Metallic nanoparticles: synthesis, characterisation and application

Int. J. Nanotechnol., Vol. 8, Nos. 3/4/5, 2011 227

Copyright © 2011 Inderscience Enterprises Ltd.

Metallic nanoparticles: synthesis, characterisation and application

Nguyen Hoang Luong*, Nguyen Ngoc Long, Le Van Vu and Nguyen Hoang Hai Center for Materials Science, Hanoi University of Science, Vietnam National University, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam E-mail: [email protected] E-mail: [email protected] E-mail: [email protected] E-mail: [email protected] *Corresponding author

Phan Tuan Nghia and Nguyen Thi Van Anh Key Laboratory for Enzyme and Protein Technology, Hanoi University of Science, Vietnam National University, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam E-mail: [email protected] E-mail: [email protected]

Abstract: Colloidal sphere-like gold nanoparticles were prepared from an HAuCl4 aqueous solution by the chemical reduction method and by using X-ray irradiation, while rod-like gold nanoparticles were synthesised according to the seed-mediated growth method and by sonoelectrochemistry. Gold nanoparticles exhibit fcc structure. Sphere-like gold nanoparticles have a diameter of 20–60 nm, while rod-like gold nanoparticles have an aspect ratio of 2–4. In UV-vis spectra, the absorption bands related to surface plasmon resonance were observed. Co-Pt nanoparticles of 5–20 nm were prepared by electrochemistry, while Fe-Pt nanoparticles with a size of 5–10 nm were prepared by sonoelectrochemistry. After annealing, these magnetic nanoparticles showed a high coercivity. The gold nanoparticles were functionalised for detecting breast cancer cells.

Keywords: gold nanoparticles; Co-Pt nanoparticles; Fe-Pt nanoparticles; optical properties; magnetic properties.

Reference to this paper should be made as follows: Luong, N.H., Long, N.N., Vu, L.V., Hai, N.H., Nghia, P.T. and Anh, N.T.V. (2011) ‘Metallic nanoparticles: synthesis, characterisation and application’, Int. J. Nanotechnol., Vol. 8, Nos. 3/4/5, pp.227–240.

Biographical notes: Nguyen Hoang Luong received his PhD in Solid State Physics from the University of Hanoi in 1984. He received the Degree of Doctor of Habilitation from the University of Mining and Metallurgy, Krakow, Poland, in 1999. He was promoted to the rank of Associate Professor

228 N.H. Luong et al.

in 1996 and to Professor in 2002. He is the author/co-author of over 50 publications in international journals. His research interests include the magnetic properties of rare-earth intermetallic compounds, synthesis, characterisation and application of nanostructures based on magnetic and metallic materials.

Nguyen Ngoc Long received his PhD in Solid State Physics from Saint-Petersburg University, Russia, in 1972. He was promoted to the rank of Associate Professor in 1991 at Hanoi University. He is a former Director of the Centre for Materials Science, Hanoi University of Science, Vietnam National University. His research interests include the optical properties of semiconductors, synthesis, characterisation and application of nanostructures based on semiconductor and metal materials.

Le Van Vu graduated from the Faculty of Physics at the University of Hanoi in 1978, where he subsequently received his PhD in 1994. Currently, he is an Associate Professor at the Faculty of Physics of the Hanoi University of Science. His research interests include preparation of nanostructured materials based on metals and semiconductive metal oxides and their biological application.

Nguyen Hoang Hai received his PhD in Physics from Universite de Grenoble 1 – Joseph Fourier and Laboratoire de Magnetisme Louis Neel, France. Subsequently, he was awarded an NRI Postdoctoral Fellowship, which he took to the University of Nebraksa, Lincoln. His major interests are preparation and characterisation of magnetic, metallic nanomaterials for bioapplications, and for environmental science, biosensors; dynamics of magnetic phenomena. He has authored more than 30 publications on international journals. He is now an Associate Professor of the Faculty of Physics of Hanoi University of Science.

