Electronic Supporting information (ESI†) for Label-free Colorimetric Assay for DNA Methylation Based on Unmodified Gold Nanorods as a Signal Sensing Probe Coupled with Enzyme-Linkage Reactions

exonuclease, and the corresponding buffer solution were purchased from New England Biolabs. Ltd (Beijing, China). The oligonucleotides (P1-P4) were synthesized and purified by Invitrogen Co. Ltd (Shanghai, China). The methylated oligonucleotides (P5-P6) and DNA polymerase I were purchased from Takara Biotechnoly Co. Ltd (DaLian, China). Tetrachloroauric acid trihydrate (HAuCl 4 ·3H 2 O), cetyltrimethylammonium bromide (CTAB), L-ascorbic acid and sodium borohydride (NaBH 4) were commercially available from Shanghai Chemical Reagent Co (Shanghai, China). All other chemicals were of analytical grade and used without further purification. The ultrapure water with an electrical resistance larger than 18.2 MΩ was used for all the experiments.