Sally E. Plush

pH driven self-assembly of a ternary lanthanide luminescence complex: the sensing of anions using a β-diketonate-Eu(III) displacement assay

The synthesis and the photophysical evaluation of a novel pH dependent lanthanide luminescent self-assembly in water between a cyclen based europium complex and a beta-diketonate is described and its use as a luminescent sensor in displacement assays for anions such as acetate, bicarbonate and lactate, where the Eu(III) emission was quenched upon anion recognition.

Modulation of the organelle specificity in Re(I) tetrazolato complexes leads to labeling of lipid droplets

The biological behaviour in terms of cellular incubation and organelle specificity for two complexes of the type fac-[Re(CO)3(phen)L], where phen is 1,10-phenanthroline and L is either 3-pyridyltetrazolate or 4-cyanophenyltetrazolate, are herein investigated. The emission signal detected from the live insect Drosophila and human cell lines, generated by exploiting two-photon excitation at 830 nm to reduce cellular damage and autofluorescence, suggests photophysical properties that are analogous to those measured from dilute solutions, meaning that the complexes remain intact within the cellular environment. Moreover, the rhenium complex linked to 4-cyanophenyltetrazolate shows high specificity for the lipid droplets, whereas the complex bound to 3-pyridyltetrazolate tends to localise within the lysosomes. This differential localisation implies that in these complexes, organelle specificity can be achieved and manipulated by simple functional group transformations thus avoiding more complex bioconjugation strategies. More importantly, these results highlight the first example of phosphorescent labeling of the lipid droplets, whose important cellular functions have been recently highlighted along with the fact that their role in the metabolism of healthy and diseased cells has not been fully elucidated.

Lanthanide luminescent anion sensing : evidence of multiple anion recognition through hydrogen bonding and metal ion coordination

The delayed lanthanide luminescence of the terbium [Tb(III)] diaryl-urea complex 1xTb is significantly enhanced upon sensing of dihydrogenphosphate (H2PO4(-)) in CH3CN, which occurs through multiple anion binding through hydrogen bonding interactions and potential metal ion coordination to Tb(III).

Investigating Intracellular Localisation and Cytotoxicity Trends for Neutral and Cationic Iridium Tetrazolato Complexes in Live Cells

A family of five neutral cyclometalated iridium(III) tetrazolato complexes and their methylated cationic analogues have been synthesised and characterised. The complexes are distinguished by variations of the substituents or degree of π conjugation on either the phenylpyridine or tetrazolato ligands. The photophysical properties of these species have been evaluated in organic and aqueous media, revealing predominantly a solvatochromic emission originating from mixed metal-to-ligand and ligand-to-ligand charge transfer excited states of triplet multiplicity. These emissions are characterised by typically long excited-state lifetimes (∼hundreds of ns), and quantum yields around 5-10 % in aqueous media. Methylation of the complexes caused a systematic red-shift of the emission profiles. The behaviour and the effects of the different complexes were then examined in cells. The neutral species localised mostly in the endoplasmic reticulum and lipid droplets, whereas the majority of the cationic complexes localised in the mitochondria. The amount of complexes found within cells does not depend on lipophilicity, which potentially suggests diverse uptake mechanisms. Methylated analogues were found to be more cytotoxic compared to the neutral species, a behaviour that might to be linked to a combination of uptake and intracellular localisation.

Biomolecule detection in porous silicon based microcavities via europium luminescence enhancement

In this paper, we demonstrate the detection of europium-complex-labeled streptavidin in a porous silicon microcavity (pSiMC) via luminescence enhancement. The pSiMC platform was modified for optimized luminescence enhancement which encompassed changing the pore size of the microcavity to ensure molecular infiltration and adjusting the optical quality of the microcavity. Characterization of the optimized surface was performed by infrared spectroscopy, interferometric reflectance spectroscopy and luminescence measurements. Luminescence enhancement of the bound Eu(iii) complex by a factor of 3 was observed on the optimized pSiMC as compared to that on a single pSi layer. The ability of a pSiMC to act as a luminescence enhancing sensor was confirmed using streptavidin as a model analyte on a biotin-modified pSiMC. The sensor was able to detect Eu(iii) complex labeled streptavidin with a concentration as low as 150 nM. Furthermore, streptavidin was selectively detected when spiked in human wound fluid. The concept of detecting Eu(iii) labeled bioconjugates on pSiMC may be incorporated into the design of highly sensitive and specific point-of-care biosensors.

Recent Advances on Luminescent Enhancement-Based Porous Silicon Biosensors

Luminescence–based detection paradigms have key advantages over other optical platforms such as absorbance, reflectance or interferometric based detection. However, autofluorescence, low quantum yield and lack of photostability of the fluorophore or emitting molecule are still performance-limiting factors. Recent research has shown the need for enhanced luminescence-based detection to overcome these drawbacks while at the same time improving the sensitivity, selectivity and reducing the detection limits of optical sensors and biosensors. Nanostructures have been reported to significantly improve the spectral properties of the emitting molecules. These structures offer unique electrical, optic and magnetic properties which may be used to tailor the surrounding electrical field of the emitter. Here, the main principles behind luminescence and luminescence enhancement-based detections are reviewed, with an emphasis on europium complexes as the emitting molecule. An overview of the optical porous silicon microcavity (pSiMC) as a biosensing platform and recent proof-of-concept examples on enhanced luminescence-based detection using pSiMCs are provided and discussed.

