Imaging of Colorectal Cancers Using Activatable Nanoprobes with Second Near‐Infrared Window Emission

Fluorescent probes in the second near‐infrared window (NIR‐II) allow high‐resolution bioimaging with deep‐tissue penetration. However, existing NIR‐II materials often have poor signal‐to‐background ratios because of the lack of target specificity. Herein, an activatable NIR‐II nanoprobe for visualizing colorectal cancers was devised. This designed probe displays H₂S‐activated ratiometric fluorescence and light‐up NIR‐II emission at 900–1300 nm. By using this activatable and target specific probe for deep‐tissue imaging of H₂S‐rich colon cancer cells, accurate identification of colorectal tumors in animal models were performed. It is anticipated that the development of activatable NIR‐II probes will find widespread applications in biological and clinical systems.     

A Far‐Red Emitting Fluorescent Chemogenetic Reporter for In Vivo Molecular Imaging

Far‐red emitting fluorescent labels are highly desirable for spectral multiplexing and deep tissue imaging. Here, we describe the generation of frFAST (far‐red Fluorescence Activating and absorption Shifting Tag), a 14‐kDa monomeric protein that forms a bright far‐red fluorescent assembly with (4‐hydroxy‐3‐methoxy‐phenyl)allylidene rhodanine (HPAR‐3OM). As HPAR‐3OM is essentially non‐fluorescent in solution and in cells, frFAST can be imaged with high contrast in presence of free HPAR‐3OM, which allowed the rapid and efficient imaging of frFAST fusions in live cells, zebrafish embryo/larvae, and chicken embryos. Beyond enabling the genetic encoding of far‐red fluorescence, frFAST allowed the design of a far‐red chemogenetic reporter of protein–protein interactions, demonstrating its great potential for the design of innovative far‐red emitting biosensors.     

Phosphonated Near‐Infrared Fluorophores for Biomedical Imaging of Bone

The conventional method for creating targeted contrast agents is to conjugate separate targeting and fluorophore domains. A new strategy is based on the incorporation of targeting moieties into the non‐delocalized structure of pentamethine and heptamethine indocyanines. Using the known affinity of phosphonates for bone minerals in a model system, two families of bifunctional molecules that target bone without requiring a traditional bisphosphonate are synthesized. With peak fluorescence emissions at approximately 700 or 800 nm, these molecules can be used for fluorescence‐assisted resection and exploration (FLARE) dual‐channel imaging. Longitudinal FLARE studies in mice demonstrate that phosphonated near‐infrared fluorophores remain stable in bone for over five weeks, and histological analysis confirms their incorporation into the bone matrix. Taken together, a new strategy for creating ultra‐compact, targeted near‐infrared fluorophores for various bioimaging applications is described.     

Pre‐targeted Imaging of Protease Activity through In Situ Assembly of Nanoparticles

The pre‐targeted imaging of enzyme activity has not been reported, likely owing to the lack of a mechanism to retain the injected substrate in the first step for subsequent labeling. Herein, we report the use of two bioorthogonal reactions—the condensation reaction of aromatic nitriles and aminothiols and the inverse‐electron demand Diels–Alder reaction between tetrazine and trans‐cyclooctene (TCO)—to develop a novel strategy for pre‐targeted imaging of the activity of proteases. The substrate probe ( TCO‐C‐SNAT4 ) can be selectively activated by an enzyme target (e.g. caspase‐3/7), which triggers macrocyclization and subsequent in situ self‐assembly into nanoaggregates retained at the target site. The tetrazine‐imaging tag conjugate labels TCO in the nanoaggregates to generate selective signal retention for imaging in vitro, in cells, and in mice. Owing to the decoupling of enzyme activation and imaging tag immobilization, TCO‐C‐SNAT4 can be repeatedly injected to generate and accumulate more TCO‐nanoaggregates for click labeling.     

