Co no3 2 6h2o

InN/titanium paste electrodes were prepared to examine the photoelectrochemical properties of InN films with a thickness of 0.5 μm. To prepare InN electrodes, the as-synthesized InN powder was mixed with a 2-butanol solution (20 wt%, Wako, 99%) for 24 h. The paste was deposited on a Ti substrate (Nilaco) by the doctor blade technique using scotch tape as a spacer. Prior to deposition, the Ti substrate was cleaned with an etching solution (a mixture of 7 mL distilled water, 5 mL HNO₃ (Nacalai Tesque, 60%), and 1 mL HF (Wako, 46%)). The heat treatment was performed at 350 °C for 2 h under a N₂ atmosphere. Then, 5 mL of a NaOH (5 mM, Kanto, 97%) solution was added to 20 mL of a Co(NO₃)₂·6H₂O (5 mM, Wako, 99.5%) solution, and a portion of this mixture was dropped onto the InN film. Subsequently, heat treatment was performed at 350 °C for 2 h under a N₂ atmosphere.

Deoxyribonucleic acid (DNA) from salmon milt (ca. 100–300 bp, purity >90%) was purchased from Fujifilm Wako (Osaka, Japan). RNA from yeast was purchased from Tokyo Chemical Industry Inc. (Tokyo, Japan). Cytidine-5′-monophosphate (purity 98%), adenosine-5′-monophasphate (purity 98%), guanosine-5′-monophasphate (purity 97%), and uridine-5′-monophasphate (purity 98%) were purchased from Combi Blocks Inc. (San Diego, CA, USA). KNO₃, NaCl, CaCl₂·2H₂O, Al(NO₃)₃·9H₂O, Zn(NO₃)₂·6H₂O, Co(NO₃)₂·6H₂O, Pb(NO₃)₂, NiCl₂·6H₂O, Cu(NO₃)₂·3H₂O from Fujifilm Wako (Osaka, Japan), Hg(NO₃)₂·H₂O and AgNO₃ from Sigma-Aldrich (St. Louis, MO, USA), Cd(NO₃)₂·9H₂O from Combi-Blocks (San Diego, CA, USA), and MgCl₂·6H₂O from Kishida Chemicals (Osaka, Japan) were used for metal ion sensing experiments, as received. Unless otherwise mentioned, deionized water of resistivity 18.2 MOhm⋅cm and purified using a Purelab Chorus 1 Life Science apparatus was used in all experiments.