Deionized water

The 4-methoxybenzoic acid, pyridine-2,6-dicarbaldehyde, phosphorous oxychloride, carbohydrazide, isocyanate and isothiocyanates, Hydrazine hydrate (80%), TEA, CS₂, KOH, sodium hydrogen carbonate, and glacial acetic acid were purchased from Sigma-Aldrich, Darmstadt, Germany. The chloride salts of the transition metals were obtained from Aldrich and Alfa Aesar. Ethanol, mEthanol, chloroform, deionized water, acetonitrile, dimethyl sulfoxide, petroleum ether, ethyl acetate, n-hexane, toluene (Samchun Chemicals, Seoul, Korea), H₂SO₄, acetic acid, and HCl (Jin Chemical and Pharmaceutical Co. Ltd., Seoul, Korea) were used in this experiment. Urease from jack bean (EC 3.5.1.5), Thio-urea, sodium nitroprusside, and active chloride were purchased from Sigma (St. Louis, MO, USA). Stock solutions of the reducing substrates were prepared in phosphate buffer (20 mM, pH 6.8).

All KCl solutions were prepared by using deionized water (SAMCHUN Chemical, Korea). In self-alignment and self-assembly of sequentially dispensed multiple droplet experiments, highly viscous silicone oil (Shin-Etsu, KF96 50 cSt) was used as the surrounding medium to make aqueous droplets moving in the low Reynolds number regime.