Synthesis and Characterization of N-Doped Carbon Quantum Dots and its Application for Efficient Delivery of Curcumin in Live Cell.

To improve bioavailability, enhance the solubility and stability of the hydrophobic drug curcumin, nanoparticles such as carbon quantum dots (CQDs) are unique choices. In this study, we present a simple, cost-effective, and eco-friendly method for synthesizing nitrogen-doped carbon quantum dots (N-CQDs) and their application in the efficient delivery of hydrophobic drugs curcumin into live cancer cells. The N-CQDs produced in this study exhibit excellent water solubility, remarkable stability, and high biocompatibility.

Single-Molecule Patch-Clamp FRET Anisotropy Microscopy Studies of NMDA Receptor Ion Channel Activation and Deactivation under Agonist Ligand Binding in Living Cells.

N-methyl-d-aspartate (NMDA) receptor ion channel is activated by the binding of two pairs of glycine and glutamate along with the application of action potential. Binding and unbinding of ligands changes its conformation that plays a critical role in the open-close activities of NMDA receptor. Conformation states and their dynamics due to ligand binding are extremely difficult to characterize either by conventional ensemble experiments or single-channel electrophysiology method.

Single-molecule patch-clamp FRET microscopy studies of NMDA receptor ion channel dynamics in living cells: revealing the multiple conformational states associated with a channel at its electrical off state.

Conformational dynamics plays a critical role in the activation, deactivation, and open-close activities of ion channels in living cells. Such conformational dynamics is often inhomogeneous and extremely difficult to be directly characterized by ensemble-averaged spectroscopic imaging or only by single channel patch-clamp electric recording methods. We have developed a new and combined technical approach, single-molecule patch-clamp FRET microscopy, to probe ion channel conformational dynamics in living cell by simultaneous and correlated measurements of real-time single-molecule FRET spectroscopic imaging with single-channel electric current recording.

Solvation dynamics of biological water in a single live cell under a confocal microscope.

Time-resolved confocal microscopy has been applied to study the cytoplasm and nucleus region of a single live Chinese hamster ovary (CHO) cell. To select the cytoplasm and the nucleus region, two different fluorescent probes are used. A hydrophobic fluorescent dye, DCM, localizes preferentially in the cytoplasm region of a CHO cell.

Deoxycholate induced tetramer of αA-crystallin and sites of phosphorylation: fluorescence correlation spectroscopy and femtosecond solvation dynamics.

Structure and dynamics of acrylodan labeled αA-crystallin tetramer formed in the presence of a bile salt (sodium deoxycholate, NaDC) has been studied using fluorescence correlation spectroscopy (FCS) and femtosecond up-conversion techniques. Using FCS it is shown that, the diffusion constant (D(t)) of the αA-crystallin oligomer (mass ~800 kDa) increases from ~35 μm(2) s(-1) to ~68 μm(2) s(-1). This corresponds to a decrease in hydrodynamic radius (r(h)) from ~6.

An FCS study of unfolding and refolding of CPM-labeled human serum albumin: role of ionic liquid.

The effect of a room temperature ionic liquid (RTIL) on the conformational dynamics of a protein, human serum albumin (HSA), is studied by fluorescence correlation spectroscopy (FCS). For this, the protein was covalently labeled by a fluorophore, 7-dimethylamino-3-(4-maleimidophenyl)-4-methylcoumarin (CPM). On addition of a RTIL ([pmim][Br]) to the native protein, the diffusion coefficient (D(t)) decreases and the hydrodynamic radius (R(h)) increases.

Femtosecond study of ultrafast fluorescence resonance energy transfer in a catanionic vesicle.

Ultrafast fluorescence resonance energy transfer (FRET) in a catanionic [sodium dodecyl sulfate (SDS)-dodecyltrimethyl ammonium bromide (DTAB)] vesicle is studied by femtosecond up-conversion. The vesicles (diameter ∼400 nm for SDS-rich and ∼250 nm for DTAB-rich vesicles) are much larger than the SDS and DTAB micelles (diameter ∼4 nm). In both micelle and vesicles, FRET occurs in multiple time scales and the time scales of FRET correspond to a donor-acceptor distance varying between 12 and 36 Å.

