Cas 78 10 4

The sol–gel process is a synthesis method in which, starting from molecular precursors such as metal alkoxides or inorganic salts, an oxide skeleton is obtained through hydrolysis and polymerization reactions at low temperatures, which allows the synthesis of metastable phases of rust and even mixed organic–inorganic solids [24 ]. The chemicals used were:

Tetraethyl orthosilicate (TEOS) 98%; CAS 78-10-4 (Sigma-Aldrich, St. Louis, MO, USA);

Glucose oxidase (GOD), type X-S from Aspergillus niger, lyophilized powder; CAS 9000137-0 (Sigma-Aldrich, USA);

Peroxidase from horseradish; CAS 9003-99-0 (Sigma-Aldrich, USA);

Ethanol CH3CH2OH 98%; CAS 64-17-5 (Sigma-Aldrich, USA);

Chlorhydric acid HCl 37%; CAS 7647-01-0 (Sigma-Aldrich, USA);

Acetic sodium salt trihydrate, pH 4.6; CAS 6131-90-4 (Hampton Research, USA);

Distilled water.

All the chemicals were used without any further purification. The equipment used was:

Beaker, 20 mL;

Magnetic stirrer with hot plate;

Analytical balance, 0.1 mg precision;

Adjustable micropipette, 0.1 μL–1 mL;

Hand-held optical power meter, brand Newport, model 1918-C;

Silicon photodetector, brand Newport, model 918D-SL-OD1R;

Dip coater.

For each used material, its chemical formula, purity, molar mass, density at 25 °C, and Chemical Abstract Service (CAS) number and supplier are given as follows: 2-propanol (C₃H₈O, 99.8%, 60.1 g/mol, 0.785 g/mL, CAS 67-63-0, Gram Mol), 3-aminopropyltrimethoxysilane (APTMS) (C₆H₁₇NO₃Si, 97%, 179.29 g/mol, 1.027 g/mL, CAS 13822-56-5, Merck), ammonium hydroxide (NH₄OH, 25%, 35.05 g/mol, 0.91 g/mL, CAS 1336-21-6, Gram Mol), ethanol (C₂H₅OH, 96%, 46.07 g/mol, 0.810 g/mL, CAS 64-17-5, Honeywell), ferric chloride hexahydrate (FeCl₃·6H₂O, 270.3 g/mol, 1.82 g/mL, CAS 10025-77-1, Sigma Aldrich), ferrous chloride tetrahydrate (FeCl₂·4H₂O, 198.81 g/mol, 1.93 g/mL, CAS 13478-10-9, Sigma Aldrich), terbium(III)chloride hexahydrate (TbCl₃·6H₂O, 99.9%, 373.38 g/mol, 4.35 g/mL, CAS 13798-24-8, Sigma Aldrich), tetraethyl orthosilicate (TEOS) (C₆H₂₀O₄Si, 99%, 208.33 g/mol, 0.94 g/mL, CAS 78-10-4, Sigma Aldrich), tiron monohydrate (C₆H₄Na₂O₈S₂·H₂O, 98%, 314.2 g/mol, CAS 149-45-1, Sigma Aldrich), tris(hydroxymethyl) aminomethane (H₂NC(CH₂OH)₃, 121.14 g/mol, 0.8 g/mL, CAS 77-86-1, Merck). All chemicals were used as received without further purification. For the preparation of all suspensions and solutions, deionized water (dH₂O) was used.