Mixed-Charge Nanocarriers Allow for Selective Targeting of Mitochondria by Otherwise Nonselective Dyes.

Targeted delivery of molecular cargos to specific organelles is of paramount importance for developing precise and effective therapeutics and imaging probes. This work describes a disulfide-based delivery method in which mixed-charged nanoparticles traveling through the endolysosomal tract deliver noncovalently bound dye molecules selectively into mitochondria. This system comprises three elements: (1) The nanoparticles deliver their payloads by a kiss-and-go mechanism - that is, they drop off their dye cargos proximate to mitochondria but do not localize therein; (2) the dye molecules are by themselves nonspecific to any cellular structures but become so with the help of mixed-charge nanocarriers; and (3) the dye is engineered in such a way as to remain in mitochondria for a long time, up to days, allowing for observing dynamic remodeling of mitochondrial networks and long-term tracking of mitochondria even in dividing cells.

Master curve of boosted diffusion for 10 catalytic enzymes.

Molecular agitation more rapid than thermal Brownian motion is reported for cellular environments, motor proteins, synthetic molecular motors, enzymes, and common chemical reactions, yet that chemical activity coupled to molecular motion contrasts with generations of accumulated knowledge about diffusion at equilibrium. To test the limits of this idea, a critical testbed is the mobility of catalytically active enzymes. Sentiment is divided about the reality of enhanced enzyme diffusion, with evidence for and against.

Enhanced Diffusion and Oligomeric Enzyme Dissociation.

The concept that catalytic enzymes can act as molecular machines transducing chemical activity into motion has conceptual and experimental support, but experimental support has involved oligomeric enzymes, often studied under conditions where the substrate concentration is higher than biologically relevant and accordingly exceeds , the Michaelis constant. Urease, a hexamer of subunits, has been considered to be the gold standard demonstrating enhanced diffusion. Here we show that urease and certain other oligomeric enzymes dissociate above into their subunits that diffuse more rapidly, thus providing a simple physical mechanism that contributes to enhanced diffusion in this regime of concentrations.

Robustness of FCS (Fluorescence Correlation Spectroscopy) with Quenchers Present.

Inspired by recent publications doubtful of the FCS technique, we scrutinize how irreversible ("static") and reversible ("dynamic") quenching can influence the interpretation of such data. Textbook presentations often emphasize only how to analyze data in extremes, the absence of quenching or the presence of substantial quenching. Here, we consider intermediate cases where the assessment of photophysics (static quenching, blinking-like triplet-state relaxation) influence on autocorrelation curves can be delicate if dye-labeled objects diffuse on comparably rapid time scales.

Catalytic enzymes are active matter.

Using a microscopic theory to analyze experiments, we demonstrate that enzymes are active matter. Superresolution fluorescence measurements-performed across four orders of magnitude of substrate concentration, with emphasis on the biologically relevant regime around or below the Michaelis-Menten constant-show that catalysis boosts the motion of enzymes to be superdiffusive for a few microseconds, enhancing their effective diffusivity over longer timescales. Occurring at the catalytic turnover rate, these fast ballistic leaps maintain direction over a duration limited by rotational diffusion, driving enzymes to execute wormlike trajectories by piconewton forces performing work of a few against viscosity.

DNA molecules deviate from shortest trajectory when driven through hydrogel.

Dynamic fluorescence-based single-molecule imaging of -DNA molecules driven through agarose hydrogels by DC electric fields reveals that passage through the hydrogel (98.5% water content) induces mobility orthogonal to the external field. Tortuous paths followed by the DNA molecules, which are heavily entangled in the hydrogel mesh as their contour length is nearly 100 times the hydrogel mesh size of 200 nm, cause them to appear to diffuse orthogonal to the driving force.

Comparing Geometry and Chemistry When Confined Molecules Diffuse in Monodisperse Metal-Organic Framework Pores.

The monodisperse pore structure of MOFs (metal-organic frameworks) is advantageous for investigating how porosity influences diffusion. Here we report translational and rotational diffusion using fluorescence correlation spectroscopy and time-correlated single-photon counting, using the three-dimensional pores of the zeolitic-like metal-organic framework family. We compare the influence of size and electric charge as well as dependence on pore size that we controlled through postsynthetic cation-exchange modifications.

