Early Detection of Myeloid-Derived Suppressor Cells in the Lung Pre-Metastatic Niche by Shortwave Infrared Nanoprobes.

Metastatic breast cancer remains a significant source of mortality amongst breast cancer patients and is generally considered incurable in part due to the difficulty in detection of early micro-metastases. The pre-metastatic niche (PMN) is a tissue microenvironment that has undergone changes to support the colonization and growth of circulating tumor cells, a key component of which is the myeloid-derived suppressor cell (MDSC). Therefore, the MDSC has been identified as a potential biomarker for PMN formation, the detection of which would enable clinicians to proactively treat metastases. However, there is currently no technology capable of the in situ detection of MDSCs available in the clinic. Here, we propose the use of shortwave infrared-emitting nanoprobes for the tracking of MDSCs and identification of the PMN. Our rare-earth albumin nanocomposites (ReANCs) are engineered to bind the Gr-1 surface marker of murine MDSCs. When delivered intravenously in murine models of breast cancer with high rates of metastasis, the targeted ReANCs demonstrated an increase in localization to the lungs in comparison to control ReANCs. However, no difference was seen in the model with slower rates of metastasis. This highlights the potential utility of MDSC-targeted nanoprobes to assess PMN development and prognosticate disease progression.

Defect Engineering of Low-Coordinated Metal-Organic Frameworks (MOFs) for Improved CO2 Access and Capture.

While metal-organic frameworks (MOFs) are promising gas adsorbents, their tortuous microporous structures cause additional resistance for gas diffusion, thus hindering the accessibility of interior active sites. Here, we present a practical strategy to incorporate missing cluster defects into a representative low-coordinated MOFs structure, Mg-MOF-74, while maintaining the stability of a defect-rich structure. In this proposed method, graphene oxide (GO) is employed as modulator, and crystallization time is varied to promote defect formation by altering the nucleation and crystal growth processes. The best performing GO-modified Mg-MOF-74 sample (MOF@GO 40 h) achieved 18% and 15% improvement in surface area and total pore volume, respectively, over pristine Mg-MOF-74. The reduced diffusion resistance to gas flow translates to increased accessibility for gas molecules to active Mg adsorption sites inside the MOFs, leading to enhanced CO2 capture performance; the CO2 uptake quantity of MOF@GO 40 h arrives at 6.06 mmol/g at 0.1 bar and at 9.17 mmol/g at 1 bar and 25 °C, 19.29% and 16.37% higher, respectively, than that of the pristine Mg-MOF-74, with a CO2/N2 selectivity around 17.36% greater than that of pristine Mg-MOF-74. Our study demonstrates a facile approach for incorporating defects into MOFs systems with low coordination environments, thus expanding the library of defect-rich MOFs beyond the current highly coordinated MOF systems.

Short-Wave Infrared Emitting Nanocomposites for Fluorescence-Guided Surgery.

Fluorescence-guided surgery (FGS) is an emerging technique for tissue visualization during surgical procedures. Structures of interest are labeled with exogenous probes whose fluorescent emissions are acquired and viewed in real-time with optical imaging systems. This study investigated rare-earth-doped albumin-encapsulated nanocomposites (REANCs) as short-wave infrared emitting contrast agents for FGS. Experiments were conducted using an animal model of 4T1 breast cancer. The signal-to-background ratio (SBR) obtained with REANCs was compared to values obtained using indocyanine green (ICG), a near-infrared dye used in clinical practice. Prior to resection, the SBR for tumors following intratumoral administration of REANCs was significantly higher than for tumors injected with ICG. Following FGS, evaluation of fluorescence intensity levels in excised tumors and at the surgical bed demonstrated higher contrast between tissues at these sites with REANC contrast than ICG. REANCs also demonstrated excellent photostability over 2 hours of continuous illumination, as well as the ability to perform FGS under ambient lighting, establishing these nanocomposites as a promising contrast agent for FGS applications.

Synthesis of deep red emitting Cu-In-Zn-Se/ZnSe quantum dots for dual-modal fluorescence and photoacoustic imaging.

