Light-sheet microscopy in the near-infrared II window

Functionalized NIR-II Semiconducting Polymer Nanoparticles for Single-cell to Whole-Organ Imaging of PSMA-Positive Prostate Cancer

Development of molecular probes holds great promise for early diagnosis of aggressive prostate cancer. Here, 2-[3-(1,3-dicarboxypropyl) ureido] pentanedioic acid (DUPA)-conjugated ligand and bis-isoindigo-based polymer (BTII) are synthesized to formulate semiconducting polymer nanoparticles (BTII-DUPA SPN) as a prostate-specific membrane antigen (PSMA)-targeted probe for prostate cancer imaging in the NIR-II window. Insights into the interaction of the imaging probes with the biological targets from single cell to whole organ are obtained by transient absorption (TA) microscopy and photoacoustic (PA) tomography. At single-cell level, TA microscopy reveals the targeting efficiency, kinetics, and specificity of BTII-DUPA SPN to PSMA-positive prostate cancer. At organ level, PA tomographic imaging of BTII-DUPA SPN in the NIR-II window demonstrates superior imaging depth and contrast. By intravenous administration, BTII-DUPA SPN demonstrates selective accumulation and retention in the PSMA-positive tumor, allowing noninvasive PA detection of PSMA overexpressing prostate tumors in vivo. The distribution of nanoparticles inside the tumor tissue is further analyzed through TA microscopy. These results collectively demonstrate BTII-DUPA SPN as a promising probe for prostate cancer diagnosis by PA tomography.

Fast widefield imaging of neuronal structure and function with optical sectioning in vivo

Optical microscopy, owing to its noninvasiveness and subcellular resolution, enables in vivo visualization of neuronal structure and function in the physiological context. Optical-sectioning structured illumination microscopy (OS-SIM) is a widefield fluorescence imaging technique that uses structured illumination patterns to encode in-focus structures and optically sections 3D samples. However, its application to in vivo imaging has been limited. In this study, we optimized OS-SIM for in vivo neural imaging. We modified OS-SIM reconstruction algorithms to improve signal-to-noise ratio and correct motion-induced artifacts in live samples. Incorporating an adaptive optics (AO) module to OS-SIM, we found that correcting sample-induced optical aberrations was essential for achieving accurate structural and functional characterizations in vivo. With AO OS-SIM, we demonstrated fast, high-resolution in vivo imaging with optical sectioning for structural imaging of mouse cortical neurons and zebrafish larval motor neurons, and functional imaging of quantal synaptic transmission at Drosophila larval neuromuscular junctions.

Depth-resolved NIR-II fluorescence mesoscope

NIR-II fluorescence imaging is a promising method for visualizing biological structures in deep tissue, owing to the advantages of significantly suppressed optical scattering and diminished autofluorescence in biological tissues. However, few NIR-II fluorescence imaging approaches can simultaneously achieve a large field of view, high resolution and superior penetration depth, while exhibiting optical sectioning capability. In this paper, we present a novel NIR-II fluorescence mesoscopy system based on the f-θ scanning scheme and confocal detection to overcome these limitations. When used with NIR-II fluorescent dyes, our setup performs NIR-II fluorescence imaging on samples as large as 7.5×7.5 mm2 with a lateral resolution of 6.3 µm. In addition, our system provides a depth-resolved imaging ability and zooming function. We successfully demonstrate in vivo cerebrovascular imaging of a mouse with local ischemia. Thus, our system provides new opportunities to explore the mechanism of cerebrovascular disease.

A mini-review on rare-earth down-conversion nanoparticles for NIR-II imaging of biological systems

Rare-earth (RE) based luminescent probes exhibit rich optical properties including upconversion and down-conversion luminescence spanning a broad spectral range from 300 to 3,000 nm, and have generated great scientific and practical interest from telecommunication to biological imaging. While upconversion nanoparticles have been investigated for decades, down-conversion luminescence of RE-based probes in the second near-infrared (NIR-II, 1,000-1,700 nm) window for in vivo biological imaging with sub-centimeter tissue penetration and micrometer image resolution has come into light only recently. In this review, we present recent progress on RE-based NIR-II probes for in vivo vasculature and molecular imaging with a focus on Er3+-based nanoparticles due to the down-conversion luminescence at the long-wavelength end of the NIR-II window (NIR-IIb, 1,500-1,700 nm). Imaging in NIR-IIb is superior to imaging with organic probes such as ICG and IRDye800 in the ~ 800 nm NIR range and the 1,000-1,300 nm short end of NIR-II range, owing to minimized light scattering and autofluorescence background. Doping by cerium and other ions and phase engineering of Er3+-based nanoparticles, combined with surface hydrophilic coating optimization can afford ultrabright, biocompatible NIR-IIb probe towards clinical translation for human use. The Nd3+-based probes with NIR-II emission at 1,050 and 1,330 nm are also discussed, including Nd3+ doped nanocrystals and Nd3+-organic ligand complexes. This review also points out future directions for further development of multi-functional RE NIR-II probes for biological imaging.