Deep line-temporal focusing with high axial resolution and a large field-of-view using intracavity control and incoherent pulse shaping.

Line-temporal focusing has been recognized as an elegant strategy that provides two-photon microscopy with an effective means for fast imaging through parallelization, together with an improved resilience to scattering for deep imaging. However, the axial resolution remains sub-optimal, except when using high NA objectives and a small field-of-view. With the introduction of an intracavity control of the spectral width of the femtosecond laser to adaptively fill the back aperture of the objective lens, line-temporal focusing two-photon microscopy is demonstrated to reach near-diffraction-limited axial resolution with a large back-aperture objective lens, and improved immunity to sample scattering.

Enzyme leaps fuel antichemotaxis.

There is mounting evidence that enzyme diffusivity is enhanced when the enzyme is catalytically active. Here, using superresolution microscopy [stimulated emission-depletion fluorescence correlation spectroscopy (STED-FCS)], we show that active enzymes migrate spontaneously in the direction of lower substrate concentration ("antichemotaxis") by a process analogous to the run-and-tumble foraging strategy of swimming microorganisms and our theory quantifies the mechanism. The two enzymes studied, urease and acetylcholinesterase, display two families of transit times through subdiffraction-sized focus spots, a diffusive mode and a ballistic mode, and the latter transit time is close to the inverse rate of catalytic turnover.

Nanoparticle puzzles and research opportunities that go beyond state of the art.

We present an overview of current progress and research challenges in the field of nanoparticle assembly, touching on the following topics: (1) historical perspective; (2) consideration of what is a nanoparticle; (3) contrast between nanoparticle self-assembly and top-down construction; (4) opportunities for nanoparticles with more intelligent sub-structures; (5) opportunities for nanoparticle systems cued to interact subtly in space and time. In this personal and subjective account, certain holy grails for nanoparticle science and technology are identified.

Colloidal-sized metal-organic frameworks: synthesis and applications.

Colloidal metal-organic frameworks (CMOFs), nanoporous colloidal-sized crystals that are uniform in both size and polyhedral shape, are crystals composed of metal ions and organic bridging ligands, which can be used as building blocks for self-assembly in organic and aqueous liquids. They stand in contrast to conventional metal-organic frameworks (MOFs), which scientists normally study in the form of bulk crystalline powders. However, powder MOFs generally have random crystal size and shape and therefore do not possess either a definite mutual arrangement with adjacent particles or uniformity.

Shape-selected colloidal MOF crystals for aqueous use.

Methods are described to synthesize shape-selectable, monodisperse, aqueous-stable metal-organic frameworks (MOFs) by the reaction of aluminium nitrate with benzene tricarboxylic acid in various aqueous solvent mixtures and acetic acid as the capping ligand. Environmental stability was confirmed by thermal analysis and immersion in aqueous acidic media.

Communication: Time-resolved fluorescence of highly single crystalline molecular wires of azobenzene.

We report the enhanced fluorescence with the remarkably long lifetime (1.17 ns) in the first excited state (S(1)) of highly crystalline molecular wires of azobenzene at the excitation wavelength of 467 nm for the first time. This observation suggests that trans-cis photoisomerization through the rotation or inversion mechanism may not be a favorable pathway after excitation to the S(1) state in highly single crystalline molecular wires of azobenzene due to the hindered motion within densely packed crystal structure.

Nanodiamonds as photocatalysts for reduction of water and graphene oxide.

Detonated nanodiamonds (NDs) exhibit remarkable photocatalytic activity towards the hydrogen gas generation upon 532 nm laser pulse irradiation. Hydrogenation dramatically increases the quantum yield, suggesting that hydrogen-terminated sites work as electron reservoirs. NDs can also be used as effective photocatalysts to reduce graphene oxide.

Photomechanical effects in a dye-doped polymer nanocomposite.

Nile Red (NR) has been widely used as a microenvironmental probe since its luminescence characteristics depend strongly on medium polarity, viscosity, and hydrophobicity. The driving source for the internal motion of NR in rigid media is an absorbed photon that induces the molecule to rotate internally, causing the matrix deformed. Reversible (elastic) deformation and irreversible (plastic) deformation will influence the twisting dynamics in a different manner.

