Sodium sulfite na2so3

Methyl acrylate (MA, 99%, Aldrich, St. Louis, MO, USA) was passed through a column filled with basic alumina prior to use. Methyl 2-bromopropionate (MBrP, 99%, Acros Organics, Morris Plains, NJ, USA), tris[2-(dimethylamino)ethyl]amine (Me₆TREN, 99+%, Alfa Aesar, Tewksbury, MA, USA), copper(II) bromide (CuBr₂ 99+%, Acros Organics), copper(II) sulfate pentahydrate (CuSO₄·5H₂O, 98+%, Acros Organics), sodium bromide dihydrate (NaBr·2H₂O, 98+%, Alfa Aesar), sodium sulfite (Na₂SO₃, 98+%, Acros Organics), N,N-dimethylformamide (DMF, ACS Certified, Fisher Chemical, Waltham, MA, USA), and acetonitrile (MeCN, HPLC grade, Oakwood Chemical, Estill, SC, USA) were used as received.

Silver nitrate (AgNO₃) was acquired from Panreac Appliechem (Ottoweg, Darmstadt, Germany), trisodium citrate (99.95%), hydrogen peroxide (H₂O₂, >30%) and sodium hydroxide (NaOH, 99.1%) from Fisher Scientific (Loughborough, Leicester, United Kingdom), sodium sulfite (Na₂SO₃, 97%) from Acros Organics (New Jersey, USA), sucrose (>99%) and gold(III) chloride solution (HAuCl₄, >49% Au bases) from Sigma-Aldrich (St. Louis, MO, USA), polyvinylpyrrolidone (PVP, MW = 10,000) and L-(+)-ascorbic acid (L-AA, >99%) from Alfa Aesar by Thermo Fischer Scientific (Erlenbachweg, Kandel, Germany), and sodium borohydride (NaBH₄) from Aldrich. DNA oligonucleotides of 10-nt labeled with ATTO-655 dye and purified by HPLC was purchased from STAB Vida (Monte da Caparica, Portugal). The sequence used was the following: (ATTO-655)-5′-GAGTCTGGAC-(C6-SH)-3′. Ultrapure water (18.2 MΩ⋅cm) was obtained with a Milli-Q purification system (Merck-Millipore) and used in all preparations. All reagents were used as acquired.