NP Aggregation Research Articles

Colorimetric assay of matrix metalloproteinase activity based on metal-induced self-assembly of carboxy gold nanoparticles

Among proteases, matrix metalloproteinases (MMPs) have been of significant interest because they are considered as one of the promising biomarkers in association with cancer metastasis, inflammation and other degenerative diseases. Many attempts based on the optical sensing have been made to analyze the activity of MMPs, but most of them require an expensive fluorescence readout and a labor-intensive process. To circumvent this issue, we demonstrated a simple colorimetric detection of protease activity by using carboxy gold nanoparticles (AuNPs) and histidine-containing peptides via metal-affinity coordination. Due to their higher surface-to-volume ratio, the nanometer size of AuNPs enables the surface ligands to function like a chelator, providing greater affinity with metal ions, even in the absence of chelators. With no additional modification by multidentate ligands, the carboxy AuNPs were easily aggregated and changed in color (from reddish-brown to violet) after adding peptide substrates with hexahistidine at both ends and metal ions, whereas the presence of proteases in solution prevented NP aggregation by cleaving the peptides, thereby retaining the original color of the AuNPs. When the extinction ratio (E520/E700) of the AuNP solution was measured as a function of matrix metalloproteinase concentration in a single reaction, there was good linearity from as low as 3nM to 52nM. This approach is anticipated to be useful in designing other diagnostic nanosensors.

Surfactant protein D (SP-D) alters cellular uptake of particles and nanoparticles

Surfactant protein D (SP-D) is primarily expressed in the lungs and modulates pro- and anti-inflammatory processes to toxic challenge, maintaining lung homeostasis. We investigated the interaction between NPs and SP-D and subsequent uptake by cells involved in lung immunity. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) measured NP aggregation, particle size and charge in native human SP-D (NhSP-D) and recombinant fragment SP-D (rfhSP-D). SP-D aggregated NPs, especially following the addition of calcium. Immunohistochemical analysis of A549 epithelial cells investigated the co-localization of NPs and rfhSP-D. rfhSP-D enhanced the co-localisation of NPs to epithelial A549 cells in vitro. NP uptake by alveolar macrophages (AMs) and lung dendritic cells (LDCs) from C57BL/6 and SP-D knock-out mice were compared. AMs and LDCs showed decreased uptake of NPs in SP-D deficient mice compared to wild-type mice. These data confirmed an interaction between SP-D and NPs, and subsequent enhanced NP uptake.

Gene Expression in Liver Injury Caused by Long-term Exposure to Titanium Dioxide Nanoparticles in Mice

Although liver toxicity induced by titanium dioxide nanoparticles (TiO(2) NPs) has been demonstrated, very little is known about the molecular mechanisms of multiple genes working together underlying this type of liver injury in mice. In this study, we used the whole-genome microarray analysis technique to determine the gene expression profile in the livers of mice exposed to 10 mg/kg body weight TiO(2) NPs for 90 days. The findings showed that long-term exposure to TiO(2) NPs resulted in obvious titanium accumulation in the liver and TiO(2) NP aggregation in hepatocyte nuclei, an inflammatory response, hepatocyte apoptosis, and liver dysfunction. Furthermore, microarray data showed striking changes in the expression of 785 genes related to the immune/inflammatory response, apoptosis, oxidative stress, the metabolic process, response to stress, cell cycle, ion transport, signal transduction, cell proliferation, cytoskeleton, and cell differentiation in TiO(2) NP-exposed livers. In particular, a significant reduction in complement factor D (Cfd) expression following long-term exposure to TiO(2) NPs resulted in autoimmune and inflammatory disease states in mice. Therefore, Cfd may be a potential biomarker of liver toxicity caused by TiO(2) NPs exposure.

Using polysorbate 40-stabilized gold nanoparticles in colorimetric assays of hydrogen cyanide in cyanogenic glycoside-containing plants

This study presents a convenient and homogeneous method for the selective detection of hydrogen cyanide in cyanogenic glycoside-containing plants using polysorbate 40-stabilized gold nanoparticles (PS 40-AuNPs). Neutral PS 40 molecules stabilized citrate-capped AuNPs in a high-salinity solution. When the plant tissue is damaged, β-glucosidase rapidly hydrolyzes cyanogenic glycosides to produce hydrogen cyanide. The addition of the released hydrogen cyanide to a solution of PS 40-AuNPs resulted in the formation of AuCN(s) on the NP surface and Au(CN)2− in an aqueous solution. The removal of PS 40 molecules from the NP surface rendered the AuNPs unstable in a high-salinity solution, leading to NP aggregation. We used surface-assisted laser desorption/ionization time-of-flight mass spectrometry to detect the formation of AuCN(s). This probe was also successfully used to determine the total cyanide in cassava roots, peach kernels, and loquat kernels. When the three cyanogenic glycoside-containing plants were separately heated, this probe was capable of monitoring the removal of hydrogen cyanide during heating. In addition, the use of thiosulfate to detoxify the three cyanogenic glycoside-containing plants was evaluated using PS 40-AuNPs.

