Key Publications

Key publications using nanoComposix's materials:

Nanotoxicology

Spherical Silver Nanoparticles

Bouwmeester, H., et al., Characterization of Translocation of Silver Nanoparticles and Effects on Whole-Genome Gene Expression Using an In Vitro Intestinal Epithelium Coculture Model. ACS Nano, 2011. In press.

Applications of nanoparticles in the food sector are eminent. Silver nanoparticles are among the most frequently used, making consumer exposure to silver nanoparticles inevitable. Information about uptake through the intestines and possible toxic effects of silver nanoparticles is therefore very important but still lacking. In the present study, we used an in vitro model for the human intestinal epithelium consisting of Caco-2 and M-cells to study the passage of silver nanoparticles and their ionic equivalents and to assess their effects on whole-genome mRNA expression. This in vitro intestine model was exposed to four sizes of silver nanoparticles for 4 h. Exposure to silver ions was included as a control since 6â€"17% of the silver nanoparticles were found to be dissociated into silver ions. The amount of silver ions that passed the Caco-2 cell barrier was equal for the silver ion and nanoparticle exposures. The nanoparticles induced clear changes in gene expression in a range of stress responses including oxidative stress, endoplasmatic stress response, and apoptosis. The gene expression response to silver nanoparticles, however, was very similar to that of AgNO3. Therefore, the observed effects of the silver nanoparticles are likely exerted by the silver ions that are released from the nanoparticles.

Kennedy, A.J., et al., Fractionating Nanosilver: Importance for Determining Toxicity to Aquatic Test Organisms. Environmental Science & Technology, 2010. 44(24): p. 9571-9577.

This investigation applied novel techniques for characterizing and fractionating nanosilver particles and aggregates and relating these measurements to toxicological endpoints. The acute toxicity of eight nanosilver suspensions of varying primary particle sizes (10 - 80 nm) and coatings (citrate, polyvinylpyrrolidone, EDTA, proprietary) was assessed using three aquatic test organisms (Daphnia magna, Pimephales promelas, Pseudokirchneriella subcapitata). When 48-h lethal median concentrations (LC50) were expressed as total silver, both D. magna and P. promelas were significantly more sensitive to ionic silver (Ag+) as AgNO3 (mean LC50 = 1.2 and 6.3 ug/L, respectively) relative to a wide range in LC50 values determined for the nanosilver suspensions. However, when LC50 values for nanosilver suspensions were expressed as fractionated nanosilver (Ag+ and/or <4 nm particles), determined by ultracentrifugation of particles and confirmed field-flow-fractograms, the LC50 values were comparable to the values obtained for ionic Ag+ as AgNO3. These results suggest that dissolved Ag+ plays a critical role in acute toxicity and underscores the importance of characterizing dissolved fractions in nanometal suspensions.

Laborda, F., et al., Selective identification, characterization and determination of dissolved silver(i) and silver nanoparticles based on single particle detection by inductively coupled plasma mass spectrometry. Journal of Analytical Atomic Spectrometry, 2011. In Press.

The different behaviours of dissolved silver and silver nanoparticles under ICP-MS single particle detection conditions have been used to differentiate directly between both forms of silver in aqueous samples. Suspensions containing silver nanoparticles at number concentrations below 109 L-1 and/or dissolved Ag(i) are introduced into the ICP-MS by conventional pneumatic nebulization and measured with a time resolution of 5 ms. Each silver nanoparticle is converted in the ICP into a packet of ions, which are detected as a single pulse, whose intensity is proportional to the number of silver atoms in the nanoparticle, whereas dissolved silver produces pulses of averaged constant intensity. The frequency plots with respect to the intensity measured for each pulse show independent distributions for dissolved silver and silver nanoparticles, whose profiles are also different (Poisson and lognormal, respectively). Size limits of detection for pure Ag nanoparticles of 18 nm, equivalent to a silver mass of 32 ag, were obtained. Number concentration limits of detection of 1 [times] 104 L-1 can be achieved. A methodological approach for identification, characterization and determination of mass and number concentration of dissolved Ag(i) and silver nanoparticles at environmentally relevant concentrations is presented.

