Dramatic Fluorescence Changes Research Articles

(Invited) Energy Transfer in Stimuli-Responsive Multiblock Nanofibers from Organic Electronic Materials

Techniques for the assembly of hierarchical nanostructures from soft matter have opened the door to many new applications of nanotechnology. Despite these achievements, nanoscale syntheses that rely on self-assembly can be highly dependent on conditions such as solvent and temperature if the integrity of the nanomaterial is to be maintained. Bottlebrush copolymers provide a compelling bottom-up approach to the synthesis of hierarchical nanostructures from soft material, allowing for the preparation of multicompartment structures that remain nanosegregated by virtue of their covalent chemistry. Here we describe methods for the preparation of fiber-like nanomaterials that mimic the multilayer structure of organic electronic devices on individual polymer chains. Narrowly dispersed fibers are prepared from materials commonly used as the hole transport, electron transport, and host materials in organic electronics, with molecular weights on the order of 106 Da. Energy transfer interactions can be regulated by the reversible expansion and collapse of polymer chains, creating dramatic fluorescence changes or activating thermaly activated delayed fluorescence (TADF).

Impact of double-chain surfactant stabilizer on the free active surface sites of gold nanoparticles

Positive and negative charged stabilizing ligands, for example, ammonium surfactants and citrate, influence the catalytic activity of AuNPs greatly, due to their different electrostatic attraction ability with substrates. However, as for the more decisive factor in AuNPs catalyzed reactions, the free active surface sites of AuNPs influenced by different kinds of ammonium surfactants has not been studied yet. In this work, we prepared double chain and mono chain ammonium surfactants capped gold nanoparticles, DDAB-Au and CTAB-Au, and put them into the reduction reaction of uranine by NaBH4. Compared to CTAB-Au, DDAB-Au favors the adsorption of BH4− and generation of metal hydride on the active sites. As a result, DDAB-Au catalyzed reduction of uranine could give shorter induction time. We attribute this phenomenon to a weaker binding affinity of DDAB to the active sites of AuNPs, resulting from the more flexible, less polar and low charge-to-molecular weight ratio properties of DDAB. Fast responding time is one of important criteria in analytical chemistry and sensor chemistry. With dramatic fluorescence changes, some DDAB-Au catalyzed reactions would facilitate the related studies in the fields of catalysis, analysis and biosensors.

A Luminescent Mg-Metal-Organic Framework for Sustained Release of 5-Fluorouracil: Appropriate Host-Guest Interaction and Satisfied Acid-Base Resistance.

It is important to achieve a moderate sustained release rate for drug delivery, so it is critical to regulate the host-guest interactions for the rational design of a carrier. In this work, a nano-sized biocompatible metal-organic framework (MOF), Mg(H2TBAPy)(H2O)3·C4H8O2 (TDL-Mg), was constructed by employing π-conjugated 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4TBAPy) as a ligand and used for 5-fluorouracil (5-FU) loading (28.2 wt %) and sustained slow release. TDL-Mg exhibits a 3D supramolecular architecture featuring a 1D rectangle channel with a size of 6.2 × 8.1 Å2 and a Brunauer-Emmett-Teller surface area of 627 m2·g-1. Channel microenvironment analysis shows that the rigid H2TBAPy2- ligand adopts special torsion to stabilize the channels and offer rich π-binding sites; the partially deprotonated carboxyls not only participate in the formation of strong hydrogen bonds but also create a mild pH buffer environment for biological applications. Suitable host-guest interactions are generated by the synergistic effect of polydirectional hydrogen bonds, multiple π-interactions, and confined channels, which allow 5-FU@TDL-Mg to release 76% of load in 72 h, a medically reasonable rate. Microcalorimetry was used to directly quantify these host-guest interactions with a moderate enthalpy of 22.3 kJ·mol-1, which provides a distinctive thermodynamic interpretation for understanding the relationship between the MOF design and the drug release rate. Additionally, the nano-sized 5-FU@TDL-Mg can be taken up by mouse breast cancer cells (4T1 cells) for imaging based on the dramatic fluorescence change during the release of 5-FU, exhibiting potential applications in biological systems.

