Core shell hybrids based on noble metal nanoparticles and conjugated polymers: synthesis and characterization
© Fratoddi et al; licensee Springer. 2011
Received: 14 September 2010
Accepted: 21 January 2011
Published: 21 January 2011
Noble metal nanoparticles of different sizes and shapes combined with conjugated functional polymers give rise to advanced core shell hybrids with interesting physical characteristics and potential applications in sensors or cancer therapy. In this paper, a versatile and facile synthesis of core shell systems based on noble metal nanoparticles (AuNPs, AgNPs, PtNPs), coated by copolymers belonging to the class of substituted polyacetylenes has been developed. The polymeric shells containing functionalities such as phenyl, ammonium, or thiol pending groups have been chosen in order to tune hydrophilic and hydrophobic properties and solubility of the target core shell hybrids. The Au, Ag, or Pt nanoparticles coated by poly(dimethylpropargylamonium chloride), or poly(phenylacetylene-co-allylmercaptan). The chemical structure of polymeric shell, size and size distribution and optical properties of hybrids have been assessed. The mean diameter of the metal core has been measured (about 10-30 nm) with polymeric shell of about 2 nm.
The field of nanoscience and nanotechnology has found a dramatic attention in recent years and applicative perspectives of nanomaterials are widely studied . One of the main goals in nanoscience is the understanding of materials behaviour when the size becomes close to atomic dimensions. Increased attention has been recently paid to metallic nanoparticles and in particular to noble metal nanoparticles (Au, Ag, Pt) that can be used in several fields: biomedicine, diagnostics , drug delivery systems , sensors [4, 5], catalysis  and optics [7, 8]. Optical tuneable properties have been deeply investigated  and arise from collective oscillation of conduction electrons within the nanoparticles resulting in the so-called plasmon resonance [10, 11].
AuNPs have emerged as a broad new research field in the domain of colloids not only for their optical properties [12, 13], but also for high chemical stability, catalytic use and size-dependent properties [14, 15]. Aggregation phenomena can be avoided by protecting agents such as thiols or aminic compounds. Different synthetic protocols have been developed for the preparation of small, monodisperse nanoparticles [16, 17]. One phase methods, based on organic solvents such as methanol  or tetrahydrofuran  have also been successfully developed. Thiol-protected AuNPs usually show high stability lasting even for years; recently Pd(II) containing organometallic thiols have also been used for the stabilization of AuNPs [20, 21]. A number of functional groups such as thiopronin , succinic acid , sulfonic acid  and ammonium ions [24, 25] have shown to result in stable and readily water dispersible AuNPs.
Silver nanoparticles (AgNPs) have gained interest over the years because of appealing properties, such as catalytic and antibacterial activity [26, 27] which open perspectives in medical applications . There are many methods for the synthesis as well as the control of the shape of AgNPs . Silver nanoparticles can be synthesized by means of several methods and chemical reduction is one of the most frequently applied methods for their preparation as colloidal dispersions in water or organic solvents [30, 31]. The reduction of silver ions in aqueous solution generally yields colloidal silver with particle diameters of several nanometres . The synthesis is often carried out in the presence of stabilizers in order to prevent unwanted agglomeration of the colloids. Among others, tertiary amines have been recently used to form Ag nanoparticles in organic medium . Amine derivative complexes have been used to synthesize Au nanoparticles as well [34, 35].
Platinum metal is used in industrial catalysts and can be found in the catalytic converters, and platinum nanoparticles (PtNPs) have been recently used as a novel hydrogen storage medium . Colloidal PtNPs are synthesized in a fashion similar to that of AuNPs and AgNPs, by reduction of H2PtCl6 in the presence of a citrate capping agent. Colloidal platinum can be functionalized with nucleic acids and has been used as label for the amplified biorecognition of DNA hybridization, aptamer/protein recognition events and tyrosinase activity . Colloidally prepared Pt nanoparticles capped with organic ligands appear to be suitable as supported catalysts, and CO adsorption experiments have clearly shown that small molecules can pass through the ligand shell and adsorb on free areas of the Pt surface .
