Physica Medica (2012) 28, 288e295
Available online at www.sciencedirect.com
journal homepage: http://intl.elsevierhealth.com/journals/ejmp
ORIGINAL PAPER
Biophysical characterization of gold nanoparticles-loaded liposomes Mohsen Mahmoud Mady a,b,*, Mohamed Mahmoud Fathy a, Tareq Youssef c, Wafaa Mohamed Khalil a a
Biophysics Department, Faculty of Science, Cairo University, 12613 Giza, Egypt Department of Physics and Astronomy, Faculty of Science, King Saud University, Riyadh-11451, Saudi Arabia c Photochemistry and Photobiology Unit, National Institute of Laser Enhanced Sciences, Cairo University, 12613 Giza, Egypt b
Received 1 June 2011; received in revised form 30 September 2011; accepted 6 October 2011 Available online 24 October 2011
KEYWORDS Liposomes; Gold nanoparticles; DPPC; FTIR; Characterization
Abstract Gold nanoparticles were prepared and loaded into the bilayer of dipalmitoylphosphatidylcholine (DPPC) liposomes, named as gold-loaded liposomes. Biophysical characterization of gold-loaded liposomes was studied by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy as well as turbidity and rheological measurements. FTIR measurements showed that gold nanoparticles made significant changes in the frequency of the CH2 stretching bands, revealing that gold nanoparticles increased the number of gauche conformers and create a conformational change within the acyl chains of phospholipids. The transmission electron micrographs (TEM) revealed that gold nanoparticles were loaded in the liposomal bilayer. The zeta potential of DPPC liposomes had a more negative value after incorporating of Au NPs into liposomal membranes. Turbidity studies revealed that the loading of gold nanoparticles into DPPC liposomes results in shifting the temperature of the main phase transition to a lower value. The membrane fluidity of DPPC bilayer was increased by loading the gold nanoparticles as shown from rheological measurements. Knowledge gained in this study may open the door to pursuing liposomes as a viable strategy for Au NPs delivery in many diagnostic and therapeutic applications. ª 2011 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
Introduction Nanoparticles are typically smaller than several hundred nanometers in size, comparable to large biological
molecules such as enzymes, receptors, and antibodies. With the size of about one hundred to ten thousand times smaller than human cells, these nanoparticles can offer unprecedented interactions with biomolecules both on the
* Corresponding author. Biophysics Department, Faculty of Science, Cairo University, 12613 Giza, Egypt. Tel.: þ202 5675745 ; fax: þ202 5727556. E-mail address:
[email protected] (M.M. Mady). 1120-1797/$ - see front matter ª 2011 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ejmp.2011.10.001
Biophysical characterization of gold nanoparticles-loaded liposomes surface of and inside the cells, which may revolutionize cancer diagnosis and treatment. Among all nanostructured materials, gold nanoparticles (Au NPs) have attracted particular interest due to their stability, biocompatibility, surface plasmon resonance effect, and unique catalytic activities [1]. Recent advances in nano-biotechnology have led to the development of many new nanoscale platforms, including quantum dots, nanoshells, gold nanoparticles, paramagnetic NPs, carbon nanotubes, and improvements in traditional, lipid-based platforms [2e10]. Currently Au NPs are used in different biomedical applications, such as intracellular gene regulation [11], chemotherapy [12] and drug delivery [13,14], as well as in optical and electronic applications [15]. Owing to the unique optoelectronic properties with their controlled size and morphology, Au NPs find significance in the field of bionanotechnology [14] as biomarkers [16], biosensors [17], cancer diagnostic [18] and vehicles for drug delivery [14]. Au NPs have been shown to provide therapeutic enhancement in cancer treatment where their efficacy relies on the successful delivery of the particles to the tumor site and internalization into tumor cells [19e22]. However, there are significant challenges with regard to the delivery of Au NPs at the whole body and cellular levels. For example, in vivo evaluation of Au NPs in preclinical animal models has revealed short circulation lifetimes, cellular toxicity and only limited accumulation of the particles at the tumor site [20,23]. It was shown that Au NPs are capable of inducing an antibody response in mice, which indicates that factors other than cytotoxicity may be involved and