Butvar b 98

Selective functionalization was performed by electrodeposition using the three-electrode method with the reference electrode (commercial Ag/AgCl electrode), Pt counter electrode, and the fabricated working electrode via electrochemical analyzer (CH Instrument, Inc). Polyaniline (PANi) was electrodeposited onto the sensing component of the pH sensor. An aqueous solution of 0.1 M aniline (Sigma-Aldrich) in 1 M HCl was prepared. The fabricated Au working electrode was submerged into the solution, and the potential was swept from −0.2 to 1 V versus a commercial Ag/AgCl electrode for 60 segments at a scan rate of 0.1 V s⁻¹. Here poly(3,4-ethylenedioxythiphene) polystyrene sulfonate was used as the ion-electron transducer of K⁺ sensor. Then an aqueous solution of 0.01 M 3,4-ethylenedioxythiphene (Sigma-Aldrich) and 0.1 M sodium polystyrene sulfonate (Sigma-Aldrich) was prepared. The working electrode was submerged into the solution and the chronopotentiometric electrodeposition was conducted at 0.02 mA anodic current (potential versus commercial Ag/AgCl electrode) for 200 s. The common reference electrode was fabricated with screen printing of Ag/AgCl paste (Gwent Electronic Materials) onto an Au electrode that was subsequently coated with polyvinyl butyl resin (PVB) (BUTVAR B-98, Sigma-Aldrich).

Potassium hydrogen phthalate, potassium phosphate monobasic, tris(hydroxymethyl)aminomethane, aniline (99.5%), ammonium persulfate, sodium hydroxide, hydrochloric acid, calcium chloride, magnesium chloride, ammonium chloride, potassium chloride, methanol and butvar® B-98 were purchased from Sigma-Aldrich (USA). Borax anhydrous was purchased from Fluka (UK). Sodium chloride was purchased from Junsei (Japan). Sulfuric acid was purchased from Showa (Japan). Carbon paste (7105 conductor) was purchased from Dupont (USA). Silver/silver chloride was purchased from ERCON (USA). Deionized (DI) water (18.2 MΩ/cm) was employed in all experiment.

The following chemicals were obtained from Sigma‒Aldrich (USA): Na⁺-selective grade ionic carrier X, Na⁺ tetra [3,5-bis(trifluoromethyl)phenyl]borate (Na–TFPB), valinomycin (ionic carrier K⁺), Na⁺ tetraphenylborate (NaTPB), ETH 129 (Ca²⁺ carrier), 1-nitro-2-(n-octyloxy)benzene (NPOE), bis(2-ethylhexyl)sebacate (DOS), 3,4-ethylenedioxythiophene (EDOT), poly(4-styrenesulfonate) (NaPSS), HCl, H₂SO₄, urease (≥2 units/mg solid, from Candida spp.), bovine serum albumin (BSA), glutaraldehyde solution (20–25%), polyvinyl butyral resin BUTVAR B-98 (PVB), sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl₂), magnesium chloride (MgCl₂), PBS (pH = 7.2), and methanol.
Au sulfite solution and Ag/AgCl ink were obtained from Yuncaitaotao Company. All the chemicals were used as received. All solutions were prepared using deionized water produced by Millipore Water Purification Systems, unless otherwise noted.

Sodium ionophore X, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (Na-BARF), bis(2-ethylhexyl) sebacate (DOS), poly(vinyl chloride) (PVC) with high molecular weight, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, ammonium chloride, ethyl cellulose with viscosity 10 cP, terpineol, BUTVAR® B-98 (polyvinyl butyral, PVB), methanol, and tetrahydrofuran (THF) were purchased from Sigma Aldrich. Ethyl alcohol was purchased from Samchun Chemicals Co. Ltd. Ag and Ag/AgCl inks were obtained from Asahi chemical research laboratory Co. Ltd. Deionized (DI) water was prepared by using a Milli-Q unit (resistivity: 18.2 MΩ cm⁻¹, Millipore System, Darmstadt, Germany).