KEYWORDS: Super resolution, Upconversion, Near infrared, Light sources and illumination, Nanoparticles, Biological imaging, Multiplexing, Microscopy, Super resolution microscopy, Deep tissue imaging
Super-resolution microscopy provides a high spatial resolution that is beyond the diffraction barrier and can visualize nano-sized structures and interactions in biological and material study. In recent years, lanthanide-doped upconversion nanoparticles (UCNPs) that can upconvert the near-infrared (NIR) excitation photons to visible emission photons, have been developing as a kind of novel nanoprobes for bioimaging. Here we report the recently developed NIR superresolution imaging techniques by exploring the nonlinear fluorescence responses in UCNPs. Upconversion Nonlinear Structured Illumination Microscopy (U-NSIM) employes nonlinear fluorescence, along with NIR excitation and emission light, to deliver rapid frame rates and high-resolution capabilities, enabling in-depth super-resolution imaging. The tunability of lifetime in UCNPs is also introduced to develop the multiplexed super-resolution imaging with lifetime-engineered nanoprobes. By detecting two emission channels with different nonlinear fluorescence responses, a single doughnut illumination beam is used to scan the sample to generate a Gaussian-like emission point spread function (PSF) and a doughnut-emission PSF simultaneously, which can be fused by algorithms to an optimized super-resolution nanoscopy. These upconversion super-resolution imaging techniques provide new strategies to develop deep-tissue and multiplexed super-resolution imaging and also help to achieve it in a simple optical scheme.
Lensless diffuser camera is a novel and flexible approach to capture object’s images. Here, we propose a compact spectral and polarization diffuser camera (SPDC) enabled by a diffuser and a complementary metal oxide semiconductor (COMS) sensor. We demonstrated SPDC to reconstruct images with spectral and polarization by simulations. It can be highly integrated with lightweight, and lower cost, compared with traditional multi-dimensional imaging systems. SPDC has great potential in many applications, such as compact bioimaging systems, portable optical sensing, and consumer applications.
Upconversion nanoparticles (UCNPs) is a series of lanthanoid ions doped nanocrystals that are of great interest for biomedical applications, including nanoscale optical sensing and imaging, benefiting from its bright, stable, multicolour emission. Each of the nanoparticles contains thousands of Lanthanide ions, which works as both sensitizers and activators to absorb the near-infrared photons and transfer the energy from sensitizers to activators through nonlinear energy transferring process for an upconverting emission. A few new super-resolution imaging methods have been developed recently based on UCNPs’ unique nonlinear energy transferring process. Most recently, upon these advances, we have found that the thousands of Lanthanide ions provide a strong dielectric resonance effect in a single UCNP. In this work, we will review using the nonlinear response of lanthanoid ions to improve super-resolution nanoscopy. We will also report the ion resonance effect in UCNPs could substantially increase the permittivity and polarizability of nanocrystals, leading to an enhanced optical force on a single 23.3 nm radius UCNP, more than 30 times stronger than the reported value for gold nanoparticles with the same size. The enhanced optical force also provides a way to bypass the optical trapping requirement of “refractive index mismatch”. We further report that the resonance effect could engineer the Rayleigh scattering of UCNPs. These applications suggest a new potential of UCNPs as force probe, scattering probe and fluorescence probe simultaneously for multiplexed imaging.
Dual beam fiber traps are potentially useful for integrated trapping devices aimed at studying aerosols, and offer opportunities for cavity-enhanced traps. The alignment of such traps is typically seen to be critical. Here we explore the impact of the angular alignment of the optical fibers, and assess trapping viability as a function of misalignment and how particle dynamics change when interacting with displaced fibers. We find that good trapping capability for dual fibers tilted at the same angle, while more complex aerosol dynamics become apparent at higher single fiber tilt angles.
