Lewis Edward MacKenzie

A multispectral microscope for in vivo oximetry of rat dorsal spinal cord vasculature

Quantification of blood oxygen saturation (SO2) in vivo is essential for understanding the pathogenesis of diseases in which hypoxia is thought to play a role, including inflammatory disorders such as multiple sclerosis (MS) and rheumatoid arthritis (RA). We describe a low-cost multispectral microscope and oximetry technique for calibration-free absolute oximetry of surgically exposed blood vessels in vivo. We imaged the vasculature of the dorsal spinal cord in healthy rats, and varied inspired oxygen (FiO2) in order to evaluate the sensitivity of the imaging system to changes in SO2. The venous SO2 was calculated as 67.8  ±  10.4% (average  ±  standard deviation), increasing to 83.1  ±  11.6% under hyperoxic conditions (100% FiO2) and returning to 67.4  ±  10.9% for a second normoxic period; the venous SO2 was 50.9  ±  15.5% and 29.2  ±  24.6% during subsequent hypoxic states (18% and 15% FiO2 respectively). We discuss the design and performance of our multispectral imaging system, and the future scope for extending this oximetry technique to quantification of hypoxia in inflamed tissue.

Science podcasts: analysis of global production and output from 2004 to 2018

Podcasts have emerged as a new decentralised global medium for science communication to the global public. However, despite their popularity and proliferation, there have been no studies of the production and dissemination of science podcasts. To address this need, this study identified 952 English language science podcasts and analysed key indicators of podcast production and output. It was found that between 2004 and 2010, the number of science podcasts grew linearly, but has subsequently grown exponentially. 65% of science were hosted by scientists and 77% were targeted to public audiences. 38% of science podcasts were created by independent producers, compared to 62% produced with an organisational affiliation. ‘General Science’ was the most common topic for science podcasts, but a diverse range of topics was covered. Notably, chemistry is under-represented in comparison to physics and biology. The USA and UK dominate English language science podcast production. Podcasts affiliated to organisations released more episodes compared to independent podcasts (median = 24 and 16 respectively). Only 24% of science podcasts had some form of overt supplementary income. It is anticipated that these results will inform future science communication strategy.

Selective cellular imaging with lanthanide based upconversion nanoparticles

Upconversion nanoparticles (UCNPs) with sodium yttrium fluoride, NaYF4 (host lattice) doped with Yb3+ (sensitizer) and Er3+ (activator) were synthesized via hydrothermal route incorporating polyethyleneimine (PEI) for their long‐term stability in water. The cationic PEI‐modified UCNPs with diameter 20 ± 4 nm showed a zeta potential value of +36.5 mV and showed an intense, visible red luminescence and low‐intensity green emission with 976 nm laser excitation. The particles proven to be nontoxic to endothelial cells, with a 3‐(4,5‐dimethylthiazol‐2yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay, showing 90% to 100% cell viability, across a wide range of UCNP concentrations (0.3 ng/mL‐0.3 mg/mL) were used in multiphoton imaging. Multiphoton cellular imaging and emission spectroscopy data reported here prove that the UCNPs dispersed in cell culture media are predominantly concentrated in the cytoplasm than the cell nucleus. The energy transfer from PEI‐coated UCNPs to surrounding media for red luminescence in the biological system is also highlighted with spectroscopic measurements. Results of this study propose that UCNPs can, therefore, be used for cytoplasm selective imaging together with multiphoton dyes (eg, 4′,6‐diamidino‐2‐phenylindole (DAPI)) that are selective to cell nucleus.