In Vivo Spectral Distortions of Infrared Luminescent Nanothermometers Compromise Their Reliability

Luminescence nanothermometry has emerged over the past decade as an exciting field of research due to its potential applications where conventional methods have demonstrated to be ineffective. Preclinical research has been one of the areas that have benefited the most from the innovations proposed in the field. Nevertheless, certain questions concerning the reliability of the technique under in vivo conditions have been continuously overlooked by most of the scientific community. In this proof-of-concept, hyperspectral in vivo imaging is used to explain how unverified assumptions about the thermal dependence of the optical transmittance of biological tissues in the so-called biological windows can lead to erroneous measurements of temperature. Furthermore, the natural steps that should be taken in the future for a reliable in vivo luminescence nanothermometry are discussed together with a perspective view of the field after the findings here reported.

Multiplexed NIR-II Probes for Lymph Node-Invaded Cancer Detection and Imaging-Guided Surgery

Tumor-lymph node (LN) metastasis is the dominant prognostic factor for tumor staging and therapeutic decision-making. However, concurrently visualizing metastasis and performing imaging-guided lymph node surgery is challenging. Here, a multiplexed-near-infrared-II (NIR-II) in vivo imaging system using nonoverlapping NIR-II probes with markedly suppressed photon scattering and zero-autofluorescence is reported, which enables visualization of the metastatic tumor and the tumor metastatic proximal LNs resection. A bright and tumor-seeking donor-acceptor-donor (D-A-D) dye, IR-FD, is screened for primary/metastatic tumor imaging in the NIR-IIa (1100-1300 nm) window. This optimized D-A-D dye exhibits greatly improved quantum yield of organic D-A-D fluorophores in aqueous solutions (≈6.0%) and good in vivo performance. Ultrabright PbS/CdS core/shell quantum dots (QDs) with dense polymer coating are used to visualize cancer-invaded sentinel LNs in the NIR-IIb (>1500 nm) window. Compared to clinically used indocyanine green, the QDs show superior brightness and photostability (no obvious bleaching even after continuous laser irradiation for 5 h); thus, only a picomolar dose is required for sentinel LNs detection. This combination of dual-NIR-II image-guided surgery can be performed under bright light, adding to its convenience and appeal in clinical use.

Cellular and Molecular Probing of Intact Human Organs

Optical tissue transparency permits scalable cellular and molecular investigation of complex tissues in 3D. Adult human organs are particularly challenging to render transparent because of the accumulation of dense and sturdy molecules in decades-aged tissues. To overcome these challenges, we developed SHANEL, a method based on a new tissue permeabilization approach to clear and label stiff human organs. We used SHANEL to render the intact adult human brain and kidney transparent and perform 3D histology with antibodies and dyes in centimeters-depth. Thereby, we revealed structural details of the intact human eye, human thyroid, human kidney, and transgenic pig pancreas at the cellular resolution. Furthermore, we developed a deep learning pipeline to analyze millions of cells in cleared human brain tissues within hours with standard lab computers. Overall, SHANEL is a robust and unbiased technology to chart the cellular and molecular architecture of large intact mammalian organs.

Specific Small-Molecule NIR-II Fluorescence Imaging of Osteosarcoma and Lung Metastasis

Osteosarcoma is an aggressive tumor of mesenchymal origin that is more likely to spread to the lung than others, with a major impact on patients' prognosis. The optimal imaging method that can reliably detect or exclude pulmonary metastases from osteosarcoma is still scarce. Herein, two homologous types of fluorescent probes CH1055-PEG-PT and CH1055-PEG-Affibody, which show highly promising results for targeting imaging of osteosarcoma and its lung metastasis, respectively, are designed and synthesized. It is found that the NIR-II imaging quality of CH1055-PEG-PT is far superior to that of computed tomography for the early in vivo 143B tumor imaging, and this probe-guided surgery for accurate resection of 143B tumor is further performed. The high-resolution visualization of primary and micrometastatic lung lesions of osteosarcoma by using CH1055-PEG-Affibody is also demonstrated. Therefore, the attractive imaging properties of CH1055-PEG-PT and CH1055-PEG-Affibody, including high levels of uptakes, and high spatial and temporal resolution, open up opportunities for molecular imaging and clinical translation of osteosarcoma and its lung metastasis in the unique second near-infrared window.

Novel NIR-II organic fluorophores for bioimaging beyond 1550 nm

Novel NIR-II organic fluorophores were designed and synthesized using an AIE and highly twisted donor–acceptor distortion strategy for bio-imaging beyond 1550 nm.

A Review on Microscopic Visual Servoing for Micromanipulation Systems: Applications in Micromanufacturing, Biological Injection, and Nanosensor Assembly

Micromanipulation is an interdisciplinary technology that integrates advanced knowledge of microscale/nanoscale science, mechanical engineering, electronic engineering, and control engineering. Over the past two decades, it has been widely applied in the fields of MEMS (microelectromechanical systems), bioengineering, and microdevice integration and manufacturing. Microvision servoing is the basic tool for enabling the automatic and precise micromanipulation of microscale/nanoscale entities. However, there are still many problems surrounding microvision servoing in theory and the application of this technology's micromanipulation processes. This paper summarizes the research, development status, and practical applications of critical components of microvision servoing for micromanipulation, including geometric calibration, autofocus techniques, depth information, and visual servoing control. Suggestions for guiding future innovation and development in this field are also provided in this review.

