Near‐Infrared‐Light‐Mediated Imaging of Latent Fingerprints based on Molecular Recognition

Photoluminescence is one of the most sensitive techniques for fingerprint detection, but it also suffers from background fluorescence and selectivity at the expense of generality. The method described herein integrates the advantages of near‐infrared‐light‐mediated imaging and molecular recognition. In principle, upconversion nanoparticles (UCNPs) functionalized with a lysozyme‐binding aptamer were used to detect fingerprints through recognizing lysozyme in the fingerprint ridges. UCNPs possess the ability to suppress background fluorescence and make it possible for fingerprint imaging on problematic surfaces. Lysozyme, a universal compound in fingerprints, was chosen as the target, thus simultaneously meeting the selectivity and generality criteria in photoluminescence approaches. Fingerprints on different surfaces and from different people were detected successfully. This strategy was used to detect fingerprints with cocaine powder by using UCNPs functionalized with a cocaine‐binding aptamer.     

Near‐Infrared Light and pH‐Responsive Polypyrrole@Polyacrylic acid/Fluorescent Mesoporous Silica Nanoparticles for Imaging and Chemo‐Photothermal Cancer Therapy

We have rationally designed a new theranostic agent by coating near‐infrared (NIR) light‐absorbing polypyrrole (PPY) with poly(acrylic acid) (PAA), in which PAA acts as a nanoreactor and template, followed by growing small fluorescent silica nanoparticles (fSiO₂ NPs) inside the PAA networks, resulting in the formation of polypyrrole@polyacrylic acid/fluorescent mesoporous silica (PPY@PAA/fmSiO₂) core–shell NPs. Meanwhile, DOX‐loaded PPY@PAA/fmSiO₂ NPs as pH and NIR dual‐sensitive drug delivery vehicles were employed for fluorescence imaging and chemo‐photothermal synergetic therapy in vitro and in vivo. The results demonstrate that the PPY@PAA/fmSiO₂ NPs show high in vivo tumor uptake by the enhanced permeability and retention (EPR) effect after intravenous injection as revealed by in vivo fluorescence imaging, which is very helpful for visualizing the location of the tumor. Moreover, the obtained NPs inhibit tumor growth (95.6 % of tumors were eliminated) because of the combination of chemo‐photothermal therapy, which offers a synergistically improved therapeutic outcome compared with the use of either therapy alone. Therefore, the present study provides new insights into developing NIR and pH‐stimuli responsive PPY‐based multifunctional platform for cancer theranostics.     

A Renal‐Clearable Macromolecular Reporter for Near‐Infrared Fluorescence Imaging of Bladder Cancer

Bladder cancer (BC) is a prevalent disease with high morbidity and mortality; however, in vivo optical imaging of BC remains challenging because of the lack of cancer‐specific optical agents with high renal clearance. Herein, a macromolecular reporter (CyP1) was synthesized for real‐time near‐infrared fluorescence (NIRF) imaging and urinalysis of BC in living mice. Because of the high renal clearance (ca. 94 % of the injection dosage at 24 h post‐injection) and its cancer biomarker (APN=aminopeptidase N) specificity, CyP1 can be efficiently transported to the bladder and specially turn on its NIRF signal to report the detection of BC in living mice. Moreover, CyP1 can be used for optical urinalysis, permitting the ex vivo tracking of tumor progression for therapeutic evaluation and easy translation of CyP2 as an in vitro diagnostic assay. This study not only provides new opportunities for non‐invasive diagnosis of BC, but also reveals useful guidelines for the development of molecular reporters for the detection of bladder diseases.     

Dual‐Luminophore‐Labeled Gold Nanoparticles with Completely Resolved Emission for the Simultaneous Imaging of MMP‐2 and MMP‐7 in Living Cells under Single Wavelength Excitation

Although considerable effort has been devoted to the design of various nanoprobes for the fluorescent detection of multiple biomarkers in a single assay, they often suffer from emission‐overlapping, owing to small Stokes shifts and wide emission spectra, which results in cross‐talk and inaccurate quantification. Herein, we report the design and synthesis of a new nanoprobe for multienzyme detection with completely resolved emission peaks under single‐wavelength excitation. The probe was assembled by attaching a cleavable peptide spacer, which was comprised from a matrix metalloproteinase‐2 (MMP‐2) substrate and a MMP‐7 substrate, onto the surface of gold nanoparticles (AuNPs) through cysteine residues. A lanthanide complex, BCTOT‐Eu^III (BCTOT=1,10‐bis(5′‐chlorosulfo‐thiophene‐2′‐yl)‐4,4,5,5,6,6,7,7‐octafluorodecane‐1,3,8,10‐tetraone), and 7‐amino‐4‐methylcoumarin (AMC) were attached to the N terminus and the C terminus of the peptide, respectively. In the presence of one or both targeting enzymes, the substrate was cleaved and fluorescence resonance energy transfer (FRET) between the dyes and AuNPs was prohibited, thereby resulting in the dramatic fluorescence emission of dyes. Importantly, there was no emission cross‐talk between the two dyes, thereby ensuring accurate detection of each enzyme. Based on this, the simultaneous fluorescence image of MMP‐2 and MMP‐7 was accomplished in living cells under single wavelength excitation. The apparent differences in the fluorescence imaging indicated distinct differences between the expression levels of MMPs between the human normal liver cells and the human hepatoma cells.     