complicates in vivo application of Au NPs. However, Au NPs generally aggregate and lose their unique photo-properties under physiological conditions due to the shielding of the repulsion at the surface. Therefore, it is desirable to develop a proper modification of Au NPs to overcome these challenges to enhance their efficacy in biomedical applications. The direct complexation of biocompatible or bioactive molecules to Au NPs can improve the stability of the particle and the targeting ability. One of the approaches for improving the in vivo stability, circulation lifetime, reducing cellular toxicity, enhancing targeting ability and cellular uptake of small Au NPs has been to incorporate the particles into or on the surface of liposomes [21,24]. Liposomes are the most established of the advanced delivery technologies and consist of a lipid bilayer that envelops an internal aqueous compartment. Liposomes provide an efficient method of intracellular delivery of small Au NPs. The cellular uptake of smaller Au NPs will enhance by using liposomes as a carrier. Considering the well characterized biodistribution of liposomes in vivo, the use of this technology for delivery of Au NPs will result in improved biodistribution properties for the NPs in vivo, such as increased tumor accumulation. Furthermore, targeting ligands can be easily conjugated to the surfaces of the Au NPseliposomes to pursue active targeting to specific cell populations. Biophysical characterization of gold-loaded liposomes was studied by TEM and Fourier transform infrared (FTIR)
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spectroscopy as well as turbidity, zeta potential and rheological measurements.
Material and methods Materials 1,2-a-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) lipid was purchased from Avanti Polar Lipids (Alabaster, AL, USA), Hydrogen tetrachloroaurate (HAuCl4.3H2o), chloroform (CHCl3), sodium citrate (HOC) (COONa) (CH2COONa)2(2H2O) were purchased from SigmaeAldrich (St. Louis, MO, USA). All other reagent and solvents were of analytical grade and were used without further purification.
Liposome preparation The lipids must first be dissolved and mixed in chloroform to assure a homogeneous mixture of lipids. The organic solvent should be removed by rotary evaporation yielding a thin lipid film on the sides of a round bottom flask. The lipid film is thoroughly dried to remove residual organic solvent by placing flask on a vacuum pump. Hydration of the dry lipid film is accomplished simply by adding deionized water to the container of dry lipid and agitating at temperature above phase transition temperature of the lipid (50 C). Multilamellar vesicles (MLV) are formed [25] of final lipid concentration of 5 mg/ml.
Preparation of gold nanoparticles The Frens method [26] was used to synthesize a solution of gold nanoparticles. 5.0 106 mol of HAuCl4 was dissolved in 19 mL of deionized water producing a faint yellowish solution. This solution was heated with vigorous stirring in a rotary evaporator for 45 min. 1 mL of sodium citrate solution (0.5%) was added and the solution was stirred for an additional 30 min. The colour of the solution gradually changed from the initial faint yellow to clear, grey, purple, and finally a tantalizing wine-red colour similar to merlot. The citric acid acts as a reducing agent and a capping agent. It is chemically bonding to the gold NP surface and not adsorbed onto the surface, producing negative citrate ions and introducing surface charge that repels the particles and preventing nanocluster formation.
Preparation of Au NPs-loaded liposomes Gold nanoparticles were then loaded into liposomes by adding gold nanoparticles solution by ratio 1:3. Then the dried thin film of lipids was dispersed into deionized water by hand shaking of the flask, causes the entire dried lipid to be dispersed. The non-loaded gold nanoparticles are removed by using centrifugation.
Transmission electron microscopy DPPC liposomes loaded gold nanoparticles were analyzed by negative stain electron microscopy using a JEM 1230 electron microscope (Jeol, Tokyo, Japan). A drop of
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liposomes loaded nanogold suspension was applied to copper coated with carbon grid and the excess sample was drawn off with filter paper. An aqueous solution of ammonium molybdate (1% w/v) was used as a negative staining agent. Staining was followed by a 2-min wait at room temperature, removal of the excess solution with a filter paper, and then examination under the electron microscope.