There has been recently a strong interest in the self-assembly of metal nanoparticles into ordered structures, mainly by using bifunctional molecules such as organic dithiols , surfactants  and polymers . Noble metal nanoparticles protected by synthetic polymers, i.e. core shell systems, are envisioned to be superior to polymeric micelles, for example as thermosensitive materials for biomedical applications . Metal nanoparticles stabilized by polymers can be prepared by postmodification of preformed gold nanoparticles and physisorption  or by "graft-from" and "graft-to" methods. For example, surface-initiated atom transfer radical polymerization technique has been successfully used to modify Ni nanoparticles and poly(methylmethacrylate) and poly(n-isopropylacrylamide) were grafted from the immobilized initiators . A facile approach to prepare thiol-terminated poly(styrene-ran-vinyl phenol) (PSVPh) copolymers and PSVPh-coated gold nanoparticles is reported with the goal of creating stabilizing ligands for nanoparticles with controlled hydrophilicity . Polymer shells have been formed around AgNPs by polymerization of adsorbed and solution-free monomers [45, 46] and the reduction of Ag salts in polymer micelles . Both hydrophilic and hydrophobic polymers [48, 49] have been tested and the development of synthesis protocols has received considerably attention. Water-dispersible metal nanoparticles are expected to have applications in catalysis, sensors, molecular markers and in particular, biological applications such as biolabelling and drug delivery.
In this paper, the synthesis and characterization of core shell systems based on noble metal nanoparticles and hydrophilic and hydrophobic polymer shells are reported. In particular, the "graft-to" strategy was applied starting from the ammonium-containing conjugated polymer, i.e. poly(dimethylpropargylamonium chloride) [P(DMPAHCl)] and a thiol-containing co-polymer, poly(phenylacetylene-co-allylmercaptan) [P(PA-co-AM)]. The polymers were used as stabilizer during the generation of Au, Ag and Pt nanoparticles and the materials were fully characterized by means of basic spectroscopic techniques, dynamic light scattering (DLS), Z-potential and X-ray photoelectron spectroscopy (XPS) and, for the investigation of morphology and dimensions of self-assembled structures, by transmission electron microscopy (TEM) techniques.
Gold(III) chloride trihydrate (HAuCl4 3H2O) (99.9%), silver nitrate (AgNO3) (99.9%), potassiumtetrachloroplatinate(II) (K2PtCl4) (99.9%), tetra-n-octylammonium bromide (TOAB) (98%), sodium borohydride (NaBH4) (98%), 3-dimethylamino-1-propyne (DMPA) (98%), phenylacetylene (PA) (98%), allylmercaptane (AM) (98%), potassium persulphate (99%), toluene, ethanol, and chloroform were purchased from Sigma Aldrich. All reagents were used as received without further purification. Water was purified through a Millipore-SIMPAKOR1system (Simplicity 185) and degassed for 30 min with Argon, before use. Conjugated polymer P(DMPAHCl) was synthesized in analogy to the method reported in our previous work , using Rh(I) dimer complex [Rh(cod)Cl]2 (cod = cyclooctadiene) with complex/monomer ratio 1/100 (a typical procedure is reported in Additional file 1). P(PA-co-AM) was prepared by using the emulsion polymerization technique in analogy to the synthesis of similar copolymers reported in our recent paper , with co-monomer ratios PA/AM = 5/1 and 10/1 (a typical procedure is reported in Additional file 1, together with the main characterizations of the precursor polymers).
Synthesis of hydrophilic metal nanoparticles
The hydrophilic metal core shell systems (Au, Ag, Pt) were prepared using the following procedure: gold(III) chloride trihydrate (0.02 g, 0.051 mmol) or silver nitrate (0.02 g 0.118 mmol) or potassiumtetrachloroplatinate (0.02 g 0.048 mmol) was dissolved in water (10 ml) to form a clear solution to which the polymer solution was then added (0.02 g of P(DMPAHCl) in 10 ml water). The mixture was vigorously stirred and degassed with Ar for 15 min. A water solution of sodium borohydride (0.02 g in 10 ml) was put into the mixture slowly. The reaction was stopped after 12 h and the water phase was left overnight in freezer (-20°C); the next day the dark precipitate, i.e. Au@P(DMPAHCl), Ag@P(DMPAHCl) or Pt@P(DMPAHCl), was washed several times with water by centrifugation and finally dried at 40°C (Yield 35 wt%). Main characterizations: Au@P(DMPAHCl): IR (film, cm-1):1615, 1250, 1120; UV-Vis (CHCl3): λmax = 296, 540 nm; Ag@P(DMPAHCl): IR (film, cm-1):1615, 1250, 1120; UV-Vis (CHCl3): λmax = 296, 410 nm; Pt@P(DMPAHCl): IR (film, cm-1):1615, 1250, 1120; UV-Vis (CHCl3): λmax = 300 nm.
