Single NPs Research Articles

Probing of multidrug ABC membrane transporters of single living cells using single plasmonic nanoparticle optical probes

Currently, molecular mechanisms of multidrug ABC (ATP-binding cassette) membrane transporters remain elusive. In this study, we synthesized and characterized purified spherically shaped silver nanoparticles (Ag NPs) (11.8 +/- 2.6 nm in diameter), which were stable (non-aggregation) in PBS buffer and inside single living cells. We used the size-dependent localized surface plasmon resonance (LSPR) spectra of single Ag NPs to determine their sizes and to probe the size-dependent transport kinetics of the ABC (BmrA, BmrA-EGFP) transporters in single living cells (Bacillus subtilis) in real time at nanometer resolution using dark-field optical microscopy and spectroscopy (DFOMS). The results show that the smaller NPs stayed longer inside the cells than larger NPs, suggesting size-dependent efflux kinetics of the membrane transporter. Notably, accumulation and efflux kinetics of intracellular NPs for single living cells depended upon the cellular expression level of BmrA, NP concentrations, and a pump inhibitor (25 muM, orthovanadate), suggesting that NPs are substrates of BmrA transporters and that passive diffusion driven by concentration gradients is the primary mechanism by which the NPs enter the cells. The accumulation and efflux kinetics of intracellular NPs for given cells are similar to those observed using a substrate (Hoechst dye) of BmrA, demonstrating that NPs are suitable probes for study of multidrug membrane transporters of single living cells in real-time. Unlike fluorescent probes, single Ag NPs exibit size-dependent LSPR spectra and superior photostability, enabling them to probe the size-dependent efflux kinetics of membrane transporters of single living cells in real-time for better understanding of multidrug resistance.

Study of cytotoxic and therapeutic effects of stable and purified silver nanoparticles on tumor cells.

We have synthesized and purified silver nanoparticles (Ag NPs) (11.3+/-2.3 nm) that are stable (non-aggregated) in cell culture medium and inside single living cells. We have developed new imaging methods to characterize sizes and number of single NPs in the medium and in single living cells in real-time and determine their stability (non-aggregation) in the medium and in single living cells at single NP resolution. These new approaches allow us to study toxic and therapeutic effects of single Ag NPs on tumor cells (L929, mouse fibroblast cells) with determined sizes and concentrations (doses) of NPs over time at single NP and single cell resolution. We found that Ag NPs inhibited the growth and division of tumor cells and their nuclei, in a dose and time dependent manner, showing significant inhibitory effects and abnormal cells with giant undivided nuclei or multiple nuclei beyond 12 h incubation. The results show that Ag NPs inhibited the segregation of chromosomes, but not their replication. Intracellular Ag NPs were well distributed in the cell population, and located in the nuclei and cytoplasm with higher numbers in the cytoplasm. This study demonstrates the possibility of using Ag NPs to inhibit the growth and division of tumor cells and using their cytotoxicity for potential therapeutic treatments. This study offers a new method to count the number of single NPs in the medium for characterization of their concentration and stability at single NP resolution over time.

A Novel Approach for Monodisperse Samarium Orthovanadate Nanocrystals: Controlled Synthesis and Characterization

A new solvothermal approach has been developed for the synthesis of monodisperse and well-crystallized SmVO4 nanocrystals with different morphologies from the reaction of Sm(OA)3 and VO4(TOA)3 complexes in toluene in the presence of surfactant (oleylamine or oleic acid) through a solvothermal pathway. The present solvothermal approach is simple and reproducible and employs a relatively mild reaction temperature. The obtained SmVO4 nanocrystals were characterized by means of transmission electron microscopy, selected area electronic diffraction (SAED), X-ray diffraction (XRD), Elemental dispersive spectrum, X-ray photoelectron spectra (XPS), UV−visible, thermogravimetric differential thermal analysis TGA−DTA, FTIR, and N2 adsorption/desorption isotherms (BET) techniques. The SAED and XRD patterns confirmed that the structure of the synthized SmVO4 nanocrystals is single-crystalline tetragonal. The size, shape, and aspect ratio of products can be readily controlled by adjusting the reaction parameters, such as the nature and amount of surfactant, and the concentration of the metal complex precursors. The SmVO4 nanocrystals with spherical and hexagonal shapes were obtained by using oleylamine or oleic acid as a nonselective and selective surfactant, respectively, under the same synthesis conditions. Furthermore, the average particle size is tunable from 30 to 3 nm by increasing the oleylamine concentration from 0.025 to 0.43 M in the synthesis solution. The shape evolution from nanocores to nanowires can also be obtained by increasing the metal complex precursor concentration; it is associated with the increase in the chemical potential in the reaction solution. The XPS results revealed only one oxidation state for Sm3+ and V5+ on the SmVO4 nanocrystal surface, even after calcinations compared two oxidation states (e.g., Sm2+/Sm3+ and V4+/V5+) of the single samarium oxide and vanadium oxide NPs, respectively. Our synthetic approach can be further extended to the synthesis of other uniform rare earth orthovanadate, molybdate, and tungstate nanocrystals.

