N-Cholyl d-Penicilamine Micelles Templated Red Light-Emitting Silver Nanoclusters: Fluorometric Sensor for S2- Ions and Bioimaging Application Using Zebrafish Model.

Red-light-emitting silver nanoclusters (AgNCs) are recently emerged as a promising nanoprobe in the field of biomedical applications, because of their attractive properties, including brightness, luminescence stability, and better biocompatibility. In this report, we have developed highly water-soluble red-light-emitting AgNCs by using N-cholyl d-penicilamine (NCPA) as a biosurfactant at above the critical micelle concentration (CMC) at room temperature. Moreover, the NCPA was initially synthesized by demonstrating the reaction between cholic acid and d-penicilamine via a simple coupling reaction strategy. The primary and secondary critical micellar concentration (CMC) of NCPA surfactant was measured using pyrene (1 × 10-6 M) as a fluorescent probe, and the values were found to be 3.18 and 10.6 mM, respectively. Steady-state fluorescence measurements reveal that the prepared AgNCs shows the excitation and emission maxima at 365 and 672 nm, respectively, with a large Stokes shift (307 nm). The average lifetime measurements and quantum yield of the AgNCs were calculated to be 143.43 ns and 16.34%, respectively. Also, the red luminescent NCPA-templated AgNCs was synthesized in various protic and aprotic polar solvents, among which DMF and DMSO exhibit bright emission at longer wavelength as synthesized in aqueous medium. At higher concentration of AgNO3, bright luminescent and highly stable solid AgNCs was obtained with excitation and emission maxima at 607 and 711 nm, respectively. Furthermore, the synthesized AgNCs has been successfully utilized as a fluorescent probe for selective and sensitive detection of S2- ions at nanomolar level in water samples, showing its potential applicability for the detection of S2- ions in drinking, river, and tap water samples. Finally, toxicity and bioimaging studies of NCPA-templated AgNCs was demonstrated using zebrafish as in vivo model, showing no significant toxicity up to 200 µL/mL. The AgNCs-stained embryos exhibited red fluorescence with high intensity, which shows that AgNCs are stable in a living system.

Hierarchical Self-Assembly of Bile-Acid-Derived Dicationic Amphiphiles and Their Toxicity Assessment on Microbial and Mammalian Systems.

A thiol-yne click chemistry approach was adopted for the first time to prepare highly water-soluble bile acid derived dicationic amphiphiles. The synthesized amphiphiles dicationic cysteamine conjugated cholic acid (DCaC), dicationic cysteamine conjugated deoxycholic acid (DCaDC), and dicationic cysteamine conjugated lithocholic acid (DCaLC) exhibited hierarchically self-assembled microstructures at various concentrations in an aqueous medium. Interestingly at below critical micellar concentration (CMC) the amphiphiles showed distinct fractal patterns such as fractal grass, microdendrites and fern leaf like fractals for DCaC, DCaDC and DCaLC respectively. The fractal dimension (Df) analysis indicated that the formation of fractal like aggregates is a diffusion limited aggregation (DLA) process. The preliminary aggregation studies such as determination of CMC, fluorescence quenching, wettability and contact angle measurements were elaborately investigated. The morphology of the aggregates were analyzed by SEM and OPM techniques. Further, we demonstrated the antimicrobial and hemolytic activity for the cationic amphiphiles. DCaC had potent antimicrobial activity and showed no toxicity on human RBCs indicating that DCaC could be used in biomedical applications, in addition to their industrial and laboratory applications such as detergency, surface cleaning, and disinfection agent.

Sodium cholate-templated blue light-emitting Ag subnanoclusters: in vivo toxicity and imaging in zebrafish embryos.

We report a novel green chemical approach for the synthesis of blue light-emitting and water-soluble Ag subnanoclusters, using sodium cholate (NaC) as a template at a concentration higher than the critical micelle concentration (CMC) at room temperature. However, under photochemical irradiation, small anisotropic and spherically shaped Ag nanoparticles (3-11 nm) were obtained upon changing the concentration of NaC from below to above the CMC. The matrix-assisted laser desorption ionization time-of-flight and electrospray ionization mass spectra showed that the cluster sample was composed of Ag4 and Ag6. The optical properties of the clusters were studied by UV-visible and luminescence spectroscopy. The lifetime of the synthesized fluorescent Ag nanoclusters (AgNCs) was measured using a time-correlated single-photon counting technique. High-resolution transmission electron microscopy was used to assess the size of clusters and nanoparticles. A protocol for transferring nanoclusters to organic solvents is also described. Toxicity and bioimaging studies of NaC templated AgNCs were conducted using developmental stage zebrafish embryos. From the survival and hatching experiment, no significant toxic effect was observed at AgNC concentrations of up to 200 µL/mL, and the NC-stained embryos exhibited blue fluorescence with high intensity for a long period of time, which shows that AgNCs are more stable in living system.

Label free fluorometric characterization of DNA interaction with cholate capped gold nanoparticles using ethidium bromide as a fluorescent probe.

We demonstrated label free ethidium bromide assisted characterization of DNA interaction with cholate capped AuNPs. Interactions between ss/ds DNA and AuNPs with two different lengths (0.5 and 0.85 kb) were analyzed through fluorescence spectrophotometer and agrose gel electrophoresis analysis. Further results were confirmed by UV-globally visible spectrophotometer, DLS and TEM. As 0.5 and 0.85 kb of ssDNA effectively interacted with AuNPs through the van der Waals interaction which consequently led to the prevention of salt induced aggregation, EtBr intercalations as well as fluorescence shift with less binding constant 0.098 and 0.108 µM, respectively. On the contrary, the same length of dsDNA (0.5 and 0.85 kb) not interacted with AuNPs which led to the NPs aggregation, EtBr intercalation as well as fluorescence shift with increased binding constant 0.166 and 0.599 µM, respectively. This approach helped to understand the mode of interactions of DNA with cholate capped AuNPs without any modifications in a simple method and the results could be readout through the naked eye under the UV transilluminator.