Synthesis of hydrophobic metal nanoparticles
The hydrophobic metal (Au, Ag) nanoparticles were prepared by the following route: gold(III) chloride trihydrate (0.02 g, 0.05078 mmol) or silver nitrate (0.02 g, 0.1177 mmol) was dissolved in water (20 ml) to form a clear yellow solution, then polymeric solution (0.01 g P(PA-co-AM) in 10 ml toluene) and TOAB in toluene solution (0.035 mg in 4 ml) were added. The mixture was vigorously stirred and degassed with Ar for 15 min at room temperature. A water solution of sodium borohydride (0.02 g in 10 ml) was added to the mixture drop-by-drop. The reaction was allowed to react and maintained under stirring for 12 h. The black product, i.e. Au@P(PA-co-AM) or Ag@P(PA-co-AM) was extracted with a separator funnel two times with water (10 ml each) and, after that, the organic phase was left overnight in freezer (-20°C); the next day the dark precipitate was washed several times by centrifugation with ethanol and finally dried at 40°C (Yield 25 wt%). Main characterizations: Au@P(PA-co-AM): IR (film, cm-1): 3050, 2580, 1597; UV-Vis (CHCl3): λmax = 525 nm; Ag@P(PA-co-AM): IR (film, cm-1): 3050, 2580, 1597; UV-Vis (CHCl3): λmax = 400 nm.
UV-Vis spectra were recorded on a VARIAN Cary 100. All optical measurements were performed at room temperature using quantitative H2O or CHCl3 solutions. NMR spectra were recorded on a Varian XL-300 spectrometer at 300 MHz, in appropriate solvents (CDCl3, D2O); the chemical shifts (ppm) were referenced to TMS for 1H NMR assigning the residual 1H impurity signal in the solvent at 7.24 ppm (CDCl3). Molecular weights were determined at 25°C by gel permeation chromatography on a PL-gel column containing a highly cross-linked polystyrene/divinylbenzene matrix packed with 10 μm particles of 100 Å pore size using CHCl3 (HPLC grade) as eluent (details in Additional file 1). Samples for TEM measurement were prepared by placing a drop of suspension onto a carbon-coated copper grid and examined using a Philips CM120 Analytical transmission electron microscope with LaB6 filament, operating at 120 kV, magnification up to 660.000 ×, resolution up to 0.2 nm. DLS measurements were carried out using a Brookhaven instrument (Brookhaven, NY, USA) equipped with a 10 mW HeNe laser at a 632.8 nm wavelength, at the temperature of 25.0 ± 0.2°C. Correlation data were collected at 90° relative to incident beam and delay times from 0.8 μs to 10 s were explored. Correlation data were fitted using the non-negative least squares or CONTIN algorithms [52, 53], supplied with the instrument software. The average hydrodynamic radius R H of the diffusing objects was calculated from the diffusion coefficient D and the Stokes-Einstein relationship, R H = (K B T)/(6πηD), where K B T is the thermal energy and η is the solvent viscosity. XPS spectra were obtained using a custom-designed spectrometer. A non-monochromatic MgKα X-rays source (1253.6 eV) was used and the pressure in the instrument was maintained at 1 × 10-9 Torr throughout the analysis; binding energies (BE) were corrected by adjusting the position of the C1s peak to 285.0 eV in those samples containing mainly aliphatic carbons and to 284.7 eV in those containing more aromatic carbon atoms, in agreement with literature data  (see details in Additional file 1).
Results and discussion
The size and shape of the nanoparticles prepared by the reduction of the ions in solution normally depends on a number of parameters, such as the kind of reducing agent and the loading of the metal precursor. The reducing agent determines the rate of nucleation and particle growth: slow reduction produces large particles, while fast reduction gives small particles. In every case the NaBH4 was chosen as the reducing agent, which leads to a fast rate of nucleation and usually small metal cores.
In the case of P(DMPAHCl)-based core shell systems, due to their high water solubility, the reaction was carried out in aqueous phase, without the need of TOAB stabilizer. On the other hand, in the case of hydrophobic P(PA/AM)-based systems, a classical two phase procedure has been used allowing the TOAB to act as the phase transfer from the organic to the aqueous one.
The characteristic plasmon band for gold and silver has been observed at about 540 and 410 nm, respectively, with shoulders at about 300 nm, due to the absorption of polymeric shell. As expected, in the spectra of PtNPs, recorded at the end of the reaction, no characteristic peaks of the nanoparticles have been observed and a broad absorption at about 300 nm has been assigned to the polymer shell. During the evolution of the metal nanoparticles, UV-Vis spectra of the metal sols at different times have also been recorded and it was found that as the time progresses the absorption bands for Au and Ag narrowed and shifted continuously to the shorter wavelength regions. Purification of the nanoparticles has been performed by centrifugation of the pristine suspension, giving rise to samples a, b, c with the characteristic plasmon band split in two components, centred at 540 and 695 nm (sample Au@P(DMPAHCl-c). This behaviour can be explained as a consequence of the isolation of core shell hybrids with different shapes, sizes, and compositions. While gold nanospheres usually show one absorption band in the visible region, gold nanorods are reported to show two bands . The IR spectra of the core shell hybrids show the characteristic features of the structural units of the polymeric shell, not affected by the reduction procedures, thus confirming the achievements of a defined and stable polymeric shell.
