K2cr2o7

The following compounds were used for the chromium K-edge XANES spectroscopy measurements: CaCrO₄, Cr₂(SO₄)₃·H₂O, Cr₂S₃ (all ABCR, Karlsruhe, Germany), CrPO₄·4H₂O (Alfa Aesar, Karlsruhe, Germany), Cr₂O₃, CrCl₃·6H₂O, K₂Cr₂O₇ (all Merck, Darmstadt, Germany), K₂CrO₄ (AppliChem, Darmstadt, Germany), and Na₂CrO₄ (Acros, Geel, Belgium). Cr(OH)₃ was precipitated from an aqueous solution of chromium chloride (CrCl₃; p.a., Sigma-Aldrich, Australia) with ammonia. CaCr₂O_4, MgCr₂O₄, and FeCr₂O₄ were prepared from Cr₂O₃ (p.a., Merck, Darmstadt, Germany) with calcium carbonate (CaCO₃; Sigma-Aldrich, Steinheim, Germany), magnesium carbonate (MgCO₃; Merck, Darmstadt, Germany), and Fe₃O₄ (ABCR, Karlsruhe, Germany) at 1250 °C, 1000 °C, and 1500 °C, respectively, in platinum crucibles by thermal treatment (6–16 h) in a muffle furnace (Nabertherm LH 15/14, Lillenthal, Germany). Cr-substituted FeOOH was prepared after Frommer et al. (2009 (link)).

Davis minimal medium (DMM), 4-aminoantipyrine, potassium ferrocyanide, catechol, sodium hydroxide pellets used in this study were purchased from HiMedia Laboratories Pvt. Ltd. Mumbai, phenol, 2-mercaptoethanol, ammonium hydroxide, glycerol, disodium EDTA, primers, acids and solvents were procured from Sigma, Aldrich, Tris Base, Agarose from Bio Basic Inc. All the following heavy metals CoCl₂.2H₂O, ZnSO₄.H₂O, (CH₃COO)₂Pb.3H₂O, HgCl₂, CdCl₂, CuSO₄.5H₂O, NiCl₂.6H₂O, MnCl₂.4H₂O, and K₂Cr₂O₇ were purchased from Merck Millipore, Taq DNA polymerase Master Mix from Ampliqon and PCR purification Kit from Favorgen Biotech Corp. were used.

All the chemicals used were either AR or GR grades. Lead nitrate, Pb (NO₃)₂ (99%), potassium dichromate, K₂Cr₂O₇ (99%), ethanol (99%), hydrochloric acid, HCl and sodium hydroxide, NaOH (98%) were obtained from Merck, India. Ferric chloride hexahydrate, FeCl₃ . 6H₂O (97%) and ferrous chloride tetra hydrate, FeCl₂ . 4H₂O (97%) were purchased from CDH, India. L-Cysteine (L-Cyst 98%) was purchased from Sigma Aldrich. Chemicals including Roswell Park Memorial Institute (RPMI) 1640 medium, fetal bovine serum (FBS), antibiotic-antimycotic solution 100X, Trypsin-EDTA Solution 1X, dimethyl sulphoxide (DMSO), Dulbecco’s phosphate buffered saline (DPBS) 1X and 3-(4, 5-dimethyle-2-thiazolyl)-2 and 5-diphenyl-2H-tetrazolium bromide (MTT) for biocompatibility studies were procured from HiMedia Laboratories Pvt. Ltd. Tissue culture treated plate (96-wells) and T-20 flask received from Costar 3599 and Nucleon respectively. MTT stock solution (5 mg/mL) was prepared in DPBS by dissolving MTT with the help of vortex. All chemicals were used as received without further purification.

Magnetite nanoparticles were synthesized using FeCl₃·6H₂O, FeSO₄·7H₂O, and NH₃·H₂O 25% solution (Stanlab, Lublin, Poland). The solution of the modifying substance at 1% concentration was prepared with the use of poly(sodium acrylate) (M_w = 30,000) in the form of a 40% aqueous solution (Sigma Aldrich, St. Louis, MI, USA). Model solutions of heavy metals were prepared using their inorganic salts Zn(NO₃)₂·9H₂O, Cu(NO₃)₂·3H₂O, Cd(NO₃)₂·4H₂O, Ni(NO₃)₂·6H₂O, Pb(NO₃)₂, Cr(NO₃)₃·9H₂O, (Avantor Performance Materials Poland S.A., Gliwice, Poland), and K₂Cr₂O₇ (Merck, Darmstadt, Germany). Diluted solutions of NaOH and HNO₃ (Avantor Performance Materials Poland S.A., Gliwice, Poland) were used for pH adjustment. The concentrated 65% solution of HNO₃ (Avantor Performance Materials Poland S.A., Gliwice, Poland) was applied for the stabilization of samples before metal content analysis. The reagents were used without additional purification.

C₆₀ buckminsterfullerene, hydrogen peroxide solution (30%), and THF were purchased from Sigma–Aldrich (St. Louis, MO, USA). Ammonium hydroxide solution (28%) was ordered from VWR Chemicals (VWR International, Radnor, PA, USA). The water used in all of the experiments was doubly distilled and purified using a Milli-Q system (Millipore, Milford, MA, USA). All of the metal salts (AgNO₃, Cd(NO₃)₂, Cu(NO₃)₂, CrCl₃, Na₃AsO₃, CoCl₂, FeCl₂, FeCl₃, HgCl₂, NiCl₂, PbCl₂, K₂Cr2O₇, CaCl₂) were purchased from Merck Chemicals. All of the chemicals used in this work were of analytical grade. The metal salt solutions to be used for sensitivity measurements were prepared at the concentration of 1000 µM in deionized water the day before use and were stored in the dark at 5 °C to avoid degradation due to accidental collateral reactions. The stock salt solutions were then diluted to the appropriate concentration immediately before the sensitivity measurements.