Fluorescent Dyes and Their Supramolecular Host/Guest Complexes with Macrocycles in Aqueous Solution Roy N. Dsouza, Uwe Pischel,* and Werner M. Nau* School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany Centro de Investigaci on en Química Sostenible (CIQSO) and Departamento de Ingeniería Química, Química Física y Química Org anica, Universidad de Huelva, Campus de El Carmen s/n, E-21071 Huelva, Spain

Fluorescent dyes and their supramolecular host/guest complexes with macrocycles in aqueous solution.

Luminescence techniques are among the most widely used detection methods in the life and material sciences. At the core of these methods is an ever-increasing variety of fluorescent reporters (i.e., simple dyes, fluorescent labels, probes, sensors and switches) from different fluorophore classes ranging from small organic dyes and metal ion complexes, quantum dots and upconversion nanocrystals to differently sized fluorophore-doped or fluorophore-labeled polymeric particles. A key parameter for fluorophore comparison is the fluorescence quantum yield (Φf), which is the direct measure for the efficiency of the conversion of absorbed light into emitted light. In this protocol, we describe procedures for relative and absolute determinations of Φf values of fluorophores in transparent solution using optical methods, and we address typical sources of uncertainty and fluorophore class-specific challenges. For relative determinations of Φf, the sample is analyzed using a conventional fluorescence spectrometer. For absolute determinations of Φf, a calibrated stand-alone integrating sphere setup is used. To reduce standard-related uncertainties for relative measurements, we introduce a series of eight candidate quantum yield standards for the wavelength region of ∼350-950 nm, which we have assessed with commercial and custom-designed instrumentation. With these protocols and standards, uncertainties of 5-10% can be achieved within 2 h.

Relative and absolute determination of fluorescence quantum yields of transparent samples

Absolute fluorescence quantum yields are reported for the rhodamine 6G cation and the fluorescein dianion dyes in nine solvents. This information is combined with previously reported fluorescence lifetimes to deduce radiative and nonradiative decay rates. Along the alcohol series from methanol to octanol, rhodamine 6G displays an increasing radiative rate, in parallel with the square of the refractive index increase, and a slightly decreasing nonradiative rate. Fluorescein is different: the apparent radiative rate actually decreases, suggesting that the emissive species is perturbed in some fashion. For both dyes, fluorescence yields are enhanced in D2O, rising to 0.98, in parallel with a corresponding increase in lifetimes. Protonated solvents invariably give shorter lifetimes and lower quantum yields, contrary to some previous speculation. From this work and an analysis of existing literature values, more precise values have been obtained for two previously proposed absolute quantum yield standards. The yield of fluorescein in 0.1 N NaOH(aq) is 0.925+/-0.015, and for rhodamine 6G in ethanol, it is 0.950+/-0.015. In both cases, the solutions are assumed to be in the limit of low concentration, excited close to their long-wave absorption band and at room temperature but may be either air-saturated or free of oxygen.

Fluorescence quantum yields and their relation to lifetimes of rhodamine 6G and fluorescein in nine solvents: improved absolute standards for quantum yields.

Two series of Pt(diimine)(dithiolate) complexes have been prepared in order to investigate the effects of molecular design on the excited-state properties of this chromophore. The first series comprises Pt(dbbpy)(dithiolate) complexes where dbbpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine and the dithiolates are 1-(tert-butylcarboxy)-1-cyanoethylene-2,2-dithiolate (tbcda), 1-diethylphosphonate-1-cyanoethylene-2,2-dithiolate (cpdt), 6,7-dimethyl-quinoxaline-2,3-dithiolate (dmqdt), maleonitriledithiolate (mnt), and toluene-3,4-dithiolate (tdt). The second series comprises Pt(diimine)(tdt) complexes where the diimines are 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen), 4,4‘-di-tert-butyl-2,2‘-bipyridine (dbbpy), 4,4‘-dimethyl-2,2‘-bipyridine (dmbpy), 2,2‘-bipyridine (bpy), 1,10-phenanthroline (phen), 5-chloro-1,10-phenanthroline (Cl-phen), 4,4‘-dichloro-2,2‘-bipyridine (Cl2bpy), and 4,4‘-bis(ethoxycarbonyl)-2,2‘-bipyridine (EC-bpy). All of the compounds display solvatochromic absorption bands and solution lumine...