In the case of Au@P(PA-co-AM) and Ag@P(PA-co-AM) samples, upon addition of NaBH4 to AuCl4 - solution in the presence of P(PA/AM) copolymer, the colour of the solution rapidly turned to brown during the reaction and UV-Vis spectra of the purified samples show the characteristic plasmon band of gold and silver at about 525 and 400 nm, partially overlapped the typical large absorption band of the P(PA-co-AM) copolymer at about 370 nm. Also in this case the IR characterization confirmed the presence of the functional group characteristics of the polymeric shell.
XPS characterization has been carried out on our materials and allowed to investigate the interaction at the interface between metal nanoclusters and polymers, as well as the chemical composition of the resulting core shell materials. C1s, N1s, S2p, Cl2p and Au4f, Ag3d or Pt4f signals have been acquired. For comparison, pristine P(DMPAHCl) and P(PA-co-AM) polymers were also investigated.
C1s spectra of all samples appear structured and three components were individuated by peak fitting: a main signal at 285.0 eV due to aliphatic carbon atoms that was used for the calibration procedure (see "Experimental" section), a component at about 286.5 eV belonging to C atoms bridged to aminic (C*-N) or thiol (C*-S) groups, and a third signal of very low intensity at higher BE values (288.5 eV) that is due to organic contaminants chemisorbed on the sample surface. Metal XPS spectra, i.e. Au4f, Ag3d and Pt4f, show a couple of spin orbit pairs. The signal at lower BE values (83.80 eV for Au4f7/2, 369.07 eV for Ag3d5/2 and 73.49 eV for Pt4f7/2) was assigned to metallic gold, silver and platinum, respectively; the feature at higher BE values (84.65 eV for Au4f7/2, 369.80 eV for Ag3d5/2 and 74.91 eV for Pt4f7/2) was attributed to metal atoms interacting with the co-polymer functional group, i.e. -N(CH3)2 for P(DMPAHCl) and -SH for P(PA-co-AM). The direction of the shift in metal XPS spectra clearly indicates that part of the metal atoms are in an oxidized state, i.e. the metal-polymer interaction causes a decreased electron density on the interacting metal atoms. For example, a BE value of 84.6 eV for Au4f7/2 component is consistent with the BE value of 84.4 eV reported in the literature for Au(1) complexes . N1s spectra of Au@P(DMPAHCl), Ag@P(DMPAHCl) and Pt@P(DMPAHCl) revealed two components at about 400.2 and 402.5 eV. The signal at higher BE values was attributed to the unperturbed aminic groups, by comparison with the pristine P(DMPAHCl) polymer. The N1s spectrum of P(DMPAHCl) shows a single signal at about 402.3 eV, as expected for aminic groups interacting with Cl- ions, alike for example in NH4X or (CH3)4NX ; Cl2p spectra were also collected and the observed Cl2p3/2 signal is found at about 197.80 eV in both pristine polymers and core shell systems, and attributed to Cl- ions alike for NH4Cl . The second N1s peak observed for the core shell M@P(DMPAHCl) samples at 400.2 eV was assigned to aminic groups bonded to Au and, respectively, Ag and Pt. The observed decrease in N1s BE value is related to the increased charge density on N atoms, as a consequence of the nitrogen-metal interaction. A completely similar behaviour was observed for S-containing polymers grafting Au and Ag nanoparticles in Au@P(PA-co-AM) and Ag@P(PA-co-AM), where S2p3/2 signal BE decreases from 163.2 to about 162.0 eV going from pristine P(PA-co-AM) co-polymer to the core shell systems. A completely similar trend was observed for thiols anchored on metal nanoclusters as well as metal surfaces, and extensively discussed in the literature [59, 60]. The above discussed XPS analysis lead to ascertain that a covalent bond occurs between the metal atoms and the polymer functional group, DMPA (N atoms) and AM (S atoms), respectively.
