Fig. 1. Pancreas's glucose regulatory pathways[13]

Fig. 2. Bihormonal closed-loop insulin and glucagon delivery system[21]

Fig. 3. Nanotechnology-based glucose sensor technologies[23]

Fig. 4. Three generations of amperometric enzyme electrodes for glucose based on the use of (a) natural oxygen cofacto, (b) artificial redox mediators (b), and (c) direct electron transfer between GOx and the electrode [45]

Fig. 5. Cross section of a commercial strip for self-testing of blood glucose

Fig. 6. Sensor design of percutaneous (left) and fully implantable subcutaneous (right) biosensors

Fig. 7. Images and schematic illustrations of the FISA for multiplexed perspiration analysis[61]

Fig. 8. Schematic illustration of wearable sensor for tears analysis[62]

Fig. 9. Schematic illustration of detection principle of LSPR-based optical enzyme biosensor[73]

Fig. 10. Schematic illustration of detection principle of H2O2-based optical enzyme biosensor

Fig. 11. Schematic diagram of a layer-by-layer hydrogel pad and the entrapped Q-Concanavalin A/R_dextran glucose-sensing system[81]

Fig. 12. Schematic illustration of detection principle of PBA-based optical glucose biosensor[89]

Fig. 13. Schematic illustration of detection principle of PBA-SWNT-based near infrared optical glucose biosensor[99]

Fig. 14. Schematic illustration of the injectable fluorescent microbeads for in vivo CGM[100]

Fig. 15. Schematic illustration of the formation of Pdot-GOx bioconjugates for in vivo glucose monitoring[106]