Colloidal gold

Not to be confused with Gold Nanoparticles (Chemotherapy).
Solutions of gold nanoparticles of various sizes. The size difference causes the difference in colors.

Colloidal gold is a sol or colloidal suspension of submicrometre-size nanoparticles of gold in a fluid, usually water. The liquid is usually either an intense red colour (for particles less than 100 nm) or blue/purple (for larger particles).[1][2] Due to the unique optical, electronic, and molecular-recognition properties of gold nanoparticles, they are the subject of substantial research, with applications in a wide variety of areas, including electron microscopy, electronics, nanotechnology,[3][4] and materials science.

The properties of colloidal gold nanoparticles, and thus their applications, depend strongly upon their size and shape.[5] For example, rodlike particles have both transverse and longitudinal absorption peak, and anisotropy of the shape affects their self-assembly.[6]

History

This cranberry glass bowl was made by adding a gold salt (probably gold chloride) to molten glass.

Known, or at least used (perhaps proceeding by accident without much understanding of the process) since ancient times, the synthesis of colloidal gold was crucial to the 4th-century Lycurgus Cup, which changes color depending on the location of light source.[7] Later it was used as a method of staining glass.

During the Middle Ages, soluble gold, solution containing gold salt, had a reputation for its curative property for various diseases. In 1618, Francisci Antonii, a philosopher and member of the medical profession, published a book called Panacea Aurea, sive tractatus duo de ipsius Auro Potabili[8] (Latin: gold potion, or two treatments of potable gold). The book introduces information on the formation of colloidal gold and its medical uses. About half centuries after, English botanist Nicholas Culpepper published book in 1656, Treatise of Aurum Potabile,[9] solely talking about medical uses of colloidal gold.

In 1676, Johann Kunckel, German Chemist, published book on industrial manufacturing of stained glass. In his book Valuable Observations or Remarks About the Fixed and Volatile Salts-Auro and Argento Potabile, Spiritu Mundi and the Like,[10] Kunckel assumed that slight pink color of Aurum Potabile is coming from small particle of metallic gold that is not visible to human eyes. In 1842, John Herschel invented a photographic process called chrysotype (from the Greek χρῡσός meaning "gold") that used colloidal gold to record images on paper.

Modern scientific evaluation of colloidal gold did not begin until Michael Faraday's work of the 1850s.[11][12] In 1856 basement laboratory of Royal Institution, Michael Faraday accidentally creates ruby red solution while he was mounting thin sheets of gold leaf onto microscope slides.[13] Since he was already interested in properties of light and matter, Faraday soon investigate more on optical properties of the colloidal gold. He prepared the first pure sample of colloidal gold, which he called 'activated gold', in 1857. He used phosphorus to reduce a solution of gold chloride. The colloidal gold Faraday made 150 years ago is still optically active. For a long time, the composition of the 'ruby' gold was unclear. Several chemists suspected it to be a gold tin compound, due to its preparation.[14][15] Faraday recognized that the color was actually due to the miniature size of the gold particles. He notes the light scattering properties from suspended small gold particles, which is now called Faraday-Tyndall effect.[16]

In 1898, Richard Adolf Zsigmondy prepared the first colloidal gold in diluted solution.[17] Apart from Zsigmondy, Theodor Svedberg, who invented ultracentrifugation, and Gustav Mie, who provided the theory for scattering and absorption by spherical particles, were also interested in understanding synthesis and properties of colloidal gold.[6][18]

With advances in various analytical technology in 20th century, studies on gold nanoparticle has accelerated. Especially, the advanced microscopy, like atomic force microscopy and electron microscopy in late 20th century, contributed most to nanoparticle research. Due to their known for their comparably easy synthesis and stability, various gold particles are studied for their practical uses. Different types of gold nanoparticle is already used in many industries including medical and electronic fields. For example, Several FDA approved nanoparticle is actively used for drug deliveries.[19]

Synthesis

Potential difference as a function of distance from particle surface.

Generally, gold nanoparticles are produced in a liquid ("liquid chemical methods") by reduction of chloroauric acid (H[AuCl4]). After dissolving H[AuCl4], the solution is rapidly stirred while a reducing agent is added. This causes Au3+ ions to be reduced to Au+ions. Then a disproportionation reaction occurs whereby 3 Au+ ions give rise to Au3+ and 2 Au0 atoms. The Au0 atoms act as center of nucleation around which further Au+ ions gets reduced. To prevent the particles from aggregating, some sort of stabilizing agent that sticks to the nanoparticle surface is usually added.In the turkevich method of Au NP synthesis, citrate initially acts as the reducing agent and finally as the capping agent which stabilizes the Au NP through electrostatic interactions between the lone pair of electrons on the oxygen and the metal surface. Also, gold colloids can be synthesised without stabilizers by laser ablation in liquids.[20]

They can be functionalized with various organic ligands to create organic-inorganic hybrids with advanced functionality.[11]

Turkevich method

The method pioneered by J. Turkevich et al. in 1951 [21][22] and refined by G. Frens in the 1970s,[23][24] is the simplest one available. In general, it is used to produce modestly monodisperse spherical gold nanoparticles suspended in water of around 10–20 nm in diameter. Larger particles can be produced, but this comes at the cost of monodispersity and shape. It involves the reaction of small amounts of hot chloroauric acid with small amounts of sodium citrate solution. The colloidal gold will form because the citrate ions act as both a reducing agent and a capping agent.

