Biomedical subjects
Publications and source records attributed to Cengiz S Ozkan.
Fabrication of perforated organometallic nanotubes using a di-rhodium bis(N-heterocyclic carbene) complex by a simple nanoporous template wetting technique is described along with characterization data from scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), proton NMR and Mass spectroscopy.
Biological molecules such as deoxyribonucleic acid (DNA) possess inherent recognition and self-assembly capabilities, and are attractive templates for constructing functional hierarchical material structures as building blocks for nanoelectronics. Here we report the assembly and electronic functionality of nanoarchitectures based on conjugates of single-walled carbon nanotubes (SWNTs) functionalized with carboxylic groups and single-stranded DNA (ssDNA) sequences possessing terminal amino groups on both ends, hybridized together through amide linkages by adopting a straightforward synthetic route. Morphological and chemical-functional characterization of the nanoarchitectures are investigated using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. Electrical measurements (I-V characterization) of the nanoarchitectures demonstrate negative differential resistance in the presence of SWNT/ssDNA interfaces, which indicates a biomimetic route to fabricating resonant tunneling diodes. I-V characterization on platinum-metallized SWNT-ssDNA nanoarchitectures via salt reduction indicates modulation of their electrical properties, with effects ranging from those of a resonant tunneling diode to a resistor, depending on the amount of metallization. Electron transport through the nanoarchitectures has been analyzed by density functional theory calculations. Our studies illustrate the great promise of biomimetic assembly of functional nanosystems based on biotemplated materials and present new avenues toward exciting future opportunities in nanoelectronics and nanobiotechnology.
The influence of single-walled carbon nanotubes (SWCNTs) on human HEK293 cells is investigated with the aim of exploring SWCNTs biocompatibility. Results showed that SWCNTs can inhibit HEK293 cell proliferation, decrease cell adhesive ability in a dose- and time-dependent manner. HEK293 cells exhibit active responses to SWCNTs such as secretion of some 20-30 kd proteins to wrap SWCNTs, aggregation of cells attached by SWCNTs and formation of nodular structures. Cell cycle analysis showed that 25 microg/ml SWCNTs in medium induced G1 arrest and cell apoptosis in HEK293 cells. Biochip analysis showed that SWCNTs can induce up-regulation expression of cell cycle-associated genes such as p16, bax, p57, hrk, cdc42 and cdc37, down-regulation expression of cell cycle genes such as cdk2, cdk4, cdk6 and cyclin D3, and down-regulation expression of signal transduction-associated genes such as mad2, jak1, ttk, pcdha9 and erk. Western blot analysis showed that SWCNTs can induce down-regulation expression of adhesion-associated proteins such as laminin, fibronectin, cadherin, FAK and collagen IV. These results suggest that down-regulation of G1-associated cdks and cyclins and upregulation of apoptosis-associated genes may contribute to SWCNTs induced G1 phase arrest and cell apoptosis. In conclusion, SWCNTs can inhibit HEK293 cells growth by inducing cell apoptosis and decreasing cellular adhesion ability.
The detection of chemical agents is important in many areas including environmental pollutants, toxins, biological and chemical pollutants. As "smart" cells, with strong information encoding ability, neurons can be treated as independent sensing elements. A hybrid circuit of a semiconductor chip with dissociated neurons formed both sensors and transducers. Stochastic frequency spectrum was used to differentiate a mixture of chemical agents with effect on the opening of different ion channels. The frequency of spike trains revealed the concentration of the chemical agent, where the characteristic tuning curve revealed the identity. "Fatigue" experiment was performed to explore the "refreshing" ability and "memory" effect of neurons by cyclic and cascaded sensing. "Neuronelectronic noses" such as this should have wide potential applications, most notably in environmental and medical monitoring.
A single neuron sensor has been developed based on the interaction of gradient electric fields and the cell membrane. Single neurons are rapidly positioned over individual microelectrodes using positive dielectrophoretic traps. This enables the continuous extracellular electrophysiological measurements from individual neurons. The sensor developed using this technique provides the first experimental method for determining single cell sensitivity; the speed of response and the associated physiological changes to a broad spectrum of chemical agents. Binding of specific chemical agents to a specific combination of receptors induces changes to the extracellular membrane potential of a single neuron, which can be translated into unique "signature patterns" (SP), which function as identification tags. Signature patterns are derived using Fast Fourier Transformation (FFT) analysis and Wavelet Transformation (WT) analysis of the modified extracellular action potential. The validity and the sensitivity of the system are demonstrated for a variety of chemical agents ranging from behavior altering chemicals (ethanol), environmentally hazardous agents (hydrogen peroxide, EDTA) to physiologically harmful agents (pyrethroids) at pico- and femto-molar concentrations. The ability of a single neuron to selectively identify specific chemical agents when injected in a serial manner is demonstrated in "cascaded sensing".
Experimental investigations into the dynamics of neuronal networks are a fundamental step towards understanding how the nervous system works. Memory formation and development are associated with changes in the electrical activity of the neurons. To understand the changes in the electrical activity, it is essential to conduct in vitro studies on individual neurons. Hence, there is an enormous need to develop novel ways for isolating and localizing individual neurons. To this end, we designed and fabricated a 4x4 multiple microelectrode array system to spatially arrange neurons by generating dielectrophoretic traps using gradient alternating current (AC) fields. We characterized the electric field distribution inside our test platform by using three-dimensional finite element modeling (FEM) and estimated the location of neurons over the electrode array. As the first stage in forming a neuronal network, dielectrophoretic AC fields were employed to separate the neurons from the glial cells and to position individual neurons over single electrodes. The extracellular electrical activity from a single neuron was recorded. The frequency spectrum of the electrical activity was generated using fast Fourier transformation analysis (FFT) to determine the characteristic burst rates of individual neurons.
We present a novel sensing scheme for detecting the effects of unburned fossil fuels by integrating microarray technology and dielectrophoresis to develop single-neuron arrays. These arrays have the capability to sense and identify the two fuels, at parts per billion (ppb) concentrations, as well to determine the associated physiological changes at the single-cell level. Identification is achieved through frequency domain analysis of the measured changes to the extracellular electrical activity due to the effect of the fossil fuels. This yields unique electrical identifiers known as "signature patterns". Simultaneous optical visualization to the physiological changes is obtained by specific fluorescent staining. The correlation between the signature patterns and the cellular biological behavior establishes the veracity of this identification technique.
Experiments on encapsulating Pt-labelled DNA molecules inside multiwalled carbon nanotubes (MWCNT) were performed under temperature and pressure conditions of 400K and 3 Bar. The DNA-CNT hybrids were purified via agarose gel electrophoresis and analyzed via high resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that the Pt-labelled DNA molecules attached to the outside walls of CNTs could be removed by electrophoresis. The HR-TEM and EDX results demonstrated that 2-3% of the Pt-labelled DNA molecules were successfully encapsulated inside the MWCNTs. The experimental study complements our previous molecular dynamics simulations on encapsulation of single stranded DNA oligonucleotides inside single wall carbon nanotubes under similar conditions in water. The van der Waals interaction between CNT and Pt-labelled DNA is believed to be the main driving force for this phenomenon. The DNA-CNT molecular complex could be further explored for potential applications in bio-nanotechnology.