Linyong Zhu

Highly discriminating photorelease of anticancer drugs based on hypoxia activatable phototrigger conjugated chitosan nanoparticles.

An ultimately selective photorelease system of chitosan-nanoparticles is constructed. Only under unique aspects of tumor-hypoxia physiological conditions, the preliminary locked phototrigger is unlocked by biological reduction to enable the release of the caged drug either by visible light or two-photon near-IR (NIR) excitation. This approach provides a highly discriminating photorelease of anticancer drug to hypoxic tumor cells, but not to healthy normal cells.

Development of an Indole-Based Boron-Dipyrromethene Fluorescent Probe for Benzenethiols

Discrimination between chemically related benzenethiols and aliphatic thiols represents a big problem. In this paper, a fluorescent probe, Bodipy-1, containing an indole-based Bodipy as a fluorophore and a 2,4-dinitrobenzenesulfonyl group as a recognition unit was constructed to achieve the selectivity between them. The Bodipy group in the prepared probe was selectively released through aromatic nucleophilic substitution by thiolate anions from benzenethiols, resulting in blue-red switching in the emission spectra in buffer solutions; that is, two new peaks of the phenol/phenolate state of Bodipy-2 at 565 and 629 nm appeared in emission spectra. By varying the pH value from 6.6 to 8.8, the intensity ratio of I(565)/I(629) varies from 2.0 to 0.3 after complete conversion to Bodipy-2, a ca. 7-fold emission ratio change. This ratiometric emission property by varying the pH value makes Bodipy-1 a promising probe to discriminate benzenethiols from aliphatic thiols by careful selection of the reaction pH.

Target-activated coumarin phototriggers specifically switch on fluorescence and photocleavage upon bonding to thiol-bearing protein.

A new concept in which only the molecular target, such as a thiol-bearing protein, can activate the phototrigger has been demonstrated. Such target-activatable phototriggers comprise three parts: a 7-aminocoumarin phototrigger, an electron acceptor (maleimide) that efficiently quenches the coumarin excited state, and a caged leaving group attached to the coumarin. In the absence of mercaptans, photoinduced electron transfer between coumarin and maleimide effectively blocks both the fluorescence and photocleavage pathways. Thiol-bearing molecules, however, readily annihilate the electron acceptor and thus restore the phototrigger for photorelease of the caged cargo (e.g., biotin). Unlike traditional phototriggers, functional-group-activated phototriggers allow easy handling under ambient light, report specific bonding to the target, and enable photocleavage capability selectively at the binding site in situ, thus effectively positioning the photoreleased cargo at the target. Meanwhile, the unique feature of thiol-specific activation of the fluorescence and photocleavage make our new phototrigger a universal tool that can be used to identify accurately protein cysteine S-nitrosylation, a physiologically important posttranslational modification.

Preparation of highly luminescent CdTe/CdS core/shell quantum dots.

An effective shell-coating route is developed for covering oil-soluble CdTe quantum dots (QDs), which usually tend to aggregate during the heating-up process involved in shell formation. The new route is based on balancing the coordinating capacity and the activation effect of selected surfactants. The thus obtained highly luminescent CdTe/CdS core/shell QDs exhibit photoluminescence quantum yields as high as 92%--among the best results obtained so far for luminescent semiconductor nanocrystals. By changing the size of the CdTe core, or the thickness of the CdS shell, the emission colors of the obtained core/shell nanocrystals can be tuned between the visible and near-infrared regions of the spectrum following an identical procedure.

Spatiotemporally Controllable and Cytocompatible Approach Builds 3D Cell Culture Matrix by Photo‐Uncaged‐Thiol Michael Addition Reaction

DOI: 10.1002/adma.201306061 proved harmless to live cells. [ 5a , 9 ] However, the spontaneous reaction caused by intrinsic Michael reactivity forfeits all spatial and temporal control. In addition, free thiol groups are susceptible to air oxidation and thus severely limit the storage and extent of crosslinking reactions, [ 1c ] which is indispensable in 3D gel forming, both in thiol-ene and thiol-Michael reactions. Herein, a new concept of photocrosslinking mechanism is demonstrated, in which light controls where and when thiolMichael addition occurs in 3D and light dose controls gel stiffness, thus providing a unique approach particularly suitable for fabricating 3D cell-culture matrix. Specifi cally, Scheme 1 depicts a distinct methacrylate monomer attached with macrocyclic coumarin-caged thiol (MCT) was copolymerized with polyethyleneglycol methacrylate (PEG-MA) to generate the desired photo-responsive gelling macromolecule (PGM). Upon photo-excitation, the intramolecular photocleavage of PGM liberated free thiols by a photoheterolysis mechanism through ion pairs but not free radical intermediates, [ 10 ] which subsequently reacted with another macromolecule bearing multimaleimide groups via thiol-Michael addition to generate hydrogels. The results of the photo-uncaged-thiol Michael addition reaction produce a spatiotemporally controllable gelation without reliance on the free radical formation. Such a phototriggered thiol-Michael addition offers additional salient features: (i) no oxygen inhibition and less thiols oxidation because thiols are generated in situ; (ii) no cytotoxic smallmolecules generated during the photo-gelling because of the unique macrocyclic photo-uncaging mechanism; (iii) no UV-damage to live cells because visible light (λ > 400 nm) or two photon excitation is used to phototrigger gelation. A series of PGMs have been prepared by varying the molar ratio of MCT to PEG-MA (Figure S1 and Table S1), and PGM4 (the molar ratio of MCT to PEG-MA is 1:4, as verifi ed by nitrogen elemental analysis (N% = 4.4%) and GPC (M n = 32 662 g mol −1 , PDI = 2.23)) was chosen as the gelling material because of its appropriate content of caged thiols and hydrophilic properties. Photo-irradiating PGM4 produced free thiols in situ, which crossed linked four-arm PEG tetra-maleimide (PEG-4Mal, 10 kDa) or a Dextran maleimide (Dextran-Mal, 10 kDa) via a Michael addition reaction. Eliminating non-specifi c interactions to biomolecules, PEGyl molecule was chosen as a model building material and enabled us to tailor the biophysical properties of the polymeric gels as a “blank slate” material. [ 11 ] Dextran-Mal was utilized as another alternative building materials due to its biodegradable feature With the rapid progress of tissue engineering and regenerative medicine, the cell-friendly construction of 3D extracellular matrix (ECM) in a precisely controlled manner is urgently needed. [ 1 ] This important concept in 3D cell culture resides in the biomimicry of native extracellular matrix, which recapitulates major aspects of the native cellular microenvironment, infl uencing cell differentiation, proliferation, survival and migration through both biochemical interactions and mechanical cues. [ 2 ] Among all ECM candidates, hydrogels—a highly hydrated and cross-linked polymeric network emerges as an attractive one because their biocompatibility and controllable intrinsic structures allow facilely incorporating essential biophysical and biochemical signals to cells. [ 3 ]