CuInSe2 quantum dots (QDs) are one of the most important Cd-free fluorescent probes; they usually exhibited low fluorescence intensity, suggesting that a considerable amount of absorbed photon energy was lost as heat. In this study we aimed to improve the fluorescence intensity of CuInSe2 QDs and investigate their photoacoustic (PA) signal resulting from the heat dissipation, which was previously rarely reported. Cu-In-Zn-Se/ZnSe QDs were synthesized by adopting two strategies of Zn doping and ZnSe shell growth. It was found that there was an upper limit for Zn concentration beyond which the fluorescence intensity began to decrease. In addition, a blue shift of the emission peak of Cu-In-Zn-Se/ZnSe QDs was observed at high concentrations of ZnSe precursor due to the diffusion of excessive Zn. To prepare the dual-modal fluorescence and PA imaging probe, poly(maleic anhydride-alt-1-octadecene) (PMAO) modified with polyethylene glycol (PEG) was coated on the QDs, which led to a slight reduction in fluorescence. Cellular labeling on HeLa cells was performed to demonstrate the utility of these probes for fluorescence imaging. We further studied the in vitro PA imaging capabilities of the Cu-In-Zn-Se/ZnSe/PMAO-g-PEG nanoparticles, which showed a distinct PA signal beyond 1.0 mg ml-1. The current work demonstrated that a moderate amount of Zn doping is necessary for enhancing fluorescence and there is a limit beyond which the fluorescence will be diminished. We also demonstrated the proof of concept that Cu-In-Zn-Se/ZnSe QDs are able to serve as a potential PA imaging contrast agent.

Shortwave infrared emitting multicolored nanoprobes for biomarker-specific cancer imaging in vivo.

BACKGROUND: The ability to detect tumor-specific biomarkers in real-time using optical imaging plays a critical role in preclinical studies aimed at evaluating drug safety and treatment response. In this study, we engineered an imaging platform capable of targeting different tumor biomarkers using a multi-colored library of nanoprobes. These probes contain rare-earth elements that emit light in the short-wave infrared (SWIR) wavelength region (900-1700 nm), which exhibits reduced absorption and scattering compared to visible and NIR, and are rendered biocompatible by encapsulation in human serum albumin. The spectrally distinct emissions of the holmium (Ho), erbium (Er), and thulium (Tm) cations that constitute the cores of these nanoprobes make them attractive candidates for optical molecular imaging of multiple disease biomarkers. METHODS: SWIR-emitting rare-earth-doped albumin nanocomposites (ReANCs) were synthesized using controlled coacervation, with visible light-emitting fluorophores additionally incorporated during the crosslinking phase for validation purposes. Specifically, HoANCs, ErANCs, and TmANCs were co-labeled with rhodamine-B, FITC, and Alexa Fluor 647 dyes respectively. These Rh-HoANCs, FITC-ErANCs, and 647-TmANCs were further conjugated with the targeting ligands daidzein, AMD3100, and folic acid respectively. Binding specificities of each nanoprobe to distinct cellular subsets were established by in vitro uptake studies. Quantitative whole-body SWIR imaging of subcutaneous tumor bearing mice was used to validate the in vivo targeting ability of these nanoprobes. RESULTS: Each of the three ligand-functionalized nanoprobes showed significantly higher uptake in the targeted cell line compared to untargeted probes. Increased accumulation of tumor-specific nanoprobes was also measured relative to untargeted probes in subcutaneous tumor models of breast (4175 and MCF-7) and ovarian cancer (SKOV3). Preferential accumulation of tumor-specific nanoprobes was also observed in tumors overexpressing targeted biomarkers in mice bearing molecularly-distinct bilateral subcutaneous tumors, as evidenced by significantly higher signal intensities on SWIR imaging. CONCLUSIONS: The results from this study show that tumors can be detected in vivo using a set of targeted multispectral SWIR-emitting nanoprobes. Significantly, these nanoprobes enabled imaging of biomarkers in mice bearing bilateral tumors with distinct molecular phenotypes. The findings from this study provide a foundation for optical molecular imaging of heterogeneous tumors and for studying the response of these complex lesions to targeted therapy.

Shortwave Infrared-Emitting Theranostics for Breast Cancer Therapy Response Monitoring.