Water‐Soluble Triarylborane Chromophores for One‐ and Two‐Photon Excited Fluorescence Imaging of Mitochondria in Cells

Three water‐soluble tetracationic quadrupolar chromophores comprising two three‐coordinate boron π‐acceptor groups bridged by thiophene‐containing moieties were synthesised for biological imaging applications. Compound 3 containing the bulkier 5‐(3,5‐Me₂C₆H₂)‐2,2′‐(C₄H₂S)₂‐5′‐(3,5‐Me₂C₆H₂) bridge is stable over a long period of time, exhibits a high fluorescence quantum yield and strong one‐ and two‐photon absorption (TPA), and has a TPA cross section of 268 GM at 800 nm in water. Confocal laser scanning fluorescence microscopy studies in live cells indicated localisation of the chromophore at the mitochondria; moreover, cytotoxicity measurements proved biocompatibility. Thus, chromophore 3 has excellent potential for one‐ and two‐photon‐excited fluorescence imaging of mitochondrial function in cells.     

In vivo Fluorescence Imaging of Tumors using Molecular Aptamers Generated by Cell‐SELEX

Poor sensitivity and low specificity of current molecular imaging probes limit their application in clinical settings. To address these challenges, we used a process known as cell‐SELEX to develop unique molecular probes termed aptamers with the high binding affinity, sensitivity, and specificity needed for in vivo molecular imaging inside living animals. Importantly, aptamers can be selected by cell‐SELEX to recognize target cells, or even surface membrane proteins, without requiring prior molecular signature information. As a result, we are able to present the first report of aptamers molecularly engineered with signaling molecules and optimized for the fluorescence imaging of specific tumor cells inside a mouse. Using a Cy5‐labeled aptamer TD05 (Cy5‐TD05) as the probe, the in vivo efficacy of aptamer‐based molecular imaging in Ramos (B‐cell lymphoma) xenograft nude mice was tested. After intravenous injection of Cy5‐TD05 into mice bearing grafted tumors, noninvasive, whole‐body fluorescence imaging then allowed the spatial and temporal distribution to be directly monitored. Our results demonstrate that the aptamers could effectively recognize tumors with high sensitivity and specificity, thus establishing the efficacy of these fluorescent aptamers for diagnostic applications and in vivo studies requiring real‐time molecular imaging.     

High‐contrast Noninvasive Imaging of Kidney Clearance Kinetics Enabled by Renal Clearable Nanofluorophores

Noninvasive imaging of kidney clearance kinetics (KCK) of renal clearable probes is key to studying unilateral kidney function diseases, but such imaging is highly challenging to achieve with in vivo fluorescence. While this long‐standing challenge is often attributed to the limited light penetration depth, we found that rapid and persistent accumulation of conventional dyes in the skin “shadowed” real fluorescence signals from the kidneys and prevented noninvasive imaging of KCK, which, however, can be addressed with renal clearable nanofluorophores. By integrating near infrared emission with efficient renal clearance and ultralow background interference, the nanofluorophores can increase kidney‐contrast enhancement and imaging‐time window by approximately 50‐ and 1000‐fold over conventional dyes, and significantly minimize deviation between noninvasive and invasive KCK, laying down a foundation for translating in vivo fluorescence imaging in preclinical noninvasive kidney function assessments.     

Enhanced Fluorescence Imaging and Photodynamic Cancer Therapy Using Hollow Mesoporous Nanocontainers

Here we show that “off‐on” type of photodynamic therapy agents could be developed using hollow mesoporous silica nanoparticles (HMSNPs), which can be used not only for enhancing delivery of photosensitizers to cancer cells but also for enabling switchable optical properties of the photosensitizers. Fluorescence and singlet oxygen generation of the photosensitizer‐loaded HMSNP are turned off in its native state. In vitro cell studies showed that this HMSNP‐based “off‐on” agent may have potential utility in selective fluorescence detection and photodynamic therapy of cancers.     

