Iron 3 ferrocyanide

Sodium alginate, calcium chloride (CaCl₂), polyvinylpyrrolidone (PVP, Mw = 40,000), polyethylene glycol diacrylate (PEG-DA, Mw = 700), ferric chloride hexahydrate (FeCl₃·6H₂O), iron (III) ferrocyanide (PB, Prussian blue, Fe₄[Fe(CN)₆]₃·nH₂O, n = 14–16), and fluorescein isothiocyanate-dextran (FITC-dextran, Mw = 20,000) were purchased from Sigma-Aldrich Chemicals (MO, USA). Both alginate and calcium chloride solutions were prepared using experimental solutions and further diluted to the required concentrations before use. Milli-Q water having a resistance of less than 18.2 mΩ was used in all procedures.

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.