Phan Tuan Nghia is a Lecturer at the Faculty of Biology, Hanoi University of Science. He received his PhD from the University of Hanoi in 1988 and held a Postdoctoral position at the International Centre for Genetic Engineering and Biotechnology (ICGEB) in New Delhi, India (1995–1997), and a Postdoctoral Associate Research Fellow position at the University of Rochester in New York, USA (1998–2001). His recent research interests include investigation and characterisation of antibacterial and antiviral agents, development of assays for the detection of bacterial and viral pathogens in humans and molecular characterisation of stress response in bacteria.

Nguyen Thi Van Anh received her PhD in Life Science from Tohoku University, Japan. She is currently a Researcher at the Key Laboratory of Enzyme and Protein Technology, Hanoi University of Science. She has received a research grant for young women scientist by The Third World Academy (TWAS) of Science (2005–2007). Her major interest is application of metal nanoparticles in diagnostics and drug delivery.

1 Introduction

Gold nanoparticles (NPs) are very unusual because of their size- and shape-dependent properties [1]. Gold nanospheres have a characteristic red colour, but anisotropic gold nanorods have a dramatically different colour due to the surface plasmon oscillation [2].

Metallic nanoparticles: synthesis, characterisation and application 229

Gold NPs generate enhanced electromagnetic fields that affect the local environment. The field is determined by the geometry of the NP and can enhance fluorescence of the gold itself, the Raman signal of a molecule on the surface, and the scattering of light. Because of the above-mentioned factors, many applications in biomedicine of gold NPs became possible [3].

Magnetic nanostructured materials based on transition metals Co and Fe such as CoPt and FePt have a very high potential application in producing new-generation ultra-high density magnetic recording media because of their good chemical stability and high magnetocrystalline anisotropy observed in the ordered intermetallic phase with L10 structure [4,5]. These materials will contribute to an effort to design a magnetic medium capable of recording densities beyond 1 Tbits/in2. Besides, these materials have potential applications in permanent magnetic nanocomposites and biomedicine.

In this paper, we report on the synthesis and characterisation of gold NPs as well as Co-Pt and Fe-Pt NPs. We also studied the application of gold NPs for detecting breast cancer cells.

2 Experiment

Using a chemical reduction method, synthesis of gold nanospheres was carried out as follows: 50 ml of 0.01 wt% chlorauric acid (HAuCl4 ⋅ 3H2O) solution was heated to boiling while stirred in a 100 ml beaker. Then, a few hundred microlitres (µl) of 1 wt% trisodium citrate dihydrate (Na3C6H5O7 ⋅ 2H2O) solution were quickly added to the auric solution. The solution changed colour within several minutes from yellow to black and then to red or purple. Gold nanospheres were also synthesised using a stronger reductive agent (sodium borohydride (NaBH4)) as follows: 5 ml NaBH4 0.01 M at 0°C was added to 25 ml HAuCl4 1 mM in a 50 ml flask and stirred for 15 min, until the colour of the solution changed from light yellow to dark red.

Gold NPs were also synthesised via a photochemical approach by using X-ray irradiation. In this approach, a few µl of 1 mM Triton X-100 (TX-100) solution were mixed with 3 ml of 1 mM HAuCl4 ⋅ 3H2O solution. Pure HAuCl4 solution without TX-100 addition was also prepared for comparison. The X-ray radiation was Cu-Kα radiation of an X-ray diffractometer Bruker D5005 with the parameters of 40 kV and 40 mA. The X-ray irradiation time was set up to 40 min or 60 min to guarantee the complete reduction of gold precursor solution.

Gold nanorods have been synthesised according to the seed-mediated growth method from the following precursors: the solutions of 1 mM chlorauric acid (HAuCl4 ⋅ 3H2O), 0.2 M cetyltrimethylammonium bromide (CTAB: C19H42BrN), 0.01 M NaBH4, 4 mM silver acetate (AgC2H3O2) and 0.08 M ascorbic acid (C6H8O6). The detailed procedure was reported in Long et al. [6].