Lankveld, D.P.K., et al., The kinetics of the tissue distribution of silver nanoparticles of different sizes. Biomaterials, 2010. 31(32): p. 8350-8361.

Blood kinetics and tissue distribution of 20, 80 and 110　nm silver nanoparticles were investigated in rats up to 16 days after intravenous administration once daily for 5 consecutive days. Following both single and repeated injection, silver nanoparticles disappeared rapidly from the blood and distributed to all organs evaluated (liver, lungs, spleen, brain, heart, kidneys and testes) regardless of size. The 20　nm particles distributed mainly to liver, followed by kidneys and spleen, whereas the larger particles distributed mainly to spleen followed by liver and lung. In the other organs evaluated, no major differences between the sizes were observed. Size-dependent tissue distribution suggests size-dependent toxicity and health risks. Repeated administration resulted in accumulation in liver, lung and spleen, indicating that these organs may be potential target organs for toxicity after repeated exposure. A　physiologically based pharmacokinetic (PBPK) model for nanoparticles which describes the kinetics of silver nanoparticles was developed. Model parameter values were estimated by fitting to data. No clear relation between parameter values and corresponding particle diameters became apparent.

MacCuspie, R.I., et al., Challenges for physical characterization of silver nanoparticles under pristine and environmentally relevant conditions. Journal of Environmental Monitoring, 2011.

The reported size distribution of silver nanoparticles (AgNPs) is strongly affected by the underlying measurement method, agglomeration state, and dispersion conditions. A selection of AgNP materials with vendor-reported diameters ranging from 1 nm to 100 nm, various size distributions, and biocompatible capping agents including citrate, starch and polyvinylpyrrolidone were studied. AgNPs were diluted with either deionized water, moderately hard reconstituted water, or moderately hard reconstituted water containing natural organic matter. Rigorous physico-chemical characterization by consensus methods and protocols where available enables an understanding of how the underlying measurement method impacts the reported size measurements, which in turn provides a more complete understanding of the state (size, size distribution, agglomeration, etc.) of the AgNPs with respect to the dispersion conditions. An approach to developing routine screening is also presented.

Poda, A.R., et. al., Characterization of silver nanoparticles using flow-field flow fractionation interfaced to inductively coupled plasma mass spectrometry., J. Chrom A., 2011. 1218: p. 4219-4225

The ability to detect and identify the physiochemical form of contaminants in the environment is important for degradation, fate and transport, and toxicity studies. This is particularly true of nanomaterials that exist as discrete particles rather than dissolved or sorbed contaminant molecules in the environment. Nanoparticles will tend to agglomerate or dissolve, based on solution chemistry, which will drastically affect their environmental properties. The current study investigates the use of field flow fractionation(FFF) interfaced to inductively coupled plasma-mass spectrometry (ICP-MS) as a sensitive and selective method for detection and characterization of silver nanoparticles. Transmission electron microscopy(TEM) is used to verify the morphology and primary particle size and size distribution of precisely engineered silver nanoparticles. Subsequently, the hydrodynamic size measurements by FFF are compared to dynamic light scattering (DLS) to verify the accuracy of the size determination. Additionally, the sensitivity of the ICP-MS detector is demonstrated by fractionation of g/L concentrations of mixed silver nanoparticle standards. The technique has been applied to nanoparticle suspensions prior to use in toxicity studies, and post-exposure biological tissue analysis. Silver nanoparticles extracted from tissues of these diment-dwelling, freshwater oligochaete Lumbriculus variegatus increased in size from approximately 31–46 nm, indicating a significant change in the nanoparticle characteristics during exposure.

Samberg, M.E., S.J. Oldenburg, and N.A. Monteiro-Riviere, Evaluation of Silver Nanoparticle Toxicity in Skin in Vivo and Keratinocytes in Vitro. Environ Health Perspect., 2010. 118(3): p. 407-413.

Samberg, M.E., P.E. Orndorff, and N.A. Monteiro-Riviere, Antibacterial efficacy of silver nanoparticles of different sizes, surface conditions and synthesis methods. Nanotoxicology, 2010. In Press.

