Applications In Super-resolution Imaging Research Articles

Recent advances in super-resolution optical imaging based on aggregation-induced emission.

Super-resolution imaging has rapidly emerged as an optical microscopy technique, offering advantages of high optical resolution over the past two decades; achieving improved imaging resolution requires significant efforts in developing super-resolution imaging agents characterized by high brightness, high contrast and high sensitivity to fluorescence switching. Apart from technical requirements in optical systems and algorithms, super-resolution imaging relies on fluorescent dyes with special photophysical or photochemical properties. The concept of aggregation-induced emission (AIE) was proposed in 2001, coinciding with unprecedented advancements and innovations in super-resolution imaging technology. AIE probes offer many advantages, including high brightness in the aggregated state, low background signal, a larger Stokes shift, ultra-high photostability, and excellent biocompatibility, making them highly promising for applications in super-resolution imaging. In this review, we summarize the progress in implementation methods and provide insights into the mechanism of AIE-based super-resolution imaging, including fluorescence switching resulting from photochemically-converted aggregation-induced emission, electrostatically controlled aggregation-induced emission and specific binding-regulated aggregation-induced emission. Particularly, the aggregation-induced emission principle has been proposed to achieve spontaneous fluorescence switching, expanding the selection and application scenarios of super-resolution imaging probes. By combining the aggregation-induced emission principle and specific molecular design, we offer some comprehensive insights to facilitate the applications of AIEgens (AIE-active molecules) in super-resolution imaging.

Self-quenched Fluorophore Dimers for DNA-PAINT and STED Microscopy.

Super-resolution techniques like single-molecule localisation microscopy (SMLM) and stimulated emission depletion (STED) microscopy have been extended by the use of non-covalent, weak affinity-based transient labelling systems. DNA-based hybrid systems are a prominent example among these transient labelling systems, offering excellent opportunities for multi-target fluorescence imaging. However, these techniques suffer from higher background relative to covalently bound fluorophores, originating from unbound fluorophore-labelled single-stranded oligonucleotides. Here, we introduce short-distance self-quenching in fluorophore dimers as an efficient mechanism to reduce background fluorescence signal, while at the same time increasing the photon budget in the bound state by almost 2-fold. We characterise the optical and thermodynamic properties of fluorophore-dimer single-stranded DNA, and show super-resolution imaging applications with STED and SMLM with increased spatial resolution and reduced background.

Hyperbolic metamaterial structures based on graphene for THz super-resolution imaging applications: publisher’s note

This publisher’s note contains corrections to a production-related error to Opt. Mater. Express 13, 247 (2023)10.1364/OME.477107.

Compound super-oscillation lens for reflective confocal imaging

The super-oscillation lens (SOL) can achieve super-resolution focusing but have to trade-off with weaker hotspots and higher sidebands. We propose a single compound SOL to achieve reflective confocal imaging in principle without additional lenses. The designed SOL consists of an outer lens and an inner lens which play the role of focusing lens and collective lens respectively. As a result, focusing and collecting functions can be simultaneously realized. The improved system can achieve excellent imaging performance with an ultra-high resolution (<0.314λ/NA, NA stands for numerical aperture), and almost negligible side lobe ratio and no side bands, which proved superior to conventional laser scanning confocal microscopy and single SOL. This technology can be attractive for a variety of applications in super-resolution imaging and biomedical sciences.

Photothermal nonlinear scattering of shell-isolated gold nanoparticles and applications in super-resolution imaging

Photothermal nonlinear scattering of shell-isolated gold nanoparticles and applications in super-resolution imaging

Hyperbolic metamaterial structures based on graphene for THz super-resolution imaging applications

The diffraction limit of light due to the loss of evanescent waves that carry high spatial frequency information in the far field restricts the practical applications of terahertz imaging technology. In order to break the diffraction limit, we investigate the super-resolution capability of different types of multilayered graphene-dielectric hyperbolic metamaterials. A super-resolution of λ/10 is achieved for both the cylindrical and planar structures. A prominent advantage of graphene-dielectric hyperbolic structures is the dynamic tunability of the dispersion and super-resolution performance by adjusting the chemical potential of graphene through conveniently changing the gate voltage without modifying the geometry of the hyperbolic structures. Furthermore, we have investigated the influence of bilayer thickness variations on the super-resolution performance. Finally, we apply the planar hyperbolic structures for the super-resolution imaging and a roughly five-fold lateral resolution enhancement is realized in our approach. Due to many prominent advantages including super-resolution over broad spectral range, dynamic tunability, good stability and robustness, we believe this work could contribute to the improvement of the resolutions of terahertz imaging systems and the development of hyperbolic metamaterial modulation devices in the terahertz band.