Zeta potential measurements Zeta potential of gold nanoparticles, DPPC liposomes and Au NPs/DPPC liposomes were determined using the Malvern Zetasizer 2000 (Malvern Instruments, U.K.) after samples centrifugation at 13,000 rpm for 20 min. Pellets were then re-suspended in double distilled deionised water. The zeta potential of the Au NPs/DPPC liposomes was measured after centrifugation to confirm that the Au NPs are loaded into liposomal membranes.
FTIR spectroscopy FTIR spectra of lyophilized samples of DPPC liposomes and Au NPs/DPPC liposomes deposited in KBr disks were recorded on a NICOLET 6700 FTIR Thermo scientific spectrometer, England. The scanning was done in the range 400e4000 cm1 with speed of 2 mm/s a resolution of 4 cm1 at room temperature.
Results and discussion Physical structures of Au NPs-loaded liposomes The morphologies and the size of Au NPs loaded liposome were investigated by TEM. Lipid vesicles were formed with Au NPs in the apolar phase as revealed by TEM of negatively stained images of the specimen. In the TEM image of DPPC liposome loading Au NPs, Au NPs were observed at the boundary surface within the liposomal assembly. The Au NPs size was in the range of 15 5 nm (Fig. 1A) while most nanoparticles-loaded liposomes were spherical shapes and they have less aggregation as shown from Fig. 1B. In the TEM image of Au NPs/DPPC liposomes (Fig. 1B), Au NPs were observed at the boundary surface within the liposomal assembly. The liposomes may be physically associated with the Au NPs at the surface without disturbing the membrane packing. From these results, it is supported that gold nanoparticles could be entrapped in the hydrophobic part of the bilayer. The darker colour of the liposomes is due to the presence of Au NPs on the surface. The negatively stained TEM images confirm that the hydrophobic nature of Au NPs surfaces since they are located outside the polar phase in the hydrophobic phase.
Phase transition temperature (turbidity test)
Zeta potential
Turbidity of DPPC liposomes and Au NPs/DPPC liposomes was monitored as a function of temperature by continuous recording of absorbance at 400 nm using a UV/visible spectrophotometer (Jenway 6405, Barloworld Scientific, Essex, UK). The suspensions were maintained under constant agitation using a rotation speed-controlled paddle stirrer that did not interfere with the light path. The samples were heated by means of a temperature-controlled bath at a rate of 1 C/min.
The magnitude of the zeta potential gives an indication of the potential stability of the colloidal system. As the zeta potential increases, repulsion between particles will be greater, leading to a more stable colloidal dispersion. If all particles in suspension have a large negative or positive zeta potential then they will tend to repel each other and there will be no tendency for the particles to come together [29]. Information on the overall charge of goldDPPC liposomes by zeta potential measurements can speed up the development of gold/liposomal system with specific, prolonged and controlled release. DPPC liposomes showed a slight negative zeta potential, in agreement with the observations of previous studies [30e34]. It is clear from Fig. 2 that Au NPs loaded liposomes had higher negatively zeta potential than DPPC liposomes due to the incorporation of some gold nanoparticles into the liposomal membranes. As revealed from the TEM image of Au NPs/DPPC liposomes (Fig. 1B), Au NPs were observed at the boundary surface within the liposomal assembly. The liposomes may be physically associated with the Au NPs at the surface without disturbing the membrane packing. From these results, it is supported that gold nanoparticles might be entrapped in the hydrophobic part of the bilayer. Since gold nanoparticles showing highly negative zeta potential due to presence of citrate group on the gold nanoparticles surface witch act as stabilizing and capping material, the incorporation of Au NPs into liposomal membranes appears to increase the density of negative charge and hence made the zeta potential negative.
Rheological measurements The DPPC liposomes and Au NPs/DPPC liposomes are analyzed by (Anton Pear, Physica type MCR 301, Austria), where the sample was introduced between two plates at distance of 0.5 mm. The flow curves were plotted for each sample between shear stress (Pa) and shear rate (s1) at 25 C for each sample. Plastic viscosity and yield stress were calculated from the linear fitting of the flow curves [27-28]. The rheological properties of liposomal formulations can be described by the power law model [27]: tZkg_ n
ð1Þ
where t is the shear stress, k is the consistency index, g_ is the shear rate, and n is the flow behaviour index. In order to obtain the flow behaviour index (n) and consistency index (k) values, Eq. (1) was used to fit the experimental data of different samples, and the rheological parameters are shown in Table 1. The final lipid concentration of 0.8 mM was used.