Recently, the evolution of the spherical gold nanoparticles in the Turkevich reaction has been elucidated. It is interesting to note that extensive networks of gold nanowires are formed as a transient intermediate. These gold nanowires are responsible for the dark appearance of the reaction solution before it turns ruby-red.[25]

To produce larger particles, less sodium citrate should be added (possibly down to 0.05%, after which there simply would not be enough to reduce all the gold). The reduction in the amount of sodium citrate will reduce the amount of the citrate ions available for stabilizing the particles, and this will cause the small particles to aggregate into bigger ones (until the total surface area of all particles becomes small enough to be covered by the existing citrate ions).

Brust method

This method was discovered by Brust and Schiffrin in the early 1990s,[26] and can be used to produce gold nanoparticles in organic liquids that are normally not miscible with water (like toluene). It involves the reaction of a chlorauric acid solution with tetraoctylammonium bromide (TOAB) solution in toluene and sodium borohydride as an anti-coagulant and a reducing agent, respectively.

Here, the gold nanoparticles will be around 5–6 nm.[27] NaBH4 is the reducing agent, and TOAB is both the phase transfer catalyst and the stabilizing agent.

It is important to note that TOAB does not bind to the gold nanoparticles particularly strongly, so the solution will aggregate gradually over the course of approximately two weeks. To prevent this, one can add a stronger binding agent, like a thiol (in particular, alkanethiols), which will bind to gold, producing a near-permanent solution. Alkanethiol protected gold nanoparticles can be precipitated and then redissolved. Some of the phase transfer agent may remain bound to the purified nanoparticles, this may affect physical properties such as solubility. In order to remove as much of this agent as possible, the nanoparticles must be further purified by soxhlet extraction.

Perrault method

This approach, discovered by Perrault and Chan in 2009,[28] uses hydroquinone to reduce HAuCl4 in an aqueous solution that contains 15 nm gold nanoparticle seeds. This seed-based method of synthesis is similar to that used in photographic film development, in which silver grains within the film grow through addition of reduced silver onto their surface. Likewise, gold nanoparticles can act in conjunction with hydroquinone to catalyze reduction of ionic gold onto their surface. The presence of a stabilizer such as citrate results in controlled deposition of gold atoms onto the particles, and growth. Typically, the nanoparticle seeds are produced using the citrate method. The hydroquinone method complements that of Frens,[23][24] as it extends the range of monodispersed spherical particle sizes that can be produced. Whereas the Frens method is ideal for particles of 12–20 nm, the hydroquinone method can produce particles of at least 30–300 nm.

Martin method

This simple method, discovered by Martin and Eah in 2010,[29] generates nearly monodisperse "naked" gold nanoparticles in water. Precisely controlling the reduction stoichiometry by simply adjusting the ratio of NaBH4-NaOH ions to HAuCl4-HCl ions within the "sweet zone," along with heating, enables reproducible diameter tuning between 3–6 nm. The aqueous particles are colloidally stable due to their high charge from the excess ions in solution. These particles can be coated with various hydrophilic functionalities, or mixed with hydrophobic molecules for applications in non-polar solvents. Interestingly, in non-polar solvents the nanoparticles curiously remain highly charged, and self-assemble on liquid droplets to form 2D monolayer films of monodisperse nanoparticles.

Nanotech applications

Bacillus licheniformis can be used in synthesis of gold nanocubes.[30] Researchers have synthesized gold nanoparticles with sizes between 10 to 100 nanometres. Gold nanoparticles are usually synthesized at high temperatures, in organic solvents and using toxic reagents. The bacteria produce them in much milder conditions.

Navarro et al. method

As pointed out before, the precise size control with a low polydispersity of spherical gold nanoparticles remains difficult for particles larger than 30 nm. In order to provide maximum control on the NP structure along with synthetic straightforwardness, Navarro and co-workers used a 'one-pot' protocol, relying on a modified Turkevitch-Frens procedure. The method consist in the addition of sodium acetylacetonate (Na(acac) allowing the complexation and reduction of AuIII to AuI) immediately followed by the addition of sodium citrate (reduction of AuI to Au0). For this experiment, sodium acetylacetonate purity is really important. The concentration of sodium acetylacetonate directly impacts the nuclei numbers inducing a size evolution of the gold core up to 90 nm with a narrow size distribution. Practically, the tetrachloroaurate and sodium citrate concentration are fixed to 0.30 mM and 0.255 mM (ratio sodium citrate to gold: 0.85). In these conditions, and without sodium acetylacetonate, the obtained nanoparticles precipitate immediately. The concentration of sodium acetylacetonate can be tuned from 0.33 mM to 1.0 mM. The addition of the Na(acac) and sodium citrate to the yellow boiling gold ions solution results in a colorless one indicating the complexation and reduction of AuIII to AuI. Within a few minutes, the solution turns light blue-purple, featuring the formation of the gold nuclei. The small crystalline structures will then diffuse over the solution allowing the growth of the final spherical particles.[31]

Sonolysis

Another method for the experimental generation of gold particles is by sonolysis. The first method of this type was invented by Baigent and Müller.[32] This work pioneered the use of ultrasound to provide the energy for the processes involved and allowed the creation of gold particles with a diameter of under 10 nm. In another method using ultrasound, the reaction of an aqueous solution of HAuCl4 with glucose,[33] the reducing agents are hydroxyl radicals and sugar pyrolysis radicals (forming at the interfacial region between the collapsing cavities and the bulk water) and the morphology obtained is that of nanoribbons with width 30–50 nm and length of several micrometers. These ribbons are very flexible and can bend with angles larger than 90°. When glucose is replaced by cyclodextrin (a glucose oligomer), only spherical gold particles are obtained, suggesting that glucose is essential in directing the morphology toward a ribbon.

