Point-of-care beta-hydroxybutyrate determination for the management of diabetic ketoacidosis based on flexible laser-induced graphene electrode system

Abstract: Diabetic ketoacidosis (DKA) is a life-threatening condition that can appear in patients with diabetes. High ketones in the blood lead to acidity of the blood. For DKA diagnosis and management, ketones such as hydroxybutyrate (HB) can be used to quantify the severity of the disease. The fabrication of electrochemical biosensors for the detection of HB is attractive since their capability to deliver fast response, high sensitivity, good selectivity and potential for miniaturisation. In this thesis, an integrated electrode system was prepared for the detection of HB. Laser-induced graphene (LIG) with a 3D porous structure was used as the flexible platform. Poly (toluidine blue O) (PTB) was electro-deposited on LIG (PTB/LIG) under the optimised conduction (pH of 9.7 and from 0.4 to an upper cyclic potential of 0.8 V). The single PTB/LIG working electrode demonstrated excellent performance towards the detection of NADH with a linear range of 6.7 M to 3 mM using chronoamperometry, high sensitivity of detecting NADH and excellent anti-fouling ability (94 % response current retained after 1500 s). Further integration of the 3-electrode system realised the static amperometric detection of NADH over the range of 78 M to 10 mM. Based on the excellent performance of PTB/LIG to NADH sensing, hydroxybutyrate dehydrogenase was immobilised via encapsulation with chitosan and polyvinyl butyral (PVB) which was used for HB biosensing over the linear range of 0.5 M to 1 mM with NAD+ dissolved in solution. In addition, the co-immobilisation of NAD+ and HBD on PTB/LIG was conducted by optimisation of enzyme and NAD+ amount per electrode, which shows excellent reproducibility and satisfactory HB biosensing performance. Further experiments to improve the long-term stability of the enzyme electrode is expected in the future. The proposed integrated electrode system also possesses the potential to extend to a multichannel sensor array for the detection of multiple biomarkers (e.g. pH and glucose) for diagnosis and management of DKA.