Biophysical characterization of gold nanoparticles-loaded liposomes
Figure 1 Negative stain micrographs of A) Au NPs and B) Au NPs loaded into DPPC liposomes. Arrows indicate the Au NPs.
Phase transition temperature of liposomes The turbidity technique at visible range is one of the spectroscopic techniques which provides valuable information about membrane phase transition temperature and membrane order [34e36]. Lipid turbidity study has been previously applied to membrane research by others [34e38]. It is known that when temperature is increased, phosphatidylcholines undergo phase transitions from the
-35
zeta potential (mV)
-30 -25
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lamellar gel phase Lb0 to the ripple phase Pb0 , and further to the fluid lamellar phase La. However, the phase transition of phospholipids from the gel to the liquid crystalline phase causes a decrease in turbidity. This is mainly due to the changes that occur in the refractive index of the lipids, as a consequence of changes in the lipid density during melting [39]. Turbidity measurements provide a useful tool in studying the effects of additives such as ions, peptides, proteins, drugs etc. on the size, structure, aggregation and fusion process of lipid vesicles and such studies would provide a better understanding of vesicles [35]. In the present study, the effect of Au NPs on lipid-phasetransition, order and dynamics, and hydration states of the head and the region near the aqueous region of zwitterionic DPPC MLVs as a function of temperature is investigated. Figure (3) represents the variation of the absorbance at 400 nm as a function of temperature for DPPC liposomes and Au NPs-loaded DPPC liposomes. As seen from the figure, for pure DPPC liposomes, the absorbance values decreased as a function of increasing temperature and show two transitions: a pre-transition is observed at nearly 35 C and a main transition is seen around 41 C of DPPC. These temperatures are very close to the values reported by calorimetric [40e41] and turbidity studies [36e37]. Turbidity studies revealed that loading of DPPC liposomes by Au NPs led to the disappearance of pre-transition and lowering of the main transition temperature by nearly 2 C relative to the control. The results indicated that the gold nanoparticles interact strongly with DPPC vesicles and cause their melting points to be decreased. This might be due to the structural modifications and interactions between DPPC molecules and gold nanoparticles within the bilayer. Gold nanoparticles absorb light energy and transfer it to heat, thereby causing lipid-phase-transition from gel phase to rippled phase, and further to fluid phase. This induces their permeability increment which may have numerous future therapeutic applications. Heat sensitive liposome technology is a potential method to produce triggered systems for controlled contents delivery. The temperature required for gel-toliquid crystalline phase transition in the liposomes can be adjusted by lipid composition. This property has been used for example in the cancer treatments, where the slightly higher temperature in the tumor triggers the drug release from the liposomes with a phase transition below 41 C [42e43].
-20
Rheological measurements
-15 -10 -5 0 DPPC Liposomes
Au NPs/liposomes
Au NPs
Figure 2 Zeta potential measurements of different formulations (n Z 5). Liposomal lipid concentration is 1 mM and Au NPs concentration is 0.05 mM.
Viscoelastic can be used for quality control of raw materials, final products, and manufacturing processes. Furthermore, the release of drug from semi-solid carriers is influenced by the rheological behaviour as well. The effect of certain parameters such as storage time, and temperature on the quality of GNPs as pharmaceutical products can be also investigated via rheological measurements. The rheological properties of liposomes were measured to evaluate the interaction between Au NPs and DPPC
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0.30
Table 1 Rheological parameters of DPPC and Au NPs/ DPPC liposomes. Liposomal lipid concentration is 0.8 mM. Sample
DPPC liposomes
Au NPs/DPPC liposomes
Plastic viscosity (cP) Yield Stress (dyne/cm2) Consistency index (cP) Flow index
0.76 0.61 0.064 0.008 1.1 0.0188
0.64 0.129 1.03 0.064 0.93 0.01
Absorabnce
0.25
0.20
Pre-transition 0.15
Main transition
0.10
0.05 15
20
25
30
35
40
45
50
55
60
o
Temperature ( C)
Figure 3 Temperature dependence of absorbance at 400 nm for: DPPC liposomes and Au NPs/DPPC liposomes. Liposomal lipid concentration is 0.8 mM.