Gold nanorods were synthesised from metallic gold by sonoelectrochemical technique as well. A gold metal plate (1 cm × 1 cm × 0.05 cm) was used as the anode and a platinum plate (1 cm × 1 cm × 0.05 cm) was used as the cathode. These two electrodes were placed in a glass containing 25 ml of electrolytic solution consisting of 0.08 M CTAB and 83 mg tetradodecylammonium-bromide (TCAB). 2 ml of acetone and 1 ml of cyclohexane were added into the above-mentioned mixed solution prior to electrolysis. Then, the glass with the electrolytic solution was put in an ultrasonic bath (Ultrasonic LC 30H) and ultrasonicated throughout the electrolysis time.


Co-Pt NPs were synthesised by an electrochemical method. The electrolytes were prepared by using grade chemical reagent and were composed of 0.1 M/l CoCl2 ⋅ 6H2O, 0.01 M/l H2PtCl6 and 0.525 M/l Na2SO4. The pH of 3 of the electrolyte was adjusted by H2SO4. Poly(vinyl-pyrrolidone) (PVP) was added as a surfactant. Electrodeposition has been conducted at room temperature. A platinum plate with a square of 1 cm2 was used as a counter electrode. A titanium cathode has the same area. The current pulse J was changed from 13 mA/cm2 to 40 mA/cm2. The duration of the current pulse was 0.5 s, then the current was turned off for a fixed duration of 0.3 s. The electrodeposition was carried out in a nitrogen atmosphere. After 1 h deposition, a black solution was obtained and as-prepared nanoparticle powder was collected by using centrifuging at 9000 rpm for 30 min. The powder was annealed at 700°C for 1 h under a mixture of 5% H2 and 95% Ar atmosphere.

The sonoelectrochemical method has been used for the synthesis of Fe-Pt NPs. The sonoelectrochemical device employed is similar to that described in Zhu et al. [7]. A titanium horn with a diameter of 1.3 cm acted as both the cathode and the ultrasound emitter (Sonics VCX 750). The electroactive part of the sonoelectrode was the planar circular surface at the bottom of the Ti horn. This sonoelectrode produced a sonic pulse that immediately followed a current pulse. A platinum plate with a square of 1 cm2 was used as a counter electrode. The current pulse was changed from 15 mA/cm2 to 30 mA/cm2. The ultrasound power density was 100 W/cm2. The duration ton of the current pulse was 0.5 s, then the current was turned off for a fixed duration of 0.5 s. During ton, Fe-Pt NPs were deposited on the surface of the electrode. When the current was switched off, an ultrasound was activated to remove the nanoparticles from the electrode. The duration of ultrasound was 0.2 s for all samples. The temperature during the reaction was room temperature. After deposition, FePt NPs were collected by using a centrifuge (Hettich Universal 320) at 9000 rpm for 20 min. All samples were annealed at 700°C for 1 h under a mixture of 5% H2 and 95% Ar atmosphere.

The obtained products were characterised by X-ray diffraction (XRD) by using a Brucker D5005 diffractometer and transmission electron microscopy (TEM) by using a JEOL JEM1010 electron microscope. UV-vis absorption spectra of the nanoparticle solutions were collected with a Shimadzu UV 2450 PC spectrometer. The chemical composition of the Co-Pt and Fe-Pt NPs was studied by using an energy dispersion spectroscopy (EDS OXFORD-ISIS 300). Magnetic measurement was conducted by using a DMS-880 sample vibrating magnetometer (VSM) with maximum magnetic field of 13.5 kOe at room temperature.

