We show that metal nanoparticles can be used to improve the performance of super-resolution fluorescence nanoscopes based on stimulated-emission-depletion (STED). Compared with a standard STED nanoscope, we show theoretically a resolution improvement by more than an order of magnitude, or equivalently, depletion intensity reductions by more than 2 orders of magnitude and an even stronger photostabilization. Moreover, we present experimental evidence that an optimum resolution, limited by the sizes of the particles used, can be reached for the hybrid NPs for a power of the STED beam one order of magnitude smaller than for the bare cores.

We present a new technology for super-resolution fluorescence imaging, based on conical diffraction. Conical diffraction is a linear, singular phenomenon taking place when a polarized beam is diffracted through a biaxial crystal. The illumination patterns generated by conical diffraction are more compact than the classical Gaussian beam; we use them to generate a super-resolution imaging modality. Conical Diffraction Microscopy (CODIM) resolution enhancement can be achieved with any type of objective on any kind of sample preparation and standard fluorophores. Conical diffraction can be used in multiple fashion to create new and disruptive technologies for super-resolution microscopy. This paper will focus on the first one that has been implemented and give a glimpse at what the future of microscopy using conical diffraction could be.

Investigating the characteristics of the electromagnetic field generated inside plasmonically coupled metallic nanostructures with a small nanogap <1 nm is significantly important for the rational deign of plasmonic nanostructures with enormously enhanced electric field. Especially, plasmonic dimeric nanostructures have been heavily studied, mainly because of relatively easier structural reproducibility among the coupled multimeric nanostructures. However, controlling the geometrical structure with ~sub nm accuracy and the corresponding change in the magnitude of the electric field in a single dimeric nanostructure is still highly challenging, such that it is difficult to obtain reliable and reproducible surface-enhanced Raman scattering (SERS) signal essentially originating from the enhanced electric field inside the nanogap. This is indeed a critical issue because the SERS enhancement factors (EFs) exhibit a broad distribution (>10⁶) with a long population tail even within a single SERS hot-spot, which could be largely attributable to subtle change in the plasmonic nanostructures and the random orientation and position of an analyte molecule within the plasmonic hot spot. Therefore, it is of paramount importance to systematically investigate a relationship between the geometry of nanostructure and the optical signals at the singlemolecule and single-particle levels.

Modern farming relies highly on pesticides to protect agricultural food items from insects for high yield and better quality. Increasing use of pesticide has raised concern about its harmful effects on human health and hence it has become very important to detect even small amount of pesticide residues. Raman spectroscopy is a suitable nondestructive method for pesticide detection, however, it is not very effective for low concentration of pesticide molecules. Here, we report an approach based on plasmonic enhancement, namely, particle enhanced Raman spectroscopy (PERS), which is rapid, nondestructive and sensitive. In this technique, Raman signals are enhanced via the resonance excitation of localized plasmons in metallic nanoparticles. Gold nanostructures are promising materials that have ability to tune surface plasmon resonance frequency in visible to near-IR, which depends on shape and size of nanostructures. We synthesized gold nanorods (GNRs) with desired shape and size by seed mediated growth method, and successfully detected very tiny amount of pesticide present on food items. We also conformed that the detection of pesticide was not possible by usual Raman spectroscopy.

Being a scanning microscopy, Stimulated Emission Depletion (STED) needs to be parallelized for fast wide-field imaging. Here, we achieve large parallelization of STED microscopy using well-designed Optical Lattice (OL) for depletion, together with a fast camera for detection. Depletion optical lattices with 100 intensity “zeros” are generated by four-beam interference. Scanning only a unit cell, as small as 290 nm by 290 nm, of the depletion OL is sufficient for STED imaging. The OL-STED microscopy acquires super-resolution images with 70 nm resolution and at the speed of 80 ms per image.

