Supporting Information A series of DNA logic gates based on electrochemical reduction of lead in self-assembled G-quadruplex on the gold electrode

Chemicals and materials NaClO4, Pb(ClO4)2·3H2O, KClO4·3H2O, K3[Fe(CN)6], K4[Fe(CN)6], 6-mercaptohexanol, Tris(tris-(hydroxymethyl)-aminomethane), dimethyl sulfoxide (DMSO) were purchased from Sigma-Aldrich Inc. Ethylenediamine tetraacetic acid (EDTA), Ethylenediamine tetraacetic acid dipotassium salt (EDTA-2K) were purchased from J&K Scientific Ltd. Mg(ClO4)2 was purchased from Fluka. The oligonucleotide and hemin (from bovine) were purchased from Sangon Biotechnology Co., Ltd. (Shanghai, PRC). The applied DNA sequences were given from 5’ to 3’: PW17: 5’-HO-(CH2)6-S-S-(CH2)6-GGGTAGGGCGGGTTGGG-3’ Poly-T: 5’-HO-(CH2)6-S-S-(CH2)6-TTTTTTTTTTTTTTTTTTTTTTT-3’ Poly-A: 5’-HO-(CH2)6-S-S-(CH2)6-AAAAAAAAAAAAAAAAAAAAAAA-3’ Poly-C: 5’-HO-(CH2)6-S-S-(CH2)6-CCCCCCCCCCCCCCCCCCCCCCC-3’ DNA (1): 5’-AAAAAAAAAAAAAAAAAAAAAAA-3’ The stock solution of 20 μM thiolated DNA was prepared in 20 mM Tris-HClO4 buffer (pH = 7.4). The thiolated DNA solution was heated at 80 °C for 5 min to dissociate any intermolecular interaction, and gradually cooled to room temperature before use. The stock solution of hemin (20 μM) was prepared in DMSO, stored in darkness at -20 °C. The solutions of NaClO4, Pb(ClO4)2, EDTA, EDTA-2K, KClO4 and Mg(ClO4)2 were prepared in 20 mM Tris-HClO4 buffer and the final pH of these solutions was 7.4, respectively. All solutions were prepared with Milli-Q water (18.2 MΩcm resistivity) from a Millipore Milli-Q system (Thermo Scientific EASY pure II). The working gold electrodes, 99.99% (w/w) polycrystalline with a diameter 1 mm were obtained from Aida Instrument Inc. in Tianjin (China) and cleaned prior to use as reported before. 1