Low‐Fouling Fluoropolymers for Bioconjugation and In Vivo Tracking

The conjugation of hydrophilic low‐fouling polymers to therapeutic molecules and particles is an effective approach to improving their aqueous stability, solubility, and pharmacokinetics. Recent concerns over the immunogenicity of poly(ethylene glycol) has highlighted the importance of identifying alternative low fouling polymers. Now, a new class of synthetic water‐soluble homo‐fluoropolymers are reported with a sulfoxide side‐chain structure. The incorporation of fluorine enables direct imaging of the homopolymer by ¹⁹F MRI, negating the need for additional synthetic steps to attach an imaging moiety. These self‐reporting fluoropolymers show outstanding imaging sensitivity and remarkable hydrophilicity, and as such are a new class of low‐fouling polymer for bioconjugation and in vivo tracking.     

Fluorescence Imaging In Vivo at Wavelengths beyond 1500 nm

Compared to imaging in the visible and near‐infrared regions below 900 nm, imaging in the second near‐infrared window (NIR‐II, 1000–1700 nm) is a promising method for deep‐tissue high‐resolution optical imaging in vivo mainly owing to the reduced scattering of photons traversing through biological tissues. Herein, semiconducting single‐walled carbon nanotubes with large diameters were used for in vivo fluorescence imaging in the long‐wavelength NIR region (1500–1700 nm, NIR‐IIb). With this imaging agent, 3–4 μm wide capillary blood vessels at a depth of about 3 mm could be resolved. Meanwhile, the blood‐flow speeds in multiple individual vessels could be mapped simultaneously. Furthermore, NIR‐IIb tumor imaging of a live mouse was explored. NIR‐IIb imaging can be generalized to a wide range of fluorophores emitting at up to 1700 nm for high‐performance in vivo optical imaging.     

水溶性近红外Ⅱ区荧光Ag2Te量子点的合成

量子点具有独特的光学性质, 在生物医学领域有着广泛的应用. Ag₂Te作为Ⅰ-Ⅵ族量子点中的一员, 因具有生物毒性小和带隙窄等优势而备受关注, 但是目前直接合成水溶性Ag₂Te量子点的方法较少, 而且可调节的荧光发射波长范围有限. 本文提出了一种合成荧光发射波长位于近红外Ⅱ区窗口的水溶性Ag₂Te量子点的新方法. 该方法以硝酸银为银前体, N-乙酰-L-半胱氨酸为配体, 碲前体利用硼氢化钠还原亚碲酸钠得到, 反应条件温和(室温、 大气氛围)且不涉及有毒的有机试剂, 绿色环保. 通过进一步的阳离子处理钝化其表面缺陷, 可以得到尺寸均一的超小粒径水溶性Ag₂Te量子点, 量子点的荧光发射波长为1160 nm, 量子产率为8.0% (以IR26染料为参照). 该方法所合成的Ag₂Te量子点具有良好的生物相容性, 注入小鼠体内后能观察到明显的近红外荧光, 具有进一步生物应用的潜力.     

In Vivo Solid‐Phase Microextraction for Sampling of Oxylipins in Brain of Awake,Moving Rats

Oxylipins are key lipid mediators of important brain processes, including pain, sleep, oxidative stress, and inflammation. For the first time, an in‐depth profile of up to 52 oxylipins can be obtained from the brains of awake moving animals using in vivo solid‐phase microextraction (SPME) chemical biopsy tool in combination with liquid chromatography–high resolution mass spectrometry. Among these, 23 oxylipins are detectable in the majority of healthy wildtype samples. This new approach successfully eliminates the changes in oxylipin concentrations routinely observed during the analysis of post‐mortem samples, allows time‐course monitoring of their concentrations with high spatial resolution in specific brain regions of interest, and can be performed using the same experimental set‐up as in vivo microdialysis (MD) thus providing a new and exciting tool in neuroscience and drug discovery.     

