Sensorless adaptive optics in the second near-infrared window for deep vascular imaging in vivo.

We have experimentally validated the use of sensorless adaptive optics (AO) to enhance laser scanning confocal microscopy in the second near-infrared (NIR II) spectral range, termed as AO-NIR II confocal microscopy. This approach harnesses a NIR II fluorophore, excited by an 808 nm wavelength and emitting beyond 1000 nm, to visualize intricate structures in deep brain tissues with the intact skull. By leveraging the reduced scattering and aberrations in the NIR II spectrum, we successfully captured a three-dimensional (3D) vascular structure map extending 310 µm beneath the skull. AO typically boosts the fluorescence signal by approximately 2-3 times, leading to a superior contrast and diminished smearing effects. Consequently, small blood vessels at various depths can be clearly visualized, which might otherwise remain undetectable without AO corrections.

Deep Red Light Driven Hydrogen Evolution by Heterojunction Polymer Dots for Diabetic Wound Healing.

We describe small heterojunction polymer dots (Pdots) with deep-red light catalyzed H2 generation for diabetic skin wound healing. The Pdots with donor/acceptor heterojunctions showed remarkably enhanced photocatalytic activity as compared to the donor or acceptor nanoparticles alone. We encapsulate the Pdots and ascorbic acid into liposomes to form Lipo-Pdots nanoreactors, which selectively scavenge ⋅OH radicals in live cells and tissues under 650 nm light illumination. The antioxidant capacity of the heterojunction Pdots is ~10 times higher than that of the single-component Pdots described previously. Under a total light dose of 360 J/cm2, the Lipo-Pdots nanoreactors effectively scavenged ⋅OH radicals and suppressed the expression of pro-inflammatory cytokines in skin tissues, thereby accelerating the healing of skin wounds in diabetic mice. This study provides a feasible solution for safe and effective treatment of diabetic foot ulcers.

Self-Immolative Photosensitizers for Self-Reported Cancer Phototheranostics.

Photosensitizers to precise target and change fluorescence upon light illumination could accurately self-report where and when the photosensitizers work, enabling us to visualize the therapeutic process and precisely regulate treatment outcomes, which is the unremitting pursuit of precision and personalized medicine. Here, we report self-immolative photosensitizers by adopting a strategy of light-manipulated oxidative cleavage of C═C bonds that can generate a burst of reactive oxygen species, to cleave to release self-reported red-emitting products and trigger nonapoptotic cell oncosis. Strong electron-withdrawing groups are found to effectively suppress the C═C bond cleavage and phototoxicity via studying the structure-activity relationship, allowing us to elaborate NG1-NG5 that could temporarily inactivate the photosensitizer and quench the fluorescence by different glutathione (GSH)-responsive groups. Thereinto, NG2 with 2-cyano-4-nitrobenzene-1-sulfonyl group displays excellent GSH responsiveness than the other four. Surprisingly, NG2 shows better reactivity with GSH in weakly acidic condition, which inspires the application in weakly acidic tumor microenvironment where GSH elevates. To this end, we further synthesize NG-cRGD by anchoring integrin αvß3 binding cyclic pentapeptide (cRGD) for tumor targeting. In A549 xenografted tumor mice, NG-cRGD successfully deprotects to restore near-infrared fluorescence because of elevated GSH in tumor site, which is subsequently cleaved upon light irradiation releasing red-emitting products to report photosensitizer working, while effectively ablating tumors via triggered oncosis. The advanced self-immolative organic photosensitizer may accelerate the development of self-reported phototheranostics in future precision oncology.

Site-Specific Modification of Single Domain Antibodies by Enzyme-Immobilized Magnetic Beads.

Nanobodies as imaging agents and drug conjugates have shown great potential for cancer diagnostics and therapeutics. However, site-specific modification of a nanobody with microbial transglutaminase (mTGase) encounters problems in protein separation and purification. Here, we describe a facile yet reliable strategy of immobilizing mTGase onto magnetic beads for site-specific nanobody modification. The mTGase immobilized on magnetic beads (MB-mTGase) exhibits catalytic activity nearly equivalent to that of the free mTGase, with good reusability and universality. Magnetic separation simplifies the protein purification step and reduces the loss of nanobody bioconjugates more effectively than size exclusion chromatography. Using MB-mTGase, we demonstrate site-specific conjugation of nanobodies with fluorescent dyes and polyethylene glycol molecules, enabling targeted immunofluorescence imaging and improved circulation dynamics and tumor accumulation in vivo. The combined advantages of MB-mTGase method, including high conjugation efficiency, quick purification, less protein loss, and recycling use, are promising for site-specific nanobody functionalization and biomedical applications.