liposomal membranes. Fig. 4 shows the flow curves of DPPC and Au NPs/DPPC liposomal samples. The rheological parameters are shown in Table 1. The yield stress (the minimum stress needed to cause a Bingham plastic to flow) decreases from 0.61 dyn/cm2 for DPPC liposomes to 0.129 dyn/cm2 for Au NPs/DPPC liposomes. The k and n values of DPPC and Au NPs/DPPC liposomes, ranged from 0.064 to 1.03 and from 1 to 0.93, respectively. Liposome suspension exhibited a pseudoplastic behaviour because the values of the flow behaviour index (n), a measure of departure from Newtonian flow, were 1. The consistency index (k), an indication of the viscous nature of liposomes [27e28], can be used to describe the variation in plastic viscosity (a measure of the internal
DPPC Au NPs/DPPC
9 8
Shear Stress (Pa)
7 6 5 4 3 2 1 0 0
100
200
300
400
500
600
700
800
900
Shear Rate (1/s)
Figure 4 The relation between shear rate and shear stress of DPPC and Au NPs/DPPC liposomes at 25 C. Liposomal lipid concentration is 0.8 mM.
resistance to fluid flow of a Bingham plastic, expressed as the tangential shear stress in excess of the yield stress divided by the resulting rate of shear) after loading of gold nanoparticles into DPPC liposomes. The plastic viscosity of DPPC liposomes is decreased after Au NPs loading into DPPC liposomes (from 0.76 cP to 0.64 cP) which indicate that the membrane fluidity is increased. Based on the present results of liposomal rheological properties, it can be concluded that interaction between Au NPs and DPPC phospholipid would cause a reduction in the DPPC liposomes plastic viscosity and increase the membrane fluidity.
The structure and organization of phospholipid bilayers as revealed by infrared spectroscopy FTIR spectroscopy was used to monitor subtle changes in the structure and function of the lipid assemblies by analyzing the frequency and bandwidth changes of different vibrational modes representing the acyl chains, interfacial, and head group region of lipid molecules. For example, the frequencies of the CH2 stretching bands of acyl chains depend on the degree of conformational disorder and hence the frequency values can be used to monitor the average trans/gauche isomerization in the systems. The shifts to higher wave numbers correspond to an increase in number of gauche conformers. Figure (5) shows the full FTIR spectrum of DPPC liposomal sample. As shown from this figure, the spectrum of DPPC liposomes displays the main characteristic bands of DPPC vesicles, especially those are due to the symmetric and antisymmetric CH2 stretching vibrations of the acyl chain (2850 and 2920 cm1, respectively), and the carbonyl stretching vibration C]O (1740 cm1), the CH2 bending vibration (1470 cm1), and the symmetric and antisym1 metric PO 2 stretching vibrations (1090 and 1220 cm , respectively). These findings are in good accordance with the data reported in the literature [28,44e48]. Meanwhile, the peaks of the symmetric and asymmetric stretching vibrations of CH2 have been used as a sensitive indicator of the ordering of the alkyl chains. There are significant changes in the frequency of the CH2 stretching bands, revealing that Au NPs increased the number of gauche conformers and this implies an increase in the conformational disorder (transegauche isomerization) of the bilayer. The CH2 asymmetric stretching band frequency shifted towards higher frequency with the addition of Au NPs in the gel and liquid crystalline phase in comparison to those of DPPC (Fig. 6). The two peaks at 2850 and 2920 cm1 for the
Biophysical characterization of gold nanoparticles-loaded liposomes 0.018
DPPC Au NPs/DPPC
0.024 0.022
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DPPC Au NPs/DPPC 0.016
Absorbance
Absorbance
0.020 0.018 0.016
0.014
0.012
0.014 0.010
0.012 0.010
0.008 800
1000
0.008
1400
1600
1800
-1
0
500
1000
1500
2000
2500
3000
3500
4000
4500
Figure 7 The magnified part (800e1800 cm1) of FTIR spectra of DPPC and Au NPs/DPPC liposomal samples.