One‐Pot Synthesis of Highly Luminescent Carbon Quantum Dots and Their Nontoxic Ingestion by Zebrafish for In Vivo Imaging

Photoluminescent carbon and/or silicon‐based nanodots have attracted ever increasing interest. Accordingly, a myriad of synthetic methodologies have been developed to fabricate them, which unfortunately, however, frequently involve relatively tedious steps, such as initial surface passivation and subsequent functionalization. Herein, we describe a green and sustainable synthetic strategy to combine these procedures into one step and to produce highly luminescent carbon quantum dots (CQDs), which can also be easily fabricated into flexible thin films with intense luminescence for future roll‐to‐roll manufacturing of optoelectronic devices. The as‐synthesized CQDs exhibited enhanced cellular permeability and low or even noncytotoxicity for cellular applications, as corroborated by confocal fluorescence imaging of HeLa cells as well as cell viability measurements. Most strikingly, zebrafish were directly fed with CQDs for in vivo imaging, and mortality and morphologic analysis indicated ingestion of the CQDs posed no harm to the living organisms. Hence, the multifunctional CQDs potentially provide a rich pool of tools for optoelectronic and biomedical applications.     

Defining a Polymethine Dye for Fluorescence Anisotropy Applications in the Near‐Infrared Spectral Range

Fluorescence anisotropy in the near‐infrared (NIR) spectral range is challenging because of the lack of appropriate NIR fluorescent labels. We have evaluated polymethine fluorescent dyes to identify a leading candidate for NIR anisotropy applications. The NIR dye LS601 demonstrated low fluorescence anisotropy values (r) as a result of its relatively long fluorescent lifetime 1.3 ns. The r value of LS601 unbound and coupled to biological macromolecules was found to have a sufficient dynamic range from 0.24 to 0.37, demonstrating the feasibility of fluorescence anisotropy in the NIR. The viability of fluorescence anisotropy using a NIR label was demonstrated by characterization of dye–protein conjugates. These results open the door to a number of applications in drug discovery, fluorescence anisotropy imaging and contrast agent development.     

Real‐Time In Vivo Detection of Cellular Senescence through the Controlled Release of the NIR Fluorescent Dye Nile Blue

In vivo detection of cellular senescence is accomplished by using mesoporous silica nanoparticles loaded with the NIR‐FDA approved Nile blue (NB) dye and capped with a galactohexasaccharide ( S3 ). NB emission at 672 nm is highly quenched inside S3 , yet a remarkable emission enhancement is observed upon cap hydrolysis in the presence of β‐galactosidase and dye release. The efficacy of the probe to detect cellular senescence is tested in vitro in melanoma SK‐Mel‐103 and breast cancer 4T1 cells and in vivo in palbociclib‐treated BALB/cByJ mice bearing breast cancer tumor.     

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.     

Fluorescence Protection of CdTe Quantum Dots and Usages in Cellular and in vivo Imaging

The nanocomposites of poly(diallyldimethylammonium chloride) (PDADMAC) and CdTe quantum dots (QDs) (i.e., QD-PDADMAC nanocomposites) have been prepared based on electrostatic interaction. Transmission electron microscopy, Fourier transform infrared spectroscopy, and Zeta potential analysis were used to characterize the prepared QD-PDADMAC nanocomposites. It was shown that the QD-PDADMAC nanocomposites have the specific curly-shaped band-like morphology with the width of 4–8 nm and unequal length, and there are rich positive charges on the surface of the nanocomposites. The prepared QD-PDADMAC nanocomposites also had good fluorescence stability. The usage based on their good stability has also been studied by cellular and in vivo imaging. In comparison with the QDs without PDADMAC protection, the obtained QD-PDADMAC nanocomposites have better fluorescence stability and staining effect in biology imaging. After incubation for 24 h at 37°C, A549 lung cancer cells were almost not stained by QDs, similarity to the culture medium control group, and could be clearly stained by QD-PDADMAC nanocomposites. For in vivo imaging of mice by intraperitoneal injection, the fluorescence of QDs could not be seen in abdominal cavity at 30 min, and the nanocomposites' one could still be clearly observed at a longer time (1 h). Moreover, the intestine in the large area of the abdominal cavity was effectively stained.     

