Cellular imaging using temporally flickering nanoparticles

Roadmap on Label-Free Super-Resolution Imaging

Label-free super-resolution (LFSR) imaging relies on light-scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super-resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state-of-the-art in this field, and to discuss the resolution boundaries and hurdles which need to be overcome to break the classical diffraction limit of the LFSR imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction-limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super-resolution capability which are based on understanding resolution as an information science problem, on using novel structured illumination, near-field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere-assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field.

Gold nanoparticles conjugated with anti-CD133 monoclonal antibody and 5-fluorouracil chemotherapeutic agent as nanocarriers for cancer cell targeting

The enhanced permeability and retention effect allows for passive targeting of solid tumours by nanoparticles carrying anticancer drugs. However, active targeting by incorporation of various ligands onto nanoparticles can provide for a more selective and enhanced chemotherapeutic effect and complement the deficiencies of the passive targeting approach. Here we report on the design of the carboxyl-terminated PEGylated gold nanoparticles (AuNPs), their functionalization with anti-CD133 monoclonal antibody (mAb) via a crosslinking reaction, and subsequent 5-fluorouracil (5-FU) drug loading. The synthesized products in the form of stable colloids were characterised using a range of physicochemical techniques, including X-ray diffraction (XRD), UV-Vis spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). Conjugation of anti-CD133 mAb onto PEGylated AuNPs was confirmed with the use of UV-Vis, BCA protein assay and fluorescence microscopy. HCT116 colorectal cancer cells abundantly expressed CD133: 92.4 ± 1.3%, as measured by flow cytometry. Whereas PEGylated AuNPs not conjugated with anti-CD133 mAb accumulated mainly at the cellular membrane, nanoparticles conjugated with anti-CD133 mAb were contained within the nuclear region of the cells. Anti-CD133 mAb conjugation facilitated the specific intracellular uptake due to specific antigen-antibody binding interaction. In vitro cytotoxicity studies on HCT116 cells showed that PEGylated AuNPs and PEGylated AuNPs-CD133 did not elicit any toxicity at any of the tested concentrations. Meanwhile, 5-FU-PEGylated AuNPs-CD133 significantly reduced the cell viability relative to the treatment with 5-FU-PEGylated AuNPs without anti-CD133 mAb conjugates (p < 0.0001). This study shows that the conjugation of nanocarriers with the anti-CD133 antibody improves the specific targeting of 5-FU against colorectal cancer cells. These results demonstrate that simultaneous functionalisation of PEGylated AuNPs with antibodies and chemotherapeutic drugs is a viable strategy to combat cancer through targeted drug delivery.

Imaging of nanoparticle dynamics in live and apoptotic cells using temporally-modulated polarization

Gold nanoparticles are widely exploited in phototherapy. Owing to their biocompatibility and their strong visible-light surface plasmonic resonance, these particles also serve as contrast agents for cell image enhancement and super-resolved imaging. Yet, their optical signal is still insufficiently strong for many important real-life applications. Also, the differentiation between adjacent nanoparticles is usually limited by the optical resolution and the orientations of non-spherical particles are unknown. These limitations hamper the progress in cell research by direct optical microscopy and narrow the range of phototherapy applications. Here we demonstrate exploiting the optical anisotropy of non-spherical nanoparticles to achieve super-resolution in live cell imaging and to resolve the intracellular nanoparticle orientations. In particular, by modulating the light polarization and taking advantage of the polarization-dependence of gold nanorod optical properties, we realize the 'lock-in amplification', widely-used in electronic engineering, to achieve image enhancement in live cells and in cells that undergo apoptotic changes.

Nanoparticles: synthesis and applications

This chapter focuses on the synthesis, functionalization, and applications of metallic, semiconductor, magnetic, and multifunctional nanoparticles. Synthesis methods such as chemical reduction, coprecipitation, seeding, microemulsion, hydrothermal synthesis, and sonoelectrodeposition are outlined. Functionalized nanoparticles are suitable for numerous applications. Several applications of nanoparticles in life sciences and the enviromment are discussed. Finally, some future trends are pointed out.