Block copolymer-mediated method

An economical, environmentally benign and fast synthesis methodology for gold nanoparticles using block copolymer has been developed by Sakai et al.[34] In this synthesis methodology, block copolymer plays the dual role of a reducing agent as well as a stabilizing agent. The formation of gold nanoparticles comprises three main steps: reduction of gold salt ion by block copolymers in the solution and formation of gold clusters, adsorption of block copolymers on gold clusters and further reduction of gold salt ions on the surfaces of these gold clusters for the growth of gold particles in steps, and finally its stabilization by block copolymers. But this method usually has a limited-yield (nanoparticle concentration), which does not increase with the increase in the gold salt concentration. Recently, Ray et al. demonstrated that the presence of an additional reductant (trisodium citrate) in 1:1 molar ratio with gold salt enhances the yield by manyfold at ambient conditions and room temperature.[35]

"Green Chemistry" based methods

Phytochemicals found in various plant sources have been utilized as a means of developing a more economical and environmentally friendly synthetic pathway in the formation of gold nanoparticles. In accordance to the principles of "green chemistry," these methods employ the use of nontoxic chemicals, marginal energy consumption, renewable materials, and environmentally benign solvents to minimize the use, disposal, and health repercussions of hazardous chemicals.[36] Additionally, these methods provide a more efficient synthetic pathway through a one-step process without the use of supplementary surfactants or polymers, capping agents, or templates to restrict agglomeration of the gold nanoparticles. This method is effective in producing well-defined gold nanoparticles since the phytochemicals perform a dual role as both a reducing agent of gold and as a stabilizer in the formation of a sturdy coating on the nanoparticles.[36] One "green" method that has been employed in the formation of gold nanoparticles utilizes the phytochemicals and polyphenols in Darjeeling black tea leaves, with water acting as a benign solvent at room temperature. The phytochemicals in the black tea reduce HAuCl4 to its salt and stabilize the aggregation of the gold atoms as the nanoparticle is formed. In addition to the "green" benefits of using black tea, the size of the nanoparticle is influenced by the concentration of the tea, and the absorbance and size of the gold nanoparticles formed can be easily determined using UV-Vis spectrometry abiding that an increase in λmax correlates to an increase in the size of the nanoparticle.[36][37] Other "green" methods that have been studied and employed include the use of Elettaria cardamomum (cardamom) and cinnamon in the synthesis of gold nanoparticles, as well as Syzygium aromaticum (cloves) in the formation of copper nanoparticles and table sugar in the formation of silver nanoparticles.[38][39][40][41][42]

Electron microscopy

Main article: Immunogold labelling

Colloidal gold and various derivatives have long been among the most widely used labels for antigens in biological electron microscopy.[43][44][45][46][47] Colloidal gold particles can be attached to many traditional biological probes such as antibodies, lectins, superantigens, glycans, nucleic acids,[48] and receptors. Particles of different sizes are easily distinguishable in electron micrographs, allowing simultaneous multiple-labelling experiments.[49]

In addition to biological probes, gold nanoparticles can be transferred to various mineral substrates, such as mica, single crystal silicon, and atomically flat gold(III), to be observed under atomic force microscopy (AFM).[50]

Medical research

Drug delivery system

Gold nanoparticles can be used to optimize the biodistribution of drugs to diseased organs, tissues or cells, in order to improve and target drug delivery.[51][52] It is important to realize that the nanoparticle-mediated drug delivery is feasible only if the drug distribution is otherwise inadequate. These cases include drug targeting of difficult, unstable molecules (proteins, siRNA, DNA), delivery to the difficult sites (brain, retina, tumors, intracellular organelles) and drugs with serious side effects (e.g. anti-cancer agents). The performance of the nanoparticles depends on the size and surface functionalities in the particles. Also, the drug release and particle disintegration can vary depending on the system (e.g. biodegradable polymers sensitive to pH). An optimal nanodrug delivery system ensures that the active drug is available at the site of action for the correct time and duration, and their concentration should be above the minimal effective concentration (MEC) and below the minimal toxic concentration (MTC).[53]

Gold nanoparticles are being investigated as carriers for drugs such as Paclitaxel.[54] The administration of hydrophobic drugs require molecular encapsulation and it is found that nanosized particles are particularly efficient in evading the reticuloendothelial system.

Gold nanoparticles are also used to circumvent multidrug resistance (MDR) mechanisms.[55] Mechanisms of MDR include decreased uptake of drugs, reduced intracellular drug concentration by activation of the efflux transporters, modifications in cellular pathways by altering cell cycle checkpoints, increased metabolism of drugs, induced emergency response genes to impair apoptotic pathways and altered DNA repair mechanisms.

