Autofluorescence lifetime metrology for label-free readouts of heart disease and arthritis

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This project aims to provide new label-free detection and imaging tools for minimally invasive diagnosis of arthritis and heart disease. When biological tissue is illuminated with light at appropriate wavelengths, certain naturally occurring biomolecules can absorb this excitation energy and emit new radiation called fluorescence. By analysing such autofluorescence signals, it is possible to detect particular biochemical or structural changes in tissue, which may be exploited to detect the early onset of diseases such as arthritis, heart disease and cancer, which can cause changes in the concentration, distribution and interaction of these autofluorescent biomolecules. Unfortunately, biological tissue is heterogeneous, typically containing many kinds of biomolecule in unknown quantities that can interact with autofluorescence measurements. It also strongly scatters optical radiation, making quantitative fluorescence measurements unreliable. It is therefore desirable to analyse tissue autofluorescence in a way that avoids artefacts arising from unknown variations in molecular concentrations and light intensity. One way to do this is to exploit the fact that excited molecules can radiate fluorescence at different rates, depending on the particular biomolecule or on how it is interacting with its surroundings. By observing the fluorescence decay times (lifetimes), it is possible to distinguish different chemical species or different molecular environments that can correlate with different tissue structures. Although this technique is attracting increasing interest in laboratory-based research, there is very little work, to date, on translating this to clinical practice. Here, we propose to develop fibre-optic-based probes that clinicians can use to measure fluorescence lifetimes in situ in biological tissue samples or live subjects including patients. We will also develop a fluorescence lifetime imaging (FLIM) system that will be able to rapidly map the spatial variation of autofluorescence lifetime, which can provide diagnostic functional images for medical research and clinical practice.We will develop one fibre-optic autofluorescence lifetime (AFL) probe to be applied to changes in tissue matrix components associated with arthritis, which leads to loss of joint function and pain in ~9 million people in the UK's aging population. Arthritis is caused by the degradation of cartilage in our limb joints. Currently, there is no way to examine the integrity of cartilage tissue without invasive surgical biopsy. In preliminary work, we have shown that degraded cartilage exhibits significantly different AFL compared to healthy cartilage. Here we aim to investigate how AFL measurements can provide label free information on the structure and health of cartilage. We would also investigate the prognostic value of FLIM arthroscopy of cartilage in early rheumatoid and osteoarthritis and monitor the effect of drugs applied to repair cartilage.A second AFL probe will be applied to the study of heart disease - the major cause of death in the developed world - which is characterised by abnormalities of heart muscle energetics. Energetic inefficiency accelerates further disease progression, manifesting as changes in the mechanical and electrical properties of the heart. Two important autofluorescent molecules, NAD(P)H and flavins, are intimately involved in metabolism but, apart from our preliminary results presented below, no AFL measurements have been made in situ in live heart tissue. We aim to investigate how cardiac AFL can provide a quantitative label-free readout of the metabolic state of the beating heart and to identify signatures of disease through AFL measurements and FLIM of cardiac tissue matrix adaptations associated with heart disease and electrical disturbances. These label-free readouts of diseased heart tissue could provide a novel means to determine treatment of patients following a heart attack.