Review
Fluorescence-based glucose sensors

https://doi.org/10.1016/j.bios.2004.10.002Get rights and content

Abstract

There is an urgent need to develop technology for continuous in vivo glucose monitoring in subjects with diabetes mellitus. Problems with existing devices based on electrochemistry have encouraged alternative approaches to glucose sensing in recent years, and those based on fluorescence intensity and lifetime have special advantages, including sensitivity and the potential for non-invasive measurement when near-infrared light is used. Several receptors have been employed to detect glucose in fluorescence sensors, and these include the lectin concanavalin A (Con A), enzymes such as glucose oxidase, glucose dehydrogenase and hexokinase/glucokinase, bacterial glucose-binding protein, and boronic acid derivatives (which bind the diols of sugars). Techniques include measuring changes in fluorescence resonance energy transfer (FRET) between a fluorescent donor and an acceptor either within a protein which undergoes glucose-induced changes in conformation or because of competitive displacement; measurement of glucose-induced changes in intrinsic fluorescence of enzymes (e.g. due to tryptophan residues in hexokinase) or extrinsic fluorophores (e.g. using environmentally sensitive fluorophores to signal protein conformation). Non-invasive glucose monitoring can be accomplished by measurement of cell autofluorescence due to NAD(P)H, and fluorescent markers of mitochondrial metabolism can signal changes in extracellular glucose concentration. Here we review the principles of operation, context and current status of the various approaches to fluorescence-based glucose sensing.

Section snippets

Introduction: diabetes and glucose sensing

There is now good evidence that the chronic complications of diabetes are related to the duration and severity of hyperglycaemia (Diabetes Control and Complications Trial Research Group, 1993, UK Prospective Diabetes Study Group, 1998). However, good diabetic control is very difficult to achieve in many diabetic patients and frequent blood glucose testing is needed to detect hyper- and hypoglycaemia, and to adjust treatment to correct these deviations and maintain long-term near-normoglycaemia.

Why fluorescence?

The advantages of molecular fluorescence for biosensing include the following:

  • The technique is extremely sensitive. There are increasing examples of even single-molecule detection using fluorescence methods (Weiss, 1999).

  • Fluorescence measurements cause little or no damage to the host system. In addition, since near-infrared light passes through several centimetres of tissue, with the appropriate choice of fluorophore, molecules can in theory be excited and the emission interrogated from outside

Fluorescence-based glucose sensors

A convenient way of classifying glucose sensors that involve measurements of fluorescence is either according to the type of molecular receptor for glucose, or whether cells or tissues are used to signal glucose concentrations and/or glucose metabolism.

Intrinsic fluorescence of cells

Recently, we have been investigating the notion that the intrinsic fluorescence of tissues such as skin can be used as a reporter of glucose metabolism and thus blood glucose concentrations (Evans et al., 2003). We hypothesized that the fluorescent cofactor NAD(P)H is produced from non-fluorescent NAD in many glucose-dependent metabolic pathways, including the tricarboxylic acid cycle, glycolysis and the hexose monophosphate pathway. NAD(P)H has a fluorescence with a maximum at about 440–480 nm

Conclusions

There are few fluorescence-based glucose detection methods that have reached the stage of testing in vivo, and none have entered clinical practice in diabetes management. This will clearly be an area of active investigation in the coming years—we will need, for example, to explore potential interferents and the stability and accuracy under real-life conditions. Given the problems associated with the presently available in vivo glucose sensors based on implanted amperometric enzyme electrodes

Acknowledgements

We are grateful to the Engineering and Physical Sciences Research Council, the Wellcome Trust and the Diabetes Foundation for financial support.

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