-1
Wavenumber (cm )
Figure 5 The full FTIR spectra of lyophilized DPPC and Au NPs/DPPC liposomal samples.
DPPC are shifted towards higher wave numbers (2854 and 2923 cm1, respectively for Au NPs/DPPC liposomes, implying that gold nanoparticles create a conformational disorder within the acyl chains of phospholipids. Interestingly the signal intensity became less intensive for gold loaded liposomes. The interaction between gold and head group of DPPC liposomes was monitored by PO 2 symmetric and antisymmetric stretching bands which are located at 1090 cm1 and 1220 cm1, respectively [46,48]. Fig. 7 shows PO 2 symmetric and antisymmetric stretching band for DPPC liposomes in the absence and presence of gold nanoparticles. As seen from the figure, the PO 2 symmetric and antisymmetric stretching bands are vanished (altogether upon matrix formation.) after the loading of gold nanoparticles into DPPC liposomes, which implies the absence of hydrogen bonding between the head group of liposomes
0.024 0.022
DPPC Au NPs/DPPC
0.020
Absorbance
1200
Wavenumber (cm )
0.018 0.016 0.014 0.012
with Au NPs. Also, the Nþ(CH3)3 asymmetric stretching band at 975 cm1 is shifted to higher wave number 989 cm1 for Au NPs/DPPC liposomal sample. The P]O stretch at 1220 cm1 of the DPPC sample has been vanished in the Au NPs/DPPC liposomal sample, possibly due to the broadening and shift of the CeO ester band at 1152 cm1. The spectral changes may be due to some molecular conformational changes. Such conformational changes may be the formation of curved and lipid planes that lead to the lipid lateral diffusion occurring in the intermediate motional regime.
Conclusion In the present study, we demonstrate that gold nanoparticles are interacting strongly with lipid membrane. The improved understanding generated by this study may pave the way for optimising Au NPs-loaded liposomes application in liposomal drug delivery systems and employing them to specifically engineer the properties of cell membranes and other biologically relevant lipid layers. Future studies will evaluate the pharmacokinetics and biodistribution of the Au NPs-loaded liposomes in vivo as well as their efficacy to enhance their therapeutic applications. Furthermore, targeting ligands can be easily conjugated to the surfaces of the Au NPs-loaded liposomes to pursue active targeting to specific cell populations. We propose that Au NPs-loaded liposomes will find useful applications as a nanomedicine with diagnostic and therapeutic ability owing to the dual drive to reduce the toxicity and side effects of existing treatments and increase efficacy by selective targeting of tumours.
0.010 0.008 2800
2850
2900
2950
3000
Acknowledgement
-1
Wavenumber (cm )
Figure 6 The magnified part (2800e3000 cm1) of FTIR spectra of DPPC and Au NPs/DPPC liposomal samples.
The authors extend their appreciation to the GRADUATE RESEARCH CHALLENGE FUND (GRCF) through the Faculty of Science and Cairo University, Egypt, for funding this work.