Long-Term In Vivo Glucose Monitoring by Polymer-Dot Transducer in an Injectable Hydrogel Implant.

Optical sensors have attracted a great deal of interest for glucose detection. However, their practical applications for continuous glucose monitoring are still constrained by operational reliability in subcutaneous tissues. Here, we show an implantable hydrogel platform embedded with luminescent polymer dots (Pdots) for sensitive and long-term glucose monitoring. We use Pdot transducer in a polyacrylamide hydrogel matrix to construct an implantable platform. The hydrogel-Pdot transducer showed bright luminescence with ratiometric response to glucose changes. The in vitro and in vivo sensitivities of the hydrogel implant were enhanced by varying the enzyme concentration and injection volume. After implantation, the hydrogel with Pdot transducer remained at the implanted site without migration for 1 month and can be removed from the subcutaneous tissue for further analysis. Our results indicate that the hydrogel-Pdot platform maintains the intrinsic sensing property with excellent stability during 1 month implantation, while fibrous capsule formation on the implant in some cases needs to be solved for long-term continuous glucose monitoring.

Near-Infrared Optical Transducer for Dynamic Imaging of Cerebrospinal Fluid Glucose in Brain Tumor.

Aberrant cerebral glucose metabolism is related to many brain diseases, especially brain tumor. However, it remains challenging to measure the dynamic changes in cerebral glucose. Here, we developed a near-infrared (NIR) optical transducer to sensitively monitor the glucose variations in cerebrospinal fluid in vivo. The transducer consists of an oxygen-sensitive nanoparticle combined with glucose oxidase (GOx), yielding highly sensitive NIR phosphorescence in response to blood glucose change. We demonstrated long-term continuous glucose monitoring by using the NIR transducer. After subcutaneous implantation, the glucose transducer provides a strong luminescence signal that can continuously monitor blood glucose fluctuations for weeks. By using the NIR emission of the transducer, we further observed abnormal dynamic changes in cerebrospinal fluid glucose and quantitatively assessed cerebral glucose uptake rates in transgenic mice bearing brain tumors. This study provides a promising method for the diagnosis of various metabolic diseases with altered glucose metabolism.

In Vivo Imaging of Exosomes Labeled with NIR-II Polymer Dots in Liver-Injured Mice.

Mesenchymal stem cell-derived exosomes (MSC-Exos) are emerging as a promising platform for treating various intractable diseases and organ injuries. Monitoring their migration, homing, and therapeutic capability in vivo is essential to develop exosome-based theranostics. Here, we designed fluorescent semiconductor polymer dots (Pdots) in the second near-infrared window (NIR-II) for bright labeling and tracking of MSC-Exos. Glucose-coated Pdots (Pdots-Glu) were able to label MSC-Exos without changing their biological properties. The NIR-II fluorescent Pdots allow for high labeling brightness and long-term in vivo tracking of MSC-Exos. We investigated the biodistributions and therapeutic functions of these labeled MSC-Exos in liver-resected mice. In vivo and ex vivo imaging demonstrated that the Pdot-labeled MSC-Exos injected via the tail vein mainly accumulated in the residual liver tissue. In terms of the therapeutic effect, MSC-Exos may accelerate postoperative liver function recovery by inhibiting inflammatory responses, promoting cell proliferation, and resisting apoptosis. Our results indicated that MSC-Exos therapeutic systems hold promising applications in liver regenerative medicine.

NIR-II Fluorescence Imaging Reveals Bone Marrow Retention of Small Polymer Nanoparticles.

