Glassy carbon gc

All solutions were prepared with distilled/deionized water (18 MΩ resistivity, Darmstadt, Germany). Carbon nanotubes were obtained from NANOCYL®NC7000(Austin, TX, USA). Nitric acid (HNO₃, 69.2 wt%) and hydrogen peroxide ( ${\mathrm{H}}_2{\mathrm{O}}_2$ 30% v/v) were purchased from Sigma-Aldrich (Darmstadt, Germany). Potassium phosphate monobasic ( $\mathrm{K}{\mathrm{H}}_2\mathrm{P}{\mathrm{O}}_4$ ) and sodium hydroxide (NaOH, 99.9% p/p) were purchased from Fisher Scientific (Waltham, MA, USA). Phosphate-buffered saline (PBS: $\mathrm{K}{\mathrm{H}}_2\mathrm{P}{\mathrm{O}}_4$ + ${\mathrm{K}}_2\mathrm{HP}{\mathrm{O}}_4$ + KCl, at different pH values) was used as a supporting electrolyte. Potassium ferricyanide ( ${\mathrm{K}}_3\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$ ), iron trichloride hexahydrated ( $\mathrm{FeC}{\mathrm{I}}_3\cdot 6{\mathrm{H}}_2\mathrm{O}$ ), and potassium chloride (KCl) were obtained from BDH Chemicals (Philadelphia, PA, USA); hydrochloric acid (HCl, 37%) was from Fisher Scientific (Waltham, MA, USA); glassy carbon (GC, $\Phi =3\mathrm{mm}$ , geometric area = 0.0706 cm²), silver/silver chloride reference electrode (Ag/AgCl), and graphite rod counter electrode were from CH Instruments (Austin, TX, USA); sulfuric acid ( ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$ , 98%) was from Fisher Scientific (Waltham, MA, USA); 1 μm, 0.3 µm, and 0.05 µm alumina powder were from CH Instruments (Austin, TX, USA); dimethylformamide (DMF) was from BDH Chemicals (Philadelphia, PA, USA); and poly (diallyldimethylammonium chloride) (PDDA, 4% w/w in water) was from Sigma.

All solutions were prepared with distilled/deionized water (18 MΩ resistivity, Darmstadt, Germany). Carbon nanotubes were obtained from Material Science & Nanotechnology Laboratory (IVIC, Caracas, Venezuela). Nitric acid (HNO₃, 69.2 wt.%) and hydrogen peroxide (H₂O₂, 30%V/V) were purchased from Sigma-Aldrich Sigma, (Darmstadt, Germany). Potassium phosphate monobasic (KH₂PO₄) and sodium hydroxide (NaOH, 99.9% p/p) were purchased from Fisher Scientific (Waltham, MA, USA). Phosphate-buffered saline (PBS, 20 mmol·L⁻¹ KH₂PO₄ + 20 mmol·L⁻¹ K₂HPO₄ + 0.1 mol·L⁻¹ KCl, pH 6.8) was used as a supporting electrolyte. Potassium ferricyanide (K₃[Fe(CN)₆]), iron trichloride hexahydrated (FeCl₃·6H₂O), and potassium chloride (KCl) were from BDH Chemicals (Philadelphia, PA, USA), hydrochloric acid (HCl, 37%) was from Fisher Scientific (Waltham, MA, USA), glassy carbon (GC, diameter ( $\mathsf{\Phi }=3\mathrm{mm}$ ), geometric area = 0.0706 cm²), silver/silver chloride reference electrode (Ag/AgCl), and graphite rod counter-electrode were from CH-Instruments (Austin, TX, USA), sulfuric acid (H₂SO₄, 98%) was from Fisher Scientific (Waltham, MA, USA), and 1 µm, 0.3 µm, and 0.05 µm alumina powder were from CH-Instruments (Austin, TX, USA), dimethylformamide (DMF) was from BDH Chemicals (Philadelphia, PA, USA), poly (diallyldimethylammonium chloride) (PDDA, 4% w/w in water) were from Sigma.