Re-usable electrochemical glucose sensors integrated into a smartphone platform

Abstract

This article demonstrates a new smartphone-based reusable glucose meter. The glucose meter includes a custom-built smartphone case that houses a permanent bare sensor strip, a stylus that is loaded with enzyme-carbon composite pellets, and sensor instrumentation circuits. A custom-designed Android-based software application was developed to enable easy and clear display of measured glucose concentration. A typical test involves the user loading the software, using the stylus to dispense an enzymatic pellet on top of the bare sensor strip affixed to the case, and then introducing the sample. The electronic module then acquires and wirelessly transmits the data to the application software to be displayed on the screen. The deployed pellet is then discarded to regain the fresh bare sensor surface. Such a unique working principle allows the system to overcome challenges faced by previously reported reusable sensors, such as enzyme degradation, leaching, and hysteresis effects. Studies reveal that the enzyme loaded in the pellets are stable for up to 8 months at ambient conditions, and generate reproducible sensor signals. The work illustrates the significance of the pellet-based sensing system towards realizing a reusable, point-of-care sensor that snugly fits around a smartphone and which does not face issues usually common to reusable sensors. The versatility of this system allows it to be easily modified to detect other analytes for application in a wide range of healthcare, environmental and defense domains.

Controlling Redox Enzyme Orientation at Planar Electrodes

“…The increasing knowledge of the parameters that control enzymatic activity on electrodes has enabled the design of the current commercially available «finger-pricking» approach, and has opened the way to implantable glucose biosensors. Advanced technology allows us to now envision the integration of the glucose bioelectrochemical sensor in a smartphone platform, simplifying the lives of diabetic patients [8]. Furthermore, it is possible to measure glucose in other fluids than blood, i.e., interstitial liquid, urine, saliva, sweat, or ocular fluid [9].…”

“…Concomitantly, stabilization of the enzymes once immobilized would be desired. Many recent reviews analyze the issues relative to protein behavior once immobilized on solid Catalysts 2018, 8,192 5 of 38 supports [22]. Although no general rules can be formulated, it is plausible to expect that the interaction between the solid support and the enzyme may cause an alteration in protein structure and/or flexibility, hence modifying its properties.…”

“…The consequence is that for interfacial ET to proceed, it is mandatory to place the active site at a distance compatible with ET, using controlled tethering to the surface. Because the active site is often protected from the external environment by deep embedding inside the protein Catalysts 2018, 8,192 6 of 38 moiety, one has to play with the electronic relays inside the enzyme which allow fast intramolecular ET. The electron entry or exit point will be the particular electronic relay on the surface of the enzyme that must be located at a close distance from the electrode (Figure 2).…”

“…Molecular Dynamics simulations on [NiFe] hydrogenases from A. aeolicus and Desulfovibrio fructosovorans have shown how these two homologous enzymes display their own specific internal tunnel network [31]. In the case of the Catalysts 2018, 8,192 7 of 38 membrane-bound A. aeolicus hydrogenase, all the substrate entry points are located on the same side of the enzyme's surface. As a consequence, the enzyme's adsorption on an electrode with the wrong orientation might result in the shielding of some parts of its surface, such that a small substrate could no longer use it as an entry point to reach the active site.…”

Cluster Analysis Based on Fasting and Postprandial Plasma Glucose and Insulin Concentrations

“…The first clustering experiment was performed using only fasting glucose levels (G0). This experiment is important since estimating the fasting glucose concentration is a feasible task to be performed by an inexperienced person using, for example, commercial devices, such as a glucometer or a smartphone application [8,27], or wearable technology, such as a contact lens [16,7]. Therefore, discovering physiological patterns or clinical indicators using only fasting blood glucose concentration could have a significant impact on society since people could obtain useful information without going to a specialized clinical laboratory.…”