Mitochondrial imaging in live or fixed tissues using a luminescent iridium complex

Mitochondrial morphology is important for the function of this critical organelle and, accordingly, altered mitochondrial structure is exhibited in many pathologies. Imaging of mitochondria can therefore provide important information about disease presence and progression. However, mitochondrial imaging is currently limited by the availability of agents that have the capacity to image mitochondrial morphology in both live and fixed samples. This can be particularly problematic in clinical studies or large, multi-centre cohort studies, where tissue archiving by fixation is often more practical. We previously reported the synthesis of an iridium coordination complex [Ir(ppy)2(MeTzPyPhCN)]+; where ppy is a cyclometalated 2-phenylpyridine and TzPyPhCN is the 5-(5-(4-cyanophen-1-yl)pyrid-2-yl)tetrazolate ligand; and showed that this complex (herein referred to as IraZolve-Mito) has a high specificity for mitochondria in live cells. Here we demonstrate that IraZolve-Mito can also effectively stain mitochondria in both live and fixed tissue samples. The staining protocol proposed is versatile, providing a universal procedure for cell biologists and pathologists to visualise mitochondria.

Intracellular distribution and stability of a luminescent rhenium(I) tricarbonyl tetrazolato complex using epifluorescence microscopy in conjunction with X-ray fluorescence imaging

Optical epifluorescence microscopy was used in conjunction with X-ray fluorescence imaging to monitor the stability and intracellular distribution of the luminescent rhenium(i) complex fac-[Re(CO)3(phen)L], where phen = 1,10-phenathroline and L = 5-(4-iodophenyl)tetrazolato, in 22Rv1 cells. The rhenium complex showed no signs of ancillary ligand dissociation, a conclusion based on data obtained via X-ray fluorescence imaging aligning iodine and rhenium distributions. A diffuse reticular localisation was detected for the complex in the nuclear/perinuclear region of cells, by either optical or X-ray fluorescence imaging techniques. X-ray fluorescence also showed that the rhenium complex disrupted the homeostasis of some biologically relevant elements, such as chlorine, potassium and zinc.

A molecular probe for the detection of polar lipids in live cells

Lipids have an important role in many aspects of cell biology, including membrane architecture/compartment formation, intracellular traffic, signalling, hormone regulation, inflammation, energy storage and metabolism. Lipid biology is therefore integrally involved in major human diseases, including metabolic disorders, neurodegenerative diseases, obesity, heart disease, immune disorders and cancers, which commonly display altered lipid transport and metabolism. However, the investigation of these important cellular processes has been limited by the availability of specific tools to visualise lipids in live cells. Here we describe the potential for ReZolve-L1™ to localise to intracellular compartments containing polar lipids, such as for example sphingomyelin and phosphatidylethanolamine. In live Drosophila fat body tissue from third instar larvae, ReZolve-L1™ interacted mainly with lipid droplets, including the core region of these organelles. The presence of polar lipids in the core of these lipid droplets was confirmed by Raman mapping and while this was consistent with the distribution of ReZolve-L1™ it did not exclude that the molecular probe might be detecting other lipid species. In response to complete starvation conditions, ReZolve-L1™ was detected mainly in Atg8-GFP autophagic compartments, and showed reduced staining in the lipid droplets of fat body cells. The induction of autophagy by Tor inhibition also increased ReZolve-L1™ detection in autophagic compartments, whereas Atg9 knock down impaired autophagosome formation and altered the distribution of ReZolve-L1™. Finally, during Drosophila metamorphosis fat body tissues showed increased ReZolve-L1™ staining in autophagic compartments at two hours post puparium formation, when compared to earlier developmental time points. We concluded that ReZolve-L1™ is a new live cell imaging tool, which can be used as an imaging reagent for the detection of polar lipids in different intracellular compartments.

Imaging nuclear, endoplasmic reticulum and plasma membrane events in real time.

Live cell imaging can provide important information on cellular dynamics; however, the full utilisation of this technology has been hampered by the limitations of imaging reagents. Metal‐based complexes have the potential to overcome many of the issues common to many current imaging agents. The rhenium (I)‐based complex fac‐[Re(CO)3(1,10‐phenanthroline)(4‐pyridyltetrazolate)], herein referred to as ReZolve‐ER™, shows promise as a live cell imaging agent with rapid cell uptake, low cytotoxicity, resistance to photobleaching and compatibility with multicolour imaging. ReZolve‐ER™ localised to the nuclear membrane/endoplasmic reticulum (ER) and allowed the detection of exocytotic events at the plasma membrane. Thus, we present a new imaging agent for monitoring live cell events in real time, which is ideal for imaging either short‐ or long‐time courses.