On the use of core-shell type semiconductor nanocrystals as sensors

Here we describe progress towards our objective of non contact transition metal ion sensing. Semiconductor nanocrystals show complex photophysical properties and require a very careful setup of the measurement parameters. Under these conditions they allow for very high resolution sensing of ions

Bayesian Model Selection and Emulation for Protein Fluorescence

Fluorescence decay of amino acids in protein is a complex process for which multiple models have been proposed. Likelihood function evaluation for certain models can be computationally expensive, and as such surrogate models may be introduced to speed up inference. In this paper, Gaussian processes are implemented in likelihood estimation of a range of models defined by convolutions of an initial excitation input and a decay function using both synthetic and real world data. Parameter inference and model selection using the surrogate models are performed and compared against the exact results. Model selection when incorporating surrogate models into the inference process is shown to be consistent

Insulin aggregation tracked by its intrinsic TRES

Time-resolved emission spectra (TRES) have been used to detect conformational changes of intrinsic tyrosines within bovine insulin at a physiological pH. The approach offers the ability to detect the initial stages of insulin aggregation at the molecular level. The data analysis has revealed the existence of at least three fluorescent species undergoing dielectric relaxation and significant spectral changes due to insulin aggregation. The results indicate the suitability of the intrinsic TRES approach for insulin studies and for monitoring its stability during storage and aggregation in insulin delivery devices

Protein fibrillogenesis model tracked by its intrinsic time-resolved emission spectra

The excited-state kinetics of the fluorescence of tyrosine in a de novo protein fibrillogenesis model was investigated as a potential tool for monitoring protein fibre formation and complexation with glucose (glycation). In stark contrast to insulin the time-resolved emission spectra (TRES) recorded over the period of 700 hours in buffered solutions of the model with and without glucose revealed no apparent changes in Tyr fluorescence responses. This indicates the stability of the model and provides a measurement-supported basis for its use as a reference material in fluorescence studies of protein aggregation

Impact of the flavonoid quercetin on beta-amyloid aggregation revealed by intrinsic fluorescence

We report the effects of quercetin, a flavonoid present in human diet, on early stage beta-amyloid (Aβ) aggregation – a seminal event in Alzheimer’s disease. Molecular level changes in Aβ arrangements are monitored by time-resolved emission spectral (TRES) measurements of the fluorescence of Aβ’s single tyrosine intrinsic fluorophore (Tyr). The results suggest that quercetin binds beta-amyloid oligomers at early stages of their aggregation, which leads to the formation of modified oligomers and hinders the creation of beta-sheet structures, potentially preventing the onset of Alzheimer’s disease

Detecting beta-amyloid aggregation from the time-resolved emission spectra

The aggregation of beta-amyloids is one of the key processes responsible for the development of Alzheimer's disease. Early molecular-level detection of beta-amyloid oligomers may help in early diagnosis and in the development of new intervention therapies. Our previous studies on the changes in beta-amyloid's single tyrosine intrinsic fluorescence response during aggregation demonstrated a four-exponential fluorescence intensity decay, and the ratio of the pre-exponential factors indicated the extent of the aggregation in the early stages of the process before the beta-sheets were formed. Here we present a complementary approach based on the time-resolved emission spectra (TRES) of amyloid's tyrosine excited at 279 nmand fluorescent in the window 240–450 nm. TRES has been used to demonstrate sturctural changes occuring on the nanosecond time scale after excitation which has significant advantages over using steady-state spectra.Wedemonstrate this by resolving the fluorescent species and revealing that beta-amyloid's monomers show very fast dielectric relaxation, and its oligomers display a substantial spectral shift due to dielectric relaxation, which gradually decreases when the oligomers become larger

Towards single metal ion sensing by Förster resonance energy transfer

Here we describe progress towards our objective of detecting single non-fluorescent hydrated metal ions

Tyrosine photophysics during the early stages of β-amyloid aggregation leading to Alzheimer's

We have monitored the formation of toxic β-amyloid oligomers leading to Alzheimer's disease by detecting changes in the fluorescence decay of intrinsic tyrosine. A new approach based on the non-Debye model of fluorescence kinetics resolves the complexity of the underlying photophysics. The gradual disappearance of nonmonotonic fluorescence decay rates, at the early stages of aggregation as larger, tighter-packed oligomers are formed, is interpreted in terms of tyrosine-peptide dielectric relaxation influencing the decay. The results demonstrate the potential for a new type of fluorescence lifetime sensing based on dual excited-state/dielectric relaxation, with application across a broad range of biological molecules. The results also reconcile previously conflicting models of protein intrinsic fluorescence decay based on rotamers or dielectric relaxation by illustrating conditions under which both are manifest

Keratin intrinsic fluorescence as a mechanism for non-invasive monitoring of its glycation

We have studied the evolution of keratin intrinsic fluorescence as an indicator of its glycation. Steadystate and time-resolved fluorescence of free keratin and keratin-glucose samples were detected in PBS solutions in vitro. The changes in the fluorescence response demonstrate that the effect of glucose is manifest in the accelerated formation of fluorescent cross-links with an emission peak at 460 nm and formation of new cross-links with emission peaks at 525 nm and 575 nm. The fluorescence kinetics of these structures is studied and their potential application for the detection of long-term complications of diabetes discussed

Probing beta amyloid aggregation using fluorescence anisotropy : experiments and simulation

The aggregation of beta amyloid (Ab) protein is associated with the development of Alzheimer's disease. In this work we monitor Ab aggregation using fluorescence anisotropy, a technique that provides information on the rotational diffusion of the fluorescing tyrosine (Tyr) side chains. We also perform Monte Carlo (MC) and fully atomistic Molecular Dynamics (MD) simulations to interpret the experiments. The experimental results show that there are two different rotational timescales contributing to the anisotropy. Our MC simulation captures this behaviour in a coarse-scale manner, and, more importantly, shows that the Tyr side chains must have their movements restricted in order to reproduce the anisotropy. The MD simulations provide a molecular scale view, and indeed show that aggregation restricts the Try side chains to yield anisotropy in line with the experimental results. This combination of experiment and simulation therefore provides a unique insight into the aggregation process, and we suggest how this approach might be used to gain further information on aggregating protein systems