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References [1] Lu X, Tuan H, Korgel BA, Xia Y. Facile synthesis of gold nanoparticles with narrow size distribution by using AuCl or AuBr as the precursor. Chem Eur J 2008;14:1584e91. [2] Alivisatos P. The use of nanocrystals in biological detection. Nat Biotechnol 2003;22:47e51. [3] Colvin VL, Schlamp MC, Alivisatos P. Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer. Nature 1994;370:354e7. [4] Souza GR, Christianson DR, Staquicini FI, Ozawa MG, Snyder EY, Sidman RL, et al. Networks of gold nanoparticles and bacteriophage as biological sensors and cell-targeting agents. P Natl Acad Sci USA 2006;103:1215e20. [5] Jin H, Heller DA, Strano MS. Single-particle tracking of endocytosis and exocytosis of single-walled carbon nanotubes in NIH-3T3 cells. Nano Lett 2008;8:1577e85. [6] Ruenraroengsak P, Al-Jamal KT, Hartell N, Braeckmans K, Smedt SCD, Florence AT. Cell uptake, cytoplasmic diffusion and nuclear access of a 6.5 nm diameter dendrimer. Int J Pharm 2007;331:215e9. [7] Kneipp JK, Kneipp H, McLaughlin M, Brown D, Kneipp K. In vivo molecular probing of cellular compartments with gold nanoparticles and nanoaggregates. Nano Lett 2006;6:2225e31. [8] Sokolov K, Follen M, Aaron J, Pavlova I, Malpica A, Lotan R, et al. Real-time vital optical imaging of precancer using antiepidermal growth factor receptor antibodies conjugated to gold nanoparticles. Cancer Res 2003;63:1999e2004. [9] Mulde WJM, Strijkers GJ, Van Tilborg GAF, Griffioen AW, Nicolay K. Lipid-based nanoparticles for contrast-enhanced MRI and molecular imaging. NMR Biomed 2006;19:142e64. [10] Nativo P, Prior IA, Brust M. Uptake and intracellular fate of surface modified gold nanoparticles. ACS Nano 2008;2: 1639e44. [11] Baptista P, Pereira E, Eaton P, Doria G, Miranda A, Gomes I, et al. Gold nanoparticles for the development of clinical diagnosis methods. Anal Bioanal Chem 2008;391:943e50. [12] West JL, Halas NJ. Engineered nanomaterials for biophotonics applications: improving sensing, imaging, and therapeutics. Annu Rev Biomed Eng 2003;5:285e92. [13] Kuwahara Y, Akiyama T, Yamada S. Facile Fabrication of Photoelectrochemical assemblies consisting of gold nanoparticles and a Tris(2,20 -bipyridine)ruthenium(II)Viologen linked Thiol. Langmuir 2001;17:5714e6. [14] Sperling RA, Gil PR, Zhang F, Zanella M, Parak WJ. Biological applications of gold nanoparticles. Chem Soc Rev 2008;37: 1896e908. [15] Maier SA, Atwater HA. Plasmonics: localization and guiding of electromagnetic energy in metal/dielectric structures. J Appl Phys 2005;98:1e10. [16] Wan H, Chen L, Chen J, Zhou H, Zhang D, Liu L. Synthesis and fluorescence property of the gold nanoparticles modified with 9-methyl-9-(8-thiooctyl)-fluorene. J Dispersion Sci Technol 2008;29:999e1002. [17] Tokonami S, Shiigi H, Nagaoka T. Preparation of nanogapped gold nanoparticle array for DNA detection. Electroanalysis 2008;20:355e60. [18] Huang X, Jain PK, El-Sayed IH, El-Sayed MA. Gold nanoparticles: interesting optical properties and recent applications in cancer diagnostics and therapy. Nanomedicine 2007;2: 681e93. [19] Zheng Y, Hunting DJ, Ayotee P, Sanche L. Radiosensitization of DNA by gold nanoparticles irradiated with high-energy electrons. Radiat Res 2008;169:19e27. [20] Hainfeld JF, Slatkin DN, Smilowitz HM. The use of gold nanoparticles to enhance radiotherapy in mice. Phys Med Biol 2004;49:N309e15.
