Chloroauric acid

Natural graphite flake (99.8% purity) was purchased from Sigma–Aldrich. Chloroauric acid (HAuCl₄·3H₂O, ≥49.0% Au basis), disodium hydrogen phosphate (Na₂HPO₄), sodium dihydrogen phosphate (NaH₂PO₄), phosphoric acid (H₃PO₄), sulfuric acid (H₂SO₄), HCl, NaBH₄, potassium permanganate (KMnO₄), BSA, ClCH₂COONa, N-ethyl-N’-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS) were purchased from J&K company (Beijing, China). Ethanol was purchased from Beijing Chemicals Co., Ltd. (Beijing, China). All the chemicals used are at least of analytical grade and directly used without additional purification. The water purified through a Millipore system (18.2 MΩ·cm) was used throughout.

Ti₃AlC₂ MAX was acquired from Aladdin (Shanghai, China). Tris (hydroxymethyl)aminomethane (Tris), and 6-Mercapto-1-hexanol (MCH) were acquired from Sigma. Tris (2-carboxyethyl) phosphine hydrochloride (TCEP) and chloroauric acid (HAuCl₄·4H₂O, ≥99.9%) were ordered from J&K scientific. Hydrofluoric acid was acquired from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). 0.1 M pH 7.4 Tris-HCl buffer (100 mM NaCl and 20 mM MgCl₂) was used for electrochemical measurement, and 10 mM pH 7.4 Tris-HCl buffer was used as washing buffer. All DNA strands were ordered from Sangon Biotech Co., Ltd. (Shanghai, China), and the DNA sequences were provided in Table 1. 18.2 MΩ cm ultrapure water was used in whole experiments.