Generation of Photonic Hooks under Point-Source Illumination from Patchy Microcylinders

Photonic hook (PH) is a new type of non-evanescent light beam with subwavelength curved structures. It has shown promising applications in super-resolution imaging and has the potential to be used in micromachining, optical trapping, etc. PHs are generally produced by illuminating mesoscale asymmetric particles with optical plane waves. In this work, we used the finite-difference time-domain (FDTD) method to investigate the PH phenomenon under point-source illumination. We found that the PHs can be effectively generated from point-source illuminated patchy particles. By changing the background refractive index, particle diameters and the position and coverage ratio of Ag patches, the characteristics of the PHs can be effectively tuned. Moreover, the structure of the intensity distribution of the light field generated from small and large particles can have an opposite bending direction due to the near-field light-matter interaction.

Aggregation-Induced Emission (AIE) in Super-resolution Imaging: Cationic AIE Luminogens (AIEgens) for Tunable Organelle-Specific Imaging and Dynamic Tracking in Nanometer Scale.

Organelle-specific imaging and dynamic tracking in ultrahigh resolution is essential for understanding their functions in biological research, but this remains a challenge. Therefore, a facile strategy by utilizing anion-π+ interactions is proposed here to construct an aggregation-induced emission luminogen (AIEgen) of DTPAP-P, not only restricting the intramolecular motions but also blocking their strong π-π interactions. DTPAP-P exhibits a high photoluminescence quantum yield (PLQY) of 35.04% in solids, favorable photostability and biocompatibility, indicating its potential application in super-resolution imaging (SRI) via stimulated emission depletion (STED) nanoscopy. It is also observed that this cationic DTPAP-P can specifically target to mitochondria or nucleus dependent on the cell status, resulting in tunable organelle-specific imaging in nanometer scale. In live cells, mitochondria-specific imaging and their dynamic monitoring (fission and fusion) can be obtained in ultrahigh resolution with a full-width-at-half-maximum (fwhm) value of only 165 nm by STED nanoscopy. This is about one-sixth of the fwhm value in confocal microscopy (1028 nm). However, a migration process occurs for fixed cells from mitochondria to nucleus under light activation (405 nm), leading to nucleus-targeted super-resolution imaging (fwhm= 184 nm). These findings indicate that tunable organelle-specific imaging and dynamic tracking by a single AIEgen at a superior resolution can be achieved in our case here via STED nanoscopy, thus providing an efficient method to further understand organelle's functions and roles in biological research.

A Fluorescent Sensor for Quantitative Super-Resolution Imaging of Amyloid Fibril Assembly.

Many soluble proteins can self-assemble into macromolecular structures called amyloids, a subset of which are implicated in a range of neurodegenerative disorders. The nanoscale size and structural heterogeneity of prefibrillar and early aggregates, as well as mature amyloid fibrils, pose significant challenges for the quantification of amyloid morphologies. We report a fluorescent amyloid sensor AmyBlink-1 and its application in super-resolution imaging of amyloid structures. AmyBlink-1 exhibits a 5-fold increase in ratio of the green (thioflavin T) to red (Alexa Fluor 647) emission intensities upon interaction with amyloid fibrils. Using AmyBlink-1, we performed nanoscale imaging of four different types of amyloid fibrils, achieving a resolution of ≈30 nm. AmyBlink-1 enables nanoscale visualization and subsequent quantification of morphological features, such as the length and skew of individual amyloid aggregates formed at different times along the amyloid assembly pathway.