Study on the Ultrahigh Quantum Yield of Fluorescent P,O‐g‐C3N4 Nanodots and its Application in Cell Imaging

Graphitic carbon nitride nanodots (g‐C₃N₄ nanodots), as a new kind of heavy‐metal‐free quantum dots, have attracted considerable attention because of their unique physical and chemical properties. Although various methods to obtain g‐C₃N₄ nanodots have been reported, it is still a challenge to synthesize g‐C₃N₄ nanodots with ultrahigh fluorescence quantum yield (QY). In this study, highly fluorescent phosphorus/oxygen‐doped graphitic carbon nitride (P,O‐g‐C₃N₄) nanodots were prepared by chemical oxidation and hydrothermal etching of bulk P‐g‐C₃N₄ derived from the pyrolysis of phytic acid and melamine. The as‐prepared P,O‐g‐C₃N₄ nanodots showed strong blue fluorescence and a relatively high QY of up to 90.2 %, which can be ascribed to intrinsic phosphorus/oxygen‐containing groups, and surface‐oxidation‐related fluorescence enhancement. In addition, the P,O‐g‐C₃N₄ nanodots were explored for cell imaging with excellent stability and biocompatibility, which suggest that they have great potential in biological applications.     

Photoswitching Kinetics and Phase‐Sensitive Detection Add Discriminative Dimensions for Selective Fluorescence Imaging

Non‐invasive separation‐free protocols are attractive for analyzing complex mixtures. To increase selectivity, an analysis under kinetic control, through exploitation of the photochemical reactivity of labeling contrast agents, is described. The simple protocol is applied in optical fluorescence microscopy, where autofluorescence, light scattering, as well as spectral crowding presents limitations. Introduced herein is OPIOM (out‐of‐phase imaging after optical modulation), which exploits the rich kinetic signature of a photoswitching fluorescent probe to increase selectively and quantitatively its contrast. Filtering the specific contribution of the probe only requires phase‐sensitive detection upon matching the photoswitching dynamics of the probe and the intensity and frequency of a modulated monochromatic light excitation. After in vitro validation, we applied OPIOM for selective imaging in mammalian cells and zebrafish, thus opening attractive perspectives for multiplexed observations in biological samples.     

Cathepsin B‐Specific Metabolic Precursor for In Vivo Tumor‐Specific Fluorescence Imaging

Recently, metabolic glycoengineering with bioorthogonal click reactions has focused on improving the tumor targeting efficiency of nanoparticles as delivery vehicles for anticancer drugs or imaging agents. It is the key technique for developing tumor‐specific metabolic precursors that can generate unnatural glycans on the tumor‐cell surface. A cathepsin B‐specific cleavable substrate (KGRR) conjugated with triacetylated N‐azidoacetyl‐d ‐mannosamine (RR‐S‐Ac₃ManNAz) was developed to enable tumor cells to generate unnatural glycans that contain azide groups. The generation of azide groups on the tumor cell surface was exogenously and specifically controlled by the amount of RR‐S‐Ac₃ManNAz that was fed to target tumor cells. Moreover, unnatural glycans on the tumor cell surface were conjugated with near infrared fluorescence (NIRF) dye‐labeled molecules by a bioorthogonal click reaction in cell cultures and in tumor‐bearing mice. Therefore, our RR‐S‐Ac₃ManNAz is promising for research in tumor‐specific imaging or drug delivery.     

Diiminic Schiff Bases: An Intriguing Class of Compounds for a Copper‐Nanoparticle‐Induced Fluorescence Study

The condensation products of salicylaldehyde and different diamines constitute an important class of diiminic Schiff bases (DSBs). This class of compounds has been rediscovered as reducing as well as capping agents under UV irradiation. UV irradiation of alkaline DSB solutions in the presence of water‐soluble copper salts has been employed to produce copper nanoparticles (CuNPs). Intriguing CuNP‐stimulated fluorescence behavior of the solution has been observed. Depending upon the nature of the spacer in between two iminic bonds, fluorescence enhancement or quenching is observed. Such surprising fluorescence contrast has been ascribed to far‐field radiation and lossy surface waves.     

CXCR4‐Targeted and MMP‐Responsive Iron Oxide Nanoparticles for Enhanced Magnetic Resonance Imaging

MRI offers high spatial resolution with excellent tissue penetration but it has limited sensitivity and the commonly administered contrast agents lack specificity. In this study, two sets of iron oxide nanoparticles (IONPs) were synthesized that were designed to selectively undergo copper‐free click conjugation upon sensing of matrix metalloproteinase (MMP) enzymes, thereby leading to a self‐assembled superparamagnetic nanocluster network with T₂ signal enhancement properties. For this purpose, IONPs with bioorthogonal azide and alkyne surfaces masked by polyethylene glycol (PEG) layers tethered to CXCR4‐targeted peptide ligands were synthesized and characterized. The IONPs were tested in vitro and T₂ signal enhancements of around 160 % were measured when the IONPs were incubated with cells expressing MMP2/9 and CXCR4. Simultaneous systemic administration of the bioorthogonal IONPs in tumor‐bearing mice demonstrated the signal‐enhancing ability of these ‘smart’ self‐assembling nanomaterials.     

