Tellurium

To extract iodine and selenium prior to analysis, milk samples were digested. For iodine determination, 0.5 mL of milk was added to 5 mL of 5% tetramethylammonium hydroxide (TMAH) (>99%, Acros Organics, Loughborough, UK). Samples were placed in the oven at 90 °C for 3 h. Samples were removed from the oven to cool and 0.5 mL of 1300 ng/g tellurium, an internal standard (Sigma Aldrich, Dorset, UK) in 1% TMAH was added and samples were made up to 50 g with 1% TMAH. For selenium determination, 3 g of milk was added to 1 mL high purity water and 6 mL concentrated nitric acid (VWR International, Leicestershire, UK). Samples were pre-heated for 10 min on a thermal plate before being placed in a Transform 680 Microwave Digestion System (Aurora, Vancover, BC, Canada). Following digestion, samples were cooled and 1.5 mL of 30% hydrogen peroxide added (Sigma Aldrich, Dorset, UK). Samples were made up to 50 g with high-purity water.

Acetone (≥99.5%, Sigma-Aldrich), ammonium persulfate (≥98.0% Sigma-Aldrich), chlorobenzene (99.9%, Sigma-Aldrich), didodecyldimethylammonium bromide (98.0%, Sigma-Aldrich), 1-dodecanethiol (98.0%, ACROS Organics), 1,2-ethanedithiol (≥98.0%, Sigma-Aldrich), hydrochloric acid (37.0%, VWR Chemicals), mercury(ii) chloride (≥99.5%, Sigma-Aldrich), methanol (≥99.9%, Sigma-Aldrich), methyl-iso-butyl ketone (MIBK; 99.8%, VWR Chemicals), oleylamine (>95.0%, Strem Chemicals), tellurium (99.999%, Sigma-Aldrich), anhydrous tetrachloroethylene (≥99.0%, Sigma-Aldrich), tri-n-octylphosphine (97.0%, STREM), 50 K PMMA (4.0% in anisole, Allresist), 950 K PMMA (4.5% in anisole, Allresist) and 2-propanol (≥99.8%, Sigma-Aldrich).
All the chemicals were used as received, unless otherwise stated. oleylamine was dried and degassed under reduced pressure at a temperature of 120 °C for 1 h before its use.
Trioctylphosphine telluride (TOP:Te) was synthesized by stirring 5.08 g tellurium (0.04 mol) in dry trioctylphosphine (20 ml) for three days yielding a 2 M TOP:Te solution. The solution was filtered through a 0.45 μm polytetrafluoroethylene syringe filter resulting in a clear, yellowish solution.
Cleanroom: 21.5 °C; 45–50% relative humidity; particle class, 10–10,000; >18 MΩ cm purified water.

Palm oil (Softisan 154 or S154), a gift from Condea (Witten, Germany), and stearic acid (Merck, Germany) were the lipids used in this study. Surfactants include the following: Poloxamer407 (Sigma Aldrich, St. Louis, MI, United States) and polioxiethylene-20-sorbitan monooleate (tween 80- Sigma Aldrich, St. Louis, MI, United States), lipo-soluble surfactants including Span 80 (Sigma Aldrich, St. Louis, MI, United States) and lecithin (Sigma Aldrich, St. Louis, MI, United States), doxycycline (Sigma Aldrich, St. Louis, MI, United States), and hydroxychloroquine sulfate (Sigma Aldrich, St. Louis, MI, United States). Sodium borohydride (NaBH4) (Merck, Germany), tellurium (Sigma Aldrich), cadmium salt (Scharlau, Spain), thioglycolic acid (TGA) (Merck, Germany), and distilled water were used throughout the study.

Cadmium chloride hemi(pentahydrate) (CdCl₂·2.5H₂O, >99%), zinc acetate dihydrate (Zn(OAc)₂·2H₂O, >99%), tellurium (Te, >99.8%), sodium borohydride (NaBH₄, >96%), 3-mercaptopropionic acid (MPA, 99%), acrylamide (>98%), ethylene glycol dimethylacrylate (EGDMA, 98%), potassium persulfate (K₂S₂O₈, >99%), dopamine hydrochloride (DA·HCl, 99%), adenosine 5′-diphosphate (ADP, >95%), l-arginine (Arg, >98%), l-histidine monohydrochloride monohydrate (His, >98%), l-lysine (Lys, >98%), l-serine (Ser, >99%), l-cysteine (Cys, 97%), l-tyrosine (Tyr, >98%), glycine (Gly, >98.5%), homovanillic acid (HVA, fluorimetric reagent), l-glutathione (GSH, >98%), bovine serum albumin (BSA, >96%), (d)-(+)-glucose (>99.5%), ascorbic acid (AA, >99%), l-aspartic acid (Asp, >98%), KCl (>99%), NaCl (>99%), CaCl₂ (>96%), and MgCl₂·6H₂O (>99%) were purchased from Sigma-Aldrich (Saint-Quentin Fallavier, France) and were used without purification. All solutions were prepared with deionized water (18.2 MΩ cm). Phosphate-buffered saline (PBS) solution was prepared using [Na₂HPO₄·2H₂O] = 0.2 M, [NaH₂PO₄·H₂O] = 0.2 M and the final pH was adjusted to 7.4.

Tellurium (200 mesh, 99.85%), selenium, sulfur, sodium borohydride (powder, 98%), bromine, iodine, n-butyl lithium solution, and 1-bromobutane (BuBr, 99%) were purchased from Aldrich. Sodium sulfite was purchased from EMScience. Tetrabutylammonium bromide (TBAB, 98%) was obtained from Alfa Aesar, and hydrogen tetrachloroaurate hydrate (49 wt% Au) was obtained from Strem Chemicals. The organic solvents dimethyl formamide, hexane, toluene, methanol, dichloromethane, ethanol, and tetrahydrofuran were of analytical grade. They were all used as received. Milli-Q water (18.2 MΩ) was used. All glassware was cleaned in sulfuric acid with Nochromix and rinsed with a large amount of water before use.
Di-butyl disulfide was prepared by addition of n-butyl lithium (1 eq.) to a THF suspension of elemental sulfur followed by water and iodine. A similar procedure was adopted to prepare dibutyl ditelluride, omitting the treatment of the reaction media with iodine and exposing the intermediate tellurol to an oxygen atmosphere for the oxidation step. Di-butyl diselenide was prepared by reacting elemental selenium in aqueous basic media with hydrazine hydrate followed by addition of butyl bromide and Tetrabutylammonium bromide. The synthetic reaction is summarized in Fig. 6. A detailed experimental procedure is presented in the ESI.†