In Figure 4a,b the TEM images of Au@P(PA-co-AM) and Ag@ P(PA-co-AM) obtained from P(PA-co-AM) with co-monomer ratio 5/1, are reported. In this case dispersed nanoparticles have been observed and the dimensions are distributed in the range of 5-15 nm for AuNPs and 10-30 nm for AgNPs.
The reported results show the achievement of an easy and versatile synthesis of core shell systems based on noble metal nanoparticles that allows the modulation of morphology, dimensions and chemical-physical properties of these nanoparticles, such as the hydrophilic-hydrophobic character, using an appropriate conjugated polymeric shell.
A versatile and facile synthesis of core shell systems based on noble metal nanoparticles (AuNPs, AgNPs, PtNPs), coated by polymers and copolymers belonging to the class of substituted polyacetylenes has been developed. The polymeric shells containing different functionalities have been chosen in order to tune the hydrophilic and hydrophobic properties of the target core shell hybrids. The core shell dimensions can be tailored by the synthesis and obtained in the range of 10-30 nm. The nanoparticles show hydrophilic and hydrophobic groups on the surface of the spherical shell and this functional property is a suitable tool for future applications of these coated metal nanoparticles for biomedicine and sensors.
dynamic light scattering
transmission electron microscopy
X-ray photoelectron spectroscopy.
The authors acknowledge the financial support Ateneo Sapienza 2008 prot. C26A08LHEK and AST 2009 prot. 26F09MA27.
- Ozin GA, Arsenault AC, Cademartori L: Nanochemistry. 2nd edition. London: RSC Publishing; 2009.Google Scholar
- Hyukjin L, Kyuri L, Kyoung KI, Tae Gwan P: Synthesis, characterization, and in vivo diagnostic applications of hyaluronic acid immobilized gold nanoprobes. Biomaterials 2008, 29: 4709. 10.1016/j.biomaterials.2008.08.038View ArticleGoogle Scholar
- Ghosh P, Han G, De M, Kim CK, Rotello VM: Gold nanoparticles in delivery applications. Adv Drug Deliv Rev 2008, 60: 1307. 10.1016/j.addr.2008.03.016View ArticleGoogle Scholar
- Scampicchio M, Arecchi A, Mannino S: Optical nanoprobes based on gold nanoparticles for sugar sensing. Nanotechnology 2009, 20: 135501. 10.1088/0957-4484/20/13/135501View ArticleGoogle Scholar
- Lee JS, Ulmann PA, Han MS, Mirkin CA: A DNA-Gold Nanoparticle-Based Colorimetric Competition Assay for the Detection of Cysteine. Nano Lett 2008, 8: 529. 10.1021/nl0727563View ArticleGoogle Scholar
- Pasricha R, Bala T, Biradar AV, Umbarkar S, Sastry M: Synthesis of Catalytically Active Porous Platinum Nanoparticles by Transmetallation Reaction and Proposition of the Mechanism. Small 2009, 5: 1467. 10.1002/smll.200801863View ArticleGoogle Scholar
- Ghosh SK, Pal T: Interparticle Coupling Effect on the Surface Plasmon Resonance of Gold Nanoparticles: From Theory to Applications. Chem Rev 2007, 107: 4797. 10.1021/cr0680282View ArticleGoogle Scholar
- Yang ZX, Zhong W, Deng Y, Au C, Du YW: Thermal Contraction of Electrodeposited Bi/BiSb Superlattice Nanowires. Nanoscale Res Lett 2010, 5: 1124. 10.1007/s11671-010-9612-3View ArticleGoogle Scholar
- Seker F, Malenfant PRL, Larsen M, Alizadeh A, Conway K, Kulkarni AM, Goddard G, Garaas R: On-Demand Control of Optoelectronic Coupling in Gold Nanoparticle Arrays. Adv Mater 2005, 17: 1941. 10.1002/adma.200400734View ArticleGoogle Scholar
- Ramakrishna G, Dai Q, Zou JH, Huo Q, Goodson T: Quantum-Sized Gold Clusters as Efficient Two-Photon Absorbers. J Am Chem Soc 2007, 129: 1848. 10.1021/ja067123pView ArticleGoogle Scholar
