Highly Sensitive Enzymatic Biosensor

All reagents were not purified further before use. Methylbenzene, hydrochloric acid (HCl), lysine (Lys), arginine (Arg), titanium tetrachloride (TiCl₄), tetrabutyltitanate, gold (III) chloride (HAuCl₄·3H₂O), leucine (Leu), cysteine (Cys), proline (Pro), glycine (Gly), barium hydroxide octahydrate (Ba(OH)₂·8H₂O), formic acid, ethylene diamine tetraacetic disodium (EDTA−2Na), chloroplatinic acid (H₂PtCl₆), 3,3′,5,5′−tetramethylbenzidine (TMB, ≥99%), L−histidine (L−His), glutathione (GSH), glutamic acid (Glu), and fetal bovine serum were purchased from Macklin Biochemical Co., Ltd. (Shanghai, China). Sodium borohydride (NaBH₄), disodium hydrogen phosphate (Na₂HPO₄), p−Benzoquinone (p−BQ), isopropanol (IPA), potassium nitrate (KNO₃), citric acid, ascorbic acid (AA), and sodium nitrate (NaNO₃) were purchased from Sinopharm Chemical Reagents Co., Ltd. (Shanghai, China).