Sodium polystyrene sulfonate

All reagents were used as received without further purification. Rose Bengal (RB), sodium poly(styrene sulfonate) (PSS, average M_w ∼ 70 000), poly(allylamine hydrochloride) (PAH, average M_w ∼ 58 000), 1-ethyl-3-(3-dimethylamino-propyl)carbodiimide (EDC), anthracene-9,10-dipropionic acid disodium salt (ADPA) and 2′-deoxyguanosine 5′-monophosphate (dGMP) were purchased from Sigma-Aldrich (Sigma-Aldrich, Argentina). Poly(ethyleneimine) solution 50 wt% in H₂O (PEI, average M_w ∼ 750 000) and N-hydroxysulfo succinimide sodium salt (sulfo-NHS) were purchased from Fluka (Argentina). Pro-analysis anhydrous sodium carbonate, calcium chloride dihydrate, sodium chloride, hydrochloric acid, sodium hydroxide, and ethanol were obtained from Cicarelli (Argentina). Ultrapure deionized water was used for all experiments.

Bovine serum albumine (fatty acid-free; LOT number: SLCB1005), hen egg-white lysozyme (LOT number: K49054981), sodium polystyrene sulfonate (average molecular weight 70,000 g/mol), polyethylene glycols with an average molecular weight of 400 g/mol (PEG-400) and 3000 g/mol (PEG-3000), sucrose, sucralose, and NaI (>99%) were purchased from Sigma Aldrich, Burlington, MA, USA. Alkaline metal salts of >99% purity (NaCl, NaBr), concentrated acetic acid (CH₃COOH), sodium acetate (CH₃COONa), and 1 $\mathrm{mol}/\mathrm{L}$ NaOH solution were purchased from Merck KGaA. Polyethylene glycol with an average molecular weight of 20,000 g/mol (PEG-20000) was obtained from Fluka.

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).