Self-Assembled Plasmonic Dimers of Amphiphilic Gold Nanocrystals

We report a new strategy to assemble large (>40 nm) gold nanoparticles with isotropic surface chemistry into anisotropic plasmonic dimers by taking advantage of the chain reorganization of the amphiphilic polymer brushes grafted on nanoparticle surfaces in selective solvents. Production of high-purity dimers is of considerable interest for applications requiring strong near-field coupling of surface plasmon resonances. The formation of nanoparticle dimers is confirmed by imaging and spectroscopic characterization at both bulk and single-particle levels. The interparticle plasmonic coupling can be reversibly controlled by modulating the assembly/disassembly of the amphiphilic nanocrystals. The general applicability of surface modification of nanocrystals of diverse chemical compositions and morphologies through tandem “grafting to” and “grafting from” reactions offers the possibility to extend this concept to other types of functional nanocrystals

Biodegradable Theranostic Plasmonic Vesicles of Amphiphilic Gold Nanorods

We have developed surface-initiated organocatalytic ring-opening polymerization on functional nanocrystals and synthesized amphiphilic gold nanorods carrying well-defined mixed polymer brushes of poly(ethylene glycol) and polylactide. Self-assembly of the amphiphilic gold nanorods affords biodegradable plasmonic vesicles that can be destructed by both enzymatic degradation and near-infrared photothermal heating. When tagged with Raman probes, strongly coupled gold nanorods in the self-assembled vesicles give rise to highly active SERS signals. The biodegradable plasmonic vesicles exhibit a unique combination of optical and structural properties that are of particular interest for theranostic applications. We have demonstrated that bioconjugated SERS-active plasmonic vesicles can specifically target EpCAM-positive cancer cells, leading to ultrasensitive spectroscopic detection of cancer cells. Furthermore, integration of photothermal effect of gold nanorods and large loading capacity of the vesicles provides opportunities for localized synergistic photothermal ablation and photoactivated chemotherapy, which have shown higher efficiency in killing targeted cancer cells than either single therapeutic modality. The versatile chemistry of organocatalytic ring-opening polymerization, in conjugation with recent development in synthesizing functional nanocrystals with tailored optical, electronic, and magnetic properties opens the possibilities for constructing multifunctional biodegradable platforms for clinical translation

Flexible All-Solid-State Asymmetric Supercapacitors Based on Free-Standing Carbon Nanotube/Graphene and Mn₃O₄ Nanoparticle/Graphene Paper Electrodes

We report the design of all-solid-state asymmetric supercapacitors based on free-standing carbon nanotube/graphene (CNTG) and Mn₃O₄ nanoparticles/graphene (MG) paper electrodes with a polymer gel electrolyte of potassium polyacrylate/KCl. The composite paper electrodes with carbon nanotubes or Mn₃O₄ nanoparticles uniformly intercalated between the graphene nanosheets exhibited excellent mechanical stability, greatly improved active surface areas, and enhanced ion transportation, in comparison with the pristine graphene paper. The combination of the two paper electrodes with the polymer gel electrolyte endowed our asymmetric supercapacitor of CNTG//MG an increased cell voltage of 1.8 V, a stable cycling performance (capacitance retention of 86.0% after 10 000 continuous charge/discharge cycles), more than 2-fold increase of energy density (32.7 Wh/kg) compared with the symmetric supercapacitors, and importantly a distinguished mechanical flexibility

High-Performance Asymmetric Supercapacitor Based on Graphene Hydrogel and Nanostructured MnO₂

We have successfully fabricated an asymmetric supercapacitor with high energy and power densities using graphene hydrogel (GH) with 3D interconnected pores as the negative electrode and vertically aligned MnO₂ nanoplates on nickel foam (MnO₂-NF) as the positive electrode in a neutral aqueous Na₂SO₄ electrolyte. Because of the desirable porous structure, high specific capacitance and rate capability of GH and MnO₂-NF, complementary potential window of the two electrodes, and the elimination of polymer binders and conducting additives, the asymmetric supercapacitor can be cycled reversibly in a wide potential window of 0–2.0 V and exhibits an energy density of 23.2 Wh kg^–1 with a power density of 1.0 kW kg^–1. Energy density of the asymmetric supercapacitor is significantly improved in comparison with those of symmetric supercapacitors based on GH (5.5 Wh kg^–1) and MnO₂-NF (6.7 Wh kg^–1). Even at a high power density of 10.0 kW kg^–1, the asymmetric supercapacitor can deliver a high energy density of 14.9 Wh kg^–1. The asymmetric supercapacitor also presents stable cycling performance with 83.4% capacitance retention after 5000 cycles

Multifunctional Magnetic Nanochains: Exploiting Self-Polymerization and Versatile Reactivity of Mussel-Inspired Polydopamine

We present a new strategy, built upon the use of mussel-inspired polydopamine (PDA), for constructing multifunctional nanochains of magnetic nanoparticles. One key finding is that self-polymerization of PDA around magnetically aligned nanoparticles affords robust rigid magnetic nanochains with versatile reactivity imparted by PDA. In particular, we have shown that loading of metal nanoparticles on the nanochains via localized reduction by PDA gave rise to magnetically recyclable, self-mixing nanocatalysts. Surface coupling of PDA with nucleophilic thiol and amine groups via Michael addition and/or Schiff base reactions, on the other hand, enabled easy bioconjugation of targeting ligands such as DNA aptamer for specific recognition of the nanochains to cancer cells, which led to magnetolysis of the cancer cells in a spinning magnetic field. The PDA-enabled strategy allows for flexible selection of magnetic building blocks and postsynthesis functionalization, which are of considerable interest for a wide spectrum of chemical and biomedical applications