3 Results and discussion

3.1 Gold nanoparticles

Figure 1 illustrates a typical XRD pattern of the gold NPs obtained from the solution with 400 µl of trisodium citrate solution. It can be seen from the figure that all the diffraction peaks corresponding to the diffraction planes (111), (200) and (220) were indexed to the gold metal with face-centred cubic (fcc) structure. The lattice constant determined from XRD pattern is a = 4.078 Ǻ, in good agreement with the standard diffraction pattern of cubic gold metal (Pattern 4-784) [6]. Surface plasmon absorption spectra of spherical gold NPs prepared with different amounts of 1% trisodium citrate


solution are shown in Figure 2. As seen from the figure, the maximum of the absorption spectrum is shifted to the short wavelength side (from 539.9 nm to 521.1 nm) and the full width at half maximum (FWHM) of the spectrum is decreased with increasing amount of trisodium citrate from 200 µl to 400 µl. Thus, the amount of citrate solution determines the size of the NPs. The faster the capping of the NPs by the citrate, the smaller the resulting NPs.

Figure 1 XRD pattern of the gold NPs prepared by chemical reduction technique

Figure 2 Surface plasmon absorption spectra of spherical gold NPs prepared with different amounts of 1% trisodium citrate solution: 200, 240, 280, 320, 360 and 400 µl (see online version for colours)

Typical TEM images of the gold NPs prepared with different amounts of 1% trisodium citrate solution are shown in Figure 3. From the figure, one can see that when the amount of trisodium citrate increases from 200 µl to 400 µl, the size of the synthesised gold NPs decreases from 60 nm to 30 nm. That means the more amount of trisodium citrate, the smaller obtained NPs.

Gold NPs were also synthesised via a photochemical approach by using X-ray irradiation as mentioned earlier. The TEM image [6] showed that the addition of TX-100 as a particle stabiliser and reducing agent into HAuCl4 solution tremendously affected the formation and growth of the gold NPs.


Gold nanorods were synthesised according to the seed-mediated growth method. A typical TEM image of gold NPs for the as-prepared sample (not shown) showed that two major components of the sample are spherical NPs and nanorods. After centrifugation at 3000 rpm for 10 min, the nanorods were separated from spherical NPs.

Figure 3 TEM images of the gold NPs prepared with different amounts (200, 280 and 400 µl) of 1 % trisodium citrate solution. All the scale bars are 100 nm. On the pictures are shown the size of the NPs and the wavelength of the maximum of surface plasmon absorption spectra

Surface plasmon absorption spectra of anisotropic gold nanorods prepared with different amounts of 4 mM silver acetate solution are shown in Figure 4. As seen from the figure, when the shape of the NPs changes from nanospheres to nanorods, the surface plasmon absorption spectra also change. The surface plasmon absorption spectra of the gold nanorods have two bands: one band in the blue-green region around 525 nm due to the transverse oscillation of electrons and another band in the red-nearinfrared region due to the longitudinal electronic oscillation. In addition, the position of the band due to the transverse electronic oscillation is almost unvaried; meanwhile with increasing the silver acetate content from 70 µl to 120 µl, the position of the band due to the longitudinal oscillation is increased from 654 nm to 830 nm, which corresponds to the enhanced aspect ratio (the length-to-width ratio: AR) of the gold nanorods.

Figure 4 Surface plasmon absorption spectra of the gold nanorods prepared with different amounts (70, 80, 100 and 120 µl) of 4 mM silver acetate solution (see online version for colours)


Gold nanorods were synthesised from metallic gold by sonoelectrochemical technique as well. Typical TEM images of the gold nanorods shown in Figure 5 indicate that the nanorods are of uniform size. The aspect ratio (AR) distribution histogram presented in the inset of Figure 5 shows that the size of the nanorods has a narrow distribution: the nanorods with an AR of 3 make up 55% and those with an AR of 4 make up 25%.

