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Principles Of Fluorescence Spectroscopy

Functional π-Gelators and Their Applications

Over the past few years, there has been a great deal of interest in the development of hydrogel materials with tunable structural, mechanical, and rheological properties, which exhibit rapid and autonomous self-healing and self-recovery for utilization in a broad range of applications, from soft robotics to tissue engineering. However, self-healing hydrogels generally either possess mechanically robust or rapid self-healing properties but not both. Hence, the development of a mechanically robust hydrogel material with autonomous self-healing on the time scale of seconds is yet to be fully realized. Here, the current advances in the development of autonomous self-healing hydrogels are reviewed. Specifically, methods to test self-healing efficiencies and recoveries, mechanisms of autonomous self-healing, and mechanically robust hydrogels are presented. The trends indicate that hydrogels that self-heal better also achieve self-healing faster, as compared to gels that only partially self-heal. Recommendations to guide future development of self-healing hydrogels are offered and the potential relevance of self-healing hydrogels to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.

Self-Healing Hydrogels

Detection Ying Zhou,†,‡ Jun Feng Zhang, and Juyoung Yoon*,† †Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea ‡Key Laboratory of Medicinal Chemistry for Natural Resource, School of Chemical Science and Technology, Yunnan University, Kunming, 650091, P. R. China College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650500, P. R. China

Fluorescence and colorimetric chemosensors for fluoride-ion detection.

Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

HeLa 229 cells were treated with methotrexate (MTX) and doxorubicin (DOX), utilizing fourth generation (G4), amine terminated poly(amidoamine) {PAMAM} dendrimer as the drug carrier. In vitro kinetic studies of the release of both MTX and DOX in presence and absence of G4, amine terminated PAMAM dendrimers suggest that controlled drug release can be achieved in presence of the dendrimers. The cytotoxicity studies indicated improved cell death by dendrimer-drug combination, compared to the control experiments with dendrimer or drug alone at identical experimental conditions. Furthermore, HeLa 229 cells were imaged for the first time utilizing the intrinsic emission from the PAMAM dendrimers and drugs, without incorporating any conventional fluorophores. Experimental results collectively suggest that the decreased rate of drug efflux in presence of relatively large sized PAMAM dendrimers generates high local concentration of the dendrimer-drug combination inside the cell, which renders an easy way to image cell lines utilizing the intrinsic emission properties of PAMAM dendrimer and encapsulated drug molecule.

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Tumor cell imaging using the intrinsic emission from PAMAM dendrimer: a case study with HeLa cells

Herein, we describe the design, synthesis and drug release kinetics of a low molecular weight gel based on an aryl ether dendron, under in vitro conditions. The first generation dendron self-assembles and forms gels, resulting in a robust three-dimensional fibrous network, to facilitate controlled release of molecules. While aryl ether dendrons are known for their enhanced self-assembling propensity, these systems have not been used for drug release studies. The self-assembled system was characterized using SEM, TEM, rheology and PXRD experiments. In vitro cytotoxicity of the dendron gel was studied and the results show that the dendron gel is biocompatible. The effect of gel leaching and the exposure time on NIH/3T3 cells is also studied. Further, the gel based on poly aryl ether dendron derivative (D1) is capable of entrapping model hydrophilic dyes and a local anaesthetic drug (prilocaine hydrochloride), where the D1 gel could effectively entrap about 1.5 mg of prilocaine hydrochloride per 5 mg of gelator. The in vitro drug release suggests that the release kinetics is inversely proportional to the gelator wt%, and the lowest release rate obtained is 1.75 min−n with 0.7 gelator wt%. The release profiles of prilocaine hydrochloride are fitted with the Peppas–Korsmeyer model, and the results depict a non-Fickian diffusion mechanism. These studies indicate that the poly aryl ether dendron based gel shows desirable characteristics and also displays promising possibilities of expanding dendron based drug delivery systems for transdermal applications.

In vitro study of a glucose attached poly(aryl ether) dendron based gel as a drug carrier for a local anaesthetic

Co-facial stacking can result in aggregation-caused quenching (ACQ) in conjugated organic luminogens. This study provides an attractive 'slip-stack' self-assembly approach which can eliminate the occurrence of ACQ. The obtained results from steady-state and time-resolved optical studies, along with X-ray diffraction and computational studies demonstrate aggregation-induced emission enhancement (AIEE) of a donor-π-acceptor based 1,3-diarylpropynone, namely 1-(naphthalenyl)-3-(pyren-1-yl)prop-2-yn-1-one (PYNAP). Unlike the monomer, which exhibits poor photoluminescence in solution (φf =2 % in ACN), the twisted manifold of PYNAP allows the orientation of the molecules in a slip-stack fashion during the course of aggregation, which not only avoids a direct co-facial arrangement, but also induces augmented rigidity, leading to restricted intramolecular rotation (RIR) and enhanced emission quantum yield (φf =5 % in ACN/H2 O). The aggregation behavior of PYNAP's congener, 1-phenyl-3-(pyren-1-yl)prop-2-yn-1-one (PYPH) reinforces the hypothesis that slip-stack assembly is a useful strategy for AIEE in polycyclic hydrocarbon luminogens.

Effect of Slip-Stack Self-Assembly on Aggregation-Induced Emission and Solid-State Luminescence in 1,3-Diarylpropynones

Photoinduced electron transfer (PET) from europium(II)-complexes to variety of organic electron acceptors has been investigated in tetrahydrofuran (THF), 1,2-dimethoxyethane (DME) and acetonitrile (ACN). Laser flash photolysis (LFP) study indicates the formation of radical cation of the donor {Eu (II)} and radical/radical anion of corresponding acceptors, confirming the photoinduced electron transfer. Time resolved luminescence quenching experiments showed that rate constants of forward electron transfer are in the range of 10 8 –10 9  M −1  s −1 . Furthermore, experimentally obtained rate constants are in good agreement with calculated electron transfer rate constants using Marcus equation with a reorganization energy ( λ ) of 45 kcal/mol. Interestingly, the excited state decay from radical ion pair formed in Eu(II)-ketone systems revealed that back electron transfer (BET) rate constants are 4–5 order of magnitude less ( k bet  = 10 4 –10 5  s −1 ) compared to that of forward electron transfer, under the present experimental conditions. The significant decrease in rate is attributed to the large energy barrier for the back electron transfer process, which involves transformation of an otherwise stable trivalent lanthanide to its thermodynamically less stable divalent oxidation state. This investigation reveals, for the first time, that divalent europium complexes are promising candidates for generating long lived charge separated states in the excited state in the presence of suitable acceptors.

Edamana Prasad

Papers

Tumor cell imaging using the intrinsic emission from PAMAM dendrimer: a case study with HeLa cells

In vitro study of a glucose attached poly(aryl ether) dendron based gel as a drug carrier for a local anaesthetic

Effect of Slip-Stack Self-Assembly on Aggregation-Induced Emission and Solid-State Luminescence in 1,3-Diarylpropynones

Photoinduced electron transfer from Eu(II)-complexes to organic molecules: Rate and mechanistic investigation

Critical role of surfactants in the formation of digestively-ripened, ultra-small (r<2 nm) copper oxide quantum dots