Anhydrous ethyl alcohol

Potassium bromide, iron(iii) ferrocyanide (Prussian blue), potassium hexacyanoferrate(iii) (ACS reagent, ≥99%), kojic acid (≥98.5%, HPLC), magnesium chloride (anhydrous, ≥98%), glucose, sodium chloride (ACS reagent, ≥99.0%), sodium bicarbonate (ACS reagent, ≥99.7%), trisodium citrate dihydrate, sulfuric acid (ACS reagent, 95.0–98.0%), hydrochloric acid (ACS reagent, 37%), and Nafion perfluorinated resin solution were purchased from Sigma-Aldrich (Korea). Potassium chloride (>99.5%) was purchased from Kanto Chemicals Co., Inc. Gold colloidal nanoparticles with a diameter of 40 nm were sourced from Bore Da Biotech. Phosphate-buffered saline at pH 7.4 was acquired from Thermo Fisher Scientific. Calcium hydroxide was purchased from Daejung Chemicals in Korea, while anhydrous ethyl alcohol with a purity of 99.9% was obtained from Samchun Chemical, Korea. The working glassy carbon electrode (GCE), a spiral platinum counter electrode, and Ag/AgCl reference electrodes were procured from BASi. All the chemicals and buffers were prepared with deionized water with a resistance not less than 18.2 MΩ cm.

Sodium carboxymethyl cellulose (CMC, average M  ~ 250,000) and graphite flakes were purchased from Sigma Aldrich Korea. Sulfuric acid (H₂SO₄; 98%) and phosphoric acid (H₃PO₄; 85%) were purchased from DAEJUNG and DUKSAN, respectively. Potassium permanganate (KMnO₄; 99.3%) and hydrogen peroxide (H₂O₂; 30%) were purchased from OCI Company Ltd., Korea. Hydrochloric acid (HCl; 35%–37%) and anhydrous ethyl alcohol (99.5%) were purchased from SAMCHUN and DAEJUNG, respectively. CNTs were supplied by Nanosolution Co., Korea.

Sodium hyaluronate (Molecular weight = 200 kDa) was purchased from Lifecore Biomedical (Chaska, MN, USA). Dopamine hydrochloride with catechol and amine groups, tyramine hydrochloride with phenol and amine groups, N-hydroxysuccinimide (NHS), 2-(N-morpholino) ethanesulfonic acid (MES) solution (1 M), hydrochloric acid (HCl), sodium hydroxide (NaOH), horseradish peroxidase (HRP), hydrogen peroxide solution (H₂O₂), sodium periodate (NaIO₄), ammonium persulfate (APS), and iron (III) chloride (FeCl₃) were purchased from Sigma-Aldrich (St. Louis, MO, USA). 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC-HCl) was purchased from Tokyo Chemical Industry (Tokyo, Japan). Phosphate-buffered saline (PBS, 10X, pH 7.2) was purchased from Welgene (Gyeongsan, Korea). Sodium chloride (NaCl) was purchased from Daejung (Siheung, Korea). Anhydrous ethyl alcohol was purchased from Samchun Pure Chemical (Pyeongtaek, Korea). SpectraPor 1 Dialysis Membrane (Standard RC tubing, molecular weight cut-off (MWCO) = 6–8 kDa) was purchased from Spectrum (Rancho Dominguez, CA, USA).