Therapeutic drug monitoring (TDM) in cancer, while imperative, has been challenging due to inter-patient variability in drug pharmacokinetics. Additionally, most pharmacokinetic monitoring is done by assessments of the drugs in plasma, which is not an accurate gauge for drug concentrations in target tumor tissue. There exists a critical need for therapy monitoring tools that can provide real-time feedback on drug efficacy at target site to enable alteration in treatment regimens early during cancer therapy. Here, we report on theranostic optical imaging probes based on shortwave infrared (SWIR)-emitting rare earth-doped nanoparticles encapsulated with human serum albumin (abbreviated as ReANCs) that have demonstrated superior surveillance capability for detecting micro-lesions at depths of 1 cm in a mouse model of breast cancer metastasis. Most notably, ReANCs previously deployed for detection of multi-organ metastases resolved bone lesions earlier than contrast-enhanced magnetic resonance imaging (MRI). We engineered tumor-targeted ReANCs carrying a therapeutic payload as a potential theranostic for evaluating drug efficacy at the tumor site. In vitro results demonstrated efficacy of ReANCs carrying doxorubicin (Dox), providing sustained release of Dox while maintaining cytotoxic effects comparable to free Dox. Significantly, in a murine model of breast cancer lung metastasis, we demonstrated the ability for therapy monitoring based on measurements of SWIR fluorescence from tumor-targeted ReANCs. These findings correlated with a reduction in lung metastatic burden as quantified via MRI-based volumetric analysis over the course of four weeks. Future studies will address the potential of this novel class of theranostics as a preclinical pharmacological screening tool.

Biodegradable rare earth fluorochloride nanocrystals for phototheranostics.

Rare earth (RE) doped inorganic nanocrystals have been demonstrated as efficient contrast agents for deep tissue shortwave-infrared (SWIR) imaging with high sensitivities leading to potential early detection of tumors. However, a potential concern is the unknown long-term toxicity and incompatibility of inorganic nanocrystals. In this work, biodegradable rare earth nanocrystals of Nd doped SrFCl coated with polydopamine (SrFCl:Nd@PDA) were designed. Instead of traditional fluoride hosts, the chlorinated SrF2 (i.e. SrFCl) with low phonon energy which significantly improved the brightness of SrFCl:Nd in the SWIR region was used as the host. After coating with a NIR-absorptive PDA layer, the SrFCl:Nd nanoparticles serve as not only a contrast agent for photoacoustic imaging, but also a potential photothermal agent for cancer therapy. Moreover, these SrFCl:Nd@PDA nanoparticles can be rapidly and completely degraded in phosphate buffer solution within 1 h, which effectively addresses the concerns of the deleterious effects arising from potential long term accumulation. The increased accumulation and retention at tumor sites, and complete in vivo clearance ∼6 h after injection make these SrFCl:Nd@PDA nanoparticles a promising degradable phototheranostic agent.

High-Performance and Flexible Shortwave Infrared Photodetectors Using Composites of Rare Earth-Doped Nanoparticles.

The growing demand of infrared sensors for emerging applications such as autonomous vehicles and remote control and sensing systems has driven the development of flexible, low-power, and sensitive infrared detectors for seamless product integration. Although semiconducting polymer (SCP)-based photodetectors are promising solutions, challenges in synthesis chemistry and high thermal dark currents associated with narrowing of band gaps have limited their progress. To address these challenges, we have designed a new class of composites comprising SCPs with moderate band gap and rare earth doped-nanoparticles (RENPs) that enable photon-to-electron conversion beyond the SCP's response range. Using this RENP-SCP (RE-SCP) composite, we demonstrated detection at multiple wavelengths (808, 975, and 1532 nm) for planar-type photodetectors. Notably, the RE-SCP composite-based device detected an eye-safe, shortwave infrared (SWIR) source at 1532 nm with high SWIR responsivity of 0.02 A/W and an SWIR external quantum efficiency of 2%. The key attribute governing the excellent SWIR responsivity and sensitivity was the distinctive SWIR upconversion characteristic of RENPs that extended and improved the SCP's detection range and performance, respectively. Additionally, the absence of significant performance degradation of the SWIR photodetector for bending curvatures from 0-0.67 cm-1 highlights the promise of our RE-SCP composite-based flexible SWIR photodetectors.

Engineering the Infrared Luminescence and Photothermal Properties of Double-Shelled Rare-Earth-Doped Nanoparticles for Biomedical Applications.

