Recent strategies for noninvasive glucose monitoring

Diabetes can be defined as a complicated and worldwide epidemic metabolic disorder disease. As estimated by the World Health Organization by year 2030,366 million people will have diabetes mellitus. Blood glucose concentration is a key indicator of health of diabetic patients, so glucose is considered as a biomarker according to the definition of National Institutes of Health. Methods for measuring glucose are divided into invasive (Finger-pricking and Implantable) and non-invasive (Tissues and Fluids). Because of several disadvantages like risk of infection and damage, wearable and mobile technologies in non-invasive glucose monitoring have attracted much attention. Herein, we review recent advances in bio-fluids and tissues based non-invasive glucose measurements including new materials, concepts, and engineering techniques. Bio-fluids, such as sweat, saliva, interstitial fluid (ISF) and tears, reflecting the physiological conditions in the core body, are very attractive due to having the most sampling sites outside the body, an ease of collection, device placement and comfort. But, the major challenges for accurate fluids glucose measurements are stemming from fluctuations in environmental parameters (i.e. temperature and pH variation), low production rate, and the mixing of old sample with new fluids. Tissues are flexible, aesthetically pleasing and can be easily mated with the human skin. But, their disadvantages are skin irritation caused by the RI process, the long necessary warm up time and the need for calibration. Tissues include glucowatch (enzymatic electrochemical glucose sensor), sugar beta (a disposable adhesive skin-patch), temporary tattoo (screen-printing electrode platform on skin) and earlobe clip (using ultrasonic, electromagnetic and thermal technologies). The development of electrochemical non-invasive glucose monitoring for diabetes management is just beginning and extensive efforts are required to address its key technological challenges.