The concept that systemically administered nanoparticles are highly accumulated into the liver, spleen and kidney is a central paradigm in the field of nanomedicine. Here, we report that bone is an important organ for retention of small polymer nanoparticles using in vivo fluorescence imaging in the second near-infrared (NIR-II) window. We prepared different sized polymer nanoparticles with both visible and NIR-II fluorescence. NIR-II imaging reveals that the behavior of nanoparticle distribution in bone was largely dependent on the particle size. Small polymer nanoparticles of ∼15 nm diameter showed fast accumulation and long-term retention in bone, while the nanoparticles larger than ∼25 nm were dominantly distributed in liver. Confocal microscopy of bone sections indicated that the nanoparticles were largely distributed in the endothelial cells of sinusoidal vessels in bone marrow. The study provides promising opportunities for bone imaging and treatment of bone-related disease.

Multimode Time-Resolved Superresolution Microscopy Revealing Chain Packing and Anisotropic Single Carrier Transport in Conjugated Polymer Nanowires.

Here, we developed a novel, multimode superresolution method to perform full-scale structural mapping and measure the energy landscape for single carrier transport along conjugated polymer nanowires. Through quenching of the local emission, the motion of a single photogenerated hole was tracked using blinking-assisted localization microscopy. Then, utilizing binding and unbinding dynamics of quenchers onto the nanowires, local emission spectra were collected sequentially and assembled to create a superresolution map of emission sites throughout the structure. The hole polaron trajectories were overlaid with the superresolution maps to correlate structures with charge transport properties. Using this method, we compared the efficiency of inter- and intrachain hole transport inside the nanowires and for the first time directly measured the depth of carrier traps originated from torsional disorder and chemical defects.

Light-Harvesting Fluorescent Spherical Nucleic Acids Self-Assembled from a DNA-Grafted Conjugated Polymer for Amplified Detection of Nucleic Acids.

The ultralow concentration of nucleic acids in complex biological samples requires fluorescence probes with high specificity and sensitivity. Herein, a new kind of spherical nucleic acids (SNAs) is developed by using fluorescent π-conjugated polymers (FCPs) as a light-harvesting antenna to enhance the signal transduction of nucleic acid detection. Specifically, amphiphilic DNA-grafted FCPs are synthesized and self-assemble into FCP-SNA structures. Tuning the hydrophobicity of the graft copolymer can adjust the size and light-harvesting capability of the FCP-SNAs. We observe that more efficient signal amplification occurs in larger FCP-SNAs, as more chromophores are involved, and the energy transfer can go beyond the Förster radius. Accordingly, the optimized FCP-SNA shows an antenna effect of up to 37-fold signal amplification and the limit of detection down to 1.7 pM in microRNA detection. Consequently, the FCP-SNA is applied to amplified in situ nucleic acid detecting and imaging at the single-cell level.

Measuring Cellular Uptake of Polymer Dots for Quantitative Imaging and Photodynamic Therapy.

There is a great deal of interest in the development of nanoparticles for biomedicine. The question of how many nanoparticles are taken up by cells is important for biomedical applications. Here, we describe a fluorescence method for the quantitative measurement of the cellular uptake of polymer dots (Pdots) and a further estimation of intracellular Pdots photosensitizer for fluorescence imaging and photodynamic therapy. The approach relies on the high brightness, excellent stability, minimal aggregation quenching, and metalloporphyrin doping properties of the Pdots. We correlated the single-cell fluorescence brightness obtained from fluorescence spectrometry, confocal microscopy, and flow cytometry with the number of endocytosed Pdots, which was validated by inductively coupled plasma mass spectrometry. Our results indicated that, on average, ∼1.3 million Pdots were taken up by single cells that were incubated for 4 h with arginine 8-Pdots (40 µg/mL, ∼20 nm diameter). The absolute number of endocytosed Pdots of individual cells could be estimated from confocal microscopy by comparing the single-cell brightness with the average intensity. Furthermore, we investigated the cell viability as a result of an intracellular Pdots photosensitizer, from which the half maximal inhibitory concentration was determined to be ∼7.2 × 105 Pdots per cell under the light dose of 60 J/cm2. This study provides an effective method for quantifying endocytosed Pdots, which can be extended to investigate the cellular uptake of various conjugated polymer carriers in biomedicine.

Improving the Accuracy of Pdot-Based Continuous Glucose Monitoring by Using External Ratiometric Calibration.