Improved Margins Detection of Regions Enriched with Gold Nanoparticles inside Biological Phantom

Utilizing the surface plasmon resonance (SPR) effect of gold nanoparticles (GNPs) enables their use as contrast agents in a variety of biomedical applications for diagnostics and treatment. These applications use both the very strong scattering and absorption properties of the GNPs due to their SPR effects. Most imaging methods use the light-scattering properties of the GNPs. However, the illumination source is in the same wavelength of the GNPs' scattering wavelength, leading to background noise caused by light scattering from the tissue. In this paper we present a method to improve border detection of regions enriched with GNPs aiming for the real-time application of complete tumor resection by utilizing the absorption of specially targeted GNPs using photothermal imaging. Phantoms containing different concentrations of GNPs were irradiated with a continuous-wave laser and measured with a thermal imaging camera which detected the temperature field of the irradiated phantoms. By modulating the laser illumination, and use of a simple post processing, the border location was identified at an accuracy of better than 0.5 mm even when the surrounding area got heated. This work is a continuation of our previous research.

Three dimensional imaging of gold-nanoparticles tagged samples using phase retrieval with two focus planes

Optical sectioning microscopy can provide highly detailed three dimensional (3D) images of biological samples. However, it requires acquisition of many images per volume, and is therefore time consuming, and may not be suitable for live cell 3D imaging. We propose the use of the modified Gerchberg-Saxton phase retrieval algorithm to enable full 3D imaging of gold-particle tagged samples using only two images. The reconstructed field is free space propagated to all other focus planes using post processing, and the 2D z-stack is merged to create a 3D image of the sample with high fidelity. Because we propose to apply the phase retrieving on nano particles, the regular ambiguities typical to the Gerchberg-Saxton algorithm, are eliminated. The proposed concept is presented and validated both on simulated data as well as experimentally.

K-factor image deshadowing for three-dimensional fluorescence microscopy

The ability to track single fluorescent particles within a three dimensional (3D) cellular environment can provide valuable insights into cellular processes. In this paper, we present a modified nonlinear image decomposition technique called K-factor that reshapes the 3D point spread function (PSF) of an XYZ image stack into a narrow Gaussian profile. The method increases localization accuracy by ~60% with compare to regular Gaussian fitting, and improves minimal resolvable distance between overlapping PSFs by ~50%. The algorithm was tested both on simulated data and experimentally.

Increased localization precision by interference fringe analysis

We report a novel optical single-emitter-localization methodology that uses the phase induced by path length differences in a Mach-Zehnder interferometer to improve localization precision. Using information theory, we demonstrate that the localization capability of a modified Fourier domain signal generated by photon interference enables a more precise localization compared to a standard Gaussian intensity distribution of the corresponding point-spread function. The calculations were verified by numerical simulations and an exemplary experiment, where the centers of metal nanoparticles were localized to a precision of 3 nm.

Cellular superresolved imaging of multiple markers using temporally flickering nanoparticles

In this paper we present a technique aimed for simultaneous detection of multiple types of gold nanoparticles (GNPs) within a biological sample, using lock-in detection. We image the sample using a number of modulated laser beams that correspond to the number of GNP species that label a given sample. The final image where the GNPs are spatially separated is obtained computationally. The proposed method enables the simultaneous superresolved imaging of different areas of interest within biological sample and also the spatial separation of GNPs at sub-diffraction distances, making it a useful tool in the study of intracellular trafficking pathways in living cells.

Superresolved labeling nanoscopy based on temporally flickering nanoparticles and the K-factor image deshadowing

Localization microscopy provides valuable insights into cellular structures and is a rapidly developing field. The precision is mainly limited by additive noise and the requirement for single molecule imaging that dictates a low density of activated emitters in the field of view. In this paper we present a technique aimed for noise reduction and improved localization accuracy. The method has two steps; the first is the imaging of gold nanoparticles that labels targets of interest inside biological cells using a lock-in technique that enables the separation of the signal from the wide spread spectral noise. The second step is the application of the K-factor nonlinear image decomposition algorithm on the obtained image, which improves the localization accuracy that can reach 5nm and enables the localization of overlapping particles at minimal distances that are closer by 65% than conventional methods.