# Advancements in Glucose Monitoring: From Traditional Methods to Wearable Sensors
## 2 Invasive Methods
### Electrochemical Glucose Sensors
The result indicates that the electrode exhibits a wide range of 0.001-19.899 mM, and a low detection limit of 0.45 \(\upmu\)M (Figure 2i,j) [38]. In an attempt to improve the real-time tracking of glucose, a microdialysis-based method is introduced. In the case of microdialysis systems, a fine, hollow dialysis fiber is implanted in the subcutaneous tissue and perfused with isotonic fluid. Glucose from the tissue diffuses into the fiber and is pumped outside the body for measurement by an electrochemical sensor. Recently, [PERSON] et al. developed an integrated implantable microfluidic system that uses a microdialysis method for the non-enzymatic measurement of human body glucose [PERSON] et al. (2018). The microfluidic system consists of a small dialysis channel with a height of 60 \(\upmu\)m embedded with a non-enzymatic glucose sensor consisting of Pt-Ni nanoparticles--multiwalled carbon nanotubes/screen-printed carbon electrode (Pt-Ni NPs-MWCNTs/SPE). Figure 2k shows the SEM images of the fabricated Pt-Ni NPs-MWCNTs/SPE, and the process for the preparation of Pt-Ni NPs-MWCNTs/GCE is il  
Figure 2: **(a)** Illustration of testing method using paper-based electrochemical device. Reprinted with permission from [26] **(b)** FESEM image of electrodeposited Au nanowire array. Reprinted with permission from [28] **(c)** DPV curves of Au NW electrode in 0.1 M NaOH solution and glucose at concentrations of 0.5 and 2–20 mM with step size of 2 mM. Scan rate: 20 mV s\({}^{-1}\); step height: 5 mV; step width: 1 s; pulse width: 200 ms; pulse height: 50 mV; and sample period: 50 ms. The inset shows dependence of peak current of glucose oxidation on concentration of glucose. Reprinted with permission from [28] **(d)** Schematic illustrating formation of Co-MOF nanosheet array on nickel foam. Reprinted with permission from [6] (e) CV curves of Co-MOF/NF in 0.1 M NaOH in present of various glucose concentrations, i.e., 0, 1, 3, 5, 7, and 9 mM, with a scan rate at 30 mV s\({}^{-1}\). Reprinted with permission from [6] (f,g) The amperometric responses of Co-MOF/NF with successive addition of glucose in 0.1 M NaOH. Reprinted with permission from [6]. **(h)** Surface morphology analysis of hollow PANI nanofibers doped with CuO. Reprinted with permission from [38]. **(i)** I-T response of CuO/PANI nano-hybrid fibers modified with GCE in 0.1 M PBS with successive addition of H\({}_{2}\)O\({}_{2}\) at \(-\)0.2 V. Reprinted with permission from [38]. **(j)** Calibration curve. Reprinted with permission from [38]. **(k)** SEM images of fabricated Pt-Ni NPS-MWCNTs/SPE. Reprinted with permission from [39]. **(l)** Process illustration for preparation of Pt-Ni NPs-MWCNTs/GCE. Reprinted with permission from [39]. **(m)** Schematic view of microfluidic device showing position of microchannels and microneedles in microfluidic device. Reprinted with permission from [39]. lustrated in Figure 2l. The schematic view of the microfluidic device is shown in Figure 2m. The detection limit for this microfluidic sensor was reported as 21 uM, which was comparatively low when compared to that of the other non-enzymatic process mentioned above [39]. In the view of the growing interest towards the non-invasive approach, [PERSON] et al. designed a highly stretchable electrochemical glucose sensor based on gold fibers for monitoring glucose in sweat. By combining the intrinsic stretchability of highly conductive gold fibers with an extrinsic helical structure, the sensor demonstrated strain-insensitive and reproducible electrochemical performance across a range of 0 to 200% strain with a sensitivity of 13.9 uA mM-1 cm-2 [40].