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- Fluorescence (9)
- Multiplexing (7)
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- Dye (3)
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We investigated the correlation between the thickness of the ZnS shell of CdSeZnS quantum dots (QDs), the stability of the particles, and the fluorescence quantum yield. As a measure for stability, a new shell quality test was developed. This test is based on the reaction of the QDs with photochemically formed thiophenol radicals and communicates an imperfect ZnS shell by a rapid and complete loss of fluorescence. The quantum yield increases from less than 5% for unshelled CdSe up to 50%, with an increase in ZnS shell thickness up to 0.60.8 nm. At the same time, the particles become significantly more stable, as revealed by the shell test.
Suitable labels are at the core of luminescence and fluorescence imaging and sensing. One of the most exciting, yet also controversial, advances in label technology is the emerging development of quantum dots (QDs)inorganic nanocrystals with unique optical and chemical properties but complicated surface chemistryas in vitro and in vivo fluorophores. Here we compare and evaluate the differences in physicochemical properties of common fluorescent labels, focusing on traditional organic dyes and QDs. Our aim is to provide a better understanding of the advantages and limitations of both classes of chromophores, to facilitate label choice and to address future challenges in the rational design and manipulation of QD labels.
At the core of photoluminescence techniques are suitable fluorescent labels and reporters, the spectroscopic properties of which control the limit of detection, the dynamic range, and the potential for multiplexing. Many applications including recent developments in intracellular labeling rely on well established molecular chromophores such as small organic dyes or fluorescent proteins. However, one of the most exciting – but also controversial – advances in reporter technology, the emerging development and application of luminescent nanoparticles with unique optical properties, yet complicated surface chemistry paves new roads for fluorescence imaging and sensing as well as for in vitro and in vivo labeling. Here, we compare and evaluate the differences in physico-chemical properties of common fluorophores, focusing on traditional organic dyes and luminescent nanocrystals with size-dependent features. The ultimate goal is to provide a better understanding of the advantages and limitations of both classes of chromophores, facilitate fluorophore choice for users of fluorescence techniques, and address future challenges in the rational design and manipulation of nanoparticulate labels and probes.
The potential of semiconducting nanocrystals or so-called quantum dots (QDs) for lifetime multiplexing has not been investigated yet, despite the increasing use of QDs in (bio)analytical detection, biosensing, and fluorescence imaging and the obvious need for simple and cost-effective tools and strategies for the simultaneous detection of multiple analytes or events. This is most likely related to their multiexponential decay behavior as for multiplex chromophores, typically monoexponential decay kinetics are requested. The fluorescence decay kinetics of various mixtures of a long-lived, multiexponentially decaying CdSe QD and a short-lived organic dye were analyzed, and a model was developed for the quantification of these labels from the measured complex decay kinetics as a first proof-of-concept for the huge potential of these labels for lifetime multiplexing. In a second step, we evaluated the potential of mixtures of two types of QDs, varying in constituent material to realize distinguishable, yet multiexponential decay kinetics and similar absorption and emission spectra. Strategies for lifetime multiplexing with nanocrystalline labels were derived on the basis of these measurements.
An efficient one-pot aqueous synthesis of alloyed Cd1-xHgxTe nanocrystals (NCs) is realized and the influence of the experimental conditions and of the initial composition of the NCs on their optical properties is discussed. This approach obtains stable NCs with an emission tunable in the red and the near infrared (NIR) spectral regions ranging from 640 to 1600 nm thereby covering the second and third telecommunication windows. The high photoluminescence quantum efficiency (PL QE) of these colloids with values up to 55% for red emitting, and up to 60% for NIR emitting samples is indicative of the excellent quality of the NCs.
Unter dem Motto „Innovation und Qualitätssicherung in der (Bio)Analytik“ werden in der Arbeitsgruppe Fluoreszenzspektroskopie der BAM, Bundesanstalt für Materialforschung und -prüfung, funktionelle Chromophor-Systeme, einfache Signalverstärkungs- und Multiplexingstrategien sowie innovative Validierungs- und rückführbare Standardisierungskonzepte für verschiedene fluorometrische Messgrößen und Methoden entwickelt. Im Mittelpunkt stehen dabei molekulare Fluorophore, Nanokristalle mit größenabhängigen optischen Eigenschaften (sogenannte Quantenpunkte, QDs) und fluoreszierende Partikel variabler Größe sowie Sonden und Sensormoleküle für neutrale und ionische Analyte und für die Charakterisierung von funktionellen Gruppen. Dabei erfolgen auch methodische Entwicklungen für die Fluoreszenzspektroskopie, die Fluoreszenzmikroskopie, die Milcrofluorometrie, die Sensorik und die Mikroarraytechnologie. Ziele sind u. a. das Design und die Untersuchung von multiplexfähigen selektiven und sensitiven Sonden für die Biomarkeranalytik, die Entwicklung von Methoden zur Charakterisierung der signalrelevanten Eigenschaften dieser Chromophor-Systeme und zur Charakterisierung von funktionellen Gruppen an Oberflächen und ihre Validierung sowie die Entwicklung und Bereitstellung von formatadaptierbaren, flexibel ersetzbaren
Standards für die fluoreszenzbasierte Multiparameteranalytik.
The synthesis and characterization of the new dinuclear dipeptide [(EtOOC-tpy)Ru(tpy-NHCO-tpy)Ru(tpy-NHCOCH3)]4+ 34+ of the bis(terpyridine)ruthenium amino acid [(HOOC-tpy)Ru(tpy-NH2)]2+ 12+ are described, and the properties of the dipeptide are compared to those of the mononuclear complex [(EtOOC-tpy)Ru(tpy-NHCOCH3)]2+ 42+ carrying the same functional groups. 34+ is designed to serve a high electronic similarity of the two ruthenium sites despite the intrinsic asymmetry arising from the amide bridge. This is confirmed via UV–vis absorption and NMR spectroscopy as well as cyclic voltammetry. 42+ and 34+ are emissive at room temperature, as expected. Moreover, 34+ exhibits dual emission from two different triplet states with different energies and lifetimes at room temperature. This is ascribed to the presence of a unique thermal equilibrium between coexisting [RuII(tpy-NHCO-tpy·)RuIII] and [RuIII(tpy-NHCO-tpy·)RuII] states leading to an unprecedented excited-state RuIIRuIII mixed-valent system via the radical anion bridge tpy-NHCO-tpy·. The mixed-valent cation 35+, on the other hand, shows no measurable interaction of the RuIIRuIII centers via the neutral bridge tpy-NHCO-tpy (Robin–Day class I). Reduction of 34+ to the radical cation 33+ by decamethylcobaltocene is bridge-centered as evidenced by rapid-freeze electron paramagnetic resonance spectroscopy. Interestingly, all attempts to observe 33+ via NMR and UV–vis absorption spectroscopy only led to the detection of the diamagnetic complex 3-H3+ in which the bridging amide is deprotonated. Hence 3-H3+ (and 4-H+) appear to reduce protons to dihydrogen. The ease of single and double deprotonation of 42+ and 34+ to 4-H+, 3-H3+, and 3-2H2+ was demonstrated using a strong base and was studied using NMR and UV–vis absorption spectroscopies. The equilibrating excited triplet states of 34+ are reductively quenched by N,N-dimethylaniline assisted by hydrogen bonding to the bridging amide.