Robust Nanoparticle–DNA Conjugates Based on Mussel-Inspired Polydopamine Coating for Cell Imaging and Tailored Self-Assembly

We have demonstrated that mussel-inspired polydopamine can serve as an intermediate coating layer for covalently attaching oligonucleotides on nanostructures of diverse chemical nature, which are made possible by the universal adhesion and spontaneous reactivity of polydopamine. Our results have shown that polydopamine can strongly bond to representative nanoparticles (i.e., Au nanoparticles and magnetic polymer nanobeads) and form a thin layer of coating that allows for attachment of commercially available DNA with thiol or amine end functionality. The resulting DNA–nanoparticle conjugates not only show excellent chemical and thermal stability and high loading density of DNA, but the linked DNA also maintain their biological functions in directing cancer cell targeting and undergo DNA hybridization to form multifunctional magnetic core-plasmonic satellite assemblies. The generally applicable strategy opens new opportunities for easy adoption of DNA–nanoparticle conjugates for broad applications in biosensors and nanomedicine

Mussel-Inspired Synthesis of Polydopamine-Functionalized Graphene Hydrogel as Reusable Adsorbents for Water Purification

We present a one-step approach to polydopamine-modified graphene hydrogel, with dopamine serving as both reductant and surface functionalization agents. The synthetic method is based on the spontaneous polymerization of dopamine and the self-assembly of graphene nanosheets into porous hydrogel structures. Benefiting from the abundant functional groups of polydopamine and the high specific surface areas of graphene hydrogel with three-dimensional interconnected pores, the prepared material exhibits high adsorption capacities toward a wide spectrum of contaminants, including heavy metals, synthetic dyes, and aromatic pollutants. Importantly, the free-standing graphene hydrogel can be easily removed from water after adsorption process, and can be regenerated by altering the pH values of the solution for adsorbed heavy metals or using low-cost alcohols for synthetic dyes and aromatic molecules

Growth of Copper Nanocubes on Graphene Paper as Free-Standing Electrodes for Direct Hydrazine Fuel Cells

We have developed a new type of flexible electrodes based on Cu nanocube-decorated free-standing graphene paper (GP) using a facile electrodeposition method. The Cu nanocubes–graphene paper (Cu–GP) hybrid electrode processes remarkable electrocatalytic activity with an onset potential of −0.10 V toward hydrazine oxidation in alkaline solutions and can serve as the catalyst layer for direct hydrazine fuel cells. One interesting finding is that a copper hydroxide/oxide layer in situ formed on Cu nanocube surfaces plays an important role in enhancing the electrocatalytic activity and durability of the electrocatalyst. A totally irreversible and diffusion-controlled oxidation of hydrazine occurs on the electrocatalyst, eventually leading to environmentally friendly products such as nitrogen and water

Coating Graphene Paper with 2D-Assembly of Electrocatalytic Nanoparticles: A Modular Approach toward High-Performance Flexible Electrodes

The development of flexible electrodes is of considerable current interest because of the increasing demand for modern electronics, portable medical products, and compact energy devices. We report a modular approach to fabricating high-performance flexible electrodes by structurally integrating 2D-assemblies of nanoparticles with freestanding graphene paper. We have shown that the 2D array of gold nanoparticles at oil–water interfaces can be transferred on freestanding graphene oxide paper, leading to a monolayer of densely packed gold nanoparticles of uniform sizes loaded on graphene oxide paper. One major finding is that the postassembly electrochemical reduction of graphene oxide paper restores the ordered structure and electron-transport properties of graphene, and gives rise to robust and biocompatible freestanding electrodes with outstanding electrocatalytic activities, which have been manifested by the sensitive and selective detection of two model analytes: glucose and hydrogen peroxide (H₂O₂) secreted by live cells. The modular nature of this approach coupled with recent progress in nanocrystal synthesis and surface engineering opens new possibilities to systematically study the dependence of catalytic performance on the structural parameters and chemical compositions of the nanocrystals

Smart Sensing Based on DNA–Metal Interaction Enables a Label-Free and Resettable Security Model of Electrochemical Molecular Keypad Lock

Recently, molecular keypad locks have received increasing attention. As a new subgroup of smart biosensors, they show great potential for protecting information as a molecular security data processor, rather than merely molecular recognition and quantitation. Herein, label-free electrochemically transduced Ag⁺ and cysteine (Cys) sensors were developed. A molecular keypad lock model with reset function was successfully realized based on the balanced interaction of metal ion with its nucleic acid and chemical ligands. The correct input of “1-2-3” (i.e., “Ag⁺-Cys-cDNA”) is the only password of such molecular keypad lock. Moreover, the resetting process of either correct or wrong input order could be easily made by Cys, buffer, and DI water treatment. Therefore, our system provides an even smarter system of molecular keypad lock, which could inhibit illegal access of unauthorized users, holding great promise in information protection at the molecular level