Continuous glucose monitoring (CGM) allows type I and II diabetes patients to track changes in their glucose levels, allowing detection of impending hypoglycemia or hyperglycemia. Polymer dots (Pdots) are candidates for use in implanted CGM systems due to their exceptional brightness, photostability, sensitivity, and biocompatibility. However, Pdot glucose transducers are oxygen-dependent, and changes in tissue oxygen levels affect their measurement accuracy. Here, we describe an external ratiometric calibration method that corrects for changes in tissue oxygen levels to improve measurement accuracy. This method uses the ratio of oxygen concentrations inside and outside the Pdot glucose transducer as an indicator of glucose concentration to correct for signal deviations caused by tissue oxygen fluctuations. A second oxygen-sensitive Pdot that is not conjugated with glucose oxidase is used to measure the oxygen concentration outside the Pdot glucose transducer. We describe the theoretical basis for this approach and demonstrate its effectiveness experimentally in a subcutaneous mouse implant model. This external ratiometric system achieves higher accuracy glucose measurements than previous Pdot-based CGM systems and comparable accuracy to current commercial CGM systems, demonstrating the utility of the external ratiometric calibration strategy.

Monitoring Metabolites Using an NAD(P)H-sensitive Polymer Dot and a Metabolite-Specific Enzyme.

We introduce an NAD(P)H-sensitive polymer dot (Pdot) biosensor for point-of-care monitoring of metabolites. The Pdot is combined with a metabolite-specific NAD(P)H-dependent enzyme that catalyzes the oxidation of the metabolite, generating NAD(P)H. Upon UV illumination, the NAD(P)H quenches the fluorescence emission of Pdot at 627 nm via electron transfer, and also fluoresces at 458 nm, resulting in a shift from red to blue emission at higher NAD(P)H concentrations. Metabolite concentration is quantified ratiometrically-based on the ratio of blue-to-red channel emission intensities, with a digital camera-with high sensitivity and specificity. We demonstrate phenylalanine biosensing in human plasma for a phenylketonuria screening test, quantifying several other disease-related metabolites (lactate, glucose, glutamate, and ß-hydroxybutyrate), and a paper-based assay with smartphore imaging for point-of-care use.

Reversible Ratiometric NADH Sensing Using Semiconducting Polymer Dots.

Reduced nicotinamide adenine dinucleotide (NADH) is a key coenzyme in living cells due to its role as an electron carrier in redox reactions, and its concentration is an important indicator of cell metabolic state. Abnormal NADH levels are associated with age-related metabolic diseases and neurodegenerative disorders, creating a demand for a simple, rapid analytical method for point-of-care NADH sensing. Here we develop a series of NADH-sensitive semiconducting polymer dots (Pdots) as nanoprobes for NADH measurement, and test their performance in vitro and in vivo. NADH sensing is based on electron transfer from semiconducting polymer chains in the Pdot to NADH upon UV excitation, quenching Pdot fluorescence emission. In polyfluorene-based Pdots, this mechanism resulted in an on-off NADH sensor; in DPA-CNPPV Pdots, UV excitation resulted in NADH-sensitive emission at two wavelengths, enabling ratiometric detection. Ratiometric NADH detection using DPA-CNPPV Pdots exhibits high sensitivity (3.1 µM limit of detection), excellent selectivity versus other analytes, reversibility, and a fast response (less than 5 s). We demonstrate applications of the ratiometric NADH-sensing Pdots including smartphone-based NADH imaging for point-of-care use.

Fluorescent Bioconjugates for Super-Resolution Optical Nanoscopy.

Fluorescent microscopy techniques are widely used in biological studies. However, the spatial resolution of fluorescent microscopy is restricted by the optical diffraction limit. In the past two decades, super-resolution imaging techniques with different principles have been invented to visualize biomolecules at nanometer scales. The development of nearly all these techniques is closely related to the advances in fluorescent probes. In particular, the intrinsic properties of fluorescent probes constrain the optimal imaging performance of super-resolution nanoscopy techniques. In this review, we summarized the recent progress in fluorescent probe bioconjugates for super-resolution imaging techniques. Examples of these bioconjugates include the widely used fluorescent proteins (FPs), organic dyes, quantum dots (Qdots), carbon dots (Cdots), upconversion nanoparticles (UCNPs), aggregation induced emission (AIE) nanoparticles, and polymer dots (Pdots). Based on the characteristics of the existing probes and their adaptability in current imaging methods, we provide a perspective for further development of fluorescent probes for super-resolution imaging.

