Bipyridine hydrogel for selective and visible detection and absorption of Cd(2+)

Stimuli-directed selective detection of Cu2+ and Cr2O72- ions using a pH-responsive chitosan-poly(aminoamide) fluorescent microgel in aqueous media

In this work, the preparation of a pH-responsive fluorescent microgel, (NANO-PAMAM-CHT), is presented for the selective detection of Cu2+ and Cr2O72- ions. The NANO-PAMAM-CHT (nanosized polyaminoamide-chitosan microgel) is synthesized via aza-Michael addition reactions in a controlled and stepwise manner in water, using easily affordable starting materials like 1,4-diaminobutane, N,N'-methylene-bis-acrylamide, NIPAM and chitosan. NANO-PAMAM-CHT shows pH-responsive fluorescent properties, whereas the fluorescence intensity shows a pH-responsive change. Due to the selective fluorescence quenching, the microgel can detect both Cu2+ ions and Cr2O72- ions selectively at ambient pH in aqueous medium. Moreover, it can selectively differentiate between Cu2+ ion and Cr2O72- ions at pH ∼3 in water. The limits of detection for Cu2+ ions and Cr2O72- ions are reported as 16.9 μM and 2.62 μM, respectively (lower than the minimum allowed level in drinking water) at pH ∼7. Mechanistic study further reveals the dynamic quenching phenomenon in the presence of Cu2+ ions and static quenching in the presence of Cr2O72- ions.

Amide-decorated carbon dots as sensitive and selective probes for fluorescence enhancement detection of cadmium ion

As highly toxic metal ions, cadmium ions (Cd2+) are prevalent in varying concentrations around the world. The establishment of an accurate and effective method for Cd2+ determination with high sensitivity and selectivity is of particular concern. The present work fabricated a fluorescence chemosensor for the detection of Cd2+ based on functionalized carbon dots (CDs), which were hydrothermally prepared using amidated hyperbranched-polyethyleneimine (HPEI). As investigated by FTIR, NMR, and XPS, the stably grafted amide groups endowed the CDs with thermosensitivity and high cloud point due to the change in hydrophilic-hydrophobic behaviors. The CDs chemosensor with optimal amidation degree exhibited high sensitivity, selectivity, and stability in the determination of Cd2+ from various water environments. Notably, the fluorescence intensity enhanced with the increase of Cd2+ concentration, originating from the improved structure rigidity caused by the interactions between grafted amides and Cd2+. These impressive features made the CDs not only sensitive to detecting Cd2+ in low-concentration solutions with a limit of detection of 3.41 nM (the lowest known value for Cd2+ detection) but also accurate for the quantification in high-concentration solutions with a detectable Cd2+ concentration of 6.0 × 10-2 M. Owing to the broad detection range, the CDs developed in present work show great potential applications in various scenarios.

Colorimetric fluorescent paper strip with smartphone platform for quantitative detection of cadmium ions in real samples

Instrument-free, portable and direct read-out mini-devices have wider application prospects in various fields, especially for real-time/on-site detection in environmental science. Herein, a colorimetric fluorescent sensor for detecting cadmium ions (Cd²⁺) based on aggregation-induced emission (AIE) was established, fluorescent paper strips integrated with smartphone platform was further designed for the visualization, on-site and quantitative detection of Cd²⁺. The colorimetric fluorescent sensor was prepared by mixing orange emission glutathione-stabilized gold nanoclusters (AuNCs) with blue emission ethylenediamine functionalized graphene oxide (EDA-GO), and introducing copper ions (Cu²⁺) to quench the orange emission of AuNCs while the blue emission served as a background reference without color change. The Cd²⁺ can induce Cu²⁺-GSH-AuNCs to aggregation and emit orange fluorescence, causing the fluorescent color of the sensor changed from blue to red with the limit of detection (LOD) as low as 33.3 nM in solution. Moreover, fluorescent paper strips integrated with smartphone platform has a sensitive detection of Cd²⁺ with the LOD of 0.1 μM in rice samples. The method reported here might have great application prospects in real-time monitoring of foods safety and environmental protection.

