Self-assembly and applications of ultraconcentrated nanoparticle solutions

Acoustic Levitation Synthesis of Ultrahigh-Density Spherical Nucleic Acid Architectures for Specific SERS Analysis

Controllably regulating the electrostatic bilayer of nanogold colloids is a significant premise for synthesizing spherical nucleic acid (SNA) and building ordered plasmonic architectures. We develop a facile acoustic levitation reactor to universally synthesize SNAs with an ultra-high density of DNA strands, which is even higher than those of various state-of-the-art methods. Results reveal a new mechanism of DNA grafting via acoustic wave that can reconfigure the ligands on colloidal surfaces. The acoustic levitation reactor enables substrate-free three-dimentional (3D) spatial assembly of SNAs with controllable interparticle nanogaps through regulating DNA lengths. This kind of architecture may overcome the plasmonic enhancement limits by blocking electron tunneling and breaking electrostatic shielding in dried aggregations. Finite element simulations support the architecture with 3D spatial plasmonic hotspot matrix, and its ultrahigh surface-enhanced Raman scattering (SERS) capability is evidenced by in situ untargeted tracking of biomolecular events during photothermal stimulation (PTS)-induced cell death process. For biomarker diagnosis, the conjugation of adenosine triphosphate (ATP) aptamer onto SNAs enables in situ targeted tracking of ATP during PTS-induced cell death process. Particularly, the CD71 receptor and integrin α3β1 protein on PL45 cell membrance could be well distinguished by label-free SERS fingerprints when using specific XQ-2d and DML-7 aptamers, respectively, to synthesize SNA architectures. Our current acoustic levitation reactor offers a new method for synthesizing SNAs and enables both targeted and untargeted SERS analysis for tracking molecular events in living systems. It promises great potentials in biochemical synthesis and sensing in future.

Thermally-driven gold@poly(N-isopropylacrylamide) core-shell nanotransporters for molecular extraction

HYPOTHESIS

Molecular extraction efficiency can be boosted with the assistance of nanoparticles (NPs). It is based on adsorption of the extractants in one phase and desorption in another phase, which requires a reversible phase transfer of the NPs.

EXPERIMENTS

We synthesized the gold@poly(N-isopropylacryamide) (Au@PNIPAM) NPs via an interfacial self-assembly method enhanced by post-polymerization. We adopted Rhodamine 6G (R6G) as the model molecule for the extraction test. In comparison, UV-Vis extinction spectra were recorded to monitor the extraction processes with or without the Au@PNIPAM NPs. We further analyzed theoretically with thermodynamics and first-principle calculations.

FINDINGS

The hybrid Au@PNIPAM NPs show a reversible phase transfer between the interface and chloroform phases. The Au NPs assisted extraction efficiency of R6G shows 5 times higher than that without Au NPs. The thermodynamic analysis of the nanotransportation system agrees well with the ab initio density functional theory calculations. This nanoparticle-assisted molecular transportation modifies the extraction kinetics significantly, which will provide further implications for biphasic catalysis, pollutant treatment and drug delivery.

Using flow technologies to direct the synthesis and assembly of materials in solution

In the pursuit of materials with structure-related function, directing the assembly of materials is paramount. The resultant structure can be controlled by ordering of reactants, spatial confinement and control over the reaction/crystallisation times and stoichiometries. These conditions can be administered through the use of flow technologies as evidenced by the growing widespread application of microfluidics for the production of nanomaterials; the function of which is often dictated or circumscribed by size. In this review a range of flow technologies is explored for use in the control of self-assembled systems: including techniques for reagent ordering, mixing control and high-throughput optimisation. The examples given encompass organic, inorganic and biological systems and focus on control of shape, function, composition and size.Graphical abstract.

Experimental determination and analysis of gold nanorod settlement by differential centrifugal sedimentation

Direct measurement of the sedimentation coefficients of gold nanorods with a controlled shape factor was performed using differential centrifugal sedimentation (DCS).

Soy protein-directed one-pot synthesis of gold nanomaterials and their functional conductive devices

Gold nanomaterials were synthesized via a facile and green method, using soy protein isolate as reductant, template, and capping agent.

