Non-telecentric two-photon microscopy for 3D random access mesoscale imaging

Compact module for video-rate image mosaics in two-photon microscopy

Biological applications using multiphoton microscopy increasingly seek a larger field of view while maintaining sufficient temporal sampling to observe dynamic biological processes. Multiphoton imaging also requires high numerical aperture microscope objectives to realize efficient non-linear excitation and collection of fluorescence. This combination of low-magnification and high-numerical aperture poses a challenge for system design. To address this, the use of a liquid crystal polarization grating stack is proposed here to temporally sequence through multiple fields of view. This solution pans the native field of view with minimal latency and zero inertial movement of either the microscope or biological sample. Implemented as a simple add-on unit to existing multi-photon microscopes, this device increases the total field size by 4x, covering up to 7.6mm2. Performance constraints and functional demonstration of imaging neural activity are presented.

Three-dimensional random-access confocal microscopy with 3D remote focusing system

Understanding biological activities in cells or deep tissues requires high-speed three-dimensional (3D) imaging. Substantial progress has been made with the emergence of 3D random-access microscopy. However, current solutions for fast 3D random-access imaging remain complex and costly. Herein we propose a simple, cost-effective, and fast 3D random-access confocal microscopy with remote focusing system. Our system shows isotropic response times across the x, y, and z axes, with a 34-fold improvement in axial response time over traditional piezo stages. We demonstrate its volumetric imaging performance with fluorescent particles and live cells. Furthermore, we validate the 3D random-access imaging capability of this system by continuously monitoring the signals in three different planes, showing a refresh rate of 500 Hz on two different positions in 3D. The simplicity, versatility, and affordability of our system promise widespread applications in research and industry.

Long-working-distance high-collection-efficiency three-photon microscopy for in vivo long-term imaging of zebrafish and organoids

Zebrafish and organoids, crucial for complex biological studies, necessitate an imaging system with deep tissue penetration, sample protection from environmental interference, and ample operational space. Traditional three-photon microscopy is constrained by short-working-distance objectives and falls short. Our long-working-distance high-collection-efficiency three-photon microscopy (LH-3PM) addresses these challenges, achieving a 58% fluorescence collection efficiency at a 20 mm working distance. LH-3PM significantly outperforms existing three-photon systems equipped with the same long working distance objective, enhancing fluorescence collection and dramatically reducing phototoxicity and photobleaching. These improvements facilitate accurate capture of neuronal activity and an enhanced detection of activity spikes, which are vital for comprehensive, long-term imaging. LH-3PM's imaging of epileptic zebrafish not only showed sustained neuron activity over an hour but also highlighted increased neural synchronization and spike numbers, marking a notable shift in neural coding mechanisms. This breakthrough paves the way for new explorations of biological phenomena in small model organisms.

Dimension-based quantification of aging-associated cerebral microvasculature determined by optical coherence tomography and two-photon microscopy

Cerebral microvascular health is a key biomarker for the study of natural aging and associated neurological diseases. Our aim is to quantify aging-associated change of microvasculature at diverse dimensions in mice brain. We used optical coherence tomography (OCT) and two-photon microscopy (TPM) to obtain nonaged and aged C57BL/6J mice cerebral microvascular images in vivo. Our results indicated that artery & vein, arteriole & venule, and capillary from nonaged and aged mice showed significant differences in density, diameter, complexity, perimeter, and tortuosity. OCT angiography and TPM provided the comprehensive quantification for arteriole and venule via compensating the limitation of each modality alone. We further demonstrated that arteriole and venule at specific dimensions exhibited negative correlations in most quantification analyses between nonaged and aged mice, which indicated that TPM and OCT were able to offer complementary vascular information to study the change of cerebral blood vessels in aging.

Durable organic nonlinear optical membranes for thermotolerant lightings and in vivo bioimaging

Organic nonlinear optical materials have potential in applications such as lightings and bioimaging, but tend to have low photoluminescent quantum yields and are prone to lose the nonlinear optical activity. Herein, we demonstrate to weave large-area, flexible organic nonlinear optical membranes composed of 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate@cyclodextrin host-guest supramolecular complex. These membranes exhibited a record high photoluminescence quantum yield of 73.5%, and could continuously emit orange luminescence even being heated at 300 °C, thus enabling the fabrication of thermotolerant light-emitting diodes. The nonlinear optical property of these membranes can be well-preserved even in polar environment. The supramolecular assemblies with multiphoton absorption characteristics were used for in vivo real-time imaging of Escherichia coli at 1000 nm excitation. These findings demonstrate to achieve scalable fabrication of organic nonlinear optical materials with high photoluminescence quantum yields, and good stability against thermal stress and polar environment for high-performance, durable optoelectronic devices and humanized multiphoton bio-probes.

Multi-Mode Lanthanide-Doped Ratiometric Luminescent Nanothermometer for Near-Infrared Imaging within Biological Windows

Owing to its high reliability and accuracy, the ratiometric luminescent thermometer can provide non-contact and fast temperature measurements. In particular, the nanomaterials doped with lanthanide ions can achieve multi-mode luminescence and temperature measurement by modifying the type of doped ions and excitation light source. The better penetration of the near-infrared (NIR) photons can assist bio-imaging and replace thermal vision cameras for photothermal imaging. In this work, we prepared core-shell cubic phase nanomaterials doped with lanthanide ions, with Ba₂LuF₇ doped with Er³⁺/Yb³⁺/Nd³⁺ as the core and Ba₂LaF₇ as the coating shell. The nanoparticles were designed according to the passivation layer to reduce the surface energy loss and enhance the emission intensity. Green upconversion luminescence can be observed under both 980 nm and 808 nm excitation. A single and strong emission band can be obtained under 980 nm excitation, while abundant and weak emission bands appear under 808 nm excitation. Meanwhile, multi-mode ratiometric optical thermometers were achieved by selecting different emission peaks in the NIR window under 808 nm excitation for non-contact temperature measurement at different tissue depths. The results suggest that our core-shell NIR nanoparticles can be used to assist bio-imaging and record temperature for biomedicine.

Optogenetic Methods to Investigate Brain Alterations in Preclinical Models

Investigating the neuronal dynamics supporting brain functions and understanding how the alterations in these mechanisms result in pathological conditions represents a fundamental challenge. Preclinical research on model organisms allows for a multiscale and multiparametric analysis in vivo of the neuronal mechanisms and holds the potential for better linking the symptoms of a neurological disorder to the underlying cellular and circuit alterations, eventually leading to the identification of therapeutic/rescue strategies. In recent years, brain research in model organisms has taken advantage, along with other techniques, of the development and continuous refinement of methods that use light and optical approaches to reconstruct the activity of brain circuits at the cellular and system levels, and to probe the impact of the different neuronal components in the observed dynamics. These tools, combining low-invasiveness of optical approaches with the power of genetic engineering, are currently revolutionizing the way, the scale and the perspective of investigating brain diseases. The aim of this review is to describe how brain functions can be investigated with optical approaches currently available and to illustrate how these techniques have been adopted to study pathological alterations of brain physiology.