The nascent field of theranostics, which couples targeted therapy with diagnostics, has catalyzed efforts toward improved nanoprobe designs that facilitate both localized treatment and diagnostic imaging. Rare-earth-doped nanoparticles (RENPs) have emerged as a leading candidate for theranostics because of their versatile synthesis and modification chemistries, photostability, and relative safety. Furthermore, their bright, tunable fluorescence using near-infrared (NIR) excitation enables multispectral imaging with high signal-to-background ratios. In this work, we have synthesized double-shelled RENPs with tunable properties for optimal fluorescent imaging, photoacoustic imaging, and photothermal therapy. The properties of the double-shelled RENPs were tailored by controlling the density of rare-earth ions (i.e., activator or sensitizer) by using either a functional amorphous organic or a crystalline outermost shell. This study systematically analyzes the effects of the functional organic or inorganic outermost shell on the imaging and photothermal conversion properties of our RENPs. Despite the weaker infrared absorption enhancement, the functional organic outermost shell impregnated with a low density of rare-earth ions led to minimal reduction of fluorescence emissions. In contrast, the higher density of rare-earth ions in the inorganic shell led to higher infrared absorption and consequently significant reduction in emissions arising from the undesired optical attenuation. Inorganic shell thickness was therefore modified to reduce the deleterious attenuation, leading to brighter emissions that also enabled the in vitro SWIR detection of ∼2500 cells/cluster. Using the enhanced infrared properties that arise from this functional inorganic layer, which could be engineered to respond to either NIR or SWIR, we demonstrated that (1) bright SWIR emissions allowed detection of small cell clusters; (2) strong PA signals allowed clear visualization of particle distribution within tumors; and (3) strong photothermal effects resulted in localized elevated temperatures. Collectively, these results highlight the utility of these double-shelled RENPs as theranostic agents that are compatible with both photoacoustic or fluorescent imaging platforms.

Surface-Modified Shortwave-Infrared-Emitting Nanophotonic Reporters for Gene-Therapy Applications.

Gene therapy is emerging as the next generation of therapeutic modality with United States Food and Drug Administration approved gene-engineered therapy for cancer and a rare eye-related disorder, but the challenge of real-time monitoring of on-target therapy response remains. In this study, we have designed a theranostic nanoparticle composed of shortwave-infrared-emitting rare-earth-doped nanoparticles (RENPs) capable of delivering genetic cargo and of real-time response monitoring. We showed that the cationic coating of RENPs with branched polyethylenimine (PEI) does not have a significant impact on cellular toxicity, which can be further reduced by selectively modifying the surface characteristics of the PEI coating using counter-ions and expanding their potential applications in photothermal therapy. We showed the tolerability and clearance of a bolus dose of RENPs@PEI in mice up to 7 days after particle injection in addition to the RENPs@PEI ability to distinctively discern lung tumor lesions in a breast cancer mouse model with an excellent signal-to-noise ratio. We also showed the availability of amine functional groups in the collapsed PEI chain conformation on RENPs, which facilitates the loading of genetic cargo that hybridizes with target gene in an in vitro cancer model. The real-time monitoring and delivery of gene therapy at on-target sites will enable the success of an increased number of gene- and cell-therapy products in clinical trials.

Multiscale optical imaging of rare-earth-doped nanocomposites in a small animal model.

Rare-earth-doped nanocomposites have appealing optical properties for use as biomedical contrast agents, but few systems exist for imaging these materials. We describe the design and characterization of (i) a preclinical system for whole animal in vivo imaging and (ii) an integrated optical coherence tomography/confocal microscopy system for high-resolution imaging of ex vivo tissues. We demonstrate these systems by administering erbium-doped nanocomposites to a murine model of metastatic breast cancer. Short-wave infrared emissions were detected in vivo and in whole organ imaging ex vivo. Visible upconversion emissions and tissue autofluorescence were imaged in biopsy specimens, alongside optical coherence tomography imaging of tissue microstructure. We anticipate that this work will provide guidance for researchers seeking to image these nanomaterials across a wide range of biological models.

Synthesis of Uniform Rare Earth Doped Gd2O2S Sub-micron Sized Spheres Using Gas-Aided Sulfurization and their Optical Characteristics.

In this work, we report a detailed study of the synthesis of sub-micron sized Gd2O2S spheres using a two-step process: (1) amorphous precursor synthesis using the solvothermal method where a surfactant was used to control particle morphology, followed by (2) crystallization to form Gd2O2S polycrystalline spheres in a sulfur-rich environment. The crystallization and sulfurization processes are investigated by monitoring the crystal growth at different temperatures and under different environments using mainly x-ray diffraction and analysis of the precursor's thermal decomposition profile. The optical emissions of the Er and Yb-Er doped Gd2O2S upon excitation at 975 nm were investigated to identify the optimal dopant concentrations, optimal heat treatment temperature as well as to further elucidate any fine structure changes. Our results also show that the maximum emission intensities were obtained for a heat treatment temperature of 800 °C, where increased dopant diffusion coupled with non-uniform surface segregation at much higher temperatures led to non-uniform dopant distribution and reduced emission intensities. Our findings from these studies would be useful towards the synthesis of brightly-emitting Gd2O2S based luminescent materials as well as for the controlled gas-aided sulfurization of other metal oxysulfides.

