A highly water-soluble, fluorescence turn-on sensor for Ca(2+) is reported. The sensor affords high selectivity in sensing Ca(2+) over other biologically important metal cations. The dissociation constant of the sensor in binding Ca(2+) is 0.92 mm. Fluorescence microscopy experiments demonstrate that the sensor is cell-impermeable and capable of detecting extracellular Ca(2+) .
Two cationic conjugated
polyelectrolytes (CPEs) based on poly(phenylene
ethynylene) are found to exhibit efficient 2-photon excited fluorescence.
In particular, the CPE aggregates display enhanced 2-photon absorption
compared to the nonaggregated states. The CPEs are used as 2-photon
absorption sensitizers to harvest light and amplify the fluorescence
from green fluorescent protein (GFP) through Förster resonance
energy transfer. Considerably enhanced GFP fluorescence under near-infrared
2-photon excitation is demonstrated both in solution and in HeLa cells.
The results suggest applications in 2-photon fluorescence imaging
of cells, tissues, and organs of living animals expressing GFP.
Delivery of hydrophobic materials
in biological systems, for example,
contrast agents or drugs, is an obdurate challenge, severely restricting
the use of materials with otherwise advantageous properties. The synthesis
and characterization of a highly stable and water-soluble nanovesicle,
referred to as a quatsome (QS, vesicle prepared from cholesterol and
amphiphilic quaternary amines), that allowed the nanostructuration
of a nonwater soluble fluorene-based probe are reported. Photophysical
properties of fluorenyl–quatsome nanovesicles were investigated
via ultraviolet–visible absorption and fluorescence spectroscopy
in various solvents. Colloidal stability and morphology of the nanostructured
fluorescent probes were studied via cryogenic transmission electronic
microscopy, revealing a “patchy” quatsome vascular morphology.
As an example of the utility of these fluorescent nanoprobes, examination
of cellular distribution was evaluated in HCT 116 (an epithelial colorectal
carcinoma cell line) and COS-7 (an African green monkey kidney cell
line) cell lines, demonstrating the selective localization of C-QS and M-QS vesicles in lysosomes with high
Pearson’s colocalization coefficient, where C-QS and M-QS refer to quatsomes prepared with hexadecyltrimethylammonium
bromide or tetradecyldimethylbenzylammonium chloride, respectively.
Further experiments demonstrated their use in time-dependent lysosomal
tracking.
With the objective of developing new near-infrared fluorescent probes and understanding the effect molecular structure exerts on physical properties, a series of aniline-based squaraine dyes with different number and position of methoxy substituents adjacent to the squaraine core were synthesized and investigated. Using both computational and experimental methods, we found that the subtle changes of the number or position of the methoxy substituents influenced the twisting angle of the structure and led to significant variations in optical properties. Moreover, the methoxy substituent also affected aggregation behavior due to steric effects. The X-ray crystal structure of one of the key members of the series, SD-2a, clearly demonstrates the distortion between the four-membered squaraine core and the adjacent aniline ring due to methoxy substitution. Structurerelated fast relaxation processes were investigated by femtosecond pump−probe experiments and transient absorption spectra. Quantum chemical calculations and essential state models were exploited to analyze the primary experimental results. The comprehensive investigation of structure-related properties of dihydroxylaniline-based squaraine dyes, with systematic substitution of OH by OCH 3 functional groups, serves as a guide for the design of novel squaraine dyes for photonics applications.
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