Tumor detection

In cancer research, colloidal gold can be used to target tumors and provide detection using SERS (Surface Enhanced Raman Spectroscopy) in vivo. These gold nanoparticles are surrounded with Raman reporters, which provide light emission that is over 200 times brighter than quantum dots. It was found that the Raman reporters were stabilized when the nanoparticles were encapsulated with a thiol-modified polyethylene glycol coat. This allows for compatibility and circulation in vivo. To specifically target tumor cells, the pegylated gold particles are conjugated with an antibody (or an antibody fragment such as scFv), against, e.g. Epidermal growth factor receptor, which is sometimes overexpressed in cells of certain cancer types. Using SERS, these pegylated gold nanoparticles can then detect the location of the tumor.[56]

Gold nanoparticles accumulate in tumors, due to the leakiness of tumor vasculature, and can be used as contrast agents for enhanced imaging in a time-resolved optical tomography system using short-pulse lasers for skin cancer detection in mouse model. It is found that intravenously administrated spherical gold nanoparticles broadened the temporal profile of reflected optical signals and enhanced the contrast between surrounding normal tissue and tumors.[57]

Therefore, gold nanoparticles have the potential to join numerous therapeutic functions into a single platform, by targeting specific tumor cells, tissues and organs. Actually, Conde et al. reported the evaluation of the inflammatory response and therapeutic siRNA silencing via RGD-nanoparticles in a lung cancer mouse model. This study reported the use of siRNA/RGD gold nanoparticles capable of targeting tumor cells in two lung cancer xenograft mouse models, resulting in successful and significant c-Myc oncogene downregulation followed by tumor growth inhibition and prolonged survival of the animals. This delivery system can achieve translocation of siRNA duplexes directly into the tumour cell cytoplasm and accomplish successful silencing of an oncogene expression. Actually, RGD/siRNA-AuNPs can target preferentially and be taken up by tumor cells via integrin αvβ3-receptor-mediated endocytosis with no cytotoxicity, showing that can accumulate in tumor tissues overexpressing αvβ3 integrins and selectively delivered c-Myc siRNA to suppress tumor growth and angiogenesis.[58]

Gene therapy

Gene therapy is receiving increasing attention and, in particular, small-interference RNA (siRNA) shows importance in novel molecular approaches in the knockdown of specific gene expression in cancerous cells. The major obstacle to clinical application is the uncertainty about how to deliver therapeutic siRNAs with maximal therapeutic impact. Gold nanoparticles have shown potential as intracellular delivery vehicles for siRNA oligonucleotides with maximal therapeutic impact.

Recently, Conde et al. provided evidence of in vitro and in vivo RNAi triggering via the synthesis of a library of novel multifunctional gold nanoparticles, using a hierarchical approach including three biological systems of increasing complexity: in vitro cultured human cells, in vivo freshwater polyp (Hydra vulgaris), and in vivo mice models. The authors developed effective conjugation strategies to combine, in a highly controlled way, specific biomolecules to the surface of gold nanoparticles such as: (a) biofunctional spacers: Poly(ethylene glycol) (PEG) spacers used to increase solubility and biocompatibility; (b) cell penetrating peptides such as TAT and RGD peptides: A novel class of membrane translocating agents named cell penetrating peptides (CPPs) that exploit more than one mechanism of endocytosis to overcome the lipophilic barrier of the cellular membranes and deliver large molecules and even small particles inside the cell for their biological actions; and (c) siRNA complementary to a master regulator gene, the protooncogene c-myc, were bond covalently (thiol-siRNA) and ionically (naked/unmodified siRNA) to gold nanoparticles.[59]

Gold nanoparticles have also shown potential as intracellular delivery vehicles for antisense oligonucleotides (ssDNA,dsDNA) by providing protection against intracellular nucleases and ease of functionalization for selective targeting.[60][61] Recently, Conde et al. developed a new theranostic system capable of intersecting all RNA pathways: from gene specific downregulation to silencing the silencers, i.e. siRNA and miRNA pathways. The authors reported the development gold nanoparticles functionalized with a fluorophore labeled hairpin-DNA, i.e. gold nanobeacons, capable of efficiently silencing single gene expression, exogenous siRNA and endogenous miRNAs while yielding a quantifiable fluorescence signal directly proportional to the level of silencing.[62] This method describes a gold nanoparticle-based nanobeacon as an innovative theranostic approach for detection and inhibition of sequence-specific DNA and RNA for in vitro and ex vivo applications. Under hairpin configuration, proximity to gold nanoparticles leads to fluorescence quenching; hybridization to a complementary target restores fluorescence emission due to the gold nanobeacons' conformational reorganization that causes the fluorophore and the gold nanoparticle to part from each other.[63] This concept can easily be extended and adapted to assist the in vitro evaluation of silencing potential of a given sequence to be later used for ex vivo gene silencing and RNAi approaches, with the ability to monitor real-time gene delivery action.[64]

Photothermal agents

Gold nanorods are being investigated as photothermal agents for in-vivo applications. Gold nanorods are rod-shaped gold nanoparticles whose aspect ratios tune the surface plasmon resonance (SPR) band from the visible to near-infrared wavelength. The total extinction of light at the SPR is made up of both absorption and scattering. For the smaller axial diameter nanorods (~10 nm), absorption dominates, whereas for the larger axial diameter nanorods (>35 nm) scattering can dominate. As a consequence, for in-vivo applications, small diameter gold nanorods are being used as photothermal converters of near-infrared light due to their high absorption cross-sections. Since near-infrared light transmits readily through human skin and tissue, these nanorods can be used as ablation components for cancer, and other targets. When coated with polymers, gold nanorods have been known to circulate in-vivo for greater than 15 hours half-life. Apart from rod-like gold nanoparticles, also spherical colloidal gold nanoparticles are recently used as markers in combination with photothermal single particle microscopy.