Silver nanoparticles (Ag-nps) are used as a natural biocide to prevent undesired bacterial growth in clothing and cosmetics. The objective of this study was to assess the antibacterial efficacy of Ag-nps of different sizes, surface conditions, and synthesis methods against Escherichia coli, Ag-resistant E. coli, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and Salmonella sp. Ag-nps samples were synthesized by: Base reduction with unmodified surfaces and used as synthesized (‘unwashed’; 20, 50 and 80 nm) or after 20 phosphate buffer washes (‘washed’; 20, 50 and 80 nm), or synthesized by laser ablation with carbon-stabilized surfaces (‘carbon-coated’; 25 and 35 nm). Unwashed Ag-nps were toxic to all bacterial strains at concentrations between 3.0–8.0 μg/ml. The washed Ag-nps and carbon-coated Ag-nps were toxic to all bacterial strains except Ag-resistant E. coli at concentrations between 64.0–1024.0 μg/ml. Ag-resistant E. coli died only when treated with unwashed Ag-nps or its supernatant, both of which contained formaldehyde.

Speshock, J., et al., Silver and Gold Nanoparticles Alter Cathepsin Activity In vitro. Nanoscale Research Lett, 2011. 6(1): p. 17.

Speshock, J., et al., Interaction of silver nanoparticles with Tacaribe virus. Journal of Nanobiotechnology, 2010. 8(1): p. 19.

Silver nanoparticles possess many unique properties that make them attractive for use in biological applications. Recently they received attention when it was shown that 10 nm silver nanoparticles were bactericidal, which is promising in light of the growing number of antibiotic resistant bacteria. An area that has been largely unexplored is the interaction of nanomaterials with viruses and the possible use of silver nanoparticles as an antiviral agent.RESULTS:This research focuses on evaluating the interaction of silver nanoparticles with a New World arenavirus, Tacaribe virus, to determine if they influence viral replication. Surprisingly exposing the virus to silver nanoparticles prior to infection actually facilitated virus uptake into the host cells, but the silver-treated virus had a significant reduction in viral RNA production and progeny virus release, which indicates that silver nanoparticles are capable of inhibiting arenavirus infection in vitro. The inhibition of viral replication must occur during early replication since although pre-infection treatment with silver nanoparticles is very effective, the post-infection addition of silver nanoparticles is only effective if administered within the first 2-4 hours of virus replication.CONCLUSIONS:Silver nanoparticles are capable of inhibiting a prototype arenavirus at non-toxic concentrations and effectively inhibit arenavirus replication when administered prior to viral infection or early after initial virus exposure. This suggests that the mode of action of viral neutralization by silver nanoparticles occurs during the early phases of viral replication.

Stankus, D.P., et al., Interactions between Natural Organic Matter and Gold Nanoparticles Stabilized with Different Organic Capping Agents. Environmental Science & Technology, 2011. 45(8): p. 3238-3244.

The adsorption of natural organic matter (NOM) to the surfaces of natural colloids and engineered nanoparticles is known to strongly influence, and in some cases control, their surface properties and aggregation behavior. As a result, the understanding of nanoparticle fate, transport, and toxicity in natural systems must include a fundamental framework for predicting such behavior. Using a suite of gold nanoparticles (AuNPs) with different capping agents, the impact of surface functionality, presence of natural organic matter, and aqueous chemical composition (pH, ionic strength, and background electrolytes) on the surface charge and colloidal stability of each AuNP type was investigated. Capping agents used in this study were as follows: anionic (citrate and tannic acid), neutral (2,2,2-[mercaptoethoxy(ethoxy)]ethanol and polyvinylpyrrolidone), and cationic (mercaptopentyl(trimethylammonium)). Each AuNP type appeared to adsorb Suwannee River Humic Acid (SRHA) as evidenced by measurable decreases in zeta potential in the presence of 5 mg C Lâˆ’1 SRHA. It was found that 5 mg C Lâˆ’1 SRHA provided a stabilizing effect at low ionic strength and in the presence of only monovalent ions while elevated concentrations of divalent cations lead to enhanced aggregation. The colloidal stability of the NPs in the absence of NOM is a function of capping agent, pH, ionic strength, and electrolyte valence. In the presence of NOM at the conditions examined in this study, the capping agent is a less important determinant of stability, and the adsorption of NOM is a controlling factor.

