A unique strategy for the selective detection of micromolar concentrations of cysteine/glutathione in the presence of various other alpha-amino acids through the plasmon coupling of Au nanorods is reported.

No abstract

The unique photophysical, conformational, and electronic properties of two model phenyleneethynylene-based rigid rod molecular systems, possessing dialkoxy substitutions, are reported in comparison with an unsubstituted system. Twisting of the phenyl rings along the carbon-carbon triple bond is almost frictionless in these systems giving rise to planar as well as several twisted ground-state conformations, and this results in broad structureless absorption in the spectral region of 250-450 nm. In the case of 1,4-bis(phenylethynyl)benzene, a broad absorption band was observed due to the HOMO-LUMO transition, whereas dialkoxy-substituted compounds possess two well-separated bands. Dialkoxy substitution in the 2,5-position of the phenyl ring in phenyleneethynylenes alters its central arene pi-orbitals through the resonance interaction with oxygen lone pairs resulting in similar orbital features for HOMO and HOMO-1/HOMO-2. Electronic transition from the low-lying HOMO-1/HOMO-2 orbital to LUMO results in the high-energy band, and the red-shifted band originates from the HOMO-LUMO transition. The first excited-state transition energies at different dihedral angles, calculated by the TDDFT method, indicate that the orthogonal conformation has the highest excitation energy with an energy difference of 15 kcal/mol higher than the low-lying planar conformation. The emission of these compounds originates preferentially from the more relaxed planar conformation resulting in well-defined vibronic features. The fluorescence spectral profile and lifetimes were found to be independent of excitation wavelengths, confirming the existence of a single emitting species.

A self-assembled photoactive antenna system containing a gold nanoparticle as the central nanocore and appended fullerene moieties as the photoreceptive hydrophobic shell is designed by functionalizing a gold nanoparticle with a thiol derivative of fullerene. Upon suspension of fullerene-functionalized gold nanoparticles (Au−S−C 60 ) in toluene we observe formation of 5−30 nm diameter clusters. The ease of suspending these nanoassemblies in organic solvents allows us to probe the excited state interactions by spectroscopic methods. The quenching of fluorescence emission as well as decreased yields of triplet excited state suggest the participation of excited singlet in the energy transfer to the gold nanocore. Application of electrophoretically deposited Au−S−C 60 nanoassemblies on optically transparent electrodes in the photoelectrochemical conversion of light energy has been demonstrated. Introduction.Advances in the field of nanotechnology provide an alternate "bottom-up" approach, in which the nanoparticles and bridging molecular units are assembled together as circuits in nanoelectronics. [1][2][3] Such arrangements can lead to the design of optoelectronic nanodevices, which can perform specific functions such as light-induced energy and electron-transfer processes.The metal and semiconductor nanoparticles possess size dependent optical, electronic, and catalytic properties and their synthesis and characterization are well documented. [4][5][6][7][8][9][10] Recently, attention has been drawn toward capping of metal nanoparticles with photoactive ligands using functional groups such as thiols, amines, and isothiocynates. [11][12][13][14][15][16][17][18][19][20][21] Elucidation of photoinduced energy and electron-transfer processes in fluorophore-metal nanoparticles are important in understanding the photochemical behavior of molecules bound to metal nanoparticles. In addition, the construction of two-and three-dimensional nanoassemblies of photoactive molecules with colloidal metal particles are useful for improving photoinduced charge separation and developing sensors for biological applications. [22][23][24][25][26][27]

We describe an approach to prepare co-continuous microstructured blends of polymers and nanoparticles by formation of a percolating network of particles within one phase of a polymer mixture undergoing spinodal decomposition. Nanorods or nanospheres of CdSe were added to near-critical blends of polystyrene and poly(vinyl methyl ether) quenched to above their lower critical solution temperature. Beyond a critical loading of nanoparticles, phase separation is arrested due to the aggregation of particles into a network (or colloidal gel) within the poly(vinyl methyl ether) phase, yielding a co-continuous spinodal-like structure with a characteristic length scale of several micrometers. The critical concentration of nanorods to achieve kinetic arrest is found to be smaller than for nanospheres, which is in qualitative agreement with the expected dependence of the nanoparticle percolation threshold on aspect ratio. Compared to structural arrest by interfacial jamming, our approach avoids the necessity for neutral wetting of particles by the two phases, providing a general pathway to co-continuous micro- and nanoscopic structures.