Gnp solution

Herein, 2.0 g CS (degree of deacetylation ≥ 95%, Macklin, Shanghai, China) was dissolved in 100 mL aqueous hydrochloric acid (0.1 mol/L, Sigma-Aldrich, St. Louis, State of Missouri, USA) under sterile conditions. The pH of the resulting solution was adjusted to approximately 7.25 by β-glycerophosphate sodium solution (70% w/v, Solarbio, Beijing, China). Then, appropriate amounts of GNP solution (1% w/v, Sigma-Aldrich) and GO aqueous solution (3 mg/mL, Macklin) were added to the abovementioned solution. By mechanical stirring and ultrasonic breaking, CS/GO mixed solutions with different GO concentrations were prepared. Thereafter, these mixed solutions were centrifuged at 4°C and 3000 r/min for 10 min and then placed in a biochemical incubator at 37°C to form the hydrogels. Finally, these hydrogels were frozen at -80°C for 4 h and then placed in a vacuum freeze dryer (Biobase, Jinan, Shandong province, China) to construct hydrogel scaffolds.

galactose
oxidase (source: Dactylium dendroide, ≥3000 units/g solid),
chitosan (medium molecular weight), Nafion-117, potassium hexacyanoferrate
(III), potassium hexacyanoferrate (II), potassium chloride, sodium
chloride, hydrochloric acid, dipotassium hydrogen phosphate, monopotassium
phosphate, galactose, galactose-1-phosphate, GNP solution (with a
diameter of 5 nm), and other chemicals were obtained from Sigma-Aldrich
(USA). In the experiments PalmSens Emstat3 potentiostat (Netherlands),
screen printed carbon electrodes from Dropsens (DRP-C110, Switzerland)
that contain carbon working electrode (4 mm diameter), carbon auxiliary
electrode, and silver reference electrode were used.
A 0.1 M
KCl containing 50 mM phosphate-buffered saline (PBS) buffer at pH
7.5 was used as a working buffer. To prepare the artificial serum,
a mixture of 111 mM NaCl, 2.9 mM NaHCO₃, 2.2 mM K₂HPO₄, 0.8 mM MgCl₂, 2.5 mM urea, and 5 mM KCl
was adjusted to pH 7.4.^{34 (link)} The galactose
oxidase solution was prepared by dissolving it in 50 mM pH 7.5 PBS
to a concentration of 80 mg/mL. The galactose solution was prepared
by dissolving galactose in the artificial serum.