The GlucoDay® Diabetic monitoring device is used to continuously monitor blood glucose level all day long. Patients using invasive self-monitoring devices assess blood glucose irregularly because of the associated pain and inability to carry out measurement at night while they are sleeping (Boland et al., 2001; Maran et al., 2002). Precise and accurate continuous monitoring of blood glucose level using the GlucoDay® device is however of immense benefit to the patient as it provides an indication of the impact of medications, food intake, exercise, stress and other lifestyle factors on blood glucose profile; this is further enhanced by the in-built alarm system that alerts the patient of extreme glucose values in both low and high directions (Maran et al., 2002; Skyler, 2009). An efficient continuous monitoring of blood glucose is therefore an important part of a successful diabetes management programme; it provides patient’s blood glucose level in real time and promotes appropriate insulin dosing or administration and appropriate lifestyle modification (Sieg et al., 2004). This is a desirable situation that can help to reduce long-term impact of diabetes on individuals as confirmed by the Diabetes Control and Complications Trial Group in 1993.
DEVICE DESIGN AND PRINCIPLES
The GlucoDay® Diabetic monitoring unit produced by A. Menarini Diadnostics, Italy is a minimally or semi-invasive portable device contained in a pouch that is worn with a belt round the waist of a patient; it is basically made up of a biosensor and a micropump connected to a microdialysis system inserted subcutaneously to the abdominal (periumbilical) region of the patient (Maran and Poscia, 2002; Maran et al., 2002; Skyler, 2009). The device once calibrated, powered by 9 volts battery measures and records subcutaneous glucose level every three (3) minutes which is displayed, stored and later downloaded on a computer (Maran and Poscia, 2002). The device actually takes glucose value every second while storing an average value every 3 minutes which amounts to 480 measurements per day thereby capturing every bit of the glucose profile of the patient (Maran et al., 2002). A schematic representation of the device is shown in Figure 1.
Figure 1 – A schematic representation of the GlucoDay (Maran et al., 2002).
The programmable micropump with a flow rate of 10 to 100 µl/min controls the flow of the perfusion buffer through the microdialysis probe with the resulting dialysate flowing through the biosensor which determines and records the glucose level (Maran and Poscia, 2002). The glucose contained in the dialysate or ultrafiltrate is interstitial glucose collected from the interstitial fluid by the process of diffusion (Cengiz and Tamborlane, 2009; Chaplin, 2009). The GlucoDay® biosensor component is made up of a wall jet flow cell with platinum electrode and a membrane system of three layers consisting of cellulose acetate membrane, enzyme membrane and polycarbonate membrane (Maran and Poscia, 2002). The enzyme membrane is composed of glucose oxidase dissolved in bovine serum albumin, cross-linked with glutaraldehyde and immobilized on nylon net (Caifeng et al., 2009; Maran et al., 2002). This arrangement enhances the stability and activity of the enzymes by retaining the enzyme in the entrapment while permitting the diffusion of the substrate (glucose) and also the hydrogen peroxide formed to the electrode; proximity of the enzyme membrane to the electrode increases the current value or signal generated (Chaplin, 2009). This is very important since the GlucoDay® determines glucose level by amperometric method. The substrate glucose in the dialysate is oxidized by the enzyme glucose oxidase to gluconolactone while reducing dissolved molecular oxygen to hydrogen peroxide which is in turn oxidized at the platinum electrode to generate the current or signal measured at a potential of 0.6...