Non‐Aqueous Sol–Gel Synthesis of Ultra Small Persistent Luminescence Nanoparticles for Near‐Infrared In Vivo Imaging

Ultra‐small ZnGa₂O₄:Cr³⁺ nanoparticles (6 nm) that exhibit near‐infrared (NIR) persistent luminescence properties are synthesized by using a non‐aqueous sol–gel method assisted by microwave irradiation. The nanoparticles are pegylated, leading to highly stable dispersions under physiological conditions. Preliminary in vivo studies show the high potential for these ultra‐small ZnGa₂O₄:Cr³⁺ nanoparticles to be used as in vivo optical nanotools as they emit without the need for in situ excitation and, thus, avoid the autofluorescence of tissues.     

In Situ Optical Imaging of the Growth of Conjugated Polymer Aggregates

Understanding the mechanisms that contribute to conjugated polymer aggregate formation and growth may yield enhanced control of aggregate morphology and functional properties on the mesoscopic scale. In situ optical imaging of the growth of MEH‐PPV aggregates in real time in controlled swollen films shows that growth occurs through multiple mechanisms and is more complex than previously described. Direct evidence is provided for both Ostwald ripening and aggregate coalescence as operative modes of aggregate growth in solvent swollen films. These growth mechanisms have a distinct and strong impact on the evolution of morphological order of growing aggregates: while Ostwald ripening allows preservation of highly ordered morphology, aggregate coalescence occurs with no preferential orientation, leading to attenuation in degree of ordering.     

Synthesis of Fluorinated and Nonfluorinated Graphene Quantum Dots through a New Top‐Down Strategy for Long‐Time Cellular Imaging

Herein, a new strategy has been developed through combining a microwave‐assisted technique with hydrothermal treatment to reduce graphene waste and improve production yield of graphene quantum dots (GQDs) prepared by top‐down methods. By using fluorinated graphene oxide (FGO) as a raw material, fluorinated GQDs and nonfluorinated GQDs can be synthesized. Additionally, in the fluorinated GQDs, the protective shell supplied by fluorine improves the pH stability of photoluminescence and the strong electron‐withdrawing group, ?F, reduces the π‐ electron density of the aromatic structure; thus inhibiting reactivity toward singlet oxygen produced during irradiation and improving the photostability. Therefore, the as‐prepared fluorinated GQDs with excellent photo‐ and pH stability are suitable for long‐term cellular imaging.     

Highly Efficient Near‐Infrared Delayed Fluorescence Organic Light Emitting Diodes Using a Phenanthrene‐Based Charge‐Transfer Compound

Significant efforts have been made to develop high‐efficiency organic light‐emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) emitters with blue, green, yellow, and orange–red colors. However, efficient TADF materials with colors ranging from red, to deep‐red, to near‐infrared (NIR) have been rarely reported owing to the difficulty in molecular design. Herein, we report the first NIR TADF molecule TPA‐DCPP (TPA=triphenylamine; DCPP=2,3‐dicyanopyrazino phenanthrene) which has a small singlet–triplet splitting (ΔE_ST) of 0.13 eV. Its nondoped OLED device exhibits a maximum external quantum efficiency (EQE) of 2.1 % with a Commission International de L′Éclairage (CIE) coordinate of (0.70, 0.29). Moreover, an extremely high EQE of nearly 10 % with an emission band at λ=668 nm has been achieved in the doped device, which is comparable to the most‐efficient deep‐red/NIR phosphorescent OLEDs with similar electroluminescent spectra.     

Ubiquinone‐Rhodol (UQ‐Rh) for Fluorescence Imaging of NAD(P)H through Intracellular Activation

The nicotinamide adenine dinucleotide (NAD) derivatives NADH and NADPH are critical components of cellular energy metabolism and operate as electron carriers. A novel fluorescent ubiquinone‐rhodol derivative (UQ‐Rh) was developed as a probe for NAD(P)H. By using the artificial promoter [(η⁵‐C₅Me₅)Ir(phen)(H₂O)]²⁺, intracellular activation and imaging of NAD(P)H were successfully demonstrated. In contrast to bioorthogonal chemistry, this “bioparallel chemistry” approach involves interactions with native biological processes and could potentially be used to control or investigate cellular systems.