Teodoro, J., et al., Assessment of the toxicity of silver nanoparticles in vitro: A mitochondrial perspective. Toxicology In Vitro, 2011. 25(3): p. 664-470.

Trickler, W.J., et al., Brain microvessel endothelial cells responses to gold nanoparticles: In vitro pro-inflammatory mediators and permeability. Nanotoxicology, 2010. In Press.

Trickler, W.J., et al., Silver Nanoparticle Induced Blood-Brain Barrier Inflammation and Increased Permeability in Primary Rat Brain Microvessel Endothelial Cells. Toxicological Sciences, 2010. 118(1): p. 160-170.

The current report examines the interactions of silver nanoparticles (Ag-NPs) with the cerebral microvasculature to identify the involvement of proinflammatory mediators that can increase blood-brain barrier (BBB) permeability. Primary rat brain microvessel endothelial cells (rBMEC) were isolated from adult Sprague-Dawley rats for an in vitro BBB model. The Ag-NPs were characterized by transmission electron microscopy (TEM), dynamic light scattering, and laser Doppler velocimetry. The cellular accumulation, cytotoxicity (6.2 +/- 50 ug/cm3) and potential proinflammatory mediators (interleukin [IL], IL-2, tumor necrosis factor [TNF] Î±, and prostaglandin E2 [PGE2]) of Ag-NPs (25, 40, or 80 nm) were determined spectrophotometrically, cell proliferation assay (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) and ELISA. The results show Ag-NP induced cytotoxic responses at lower concentrations for 25 and 40 nm when compared with 80-nm Ag-NPs. The proinflammatory responses in this study demonstrate both Ag-NPs size and time-dependent profiles, with IL-1B preceding both TNF and PGE2 for 25 nm. However, larger Ag-NPs (40 and 80 nm) induced significant TNF responses at 4 and 8 h, with no observable PGE2 response. The increased fluorescein transport observed in this study clearly indicates size-dependent increases in BBB permeability correlated with the severity of immunotoxicity. Together, these data clearly demonstrate that larger Ag-NPs (80 nm) had significantly less effect on rBMEC, whereas the smaller particles induced significant effects on all the end points at lower concentrations and/or shorter times. Further, this study suggests that Ag-NPs may interact with the cerebral microvasculature producing a proinflammatory cascade, if left unchecked; these events may further induce brain inflammation and neurotoxicity.

Aluminum Nanoparticles

Darlington, T.K., et al., Nanoparticle characteristics affecting environmental fate and transport through soil. Environmental Toxicology and Chemistry, 2009. 28(6): p. 1191-1199.

Nanoparticles are being used in broad range of applications; therefore, these materials probably will enter the environment during their life cycle. The objective of the present study is to identify changes in properties of nanoparticles released into the environment with a case study on aluminum nanoparticles. Aluminum nanoparticles commonly are used in energetic formulations and may be released into the environment during their handling and use. To evaluate the transport of aluminum nanoparticles, it is necessary not only to understand the properties of the aluminum in its initial state but also to determine how the nanoparticle properties will change when exposed to relevant environmental conditions. Transport measurements were conducted with a soil-column system that delivers a constant upflow of a suspension of nanoparticles to a soil column and monitors the concentration, size, agglomeration state, and charge of the particles in the eluent. The type of solution and surface functionalization had a marked effect on the charge, stability, and agglomeration state of the nanoparticles, which in turn impacted transport through the receiving matrix. Transport also is dependent on the size of the nanoparticles, although it is the agglomerate size, not the primary size, that is correlated with transportability. Electrostatically induced binding events of positively charged aluminum nanoparticles to the soil matrix were greater than those for negatively charged aluminum nanoparticles. Many factors influence the transport of nanoparticles in the environment, but size, charge, and agglomeration rate of nanoparticles in the transport medium are predictive of nanoparticle mobility in soil.

Monteiro-Riviere, N.A., S.J. Oldenburg, and A.O. Inman, Interactions of aluminum nanoparticles with human epidermal keratinocytes. Journal of Applied Toxicology, 2009. 30(3): p. 276-285.