Radiotherapy dose enhancer

Following work by Hainfield et al.[65] there has been considerable interest in the use of gold and other heavy-atom containing nanoparticles to enhance the dose delivered to tumors. Since the gold nanoparticles are taken up by the tumors more than the nearby healthy tissue, the dose is selectively enhanced. The biological effectiveness of this type of therapy seems to be due to the local deposition of the radiation dose near the nanoparticles.[66] This mechanism is the same as occurs in heavy ion therapy.

Detection of toxic gas

Researchers have developed simple inexpensive methods for on-site detection of hydrogen sulfide H
2S present in air based on the antiaggregation of gold nanoparticles (AuNPs). Dissolving H
2S into a weak alkaline buff solution leads to the formation of HS-, which can stabilize AuNPs and ensure they maintain their red color allowing for visual detection of toxic levels of H
2S.[67]

Gold nanoparticle based biosensor

see more information on biosensor: Biosensor

Gold nanoparticles are incorporated into biosensors to enhance its stability, sensitivity, and selectivity.[68] Nanoparticle properties such as small size, high surface-to-volume ratio, and high surface energy allow immobilization of large range of biomolecules. Gold nanoparticle, in particular, could also act as "electron wire" to transport electrons and its amplification effect on electromagnetic light allows it to function as signal amplifiers.[69][70] Main types of gold nanoparticle based biosensors are optical and electrochemical biosensor.

Optical biosensor

Gold nanoparticles improve the sensitivity of optical sensor by response to the change in local refractive index. The angle of the incidence light for Surface Plasmon resonance, an interaction between light wave and conducting electrons in metal, changes when other substances are bounded to the metal surface.[71][72] Because gold is very sensitive to its surroundings' dielectric constant,[73][74] binding of an analyte would significantly shift gold nanoparticle's SPR and therefore allow more sensitive detection. Gold nanoparticle could also amplify the SPR signal.[75] When the Plasmon wave pass through the gold nanoparticle, the charge density in the wave and the electron I the gold interacted and resulted in higher energy response, so called electron coupling.[68] Since the analyte and bio-receptor now bind to the gold, it increases the apparent mass of the analyte and therefore amplified the signal.[68] These properties had been used to build DNA sensor with 1000-fold sensitive than without the Au NP.[76] Humidity senor was also build by altering the atom interspacing between molecules with humidity change, the interspacing change would also result in a change of the Au NP's LSPR.[77]

Electrochemical Biosensor

Electrochemical sensor covert biological information into electrical signals that could be detected. The conductivity and biocompatibility of Au NP allow it to act as "electron wire".[68] It transfers electron between the electrode and the active site of the enzyme.[78] It could be accomplished in two ways: attach the Au NP to either the enzyme or the electrode. GNP-glucose oxidase monolayer electrode was constructed use these two methods.[79] The Au NP allowed more freedom in the enzyme's orientation and therefore more sensitive and stable detection. Au NP also acts as immobilization platform for the enzyme. Most biomolecules denatures or lose its activity when interacted with the electrode.[68] The biocompatibility and high surface energy of Au allow it to bind to a large amount of protein without altering its activity and results in a more sensitive sensor.[80][81] Moreover, Au NP also catalyzes biological reactions.[82][83] Gold nanoparticle under 2 nm has shown catalytic activity to the oxidation of styrene.[84]

