Single cell fluorescence imaging using metal plasmon-coupled probe

Synthesis of Fluorescent Core-Shell Metal Nanohybrids: A Versatile Approach

A flexible way of fabricating core-shell noble metal-organic nanohybrids with tailored chemical and spectroscopic properties is proposed here. The synthetic protocol consists of a multi-step procedure able to guarantee acceptable reproducibility of core size and shape as well as control of the organic outer layer. The proposed method highlights limitations in obtaining highly controllable products, although the heterogeneity degree of the nanostructures is in line with that expected from bottom-up approaches in solution. Selective functionalization of the nanohybrids with properly-substituted fluorescent dyes under variable experimental conditions allowed the preparation of composite systems of tunable spectroscopic properties to be employed as nanoprobes in sensing or photonic applications. To this end, preliminary investigation on embedding the nanohybrids in compatible polymeric matrices is also reported.

Light-Enhanced Fluorescence of Multi-Level Cavitands Possessing Pyridazine Upper rim

Completely different fluorescence behaviour of cavitands based on a same calix[4]resorcinarene compound was observed. While the fluorescence intensity of the parent compound, tetramethyl-cavitand (1) slowly faded as a result of UV-light exposure, the emission of the three-level cavitand with pyridazine moieties at the upper rim (5a) was enhanced by the excitation in the UV-region. The structure of fluorescence emission (characterized by excitation-emission matrices) and the absorption of 5a remained unaltered. The analysis of fluorescence decay curves reveals the presence of two separated components assigned to two individual emitting species. The measured significant increase of the average lifetime and quantum yield is the consequence of the UV-light induced transition between the different states of 5a. These observations can be explained by the structural difference between 5a and 1. As a counterpart of the naked cavitand (1) with methyl substituents at the upper rim only, 5a has three additional moieties benzene, triazole and pyridazine levels. Computational studies proved the existence of two conformational isomers of 5a. Upon ultraviolet light excitation a "dark" to "light" conformational transition occurs between the two isomers. This hypothesis was confirmed by anisotropy decay measurements.

Toxicological studies on silver nanoparticles: challenges and opportunities in assessment, monitoring and imaging

Silver nanoparticles (Ag NPs) are becoming increasingly prevalent in consumer products as antibacterial agents. The increased use of Ag NP-enhanced products may lead to an increase in toxic levels of environmental silver, but regulatory control over the use or disposal of such products is lagging due to insufficient assessment on the toxicology of Ag NPs and their rate of release into the environment. In this article we discuss recent research on the transport, activity and fate of Ag NPs at the cellular and organismic level, in conjunction with traditional and recently established methods of nanoparticle characterization. We include several proposed mechanisms of cytotoxicity based on such studies, as well as new opportunities for investigating the uptake and fate of Ag NPs in living systems.

Single plasmonic nanoparticles for biosensing

Along with remarkable progress of nanoplasmonics over the past 10 years, single plasmonic nanoparticle sensors have introduced a completely new dimension to the sensing scale, considering that nanoparticles are comparable in size to biomolecules such as nucleic acids or antibodies. Single particle sensing methods have recently shown the possibility of detecting the adsorption of single biomolecules, and have already provided information about conformational changes of single molecules. For practical application, arrays of such compact sensor units are expected to realize massive multiplexing and high throughput in diagnostics and drug discovery in the near future. In this review, recent achievements and perspectives of this emerging biosensing technique are discussed.

Fluorescent avidin-bound silver particle: a strategy for single target molecule detection on a cell membrane

Cy5-avidin conjugate-bound silver nanoparticles were prepared as a fluorescence molecular reagent for the cell imaging. Compared with the metal-free avidin conjugate, the avidin-metal complex was observed to display a stronger emission intensity, shorter lifetime, and better photostability. The avidin-metal complexes were conjugated with the biotin-sites on the surfaces of PM1 cell lines, and the cell images were recorded using scanning confocal microscopy. It was noticed that the avidin-metal complexes bound on the cell surfaces could be identified as the isolated emission spots distinct from the cellular autofluorescence. The emission intensity over the cell image was increased with an increase of the number of avidin-metal complexes on the cell surface but the lifetime was decreased. A quantitative regression curve was achieved between the amount of avidin-metal complex on the cell surface and the emission intensity or lifetime over the entire cell image. On the basis of this curve, we expect to develop an approach that can be used to quantify the amount of target molecules on the cell surfaces using the cell intensity and lifetime images at the single cell level.