Figure 5 TEM images of the gold nanorods prepared by sonoelectrochemical method. Inset is an aspect ratio distribution histogram (see online version for colours)

3.2 Co-Pt nanoparticles

Before annealing, the XRD patterns for Co-Pt NPs (not shown) showed the reflections of pure Pt structure, which is similar to other CoPt thin films produced by electro-deposition [8]. The reflections from Co are very weak due to the fact that their atomic weight is much less than that of Pt. The Pt peaks in the as-prepared samples are broad due to the small size of the particles. Using the Scherrer formula with the FWHM of the strongest peak (111), the mean particle size of the particles was deduced to be 6 nm.

The positive Pt4+ and Co2+ ions went to the cathode surface and received electrons to make Pt and Co NPs. If there was no PVP surfactant, Co and Pt atoms would be continuously deposited on the particles and at the end we would have a film of CoPt. The presence of PVP around NPs created steric forces that limited the growth of NPs and we obtained Co and Pt NPs well dispersed in the solution.

Figure 6 is the TEM images of typical as-prepared and annealed samples. Particle size of the as-prepared Co-Pt sample was about 5 nm, which is consistent with the size obtained from the broad XRD peaks. Particle size (5–20 nm) depends on the concentration of PVP (1–5 g/l). After annealing, the particle size increased to 100 nm due to the diffusion and aggregation between particles to form face-centred tetragonal (fct) Co-Pt NPs.


Figure 6 TEM images of the as-prepared (left) and annealed (right) Co-Pt NPs

Magnetic measurements revealed low saturation magnetisation (Ms) and coercivity (Hc) in all as-prepared samples (data not shown). The low value of Ms of the as-prepared NPs may be explained by the oxidation or hydroxidation of Co atoms in NPs, which can result in the antiferromagnetic cobalt oxides and weak magnetic cobalt hydroxides. This is in agreement with the suggestion of separated Co and Pt domains in as-prepared NPs. After annealing, the hard magnetic CoPt phase was formed. Figure 7 presents the magnetic curves of the annealed samples with current density J of 13, 20 and 40 mA/cm2. The curves for J of 15, 25, 30 mA/cm2 (not shown) are similar to that of 20 mA/cm2. The curves show typical hard magnetic hysteresis loops of multiphase materials with high Hc. (For Hc in the multiphase materials, the reader is referred to discussion below for Fe-Pt NPs). Coercivity gets maximum value (around 11 kOe) in the samples with the chemical composition of the particles close to the equiatomic composition, i.e., samples with J of 15–30 mA/cm2. The atomic percent of Co increased with J, which resulted in high Ms. However, the magnetic squareness Mr/Ms reduced with J because of the presence of the Co3Pt.

Figure 7 Magnetic curves for the annealed Co-Pt samples with current density J of 13, 20, and 40 mA/cm2


3.3 Fe-Pt nanoparticles

The chemical composition of the Fe-Pt NPs was controlled by adjusting the current density (corresponding to the applied voltage). When the current density was 15–20 mA/cm2, the composition of NPs was close to the expected equiatomic composition, namely for J of 15 mA/cm2 and 20 mA/cm2, Fe45Pt55 and Fe52Pt48 NPs were obtained, respectively. At higher current densities, the atomic percent of Fe was higher because the standard electrode potential Fe2+/Fe (–0.44 V [9]) was more negative than that of Pt4+/Pt (0.742 V [10]).

As in the case of CoPt NPs, before annealing, the XRD results (not shown) showed the reflections of pure Pt structure, which is similar to other FePt thin films produced by electrodeposition [11]. Upon annealing, the formation of the ordered L10 fct phase happened by the diffusion process between Fe and Pt domains. Figure 8 is the TEM images of typical as-prepared and annealed samples. Particle size of the as-prepared FePt sample was 5–10 nm, compared with 5.2 nm obtained from the XRD results by using the Scherrer formula. After annealing, the particle size increased to 10–25 nm due to the aggregation and particle growth. In addition, the size distribution of the annealed particles was larger than that of the as-prepared samples.