See also

References

  1. ↑ Bernhard Wessling, Conductive Polymer / Solvent Systems: Solutions or Dispersions?, 1996 (on-line here)
  2. ↑ University of Wisconsin–Madison: Making and conjugating colloidal metals.
  3. ↑ Paul Mulvaney, University of Melbourne, The beauty and elegance of Nanocrystals, Use since Roman times
  4. ↑ C. N. Ramachandra Rao, Giridhar U. Kulkarni, P. John Thomasa, Peter P. Edwards, Metal nanoparticles and their assemblies, Chem. Soc. Rev., 2000, 29, 27–35. (on-line here; mentions Cassius and Kunchel)
  5. ↑ S.Zeng; Yong, Ken-Tye; Roy, Indrajit; Dinh, Xuan-Quyen; Yu, Xia; Luan, Feng; et al. (2011). "A review on functionalized gold nanoparticles for biosensing applications" (PDF). Plasmonics 6 (3): 491–506. doi:10.1007/s11468-011-9228-1.
  6. 1 2 Sharma, Vivek; Park, Kyoungweon; Srinivasarao, Mohan (2009). "Colloidal dispersion of gold nanorods: Historical background, optical properties, seed-mediated synthesis, shape separation and self-assembly". Material Science and Engineering Reports 65 (1–3): 1–38. doi:10.1016/j.mser.2009.02.002.
  7. ↑ "The Lycurgus Cup". British Museum. Retrieved 2015-12-04.
  8. ↑ Antonii, Francisci (1618). Panacea aurea sive Tractatus duo de ipsius auro potabili. Ex Bibliopolio Frobeniano.
  9. ↑ Culpeper, Nicholas (1657). Mr. Culpepper's Treatise of aurum potabile Being a description of the three-fold world, viz. elementary celestial intellectual containing the knowledge necessary to the study of hermetick philosophy. Faithfully written by him in his life-time, and since his death, published by his wife. London.
  10. ↑ Kunckel von Löwenstern, Johann (1678). Utiles observationes sive animadversiones de salibus fixis et volatilibus, auro et argento potabili (etc.). Austria: Wilson.
  11. 1 2 V. R. Reddy, "Gold Nanoparticles: Synthesis and Applications" 2006, 1791, and references therein
  12. ↑ Michael Faraday, Philosophical Transactions of the Royal Society, London, 1857
  13. ↑ "Michael Faraday's gold colloids | The Royal Institution: Science Lives Here". www.rigb.org. Retrieved 2015-12-04.
  14. ↑ Gay-Lussac (1832). "Ueber den Cassius'schen Goldpurpur". Annalen der Physik 101 (8): 629–630. Bibcode:1832AnP...101..629G. doi:10.1002/andp.18321010809.
  15. ↑ Berzelius, J. J. (1831). "Ueber den Cassius' schen Goldpurpur". Annalen der Physik 98 (6): 306–308. Bibcode:1831AnP....98..306B. doi:10.1002/andp.18310980613.
  16. ↑ Faraday, M. (1857). "Experimental Relations of Gold (and Other Metals) to Light,". Philosophical Transactions of the Royal Society 147: 145. doi:10.1098/rstl.1857.0011.
  17. ↑ Zsigmondy, Richard (December 11, 1926). "Properties of colloids" (PDF). Nobel Foundation. Retrieved 2009-01-23.
  18. ↑ Zeng, Shuwen; Yu, Xia; Law, Wing-Cheung; Zhang, Yating; Hu, Rui; Dinh, Xuan-Quyen; Ho, Ho-Pui; Yong, Ken-Tye (2013). "Size dependence of Au NP-enhanced surface plasmon resonance based on differential phase measurement". Sensors and Actuators B: Chemical 176: 1128. doi:10.1016/j.snb.2012.09.073.
  19. ↑ Hurst, Sarah J., ed. (2011-01-01). Nanoparticle Therapeutics: FDA Approval, Clinical Trials, Regulatory Pathways, and Case Study - Springer. Methods in Molecular Biology. Humana Press. doi:10.1007/978-1-61779-052-2_21. ISBN 978-1-61779-051-5.
  20. ↑ V. Amendola, M. Meneghetti, "Laser ablation synthesis in solution and size manipulation of noble metal nanoparticles", Phys. Chem. Chem. Phys., 2009,11, 3805–3821.
  21. ↑ J. Turkevich, P. C. Stevenson, J. Hillier, "A study of the nucleation and growth processes in the synthesis of colloidal gold", Discuss. Faraday. Soc. 1951, 11, 55–75.
  22. ↑ J. Kimling, M. Maier, B. Okenve, V. Kotaidis, H. Ballot, A. Plech, "Turkevich Method for Gold Nanoparticle Synthesis Revisited", J. Phys. Chem. B 2006, 110, 15700–15707.
  23. 1 2 G. Frens, "Particle size and sol stability in metal colloids", Colloid & Polymer Science 1972, 250, 736–741.
  24. 1 2 G. Frens, "Controlled nucleation for the regulation of the particle size in monodisperse gold suspensions", Nature (London), Phys. Sci. 1973, 241, 20–22.
  25. ↑ BK Pong et al. J. Phys. Chem. C, 111 (17), 6281–6287, 2007. New Insights on the Nanoparticle Growth Mechanism in the Citrate Reduction of Gold(III) Salt: Formation of the Au Nanowire Intermediate and Its Nonlinear Optical Properties
  26. ↑ M. Brust; M. Walker; D. Bethell; D. J. Schiffrin; R. Whyman (1994). "Synthesis of Thiol-derivatised Gold Nanoparticles in a Two-phase Liquid-Liquid System". Chem. Commun. (7): 801–802. doi:10.1039/C39940000801.
  27. ↑ Manna, A.; Chen, P.; Akiyama, H.; Wei, T.; Tamada, K.; Knoll, W. (2003). "Optimized Photoisomerization on Gold Nanoparticles Capped by Unsymmetrical Azobenzene Disulfides". Chem. Mater. 15 (1): 20–28. doi:10.1021/cm0207696.
