Amphiphilic Fluorinated Unimer Micelles as Nanocarriers of Fluorescent Probes for Bioimaging

The unique self-assembly properties of unimer micelles are exploited for the preparation of fluorescent nanocarriers embedding hydrophobic fluorophores. Unimer micelles are constituted by a (meth)acrylate copolymer with oligoethyleneglycol and perflurohexylethyl side chains (PEGMA90-co-FA10) in which the hydrophilic and hydrophobic comonomers are statistically distributed along the polymeric backbone. Thanks to hydrophobic interactions in water, the amphiphilic copolymer forms small nanoparticles (<10 nm), with tunable properties and functionality. An easy procedure for the encapsulation of a small hydrophobic molecule (C153 fluorophore) within unimer micelles is presented. UV-vis, fluorescence, and fluorescence anisotropy spectroscopic experimental data demonstrate that the fluorophore is effectively embedded in the nanocarriers. Moreover, the nanocarrier positively contributes to preserve the good emissive properties of the fluorophore in water. The efficacy of the dye-loaded nanocarrier as a fluorescent probe is tested in two-photon imaging of thick ex vivo porcine scleral tissue.

Aromatic micelles: toward a third-generation of micelles

Micelles are useful and widely applied molecular assemblies, formed from amphiphilic molecules, in water. The majority of amphiphiles possess an alkyl chain as the hydrophobic part. Amphiphiles bearing hydrophilic and hydrophobic polymer chains generate so-called polymeric micelles in water. This review focuses on the recent progress of "aromatic micelles", formed from bent polyaromatic/aromatic amphiphiles, for the development of third-generation micelles. Thanks to multiple host-guest interactions, e.g., the hydrophobic effect and π-π/CH-π interactions, the present micelles display wide-ranging uptake abilities toward various hydrophobic compounds in water. In addition to such host functions, new stimuli-responsive aromatic micelles with pH, light, and redox switches, aromatic oligomer micelles, saccharide-coated aromatic micelles, and related cycloalkane-based micelles were recently developed by our group.

Sub-millisecond Translational and Orientational Dynamics of a Freely Moving Single Nanoprobe

This paper presents a new experiment with which we are able to measure the 3D translational motion of a single particle at 10 μs time resolution and with ∼10 nm spatial resolution while at the same time determining the 3D orientation of the same single particle with 250 μs time resolution. These high time resolutions are ∼40 times greater than previous simultaneous measurements of 3D position and 3D orientation. Detailed numerical simulations and experiments are used to demonstrate that the technique can measure 3D orientation at the shot-noise limit. The microscope is also able to simultaneously measure the length or width (with the other assumed) of the plasmonic nanorods used here in situ and nondestructively, which should yield a greater understanding of the underlying dynamics. This technique should be applicable to a broad range of problems where environments which change in space and time may perturb physical and chemical dynamics.

Information bounds in determining the 3D orientation of a single emitter or scatterer using point-detector-based division-of-amplitude polarimetry

Determining the 3D orientation of a single molecule or particle, encoded in its polar and azimuthal angles, is of interest for a variety of fields, being relevant to a range of questions in elementary chemical reactivity, biomolecular motors, and nanorheology. A popular experimental method, known as division-of-amplitude polarimetry, for determining the real-time orientation of a single particle is to split the emitted/scattered light into multiple polarizations and to measure the light intensity using point detectors at these polarizations during a time interval Δt. Here, we derive the Cramér-Rao lower bounds for this method from the perspective of information theory in the cases of utilizing a chromophore or a scattering particle as a 3D orientation probe. Such Cramér-Rao lower bounds are new for using this experimental method to measure the full 3D orientation in both the scattering case and the fluorescence case. These results show that, for a scatterer, the information content of one photon is 1.16 deg^-2 in the polar and 58.71 deg^-2 in the azimuthal angles, respectively. For a chromophore, the information content of one photon is 2.54 deg^-2 in the polar and 80.29 deg^-2 in the azimuthal angles. In addition, the Cramér-Rao lower bound scales with the square root of the total signal photons. To determine orientation to an uncertainty of one degree requires 7.40 × 10⁴ and 2.34 × 10³ photons for the polar and the azimuthal angles, respectively, for fluorescence, whereas it takes 1.62 × 10⁵ and 3.20 × 10³ photons for scattering. This work provides experimentalists new guidelines by which future experiments can be designed and interpreted.

