*2.1. Chemicals and Instruments*

Glucose, uric acid, ascorbic acid, chitosan, and glucose oxidase (GOx, from Aspergillus niger, Type X-S, lyophilized powder, 118,000 units/g solid) were purchased from Sigma-Aldrich Corp. (St. Louis, MO, USA). A single-sided Kapton® polyimide tape with a film thickness of ~30.4 µm and a width of 50 mm was obtained from STAREK Scientific Co., Ltd. (Taipei, Taiwan). Photo/printing paper (HYA300, A4—120 gm−<sup>2</sup> , 0.15 mm) was purchased from a local book store. All the electrochemical measurements were conducted using a portable potentiostat (PalmSens 4, PalmSens, Houten, The Netherlands). Raman

spectroscopic study was conducted using a micro-Raman spectrometer (JASCO NRS-4100; Laser 532 nm) with a spectral resolution of 2 cm−<sup>1</sup> . Data processing/plotting was performed using Origin 9.1 software (OriginLab Inc., Northampton, MA, USA). *2.2. Fabrication of LIGE Sensor*  A 3-electrode system was designed using AutoCAD software with a 3 mm diameter

formed using Origin 9.1 software (OriginLab Inc., Northampton, MA, USA).

a film thickness of ~30.4 µm and a width of 50 mm was obtained from STAREK Scientific Co., Ltd. (Taipei, Taiwan). Photo/printing paper (HYA300, A4—120 gm−2, 0.15 mm) was purchased from a local book store. All the electrochemical measurements were conducted using a portable potentiostat (PalmSens 4, PalmSens, Houten, The Netherlands). Raman spectroscopic study was conducted using a micro-Raman spectrometer (JASCO NRS-4100; Laser 532 nm) with a spectral resolution of 2 cm−1. Data processing/plotting was per-

*Polymers* **2021**, *13*, x FOR PEER REVIEW 3 of 11

#### *2.2. Fabrication of LIGE Sensor* of working electrode and laser-inscribed to graphene-based electrodes. Kapton® polyi-

A 3-electrode system was designed using AutoCAD software with a 3 mm diameter of working electrode and laser-inscribed to graphene-based electrodes. Kapton® polyimide tape was pasted onto a paper substrate and cleaned with isopropanol and deionized water. Then, the designed pattern made in graphic software was inscribed on the surface of the Kapton tape using a laser engraving machine (HANLIN 7WLS, 7 W, 450 nm) to form highly conductive graphene electrodes, as shown in Figure 1. The resistance of the graphenebased electrode was optimized by adjusting the laser power intensity (22% of the machine's maximum power), engraving depth (5%), the distance between the laser head and the polyimide substrate (~13 cm). The duration for fabricating a complete LIGE sensor was 2.8 min. mide tape was pasted onto a paper substrate and cleaned with isopropanol and deionized water. Then, the designed pattern made in graphic software was inscribed on the surface of the Kapton tape using a laser engraving machine (HANLIN 7WLS, 7 W, 450 nm) to form highly conductive graphene electrodes, as shown in Figure 1. The resistance of the graphene-based electrode was optimized by adjusting the laser power intensity (22% of the machine's maximum power), engraving depth (5%), the distance between the laser head and the polyimide substrate (~13 cm). The duration for fabricating a complete LIGE sensor was 2.8 min.

**Figure 1.** LIG 3-electrode system on polyimide tape fabricated by laser inscribing. **Figure 1.** LIG 3-electrode system on polyimide tape fabricated by laser inscribing.