Probing Chromatin Compaction and Its Epigenetic States in situ With Single-Molecule Localization-Based Super-Resolution Microscopy.

Chromatin organization play a vital role in gene regulation and genome maintenance in normal biological processes and in response to environmental insults. Disruption of chromatin organization imposes a significant effect on many cellular processes and is often associated with a range of pathological processes such as aging and cancer. Extensive attention has been attracted to understand the structural and functional studies of chromatin architecture. Biochemical assays coupled with the state-of-the-art genomic technologies have been traditionally used to probe chromatin architecture. Recent advances in single molecule localization microscopy (SMLM) open up new opportunities to directly visualize higher-order chromatin architecture, its compaction status and its functional states at nanometer resolution in the intact cells or tissue. In this review, we will first discuss the recent technical advantages and challenges of using SMLM to image chromatin architecture. Next, we will focus on the recent applications of SMLM for structural and functional studies to probe chromatin architecture in key cellular processes. Finally, we will provide our perspectives on the recent development and potential applications of super-resolution imaging of chromatin architecture in improving our understanding in diseases.

Resolution Limits of Hyper-Hemispherical Silicon Lens-Integrated THz Cameras Employing Geometrical Multiframe Super-Resolution Imaging

In this article, we present a comprehensive study to understand the image formation and associated resolution limitations of hyper-hemispherical high-resistivity floating-zone silicon (HRFZ-Si) lens-integrated terahertz (THz) cameras, and we extend this understanding into THz super-resolution imaging applications. Along these lines, design tradeoffs between fixed field-of-view and frequency-dependent angular resolution of such cameras are also discussed. The present study is based on investigations of a CMOS THz camera that is made of a <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">32</b> × <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">32</b> -pixel focal plane array sensor and a 15-mm diameter objective hyper-hemispherical HRFZ-Si lens. Two experiments are performed at 0.652 THz. In the first experiment, THz geometrical multiframe super-resolution imaging is performed to demonstrate that such cameras can always reach the maximum achievable resolution in their entire operating bandwidth. In the other, a full radiation pattern scan is performed to measure aberrations of off-axis displaced pixels in order to give a comprehensive picture of the camera's resolution behavior across the full camera frame. The investigations and discussions are general in nature and should be applicable to any broadband THz camera.

Photon-avalanche-like upconversion in NdAl3(BO3)4 nanoparticles excited at 1064 nm

We report efficient nonresonant ground-state excitation at 1064 nm of trivalent neodymium (Nd3+) ions in stoichiometric neodymium aluminum borate NdAl3(BO3)4 nanoparticles, which are crystalline and, besides the large content of Nd3+ ions, present excellent photoluminescence properties. Upconversion (UC) emission was observed, and the energy pathways were identified starting from multi-phonon assisted ground-state absorption (4I9/2 → 4F3/2) and excited-state absorption (4I11/2 → 4F3/2) with the population of the 4I11/2 level by thermal coupling with the ground state. The excited state 4I11/2 is also populated by relaxations of the Nd3+ ions at upper-lying levels. Cross-relaxation between two Nd3+ ions (4F3/2, 4I9/2) → (4I15/2, 4I15/2) with subsequent phonon emission leads to two ions at the 4I11/2 level, with every iteration triggering a photon-avalanche-like emission, which greatly enhances the efficiency of the UC emissions. Ladder thermal excitation 4F3/2 → (4F5/2, 2H9/2) → (4F7/2, 4S3/2) → 4F9/2 was achieved, and the ground-state relaxation from these levels provided emission at 880 nm, 810 nm, 750 nm, and 690 nm, respectively. Energy transfer UC (Auger) between Nd3+ ions at the 4F3/2 level allowed the population of (2G3/2, 4G7/2) from which relaxations to the 4I9/2, 4I11/2, and 4I13/2 states provided emissions around 536 nm, 600 nm, and 660 nm, respectively. Associated with the nonradiative relaxations, we observed the heating of the nanoparticles (22 °C–240 °C) with subsequent thermal enhancement of the frequency UC emissions due to population redistribution between the coupled energy levels of the Nd3+ ions. The present results have potential applications in super-resolution imaging and nanothermometry.

