Portal de Periódicos da CAPES

Non-invasive continuous glucose monitoring in Type I diabetic patients with optical glucose sensors

1998; Springer Science+Business Media; Volume: 41; Issue: 7 Linguagem: Inglês

10.1007/s001250050998

1432-0428

Lutz Heinemann, G. Schmelzeisen‐Redeker,

Analytical Chemistry and Sensors

Systematic self-monitoring of glycaemia represents acornerstone in intensified insulin therapy. In fact,self-monitoring of blood glucose (SMBG) marksprobably the most important advance in diabetescare since the discovery of insulin. However, at leasttwo aspects make conventional SMBG difficult. Fin-ger pricking to obtain the droplet of blood is regardedby many patients as even more daunting and painfulthan insulin injections [1]. On the other hand, spotmeasurements of blood glucose, even if performedseveral times daily, only provide an incomplete pic-ture of the blood glucose changes occurring over thewhole day. A continuous and reliable in-vivo glucosemonitoring system would allow diabetic patients tocheck their metabolic control at their convenience.This would supply the diabetic patient with all infor-mation required to optimise insulin therapy and,possibly, to improve metabolic control. Further-more acute metabolic deteriorations, such as hypo-glycaemic episodes, should easily become detectableby a continuously working glucose sensor.Several minimally invasive and non-invasive ap-proaches have been studied to monitor blood glucosemore or less continuously: 1) Implantable subcutane-ous (s.c.) glucose sensors, 2) S.c. interstitial fluidsampling by microdialysis or open-tissue microperfu-sion, 3) Transdermal glucose monitoring systems, 4)Optical glucose sensors. The minimally invasive ap-proaches (1 and 2) are based on the analysis of inter-stitial fluid. Insertion of electrodes into the s.c. tissuehas not yet resulted in a glucose sensor that could beused reliably for longer periods of time in humans[2–5]. Lack of biocompatibility of the electrode sur-face results in drifts of the electrode signal, associatedwith a loss of glucose sensitivity. The minimally inva-sive microdialysis technique and related techniquesreduce such problems by pumping a perfusatethrough a dialysis fibre inserted in the subcutaneoustissue [6–10]. Glucose diffuses from the interstitialfluid into the perfusate and is measured ex vivo. Inother approaches devices are attached to the skin tocollect glucose containing fluid transdermally [11].We will not review these minimally invasive ap-proaches for glycaemic monitoring but will focus onnon-invasive optical glucose sensors that avoid anumber of the problems of former approaches. Wewill discuss the problems of reliable glucose monitor-ing using the spectrometric absorption technologyand present a novel approach making use of the factthat the variation of blood glucose levels changes thelight scattering properties of skin tissue.In-vivo glucose monitoringby light absorption measurementSome research groups are trying to develop non-inva-sive glucose monitoring systems based on absorptionmeasurements [12–16]. Up to now, however, nonehas been converted into a reliable glucose monitoringsystem, although a number of companies have pre-sented or announced glucose monitoring devices us-ing similar approaches.Spectrophotometry is an established method forthe quantification of solutes in liquids. It is based onsolute specific absorption bands in the visible (VIS),near infra-red (NIR) or mid infra-red (MIR) spectralrange. Quantification of the solutes is possible by de-termination of light attenuation caused by absorptionat a single wavelength when taking the light pathlength (i.e. the cuvette thickness) into account. Thesolution has to be clear, as light scattering would re-sult in an additional attenuation of light.