- Paresh CR: Size and Shape Dependent Second Order Nonlinear Optical Properties of Nanomaterials and Their Application in Biological and Chemical Sensing. Chem Rev 2010, 110: 5332. 10.1021/cr900335qView ArticleGoogle Scholar
- Hostetler MJ, Wingate JE, Zhong CJ, Harris JE, Vachet RW, Clark MR, Londono JD, Green SJ, Stokes JJ, Wignall GD, Glish GL, Porter MD, Evans MD, Murray RW: Alkanethiolate Gold Cluster Molecules with Core Diameters from 1.5 to 5.2 nm: Core and Monolayer Properties as a Function of Core Size. Langmuir 1998, 14: 17. 10.1021/la970588wView ArticleGoogle Scholar
- Daniel MC, Astruc D: Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications toward Biology, Catalysis, and Nanotechnology. Chem Rev 2004, 104: 293. 10.1021/cr030698+View ArticleGoogle Scholar
- Sardar R, Funston AM, Mulvaney P, Murray RW: Gold Nanoparticles: Past, Present, and Future. Langmuir 2009, 25: 13840. 10.1021/la9019475View ArticleGoogle Scholar
- Zabet-Khosousi A, Dhirani A: Charge transport in nanoparticle assemblies. Chem Rev 2008, 108: 4072. 10.1021/cr0680134View ArticleGoogle Scholar
- Moon SY, Tanaka S, Sekino T: Crystal Growth of Thiol-Stabilized Gold Nanoparticles by Heat-Induced Coalescence. Nanoscale Res Lett 2010, 5: 813. 10.1007/s11671-010-9565-6View ArticleGoogle Scholar
- Kimling J, Maier M, Okenve B, Kotaidis V, Ballot H, Plech A: Turkevich Method for Gold Nanoparticle Synthesis Revisited. J Phys Chem B 2006, 110: 15700. 10.1021/jp061667wView ArticleGoogle Scholar
- Brust M, Fink J, Bethell D, Schiffrin DJ, Kiely CJJ: Synthesis and reactions of functionalised gold nanoparticles. Chem Soc Chem Commun 1995, 1655. 10.1039/c39950001655Google Scholar
- Yee CK, Jordan R, Ulman A, White H, King A, Rafailovich M, Sokolov J: Novel One-Phase Synthesis of Thiol-Functionalized Gold, Palladium, and Iridium Nanoparticles Using Superhydride. Langmuir 1999, 15: 3486. 10.1021/la990015eView ArticleGoogle Scholar
- Vitale F, Vitaliano R, Battocchio C, Fratoddi I, Piscopiello E, Tapfer L, Russo MV: Synthesis and characterization of gold nanoparticles stabilized by palladium(II) phosphine thiol. J Organomet Chem 2008, 623: 1043. 10.1016/j.jorganchem.2007.12.024View ArticleGoogle Scholar
- Vitale F, Vitaliano R, Battocchio C, Fratoddi I, Giannini C, Piscopiello E, Guagliardi A, Cervellino A, Polzonetti G, Russo MV, Tapfer L: Synthesis and Microstructural Investigations of Organometallic Pd(II) Thiol-Gold Nanoparticles Hybrids. Nanoscale Res Lett 2008, 3: 461. 10.1007/s11671-008-9181-xView ArticleGoogle Scholar
- Tian F, Klabunde KJ: Nonaqueous gold colloids. Investigations of deposition and film growth on organically modified substrates and trapping of molecular gold clusters with an alkyl amine. New J Chem 1998, 22: 1275. 10.1039/a709248bView ArticleGoogle Scholar
- Brust M, Bethell D, Schiffrin DJ, Kiely CJ: Novel gold-dithiol nano-networks with non-metallic electronic properties. Adv Mater 1995, 7: 795. 10.1002/adma.19950070907View ArticleGoogle Scholar
- Hostetler MJ, Zhong CJ, Yen BKH, Andereeg J, Gross SM, Evans ND, Porter MD, Murray RW: Stable, Monolayer-Protected Metal Alloy Clusters. J Am Chem Soc 1998, 120: 9396. 10.1021/ja981454nView ArticleGoogle Scholar
- Fink J, Kiely CJ, Bethell D, Schiffrin DJ: Self-Organization of Nanosized Gold Particles. Chem Mater 1998, 10: 922. 10.1021/cm970702wView ArticleGoogle Scholar
- Mukherjee P, Ahmad A, Mandal D, Senapati S, Sainkar SR, Khan MI, Parishcha R, Ajaykumar PV, Alam M, Kumar R, Sastry M: Fungus mediated synthesis of silver nanoparticle and their immobilization in the mycelial matrix: A novel biological approach to nanoparticle synthesis. Nano Lett 2001, 10: 515. 10.1021/nl0155274View ArticleGoogle Scholar