Semiconducting Polymer Dots with Dual-Enhanced NIR-IIa Fluorescence for Through-Skull Mouse-Brain Imaging.

Fluorescence probes in the NIR-IIa region show drastically improved imaging owing to the reduced photon scattering and autofluorescence in biological tissues. Now, NIR-IIa polymer dots (Pdots) are developed with a dual fluorescence enhancement mechanism. First, the aggregation induced emission of phenothiazine was used to reduce the nonradiative decay pathways of the polymers in condensed states. Second, fluorescence quenching was minimized by different levels of steric hindrance to further boost the fluorescence. The resulting Pdots displayed a fluorescence QY of ca. 1.7 % in aqueous solution, suggesting an enhancement of ca. 21 times in comparison with the original polymer in tetrahydrofuran (THF) solution. Small-animal imaging by using the NIR-IIa Pdots exhibited a remarkable improvement in penetration depth and signal to background ratio, as confirmed by through-skull and through-scalp fluorescent imaging of the cerebral vasculature of live mice.

Fluorination Enhances NIR-II Fluorescence of Polymer Dots for Quantitative Brain Tumor Imaging.

Here, we describe a fluorination strategy for semiconducting polymers for the development of highly bright second near-infrared region (NIR-II) probes. Tetrafluorination yielded a fluorescence QY of 3.2 % for the polymer dots (Pdots), over a 3-fold enhancement compared to non-fluorinated counterparts. The fluorescence enhancement was attributable to a nanoscale fluorous effect in the Pdots that maintained the molecular planarity and minimized the structure distortion between the excited state and ground state, thus reducing the nonradiative relaxations. By performing through-skull and through-scalp imaging of the brain vasculature of live mice, we quantitatively analyzed the vascular morphology of transgenic brain tumors in terms of the vessel lengths, vessel branches, and vessel symmetry, which showed statistically significant differences from the wild type animals. The bright NIR-II Pdots obtained through fluorination chemistry provide insightful information for precise diagnosis of the malignancy of the brain tumor.

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.

Compact Conjugated Polymer Dots with Covalently Incorporated Metalloporphyrins for Hypoxia Bioimaging.

Hypoxia is closely related to multiple diseases, especially in tumors, which increases the aggressiveness and drug resistance of cancer cells. Precise hypoxia imaging is of great significance for cancer diagnosis and the evaluation of therapeutic effects. A kind of hydrophobic polymer (i.e., PFPtTFPP) as an imaging probe for hypoxia with fluorene as an energy donor and an oxygen-sensitive PtII porphyrin as an energy acceptor was developed. Compact polymer dots (Pdots) with a small size were prepared by nanoprecipitation. The PFPtTFPP Pdots showed excellent hypoxia sensing in solution with high sensitivity and full reversibility. The emission intensity, quantum yields, lifetime, and single-particle brightness significantly increased under hypoxia conditions. Remarkably, hypoxia imaging in vitro and in vivo was realized, and a clear increase in brightness was observed under hypoxia conditions and in the tumor area. Excellent hypoxia imaging ability is beneficial to potential applications in cancer diagnosis.

Polymer Dots Compartmentalized in Liposomes as a Photocatalyst for In Situ Hydrogen Therapy.

Semiconducting polymer dots (Pdots) have recently attracted considerable attention because of their photocatalytic activity as well as tunable optical band gap. In this contribution, we describe the therapeutic application of Pdots through in situ photocatalytic hydrogen generation. Liposomes were employed as nanoreactors to confine the Pdot photocatalyst, reactants, intermediates, and by-products. Upon photon absorption by the Pdots, the catalytic cycle is initiated and repeated within the aqueous interior, while the H2 product diffuses across the lipid bilayer to counteract reactive oxygen species (ROS) overexpressed in diseased tissues. Ensemble and single-particle Förster resonance energy transfer microscopy confirmed the proposed nanoreactor model. We demonstrate that a liposomal nanoreactor containing Pdots and a sacrificial electron donor is a potential photocatalytic nanoreactor for in situ hydrogen therapy.