M.M. Mady et al. [21] Herold DM, Das IJ, Stobbe CC, Iyer RV, Chapman JD. Gold microspheres: a selective technique for producing biologically effective dose enhancement. Int J Radiat Biol 2000;76: 1357e64. [22] Chen W, Zhang J. Using nanoparticles to enable simultaneous radiation and photodynamic therapies for cancer treatment. J Nanosci Nanotechnol 2006;6:1159e66. [23] Kim D, Park S, Lee JH, Jeong YY, Jon S. Antibiofouling polymercoated gold nanoparticles as a contrast agent for in vivo Xray computed tomography imaging. J Am Chem Soc 2008;129: 7661e5. [24] Zheng J, Perkins G, Kirilova A, Allen CJ, Jaffray DA. Multimodal contrast agent for combined CT and MR imaging applications. Invest Radiol 2006;41:339e48. [25] New RCR. In liposomes: a practical approach. Oxford, UK: IRL Press; 1989. 33e103. [26] Frens G. Controlled nucleation for the regulation of the particle size in monodisperse gold suspensions. Nature 1973; 241:20e2. [27] Steffe J. Rheological methods in food process engineering. 2nd ed. USA: Freeman Press, Mitchigan State University; 1996. 21. [28] Mady MM, Darwish M, Khalil S, Khalil W. Biophysical studies on chitosan-coated liposomes. Eur Biophys J 2009;38:1127e33. [29] Paolino D, Fresta M, Sinha P, Ferrari M. Drug delivery systems. In: Webester JG, editor. Encyclopedia of medical devices and instrumentation. 2nd ed. John Wiley and Sons; 2006. p. 437e95. [30] Plank L, Dahl CE, Ware BR. Effect of sterol incorporation on head group separation in liposomes. Chem Phys Lipids 1985; 36:319e28. [31] Klein JW, Ware BR, Barclay G, Petty HR. Phospholipid dependence of calcium ion effects on electrophoretic mobilities of liposomes. Chem Phys Lipids 1987;43:13e23. [32] Law SL, Lo WY, Pai SH, Teh GW. The electrokinetic behaviour of liposomes adsorbed with bovine serum albumin. Int J Pharm 1988;43:257e60. [33] Makino K, Yamada T, Kimura M, Oka T, Ohshima H, Kondo T. Temperature- and ionic strength-induced conformational changes in the lipid head group region of liposomes as suggested by zeta potential data. Biophys Chem 1991;41: 175e83. [34] Mady MM, Darwish M. Effect of chitosan coating on the characteristics of DPPC-liposomes. J Adv Res 2010;1:187e91. [35] Eker F, Durmus HO, Akinoglub BG, Severcan F. Application of turbidity technique on peptide-lipid and drug-lipid interactions. J Mol Struct 1999;482/483:693e7. [36] Severcan F, Durmus HO, Eker F, Akinoglu BG, Haris PI. Vitamin D2 modulates melittinemembrane interactions. Talanta 2000; 53:205e11. [37] Stillwell W, Wassall SR. Interactions of retinoids with phospholipid membranes: optical spectroscopy. Methods Enzymol 1990;189:373e82. [38] Severcan F, Kazanci N, Baykal U, Suzer S. IR and turbidity studies of vitamin E-cholesterol-phospholipid membrane interactions. Biosci Rep 1995;15:221. [39] Yi PN, MacDonald RC. Temperature dependence of optical properties of aqueous dispersions of phosphatidylcholine. Chem Phys Lipids 1973;11:114e34. [40] Ortiz A, Aranda FJ, Villalain J, Gomez-Fernandez JC. Influence of retinoids on phosphatidylethanolamine lipid polymorphism. Biochim Biophys Acta 1992;1112:226e34. [41] Biltonen RL, Lichtenberg D. The use of differential scanning calorimetry as a tool to characterize liposome preparations. Chem Phys Lipids 1993;64:129e42. [42] Lindner LH, Eichhorn ME, Eibl H, Teichert N, SchmittSody M, Issels RD, et al. Novel temperature-sensitive
Biophysical characterization of gold nanoparticles-loaded liposomes liposomes with prolonged circulation time. Clin Cancer Res 2004;10:2168e78. [43] Needham D, Dewhirst MW. The development and testing of a new temperature-sensitive drug delivery system for the treatment of solid tumors. Adv Drug Deliv Rev 2001;53: 285e305. [44] Mady MM, Elshemey W. Interaction of dipalmitoyl phosphatidylcholine (DPPC) liposomes and insulin. Mol Phys 2011;109: 1593e8. [45] Lewis RNAH, McElhaney RN. Vibrational spectroscopy of lipids. In: Chalmers JM, Griffiths PR, editors. Handbook of vibrational
295
spectroscopy, vol. 5. Chichester, United Kingdom: John Wiley and Sons; 2002. p. 3447e64. [46] Lefe `vreT,ToscaniS,PicquartM,Dugue ´J.Crystallizationofwaterin multilamellarvesicles.EurBiophysJ2002;31:126e35. [47] Severcan F. Vitamin E decreases the order of the phospholipid model membranes in the gel phase: an FTIR study. Bioscience Rep 1997;17:231e5. [48] Toyran N, Severcan F. Infrared spectroscopic studies on the dipalmitoyl phosphatidylcholine bilayer interactions with calcium phosphate: effect of vitamin D2. Spectroscopy 2002; 16:399e408.