Using unnatural amino acids to selectively label proteins for cellular imaging: a cell biologist viewpoint.

Twenty-five years ago, GFP revolutionized the field of cell biology by enabling scientists to visualize, for the first time, proteins in living cells. However, when it comes to current, state-of-the-art imaging technologies, fluorescent proteins (such as GFP) have several limitations that result from their size and photophysics. Over the past decade, an elegant, alternative approach, which is based on the direct labeling of proteins with fluorescent dyes and is compatible with live-cell and super-resolution imaging applications, has been introduced. In this approach, an unnatural amino acid that can covalently bind a fluorescent dye is incorporated into the coding sequence of a protein. The protein of interest is thereby site-specifically fluorescently labeled inside the cell, eliminating the need for protein- or peptide-labeling tags. Whether this labeling approach will change cell biology research is currently unclear, but it clearly has the potential to do so. In this short review, a general overview of this approach is provided, focusing on the imaging of site-specifically labeled proteins in mammalian tissue culture cells, and highlighting its advantages and limitations for cellular imaging.

Spin-Momentum-Locked Edge Mode for Topological Vortex Lasing.

Spin-momentum locking is a direct consequence of bulk topological order and provides a basic concept to control a carrier's spin and charge flow for new exotic phenomena in condensed matter physics. However, up to date the research on spin-momentum locking solely focuses on its in-plane transport properties. Here, we report an emerging out-of-plane radiation feature of spin-momentum locking in a non-Hermitian topological photonic system and demonstrate a high performance topological vortex laser based on it. We find that the gain saturation effect lifts the degeneracy of the paired counterpropagating spin-momentum-locked edge modes enabling lasing from a single topological edge mode. The near-field spin and orbital angular momentum of the topological edge mode lasing has a one-to-one far-field radiation correspondence. The methodology of probing the near-field topology feature by far-field lasing emission can be used to study other exotic phenomena. The device can lead to applications in superresolution imaging, optical tweezers, free-space optical sensing, and communication.

Large-Scale Fabrication of Photonic Nanojet Array via Template-Assisted Self-Assembly.

A large-scale homogenized photonic nanojet array with defined pattern and spacing facilitates practical applications in super-resolution imaging, subwavelength-resolution nanopatterning, nano objects trapping and detection technology. In this paper, we present the fabrication of a large-scale photonic nanojet array via the template-assisted self-assembly (TASA) approach. Templates of two-dimensional (2D) large-scale microwell array with defined pattern and spacing are fabricated. Melamine microspheres with excellent size uniformity are utilized to pattern on the template. It is found that microwells can be filled at a yield up to 95%. These arrayed microspheres on the template serve as microlenses and can be excited to generate large-scale photonic nanojets. The uniformly-sized melamine spheres are beneficial for the generation of a homogenized photonic nanojet array. The intensity of the photonic nanojets in water is as high as ~2 fold the background light signal. Our work shows a simple, robust, and fast means for the fabrication of a large-scale homogenized photonic nanojet array.

Generation of an ultra-long sub-diffracted second-harmonic optical needle from a periodically poled LiNbO3 crystal

We experimentally demonstrate the use of a periodically poled LiNbO3 (PPLN) crystal to produce an ultra-long sub-diffraction optical needle via second-harmonic generation. When we input a radially polarized fundamental wave from a femtosecond laser, a sub-diffraction beam size of 0.45λSH and an ultra-long depth of focus (DOF) of 55λSH are experimentally realized, where λSH is the second harmonic wavelength. The lateral size of the second harmonic optical needle is reduced by a factor of 2 compared to the case using the fundamental wave. The compact experimental configuration can realize wavelength conversion and wave-front shaping simultaneously in a single PPLN crystal. In addition, the ultra-long DOF is potentially useful in observing thick samples. The unique characteristics of our second harmonic optical needle open the door for practical applications in super-resolution imaging and optical manipulation.

High-power femtosecond cylindrical vector beam optical parametric oscillator.

