Glucose sensors are commercially available for continuous monitoring, primarily used in diabetes management [28]. <ref name = "Ref28">Johnston, L. et al. (2021) ‘Advances in biosensors for continuous glucose monitoring towards wearables’, Frontiers in Bioengineering and Biotechnology, 9. doi:10.3389/fbioe.2021.733810. </ref> Most of the CGM biosensors with ISF as a matrix are catalytic biosensors, using glucose oxidase (GOD) as the recognition molecule to bind with glucose [28]. <ref name = "Ref28"/> Microneedle array electrodes have been used for CGM, e.g. by functionalizing them through entrapment of GOD in an electropolymerized film [30]<ref name = "Ref30">Sharma, S. et al. (2016) ‘Evaluation of a minimally invasive glucose biosensor for continuous tissue monitoring’, Analytical and Bioanalytical Chemistry, 408(29), pp. 8427–8435. doi:10.1007/s00216-016-9961-6. </ref>, or by non-enzymatic amperometric readout [31]. <ref name = "Ref31">Lee, S.J. et al. (2016) ‘A patch type non-enzymatic biosensor based on 3D sus micro-needle electrode array for minimally invasive continuous glucose monitoring’, Sensors and Actuators B: Chemical, 222, pp. 1144–1151. doi:10.1016/j.snb.2015.08.013. </ref> Other examples of CGM biosensors in ISF include an enzymatic open circuit potential biosensor using GOD [32] <ref name = "Ref32">Song, Y. et al. (2016) ‘Design and preparation of open circuit potential biosensor for in vitro and in vivo glucose monitoring’, Analytical and Bioanalytical Chemistry, 409(1), pp. 161–168. doi:10.1007/s00216-016-9982-1. </ref> and an electrochemical glucose sensor composed of electroplated nanoporous platinum [33]. <ref name = "Ref33">Yoon, H. et al. (2018) ‘Wearable, robust, non-enzymatic continuous glucose monitoring system and its in vivo investigation’, Biosensors and Bioelectronics, 117, pp. 267–275. doi:10.1016/j.bios.2018.06.008.</ref>