Na3po4

All chemicals were of analytical grade and the highest purity available. AgNO₃, Na₃PO₄, HNO₃, phenol, p-benzoquinone, tert-butanol (t-BuOH), and ethylenediamine tetraacetate (EDTA) were purchased from Sigma-Aldrich (St. Louis, MO, USA). MB, methyl red (MR), acid blue 1, and rhodamine B (RhB) were purchased from Invitrogen (Eugene, OR, USA). Milli-Q deionized water was used to prepare all solutions in all experiments.

Trypsin-agarose, trypsin-EDTA, decane (anhydrous, ≥99%), Na₃PO₄, HCl, NaCl, and imidazole are purchased from Sigma-Aldrich Co., Ltd. (St. Louis, MO, USA). 1, 2-diphytanoyl-snglycero-3-phosphocholine (chloroform, ≥99%) is purchased from Avanti Polar Lipids, Inc. (Alabaster, Al, USA). All polynucleotides samples are synthesized and HPLC-purified by Sangon Biotech Co., Ltd. (Shanghai, China). All reagents and materials are of analytical grade. Yeast extract and peptone are purchased from OXOID Co., Ltd. (Basingstoke, UK). Glycerinum is purchased from Amresco, Inc. (Atlanta, GA, USA). IPTG is purchased from Inalco SpA, Inc. (Milano, Italy). BL21 [DE3] pLysS E. coli is purchased from TIANGEN Co., Ltd. (Beijing, China). The pET22b-proaerolysin plasmid are synthesized, and HPLC-purified by Genewiz, Inc. (Suzhou, China). All solutions are prepared using ultrapure water (18.2 MΩ cm at 25°C) from a Milli-Q system (Billerica, MA, USA).

Peptide synthesis was carried out according to a slightly modified Geysen's procedure (PEPSCAN) (Geysen et al., 1987 ; Pyclik et al., 2018 (link)) on the NCP Block of 96 hydroxypropylmethacrylate pins (MIMOTOPES), following the one-plate-one-peptide approach. Stepwise elongation of peptides from C-end to N-end was carried out for 6 h or at night in the presence of coupling solution which contained 60 mM Fmoc corresponding to amino acids diluted in N,N'-dimethylformamide (DMF, Merck KGaA), two coupling reagents: 65 mM of 1-hydroxy-7-azabenzotriazole (Sigma-Aldrich) and 60 mM of diisopropylcarbodiimide (Merck KGaA) and 10 mM bromophenol blue (Sigma-Aldrich). After completion of the synthesis, deprotection was performed. Eventually, pins were subjected to disruption in a buffer containing 1% SDS (Sigma-Aldrich), 0.1% 2-mercaptoethanol (Thermo Fisher) and 0.1 M Na3PO4 (Sigma-Aldrich) of pH = 7.2, heated to 60°C in a sonicator (Branson 2210 DTH Ultrasonic Cleaner) and sonicated for 10 min. The disruption buffer was removed from the pins by submersion in MiliQ water warmed to 60°C for 2 min, followed by washing in MeOH (CHEMPUR) warmed to 60°C for 5 min. Afterwards, the pins were fully dried and kept in dry conditions at 4°C or −20°C.

PVP, CYS, H₃PO₄, NaH₂PO₄, Na₂HPO₄, Na₃PO₄, quinine sulfate, KCl, NaCl, CuCl₂, HgCl₂, PbCl₂, ZnCl₂, MnCl₂, CoCl₂, MgCl₂, FeCl₃, CaCO₃, HCl, H₂SO₄, isopropanol and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Tris(hydroxymethyl)aminomethane (Tris) was purchased from J. T. Baker (Phillipsburg, NJ, USA). All chemical reagents were the analytical reagent grade and used without further purification. Deionized (DI) water was collected from a Barnstead Nanopure Ultrafiltration Unit (Boston, MA, USA).

Amorphous Ca-polyP microparticles were prepared as outlined before [14 ]. To obtain this phase, the weight concentration ratio between Ca [as CaCl₂] and P [as Na-polyP] was set to ≈2. In turn, 2.8 g of CaCl₂ •·2 H₂O (#223506; Sigma-Aldrich, Taufkirchen; Germany) were dissolved in 50 ml ethanol solution (96%) and added drop-wise to 1 g of Na-polyP, dissolved in 50 ml distilled water (room temperature; the pH was adjusted to 9–10). The suspension formed was kept at pH 10 (using 1 N NaOH) and stirred for 5 h. During this period microparticles assembled; they could be collected by filtration (Nalgene Filter Units [pore size 0.45 μm]; Cole-Parmer, Kehl/Rhein; Germany). Then, the sample was washed three times with ethanol and dried at 60°C. Subsequently, the material was sieved through a sieve shaker AS 200 (mesh size 100 μm; Retsch GmbH, Haan; Germany). These microparticles were termed “Ca-polyP-MP”.
In one control experiment “Ca-P particles” were prepared in the same way: 2.8 g of CaCl₂ •·2 H₂O were dropped into 1 g of Na-phosphate (Na₃PO₄; Sigma #342483). The resulting material that precipitated was filtrated and dried as described for polyP.

Dopamine hydrochloride, HZ, KCl, Na₃PO₄, CaCO₃, ZnCl₂, MgSO₄, MnCl₂, FeCl₂, CoCl₂, and Tris were acquired from Sigma–Aldrich (Yongin, Korea). Unless otherwise indicated, all reagents were used as received. Tris buffer was prepared using 0.05 M Tris, 0.138 M NaCl, and 0.0027 M KCl. All aqueous solutions were made with ultrapure water (>18 MΩ·cm, Millipore, Darmstadt, Germany). ITO electrodes (30 Ω) were purchased from Samsung Corning (Daegu, Korea). Electrochemical measurements were performed using a CHI617B device (CH Instruments, Austin, TX, USA).