Low Loss Nanostructured Polymers for Chip-scale Waveguide Amplifiers.

On-chip waveguide amplifiers offer higher gain in small device sizes and better integration with photonic devices than the commonly available fiber amplifiers. However, on-chip amplifiers have yet to make its way into the mainstream due to the limited availability of materials with ideal light guiding and amplification properties. A low-loss nanostructured on-chip channel polymeric waveguide amplifier was designed, characterized, fabricated and its gain experimentally measured at telecommunication wavelength. The active polymeric waveguide core comprises of NaYF4:Yb,Er,Ce core-shell nanocrystals dispersed within a SU8 polymer, where the nanoparticle interfacial characteristics were tailored using hydrolyzed polyhedral oligomeric silsesquioxane-graft-poly(methyl methacrylate) to improve particle dispersion. Both the enhanced IR emission intensity from our nanocrystals using a tri-dopant scheme and the reduced scattering losses from our excellent particle dispersion at a high solid loading of 6.0 vol% contributed to the outstanding optical performance of our polymeric waveguide. We achieved one of the highest reported gain of 6.6 dB/cm using a relatively low coupled pump power of 80 mW. These polymeric waveguide amplifiers offer greater promise for integrated optical circuits due to their processability and integration advantages which will play a key role in the emerging areas of flexible communication and optoelectronic devices.

Advancements in infrared imaging platforms: complementary imaging systems and contrast agents.

Recent advancements in the infrared (IR) imaging system design as well as the co-development of compatible contrast agents have facilitated the potential application of fluorescence imaging systems for deep tissue diagnostics and real-time vasculature visualization for intraoperative surgical guidance. Compared to conventional imaging techniques that achieve superior tissue penetration depth through the use of high energy or ionizing radiation sources, complementary chemical compounds, also known as imaging probes or contrast agents, are required to enable enhancement of the imaging sensitivity required for improved image quality in the IR fluorescence imaging technique. Therefore, using a systems-level approach to plan research efforts where the requirements of the imaging setup are considered at the start of the contrast agent design to effectively improve detection sensitivity would reduce the technical entry barrier for the adoption of new technologies. In this paper, we highlight (1) the recent advancements and key operating differences in the reported IR imaging systems, and (2) the recent progress in creating biocompatible IR-emitting contrast agents as well as improving detection sensitivity using targeting agents. The ability to maximize the full benefits and performance of any IR imaging platform is highly reliant on the thorough understanding of the requirements of each imaging platform and the physical characteristics of the complementary contrast agents.

Enhanced near-infrared photoacoustic imaging of silica-coated rare-earth doped nanoparticles.

Near-infrared photoacoustic (PA) imaging is an emerging diagnostic technology that utilizes the tissue transparent window to achieve improved contrast and spatial resolution for deep tissue imaging. In this study, we investigated the enhancement effect of the SiO2 shell on the PA property of our core/shell rare-earth nanoparticles (REs) consisting of an active rare-earth doped core of NaYF4:Yb,Er (REDNPs) and an undoped NaYF4 shell. We observed that the PA signal amplitude increased with SiO2 shell thickness. Although the SiO2 shell caused an observed decrease in the integrated fluorescence intensity due to the dilution effect, fluorescence quenching of the rare earth emitting ions within the REDNPs cores was successfully prevented by the undoped NaYF4 shell. Therefore, our multilayer structure consisting of an active core with successive functional layers was demonstrated to be an effective design for dual-modal fluorescence and PA imaging probes with improved PA property. The result from this work addresses a critical need for the development of dual-modal contrast agent that advances deep tissue imaging with high resolution and signal-to-noise ratio.

Facile Synthesis of Monodisperse Nanostructured Silver Micro-Colloids via Controlled Agglomeration and Coalescence.

Silver nanostructures have expansive applications in catalysis, photonic and electronic devices. In this work, nanostructured silver micro-colloids (MCs) with uniform in size and shape (size distribution <5%) were synthesized via rapid reduction of silver nitrate by ascorbic acid with controlled agglomeration and coalescence. We further propose that the formation of silver MCs was controlled by the chemical reaction kinetics which is governed by the concentration of reduced silver, Agº formed in solution. Preliminary electrical measurements of the highly conductive silver MCs demonstrated their potential application as inks for printed electronics.