Tip-enhanced Raman spectroscopy (TERS) is the technique that combines the nanoscale spatial resolution of a scanning probe microscope and the highly sensitive Raman spectroscopy enhanced by the surface plasmons. It is suitable for chemical analysis at nanometer scale. Recently, TERS exhibited powerful potential in analyzing the chemical reactions at nanoscale. The high sensitivity and spatial resolution of TERS enable us to learn the reaction processes more clearly. More importantly, the chemical reaction in TERS is assisted by surface plasmons, which provides us an optical method to manipulate the chemical reactions at nanoscale. Here using our home-built high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) setup, we successfully observed the plasmon-assisted molecule dimerization and dissociation reactions. In HV-TERS system, under laser illumination, 4-nitrobenzenethiol (4NBT) molecules can be dimerized to p,p’-dimercaptoazobenzene (DMAB), and dissociation reaction occurs for malachite green (MG) molecules. Using our HV-TERS setup, the dynamic processes of the reactions are clearly revealed. The chemical reactions can be manipulated by controlling the plasmon intensity through changing the power of the incident laser, the tunneling current and the bias voltage. We also investigated the role of plasmonic thermal effect in the reactions by measuring both the Stokes and anti- Stokes Raman peaks. Our findings extend the applications of TERS, which can help to study the chemical reactions and understand the dynamic processes at single molecular level, and even design molecules by the plasmon-assisted chemical reactions.

Advanced optical setups are continuously developed to gain deeper insight into microscopic matter. In this paper we report the expansion of a home-built parabolic mirror assisted scanning, near-field optical microscope (PMSNOM) by introducing four complementary functions. 1) We integrated a scanning tunneling feedback function in addition to an already existent shear-force feedback control mechanism. Hence a scanning tunneling microscope (STM)-SNOM is realized whose performance will be demonstrated by the tip-enhanced Raman peaks of graphene sheets on a copper substrate. 2) We integrated an ultrafast laser system into the microscope which allows us to combine nonlinear optical microscopy with hyperspectral SNOM imaging. This particular expansion was used to study influences of plasmonic resonances on nonlinear optical properties of metallic nanostructures. 3) We implemented a polarization angle resolved detection technique which enables us to analyze the local structural order of α-sexithiophene (α-6T). 4) We combined scanning photocurrent microscopy with the microscope. This allows us to study morphology related optical (Raman and photoluminescence) and electrical properties of optoelectronic systems. Our work demonstrates the great potential of turning a SNOM into an advanced multifunctional microscope.

In this work, we investigate the formation of interference patterns appearing in s-NSOM results. A single nanoslit is used to demonstrate the mechanism of formation of these interference patterns experimentaly: the interaction between the in-plane component of the incident light and SPP launched by the nanoslit. This is in contrast to some other explanations that the SPP is launched from the NSOM probe. We also use an analytical model and numerical simulations to compute the formation of interference patters. This study will help to understand s-NSOM results from plasmonic nanostructures.

We report mapping of the lateral magnetic near-field distribution of plasmonic resonant modes in different nanostructure geometries by hollow-pyramid probe aperture-SNOM. Using full-field simulations we investigate how the near-field probe acts as a confined light source and how it efficiently excites surface plasmons. This excitation occurs at lateral magnetic field maxima, enabling the visualization of the lateral magnetic near-field distribution with subwavelength spatial resolution. Our approach complements the available methods for imaging the different field components of light. [1] D. Denkova, N. Verellen et al., ACS nano 7(4), 3168-3176 (2013). [2] D. Denkova, N. Verellen et al., Small, accepted (2013).

The misfolding and self-assembly of intrinsically disordered proteins into insoluble amyloid structures is central to many neurodegenerative diseases such as Alzheimer’s and Parkinson’s Diseases. Optical imaging of this self-assembly process in vitro and in cells is revolutionising our understanding of the molecular mechanisms behind these devastating diseases. In contrast to conventional biophysical methods, optical imaging, and in particular optical super-resolution imaging, permit the dynamic investigation of the molecular self-assembly process in vitro and in cells, at molecular level resolution. In this article, current state-of-the-art imaging methods are reviewed and discussed in the context of research into neurodegeneration.

