Photonic crystals in biology - NanoTR-VI

Poster Session, Thursday, June 17AFM and Kelvin Probe Study of Emulsifier Incorporated PhospholipidsSaliha Zeyneb Akinci 1 , Tugce Bekat 2 , Sevgi Kilic Ozdemir 2,* , Salih Okur 3Theme F686 - N11231 Biotechnology Program, Izmir Institute of Technology, Gulbahce Campus, Izmir, Turkey2 Department of Chemical Engineering, Izmir Institute of Technology, Gulbahce Campus, Izmir, Turkey3 Department of Physics, Izmir Institute of Technology, Gulbahce Campus, Izmir, TurkeyAbstract- Monolayers of DSPC (1,2-dipalmitoyl-snglycerol-3-phosphocholine) and PEG 40 St (Polyoxyethylene glycol) stearate at differentcompositions (9:1 and 8:2) were analyzed with atomic force microscopy (AFM) in the Kelvin Probe (KP) mode. The effects of the compositionand the medium on compactness of the monolayer were investigated.Contrast agents for ultrasound comprise micron sized of gas(microbubbles) stabilized by a shell of biocompatiblematerial. These agents alter the scattering character of theblood under ultrasound, creating contrast with respect to theimaged tissue [1]. Microbubbles are administrated to thepatient during imaging and are expected to recirculate in theblood stream until the imaging is complete. Viability of themicrobubbles in the systemic circulation is closely related tothe shell structure. In this study, DSPC and PEG 40 St are usedas the main constituents of the microbubbles. A mixture ofDSPC/PEG 40 St at predetermined compositions was spread atair-water interface and transferred to a substrate for atomicforce microscope imaging using Langmuir-Blodgett (LB)film method. Mainly, DSPC/PEG 40 St mixtures atcompositions of 9:1 and 8:2 were analyzed both in pure waterand phosphate buffer saline at 110 mM (PBS).Monolayers showed more homogeneous and compactbehavior in buffer solution compared to pure water for bothcompositions. Additionally, the 8:2 mixed monolayersindicated more homogeneous structure both in the pure waterand buffer solution in comparison to 9:1 mixed one.As shown in Figure 1, this comparison was also performedwith the bare gold monolayer as reference monolayer in orderto evaluate the differences between surface potential values.Figure 2 shows the height profile along the scan and surfacepotential measurement of 8:2 DSPC/PEG 40 St mixture coatedfilms both in pure water and PBS. The characterization of theLangmuir-Blodgett (LB) films with AFM in Kelvin Probemode shows that 8:2 mixed monolayer in buffer solutionhave higher surface potential values than 9:1 mixed one bothin pure water and PBS (data not shown).height (nm)5040302010050gold film surface8:2 DSPC-PEG 40 St. in pure water subphase8:2 DSPC-PEG 40 St. in buffer subphase0 1 2 3 4 5x (nm)PURE GOLDabMAG_V40308:2 DSPC-PEG 40 S (PURE WATER)8:2 DSPC-PEG 40 S (110 mM PBS)2010e0-1.5 -1 -0.5 0 0.5 1 1.5 2BIAS VOLTAGEFigure 2. Surface height profile along the scan and surface potentialmeasurement of DSPC/PEG 40 St LB monolayer films with Kelvinprobe force microscope for 8:2 DSPC/PEG 40 St monolayer in purewater and PBS solution at 110 mM, and also pure gold monolayer asa reference.cdThe surface potentials have been measured as 0.030184 V forbare gold substrate, 0.4894 V and 0.43V for the 8:2DSPC/PEG 40 St monolayer in pure water and PBS,respectively. Surface roughnesses have been measured as0.544479 nm for bare gold substrate, 0.903692 nm and4.41735 nm for 8:2 DSPC/PEG 40 St monolayer in pure waterand PBS, respectively.Figure 1. Characterization of LB films at 5 m (a) topography and(b) surface potential of pure gold (as a reference); (c) topographyand (d) surface potential of 8:2 DSPC/PEG 40 St monolayer in purewater; (e) topography and (f) surface potential of 8:2 DSPC/PEG 40 Stmonolayer in 110 mM PBS solution.According to these investigations of emulsifier incorporatedphospholipids, we surmise that the increase in homogeneityand the surface potential of the monolayers may be resultingfrom intermolecular interactions between the moleculesforming the monolayer and the medium. The effect of themedium on the molecular interactions and the compactness ofthe monolayer will also be tested on microbubble formation.*sevgikilic@iyte.edu.tr[1] Moriyasu F. et al., Am. J. Roentgenol, 193:86; 2009.6th Nanoscience and Nanotechnology Conference, zmir, 2010 818