Building Biomedical Materials using Photochemical Bond Cleavage

Light can be used as an external trigger to precisely determine where and when a process is initiated as well as how much of the process is being consumed. Phototriggers are a type of photoresponsive functional group that undergo an irreversible photolysis reaction by selectively breaking a chemical bond, enabling three fundamental functions: the photoactivation of fluorescent and bioactive molecules; the photocleavable degradation of macromolecular materials; and the photorelease of drugs, active groups, or surface charges from carriers and interfaces. With the expanded applications of light-controlled technology, particularly in living systems, new challenges and improvements of phototriggers are required to fulfill the demands for better sensitivity, faster kinetics, and more-demanding biomedical applications. Here, improvements to several conventional phototriggers are highlighted, and their notable, representative biomedical applications and their challenges are discussed.

Tissue-Integratable and Biocompatible Photogelation by the Imine Crosslinking Reaction.

A novel photogelling mechanism by the phototriggered-imine-crosslinking (PIC) reaction is demonstrated. Hyaluronic acid grafted with o-nitrobenzene, a photogenerated aldehyde group, can quickly photo-crosslink with amino-bearing polymers or proteins. Once the in situ photogelling on a wound occurs, the PIC gelling process can well integrate a hydrogel with surrounding tissue by covalent bonding, thus making it a powerful tool for tissue engineering and regenerative medicine.

7-Amino coumarin based fluorescent phototriggers coupled with nano/bio-conjugated bonds: Synthesis, labeling and photorelease

By several synthetic pathways, we designed and synthesized a new series of unsymmetrical substituted 7-amino coumarin-based phototriggers with various nano/bio-conjugated bonds. The photophysical properties of most of the substituted coumarin-based phototriggers, except for compound P9 with maleimide group, showed no significant change compared with that of 7-(diethylamino)-4-(hydroxylmethyl) coumarin (DEACM-OH, the reported symmetric substituted 7-amine coumarin based phototrigger). Four compounds (P2, P4, P9, 14) were successfully conjugated with typical carriers such as mesoporous silica nanoparticles, biocompatible polymer PEG and common protein BSA, respectively. The efficient photorelease of ibuprofen (IBU) in the model cargo delivery system of MD4 confirmed that our designed phototriggers could serve well as a photo-cage for bioactive molecules and the release can be regulated precisely by manipulating the external irradiation conditions. All the results hinted at the superiority of using these coumarin functional compounds for photo-regulated release in biotechnology and biomedical areas.

Genetically encoded fluorescent sensors reveal dynamic regulation of NADPH metabolism

Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is essential for biosynthetic reactions and antioxidant functions; however, detection of NADPH metabolism in living cells remains technically challenging. We develop and characterize ratiometric, pH-resistant, genetically encoded fluorescent indicators for NADPH (iNap sensors) with various affinities and wide dynamic range. iNap sensors enabled quantification of cytosolic and mitochondrial NADPH pools that are controlled by cytosolic NAD+ kinase levels and revealed cellular NADPH dynamics under oxidative stress depending on glucose availability. We found that mammalian cells have a strong tendency to maintain physiological NADPH homeostasis, which is regulated by glucose-6-phosphate dehydrogenase and AMP kinase. Moreover, using the iNap sensors we monitor NADPH fluctuations during the activation of macrophage cells or wound response in vivo. These data demonstrate that the iNap sensors will be valuable tools for monitoring NADPH dynamics in live cells and gaining new insights into cell metabolism.

Sequential Control over Thiol Click Chemistry by a Reversibly Photoactivated Thiol Mechanism of Spirothiopyran

A novel photocontrolled thiol click chemistry based on spirothiopyran and maleimide is reported. Upon irradiation with λ=365 nm light, the spirothiopyran can isomerize to the open merocyanine form, a thiophenolate group, which can rapidly react with maleimide. The unreacted MC will readily isomerize back to the starting spirothiopyran, which can be repeatedly photoactivated as needed. Thus, this reversible photoactivated thiol confers spatiotemporal sequential control on the thiol-maleimide reaction using only one type of photochemical reaction. Polymer post-functionalization and hydrogel building with subsequent multipatterning using different maleimide molecules in a temporal sequential manner indicate that this photocontrolled Michael addition reaction can modulate the specific chemical events in a sequence.