In this study, 9 nm superparamagnetic iron oxide nanoparticles (SPION) were functionalized by polyamidoamine (PAMAM) dendrimer. Using tetracholoroauric acid (HAuCl 4), magnetodendrimer (MD) samples were conjugated by gold nanoparticles (Au-NPs). Two different reducing agents, i.e. sodium borohydride and hydrazine sulfate, and pre-synthesized 10-nm Au-NP were used to evaluate the efficiency of conjugation method. The samples were characterized using X-ray diffractometry (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy and fluorescence spectroscopy. The results confirmed that Au- NPs produced by sodium borohydrate and the pre-synthesized 10-nm Au-NPs were capped by MDs whereas the Au-NP prepared by hydrazine sulfate as a reducing agent was entrapped by MDs. Optical properties of the MDs were studied by laser-induced fluorescence spectroscopy (LIF) within a wide range of visible spectrum. Also, based on the thermal analysis, all synthesized nanostructures exhibited a temperature increase using 488 nm and 514 nm wavelengths of a tunable argon laser. The new iron oxide-dendrimer-Au NPs synthesized by sodium borohydrate (IDA- NaBH 4) produced the highest temperature increase at 488 nm whereas the other nanostructures particularly pure Au-NPs produced more heating effect at 514 nm. These findings suggest the potential application of these nanocomposites in the field of bioimaging, targeted drug delivery and controlled hyperthermia.
Recently a variety nanomaterials including magnetite superparamagnetic iron oxide nanoparticles (SPION) and nobel metal nanoparticles such as gold have been the focus of many research fields particularly in medicine and biomedical engineering which has shown a promising advancement [
Researchers explicitly assert that poly(amidoamine) (PAMAM) dendrimers can act as a template or stabilizer for preparation of inorganic nanocomposites. The resultant nanocomposites have much applicable potential such as gen vector, catalysis, resonance imaging agents and nanocapsules [
The contemporary issues in cancer treatment are production of effective nanoprobes for tumor targeting and selective therapy [
Iron chlorides (III) (FeCl3.6H2O), Iron Sulfate (FeSO4∙7H2O), and Ethanol (C2H5OH) were purchased from Merck Company. Ammonium Hydroxide (NH4OH), Methyl Acrylate (CH2 = C(CH3)COOCH3), Ethylenediamine (C2H4(NH2)2), Soduiom Borohydrate (NaBH4), Hydrazine sulfate (H6N2O4S), Gold colloid solution (10 nm), and tetracholoroauric acid (HAuCl4) were obtained from Sigma Aldrich.
Dendrimer grafted magentite nanoparticles (magnetodendrimers-MDs) were synthesized based on our previous published report [
a―Using sodium borohydrate (IDA-NaBH4): A solution of tetracholoroauric acid (HAuCl4) (5 mM) was prepared and added to the suspension of third generation magnetodendrimer (1% w/v) with the same volume under N2 atmosphere. In order to produce the complex between Au (III) and amide or amine group of dendrimer, the resulting mixture was vigorously stirred for one hour at darkness. After that, 5 mL of aqueous sodium borohydrate solution (0.1 M) was added drop wise to the reaction mixture. The following reactions lead to reducing Au (III) to zero charge Au (0) nanoparticles. The reaction was continued under a vigorous stirring for 2 hours at 25˚C. The obtained nanoparticles are referred as IDA-NaBH4. These particles were rinsed with ethanol five times using magnetic separation. The same procedure was repeated with the tenfold concentration of HAuCl4 and to evaluate the completion of the reactions, a UV-vis analysis was performed at 0, 15, 30, 45, 60, 90, and 120 minutes after addition of reducing agent. The product is referred as (IDA-10).
b―Using hydrazine sulfate (IDA-Hydr.): The stable gold nanoparticles were produced by adding hydrazine sulfate (H6N2O4S) aqueous solution (25 mM) to the solution of magnetodendrime-HAuCl4 complex and stirring for 2 hours. The particles were rinsed with ethanol five times as before and the sample was named IDA-Hydr.
c―Using gold nanoparticles (IDA-NP): Au-NPs (purchased from sigma Aldrich) were directly added to magnetodenrimer suspension under N2 atmosphere. The mixture was stirred for an hour to complete the reaction and then particles rinsed five times with ethanol.
Crystalline phase of nanoparticles was confirmed using X-ray diffraction with radiation of Cu Kα (XRD, λ = 0.15406 nm, FK60-40 X-ray diffractometer). The presence of PAMAM, gold formation on the surface of magnetite nanoparticles was proved by Fourier transform infrared (FTIR) spectroscopy (BOMEM, Canada). Particle size and morphology of nanocomposites were determined by transmission electron microscopy (TEM, Philips CM-200-FEG microscope, 120 kV). The amount of Au-NP attached to the magnetodendrimer was estimated using wavelength-dispersive X-ray spectroscopy (SEM?WDX, XL30, Philips, USA). The UV-vis spectra of nanoparticles were recorded using spectrophotometer (UV-2600, Shimadzu, Japan).
The evaluation of fluorescence emission of ID (G3), IDA-10, IDA-Hydr, and IDA-NP nanoparticles at different excitation wavelengths was performed using an ion argon laser Melles Griot-35MAP431) at 25˚C. The fluorescence signals were detected by a 600 µm core diameter optical fiber (LIBS-600-6-SR, Ocean Optics) connected to spectrometer (UV-Vis USB 4000, Ocean Optics), see
The next set up was to evaluate the efficiency of these nanoparticles in coloring the polymeric substrate, using two kinds of natural polymers, i.e., cotton and collagen. After the injection of nanoparticle solution to these substrates, fluorescence microscopy (Zeiss Axioshop-Germany) was used to study the materials colouring.