Figure 8 TEM images of the as-prepared (left) and annealed (right) Fe-Pt NPs

Magnetic measurements revealed low Ms and Hc in all as-prepared samples. The saturation magnetisation of the unannealed particles was a few emu/g and the coercivity was 20–80 Oe. The low value of Ms of the as-prepared NPs may be explained by the oxidation or hydroxidation of Fe atoms in NPs, which can result in the weak magnetic iron oxides and iron hydroxides. This is in agreement with the suggestion of separated Fe and Pt domains in as-prepared NPs.

After annealing, the hard magnetic FePt phase was formed. Figure 9 presents the magnetic curve of the annealed Fe45Pt55 sample as an example. The curve shows a typical hard magnetic hysteresis loop with high Hc. Note that, because of the limit of maximum applied field of 13.5 kOe, the curve is a minor loop. Therefore, the real coercivity must be higher than those obtained from the hysteresis curves. However, the loop shows a kink at low reversed magnetic field of 500 Oe, which indicates that there was a small soft magnetic phase. Classically, the coercivity is defined as the field for which


the magnetisation (M) vanishes ( ).cH ′ In a more physically meaningful definition, the coercivity Hc may be defined as the field where the largest number of moments reverses, i.e., the maximum of susceptibility (dM/dH). In most cases, both definitions of the coercivity are almost equivalent. However in multiphase materials, two definitions are significantly different [12]. From Figure 9, cH ′ was 6 kOe whereas Hc was 8.5 kOe. The atomic percent of Fe increased with J, which resulted in the high Ms. However, the magnetic squareness Mr / Ms reduced with J because of the presence of the Fe3Pt.

Figure 9 Magnetic curves of Fe45Pt55 sample. The maximum applied field was 13.5 kOe

3.4 Application of gold nanoparticles for detecting breast cancer cells

In order to detect breast cancer cells, we have conjugated the sodium borohydride (or sodium citrate) reduced gold NPs with anti-HER2 antibody (trastuzumab) through either non-covalent or covalent linkages. The procedure consists of the following steps:

Functionalising gold NPs with 4-ATP (C6H7NS)

Different volumes of 4-ATP 2 mM were added into 20 ml of the gold NPs containing solution. The colours of the solutions changed from dark red to dark blue, and then were incubated for 2 days.

Conjugation of trastuzumab to gold NPs

Trastuzumab was non-covalently conjugated to colloidal gold NPs, prepared by citrate reduction (named as Ci*GNPs) and NaBH4 reduction (named as BH4*GNPs). The colloidal gold suspension was adjusted with 0.1 M NaOH to pH 6.5 to react with a mixture of 6 µg/ml non-labelled trastuzumab and FITC-trastuzumab (480 nm/520 nm) at mole ratio 10 : 1 at room temperature for 5 min. Trastuzumab was covalently linked to amino-GNPs through EDC connection. Briefly, the above-prepared amino-GNPs were reacted with EDC 0.2 mM in MOPS buffer with pH 6.0, for 20 min at room temperature. Then, the EDC*GNPs were reacted with 6 µg/ml non-labelled trastuzumab and FITC-trastuzumab (480 nm/520 nm) at mole ratio 10 : 1, for 30 min


at room temperature. The absorbance profile of trastuzumab-GNPs was measured and compared with that of GNPs using Spectrophotometer (Nanodrop).

Culture of KPL4 and Hela cells

KPL4 and Hela cells were cultured in 24-well ELISA plates containing DMEM (Difco Modified Eagle Medium) plus 10% FBS (Fetal Bovine Serum). Glass coverslips were added in each well and the cells were incubated at 37°C, 5% CO2 to reach a population of about 4 × 105 to 106 cells/ml. The coverslips were picked out to new 24-well ELISA plate for further immuno-nanogold incubation.

Incubation of trastuzumab-conjugated gold NPs with KPL4, Hela cells and imaging of the cells

Coverslips containing KPL4 and Hela cells were incubated with trastuzumab-BH4*GNPs, trastuzumab-Ci*GNPs or trastuzumab-EDC*GNPs at a concentration of 3 µg/ml at room temperature, for 60 min. The coverslips were observed under epifluorescence microscope. The KPL4 cells incubated with trastuzumab-EDC*GNPs were observed under a FESEM (Field Emission Scanning Electron Microscope).