Organoid, an in vitro model to study cell behaviours in a living organism, holds great potential for human cellular biology study, especially in disease pathology, drug delivery and drug efficacy trials. However, it remains challenging to track subcellular features inside organoid, as organoid are clusters of high-density cells that highly scatters and absorbs both excitation and emission light. Here we report a strategy on nanoscopy that applying “non-diffractive” beam and near-infrared imaging probe to minimize the light scattering and absorption inside scattering bio-tissue. Using a single Bessel-doughnut beam excitation from a 980nm diode laser and detecting at 800nm, we achieved a near-infrared, “non-diffractive” nanoscopy with high resolution under-diffractive limit in water solution. We further demonstrate that this method can image single upconversion nanoparticles inside spheroids, as deep as half-100μm, with resolution of 113nm. This method provides simple solution to inspect inter-and intra-cellular trafficking and drug release of single nanoparticles in 3D biological systems.
Upconversion nanoparticles (UCNP) is a lanthanide ion-doped nanocrystal that has a natural nonlinear photo-response from their upconverting energy transfer process. The nonlinearity can be further modified by changing the doping element and concentration. Here we present a strategy that applies UCNPs as near-infrared (NIR) nonlinear fluorescence probe for in-depth super-resolution imaging. We present a method that takes advantage of “non-diffractive” Bessel beam, further employs the photon-saturation of the NIR emission from UCNPs, so that enabling super-resolution mapping of single nanoparticles located 55 μm inside a spheroid, with a resolution of 98 nm, without adaptive optics compensation. We further apply the photon-conversion of UCNPs for a high efficient NIR nonlinear structured illumination microscopy (NIRNSIM) for a rapid in-depth super-resolution imaging. With 10 kW/cm2 continuous wave (CW) excitation, NIR-NSIM achieves a resolution of 130 nm, 1/7th of the excitation wavelength, and a frame rate of 1 fps, through 50 μm biological tissues.
Bright and photo-stable luminescent nanoparticles held great potential for bioimaging, long-term molecular tracking. Rare-earth-doped upconversion nanoparticles (UCNPs) have been recently discovered with unique properties for Stimulated Emission Depletion (STED) super-resolution microscopy imaging. However, this system strictly requires optical alignment of concentric excitation and depletion beams, resulting in cost, stability, and complicity of the system. Taking the advantage of intermediate state saturation in UCNPs, emission saturation nanoscopy has been developed as a simplified modality by using a single doughnut excitation beam. In this work, we report that the emission saturation curve of fluorescence probes can modulate the performance of multi-photon emission saturation nanoscopy. With the precise synthesis of UCNPs, we demonstrate the resolution of this new imaging approach can be improved with five parameters, including emission band, activator doping, excitation power, sensitizer doping, core-shell. This approach opens a new strategy to a simple solution for super-resolution imaging and single molecule tracking at low cost, suggesting a large scope for materials science community to improve the performance of emission saturation nanoscopy.
We present a study of the trapping properties of Au nanorods of different aspect ratios in an optical tweezers and comparison with other characterization techniques like transmission electron microscope (TEM) imaging and dynamic light scattering (DLS). This study provides information on the dynamics and orientation of Au nanorods inside an optical trap based on a time study of their localised surface plasmon resonance (LSPR) features. The results indicate that the orientation of the Au nanorods trapped in our optical tweezers varies with time and LSPR spectra can provide information on the angle of the nanorod with respect to the direction of propagation of the trapping laser.
We present a novel method for spatial mapping of the luminescent properties of single optically trapped semiconductor
nanowires by combing dynamic optical tweezers with micro-photoluminescence. The technique involves the use of a
spatial light modulator (SLM) to control the axial position of the trapping focus relative to the excitation source and
collection optics. When a nanowire is held in this arrangement, scanning the axial position of the trapping beam enables
different sections of the nanowire axis to be probed. In this context we consider the axial resolution of the luminescence
mapping and optimization of the nanowire trapping by spherical aberration correction.
We report on the dynamics of micro-photoluminescence of single InP semiconductor nanowires trapped in a gradient
force optical tweezers. Nanowires studied were of zinc blende, wurtzite or mixed phase crystal poly-types and ranged in
length from one to ten micrometers. Our results show that the band-edge emission from trapped nanowires exhibits a
quenching of the initial intensity with a characteristic time scale of a few seconds and an associated spectral red shift is
also observed in the mixed phase nanowires.
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