- Sondi I, Salopek-Sondi B: Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria. J Colloid Interface Sci 2004, 275: 177. 10.1016/j.jcis.2004.02.012View ArticleGoogle Scholar
- Chen X, Schluesener HJ: Nanosilver: a nanoproduct in medical application. Toxicol Lett 2008, 176: 1. 10.1016/j.toxlet.2007.10.004View ArticleGoogle Scholar
- Mitsudome T, Mikami Y, Mori H, Arita S, Mizugaki T, Jitsukawa K, Kaneda K: Supported silver nanoparticle catalyst for selective hydration of nitriles to amides in water. Chem Commun 2009, 3258. 10.1039/b902469gGoogle Scholar
- Tao A, Sinsermsuksakul P, Yang P: Tunable plasmonic lattices of silver nanocrystals. Nature Nanotech 2007, 7: 435. 10.1038/nnano.2007.189View ArticleGoogle Scholar
- Wiley B, Sun Y, Mayers B, Xia Y: Shape-Controlled Synthesis of Metal Nanostructures: The Case of Silver. Chem A Eur J 2005, 11: 454. 10.1002/chem.200400927View ArticleGoogle Scholar
- Kapoor S, Lawless D, Kennepohl P, Meisel P, Serpone N: Reduction and Aggregation of Silver Ions in Aqueous Gelatin Solutions. Langmuir 1994, 10: 3018. 10.1021/la00021a026View ArticleGoogle Scholar
- Yamamoto M, Nakamoto M: Novel preparation of monodispersed silver nanoparticles via amine adducts derived from insoluble silver myristate in tertiary alkylamine. J Mater Chem 2003, 13: 2064. 10.1039/b307092aView ArticleGoogle Scholar
- Kumar A, Mandal S, Selvakannan PR, Pasricha R, Mandale AB, Sastry M: Investigation into the Interaction between Surface-Bound Alkylamines and Gold Nanoparticles. Langmuir 2003, 19: 6277. 10.1021/la034209cView ArticleGoogle Scholar
- Selvakannan PR, Mandal S, Phadtare S, Gole A, Pasricha R, Adyanthaya SD, Sastry M: Water-dispersible tryptophan-protected gold nanoparticles prepared by the spontaneous reduction of aqueous chloroaurate ions by the amino acid. J Colloid Interface Sci 2004, 269: 97. 10.1016/S0021-9797(03)00616-7View ArticleGoogle Scholar
- Yamauchi M, Kobayashi H, Kitagawa H: Hydrogen Storage Mediated by Pd and Pt Nanoparticles. Chem Phys Chem 2009, 10: 2566.Google Scholar
- Chen R, Maclaughlin S, Botton G, Zhu S: Preparation of Ni-g-polymer core-shell nanoparticles by surface-initiated atom transfer radical polymerization. Polymer 2009, 50: 4293. 10.1016/j.polymer.2009.07.012View ArticleGoogle Scholar
- Borchert H, Fenske D, Kolny-Olesiak J, Parisi J, Al-Shamery K, Bäumer K: Ligand-Capped Pt Nanocrystals as Oxide-Supported Catalysts: FTIR Spectroscopic Investigations of the Adsorption and Oxidation of CO. Angew Chem Int Ed 2007, 46: 2923. 10.1002/anie.200604460View ArticleGoogle Scholar
- Polavarapu L, Xu QH: Water-Soluble Conjugated Polymer-Induced Self-Assembly of Gold Nanoparticles and Its Application to SERS. Nanotechnology 2008, 19: 10608. 10.1088/0957-4484/19/7/075601View ArticleGoogle Scholar
- Yang Y, Matsubara S, Nogami M, Shi JL, Huang WM: One-Dimensional Self-Assembly of Gold Nanoparticles for Tunable Surface Plasmon Resonance Properties. Nanotechnology 2006, 17: 2821. 10.1088/0957-4484/17/11/015View ArticleGoogle Scholar
- Sardar R, Shumaker-Parry JS: Asymmetrically Functionalized Gold Nanoparticles Organized in One-Dimensional Chains. Nano Lett 2008, 8: 731. 10.1021/nl073154mView ArticleGoogle Scholar
- Yuan YY, Liu XQ, Wang YC, Wang J: Gold Nanoparticles Stabilized by Thermosensitive Diblock Copolymers of Poly(ethylene glycol) and Polyphosphoester. Langmuir 2009, 25: 10298. 10.1021/la901120xView ArticleGoogle Scholar
- Shan J, Tenhu H: Recent advances in polymer protected gold nanoparticles: synthesis, properties and applications. Chem Commun 2007, 4580. 10.1039/b707740hGoogle Scholar
