Optical Behavior of Substituted 4‑(2′-Hydroxyphenyl)imidazoles

A set of tetraarylimidazoles bearing a 2-hydroxyphenyl substituent at position 4, as well as their models lacking intramolecular hydrogen bonds, was efficiently synthesized. Structural investigations proved that the hydrogen bond strength for 4-(2′-hydroxyphenyl)­imidazoles is weaker than that for analogous 2-(2′-hydroxyphenyl)­imidazoles as estimated from dihedral angles and bond distances. Photophysical investigations revealed that these compounds have other properties than those observed for imidazoles bearing a 2-hydroxyphenyl substituent at position 2. They exhibit a negligible fluorescence quantum yield regardless of the solvent polarity. Additionally, dual fluorescence is observed in nonpolar solvents. Plausibly, although a hydrogen bond is present within their chemical structure in the solid state, it is not clear if excited-state intramolecular proton transfer occurs. The presence of OH groups triggers the radiationless deactivation channel if compared with model imidazole possessing a 2-methoxyphenyl group

Protein Quantification Using Resonance Energy Transfer between Donor Nanoparticles and Acceptor Quantum Dots

A homogeneous time-resolved luminescence resonance energy transfer (TR-LRET) assay has been developed to quantify proteins. The competitive assay is based on resonance energy transfer (RET) between two luminescent nanosized particles. Polystyrene nanoparticles loaded with Eu³⁺ chelates (EuNPs) act as donors, while protein-coated quantum dots (QDs), either CdSe/ZnS emitting at 655 nm (QD655-strep) or CdSeTe/ZnS with emission wavelength at 705 nm (QD705-strep), are acceptors. In the absence of analyte protein, in our case bovine serum albumin (BSA), the protein-coated QDs bind nonspecifically to the EuNPs, leading to RET. In the presence of analyte proteins, the binding of the QDs to the EuNPs is prevented and the RET signal decreases. RET from the EuNPs to the QDs was confirmed and characterized with steady-state and time-resolved luminescence spectroscopy. In accordance with the Förster theory, the approximate average donor–acceptor distance is around 15 nm at RET efficiencies, equal to 15% for QD655 and 13% for QD705 acceptor, respectively. The limits of detection are below 10 ng of BSA with less than a 10% average coefficient of variation. The assay sensitivity is improved, when compared to the most sensitive commercial methods. The presented mix-and-measure method has potential to be implemented into routine protein quantification in biological laboratories