In vivo molecular imaging for immunotherapy using ultra-bright near-infrared-IIb rare-earth nanoparticles

The near-infrared-IIb (NIR-IIb) (1,500-1,700 nm) window is ideal for deep-tissue optical imaging in mammals, but lacks bright and biocompatible probes. Here, we developed biocompatible cubic-phase (α-phase) erbium-based rare-earth nanoparticles (ErNPs) exhibiting bright downconversion luminescence at ~1,600 nm for dynamic imaging of cancer immunotherapy in mice. We used ErNPs functionalized with cross-linked hydrophilic polymer layers attached to anti-PD-L1 (programmed cell death-1 ligand-1) antibody for molecular imaging of PD-L1 in a mouse model of colon cancer and achieved tumor-to-normal tissue signal ratios of ~40. The long luminescence lifetime of ErNPs (~4.6 ms) enabled simultaneous imaging of ErNPs and lead sulfide quantum dots emitting in the same ~1,600 nm window. In vivo NIR-IIb molecular imaging of PD-L1 and CD8 revealed cytotoxic T lymphocytes in the tumor microenvironment in response to immunotherapy, and altered CD8 signals in tumor and spleen due to immune activation. The cross-linked functionalization layer facilitated 90% ErNP excretion within 2 weeks without detectable toxicity in mice.

Thermal monitoring during photothermia: hybrid probes for simultaneous plasmonic heating and near-infrared optical nanothermometry

The control of temperature during photothermal therapy is key to preventing unwanted damage in surrounding tissue or post-treatment inflammatory responses. Lack of accurate thermal control is indeed one of the main limitations that hyperthermia techniques present to allow their translation into therapeutic applications. We developed a nanoprobe that allows controlled local heating, combined with in situ nanothermometry. The design of the probe follows a practical rationale that aims at simplifying experimental requirements and exploits exclusively optical wavelengths matching the first and second biological windows in the near-infrared. Methods: Hybrid nanostructures were chemically synthesized, and combine gold nanostars (photothermal agents) with CaF₂:Nd³⁺,Y³⁺ nanoparticles (luminescent nanothermometers). Both components were simultaneously excited in the near-infrared range, at 808 nm. Following the goal of simplifying the thermal monitoring technique, the luminescent signal was recorded with a portable near-infrared detector. The performance of the probes was tested in 3D tumor spheroids from a human glioblastoma (U87MG) cell line. The location of the beads within the spheroids was determined measuring Nd³⁺ emission in a commercial Lightsheet microscope, modified in-house to be able to select the required near-infrared wavelengths. The temperature achieved inside the tumor spheroids was deduced from the luminescence of Nd³⁺, following a protocol that we developed to provide reliable thermal readings. Results: The choice of materials was shown to work as an optically excited hybrid probe. Depending on the illumination parameters, temperature can be controlled in a range between 37 ºC and 100 ºC. The near-infrared emission of nanothermometers also allows microscopic tracking of the hybrid nanostructures, confirming that the probes can penetrate deeper into the spheroid mass. We observed that, application of optical thermometry in biological environments requires often neglected considerations, since the optical signal changes along the optical path. Accordingly, we developed data analysis protocols that guarantee reliable thermal readings. Conclusions: The prepared hybrid probes are internalized in 3D tumor spheroids and can be used to induce cell death through photothermal effects, while simultaneously measuring the local temperature in situ. We show that luminescent thermometry in biomedical applications requires the development of protocols that guarantee accurate readings. Regarding photothermal treatments, we observe a sharp thermal threshold at around 55 ºC (for 10 min treatments) that separates high survival ratio from complete cell death.

Boosting often overlooked long wavelength emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of orthotopic glioblastoma

Rare-earth nanoparticles (RE NPs) with narrow long wavelength emissions have been recently investigated for their potential application for fluorescence imaging in the second near-infrared window (NIR-II). Previously these RE NPs have a very limited application in the diagnosis and treatment of deep-seated tumors such as brain tumors, due to their weak fluorescence in the range of 1300-1700 nm. Herein, we report a significant enhancement of more than 10 times regular emission of NaNdF₄ nanoparticles at 1340 nm wavelength by coating them with an inert layer of NaLuF₄, followed by sensitizing with a near-infrared dye (IR-808). We deliver these highly bright nanoparticles into the brain by using focused ultrasound to temporarily open the blood-brain barrier (BBB), and then detect the orthotopic glioblastoma by fluorescence imaging at 1340 nm. The images obtained from long wavelength fluorescence (i.e. 1340 nm) exhibited better resolution and contrast compared to the short wavelength fluorescence (i.e. 1060 nm). Our study not only provides insights for enhancing often overlooked emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of deep-seated tumors, but also demonstrates great potential of focused ultrasound based technology in delivering nanotheranostic agents.