Immune Responsive Release of Tacrolimus to Overcome Organ Transplant Rejection

Transplant rejection is the key problem in organ transplantation and, in clinic, immunosuppressive agents such as tacrolimus are directly administered to the recipients after surgery for T-cell inhibition. However, direct administration of tacrolimus may bring severe side effects to the recipients. Herein, by rational design of two hydrogelators NapPhePheGluTyrOH (1) and Nap d-Phe dPheGluTyrOH (2), a facile method of immune responsive release of tacrolimus is developed from their hydrogels to overcome organ transplantation rejection. Upon incubation with protein tyrosine kinase, which is activated in T cells after organ transplantation, the tacrolimus-encapsulating Gel 1 or Gel 2 is disassembled to release tacrolimus. Cell experiments show that both Gel 1 and Gel 2 have better inhibition effect on the activated T cells than free drug tacrolimus. Liver transplantation experiments indicate that, after 7 days of treatment of same dose tacrolimus, the recipient rats in the Gel 2 group show significantly extended median survival time of 22 days while the recipients treated with conventional tacrolimus medication have a median survival time of 13 days. It is expected herein that this "smart" facile method of immune responsive release of tacrolimus can be applied to overcome organ transplantation rejection in clinic in the near future.

Tandem Enzymatic Self-Assembly and Slow Release of Dexamethasone Enhances Its Antihepatic Fibrosis Effect

Many chronic liver diseases will advance to hepatic fibrosis and, if without timely intervention, liver cirrhosis or even hepatocellular carcinoma. Anti-inflammation could be a standard therapeutic strategy for hepatic fibrosis treatment, but a "smart" strategy of hepatic fibrosis-targeted, either self-assembly or slow release of an anti-inflammation drug ( e.g., dexamethasone, Dex), has not been reported. Herein, we rationally designed a hydrogelator precursor Nap-Phe-Phe-Lys(Dex)-Tyr(H₂PO₃)-OH (1-Dex-P) and proposed a tandem enzymatic strategy of self-assembly and slow release of Dex, with which the precursor exhibited much stronger antihepatic fibrosis effect than Dex both in vitro and in vivo. Enzymatic and cell experiments validated that 1-Dex-P was first dephosphorylated by alkaline phosphatase to yield Nap-Phe-Phe-Lys(Dex)-Tyr-OH (1-Dex), which self-assembled into nanofiber 1-Dex. The nanofiber was then hydrolyzed by esterase to transform into nanofiber 1, accompanied by slow release of Dex. We anticipate that our "smart" tandem enzymatic strategy could be widely employed to design more sophisticated drug delivery systems to achieve enhanced therapeutic efficacy than free drugs in the future.

Methionine-Capped Gold Nanoclusters as a Fluorescence-Enhanced Probe for Cadmium(II) Sensing

Gold nanoclusters (Au NCs) have been considered as novel heavy metal ions sensors due to their ultrafine size, photo-stability and excellent fluorescent properties. In this study, a green and facile method was developed for the preparation of fluorescent water-soluble gold nanoclusters with methionine as a stabilizer. The nanoclusters emit orange fluorescence with excitation/emission peaks at 420/565 nm and a quantum yield of about 1.46%. The fluorescence of the Au NCs is selectively and sensitively enhanced by addition of Cd(II) ions attributed to the Cd(II) ion-induced aggregation of nanoclusters. This finding was further used to design a fluorometric method for the determination of Cd(II) ions, which had a linear response in the concentration range from 50 nM to 35 μM and a detection limit of 12.25 nM. The practicality of the nanoprobe was validated in various environmental water samples and milk powder samples, with a fairly satisfactory recovery percent.

Ultratrace and robust visual sensor of Cd2+ ions based on the size-dependent optical properties of Au@g-CNQDs nanoparticles in mice models

Visual inspection is expected as an ideal technique, which can directly and conveniently detect heavy metal ions by observing the color change. Insensitivity of detecting weakly colored heavy transition metal ions and low adsorptivity of metal ions on nanoparticle surface are two main factors hindering the application of visual detection in heavy metal ions detection. Herein, we demonstrated an operational colorimetric sensor based on the color dependence of nanoparticles aggregation to selective and facile detect weakly colored transition heavy metal Cd²⁺ ions that have been considered as the origin of the "Itai-itai" disease. Uniform colloidal 15nm graphite-like nitride doped carbon quantum dots-capped gold nanoparticle (Au@g-CNQDs) was successfully prepared, wherein the existence of numerous heptazine, carboxyl and hydroxyl groups on the nanoparticle's surface strengthened adsorption of the Cd²⁺ ions on the surface of Au@g-CNQDs through the "cooperative effect". As a consequence, without expensive and intricate exogenous indicators or other special additives, the Cd²⁺ ions could sensitively and quickly captured to detect at ultra-low concentration within 30s by the naked-eye. Under the optimal conditions, the Cd²⁺ ions sensor possesses good analytical performances with a wide linear range of 0.01-3.0μM and a detection limit of 10nM (S/N = 3). Moreover, the biodistribution and aggregation of Cd²⁺ ions were detected effectively in mice organ tissues suggesting its great potential use for real-word applications.