Modification of single molecule fluorescence near metallic nanostructures

In recent years there has been a growing interest in the interactions of fluorophores with metallic nanostructures or nanoparticles. The spectra properties of fluorophores can be dramatically modified by near-field interactions with the electron clouds present in metals. Near-field interactions are those occurring within a wavelength distance of an excited fluorophore. These interactions modify the emission in ways not seen in ensemble fluorescence experiments. In this review we provide an insightful description of the photophysics of metal plasmons and near-field interactions. Additionally, we summarize recent works on single-molecule studies on metal-fluorophore interactions and suggest how these effects will result in new classes of experimental procedures, novel probes, bioassays and devices. The spectral properties of single fluorophores can be dramatically altered by near-field interactions with the electron clouds presented in metals.

Metallic Nanostructures as Localized Plasmon Resonance Enhanced Scattering Probes for Multiplex Dark Field Targeted Imaging of Cancer Cells

In this paper, we report the use of bioconjugated gold nanorods and silver nanoparticles as targeted localized surface plasmon resonance enhanced scattering probes for dark field multiplex and transmission electron microscopy (TEM) imaging of pancreatic cancer cells. We take advantage of the spectrally widely separated localized plasmon resonance of the gold nanorods and silver nanoparticles which produce wavelength selective plasmon resonance scattering to allow multiplex imaging with high contrast. By functionalizing the surfaces, aqueous dispersions of bioconjugated gold nanorods and silver nanoparticles are prepared. We demonstrate receptor-mediated delivery of bioconjugated gold nanorods and silver nanoparticles simultaneously into pancreatic cancer cells, using multiplexed dark field microscopy technique. We also show that the bioconjugated metallic nanostructures can be used for high contrast TEM imaging as well.

Enhanced fluorescence images for labeled cells on silver island films

Silver island films (SIFs) were deposited on glass substrates to serve as supports. T-Lymphocytic (PM1) cell lines were labeled by Alexa Fluor 680-dextran conjugates on the membranes or by YOYO in the nuclei. The fluorescence images of the cell lines were recorded in the emission intensity and lifetime using scanning confocal microscopy. The fluorescence signals by the fluorophores bound on the cell membranes were enhanced significantly by SIF supports as compared with those on the glass. In addition to the increase in the intensity, there was a dramatic shortening of the emission lifetime. In contrast to the Alexa Fluor 680 fluorophores on the membranes, the YOYO fluorophores intercalated in the cell nuclei were not influenced significantly by the silver islands. This result can be interpreted by an effect of the distance on coupling between the fluorophores and metal particles: the fluorophores on the cell membranes are localized within, but the fluorophores in the cell nuclei are beyond the region of metal-enhanced fluorescence. Thus, the metal supports can be used to improve the detection sensitivity for target molecules on cell surfaces when they are fluorescently labeled.

Single-cell fluorescence imaging using metal plasmon-coupled probe 2: single-molecule counting on lifetime image

Multiple Alexa Fluor 647-conjugated concanavalin A (conA) molecules were covalently bound to a single 20 nm silver particle to synthesize metal plasmon-coupled probes (PCPs). The fluorescence images were recorded by scanning confocal microscopy in both intensity and lifetime. The brightness of PCPs was 30-fold brighter than those of free conA and the lifetime of PCPs was shortened dramatically. PCPs were used to label T-lymphocytic ( PM1) cells. The emission spots by PCPs bound on the cell surfaces were separated clearly from the cell images by autofluorescence due to the brighter signal and shorter lifetime of PCPs. The emission spots by PCPs were also scanned in three dimensions to count the distribution of bound fluorophores on the cell surfaces. The metal-associated fluorophores thus are suggested using as novel molecular imaging agents to quantify the components and describe their distributions on the cell surfaces.