  28. ↑ S.D. Perrault; W.C.W. Chan (2009). "Synthesis and Surface Modification of Highly Monodispersed, Spherical Gold Nanoparticles of 50-200 nm". J. Am. Chem. Soc. 131 (47): 17042–3. doi:10.1021/ja907069u. PMID 19891442.
  29. ↑ M.N. Martin; J.I. Basham; P. Chando; S.-K. Eah (2010). "Charged Gold Nanoparticles in Non-Polar Solvents: 10-min Synthesis and 2D Self-Assembly". Langmuir 26 (10): 7410–7417. doi:10.1021/la100591h. A 3-min demonstration video for the Martin synthesis method is available at YouTube
  30. ↑ Kalishwaralal, Kalimuthu; Deepak, Venkataraman; Ram Kumar Pandian, Sureshbabu; Gurunathan, Sangiliyandi (1 November 2009). "Biological synthesis of gold nanocubes from Bacillus licheniformis". Bioresource Technology 100 (21): 5356–5358. doi:10.1016/j.biortech.2009.05.051.
  31. ↑ Julien R.G. Navarro, Frédéric Lerouge, Cristina Cepraga , Guillaume Micouin, Arnaud Favier, Denis Chateau, Marie-Thérèse Charreyre , Pierre-Henri Lanoë, Cyrille Monnereau, Frédéric Chaputa,Sophie Marotte, Yann Leverrier, Jacqueline Marvel, Kenji Kamada, Chantal Andraud, Patrice L. Baldeck, Stephane Parola Nanocarriers with ultrahigh chromophore loading for fluorescence bio-imaging and photodynamic therapy, Biomaterials, 2013, 34, 8344–8351
  32. ↑ Baigent, CL & Müller, G. (1980) A colloidal gold prepared using ultrasonics, Experientia 15. 4. Volume 36, Issue 4, pp 472–473.
  33. ↑ Jianling Zhang; Jimin Du; Buxing Han; Zhimin Liu; Tao Jiang; Zhaofu Zhang (2006). "Sonochemical Formation of Single-Crystalline Gold Nanobelts". Angew. Chem. 118 (7): 1134–7. doi:10.1002/ange.200503762.
  34. ↑ Sakai et al., 2005, Mechanism of Gold Metal Ion Reduction, Nanoparticle Growth and Size Control in Aqueous Amphiphilic Block Copolymer Solutions at Ambient Conditions, J. Phys. Chem. B, 2005, 109 (16), pp 7766–7777 (abstract)
  35. ↑ Ray et al., 2011, Synthesis and Characterization of High Concentration Block Copolymer-Mediated Gold Nanoparticles, Langmuir, 2011, 27 (7), pp 4048–4056 (abstact)
  36. 1 2 3 Sharma, RK, Shikha Gulati, and Shilpa Mehta. "Preparation of Gold Nanoparticles using Tea: A Green Chemistry Experiment." Journal of chemical education 89.10 (2012): 1316-8. Print.
  37. ↑ Haiss, Wolfgang, et al. "Determination of Size and Concentration of Gold Nanoparticles from UV-Vis Spectra." Analytical Chemistry 79.11 (2007): 4215–21. Print.
  38. ↑ Nune, Satish K., et al. "Green Nanotechnology from Tea: Phytochemicals in Tea as Building Blocks for Production of Biocompatible Gold Nanoparticles." Journal of materials chemistry 19.19 (2009): 2912–20. Print.
  39. ↑ Pattanayak, Monalisa, and PL Nayak. "Green Synthesis of Gold Nanoparticles using Elettaria Cardamomum (ELAICHI) Aqueous Extract." World 2.1 (2013): 01-5. Print.
  40. ↑ Chanda, Nripen, et al. "An Effective Strategy for the Synthesis of Biocompatible Gold Nanoparticles using Cinnamon Phytochemicals for Phantom CT Imaging and Photoacoustic Detection of Cancerous Cells." Pharmaceutical research 28.2 (2011): 279-91. Print.
  41. ↑ Subhankari, Ipsa, and PL Nayak. "Synthesis of Copper Nanoparticles using Syzygium Aromaticum (Cloves) Aqueous Extract by using Green Chemistry." World 2.1 (2013): 14-7. Print.
  42. ↑ KahkashanMazhar, AmbreenGull Muazzam, and Mohammad Ismail. "Novel and Cost-Effective Green Synthesis of Silver Nano Particles and their in-Vivo Antitumor Properties Against Human Cancer Cell Lines." Print.
  43. ↑ "Colloidal gold, a useful marker for transmission and scanning electron microscopy" by M Horisberger and J Rosset
    Journal of Histochemistry and Cytochemistry Volume 25, Issue 4, pp. 295–305, 4 January 1977
  44. ↑ Electron Microscopy, 2nd Edition, by John J. Bozzola, Jones & Bartlett Publishers; 2 Sub edition (October 1998) ISBN 0-7637-0192-0
  45. ↑ Practical Electron Microscopy: A Beginner's Illustrated Guide, by Elaine Evelyn Hunter. Cambridge University Press; 2nd edition (September 24, 1993) ISBN 0-521-38539-3
  46. ↑ Electron Microscopy: Methods and Protocols (Methods in Molecular Biology), by John Kuo (Editor). Humana Press; 2nd edition (February 27, 2007) ISBN 1-58829-573-7
  47. ↑ "Staphylococcal protein a bound to colloidal gold: A useful reagent to label antigen-antibody sites in electron microscopy", by Egidio L Romanoa and Mirtha Romanoa. Immunochemistry Volume 14, Issues 9–10, September–October 1977, pp. 711–715, doi:10.1016/0019-2791(77)90146-X
  48. ↑ Simultaneous visualization of chromosome bands and hybridization signal using colloidal-gold labeling in electron microscopy
  49. ↑ Double labeling with colloidal gold particles of different sizes
  50. ↑ Grobelny, Jaroslaw, et al. "Size Measurement of Nanoparticles using Atomic Force Microscopy." Characterization of Nanoparticles Intended for Drug Delivery.Springer, 2011. 71–82. Print.
