Bukem Bilen

In situ measurement of humidity induced changes in the refractive index and thickness of polyethylene glycol thin films

Humidity induced changes in the refractive index and thickness of polyethylene glycol (PEG) thin films are in situ determined by optical waveguide spectroscopy. PEG brushes are covalently attached to the surface of a thin gold film on a borosilicate crown glass using a grafting-from chemical synthesis technique. The measurements are carried out in an attenuated total internal reflection setup. At low humidity levels, both the refractive index and the thickness change gradually due to swelling of the PEG thin films upon water intake. At around 80% relative humidity, a steep decrease in the refractive index and a steep increase in the thickness are observed as a result of a phase change from a semicrystalline state to a physical gel state. The hydrogenation of PEG films causes a less pronounced phase change from a semicrystalline state to a gel state. Due to fewer ether oxygen atoms available for the water molecules to make hydrogen bonding, the polymer has a more stable structure than before and the phase ...

Scanning Acoustic Microscopy and Time-Resolved Fluorescence Spectroscopy for Characterization of Atherosclerotic Plaques

Atherosclerotic plaques constitute the primary cause of heart attack and stroke. However, we still lack a clear identification of the plaques. Here, we evaluate the feasibility of scanning acoustic microscopy (SAM) and time-resolved fluorescence spectroscopy (TRFS) in atherosclerotic plaque characterization. We perform dual-modality microscopic imaging of the human carotid atherosclerotic plaques. We first show that the acoustic impedance values are statistically higher in calcified regions compared with the collagen-rich areas. We then use CdTe/CdS quantum dots for imaging the atherosclerotic plaques by TRFS and show that fluorescence lifetime values of the quantum dots in collagen-rich areas are notably different from the ones in calcified areas. In summary, both modalities are successful in differentiating the calcified regions from the collagen-rich areas within the plaques indicating that these techniques are confirmatory and may be combined to characterize atherosclerotic plaques in the future.

Characterization of Carotid Atherosclerotic Plaques by Measurement of Acoustic Impedance

In this study, acoustic properties of carotid atherosclerotic plaques are studied ex vivo by scanning acoustic microscope (SAM). Human carotid atherosclerotic plaques were collected from patients by carotid erdarterectomy operation technique. An 80 MHz transducer was used in SAM, during the observation of the plaques. For the fibrous tissue, acoustic impedance was measured as 2.02 ± 0.06 MRayl, while for the lipid pool it was measured as 1.70 ± 0.07 MRayl and for the calcified region within the intima it was measured as 2.23 ± 0.09 MRayl. The difference in acoustic impedance values is due to the variation of elasticity within the atherosclerotic plaques. Lipid pool, together with fibrous tissue and calcified regions are the indications of vulnerable plaques, therefore, the determination of these regions within the plaques by SAM will help to evaluate the risk of thrombosis or stenosis and effect the decision making of the operations of the patients.

Decay rate measurement of perylene dye molecules attached to porous silicon nanostructures

The radiative decay rates of perylene dye molecules, attached to silicon nano-rods are investigated by means of timeresolved fluorescence experiments. The decay rates of dye molecules in the vicinity of silicon nano-rods are inhibited due to their various diameters and therefore the modification of the surrounding environment. Inhibition is caused by an increased nonradiative rate due to resonant energy transfer described by the Gersten-Nitzan model.