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An efficient and eco‐friendly procedure for the synthesis of highly stable silver (Ag) and gold (Au) nanoparticles (NPs) using phenylalanine conjugated cholic acid (CPhe) in aqueous medium has been developed.These NPs were prepared under natural sunlight irradiation, in which CPhe acts both as self‐reducing and capping agent. The size and shape of the NPs were optimized by changing the ratio of the concentration of CPheand Au3+ ions, pH of the solution, sunlight irradiation and reaction time.The optical properties of the nanoparticles (NPs) were studied using UV‐visible spectroscopy. Size and morphology of the NPs were analyzed using high resolution transmission electron microscopy (HR‐TEM) and dynamic light scattering techniques (DLS) techniques. The interaction of CPhe on the NPs surface were studied by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT‐IR) spectra.The synthesized Ag and Au NPs solutions were found to be highly stable for more than a year. The prepared NPs were used as probes for highly selective and sensitive detection of heavy metal ions (Hg2+, Cr6+ and Pb2+) by colorimetric in aqueous medium with a detection limit in the range ofnanomolar concentrations. [ABSTRACT FROM AUTHOR]

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 AgNO 3 , 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 S 2- ions at nanomolar level in water samples, showing its potential applicability for the detection of S 2- 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.