The results are shown in Figure 10. We could observe the 10 times higher fluorescent intensity of FITC (green) on KPL4 cells than that of FITC on Hela cells in all the three types of trastuzumab-conjugated gold NPs. Because KPL4 has high level of HER2-expression, while Hela has HER2 expressed normally, the remarkable difference in the fluorescent intensity between KPL4 and Hela indicated the specific binding of all the three types of trastuzumab-GNPs on KPL4 membranes. However, the covalently linked trastuzumab-EDC*GNPs is shown to be the most stable in fluorescent intensity after a long time of stocking (several months).

Figure 10 Typical luminescent microscopy images of breast cancer cells indicating the specific binding of trastuzumab-GNPs on KPL4 cells, and weak binding on Hela cells (for comparison): FITC fluorescent signal (green) emitted from KPL4 (upper panel) and from Hela (lower panel) after incubation with trastuzumab-BH4*GNPs (A1-A2), trastuzumab-Ci*GNPs (A3-A4) and trastuzumab-EDC*GNPs (A5-A6) (see online version for colours)


We also tried to conjugate the gold NPs with trastuzumab without FITC fluorescent dye. As seen from Figure 11, no signal was observed when KPL4 was incubated with the non-conjugated gold NPs (A2). However, trastuzumab-conjugated gold NPs concentrated on KPL4 and these cancer cells were clearly observed in the dark-field microscopy image (A4) by means of the scattering light of the gold NPs. When the amino-GNPs were covalently conjugated with trastuzumab through EDC connection, the gold NPs concentrated on the cancer cells as well, but these cancer cells were observed with slightly lower intensity in the dark-field microscopy image (A6) in comparison with those in the image A4. However, the non-covalent trastuzumab-conjugated GNPs were able to be stored in freezer for only two weeks before they lost their activity, while the trastuzumab-EDC*GNPs were stable for storage for about two months.

Figure 11 Typical bright-field (A1, A3, A5) and dark-field (A2, A4, A6) microscopy images of breast cancer cells after incubation with the gold NPs non-conjugated with trastuzumab (A1-A2), the gold NPs conjugated with trastuzumab (A3-A4) and the amino-GNPs covalently conjugated with trastuzumab through EDC connection (A5-A6) (see online version for colours)

The images of the cancer cells labelled with the trastuzumab-conjugated gold NPs were obtained by the EDX scanning technique for the gold element. These EDX scanning images for the gold element and normal SEM images of the cancer cells labelled with the trastuzumab-conjugated gold NPs are shown in Figure 12. As seen from the figure, the trastuzumab-conjugated gold NPs have concentrated with high density on the cancer cells.


Figure 12 SEM images of the cancer cells labelled with gold NPs (A1 and A3) and EDX scanning images of the gold NPs labelling the cancer cells (A2 and A4), respectively. The scale bars in all the images are 20 µm (see online version for colours)

4 Conclusions

Gold NPs as well as Co-Pt and Fe-Pt NPs have been prepared. After annealing, Co-Pt and Fe-Pt NPs showed a high coercivity. We succeeded in conjugating trastuzumab to gold NPs for specific detection of HER2 over-expressed breast cancer cells, here is KPL4 cell line. Among three types of conjugation, the covalently linked trastuzumab-EDC*GNPs showed long-time stability and strong binding towards breast cancer cell KPL4.

Acknowledgements

The authors thank the Ministry of Science and Technology of Vietnam (Contract No. 38/355/2008/HD-NDT for Task of Protocol with Israel) and National Foundation for Science and Technology Development – NAFOSTED (Project 103.02.72.09) for financial support.

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Metallic nanoparticles: synthesis, characterisation and application

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