Gold Nanoparticles Stabilized by Thioether Dendrimers

Ligand-stabilized gold nanoparticles (Au NPs) are promising materials for nanotechnology with applications in electronics, catalysis, and sensors. These applications depend on the ability to synthesize stable and monodisperse NPs. Herein, the design and synthesis of two series of dendritic thioether ligands and their ability to stabilize Au NPs is presented. The dendrimers have 1,3,5-trisubstituted benzene branching units bridged by either meta-xylene or ethylene moieties. A comparison between the two ligands shows how both size control and the stability of the NPs are influenced by the nature of the ligand-NP wrapping interaction. The meta-xylene-bridged ligands provided NPs with a narrow size distribution centered around a diameter of 1.2 nm, whereas the NPs formed with ethylene-bridged dendrimers lack long-term stability with NP aggregation detected by UV/Vis spectroscopy and transmission electron microscopy. The bulkier tert-butyl-functionalized meta-xylene bridges form larger ligand shells that inhibit further growth of the NPs and thus provide a simple route to stable and monodisperse Au NPs that may find use as functional components in nanoelectronic devices.

Effects of aggregation and the surface properties of gold nanoparticles on cytotoxicity and cell growth

The effect of gold nanoparticles (Au NPs) on cells remains open for investigation. Here we show that small Au NPs can be endocytosed by cells and form aggregates inside the cell, resulting in cytotoxicity. When the aggregates become too large to enter the cell and instead adhere onto the cell surface, however, the growth rate of HeLa cells increases. Printed patterns of Au NPs fabricated through inkjet printing technology were used to study the effects of Au NP aggregation on human cervical carcinoma (HeLa) cell activity. The growth of the HeLa cells was inhibited on the polymer-coated Au NPs but increased on the silicon substrate. On the uncoated Au NP surface, however, the HeLa cell growth rate was higher than that on the silicon substrate. Experiments with Escherichia coli cells showed a similar effect of the Au NPs. This phenomenon provides a new perspective for research on toxicity in nanoparticle biology. From the Clinical Editor Printed patterns of Au NPs fabricated through inkjet printing technology were used to study the effects of Au NP aggregation on human cervical carcinoma (HeLa) cell activity. Small Au NPs can be endocytosed by cells resulting in cytotoxicity; in contrast, large aggregates adhere onto the cell surface and increase the growth rate of HeLa cells.

Controlled UV−C Light-Induced Fusion of Thiol-Passivated Gold Nanoparticles

Thiol-passivated gold nanoparticles (AuNPs) of a relatively small size, either decorated with chromophoric groups, such as a phthalimide (Au@PH) and benzophenone (Au@BP), or capped with octadecanethiol (Au@ODCN) have been synthesized and characterized by NMR and UV-vis spectroscopy as well as transmission electron microscopy (TEM). These NPs were irradiated in chloroform at different UV-wavelengths using either a nanosecond laser (266 and 355 nm, ca. 12 mJ/pulse, 10 ns pulse) or conventional lamps (300 nm < λ < 400 nm and ca. 240 nm < λ < 280 nm) and the new AuNPs were characterized by X-ray and UV-vis spectroscopy, as well as by TEM. Laser irradiation at 355 nm led to NP aggregation and precipitation, while the NPs were photostable under UV-A lamp illumination. Remarkably, laser excitation at 266 nm induced a fast (minutes time-scale) increase in the size of the NPs, producing huge spherical nanocrystals, while lamp-irradiation at UV-C wavelengths brought about nanonetworks of partially fused NPs with a larger diameter than the native NPs.

Controlled Labeling of Lipids with Single Gold Nanoparticles on Living Cell Membranes

The cellular membrane is the physical boundary of cells where numerous cellular processes occur. Gold nanoparticles (Au NPs) are attractive optical tools to investigate living cell membranes due to their chemical stability and unique optical properties.[1] Direct utilization of weakly stabilized Au NPs often results in NP aggregation in biological media and in their uncontrolled attachment to biological membranes. Controlled strategies, however, are typically based on protein-mediated binding, which restricts the use of the Au NPs to protein-specific studies, and therefore limits their spectrum of sensing and optothermal applications.Here we present a general, versatile and controlled strategy to bind individual Au NPs to lipids in living cell membranes, while preserving the sensing and optothermal capabilities of the original colloid [2]. Our approach is based on the controlled and selective binding of Au NPs to phospholipids prior to cell incubation. First, CTAB-capped gold nanospheres are PEGylated and maleimide derivatized for conjugation to thiol-ended lipids in liposomes. Thereafter the Au-labeled lipids are incorporated in the cellular membrane of living cells via liposome/cell membrane fusogenesis. As a result of lipid binding, the diffusion of the Au NPs on the cell membrane is rather slow and spatially-limited. In this presentation we will show different strategies to manipulate the diffusion of those Au NPs on the cell membrane, which enables us to gain further insight into the membrane structure.

