Hexachloroplatinic acid

All chemicals were of analytical grade unless noted otherwise and used as received. Dichloroethane (DCE, 99.8%), tetrabutylammonium perchlorate (TBAP, 99%), sodium dodecyl sulfate (SDS, 99%), hexachloroplatinic acid, and iron (III) chloride were obtained from Sigma-Aldrich and used without further purification. Chromium (III) chloride, cobalt (II) chloride, manganese (II) chloride, vanadium (III) chloride, nickel (II) chloride, indium (III) chloride, cobalt (II) nitrate, nickel (II) nitrate, lanthanum (III) nitrate, iron (II) nitrate, platinum (IV) nitrate, and gadolinium (III) chloride were obtained from Fisher Scientific and used without further purification. Stock solutions (100–300 mM) of each metal were prepared in MilliQ water (>18 MΩ cm) and diluted as necessary to be used in the emulsion preparation. Metal salt solutions were stored in a dark refrigerator (4 ℃) to avoid photodecomposition. Metal salt compatibility was investigated to prevent competing reactions (Supplementary Table 4). Metal salts were analyzed by UV-vis spectroscopy to ensure no leakage into the DCE phase following sonication (Supplementary Fig. 20).

Chloroauric acid (HAuCl₄, 99.9%), graphite powder (325 mesh size), hexachloroplatinic acid (H₂PtCl₆, 99.9%), ascorbic acid (AA, 99%), acetaminophen (AP, 99%), chitosan (Ch), 20% Poly(diallyldimethylammonium chloride) solution (PDDA), uric acid (UA, 99%), β-D(+) glucose (99.5%), chitosan (Ch, Mw 50,000–190,000) and glucose oxidase (GOx) (Aspergillus niger, VII type, lyophilized powder) were purchased from Sigma (Korea). The stock solution of glucose was diluted in phosphate buffered saline (PBS) solution, and high purity water (resistivity ≥ 18 MΩ-cm) was used as a solvent to prepare other solutions. Electrochemical analyses of the fabricated electrodes were conducted by electrochemical analyzer (Model 600D series, CH Instruments Inc., USA). In a three-electrode system, an Ag/AgCl electrode with 3 M sodium chloride and a flat Pt bar were utilized as the reference electrode (RE) and counter electrode (CE), respectively. The physical properties of the chemically modified graphite oxide (CGO), RGO pellets, MRGO sheet, and developed electrode were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FESEM) with Energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy.

The monometallic Pt, Ru, Pd, and Ag catalysts were synthesized by impregnation method using natural zeolite samples as a support [20 (link),27 (link),30 (link)]. In the case of platinum, ruthenium, palladium, and silver catalysts appreciate precursor of metallic phase such us: hexachloroplatinic acid (Sigma Aldrich, Poznan, Poland), ruthenium chloride (Sigma Aldrich), palladium nitrate (Sigma Aldrich), and silver nitrate (STANLAB) were used in order to synthesize the catalytic systems. The metal loading in the case of monometallic Pt, Ru, Pd, and Ag catalysts was 0.5 or 2 wt.%, respectively. The synthesized monometallic catalysts were dried for 2 h at 120 °C, and then calcined for 4 h in an air atmosphere at 400 °C.

A solution-based method was used to deposit a Zn_0.76Co_0.24S layer on a glass substrate coated with fluorine-doped tin oxide (FTO). Before depositing the ZCS-CE layer, the FTO substrates were thoroughly cleaned by washing with soapy water, deionized water, and acetone under ultrasonic conditions. To prepare the zinc–cobalt sulfide material by solvothermal synthesis, the following steps were performed: thiourea (0.5 mmol), Zn(NO₃)₂ × 6H₂O (0.125 mmol), and Co(NO₃)₂ × 6H₂O (0.250 mmol) were dissolved in 35 mL ethanol at room temperature for 30 min. This solution was then placed in a 50 mL stainless steel reactor with a Teflon liner, where the FTO glass substrate was attached to the wall with the conducting side down. The mixture was gradually heated at a rate of 5 °C per minute until it reached 200 °C, and this temperature was maintained for 4 h. After natural cooling to room temperature, the electrodes were repeatedly rinsed with deionized water and ethanol to remove unreacted compounds. They were then dried in a vacuum oven at 80 °C for 12 h. For comparison with the fabricated ZCS-CE, a control CE was also prepared by applying Pt paste (consisting of terpineol and hexachloroplatinic acid, Sigma-Aldrich, St. Louis, MO, USA) to a clean and dry FTO glass substrate and then annealing at 500 °C for 30 min.

A solution of hexachloroplatinic acid (17.5 mM) and lead(II) acetate trihydrate (0.03 mM) (from Sigma-Aldrich, Buchs, Switzerland) dissolved in DI water was used for electrodeposition of Pt black. Platinum black was deposited by using the parameters listed in Table 1. The pulse-widths t_on were varied between 0.1 and 0.8 s, t_off was set to 0.4 s in all cases. The total t_on times (t_on* number of pulses) were kept constant for each set of pulse-widths by adapting the number of pulses. The depositions with different parameter sets were performed sequentially without renewal of the solution.
The roughness factors were determined coulometrically from the hydrogen desorption region of the CVs measured in H₂SO₄ solution at a sweep rate of 100 mV/s [24 (link)].

L-Tyrosine (L-2-Amino-3-(4-hydroxyphenyl)propanoic acid, 4-hydroxyphenylalanine), Tyrosinase (from mushroom, EC 232-653-4, activity 5370 U/mg of solid), chitosan, acetic acid, hexachloroplatinic acid (H₂PtCl₆), sulphuric acid (H₂SO₄), sodium phosphate monobasic (NaH₂PO₄), sodium phosphate dibasic (Na₂HPO₄), phosphoric acid (H₃PO₄), sodium hydroxide (NaOH), sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl₂), magnesium chloride (MgCl₂), glycine, L-lysine, L-asparagine, L-Phenylalanine, reduced L-glutathione, uric acid were purchased from Sigma-Aldrich (Saint Louis, MO, USA). d-(+)-glucose (Acros Organics, NJ, USA) and L-ascorbic acid (Riedel-de Haën, Seelze, Germany) were also purchased and used as received. All the solutions were prepared in ultrapure water (obtained in a Milli-Q Simplicity^® Water Purification System, Merk, Darmstadt, Germany).