- Lee CU, Roy D, Sumerlin D, Dadmun MD: Facile synthesis of thiol-terminated poly(styrene-ran-vinyl phenol) (PSVPh) copolymers via reversible addition-fragmentation chain transfer (RAFT) polymerization and their use in the synthesis of gold nanoparticles with controllable hydrophilicity. Polymer 2010, 51: 1244. 10.1016/j.polymer.2010.01.033View ArticleGoogle Scholar
- Quaroni L, Chumanov G: Preparation of polymer-coated functionalized silver nanoparticles. J Am Chem Soc 1999, 121: 21064. 10.1021/ja992088qView ArticleGoogle Scholar
- Kumar VRR, Pradeep T: Polymerization of benzylthiocyanate on silver nanoparticles and the formation of polymer coated nanoparticles. J Mater Chem 2006, 16: 837. 10.1039/b513487kView ArticleGoogle Scholar
- Wang H, Wang X, Winnik MA, Manners I: Redox-Mediated Synthesis and Encapsulation of Inorganic Nanoparticles in Shell-Cross-Linked Cylindrical Polyferrocenylsilane Block Copolymer Micelles. J Am Chem Soc 2008, 130: 11292. 10.1021/ja804588rView ArticleGoogle Scholar
- Peng H, Wu C, Jiang Y, Huang S, McNeill J: Highly Luminescent Eu3+ Chelate Nanoparticles Prepared by a Reprecipitation-Encapsulation Method. Langmuir 2007, 23: 1591. 10.1021/la062915iView ArticleGoogle Scholar
- Sussman EM, Clarke MB, Shastri VP: Single-Step Process to Produce Surface-Functionalized Polymeric Nanoparticles. Langmuir 2007, 23: 51227. 10.1021/la701997xView ArticleGoogle Scholar
- Venditti I, Fratoddi I, Battocchio C, Polzonetti G, Cametti C, Russo MV: Soluble poly(monosubstituted)acetylenes with quaternary ammonium pendant groups. Structure and morphology. Polym Intern 2011, in press.Google Scholar
- Venditti I, Fratoddi I, Palazzesi C, Prosposito P, Casalboni M, Cametti C, Battocchio C, Polzonetti G, Russo MV: Self-assembled nanoparticles of functional copolymers for photonic applications. J Colloid Interface Sci 2010, 348: 424. 10.1016/j.jcis.2010.04.061View ArticleGoogle Scholar
- Lawson CL, Morrison ID: Solving Least Squares Problems. A FORTRAN Program and Subroutines Called NNLS. Englewood Cliffs, NJ: Prentice-Hall; 1974.Google Scholar
- Provencher SW: CONTIN: A general purpose constrained regularization program for inverting noisy linear algebraic and integral equations. Comput Phys Commun 1982, 27: 229. 10.1016/0010-4655(82)90174-6View ArticleGoogle Scholar
- Beamson G, Briggs D: High Resolution XPS of Organic Polymers. The Scienta ESCA300 Database. New York: Wiley; 1992.Google Scholar
- Huang X, Neretina S, El-Sayed MA: Gold Nanorods: from Synthesis and Properties to Biological and Biomedical Applications. Adv Mater 2009, 21: 4880. 10.1002/adma.200802789View ArticleGoogle Scholar
- Bourg MC, Badia A, Lennox RB: Gold Sulfur Bonding in 2D and 3D Self-Assembled Monolayers: XPS Characterization. J Phys Chem B 2000, 104: 6562. 10.1021/jp9935337View ArticleGoogle Scholar
- Escard J, Mavel G, Guerchais JE, Kergoat R: X-ray photoelectron spectroscopy study of some metal(II) halide and pseudohalide complexes. Inorg Chem 1974, 13: 695. 10.1021/ic50133a036View ArticleGoogle Scholar
- Morgan WE, Van Wazer JR, Stech WJ: Inner-orbital photoelectron spectroscopy of the alkali metal halides, perchlorates, phosphates, and pyrophosphates. J Am Chem Soc 1973, 95: 751. 10.1021/ja00784a018View ArticleGoogle Scholar
- Zhang S, Leem G, Lee TR: Monolayer-Protected Gold Nanoparticles Prepared Using Long-Chain Alkanethioacetates. Langmuir 2009, 25: 13855. 10.1021/la901847sView ArticleGoogle Scholar
- Nilsson D, Watcharinyanon S, Eng M, Li L, Moons E, Johansson LSO, Zharnikov M, Shaporenko A, Albinsson B, Må J: Characterization of Self-Assembled Monolayers of Oligo(phenyleneethynylene) Derivatives of Varying Shapes on Gold: Effect of Laterally Extended π-Systems. Langmuir 2007, 23: 6170. 10.1021/la0636964View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.