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Stable oligomeric clusters of gold nanoparticles: preparation, size distribution, derivatization, and physical and biological properties.

Smithies O, Lawrence M, Testen A, Horne LP, Wilder J, Altenburg M, Bleasdale B, Maeda N, Koklic T - Langmuir (2014)

Bottom Line: The crude oligocluster preparations have narrow size distributions, and for most purposes do not require fractionation.The oligoclusters do not aggregate after ∼300-fold centrifugal-filter concentration, and at this high concentration are easily derivatized with a variety of thiol-containing reagents.Unlike conventional glutathione-capped nanoparticles of comparable gold content, large oligoclusters derivatized with glutathione do not aggregate at high concentrations in phosphate-buffered saline (PBS) or in the circulation when injected into mice.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology and Laboratory Medicine, and ‡Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.

ABSTRACT
Reducing dilute aqueous HAuCl4 with NaSCN under alkaline conditions produces 2-3 nm diameter yellow nanoparticles without the addition of extraneous capping agents. We here describe two very simple methods for producing highly stable oligomeric grape-like clusters (oligoclusters) of these small nanoparticles. The oligoclusters have well-controlled diameters ranging from ∼5 to ∼30 nm, depending mainly on the number of subunits in the cluster. Our first ["delay-time"] method controls the size of the oligoclusters by varying from seconds to hours the delay time between making the HAuCl4 alkaline and adding the reducing agent, NaSCN. Our second ["add-on"] method controls size by using yellow nanoparticles as seeds onto which varying amounts of gold derived from "hydroxylated gold", Na(+)[Au(OH4-x)Clx](-), are added-on catalytically in the presence of NaSCN. Possible reaction mechanisms and a simple kinetic model fitting the data are discussed. The crude oligocluster preparations have narrow size distributions, and for most purposes do not require fractionation. The oligoclusters do not aggregate after ∼300-fold centrifugal-filter concentration, and at this high concentration are easily derivatized with a variety of thiol-containing reagents. This allows rare or expensive derivatizing reagents to be used economically. Unlike conventional glutathione-capped nanoparticles of comparable gold content, large oligoclusters derivatized with glutathione do not aggregate at high concentrations in phosphate-buffered saline (PBS) or in the circulation when injected into mice. Mice receiving them intravenously show no visible signs of distress. Their sizes can be made small enough to allow their excretion in the urine or large enough to prevent them from crossing capillary basement membranes. They are directly visible in electron micrographs without enhancement, and can model the biological fate of protein-like macromolecules with controlled sizes and charges. The ease of derivatizing the oligoclusters makes them potentially useful for presenting pharmacological agents to different tissues while controlling escape of the reagents from the circulation.

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Diameters of gold oligoclusters formed after differentdelay timesbefore adding NaSCN. Representative TEM images of 50 nm × 50nm areas of grids prepared from the eight preparations used in theelectrophoresis together with statistical data (box plots) for thesizes of the particles (Y axis) and the delay timesused in their preparation (X axis). Both axes arelogarithmic. The heavy and light lines within the boxes mark the meanand median core diameter. The upper and lower boundaries of the boxesare the 75th and 25th percentiles. Error bars are the 90th and 10thpercentiles. The number of oligoclusters counted was 490, 2077, 385,888, 2799, 1327, 1438, and 281 for the preparations made with 2, 5,15, 45, 135, 405, 1200, and 3600 s delay times. The heavy black line(R2 = 0.973) is a best-fit empirical three-parameterequation f = y0 + a·(1– exp(−b·t)),where f is the mean diameter of clusters in nm, y0 is the minimum diameter of clusters (∼3.5nm), a is the maximum increase in core size causedby extending the delay time (∼20 nm), and b is 0.0021 s–1. Because the parameter b is an exponent, the equation indicates that a factor (or factors)that is exponentially affected by time controls the increase in sizeof the oligoclusters.
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fig3: Diameters of gold oligoclusters formed after differentdelay timesbefore adding NaSCN. Representative TEM images of 50 nm × 50nm areas of grids prepared from the eight preparations used in theelectrophoresis together with statistical data (box plots) for thesizes of the particles (Y axis) and the delay timesused in their preparation (X axis). Both axes arelogarithmic. The heavy and light lines within the boxes mark the meanand median core diameter. The upper and lower boundaries of the boxesare the 75th and 25th percentiles. Error bars are the 90th and 10thpercentiles. The number of oligoclusters counted was 490, 2077, 385,888, 2799, 1327, 1438, and 281 for the preparations made with 2, 5,15, 45, 135, 405, 1200, and 3600 s delay times. The heavy black line(R2 = 0.973) is a best-fit empirical three-parameterequation f = y0 + a·(1– exp(−b·t)),where f is the mean diameter of clusters in nm, y0 is the minimum diameter of clusters (∼3.5nm), a is the maximum increase in core size causedby extending the delay time (∼20 nm), and b is 0.0021 s–1. Because the parameter b is an exponent, the equation indicates that a factor (or factors)that is exponentially affected by time controls the increase in sizeof the oligoclusters.

Mentions: Figure 3 presents a summary of the sizedistributions and TEM images of all of the preparations that wereused for the electrophoresis experiment illustrated in Figure 1.