Aggregation and ecotoxicity of CeO 2 nanoparticles in synthetic and natural waters with variable pH, organic matter concentration and ionic strength

The influence of pH (6.0–9.0), natural organic matter (NOM) (0–10 mg C/L) and ionic strength (IS) (1.7–40 mM) on 14 nm CeO 2 NP aggregation and ecotoxicity towards the alga Pseudokirchneriella subcapitata was assessed following a central composite design. Mean NP aggregate sizes ranged between 200 and 10000 nm. Increasing pH and IS enhanced aggregation, while increasing NOM decreased mean aggregate sizes. The 48 h-E rC20s ranged between 4.7 and 395.8 mg CeO 2/L. An equation for predicting the 48 h-E rC20 (48 h-E rC20 = −1626.4 × (pH) + 109.45 × (pH) 2 + 116.49 × ([NOM]) − 14.317 × (pH) × ([NOM]) + 6007.2) was developed. In a validation study with natural waters the predicted 48 h-E rC20 was a factor 1.08–2.57 lower compared to the experimental values.

Electrolyte Solutions Improve Nanoparticle Transfer from Oil to Water

Many techniques to transfer NPs from the oil phase into the water phase have been developed, but all have limitations that remain to be addressed, specifically low transfer yields and partial NP aggregation. One of the transfer processes involves emulsifying an oil suspension of NPs in water with surfactants, followed by evaporation of the oil to produce water suspensions of surfactant-encapsulated NPs. We show here that using salt solutions instead of deionized water significantly improves this emulsion-based transfer process. With oleate-coated CdSe quantum dots as a model NP system, hexane as the oil phase, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as the emulsifying surfactant, and NaCl solution as the water phase, the resultant aqueous suspensions exhibit months-long photoluminescence stability, near 100% phase-transfer yield, and nonaggregation. These benefits are attributed to a more laterally packed AOT layer surrounding the NP, as supported by zeta-potential measurements, surface-charge calcu...

Selective extraction of melamine using 11-mercaptoundecanoic acid–capped gold nanoparticles followed by capillary electrophoresis

This study describes the use of 11-mercaptoundecanoic acid–capped gold nanoparticles (MUA–AuNPs) for selective extraction of melamine prior to analysis by capillary electrophoresis with UV detection. The highest degree of melamine-induced aggregation of MUA–AuNPs was found to occur at pH 5.0, indicating that the NP aggregation is mainly because of hydrogen bonding between the carboxylate groups of MUA and the amine groups of melamine. Moreover, the degree of melamine-induced NP aggregation gradually increased when the chain length of the mercaptoalkanoic acid was increased from two to 12 carbon atoms. At pH 5.0, the extraction efficiency of melamine was highly dependent on the concentration of MUA–AuNPs, the concentration of dithiothreitol (DTT), the extraction time between MUA–AuNPs and melamine, and the incubation time between melamine-adsorbed AuNPs and DTT. The separation of the extracted melamine and DTT (releasing agent) was accomplished using a solution of 10 mM phosphate (pH 6.0) containing 1.6% (v/v) poly(diallyldimethylammonium chloride). Under the optimum extraction and separation conditions, the limit of detection at a signal-to-noise ratio of 3 was estimated to be 77 pM for melamine, with linear range of 1–1000 nM. The proposed method was successfully applied to the determination of melamine in tap water and in milk.

Colorimetric Sensing of Silver(I) and Mercury(II) Ions Based on an Assembly of Tween 20-Stabilized Gold Nanoparticles

We have developed a rapid and homogeneous method for the highly selective detection of Hg(2+) and Ag(+) using Tween 20-modified gold nanoparticles (AuNPs). Citrate ions were found to still be adsorbed on the Au surface when citrate-capped AuNPs were modified with Tween 20, which stabilizes the citrate-capped AuNPs against conditions of high ionic strength. When citrate ions had reduced Hg(2+) and Ag(+) to form Hg-Au alloys and Ag on the surface of the AuNPs, Tween 20 was removed from the NP surface. As a result, the AuNPs were unstable under a high-ionic-strength solution, resulting in NP aggregation. The formation of Hg-Au alloys or Ag on the surface of the AuNPs was demonstrated by means of inductively coupled plasma mass spectroscopy and energy-dispersive X-ray spectroscopy. Tween 20-AuNPs could selectively detect Hg(2+) and Ag(+) at concentrations as low as 0.1 and 0.1 microM in the presence of NaCl and EDTA, respectively. Moreover, the probe enables the analysis of AgNPs with a minimum detectable concentration that corresponds to 1 pM. This probe was successfully applied to detect Hg(2+) in drinking water and seawater, Ag(+) in drinking water, and AgNPs in drinking water.