Diffusion of organic dyes in ionic liquid and giant micron sized ionic liquid mixed micelle: fluorescence correlation spectroscopy.

Diffusion of organic dyes in neat room temperature ionic liquid (RTIL) and RTIL-mixed micelle has been studied by fluorescence correlation spectroscopy (FCS). We have selected two RTILs, 3-pentyl-1-methyl imidazolium bromide ([C5C1Im][Br]) and the corresponding tetra-fluoroborate ([C5C1Im][BF(4)]). Diffusion coefficients (D(t)) of three organic dyes--DCM (neutral), C480 (neutral), and C343 (anionic)--in these RTILs are ∼100 times slower compared to water.

Excited state proton transfer in ionic liquid mixed micelles.

Excited state proton transfer (ESPT) of pyranine (8-hydroxypyranine-1,3,6-trisulfonate, HPTS) in room temperature ionic liquid (RTIL) mixed micelles is studied by femtosecond up-conversion. The mixed micelle consists of a triblock copolymer, (PEO)(20)-(PPO)(70)-(PEO)(20) (Pluronic P123), and one of the two RTILs, 1-pentyl-3-methyl-imidazolium bromide ([pmim][Br]) and 1-pentyl-3-methyl-imidazolium tetra-fluoroborate ([pmim][BF(4)]). The size and structure of the mixed micelle vary with the relative amount of the RTIL.

Deuterium isotope effect on femtosecond solvation dynamics in an ionic liquid microemulsion: an excitation wavelength dependence study.

The deuterium isotope effect on the solvation dynamics and the anisotropy decay of coumarin 480 (C480) in a room temperature ionic liquid (RTIL) microemulsion is studied by femtosecond up-conversion. The microemulsion consists of the RTIL 1-pentyl-3-methyl-imidazolium tetra-fluoroborate ([pmim][BF(4)]) in triton X-100 (TX-100)/benzene. Replacement of H(2)O by D(2)O in the microemulsion causes retardation of solvation dynamics.

Deuterium isotope effect on femtosecond solvation dynamics in methyl beta-cyclodextrins.

Deuterium isotope effect on the solvation dynamics and fluorescence anisotropy decay of coumarin 153 (C153) bound to dimethyl beta-cyclodextrin (DMB) and trimethyl beta-cyclodextrin (TMB) is studied using femtosecond upconversion. In D(2)O, there is a marked increase in the steady state emission quantum yield and fluorescence lifetime of C153 bound to DMB and TMB. This suggests strong coupling between C153 and D(2)O inside the cyclodextrin cavity.

Ultrafast FRET in a room temperature ionic liquid microemulsion: a femtosecond excitation wavelength dependence study.

Fluorescence resonance energy transfer (FRET) from coumarin 480 (C480) to rhodamine 6G (R6G) is studied in a room temperature ionic liquid (RTIL) microemulsion by picosecond and femtosecond emission spectroscopy. The microemulsion is comprised of the RTIL 1-pentyl-3-methylimidazolium tetraflouroborate, [pmim][BF4], in TX-100/ benzene. We have studied the microemulsion with and without water.

Femtosecond solvation dynamics in a micron-sized aggregate of an ionic liquid and P123 triblock copolymer.

Dynamic light scattering studies indicate that addition of a room temperature ionic liquid (RTIL, [pmim][Br]), to a triblock copolymer (P123) micelle leads to the formation of giant P123-RTIL clusters of size (diameter) 40 nm in 0.9 M and 3500 nm (3.5 microm) in 3 M RTIL.

A femtosecond study of solvation dynamics and anisotropy decay in a catanionic vesicle: excitation-wavelength dependence.

The structure and dynamics of a catanionic vesicle are studied by means of femtosecond up-conversion and dynamic light scattering (DLS). The catanionic vesicle is composed of dodecyl-trimethyl-ammonium bromide (DTAB) and sodium dodecyl sulphate (SDS). The DLS data suggest that 90 % of the vesicles have a diameter of about 400 nm, whereas the diameter of the other 10 % is about 50 nm.