We report on high-power femtosecond cylindrical vector beam (CVB) generation from a Gaussian-pumped optical parametric oscillator (OPO). By introducing a half waveplate and a vortex half-wave plate of m = 1 to realize intracavity polarization modulation to the resonant Gaussian signal, the OPO could deliver broadband signal beam in CVB profile, i.e., radially and azimuthally polarized beam profile. The central wavelength of the generated CVB signals can be tuned continuously from 1405 to 1601 nm, while the corresponding pulse durations are all around 150 fs. A maximum average output power of 614 mW at 1505 nm is obtained. Moreover, our OPO cavity design can be extended to generate high order CVB by simply changing the vortex half-wave plate with different orders. Such a high-power CVB OPO configuration has the advantages of flexible control and wide tuning range, making it a practical tool for applications in super-resolution imaging, optical communication and quantum correlations.

Realization of broadband negative refraction in visible range using vertically stacked hyperbolic metamaterials.

Negative refraction has generated much interest recently with its unprecedented optical phenomenon. However, a broadband negative refraction has been challenging because they mainly involve optical resonances. This paper reports the realization of broadband negative refraction in the visible spectrum by using vertically-stacked metal-dielectric multilayer structures. Such structure exploits the characteristics of the constituent metal and dielectric materials, and does not require resonance to achieve negative refraction. Broadband negative refraction (wavelength 270–1300 nm) is numerically demonstrated. Compared to conventional horizontally-stacked multilayer structures, the vertically-stacked multilayer structure has a broader range of working wavelength in the visible range, with higher transmittance. We also report a variety of material combinations with broad working wavelength. The broadband negative refraction metamaterial provides an effective way to manipulate light and may have applications in super-resolution imaging, and invisibility cloaks.

High focusing efficiency in subdiffraction focusing metalens

Abstract Vector beams with phase modulation in a high numerical aperture system are able to break through the diffraction limit. However, the implementation of such a device requires a combination of several discrete bulky optical elements, increasing its complexity and possibility of the optical loss. Dielectric metalens, an ultrathin and planar nanostructure, has a potential to replace bulky optical elements, but its optimization with full-wave simulations is time-consuming. In this paper, an accurate and efficient theoretical model of planar metalens is developed. Based on this model, a twofold optimization scheme is proposed for optimizing the phase profile of metalenses so as to achieve subdiffraction focusing with high focusing efficiency. Then, a metalens that enables to simultaneously generate radially polarized beam (RPB) and modulate its phase under the incidence of x-polarized light with the wavelength of 532 nm is designed. Full-wave simulations show that the designed metalens of NA = 0.95 can achieve subdiffraction focusing (FWHM = 0.429λ) with high transmission efficiency (77.6%) and focusing efficiency (17.2%). Additionally, superoscillation phenomenon is found, leading to a compromise between the subdiffraction spot and high efficiency. The proposed method may provide an accurate and efficient way to achieve sub-wavelength imaging with the expected performances, which shows a potential application in super-resolution imaging.

Cooperative Blinking from Dye Ensemble Activated by Energy Transfer for Super-resolution Cellular Imaging.

Photoblinking is a fundamental process that occurs exclusively in single fluorophores such as organic dyes, fluorescent proteins, and quantum dots. Here, we describe a strategy to achieve pronounced, high on/off ratio, and cooperative blinking in donor-acceptor multifluorophore systems. An ensemble of dye molecules doped in semiconducting polymer dots (Pdots) exhibit robust photoblinking, while the pristine Pdots and the dye in optically inert polymer matrices fluoresce continuously. Energy transfer from Pdots to dye acceptors produces photoblinking via a cooperative process, in which the bright state originates from the dye ensemble and the dark state is due to quenching of semiconducting polymer by hole polarons. Using the blinking Pdots in subcellular structures labeling, we demonstrated approximately 3.6-fold enhancement of imaging resolution in high-order super-resolution optical fluctuation nanoscopy as compared to conventional microscopy. Our findings not only demonstrate the exciting possibility of transforming a nonquantized ensemble into a single-emitter-like optical source but also provide an effective approach to generate superior photoblinking fluorescent probes for super-resolution imaging applications.