Intracellular coassembly boosts the anti-inflammation capacity of dexamethasone

Dexamethasone (Dex) is one of the essential medicines used to treat inflammation diseases but an overdose of Dex leads to severe adverse effects. The development of a new strategy to boost the anti-inflammation efficacy of Dex is, therefore, important but remains challenging. Herein, by employing an enzyme-instructed self-assembly system, we developed an intracellular coassembly strategy to boost the anti-inflammation efficacy of Dex. Under the catalysis of alkaline phosphatase (ALP), the hydrogelator precursor Nap-Phe-Phe-Tyr(H₂PO₃)-OH (1p) self-assembled to form Gel 1 but dexamethasone sodium phosphate (Dp) only yielded Dex precipitates. However, subjecting equivalent amounts of 1p and Dp together to ALP-triggered coassembly was found to result in the formation of Gel 2. Cell experiments indicated that intracellular ALP-triggered coassembly of Dp with 1p extensively boosted the anti-inflammation efficacy of Dex on two types inflammatory cell models. We envision that, in the near future, our strategy of intracellular coassembly could be widely employed to boost the therapeutic effects of more drugs, while in the meantime used to alleviate the undesired adverse effects of these drugs.

Fluorine substitution enhances the self-assembling ability of hydrogelators

When supramolecular hydrogels are applied as tissue culture scaffolds, their mechanical strength and biocompatibility are the two most important factors that must be considered. However, systematic studies on the structure-mechanical property (or structure-cytotoxicity) relationship of hydrogels are rare. Herein, we rationally designed three hydrogelators and their corresponding phosphate precursors, and systematically studied their self-assembling ability and cytotoxicity. The results indicated that fluorine substitution, but not trifluoromethyl substitution with more fluorine atoms, to the phenylalanine motif enhanced the self-assembling ability and cytotoxicity of the hydrogelators (or precursors). We envision that our preliminary study of hydrogelator fluorination would provide a strategy for the development of supramolecular hydrogels for wider biomedical applications.

Self-assembling bisphosphonates into nanofibers to enhance their inhibitory capacity on bone resorption

Osteoporosis (OP) is an important aging-related disease and the effective prevention/treatment of this disease remains challenging. Considering the acidic microenvironment of bone resorption lacunae, herein, we rationally designed two pamidronate (Pami)-derivative and alendronate (Alen)-derivative hydrogelators and which self-assemble into nanofibers to form supramolecular hydrogels under acidic conditions. Cell viability assay, osteoclastogenesis, osteoclastic gene expression, and in vitro bone resorption results indicated that both and have better inhibitory effects on osteoclastic formation and bone resorption than Pami and Alen, respectively. We anticipate that our new drugs and could "smartly" self-assemble and locally concentrate the drugs at bone resorption lacunae in vivo and subsequently prevent/treat osteoporosis more efficiently.

Dynamic biomaterials: toward engineering autonomous feedback

Dynamic biomaterials are biocompatible engineered systems capable of sensing and actively responding to their surrounding environment. They are of growing interest, both as models in basic research to understand complex cellular systems and in medical applications. Here, we review recent advances in nano-scale and micro-scale biomaterials, specifically artificial cells consisting of compartmentalized biochemical reactions and biologically compatible hydrogels. These dynamic biomaterials respond to stimuli through triggered reactions, reaction cascades, logic gates, and autonomous feedback loops. We outline the advances and remaining challenges in implementing such 'smart' biomaterials capable of autonomously responding to environmental stimuli.

Using "On/Off" (19)F NMR/Magnetic Resonance Imaging Signals to Sense Tyrosine Kinase/Phosphatase Activity in Vitro and in Cell Lysates

Tyrosine kinase and phosphatase are two important, antagonistic enzymes in organisms. Development of noninvasive approach for sensing their activity with high spatial and temporal resolution remains challenging. Herein, we rationally designed a hydrogelator Nap-Phe-Phe(CF3)-Glu-Tyr-Ile-OH (1a) whose supramolecular hydrogel (i.e., Gel 1a) can be subjected to tyrosine kinase-directed disassembly, and its phosphate precursor Nap-Phe-Phe(CF3)-Glu-Tyr(H2PO3)-Ile-OH (1b), which can be subjected to alkaline phosphatase (ALP)-instructed self-assembly to form supramolecular hydrogel Gel 1b, respectively. Mechanic properties and internal fibrous networks of the hydrogels were characterized with rheology and cryo transmission electron microscopy (cryo-TEM). Disassembly/self-assembly of their corresponding supramolecular hydrogels conferring respective "On/Off" (19)F NMR/MRI signals were employed to sense the activity of these two important enzymes in vitro and in cell lysates for the first time. We anticipate that our new (19)F NMR/magnetic resonance imaging (MRI) method would facilitate pharmaceutical researchers to screen new inhibitors for these two enzymes without steric hindrance.

