Tracking the formation of eumelanin from L-Dopa using coupled measurements

Melanin plays a crucial role as a pigment all through the animal kingdom. Being a macromolecule just on the divide between an ordered crystalline or a purely amorphous form melanin has proven a challenge to structure-function analysis. Melanin assembles from small molecules much like a jigsaw and much like in a jigsaw the fine detail quickly vanishes in the overall picture. With melanin being first and foremost a photo-active molecule we focus on spectral properties for the characterisation of its structure. We use absorption measurements to illustrate the complex nature of the formation process. To gain a better hold on the formation pathway we use coupled measurements of excitation and emission to identify 'areas of interest' in the excitation-emission matrix (EEM). We then probe one area for characteristic fluorescence lifetimes to track one melanin building block through the formation process. Comparison of the EEMs of L-Dopa derived melanin with natural Sepia melanin shows characteristic differences. We show how the presence of copper ions creates a melanin closer to its natural form

Mapping the formation of eumelanin using coupled measurements

Melanin plays a crucial role as a pigment all through the animal kingdom. Being a macromolecule just on the divide between an ordered crystalline or a purely amorphous form melanin has proven a challenge to structure-function analysis. Melanin assembles from small molecules much like a jigsaw and much like in a jigsaw the fine detail quickly vanishes in the overall picture. With Melanin being first and foremost a photo-active molecule we focus on spectral properties for the characterization of its structure using linked measurements of excitation and emission to identify ‘areas of interest’ in the Excitation-Emission Matrix (EEM). We then probe for characteristic fluorescence lifetimes in the identified areas to track melanin building blocks through the formation pathway

Influence of ions and pH on formation of solid and liquid-like melanin

Melanin is a natural pigment with broadband absorption and effective ability to dissipate the energy absorbed. The macromolecular structure of melanin shows a delicate balance between short-range ordered and disordered structures without being a random aggregate. The presence of ions or the variation in pH or ionic strength can alter the self-assembly process which subsequently changes the structure of melanin. To understand these relationships, this study investigates the influence of ions and pH in melanin formation. The types of ions present and pH have a profound influence on the formation and structure of melanin particles, while only minor changes are observed in the absorption and excitation-emission analysis. In some conditions, the formation of discernible particles with significant refractive index contrast is avoided while retaining the spectroscopic characteristics of melanin, leading to liquid-like melanin. These findings identify potential pathways which can be used to manipulate the melanin macromolecular structure while providing the desired spectral properties to enable novel bio-engineering applications.

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

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

Revealing the photophysics of gold-nanobeacons via time-resolved fluorescence spectroscopy

We demonstrate that time-resolved fluorescence spectroscopy is a powerful tool to investigate the conformation states of hairpin DNA on the surface of gold nanoparticles (AuNPs) and energy transfer processes in Au-nanobeacons. Long-range fluorescence quenching of Cy5 by AuNPs has been found to be in good agreement with electrodynamics modelling. Moreover, time-correlated single-photon counting (TCSPC) is shown to be promising for real-time monitoring of the hybridization kinetics of Au-nanobeacons, with up to 60% increase in decay time component and 300% increase in component fluorescence fraction observed. Our results also indicate the importance of the stem and spacer designs for the performance of Au-nanobeacons

Recording the Heart Beat of Cattle using a Gradiometer System of Optically Pumped Magnetometers

Monitoring of heart rate has the potential to provide excellent data for the remote monitoring of animals, and heart rate has been associated with stress, pyrexia, pain and illness in animals. However monitoring of heart rate in domesticated animals is difficult as it entails the restraint of the animal (which may in turn affect heart rate), and the application of complex monitoring equipment that is either invasive or not practical to implement under commercial farm conditions. Therefore accurate non-invasive automated remote monitoring of heart rate has not been possible in domesticated animals. Biomagnetism associated with muscle and nerve action provides a promising emerging field in medical sensing, but it is currently confined to magnetically-shielded clinical environments. In this study, we use biomagnetic sensing on commercial dairy cattle under farm conditions as a model system to show proof-of-principle for non-contact magnetocardiography (MCG) outside a controlled laboratory environment. By arranging magnetometers in a differential set-up and using purpose-built low-noise electronics, we are able to suppress common mode noise and successfully record the heart rate, the heart beat intervals and the heart beat amplitude. Comparing the MCG signal with simultaneous data recorded using a conventional electrocardiogram (ECG) allowed alignment of the two signals, and was able to match features of the ECG including the P-wave, the QRS complex and the T-wave. This study has shown the potential for MCG to be developed as a non-contact method for the assessment of heart rate and other cardiac attributes in adult dairy cattle. Whilst this study using an animal model showed the capabilities of un-shielded MCG, these techniques also suggest potentially exciting opportunities in human cardiac medicine outside hospital environments

The effect of intensity of excitation on CdSe/ZnS quantum dots : opportunities in luminescence sensing

We report changes in the photophysical properties of core-shell type CdSe/ZnS quantum dots (QDs) under optical irradiation. QDs either in aqueous solution or immobilized in a silica sol gel matrix have been excited at different wavelengths and fluxes. Illumination of the sample with 140 fs 700 nm Ti:sapphire laser pulses of the peak power of the order of 4 GW/cm(2) caused gradual increase in the luminescence lifetime from an initial value of 3.5 increasing to 4.5 ns and an increase in luminescence intensity by similar to 8%. Using about 16 GW/cm(2) peak power resulted in a shortening of the luminescence lifetime to 3 ns and a decrease in intensity by similar to 75%. Both photobrightening and photodarkening were fully reversible. We discuss the kinetics of photobrightening and photodarkening and investigate the suitability of QDs as luminescence lifetime sensors with tunable parameters

Photoactivable heterocyclic cages in a comparative release study of butyric acid as a model drug

Aiming at the improvement of the photorelease of butyric acid - a model carboxylic acid drug, a set of heteroaromatic compounds based on acridine, naphtho[2,1-b]pyran, 3H-benzopyran fused julolidine and thioxo-naphtho[2,1-b]pyran were evaluated as benzyl-type phototriggers, in comparison with the well-known o-nitrobenzyl group. The corresponding ester cages were irradiated in a photochemical reactor at 254, 300, 350 and 419 nm, in two solvent systems (methanol or acetonitrile in 80:20 mixtures with HEPES buffer). Photolysis studies showed that, for some of the cages, the release of the active molecule occurred with short irradiation times using 419 nm. Time-resolved fluorescence was used to elucidate their photophysical properties and determine the decay kinetics. Studies were also carried out to assess the suitability of using two-photon excitation to address these compounds, which is advantageous if their use in biological systems is to be considered.Fundação para a Ciência e a Tecnologia (FCT