Aluminum nanoparticles (Al NP) have been used in applications as diverse as drug delivery, material surface coatings and an ingredient for solid rocket fuel in military explosives and artillery. Although Al NP are used in many civilian and military applications, the health and safety implications of these nanosize particles are not known. To understand the interactions and biological activity of Al NP in human cells, cultured human neonatal epidermal keratinocytes (HEK) were exposed for 24 h to 50 and 80 nm Al NP in concentrations from 4.0 to 0.0004 mg ml−1 to assess the cytotoxicity and inflammatory potential. UV–Vis measurements and nanoparticle controls revealed that the Al NP interact with the assay dyes. Viability did not decrease in HEK exposed to both the 50 and the 80 nm Al NP at all treatment concentrations with MTT, CellTiter 96® AQueous One (96 AQ) and alamar Blue® (aB) viability assays. The 96 AQ and aB assays interact with the Al NP less than MTT, and proved to be the best assays to use with these Al NP. TEM depicted Al NP localized within the cytoplasmic vacuoles of the cells. Cytokine data was variable, indicating possible nanoparticle interactions with the cytokine assays. These studies illustrate the difficulties involved in assessing the biological safety of nanomaterials such as Al NP due to media- and temperature-dependent particle agglomeration and nanoparticle interactions with biomarkers of cytotoxicity.

Gold Nanoparticles

Judy, J.D., J.M. Unrine, and P.M. Bertsch, Evidence for Biomagnification of Gold Nanoparticles within a Terrestrial Food Chain. Environmental Science & Technology, 2011. 45(2): p. 776-781.

Nanoparticles from the rapidly increasing number of consumer products that contain manufactured nanomaterials are being discharged into waste streams. Increasing evidence suggests that several classes of nanomaterials may accumulate in sludge derived from wastewater treatment and ultimately in soil following land application as biosolids. Little research has been conducted to evaluate the impact of nanoparticles on terrestrial ecosystems, despite the fact that land application of biosolids from wastewater treatment will be a major pathway for the introduction of manufactured nanomaterials to the environment. To begin addressing this knowledge gap, we used the model organisms Nicotiana tabacum L. cv Xanthi and Manduca sexta (tobacco hornworm) to investigate plant uptake and the potential for trophic transfer of 5, 10, and 15 nm diameter gold (Au) nanoparticles (NPs). Samples were analyzed using both bulk analysis by inductively coupled plasma mass spectrometry (ICP-MS) as well as spatially resolved methods such as laser ablation inductively coupled mass spectrometry (LA-ICP-MS) and X-ray fluorescence (XRF). Our results demonstrate trophic transfer and biomagnification of gold nanoparticles from a primary producer to a primary consumer by mean factors of 6.2, 11.6, and 9.6 for the 5, 10, and 15 nm treatments, respectively. This result has important implications for risks associated with nanotechnology, including the potential for human exposure.

The adsorption of natural organic matter (NOM) to the surfaces of natural colloids and engineered nanoparticles is known to strongly influence, and in some cases control, their surface properties and aggregation behavior. As a result, the understanding of nanoparticle fate, transport, and toxicity in natural systems must include a fundamental framework for predicting such behavior. Using a suite of gold nanoparticles (AuNPs) with different capping agents, the impact of surface functionality, presence of natural organic matter, and aqueous chemical composition (pH, ionic strength, and background electrolytes) on the surface charge and colloidal stability of each AuNP type was investigated. Capping agents used in this study were as follows: anionic (citrate and tannic acid), neutral (2,2,2-[mercaptoethoxy(ethoxy)]ethanol and polyvinylpyrrolidone), and cationic (mercaptopentyl(trimethylammonium)). Each AuNP type appeared to adsorb Suwannee River Humic Acid (SRHA) as evidenced by measurable decreases in zeta potential in the presence of 5 mg SRHA. It was found that 5 mg SRHA provided a stabilizing effect at low ionic strength and in the presence of only monovalent ions while elevated concentrations of divalent cations lead to enhanced aggregation. The colloidal stability of the NPs in the absence of NOM is a function of capping agent, pH, ionic strength, and electrolyte valence. In the presence of NOM at the conditions examined in this study, the capping agent is a less important determinant of stability, and the adsorption of NOM is a controlling factor.

