Minimal quenching of fluorescence emission was observed when the fluorescent dye AlexaFluor 514 (AF514) was covalently bound to gold monolayer protected clusters (AuMPCs) that have negligible plasmon ...bands (diameters <2 nm). The fluorescence emission of the conjugated dye was measured as a function of dye−AuMPC mixing ratio with a combination of steady-state and time-resolved ensemble spectroscopic measurements in conjunction with single-molecule fluorescence microscopy. Fluorescence emission of the conjugated samples decreased slightly as a function of dye mixing ratio, which, in combination with a negligible change in fluorescence lifetime, was attributed to static quenching of the dye by the AuMPCs. From the single-molecule fluorescence measurements, it was observed that luminescent conjugates could still be detected, and, at all loading ratios, almost all of the dye−particle conjugates photobleached in either a single- or double-step process, with a small subpopulation exhibiting more than two photobleaching events. Beyond simple, irreversible photobleaching, no additional blinking dynamics were detected at the single-molecule level within the time resolution of the experiment. Emission intensities of coupled fluorophores were comparable with those measured of dye molecules that had not been attached to the AuMPCs, suggesting that the statically quenched fluorophores are entirely nonemissive, whereas the remaining dyes are essentially unquenched. These results are discussed in the context of other dye−AuMPC coupled systems described in the literature.
We report the synthesis of water-soluble, nearly monodisperse glycine-cysteamine (Gly-CSA) gold monolayer protected clusters (MPCs) via base deprotection of Fmoc-Gly-CSA MPCs. The resulting Gly-CSA ...MPCs, which have terminal primary amine groups, are fully characterized by 1H and 13C NMR, UV−vis spectroscopy, and TEM, and their surface properties were probed by dynamic light scattering and acid−base titrations. The characterization methods indicate that the as-synthesized particles are nearly monodisperse with an average particle size of 1.8 ± 0.3 nm, but are only stable to aggregation in water at pHs of 4 and below. Acid−base titrations of the Gly-CSA MPCs show that the primary ammonium groups have a pK a of approximately 5.5, which is several orders of magnitude lower than the pK a2 for the ammonium group of glycine (9.6). Thus, the particles are only partially protonated at intermediate pH's, which then drives the aggregation of the nanoparticles via hydrogen-bond formation. Dynamic light scattering results confirm the pH-driven aggregation of the nanoparticles, and studies with ninhydrin confirm that the primary amine groups are reactive and have potential for further functionalization. These results show that amine-terminated MPCs can be synthesized; however, their aggregation at intermediate pH’s can limit their utility as building blocks for multifunctional nanoparticle syntheses.
Aufgrund der hohen Verfügbarkeit in der Erdkruste und seiner geringen Toxizität im Vergleich zu einigen anderen Halbleitern ist Silicium der Vorreiter in der Elektroindustrie. Daher finden ...Silicium‐Nanokristalle (SiNKs) insbesondere aufgrund ihrer einzigartigen optoelektronischen Eigenschaften ein hohes Interesse in der Halbleiterindustrie und sie haben das Potenzial, die toxischen Quantenpunkte (Elemente der Gruppen II–VI und III–V) zu substituieren. Dennoch erhielten SiNKs wegen ihrer geringeren Photolumineszenz(PL)‐Quantenausbeuten, einer schwierig zu erzielenden monodispersen Partikelverteilung und ihrer Oxidationsanfälligkeit nicht dieselbe Aufmerksamkeit wie ihre schwermetallhaltigen Analoga. Daher wurde vermehrt an der Funktionalisierung von SiNK‐Oberflächen geforscht und die genannten Faktoren im Wesentlichen verbessert. Vor diesem Hintergrund fassen wir in diesem Aufsatz die neuesten Entwicklungen in der Funktionalisierung von SiNK‐Oberflächen, beschriebene SiNK/Polymer‐Hybridmaterialien und deren Anwendungen in den Bereichen Sensorentwicklung, Leuchtdioden, Katalyse und Akkumulatoren zusammen.
Vorreiter und Newcomer: Silicium‐Nanokristalle (SiNKs) sind eine vielversprechende Alternative zu den toxischen Quantenpunkt‐Halbleitern der Gruppen II–VI und III–V. Dieser Aufsatz illustriert, wie Methoden der Oberflächenchemie genutzt werden können, um die Eigenschaften von SiNKs gezielt anzupassen und sie für Anwendungen z. B. als Sensoren, in der Photovoltaik und in LEDs einsatzfähig zu machen.
We present a comprehensive computational study on plasmonic properties of group 4 transition metal nitride (TMN) nanoparticles. We compare the performance of TMN nanoparticles with gold for various ...plasmonic applications including narrowband and broadband photothermal-based uses. Furthermore, we investigate the role of size, host medium, and particle surface characteristics on the plasmonic response of TMN nanoparticles in detail. Our results reveal the potential of ceramic nanoparticles as alternative materials for noble metals for applications in visible and near infrared region.
Group 4 transition metal nitride (TMN) nanoparticles (NPs) display strong plasmonic responses in the visible and near-infrared regimes, exhibit high melting points and significant chemical stability ...and thus are potential earth-abundant alternatives to Au and Ag based plasmonic applications. However, a detailed understanding of the relationship between TMN NP properties and plasmonic response is required to maximize their utility. In this study, the localized surface plasmon resonance (LSPR) frequency, bandwidth, and extinction of titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN) NPs were examined as a function of the particle size, surface oxidation, and refractive index of the surrounding medium using finite element method (FEM). A linear redshift in the LSPR frequency and a linear increase in the associated full-width at half maximum (FWHM) was observed with increasing the particle size, oxidation layer thickness, and medium refractive index. We show that the effect of surface oxidation on plasmonic properties of TMN NPs is strongly size-dependent with a significant LSPR redshift, intensity reduction, and broadening in small NPs compared to larger NPs. Furthermore, the performance and efficiency of HfN, ZrN, TiN as well as Au NPs for a narrowband application - photothermal therapy (PTT), and a broadband application - solar energy conversion, was investigated in detail. The results indicate that narrowband and broadband photothermal performance of NPs strongly depend on the particle size, surface properties and in case of narrowband absorption, excitation wavelength.