Tuning the Excited-State Properties of Platinum(II) Diimine Dithiolate Complexes

The development of novel biosensors for highly sensitive, selective, and rapid pathogen detection is of paramount importance for medical diagnostics, food safety screening, and environmental pollution monitoring. Graphene oxide (GO), which is well known as a promising precursor for graphene, has great potential for use in biosensors because of its unique characteristics such as facile surface modification, high mechanical strength, good water dispersibility, and photoluminescence. Recently, Lu et al., and Liu et al. demonstrated the usefulness of the fluorescence quenching properties of GO in DNA biosensing. Gold nanoparticles (AuNPs) have been shown to be excellent quenchers for organic fluorescent tags, semiconductor nanocrystals, and oxidized carbon nanotubes. Herein, we demonstrate a GO-based immuno-biosensor for detecting a rotavirus as a pathogen model. The detection occurs with high sensitivity and selectivity by GO photoluminescence quenching induced by fluorescence resonance energy transfer (FRET) between GO sheets and AuNPs. A GO-based immuno-biosensor system is shown in Figure 1. GO, which was synthesized by a modified Hummers method, was deposited on an amino-modified glass surface. The disruption of the sp structure of graphene crystals during the oxidation process results in the recombination of electron–hole pairs localized within small sp carbon domains that are embedded in an sp matrix, thus resulting in photoluminescence with a quantum yield of 70.3% relative to the fluorescein dye. A homogenous solution of GO shows a broad fluorescence emission peak around 547 nm upon excitation at 400 nm (Figure S1a,b in the Supporting Information). Since the GO has negatively charged functional groups such as carboxylic acids, hydroxy groups, and epoxides, the GO sheets are bound to the positive surface through an electrostatic interaction, which is strong enough to ensure that the GO sheets are retained during a washing step. The antibodies for rotavirus are immobilized on the GO array by a carbodiimide-assisted amidation reaction, and the rotavirus cell is captured by specific antigen–antibody interaction (Figure 1). The capture of a target cell was verified by observing the fluorescence quenching of GO by FRET between the GO and AuNPs. To realize such a novel GO immuno-biosensor, we first synthesized AuNP-linked antibodies (Ab-DNA-AuNP complexes; Figure S2 in the Supporting Information) which were bridged with 100-mer singlestranded DNA molecules. The DNA molecule was used as a mediator as the synthetic method, which is based on phosphoramidite chemistry, provides facile control of distance between Ab and AuNPs, so the AuNPs are placed close to the GO surface. The high affinity of amino functional groups of the DNA nucleotides for multiple AuNPs leads to an enhancement of the quenching efficiency of GO. When the Ab-DNA-AuNP complexes were selectively bound to the target cells that were attached to the GO arrays, a reduction in the fluorescence emission of GO by quenching was detected, thus enabling the identification of pathogenic target cells. AFM analysis was performed to obtain the topographical profile for each step during the fabrication of GO immunobiosensor (Figure 2). GO sheets ranging from 500 nm to 2 mm in lateral dimension (Figure S1b in the Supporting Information) were dispersed uniformly as monoand bilayers, which were determined by measuring the height (1.1 nm) between the two black marks in Figure 2a. The antibody-linked GO array shows brighter spots, particularly at the edges, and also folded structures, which contain many carboxylic acid groups. The measured height of 11.9 nm corresponds to the theoretical value of an antibody (10–15 nm) and approximately 15.3% area per spot was linked by antibodies. Once the target rotavirus was captured, the height of the complexes increased to approximately 81 nm. Considering that the size Figure 1. Illustration of a GO-based immuno-biosensor.

Douglas Magde

Papers

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