Stable oligomeric clusters of gold nanoparticles: preparation, size distribution, derivatization, and physical and biological properties.

Smithies O, Lawrence M, Testen A, Horne LP, Wilder J, Altenburg M, Bleasdale B, Maeda N, Koklic T - Langmuir (2014)

Diameters of gold oligoclusters formed after differentdelay timesbefore adding NaSCN. Representative TEM images of 50 nm × 50nm areas of grids prepared from the eight preparations used in theelectrophoresis together with statistical data (box plots) for thesizes of the particles (Y axis) and the delay timesused in their preparation (X axis). Both axes arelogarithmic. The heavy and light lines within the boxes mark the meanand median core diameter. The upper and lower boundaries of the boxesare the 75th and 25th percentiles. Error bars are the 90th and 10thpercentiles. The number of oligoclusters counted was 490, 2077, 385,888, 2799, 1327, 1438, and 281 for the preparations made with 2, 5,15, 45, 135, 405, 1200, and 3600 s delay times. The heavy black line(R2 = 0.973) is a best-fit empirical three-parameterequation f = y0 + a·(1– exp(−b·t)),where f is the mean diameter of clusters in nm, y0 is the minimum diameter of clusters (∼3.5nm), a is the maximum increase in core size causedby extending the delay time (∼20 nm), and b is 0.0021 s–1. Because the parameter b is an exponent, the equation indicates that a factor (or factors)that is exponentially affected by time controls the increase in sizeof the oligoclusters.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230385&req=5

fig3: Diameters of gold oligoclusters formed after differentdelay timesbefore adding NaSCN. Representative TEM images of 50 nm × 50nm areas of grids prepared from the eight preparations used in theelectrophoresis together with statistical data (box plots) for thesizes of the particles (Y axis) and the delay timesused in their preparation (X axis). Both axes arelogarithmic. The heavy and light lines within the boxes mark the meanand median core diameter. The upper and lower boundaries of the boxesare the 75th and 25th percentiles. Error bars are the 90th and 10thpercentiles. The number of oligoclusters counted was 490, 2077, 385,888, 2799, 1327, 1438, and 281 for the preparations made with 2, 5,15, 45, 135, 405, 1200, and 3600 s delay times. The heavy black line(R2 = 0.973) is a best-fit empirical three-parameterequation f = y0 + a·(1– exp(−b·t)),where f is the mean diameter of clusters in nm, y0 is the minimum diameter of clusters (∼3.5nm), a is the maximum increase in core size causedby extending the delay time (∼20 nm), and b is 0.0021 s–1. Because the parameter b is an exponent, the equation indicates that a factor (or factors)that is exponentially affected by time controls the increase in sizeof the oligoclusters.
Mentions: Figure 3 presents a summary of the sizedistributions and TEM images of all of the preparations that wereused for the electrophoresis experiment illustrated in Figure 1.

Bottom Line: The crude oligocluster preparations have narrow size distributions, and for most purposes do not require fractionation.The oligoclusters do not aggregate after ∼300-fold centrifugal-filter concentration, and at this high concentration are easily derivatized with a variety of thiol-containing reagents.Unlike conventional glutathione-capped nanoparticles of comparable gold content, large oligoclusters derivatized with glutathione do not aggregate at high concentrations in phosphate-buffered saline (PBS) or in the circulation when injected into mice.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology and Laboratory Medicine, and ‡Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.

ABSTRACT
Reducing dilute aqueous HAuCl4 with NaSCN under alkaline conditions produces 2-3 nm diameter yellow nanoparticles without the addition of extraneous capping agents. We here describe two very simple methods for producing highly stable oligomeric grape-like clusters (oligoclusters) of these small nanoparticles. The oligoclusters have well-controlled diameters ranging from ∼5 to ∼30 nm, depending mainly on the number of subunits in the cluster. Our first ["delay-time"] method controls the size of the oligoclusters by varying from seconds to hours the delay time between making the HAuCl4 alkaline and adding the reducing agent, NaSCN. Our second ["add-on"] method controls size by using yellow nanoparticles as seeds onto which varying amounts of gold derived from "hydroxylated gold", Na(+)[Au(OH4-x)Clx](-), are added-on catalytically in the presence of NaSCN. Possible reaction mechanisms and a simple kinetic model fitting the data are discussed. The crude oligocluster preparations have narrow size distributions, and for most purposes do not require fractionation. The oligoclusters do not aggregate after ∼300-fold centrifugal-filter concentration, and at this high concentration are easily derivatized with a variety of thiol-containing reagents. This allows rare or expensive derivatizing reagents to be used economically. Unlike conventional glutathione-capped nanoparticles of comparable gold content, large oligoclusters derivatized with glutathione do not aggregate at high concentrations in phosphate-buffered saline (PBS) or in the circulation when injected into mice. Mice receiving them intravenously show no visible signs of distress. Their sizes can be made small enough to allow their excretion in the urine or large enough to prevent them from crossing capillary basement membranes. They are directly visible in electron micrographs without enhancement, and can model the biological fate of protein-like macromolecules with controlled sizes and charges. The ease of derivatizing the oligoclusters makes them potentially useful for presenting pharmacological agents to different tissues while controlling escape of the reagents from the circulation.

Show MeSH
Related in: MedlinePlus