Real‐Time In Vivo Quantitative Monitoring of Drug Release by Dual‐Mode Magnetic Resonance and Upconverted Luminescence Imaging

Insufficient or excess drug doses, due to unknown actual drug concentrations at the focus, are one of the main causes of chemotherapy failure for cancers. In this regard, the real‐time monitoring of the release of anticancer drugs from nanoparticle drug delivery systems is of crucial importance, but it remains a critical and unsolved challenge. Herein, we report the proposal and development of a novel concept of real‐time monitoring of NIR‐triggered drug release in vitro and in vivo by using simultaneous upconverted luminescence (UCL) and magnetic resonance (MR) imaging. Such a monitoring strategy features the high sensitivity of UCL and the high‐resolution, noninvasiveness, and tissue‐depth‐independence of MR imaging. The dual‐mode real‐time and quantitative monitoring of drug release can be applied to determine online the drug concentrations in vivo in the tissue regions of interest and, therefore, to avoid insufficient or excess drug dosings.     

Facile Solvothermal Synthesis of Mesostructured Fe3O4/Chitosan Nanoparticles as Delivery Vehicles for pH‐Responsive Drug Delivery and Magnetic Resonance Imaging Contrast Agents

We report a facile fabrication of a host–metal–guest coordination‐bonding system in a mesostructured Fe₃O₄/chitosan nanoparticle that can act as a pH‐responsive drug‐delivery system. The mesostructured Fe₃O₄/chitosan was synthesized by a solvothermal approach with iron(III) chloride hexahydrate as a precursor, ethylene glycol as a reducing agent, ammonium acetate as a porogen, and chitosan as a surface‐modification agent. Subsequently, doxorubicin (DOX), acting as a model drug (guest), was loaded onto the mesostructured Fe₃O₄/chitosan nanoparticles, with chitosan acting as a host molecule to form the NH₂? Zn^II? DOX coordination architecture. The release of DOX can be achieved through the cleavage of coordination bonds that are sensitive to variations in external pH under weakly acidic conditions. The pH‐responsive nature of the nanoparticles was confirmed by in vitro releases and cell assay tests. Furthermore, the relaxation efficiency of the nanoparticles as high‐performance magnetic resonance imaging contrast agents was also investigated. Experimental results confirm that the synthesized mesostructured Fe₃O₄/chitosan is a smart nanovehicle for drug delivery owing to both its pH‐responsive nature and relaxation efficiency.     

ZnO‐Functionalized Upconverting Nanotheranostic Agent: Multi‐Modality Imaging‐Guided Chemotherapy with On‐Demand Drug Release Triggered by pH

Limited therapeutic efficiency and severe side effects in patients are two major issues existing in current chemotherapy of cancers in clinic. To design a proper theranostic platform seems thus quite needed to target cancer cells accurately by bioimaging and simultaneously release drugs on demand without premature leakage. A novel ZnO‐functionalized upconverting nanotheranostic platform has been fabricated for clear multi‐modality bioimaging (upconversion luminescence (UCL), computed tomography (CT), and magnetic resonance imaging (MRI)) and specific pH‐triggered on‐demand drug release. In our theranostic platform multi‐modality imaging provides much more detailed and exact information for cancer diagnosis than single‐modality imaging. In addition, ZnO can play the role of a “gatekeeper” to efficiently block the drug in the mesopores of the as‐prepared agents until it is dissolved in the acidic environment around tumors to realize sustained release of the drug. More importantly, the biodegradable ZnO, which is non‐toxic against normal tissues, endows the as‐prepared agents with high therapeutic effectiveness but very low side effects. These findings are of great interests and will inspire us much to develop novel effective imaging‐guided on‐demand chemotherapies in cancer treatment.     

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.     

Polyelectrolyte‐Assisted Formation of Molecular Nanoparticles Exhibiting Strongly Enhanced Fluorescence

A polyelectrolyte‐assisted reprecipitation method is developed to fabricate nanoparticles of highly soluble molecules. The approach is demonstrated by using a zwitterionic diaminodicyanoquinodimethane molecule bearing remote ammonium functionalities with high solubility in water as well as organic solvents. Nanoparticles are prepared by injecting aqueous solutions of this compound containing an optimum concentration of sodium poly(styrenesulfonate) into methanol. The strong fluorescence exhibited by the compound in the aggregated state is reflected in the enhanced fluorescence of the polyelectrolyte complex in water. The nanoparticles formed in the colloidal state manifest even stronger fluorescence, which leads to an overall enhancement by about 90 times relative to aqueous solutions of the pure compound. The conditions for achieving the emission enhancement are optimized and a model for the molecular‐level interactions and aggregation effects is developed through a range of spectroscopy, microscopy, and calorimetry investigations and control experiments.