Exploiting the unique specialty of hydrazone functionality: Synthesis of a highly sensitive UV-Vis active solvatochromic probe

The unique physico-chemical attributes of the hydrazone functionality have been extensively studied for a diverse range of chemical, biological and analytical applications. The synthesis of a highly sensitive hydrazone based UV-Vis active solvatochromic probe that exhibits excellent sensitivity toward sensing of solvent polarity, microstructural changes and onset of micellization in aqueous systems was carried out. Specifically, synthesis of 2,4-dinitrophenyl-2-(2-nitrobenzylidene)hydrazone (DNPNBH), through an easy to carry, atom economical, one-pot single step approach via use of low-cost precursors viz. ortho-nitrobenzaldehyde and 2,4-dinitrophenyl hydrazine is presented. The UV-Vis absorption features of the synthesized hydrazone exhibit excellent sensitivity toward the polarity of its immediate microenvironment. The microenvironment polarity sensing potential of DNPNBH is demonstrated for some single solvent systems and DMF-Water mixture as a model binary solvent system and the results are supported by quantum mechanical calculations. Use of the DNPNBH as a probe (at concentrations many orders lower than required for conventional probes) to precisely reflect the onset of micellization and estimation of critical micelle concentration (CMC) of amphiphilic molecules (5.25 mM for SDS, 1.53 mM for CTAB and 0.055 mM for Brij56) in aqueous solutions is also demonstrated. The results clearly qualify the synthesized hydrazone as a highly sensitive UV-Vis probe that can be employed for reliable sensing of solvent polarity, composition dependence of physicochemical attributes in mixed solvent systems and the estimation of CMC of surfactant systems via spectrophotometry.

Solvatochromic characteristics of dansyl molecular probes bearing alkyl diamine chains

A series of dansyl-based fluorescent probes bearing linear alkyl-1,n-diamine chains of different length (DA_1.n, n = 2-8, 10, 12) was characterized in terms of the absorptive and emissive features in solvents of different polarity and hydrogen bond donor/hydrogen bond acceptor character. The probes show solvent-dependent absorption, a feature that is uncommon among dansyl derivatives. The dual emission of DA_1.n probes is strong in non-aqueous solvents and is influenced by the chain length and interactions with the solvent. Solvent effects on the spectral parameters were rationalized on the basis of the Kamlet-Taft and Catalán solvatochromic models, in order to quantify the degree of polarity-driven and hydrogen bonding interactions. A comparative discussion of the results predicted by the two models was made. In ground state, the DA_1.n probes act as hydrogen bond acceptors. In excited state, hydrogen bonding is less favoured, the solute-solvent interactions being governed by the increasing polarity of the solvent that results in a large bathochromic shift of the emission. A comparison was made with the spectral features previously reported for the corresponding series of bis-dansyl fluorescent probes (2DA_1.n).

Bent Anthracene Dimers as Versatile Building Blocks for Supramolecular Capsules

This Account provides a comprehensive summary of our 1-decade-long investigations into bent anthracene dimers as versatile building blocks for supramolecular capsules. The investigations initiated in 2008 with the design of an anthracene dimer with a meta-phenylene spacer bearing two substituents on the convex side. Using the bent polyaromatic building block, we began to develop novel supramolecular capsules from two different synthetic approaches. One is a coordination approach, which was pursued by converting the building block into a bent ligand with two pyridine units at the terminal positions. The ligands quantitatively assemble into an M₂L₄-type capsule through coordination bonding with metal ions. The other is a π-stacking approach, which was followed by utilizing the block as a bent amphiphilic molecule with two trimethylammonium groups at the spacer. In water, the amphiphiles spontaneously assemble into a micelle-type capsule through the hydrophobic effect and π-stacking interactions. Simple modification of the building block allowed us to prepare a wide variety of coordination capsules as well as π-stacking capsules, bearing different hydrophilic side-chains, terminal substitutions, connecting units, polyaromatic panels, or spacer units. The coordination capsule possesses a rigid cavity, with a diameter of ∼1 nm, surrounded by multiple anthracene panels. The spherical polyaromatic cavity binds various synthetic molecules (e.g., paracyclophanes, corannulene, BODIPY, and fullerene C₆₀) in aqueous solutions. With the aid of the polyaromatic shell, photochemically and thermally reactive radical initiators and oligosulfurs are greatly stabilized in the cavity. Biomolecules such as hydrophilic sucrose and oligo(lactic acid)s as well as hydrophobic androgenic hormones are bound by the capsule with high selectivity. In addition, long amphiphilic poly(ethylene oxide)s are threaded into the closed shell of the capsule(s) to generate unusual pseudorotaxane-shaped host-guest complexes in water. In contrast, the π-stacking capsule furnishes a flexible cavity, adaptable to the size and shape of guest molecules, encircled by multiple anthracene panels. In water, the capsule binds hydrophobic fluorescent dyes (e.g., Nile red and DCM) in the cavity. Simple grinding of the bent amphiphile with highly hydrophobic nanocarbons such as fullerenes, nanographenes, and carbon nanotubes (followed by sonication) as well as metal-complexes such as Cu(II)-phthalocyanines and Mn(III)-tetraphenylporphyrins leads to the efficient formation of water-soluble host-guest complexes upon encapsulation. Red emission from otherwise water-deactivated Eu(III)-complexes is largely enhanced in water through encapsulation. Moreover, the incorporation of pH- and photoswitches into the amphiphile affords stimuli-responsive π-stacking capsules, capable of releasing bound guests by the addition of acid and light irradiation, respectively, in water. The host functions of the coordination and π-stacking capsules are complementary to each other, which enables selection of the capsule-type depending on the envisioned target. We are convinced that continued investigation of the present supramolecular capsules featuring the bent anthracene dimer and its derivatives will further increase their value as advanced molecular tools for synthetic, analytical, material, biological, and/or medical applications.