Crystalline H-aggregate nanoparticles for detecting dopamine release from M17 human neuroblastoma cells.

Dopamine (DA) is an important neurotransmitter, which is essential for transmitting signals in neuronal communications. The deficiency of DA release from neurons is implicated in neurological disorders. There has been great interest in developing new optical probes for monitoring the release behavior of DA from neurons. H-aggregates of organic dyes represent an ordered supramolecular structure with delocalized excitons. In this paper, we use the self-assembly of 3,3'-diethylthiadicarbocyanine iodide (DiSC2(5)) in ammonia solution to develop crystalline H-aggregate nanoparticles, in which DiSC2(5) molecules show long-range π-π stacking. The crystalline H-aggregate nanoparticles are stable in cell culture medium and can serve as an efficient photo-induced electron transfer (PET) probe for the detection of DA with the concentration as low as 0.1 nM in cell culture medium. Furthermore, the crystalline H-aggregate nanoparticle-based PET probe is used to detect the release behavior of DA from the M17 human neuroblastoma cells. We find that the DA release from the cells is enhanced by nicotine stimulations. Our results highlight the potential of crystalline H-aggregate nanoparticle-based PET probes for diagnosing nervous system diseases and verifying therapies.

Fluorescent H-Aggregate Vesicles and Tubes of a Cyanine Dye and Their Potential as Light-Harvesting Antennae.

H-aggregates of π-conjugated dyes are an ordered supramolecular structure. However, the non-fluorescence behavior of H-aggregates greatly limits their potential applications. In this paper, we report the formation of fluorescent H-aggregates with vesicular and tubular morphologies by the self-assembly of 3,3'-diethylthiacarbocyanine iodide (DiSC2(3)) in ammonia/methanol mixtures. The transition from H-aggregate vesicles to H-aggregate tubes can be achieved by increasing the volume fraction of methanol in the mixtures. H-aggregate vesicles and tubes show two blue-shifted absorption bands and strong fluorescence, which result from the inclined arrangement of DiSC2(3) molecules. Furthermore, light-harvesting complexes are formed by adding dopamine (DA)-quinone (acceptor) in synthetic urine with H-aggregate vesicles or tubes. Our results show that H-aggregate tubes are more efficient than H-aggregate vesicles in transferring excited electrons to DA-quinone acceptors.

Davydov Split Aggregates of Cyanine Dyes on Self-Assembled Nanotubes.

The Davydov splitting of dye aggregates represents unique molecular excitons. In this paper, we report the formation of Davydov split aggregates of 3,3'-diethylthiacarbocyanine iodide (DiSC2 (3)) and 3,3'-diethylthiadicarbocyanine iodide (DiSC2 (5)) templated by the helical nanotubes of lithocholic acid (LCA). The templated Davydiv split aggregates show a strong J-band and a weak H-band in the adsorption spectra. As the LCA helical nanotubes transform into a straight shape, the relative intensities of the J-band and the H-band of the templated Davydov split aggregates become roughly equal. The twisted angle change of the transition moment of DiSC2 (3) and DiSC2 (5) molecules in the templated Davydov split aggregates in response to the helical-to-straight shape transformation of LCA nanotubes is estimated. The templated Dvaydov split aggregates with well-defined shapes and molecular excitons are of interest for artificial light-harvesting and optoelectronic devices.

Colorimetric Detection of Dopamine with J-Aggregate Nanotube-Integrated Hydrogel Thin Films.

The deficiency of dopamine (DA) is clinically linked to several neurological diseases. The detection of urinary DA provides a noninvasive method for diagnosing these diseases and monitoring therapies. In this paper, we report the coassembly of lithocholic acid (LCA) and 3,3'-diethythiadicarbocyanine iodide (DiSC2(5)) at the equimolar ratio in ammonia solution into J-aggregate nanotubes. By integrating the J-aggregate nanotubes into transparent agarose hydrogel films formed on the wall of quartz cuvettes, we fabricate a portable and reproducible sensor platform for the optical detection of DA in synthetic urine. The J-band intensity of the integrated J-aggregate nanotubes is found to linearly decrease with the increase of DA concentrations from 10 to 80 nM, giving the limit of detection of ∼7 nM. The detection mechanism is based on the photoinduced electron transfer (PET) from the excited J-aggregate nanotubes to adsorbed DA-quinone. The PET process used in the sensor platform can reduce the interference of ascorbic acid and uric acid in the detection of DA in synthetic urine. The high sensitivity of the sensor platform is contributed by the delocalized exciton of J-aggregate nanotubes.

Morphology Transformation of Supramolecular Structures in Aqueous Mixtures of Two Oppositely Charged Amphiphiles.

The co-assembly of oppositely charged amphiphiles provides a fascinating approach for forming complex supramolecular structures, which are interesting from both fundamental and technological viewpoints. Here, we report a stepwise morphology transformation of co-assembled supramolecular structures in the aqueous mixture of lithocholic acid (LCA) and cetyltrimethylammonium bromide (CTAB) at mixed molar ratios of 1:1 and 2:1. The co-assembly of LCA and CTAB initially forms multilamellar vesicles followed by the spontaneous growth of membrane tubes from the vesicles. The vesicle-to-tube transition is accompanied by a fluidic-to-crystalline phase transition. After being aged, the membrane tubes twist into left-handed helices, which then intertwine into left-handed double helices and multihelix bundles. The single handedness of these supramolecular structures is a reflection of the amplification of the chirality of LCA. An understanding of the co-assembly mechanism and pathway is a key step toward producing supramolecular structures with distinguished morphologies.