Fig. 4.

Modern glucose and electrochemical substance level studying methods. External skin devices: a) The skin-attachable, stretchable electrochemical sweat sensor for glucose and pH detection attached to the skin wet with sweat (Adapted with permission from Ref. [110] © 2022 American Chemical Society). b) Implantation of a robust, wearable, and non-enzymatic system for continuous glucose level monitoring in a rabbit and a cross-sectional non-enzymatic glucose sensor view (Adapted from Ref. [108] © 2022 with permission from Elsevier). c) Battery-free, wireless, and epidermal electrochemical system for in situ sweat sensing bonded to a subject's arm, with a smartphone for wireless power and data transmission (Adapted with permission from Ref. [111] under Creative Commons Attribution (CC BY) License). d) Microneedle sensor arrays for continuous glucose monitoring (Adapted from Ref. [112] with permission from the Royal Society of Chemistry). e) Self-powered implantable skin-like glucometer for real-time blood glucose level detection (Adapted from Refs. [108,113] under Creative Commons Attribution 4.0 International License).