Surveillance nanotechnology for multi-organ cancer metastases.

The identification and molecular profiling of early metastases remains a major challenge in cancer diagnostics and therapy. Most in vivo imaging methods fail to detect small cancerous lesions, a problem that is compounded by the distinct physical and biological barriers associated with different metastatic niches. Here, we show that intravenously injected rare-earth-doped albumin-encapsulated nanoparticles emitting short-wave infrared light (SWIR) can detect targeted metastatic lesions in vivo, allowing for the longitudinal tracking of multi-organ metastases. In a murine model of basal human breast cancer, the nanoprobes enabled whole-body SWIR detection of adrenal gland microlesions and bone lesions that were undetectable via contrast-enhanced magnetic resonance imaging (CE-MRI) as early as, respectively, three weeks and five weeks post-inoculation. Whole-body SWIR imaging of nanoprobes functionalized to differentially target distinct metastatic sites and administered to a biomimetic murine model of human breast cancer resolved multi-organ metastases that showed varied molecular profiles at the lungs, adrenal glands and bones. Real-time surveillance of lesions in multiple organs should facilitate pre-therapy and post-therapy monitoring in preclinical settings.

Size and Shell Effects on the Photoacoustic and Luminescence Properties of Dual Modal Rare-Earth-Doped Nanoparticles for Infrared Photoacoustic Imaging.

Infrared-emitting rare-earth (ytterbium and erbium) doped nanoparticles (REDNPs) have recently emerged as an excellent probe for both deep tissue luminescence and photoacoustic (PA) imaging with high resolutions and contrast. Here we report on the first study of the size and surface effects of the infrared PA imaging of dual modal REDNPs. We show that the PA signal amplitude generated by REDNPs is increased by increasing the size and coating the inorganic shell (undoped NaYF4 or silica). We have also discovered that the choice of the coating material is critical as undoped NaYF4 shell was able to enhance PA signal amplitude (by up to ∼30%) and infrared emission (19 times) simultaneously. The simultaneous enhancement of PA signal amplitude and infrared emission was due to increased phonon modes and reduced surface effects. The in vivo PA images obtained demonstrated that in addition to being excellent luminescent probes, the REDNPs also performed as successful PA contrast agents to visualize rodent cortical blood vessels.

Cost-Effective and Highly Photoresponsive Nanophosphor-P3HT Photoconductive Nanocomposite for Near-Infrared Detection.

The advent of flexible optoelectronic devices has accelerated the development of semiconducting polymeric materials. We seek to replace conventional expensive semiconducting photodetector materials with our cost-effective composite system. We demonstrate in this work the successful fabrication of a photoconductive composite film of poly(3-hexylthiophene-2,5-diyl) (P3HT) mixed with NaYF4:Yb,Er nanophosphors that exhibited a ultrahigh photoresponse to infrared radiation. The high photocurrent measured was enabled by the unique upconversion properties of NaYF4:Yb,Er nanophosphors, where low photon energy infrared excitations are converted to high photon energy visible emissions that are later absorbed by P3HT. Here we report, a significant 1.10 × 10(5) times increment of photocurrent from our photoconductive composite film upon infrared light exposure, which indicates high optical-to-electrical conversion efficiency. Our reported work lays the groundwork for the future development of printable, portable flexible and functional photonic composites for light sensing and harvesting, photonic memory devices, and phototransistors.

Line-scanning confocal microscopy for high-resolution imaging of upconverting rare-earth-based contrast agents.

Rare-earth (RE) doped nanocomposites emit visible luminescence when illuminated with continuous wave near-infrared light, making them appealing candidates for use as contrast agents in biomedical imaging. However, the emission lifetime of these materials is much longer than the pixel dwell times used in scanning intravital microscopy. To overcome this limitation, we have developed a line-scanning confocal microscope for high-resolution, optically sectioned imaging of samples labeled with RE-based nanomaterials. Instrument performance is quantified using calibrated test objects. NaYF4 : Er,Yb nanocomposites are imaged in vitro, and in ex vivo tissue specimens, with direct comparison to point-scanning confocal microscopy. We demonstrate that the extended pixel dwell time of line-scanning confocal microscopy enables subcellular-level imaging of these nanomaterials while maintaining optical sectioning. The line-scanning approach thus enables microscopic imaging of this emerging class of contrast agents for preclinical studies, with the potential to be adapted for real-time in vivo imaging in the clinic.