Nanosensors Based on Viologen Functionalized Silver Nanoparticles: Few Molecules Surface-Enhanced Raman Spectroscopy Detection of Polycyclic Aromatic Hydrocarbons in Interparticle Hot Spots

The functionalization of silver nanoparticles (Ag NPs) by viologen dications (VGDs) is reported in this work as well as their applications in the surface-enhanced Raman scattering (SERS) detection of polycyclic aromatic hydrocarbons (PAHs). VGDs are able to form intermolecular cavities at interparticle junctions (SERS hot spots) where the analyte can be allocated. This leads to a giant intensification of the Raman emission of the target molecule. This effect was applied in the detection of PAHs, one of the most widespread and dangerous group of pollutants existing in the atmosphere and waters. A comparison between sensing-systems based on different VGDs (lucigenin, diquat, and paraquat) was done for the detection of two PAHs (pyrene and benzo[c]phenanthrene). The functionalization with lucigenin (LG) provided the most powerful and stable VGD-NPs sensor, which allowed the SERS detection of pyrene (PYR) down to 10(-9) M in the macro setup and in the zeptomole range for spectra obtained by single NPs aggregates (micro setup). Besides, SERS spectra afforded important structural information about the interaction mechanism of VGD and PAHs, revealing the formation of a CT complex between the VGD and PYR and changes in the host conformation. The position of the nu(Ag-Cl) band and the plasmon resonance contribution assigned to Ag dimers were also used as spectral markers to monitor the host-guest interaction.

Surface chemistry and photoluminescence property of functionalized silicon nanoparticles

We report an efficient method of producing macroscopic quantity of functionalized silicon nanoparticles (Si NPs) with bright photoluminescence (PL). Single crystalline Si NPs were synthesized in a microwave plasma reactor via pyrolysis of silane (SiH 4). Organic molecules were grafted onto the Si surface by reacting freshly etched NPs with 1-hexadecene at high temperature. Both freshly prepared and coated Si NPs were analyzed by Fourier transform infrared (FTIR) spectroscopy to evaluate the effectiveness of the surface modification. An increase in the PL intensity and a blue shift in the emission spectrum of functionalized Si NPs were observed compared to as-prepared NPs. The change in particle shape and morphology before and after the surface grafting was investigated by transmission electron microscopy (TEM). The electron diffraction patterns confirmed that Si NPs maintain their crystallinity after the functionalization process. In addition, functionalized Si NPs showed a red shift in the PL emission spectrum after air oxidation, which originated from the oxidation of remaining Si–H bonds on the surface.

Thermo-optical Properties of Nanoparticles and Nanoparticle Complexes Embedded in Ice: Characterization of Heat Generation and Actuation of Larger-scale Effects

ABSTRACTWe have investigated the thermo-optical properties of gold NPs embedded in an ice matrix [1]. Resonant laser light of relatively weak intensity is able to melt ice with embedded Au NPs, whereas even a very intense laser beam does not melt ice alone. This comes from strong absorption in Au NPs in the regime of plasmon resonance. By recording time-resolved Raman signals, we observe the melting process and determine the threshold melting power , where is the background temperature. We also observe relatively large scattering in the threshold laser intensity that leads to melting of the ice because of the mesoscopic nature of the sample. We can understand this observation using the TEM images of NPs, showing that geometry of NP complexes varies greatly. In our recent theoretical paper we showed that the local temperature inside and around a NP complex depends strongly on its geometry, and this leads to large scattering for the measured as a function of the reduced temperature, for different complexes [2].We recently discovered that NPs immobilized on glass surfaces can be characterized by single particle spectroscopy. Single and small NP clusters can be discriminated using the integrated intensity of the plasmon emission band. A cluster of four gold NPs has ∼ 4 times the intensity of a single gold NP. When the NPs are aggregated into a cluster then broadening of the intensity profile plot is not observed Gold NPs that are not clustered together but are found within the excitation volume will lead to a broadening of a cross sectional slice. We will use these principles to determine the amount of heat generation from single and clustered gold NPs.[1] H. H. Richardson, Z. N. Hickman, A. O. Govorov, A. C. Thomas, W. Zhang, M. E. Kordesch, Nano Lett. (2006); DOI: 10.1021/nl060105l.[2] A. O. Govorov, H. H. Richardson, W. Zhang, and T. Skeini, Nanoscale Res. Lett. 1, 100101 (2005).