  51. ↑ Han G, Ghosh P, Rotello VM. Functionalized gold nanoparticles for drug delivery. Nanomedicine (Lond) 2007;2:113–123.
  52. ↑ Han G, Ghosh P, Rotello VM. Multi-functional gold nanoparticles for drug delivery. Adv Exp Med Biol 2007;620:48–56.
  53. ↑ Langer R. Biomaterials in drug delivery and tissue engineering: one laboratory's experience. Acc Chem Res 2000;33:94–101.
  54. ↑ Paclitaxel-Functionalized Gold Nanoparticles Jacob D. Gibson, Bishnu P. Khanal, and Eugene R. Zubarev J. Am. Chem. Soc. 2007, 129, 11653–11661 doi:10.1021/ja075181k
  55. ↑ Conde, J.; de la Fuente, JM; Baptista, PV. "Nanomaterials for reversion of multidrug resistance in cancer: a new hope for an old idea?." Front. Pharmacol.2013. Vol 4 No 134.
  56. ↑ Qian, Ximei. "In vivo tumor targeting and spectroscopic detection with surface-enhanced Raman nanoparticle tags." Nature Biotechnology. 2008. Vol 26 No 1.
  57. ↑ Sajjadi AY, Suratkar AA, Mitra KK, Grace MS. Short-Pulse Laser-Based System for Detection of Tumors: Administration of Gold Nanoparticles Enhances Contrast. J. Nanotechnol. Eng. Med.. 2012;3(2):021002-021002-6. doi:10.1115/1.4007245.
  58. ↑ Conde J, Tian F, Hernández Y, Bao C, Cui D, Janssen KP, Ibarra MR, Baptista PV, Stoeger T, de la Fuente JM. In vivo tumor targeting via nanoparticle-mediated therapeutic siRNA coupled to inflammatory response in lung cancer mouse models. Biomaterials. 2013;34(31):7744–53. doi: 10.1016/j.biomaterials.2013.06.041.
  59. ↑ Conde J, Ambrosone A, Sanz V, Hernandez Y, Marchesano V, Tian F, Child H, Berry CC, Ibarra MR, Baptista PV, Tortiglione C, de la Fuente JM. Design of multifunctional gold nanoparticles for in vitro and in vivo gene silencing. ACS Nano. 2012;6(9):8316–24. doi: 10.1021/nn3030223.
  60. ↑ Conde J, de la Fuente JM, Baptista PV. In vitro transcription and translation inhibition via DNA functionalized gold nanoparticles. Nanotechnology. 2010;21(50):505101. doi: 10.1088/0957-4484/21/50/505101.
  61. ↑ Giljohann DA, Seferos DS, Prigodich AE, Patel PC, Mirkin CA. Gene regulation with polyvalent siRNA-nanoparticle conjugates. J Am Chem Soc 2009;131:2072–2073.
  62. ↑ Conde J, Rosa J, de la Fuente JM, Baptista PV. Gold-nanobeacons for simultaneous gene specific silencing and intracellular tracking of the silencing events. Biomaterials. 2013;34(10):2516–23. doi: 10.1016/j.biomaterials.2012.12.015.
  63. ↑ Rosa J, Conde J, de la Fuente JM, Lima JC, Baptista PV. Gold-nanobeacons for real-time monitoring of RNA synthesis. Biosens Bioelectron. 2012;36(1):161-7. doi: 10.1016/j.bios.2012.04.006.
  64. ↑ Conde J, Rosa J, Baptista P. Gold-Nanobeacons as a theranostic system for the detection and inhibition of specific genes. Community Contributed Protocol Exchange. 27 November 2013. doi:10.1038/protex.2013.088.
  65. ↑ Hainfeld, James et al. "The use of gold nanoparticles to enhance radiotherapy in mice." Phys. Med. Biol. 2004. Vol 49, N309–315
  66. ↑ McMahon, Stephen et al. "Biological consequences of nanoscale energy deposition near irradiated heavy atom nanoparticles." Nature Scientific Reports http://www.nature.com/srep/2011/110620/srep00018/full/srep00018.html
  67. ↑ Zhang, Zhiyang; Zhaopeng Chen; Shasha Wang; Chengli Qu; Lingxin Chen (2014). "On-site Visual Detection of Hydrogen Sulfide in Air Based on Enhancing the Stability of Gold NanoParticles". ACS Applied Materials & Interfaces 6 (9): 6300–6307. doi:10.1021/am500564w.
  68. 1 2 3 4 5 Xu, S. et. al. Gold nanoparticle-based biosensors. Gold Bulletin. 2010, 43, p 29–41.
  69. ↑ J. Wang, R. Polsky and D. Xu, Langmuir, 2001, 17, 5739.
  70. ↑ J. Wang, D. Xu and R. Polsky, J Am Chem Soc, 2002, 124, 4028.
  71. ↑ M. C. Daniel and D. Astruc, Chem Rev, 2004, 104, 293.
  72. ↑ M. Hu, J. Chen, Z.Y. Li, L. Au, G.V. Hartland, X. Li, M. Marquez and Y. Xia, Chem Soc Rev, 2006, 35, 1084.
  73. ↑ S. Link and M.A. El-Sayed, J. Phys. Chem. B, 1996, 103, 8410.
  74. ↑ P. Mulvaney, Langmuir, 1996, 12, 788.
  75. ↑ H. Y. Lin, C. T. chen and Y. C. Chen, Anal Chem, 200, 78, 6873
  76. ↑ L. He, M.D. Musick, S. R. Nicewarner, F.G. Salinas, Journal of the American Chemical Society, 2000, 122, 9071
  77. ↑ A.M. Qi, I. Honma and H. Zhou, Opt Lett, 2000, 25, 372
  78. ↑ K.R. Brown, a.P Fox and M.J. Natan, Journal of the American Chemical society, 1996, 118, 1154.
  79. ↑ Y. Xiao, et. al. Science, 2003,299, 1877.
  80. ↑ A. Gole, et. al. Langmuir, 2001, 17, 1674
  81. ↑ A. Gole, et. al. Colloids and Surfaces B: Biointerfaces, 2002, 25, 129
  82. ↑ M. Valden, X. Lai and D.W. Goodman, Science, 1998, 281, 1647
  83. ↑ Y. Lou, M.M. Maye, L. Han, J.Luo and C. –J. Zhong, Chemical Communications, 2001, 473
  84. ↑ M. Turner, V.B. Golovko, O.P Vaughan, P. Abdulkin, A. Berenguer-Murcia, M.S. Tikhov, B.F. Johnson and R.M Lambert, Narture, 2008, 454, 981

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