The concept of dendrimer nanocomposites is based on immobilization of pre-organized metallic ions [
the second stage, a series of reactions lead to production of resultant hybrid materials. At this stage, mostly a reducing agent is added to precursor-dendrimer complex and the complex loses HCl moieties and Au-NPs are stabilized in the dendrimer structure [
In this work, in order to evaluate the formation of Au-NPs during the synthesis reaction, sampling was done at different reaction times and the UV-vis spectra of these samples were recorded.
At synthesis condition of dendrimer-gold nanocomposite and in the presence of HAuCl4 molecules, amine group loses electrons and electrostatically interacts with AuCl4− ions. In UV-vis spectrum of the condition prior to addition of reducing agent, an absorption peak was observed around 280 nm which is the characteristic peak of bound formation between
In order to evaluate the presence of Au-NP in the final structure, XRD analysis was done (
patterns contain diffraction peaks at 2θ equal to 38, 44.3, 64.5 and 77.9 which represent (111), (200), (220) and (311) crystallographic plane respectively which prove the FCC structure of gold (JCPDS No.00-04-0784) [
where, D, λ and β represent the mean diameter of particles, the wavelength of incident X-ray, and the full width at half height (FWHM) respectively and constant K is equal to 0.9.
FTIR analysis was used to prove the attachment of Au-NPs to magnetodendrimer shown in
drimers are stronger than carboxyl terminated dendrimers as the FTIR bands of dendrimer are shifted while the half generations do not show any changes [
Type I amide band (wave number of 1630 cm−1) is generally related to C=O stretching vibration (70% - 85%) and directly appertain to combination and structure of polymer backbone. Type II amide band (wave number 1570 cm−1) represents the N-H bending vibration (20%) [
of relative counts of Fe: Au where hydrazine sulfate reducing agent has shown to produce the best nanoparticles compared to other synthesis methods.
One of the early works regarding the fluorescence of PAMAM dendrimer was reported by Klajnart et al. [
Considering the chemical structures of collagen and cotton, there is a possibility of hydrogen interaction between the hydroxyl group of the substrate and amine group of dendrimer nanocomposites which produces a new fluorescent moieties with a time dependent behaviour. The longer the time, the more fluorescent moieties is produced hence, more intense fluorescence image could be obtained.
514 nm (
electron cloud which cools down in about 1 ps as a result of heat transfer within the nanoparticle lattice which is then followed by phonon-phonon interactions in 100 ps where the metallic lattice transfers the heat to its surrounding medium and cools down [
The temperature distribution around optically-stimulated plasmonic nanoparticles can be described by the following equation [
where T is the local temperature, and ρ, c, and K represent density, specific heat capacity, and thermal conductivity of material, respectively. Here
where C is the speed of light, eAu and ew are the permittivity of gold and water, respectively. This definition obtained from the original formula [
sabs is the optical absorption cross section of the gold nanoparticles and I is the intensity of incoming light.
And
After a transient evolution, materials reach steady state temperature profile under CW illumination. Dimensional analysis of the two diffusion equations demonstrates two time scale of the system:
where k = K/ρc is thermal diffusivity (m2∙s−1),
In the final steady state regime, Equation (2) reduces to:
This equation is formally equivalent to Poisson’s equation and produces a profile of temperature increase ΔT given by a Coulomb potential outside the particle [
Substituting the Equation (3) in Equation (10), it gives the temperature increase at the surface of nanoparticle (i.e. r = R),
here R represents the nanoparticle’s radius and I is the intensity of incident beam. Equation (11) shows that temperature of the system containing plasmonic nanoparticles is proportional to the square of the nanoparticle radius, i.e. ΔT µ R2. As the TEM results show, the use of sodium borohydrate as a reducing agent produced clusters of Au-NPs which consists a greater particle size than the other formulation. Based on above analysis we expect to obtain a higher temperature in IDA-NaBH4 shown in
Gold-magneto dendrimer nanocomposites were prepared using two different reducing agents and pre-synthe- sized Au-NP. To the best of our knowledge, there was no evidence of the in-situ monitoring of the Au-NP formation which was done in this study. WDX, XRD, and FTIR analysis of the nanocomposites indicated the simultaneous presence of magnetite and gold phase in the materials. Also, the WDX and TEM results suggest that the use of hydrazine sulfate as a reducing agent can both produce a uniform structure and load higher degree of Au-NPs in the materials. LIF spectroscopy and fluorescent microscopy results confirmed that synthesized metal/dendrimer nanocomposites could fluorescently dye biopolymers such as cotton and collagen. The interaction of 488 nm and 514 nm wavelengths with the all three nanocomposite media resulted in temperature increase with IDA-NaBH4 and IDA-Hydr showing the highest and the lowest temperature at 488 nm respectively. At 514 nm, however, pure-Au NP synthesized by hydrazine sulfate exhibited the highest heating effect which was closer to its maximum absorption peak of plasmonic band. Considering the outcomes of these experiments, we suggest that these novel nanocomposites can be employed as biomarker and therapeutic agents based on their magnetic, fluorescence and SPR-based optothermal properties.
MaryamTajabadi,Mohammad E.Khosroshahi,ShahinBonakdar, (2015) Imaging and Therapeutic Applications of Optical and Thermal Response of SPION-Based Third Generation Plasmonic Nanodendrimers. Optics and Photonics Journal,05,212-226. doi: 10.4236/opj.2015.57021