Sensitive Detection of Single-Cell Secreted H2O2 by Integrating a Microfluidic Droplet Sensor and Au Nanoclusters.

As an important signaling molecule, hydrogen peroxide (H2O2) secreted externally by the cells influences cell migration, immunity generation, and cellular communications. Herein, we have developed a microfluidic approach with droplets in combination with Au nanoclusters for the sensitive detection of H2O2 secreted by a single cell. Isolated in the ultrasmall volume (4.2 nL) of a microdroplet, single-cell secreted H2O2 can initiate dramatic fluorescence changes of horseradish peroxidase-Au nanoclusters. We have demonstrated an ultrahigh sensitivity (200-400 attomole H2O2 directly measured from a single cell) with good specificity. It offers a useful research tool to study the cell-to-cell differences of H2O2 secretion at the single-cell level.

Highly sensitive fluorescent sensor targeting CuCl2 based on thiophene attached anthracene compound (TA)

A novel thiophene attached anthracene (TA) based fluorescent compound was designed and synthesized. The TA showed a high quantum yield (Qy=0.34) in regard to fluorescence. We applied this TA compound to detect specific metal compound and found that it could identify CuCl2 from other metals through dramatic fluorescence change at λmax=460nm. It showed strong quenching fluorescence property with CuCl2 while with other metal compounds it exhibited strong blue fluorescence emission. UV/Vis absorption spectroscopy clearly demonstrated that the quenching property of TA at λmax=460nm was due to overlapping of the fluorescence peak of TA at λmax=460nm and the absorption band of CuCl2 (from 190nm to 525nm). Binding constant (K′), which was 0.0895mM−2, indicated a complexation ratio between TA and CuCl2 as 1:2 and this interaction induced quenching property.

Optimal Sox-based fluorescent chemosensor design for serine/threonine protein kinases

Fluorescent chemosensors of protein kinase activity provide a continuous, high-throughput sensing format for the study of the roles of these enzymes, which are crucial for regulating cellular function. Specifically, chemosensors using the nonnatural amino acid, Sox, and physiological Mg 2+ levels report phosphorylation with dramatic fluorescence changes that are amenable to real-time and high-throughput analysis. In this article, we report 15 probes for a total of six distinct serine/threonine kinases with large fluorescence increases and good reactivity toward the target kinase. The sensing mechanism is detailed, and the optimal sensing motif is determined. These versatile and powerful sensors provide tools for researchers studying the roles of the targeted kinases in signal transduction, and the design principles provide guidelines for the generation of future fluorescent chemosensors for any serine/threonine kinase.

Metal complexation with Langmuir monolayers of histidyl peptide lipids.

Langmuir monolayers made from peptide-lipid molecules represent a novel direction in the research areas of biomimetic interfaces and two-dimensional supramolecular chemistry. Peptide structures and molecular recognition activities toward other guest molecules have been the focus of previous study. This study reports the investigation of metal complexation to histidine-containing peptide lipids in the organized Langmuir, Langmuir-Schaefer, or Langmuir-Blodgett films. Three peptide lipids PEP1-PEP3, with a histidine amino acid incorporated in the middle of the peptide, were designed and synthesized. The monolayer structures and metal-binding activities of each peptide lipid and their 1:1:1 molar ratio mixture were studied by thermodynamic and spectroscopic techniques. It was found that hard Lewis acid type metal cations such as K+ and Mg2+, and borderline or soft metal cations such as Zn2+, Cu2+, and Cd2+ exhibit clearly different binding activity toward peptide-lipid monolayers. The conformational changes of peptides upon binding with Cu2+ and Zn2+ were partially revealed by FT-IR spectroscopic studies. Furthermore, by adding a fluorescent-probe lipid to the peptide monolayer, dramatic fluorescence change was observed when Cu2+ or Zn2+ bound to the Langmuir and Langmuir-Schaefer films of peptide-lipid monolayers. Metal-protein complexation plays a crucial role in the function and activity of proteins and enzymes. Investigation of metal complexation to organized peptide Langmuir monolayers may provide an alternative approach for the development of artificial metalloproteins and novel supramolecular systems or materials.