The molecular weight of NaYF4:RE photonic up-conversion nanoparticles

Luminescence up-conversion nanoparticles (UCNPs) consisting of a NaYF4 crystal lattice doped with rare earth (RE) ions have found widespread application in bio-sensing, bio-imaging, and therapeutics; yet the molecular weight of UCNPs is not known. Lack of knowledge of molecular weight of UCNPs results in sub-optimal functionalisation and dosages of UCNPs. We present a simple method for calculating the molecular weight of NaYF4:RE UCNPs from arbitrary crystal lattice parameters and UCNP diameter measurements, and we apply this method to estimate the molecular weight of various NaYF4:RE UCNPs from the literature. UCNP molecular weight scales exponentially with UCNP volume (i.e. diameter cubed). UCNPs of 10 nm diameter are estimated to be a molecular weight of ~ 1 MDa, and 45 nm UCNPs are estimated to be ~100 MDa. Hexagonal lattice UCNPs were found to have a greater molecular weight than their cubic lattice UCNP counterparts. A Gaussian distribution of nanoparticle diameters was found to produce a lognormal distribution of nanoparticle molecular weights. We provide stand-alone graphic user interfaces to calculate UCNP:RE molecular weight. This approach can be generalised to estimate the molecular weight of crystalline nanoparticles of arbitrary size, geometry, and elemental composition where nanoparticle unit cell parameters are known.Upconversion nanoparticles (UCNPs) are utilized extensively for biomedical imaging, sensing, and therapeutic applications, yet the molecular weight of UCNPs has not previously been reported. We present a theory based upon the crystal structure of UCNPs to estimate the molecular weight of UCNPs: enabling insight into UCNP molecular weight for the first time. We estimate the theoretical molecular weight of various UCNPs reported in the literature, predicting that spherical NaYF4 UCNPs ~ 10 nm in diameter will be ~1 MDa (i.e. 10 6 g/mol), whereas UCNPs ~ 45 nm in diameter will be ~100 MDa (i.e. 10 8 g/mol). We also predict that hexagonal crystal phase UCNPs will be of greater molecular weight than cubic crystal phase UCNPs. Additionally we find that a Gaussian UCNP diameter distribution will correspond to a lognormal UCNP molecular weight distribution. Our approach could potentially be generalised to predict the molecular weight of other arbitrary crystalline nanoparticles: as such, we provide standalone graphic user interfaces to calculate the molecular weight both UCNPs and arbitrary crystalline nanoparticles. We expect knowledge of UCNP molecular weight to be of wide utility in biomedical applications where reporting UCNP quantity in absolute numbers or molarity will be beneficial for inter-study comparison and repeatability.

Spectroscopic oximetry in the eye: a review

ABSTRACT Introduction: Non-invasive measurement of blood oxygen saturation via spectroscopic imaging has provided insights into ocular physiology and the development of a variety of ocular conditions, including retinal vascular occlusion, diabetic retinopathy and glaucoma. Major developments since the late 90s have been enabled by advancements in imaging technology, computational image analysis, and innovative experimental methods. Areas covered: We review the theory of spectroscopic oximetry, the ocular blood vessels targeted for oximetry, the imaging systems utilised, and methods to validate oximetry measures. We detail the main physiological and clinical insights provided by ocular oximetry. Expert commentary: Oximetry has revealed physiological norms and auto-regulatory effects in the retina, choroid, episcleral, and bulbar conjunctival blood vessels. Retinal oximetry has provided insights into the development of diabetic retinopathy and glaucoma, and may enhance the evaluation and treatment of retinal vessel occlusion. Commercially available retinal oximetry systems have enabled oximetry in the clinical setting. The development of more sophisticated phantoms that resemble in vivo environments has helped validate oximetry applications. New insights into ocular physiology and disease are likely to be gleaned from future studies.

P1 Rapid all-optical blood serum assay for heart disease biomarkers

Blood-serum assays for heart-disease biomarkers such as myoglobin (Mb) and heart-type fatty acid binding protein (HFABP) are highly useful for objective cardiac infarct diagnosis and assessment of infarct size. However, current blood-serum immunoassays are extremely time consuming, requiring several hours of highly skilled labour in a biochemical laboratory. We present a novel optical assay method for quantification of heart disease biomarkers in biological solutions (eg blood serum/urine). This method utilises the optical fluorescence properties of Europium III (Eu3+) rare-earth ions: when biomarkers are present in a solution, the fluorescence emission of Eu3+ ions is changed. This change in fluorescence can be easily measured in an automated manner, enabling the rapid quantification of biomarkers in solution. In future, this method may be multiplexed to a “lab on a chip” device to measure multiple biomarkers simultaneously from a single biological sample in ~1 minute or less. This could potentially decrease the diagnosis time for heart disease and improve patient outcomes.