Imaging live biological samples to study biomolecular dynamics requires a very high spatial and temporal resolution. Superresolution localization microscopy has allowed researchers to investigate biological systems whose sizes are below the diffraction limit (200-250 nm) using an optical microscope. Fluorescence Photoactivation Localization Microscopy (FPALM) and other localization microscopy techniques have recently been shown to be capable of rendering superresolution images obtained with acquisitions of shorter than 0.5 seconds. Here we will discuss the FPALM imaging technique, at both lower and higher imaging speeds. This talk will focus on the advantages, challenges, and drawbacks of high speed imaging localization microscopy.

Nanoscale structures made from coinage metals such as gold or silver possess localized surface plasmon-polariton (LSP) excitations when the material interacts with light of the correct frequency and polarization. LSPs generated from freestanding 2D nanorod arrays have been applied to enable surface-enhanced Raman scattering (SERS) and surface enhanced fluorescence (SEF) spectra from Rhodamine 6G molecules adsorbed on the surface of the arrays. We study the conditions that optimize SERS and SEF from self-standing Au nanorod arrays by studying the effect of changing the surrounding environment using Al₂O₃ as a dielectric spacer layer.

Optical nanoscopy allows to study biological and functional processes of sub-cellular organelles. In structured illumination microscopy (SIM) the sample is illuminated with a grid-like interference pattern to encode higher spatial frequency information into observable Moiré patterns. By acquiring multiple images and a computation trick a superresolved image is obtained. SIM provides resolution enhancement of 2X in each axis as compared to conventional microscopes. For a visible light, SIM provides an optical resolution of 100 nm. The challenges associated with optical nanoscopy of a living cell are photo-toxicity, special dye requirements and artifacts due to cell movement. SIM works with conventional dyes and is a wide-field technique making it suitable for imaging living cells. In this work, we will discuss the opportunities and challenges of imaging living cells using SIM. Two applications of optical nanoscopy of living cells will be discussed; a) imaging of mitochondria in a keratinocyte cell and Optical microscopy based on fluorescence has emerged as a vital tool in modern bio-medical imaging and diagnosis. Super-resolution bio-imaging allows gathering information from sub-cellular organelles. In structured illumination microscopy (SIM) the sample is illuminated with a grid-like interference patterns to encode higher spatial frequencies information into observable images (Moiré fringes). A super-resolved image is then decoded using computational trick. In this work, we used SIM to acquired super-resolved optical images of mitochondria from a live keratinocyte cell (see Fig 1). SIM provides resolution enhancement of 2X in each axis and contrast enhancement of 8X on a projected image. Time-lapsed imaging was used to study the dynamics of mitochondria in a live cell.

We present a new super resolution imaging method, Localized Plasmon assisted Structured Illumination Microscopy (LPSIM). Using an array of localized plasmonic antennas, LPSIM provides dynamically tunable near-field excitations which result in finely structured illumination patterns, independent of any propagating surface plasmon dispersion limitations. Antenna geometry alone limits the illumination pattern feature sizes, enabling the collection of a far-field image resolved far beyond the diffraction limit. This approach allows a wide field of view and the capacity for a high frame-rate. Recovered images for various classes of objects are presented, demonstrating significant resolution improvement over existing methods.

We use an environmental scanning transmission electron microscope (ESTEM) equipped with electron energy loss spectroscopy (EELS) and a monochromated electron source to perform energy loss measurements on metallic nanoparticles (NPs) exposed to local gaseous environments at varying pressures. In particular, we characterize the effect of exposure to CO or H₂ on the surface plasmon resonance of a gold NP. By addressing various sites around the perimeter of a triangular NP (edge length ~20 nm) with the electron beam in STEM mode, the energy loss spectrum resulting from site-specific excitation of surface plasmon resonance is probed with a spatial resolution of ~1 nm and energy resolution of ~100 meV. Local gas adsorption is evidenced by peak shifts in the energy loss spectrum, which are found to be positive for CO and negative for H₂. Strong site selectivity is evident, with CO and H₂ adsorbing preferentially at the edge and corner sites, respectively. To characterize the sign and magnitude of the energy shifts, finite-difference time-domain (FDTD) simulations of electron-beam excitation of the NP are performed using a specialized model in which the local electron concentration is allowed to vary spatially over the particle volume. This is a result of both the inhomogeneous spatial distribution of the adsorbate and its degree of electronegativity.