cells as a single array and performing impedance analysis to point out the signature difference between each cell type. Lab-on-a-chip devices having a titanium interdigitated electrode layer on a glass substrate and a PDMS microchannel are fabricated to capture each cell in a single form and perform impedance analysis. MDA-MB-231 and HeLa cells are used in our experiments.

Single cell array impedance analysis in a microfluidic device

Impedance analysis of single cells is presented in this paper. Following the separation of a target cell type by dielectrophoresis in our previous work, this paper focuses on capturing the cells as a single array and performing impedance analysis to point out the signature difference between each cell type. Lab-on-a-chip devices having a titanium interdigitated electrode layer on a glass substrate and a PDMS microchannel are fabricated to capture each cell in a single form and perform impedance analysis. HCT116 (homosapiens colon colorectal carcin) and HEK293 (human embryonic kidney) cells are used in our experiments.

Biological particle manipulation: An example of Jurkat enrichment

Separation of microparticles and living cells are studied with computational and experimental methods. The flow behaviors of particles are modeled and simulated using COMSOL Multiphysics 4.3a software. Lab-on-a-chip devices having a Ti interdigitated electrode layer on a glass substrate and a PDMS microchannel are fabricated to investigate the most effective design for separating particles based on their sizes. Polystyrene particles in different diameters (3.2 μm and 9.8 μm) are used in our experiments and experiments with T-lymphocytes and B lymphoblasts are in progress.