Plasmofluidics: Merging Light and Fluids at the Micro-/Nanoscale

Plasmofluidics is the synergistic integration of plasmonics and micro/nanofluidics in devices and applications in order to enhance performance. There has been significant progress in the emerging field of plasmofluidics in recent years. By utilizing the capability of plasmonics to manipulate light at the nanoscale, combined with the unique optical properties of fluids and precise manipulation via micro/nanofluidics, plasmofluidic technologies enable innovations in lab-on-a-chip systems, reconfigurable photonic devices, optical sensing, imaging, and spectroscopy. In this review article, the most recent advances in plasmofluidics are examined and categorized into plasmon-enhanced functionalities in microfluidics and microfluidics-enhanced plasmonic devices. The former focuses on plasmonic manipulations of fluids, bubbles, particles, biological cells, and molecules at the micro/nanoscale. The latter includes technological advances that apply microfluidic principles to enable reconfigurable plasmonic devices and performance-enhanced plasmonic sensors. The article is concluded with perspectives on the upcoming challenges, opportunities, and possible future directions of the emerging field of plasmofluidics.

Patterned Threadlike Micelles and DNA-Tethered Nanoparticles: A Structural Study of PEGylated Cationic Liposome-DNA Assemblies

The self-assembly of oppositely charged biomacromolecules has been extensively studied due to its pertinence in the design of functional nanomaterials. Using cryo electron microscopy (cryo-EM), optical light scattering, and fluorescence microscopy, we investigated the structure and phase behavior of PEGylated (PEG: poly(ethylene glycol)) cationic liposome-DNA nanoparticles (CL-DNA NPs) as a function of DNA length, topology (linear and circular), and ρ(chg) (the molar charge ratio of cationic lipid to anionic DNA). Although all NPs studied exhibited lamellar internal nanostructure, NPs formed with short (∼2 kbps), linear, polydisperse DNA were defect-rich and contained smaller domains. Unexpectedly, we found distinctly different equilibrium structures away from the isoelectric point. At ρ(chg) > 1, in the excess cationic lipid regime, threadlike micelles rich in PEG-lipid were found to coexist with NPs, cationic liposomes, and spherical micelles. At high concentrations these PEGylated threadlike micelles formed a well-ordered, patterned morphology with highly uniform intermicellar spacing. At ρ(chg) < 1, in the excess DNA regime and with no added salt, individual NPs were tethered together via long, linear DNA (48 kbps λ-phage DNA) into a biopolymer-mediated floc. Our results provide insight into what equilibrium nanostructures can form when oppositely charged macromolecules self-assemble in aqueous media. Self-assembled, well-ordered threadlike micelles and tethered nanoparticles may have a broad range of applications in bionanotechnology, including nanoscale lithograpy and the development of lipid-based multifunctional nanoparticle networks.

Blossoming of nanosheet structures via a disturbed self-assembly

Nanofabrication has been critical in all kinds of nanotechnology, not only for achieving various nanostructures or nanosystems but also for the application of the nanotechnology. To achieve controllable but simple nanofabrication is one of the central aspirations for many research communities; here, for the first time, we report the growth of nanosheet structures simply by introducing internal disturbances (adding nanoparticles and surface tension) or external disturbances (deformations) to the self-assembly of copolymers induced by evaporation. Nanoparticles, curved surface, and deformations by such as writing or extension have been employed to demonstrate the sensitivity of the nanosheet structures to various disturbances. Finally, a physical model has been proposed to explain how the disturbances contribute to the formation of the nanosheet structures. These significant results indicate a scalable, writable, cost-effective and environmentally friendly nanotechnology that will stimulate new nanofabrication research.

Self-assembly of nanoparticle arrays for use as mirrors, sensors, and antennas

The self-assembly of nanoparticles (NPs) at liquid-liquid interfaces (LLIs) has recently emerged as a promising platform for tunable optical devices, sensors, and catalysis. There are numerous advantages for such platforms when compared to more conventional solid-state counterparts. For example, they do not need engineering, self-assemble if proper conditions are provided, are self-healing, are practically nondegrading, and are easily renewable. Furthermore, they have the added benefit of being able to facilitate the interactions of analytes dissolved in often-inaccessible environments. In this Perspective, we highlight some important recent developments in understanding the mechanisms and applications of self-assembly of NPs at LLIs for use as mirrors and sensors. Finally, we explore future directions in this field, focusing on NP arrays with electrotunable properties assembled at a LLI, which has been one of the driving forces for developing such technologies.