Material Science and Composites

Ghezzo F., D.R. Smith, T.N. Starr, T. Perram, A.F. Starr, T.K. Darlington, R.K. Baldwin, and S.J. Oldenburg. Development and characterization of healable carbon fiber composites with a reversibly cross linked polymer (2010) Journal of Composite Materials, 44 (13), p. 1587-1603.

Carbon fiber reinforced polymer (CFRP) laminates with remendable cross-linked polymeric matrices were fabricated using a modified resin transfer mold (RTM) technique. The healable composite resin, bis-maleimide tetrafuran (2MEP4F), was synthesized by mixing two monomers, furan (4F) and maleimide (2MEP), at elevated temperatures. The fast kinetic rate of the reaction of polymer constituents requires a fast injection of the healable resin into the carbon fiber preform. The polymer viscosity as a function of time and temperature was experimentally quantified in order to optimize the fabrication of the composite material and to guarantee a uniform flow of the resin through the reinforcement. The method was validated by characterizing the thermo-mechanical properties of the polymerized 2MEP4F. Additionally, the thermo-mechanical properties of the remendable CFRP material were studied.

Park, J.S., T. Darlington, A.F. Starr, K. Takahashi, and T.H. Hahn. Multiple healing effect of thermally activated self-healing composites based on Diels-Alder reaction. Composites Science and Technology, 70 (15), p. 2154-2159.

Self-healing composites using a thermally mendable polymer, bis-maleimide tetrafuran (2MEP4F), based on Diels–Alder reaction and electrical resistive heating were fabricated using a vacuum assisted injection molding method. Delaminations were induced using short span three point bending on composite coupons. The induced damage and permanent deformation of the composite coupons were observed using X-ray micro-tomography. The same procedure was repeated to confirm multiple healings after electrical resistive heating and healing efficiency of the samples was determined. The permanent deformations and induced delaminations were repaired after the heating process, which is due to both healing and shape memory effects. The multiple healing ability and shape memory effect of the fabricated composite combined with electrical resistive heating realizes a noble self-healing composite.

Plasmonics and Optics

Hill, R.T., J.J. Mock, Y. Urzhumov, D.S. Sebba, S.J. Oldenburg, S.Y. Chen, A.A Lazarides, A. Chilkoti, and D.R. Smith. Leveraging Nanoscale Plasmonic Modes to Achieve Reproducible Enhancement of Light. Nano Letters 2010 10 (10), p. 4150-4154.

The strongly enhanced and localized optical fields that occur within the gaps between metallic nanostructures can be leveraged for a wide range of functionality in nanophotonic and optical metamaterial applications. Here, we introduce a means of precise control over these nanoscale gaps through the application of a molecular spacer layer that is self-assembled onto a gold film, upon which gold nanoparticles (NPs) are deposited electrostatically. Simulations using a three-dimensional finite element model and measurements from single NPs confirm that the gaps formed by this process, between the NP and the gold film, are highly reproducible transducers of surface-enhanced resonant Raman scattering. With a spacer layer of roughly 1.6 nm, all NPs exhibit a strong Raman signal that decays rapidly as the spacer layer is increased.

Schweikhard, V., A. Grubisic, T.A. Baker, and D.J. Nesbitt. Multiphoton Scanning Photoionization Imaging Microscopy for Single-Particle Studies of Plasmonic Metal Nanostructures. J Phys Chem C, 2011, 115, p. 83-91.

Photoionization studies of single Au and Ag metal nanostructures are presented, using a scanning multiphoton photoionization microscope (SPIM) with single-electron detection capability. Four-photon photoemission following ultrafast excitation at around 840 nm and two-photon photoemission following excitation at 420 nm yield high signal-to-noise 2D photoelectron images for a variety of sample materials. By way of a test demonstration of the technique, we present results obtained from SPIM imaging photolithographically patterned gold nanostructures, as well as chemically prepared crystalline gold nanorods and polycrystalline silver nanospheres. For both chemically prepared samples, striking differences in the photoemissive properties of individual nanoparticles are observed that have gone unnoticed in bulk studies. Under 840 nm excitation, for example, each Au nanorod on a Pt substrate exhibits a clear cos⁸(θ−θ₀) dependence of photoemission strength on the angle between laser polarization (θ) and the rod axis (θ₀), suggesting that four-photon photoemission is initiated by excitation of the long-axis dipolar plasmon resonance. Surprisingly, strongly polarization-dependent photoelectron signals are also observed for nominally spherical Ag nanoparticles, albeit with varying degrees of anisotropy for different particles. AFM images of identically prepared samples reveal coverages that are consistent with those observed in SPIM images, suggesting that particle aggregation is at least not a predominant effect. One possibility consistent with the data is that localized regions of concentrated electric fields (i.e., “hot spots”) or local variations of the emission propensity in these polycrystalline particles may be responsible for the polarization anisotropy, as well as dramatic temporal variations in the electron emission intensities. In summary, the studies presented here establish the SPIM technique as a new approach to exploring local electronic properties of individual metallic nanostructures.