Hierarchical self-assembly of switchable nucleolipid supramolecular gels based on environmentally-sensitive fluorescent nucleoside analogs

Exquisite recognition and folding properties have rendered nucleic acids as useful supramolecular synthons for the construction of programmable architectures. Despite their proven applications in nanotechnology, scalability and fabrication of nucleic acid nanostructures still remain a challenge. Here, we describe a novel design strategy to construct new supramolecular nucleolipid synthons by using environmentally-sensitive fluorescent nucleoside analogs, based on 5-(benzofuran-2-yl)uracil and 5-(benzo[b]thiophen-2-yl)uracil cores, as the head group and fatty acids, attached to the ribose sugar, as the lipophilic group. These modified nucleoside-lipid hybrids formed organogels driven by hierarchical structures such as fibers, twisted ribbons, helical ribbons and nanotubes, which depended on the nature of fatty acid chain and nucleobase modification. NMR, single crystal X-ray and powder X-ray diffraction studies revealed the coordinated interplay of various non-covalent interactions invoked by modified nucleobase, sugar and fatty acid chains in setting up the pathway for the gelation process. Importantly, these nucleolipid gels retained or displayed aggregation-induced enhanced emission and their gelation behavior and photophysical properties could be reversibly switched by external stimuli such as temperature, ultrasound and chemicals. Furthermore, the switchable nature of nucleolipid gels to chemical stimuli enabled the selective two channel recognition of fluoride and Hg(2+) ions through visual phase transition and fluorescence change. Fluorescent organogels exhibiting such a combination of useful features is rare, and hence, we expect that this innovative design of fluorescent nucleolipid supramolecular synthons could lead to the emergence of a new family of smart optical materials and probes.

In situ clicking methylglyoxal for hierarchical self-assembly of nanotubes in supramolecular hydrogel

Methylglyoxal (MGO) is a toxic, dicarbonyl metabolite in all living cells and its detoxification is regulated by glyoxalase I (GLOI). Herein, we rationally designed a precursor o-phenylenediamine-Phe-Phe-OH (1) which “click” reacts with MGO to yield amphiphilic methylquinoxaline-Phe-Phe-OH (2) to self-assemble into supramolecular hydrogel II (Gel II). Cryo-TEM images of Gel II suggested that there existed two orders of self-assembly to form the 32.8 nm width-nanotubes in the hydrogel. The hypothesis was validated with the analyses of the fluorescence, transmittance, and circular dichroism data of the serial dilutions of Gel II. Interference tests indicated that hydrogelation of 1 with MGO would not be affected by nitric oxide (NO). Our results suggest that 1 could be applied for specific hydrogelation with MGO, and potentially the removal of MGO in vitro.

Supramolecular nanofibers of self-assembling peptides and DDP to inhibit cancer cell growth

The addition of cis-dichlorodiamineplatinum(ii) to a taxol-peptide amphiphile results in hydrogelations.

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping address fundamental questions about the mechanisms or the consequences of the self-assembly of molecules, including low molecular weight ones. Finally, we provide a perspective on supramolecular hydrogelators. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring supramolecular hydrogelators as molecular biomaterials for addressing the societal needs at various frontiers.

Enzyme-instructed self-assembly of taxol promotes axonal branching

Axonal branching is important for vertebrate neuron signaling. Taxol has a biphasic effect on axonal branching (i.e., high concentration inhibits axonal growth but low concentration restores it). To the best of our knowledge, low concentration of taxol to promote axonal branching has not been reported yet. Herein, we rationally designed a taxol derivative Fmoc-Phe-Phe-Lys(taxol)-Tyr(H2PO4)-OH (1) which could be subjected to alkaline phosphatase (ALP)-catalyzed self-assembly to form taxol nanofibers. We found that, at 10 μM, 1 has a microtubule (MT) condensation effect similar to that of taxol on mammalian cells but with more chronic toxicity than taxol on the cells. At a low concentration of 10 nM, 1 not only promoted neurite elongation as taxol did but also promoted axonal branching which was not achieved by using taxol. We propose that self-assembly of 1 along the MTs prohibited their lateral contacts and thus promoted axonal branching. Our strategy of enzyme-instructed self-assembly (EISA) of a taxol derivative provides a new tool for scientists to study the morphology of neurons, as well as their behaviours.

Gathering nanorings via Fe2+–bipyridine coordination

Fe²⁺–bipyridine coordination was used to assemble nanorings into supernanostructures.