Light-induced isomerization dynamics of a cyanine dye in the modulus-controlled regime.

The trans-cis isomerization of an excited molecule converts light energy into mechanical motion, which interacts cooperatively with its surroundings. To understand such a photodynamic process in solids, we investigated the internal twisting motion of 1,1'-diethyl-2,2'-cyanine iodide (DCI) in a series of poly(alkyl methacrylate) (PAMA) polymers by measuring the Young's moduli of the polymers with atomic force microscopy nanoindentation and the fluorescence lifetimes of the dye with time-correlated single photon counting. We found that the isomerization rate constant obtained from the average lifetime correlated well with the mechanical property of the matrix.

Mechanical properties of polycarbonate and poly(methyl methacrylate) films reinforced with surface-functionalized nanodiamonds.

Polymer nanocomposites (PNCs) possess highly versatile characteristics, depending on the nanofiller properties such as its chemical composition, particle size, dimension, polydispersity, concentration, or surface functional groups. In comparison with micron-sized materials, the nanofiller having a large surface area facilitates stronger interaction with the matrix. In this work, various surface-functionalized nanodiamonds (sf-NDs) having hydroxyl, carboxyl, amino, and amide group were prepared, and dispersed into polycarbonate (PC) and poly(methyl methacrylate) (PMMA) polymers.

Unilamellar nanosheet of layered manganese cobalt nickel oxide and its heterolayered film with polycations.

The exfoliation of layered Li[Mn(1/3)Co(1/3)Ni(1/3)]O(2) into individual monolayers could be achieved through the intercalation of quaternary tetramethylammonium (TMA(+)) ions into protonated metal oxide. An effective exfoliation occurred when the TMA(+)/H(+) ratio was 0.5-50.

Internal motion of an electronically excited molecule in viscoelastic media.

The twisting motion of trans-4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (4-DASPI) in the excited state was investigated in solutions and various polymers in order to understand dependence of molecular rotor dynamics on viscoelasticity. It was observed that the internal motion of electronically excited 4-DASPI correlates strongly with dynamic viscosity and elastic modulus. Our results also showed that condensed phase dynamics of 4-DASPI are governed by the explicit mode coupling between the rotamerizing coordinate and mechanical properties of viscoelastic media.

Internal twisting dynamics of dicyanovinyljulolidine in polymers.

The fluorescence quantum yield of 9-dicyanovinyljulolidine (DCVJ) is very low in fluid solutions but increases markedly in solids because the medium rigidity slows down the internal motion, which acts as a major nonradiative decay channel. In this work, the excited-state twisting motion of DCVJ in polymers was investigated by time-resolved fluorescence spectroscopy, and it was observed that the fluorescence lifetime of DCVJ in polymers depends on the mechanical properties of the medium. Therefore, our results indicate that the elastic modulus is a determining factor for molecular rotor dynamics in soft matter, and its description requires a comprehensive visco-elasto-plastic theory.

Molecular rotor dynamics influenced by the elastic modulus of polyethylene nanocomposites.

We observed that the excited-state twisting motion of 3,3(')-diethyloxacarbocyanine in polymer nanocomposites (PNCs) depends strongly on the elastic modulus of medium. PNCs consist of low density polyethylene dispersed with surface-functionalized nanodiamonds with various alkyl groups. The mechanical properties of the PNCs were measured by a nanoindentation method, and the photoisomerization processes of the cyanine dye doped in the composites were investigated by time-resolved fluorescence spectroscopy.

Soft-chemical exfoliation route to layered cobalt oxide monolayers and its application for film deposition and nanoparticle synthesis.

A colloidal suspension of exfoliated, layered cobalt oxide nanosheets has been synthesized through the intercalation of quaternary tetramethylammonium ions into protonated lithium cobalt oxide. According to atomic force microscopy, exfoliated nanosheets of layered cobalt oxide show a plateau-like height profile with nanometer-level height, underscoring the formation of unilamellar 2D nanosheets. The exfoliation of layered cobalt oxide was cross-confirmed by X-ray diffraction, UV/Vis spectroscopy, and transmission electron microscopy.