Nanoparticles That “Remember” Temperature

Photoresponsive gold nanoparticles dispersed in a solid/frozen matrix provide a basis for sensors that “remember” whether the sample has ever exceeded the melting temperature of the matrix. The operation of these sensors rests on the ability to photoinduce metastable electric dipoles on NP surfaces – upon melting, these dipoles drive NP aggregation, precipitation, and crosslinking. These events are manifested by a pronounced color change.

Chemical sensing based on the plasmonic response of nanoparticle aggregation: anion sensing in nanoparticles stabilized by amino-functional ionic liquid

We report the synthesis, characterization and modellization of optical anion sensors based on gold nanoparticles (Au NPs) stabilized by amino-functional imidazolium ionic liquids (AFIL). The addition of different salts results in anion exchange of the imidazolium ionic liquid stabilizer leading to a change in the optical response of the original nanoparticle aqueous solution. In all cases except with dodecylbenzenesulfonic acid sodium salt, a sufficient amount of salt concentration (5 times larger than equimolar) leads to the appearance of an absorption band between 600 and 700 nm in the ultravioletvisible (UV-vis) spectrum. The presence of the salt produces aggregation of the particles that localise the optical response and produce a large spectral red shift. Transmission electron microscopy images demonstrated that this optical change was due to the aggregation of the nanoparticles. We simulate the optical response of both situations, before and after salt addition, and interpret the experimental observations in terms of the different response of metallic single nanoparticles and nanoparticle aggregates. Theoretical calculations for single nanoparticle and single nanoparticle dimers demonstrate that the colour change is not due to the enlargement or structural changes of the Au NPs, but due to the formation of NP aggregation. These results show the potential of nanoparticle plasmonics to perform effective chemical sensing.

Effects of Mn 2+ on oligonucleotide-gold nanoparticle hybrids for colorimetric sensing of Hg 2+: Improving colorimetric sensitivity and accelerating color change

In this paper, we present a simple and rapid colorimetric assay – using the polythymine oligonucleotide T 33, citrate-capped gold nanoparticles (AuNPs), and phosphate-buffer saline (PBS) in the presence of Mn 2+ – for the highly selective and sensitive detection of Hg 2+ in an aqueous solution. Citrate-capped AuNPs adsorbed on randomly coiled T 33 were dispersed well in PBS because of strong electrostatic repulsion between DNA molecules. In the presence of Hg 2+, the formation of Hg 2+–T 33 complexes enabled the removal of T 33 molecules from the NP surface, resulting in salt-induced NP aggregation. However, the T 33-capped AuNPs (T 33-AuNPs) were dispersed in PBS solution after the addition of 1.0 μM Hg 2+, indicating that T 33-AuNPs had poor colorimetric sensitivity toward Hg 2+. We uncovered that the addition of Mn 2+ to a solution containing 0.75 nM T 33-AuNPs and 0.2× PBS resulted in an acceleration of the analysis time (within 5 min) and a 100-fold sensitivity improvement for the detection of Hg 2+. As a result, the present approach enables the analysis of Hg 2+ with a minimum detectable concentration that corresponds to 10 nM. This is probably attributed to that Mn 2+ binds strongly to the phosphate backbone of DNA, thereby accelerating Hg 2+-induced aggregation of the T 33-AuNPs. Because Mn 2+ can stabilize the folded structure of the Hg 2+–T 33 complex, Hg 2+ facilitates the removal of T 33 from the NP surface in the presence of Mn 2+. This probe was successfully applied to the determination of Hg 2+ in pond water.

Type I collagen-templated assembly of silver nanoparticles and their application insurface-enhanced Raman scattering

Silver nanoparticles (Ag NPs) are one of the active substrates that are employedextensively in surface-enhanced Raman scattering (SERS), and aggregations of Ag NPsplay an important role in enhancing the Raman signals. In this paper, we fabricated twokinds of SERS-active substrates utilizing the electrostatic adsorption and superior assemblyproperties of type I collagen. These were collagen-Ag NP aggregation films and nanoporousAg films. Two probe molecules, 4-aminothiophenol (4-ATP) and methylene blue(MB), were studied on these substrates. These substrates showed reproducibleSERS intensities with relative standard deviations (RSDs) of 8–10% and 11–14%,respectively, while the RSDs of the traditional thick Ag films were 12–28%. Also, theintensities for the 4-ATP spectrum on the collagen-templated nanoporous Ag filmwere approximately one order higher than those on the DNA-templated Ag film.