Sebba, D.S., D.A. Watson, and J.P. Nolan. High Throughput Single Nanoparticle Spectroscopy. ACS Nano, 2009, 3 (6), p. 1477-1484.

Progress in the development and application of nanoengineered systems is limited by the availability of quantitative measurement techniques. For the engineering of nanoparticle (NP)-based systems, single NP characterization is essential, but existing methods are slow and low thoughput. We demonstrate a flow spectroscopy technique capable of analyzing hundreds of nanoparticles per second and use this technique for the high throughput analysis of nanoparticle surface-enhanced resonant Raman scattering (SERRS) tags. By measuring Rayleigh and Raman scattering from thousands of individual tags, tag preparations can be characterized based on their brightness and uniformity. The rapid analysis of individual nanoparticles using high spectral resolution flow spectroscopy will be useful in many areas of nanoengineering.

Chuntonov, L., and G. Haran. Trimeric Plasmonic Molecules: The Role of Symmetry. Nano Letters, 2011, Articles ASAP.

Artificial plasmonic molecules possess excitation modes that are defined by their symmetry and obey group theory rules, just like conventional molecules. We follow the evolution of surface-plasmon spectra of plasmonic trimers, assembled from equal-sized silver nanoparticles, as gradual geometric changes break their symmetry. The spectral modes of an equilateral triangle, the most symmetric structure of a trimer, are degenerate. This degeneracy is lifted as the symmetry is lowered when one of the vertex angles in opened, which also leads to a subtle transition between bright and dark modes. Our experimental results are quantitatively explained using numerical simulations and plasmon hybridization theory.

MALDI

Spencer, M.T., H. Furatani, S.J. Oldenburg, T.K. Darlington, and K.A. Prather. Gold Nanoparticles as a Matrix for Visible-Wavelength Single-Particle Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry of Small Biomolecules The Journal of Physical Chemistry C 2008 112 (11), p. 4083-4090.

Gold nanoparticles (GNPs) are used as the matrix for visible-wavelength matrix-assisted laser desorption/ionization (VIS-MALDI) of individual aerosol particles containing 50 attomole of a small peptide. A dual polarity time-of-flight mass spectrometer was used to obtain both positive and negative ion mass spectra simultaneously from individual particles using a tunable wavelength desorption/ionization laser. The wavelength of the laser was changed from λ = 440 to 680 nm to observe the wavelength dependence of analyte ion formation. Detection of the positive sodiated molecular ions and negative deprotonated molecular ion of a small peptide was only possible using 5-nm GNPs and not with larger sized (19- and 44-nm) GNPs. While the masses of gold within the sample particles were similar, surface areas were about 10 times more in the 5-nm GNPs, suggesting the total surface area of GNPs within the sample particles may play a role in the formation of molecular ions. At wavelengths near the peak plasmon resonance of the GNPs (λ = 500−540 nm), negative molecular ion signals from a small peptide was higher than with desorption/ionization at λ = 440 nm, with increased fragmentation observed at λ = 440 nm. At wavelengths longer than the peak plasmon absorption, the ability to generate a detectable ion signal decreased rapidly, which is consistent with the steep decrease in the absorbance of GNPs by surface plasmon resonance at these wavelengths. Silver nanoparticles, which also exhibit a surface plasmon resonance, were tested and under our conditions did not appear to work as well. The presented results demonstrate that noble metal nanoparticle matrices can be used for on-line VIS-MALDI analysis of small molecular weight species such as peptides or sugars.