Cu2+ Effects on Beta-Amyloid Oligomerisation Monitored by the Fluorescence of Intrinsic Tyrosine

A non-invasive intrinsic fluorescence sensing of the early stages of Alzheimer's beta amyloid peptide aggregation in the presence of copper ions is reported. By using time-resolved fluorescence techniques the formation of beta amyloid-copper complexes and the accelerated peptide aggregation are demonstrated. The shifts in the emission spectral peaks indicate that the peptides exhibit different aggregation pathways than in the absence of copper.     

Molecular distribution sensing in a fluorescence resonance energy transfer based affinity assay for glucose

A newly developed method for determining molecular distribution functions is applied to a widely researched glucose affinity sensor. The reduction in fluorescence resonance energy transfer (FRET) to a malachite green (MG)-dextran complex from allophycocyanin (APC) bound to concanavalin A (ConA) due to displacement of the complex by glucose from ConA provides the basis of the assay. The higher sensitivity and specificity of a new approach to fluorescence decay analysis, over the methods based on conventional Forster-type models, is demonstrated and critical parameters in competitive binding FRET sensing derived.     

Beta-amyloid oligomerisation monitored by intrinsic tyrosine fluorescence

Aggregation of the peptide beta-amyloid is known to be associated with Alzheimer's disease. According to recent findings the most neurotoxic aggregates are the oligomers formed in the initial stages of the aggregation process. Here we use beta-amyloid's (Aβ's) intrinsic fluorophore tyrosine to probe the earliest peptide-to-peptide stages of aggregation, a region often merely labelled as a time lag, because negligible changes are observed by the commonly used probe ThT. Using spectrally resolved fluorescence decay time techniques and analysis we demonstrate how the distribution of 3 rotamer conformations of the single tyrosine in Aβ tracks the aggregation across the time lag and beyond according to the initial peptide concentration. At low Aβ concentrations (≤5 μM), negligible aggregation is observed and this is mirrored by little change in the fluorescence decay parameters, providing a useful baseline for comparison. At higher concentrations (≈50 μM), and contrary to what is generally accepted from ThT studies the rate of aggregation can be described by an exponential growth to a plateau in terms of the relative contributions of two of the three rotamers, with a characteristic aggregation time of ≈33 h.     

A time-resolved near-infrared fluorescence assay for glucose: opportunities for trans-dermal sensing

We report a time-resolved near-infrared fluorescence assay for glucose detection that incorporates pulsed diode laser excitation. Reduction in fluorescence resonance energy transfer to a malachite green-Dextran complex from allophycocyanin bound to concanavalin A (ConA) due to displacement of the complex by glucose from ConA provides the basis of the assay. The fluorescence quenching kinetics are analysed and discussed in detail. The change in fluorescence decay kinetics in the presence of glucose is found from dimensionality studies to be brought about by a change in the distribution of malachite green-Dextran acceptors. Glucose concentrations are measured in solution to within +/- 10% over the range 0-30 mM.     

Glucose-dependent changes in NAD(P)H-related fluorescence lifetime of adipocytes and fibroblasts in vitro: potential for non-invasive glucose sensing in diabetes mellitus

The aim of this study was to test the hypothesis that glucose can be monitored non-invasively by measuring NAD(P)H-related fluorescence lifetime of cells in an in vitro cell culture model. Autofluorescence decay functions were measured in 3T3-L1 adipocytes by time-correlated single-photon counting (excitation 370nm, emission 420-480nm). Free NADH had a two-exponential decay but cell autofluorescence fitted best to a three-exponential decay. Addition of 30mM glucose caused a 29% increase in autofluorescence intensity, a significantly shortened mean lifetime (from 7.23 to 6.73ns), and an increase in the relative amplitude and fractional intensity of the short-lifetime component at the expense of the two longer-lifetime components. Similar effects were seen with rotenone, an agent that maximizes mitochondrial NADH. 3T3-L1 fibroblasts stained with the fluorescent mitochondrial marker, rhodamine 123 showed a 16% quenching of fluorescence intensity when exposed to 30mM glucose, and an increase in the relative amplitude and fractional intensity of the short lifetime at the expense of the longer lifetime component. We conclude that, though the effect size is relatively small, glucose can be measured non-invasively in cells by monitoring changes in the lifetimes of cell autofluorescence or of a dye marker of mitochondrial metabolism. Further investigation and development of fluorescence intensity and lifetime sensing is therefore indicated for possible non-invasive metabolic monitoring in human diabetes.     

Correlation effects in a few-particle one-dimensional Coulomb-interacting system

Summary A model of the one-dimensional Coulomb-interacting few-particle system is studied in detail. The model is similar to a many-electron system which in a zero-order approximation of the non-interacting particles has only singly occupied one-electron levels. Such model cancels the divergencies in the Coulomb and exchange interaction energies found regularly for a conventional one-dimensional system which is built up of the doubly occupied one-electron levels and is submitted to the Coulomb perturbation. In the present case, the correlated wave functions for the system can be obtained from the Slater determinants constructed for the sets of the one-electron levels and combined according to the rules given by the standard perturbation theory. The calculations allow us to discuss the correlation influence and the effect of the size of the model on: (i) the excitation energies including the criterion corresponding to the metal-insulator transition (the Mott transition), (ii) the distribution of the correlated charge along the model, (iii) the average velocity of a two-particle system being in different states, and (iv) the dipole moments and transition probabilities. In the last case, the lifetime of the uncorrelated and correlated excited states obtained in the situation of the allowed one-photon transitions can be compared with the lifetime obtained for a similar system in the case when the one-photon transitions are forbidden and two-photon transitions should be taken into account. No data other than the length of the model and the fundamental constants of nature enter the calculations.     

Star-shaped oligofluorene nanostructured blend materials: controlled micro-patterning and physical characteristics

Star-shaped oligofluorene consists of highly-fluorescent macromolecules of considerable interest for organic electronics. Here, we demonstrate controlled micro-patterning of these organic nanostructured molecules by blending them with custom-synthesized photo-curable aliphatic polymer matrices to facilitate solventless inkjet printing. The printed microstructures are spherical with minimum dimensions of 12 μm diameter and 1 μm height when using a cartridge delivering ∼1 pL droplets. We evaluate the physical characteristics of the printed structures. Photoluminescence studies indicate that the blend materials possess similar fluorescence properties to neat materials in solid films or toluene solution. The fluorescence lifetime consists of two components, respectively 0.68±0.01 ns (τ ₁) and 1.23±0.12 ns (τ ₂). This work demonstrates that inkjet printing of such blends provides an attractive method of handling fluorescent nano-scaled molecules for photonic and optoelectronic applications.