L cysteine

L-Cysteine, 2-(1H-Benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluoro-phosphate (HBTU), N,N-Diisopropylethylamine (DIPEA), N-(3-Dimethylamino-propyl)-N′-ethylcarbodiimide hydrochloride (EDC), N-Hydroxysuccinimide (NHS), and L-Glutathione (GSH) were purchased from MACKLIN (Shanghai, China). The 1-Hydroxybenzo-trizole (HOBt) were from Damas Beta (Shanghai, China). H-Glu(OBzl)-Obzl, Boc-L-Glutamic acid, and Doxorubicin hydrochloride (DOX) were from Aladdin (Shanghai, China). Sodium alginate (SA) was from Tianjin Beilian Fine Chemicals Development Co. Ltd. (Tianjin, China) The other starting chemicals were purchased from commercial vendors, all of which were of AR grade and used without purification. Reactions were monitored by TLC (Silica Gel 60 F254). The prepared compounds were purified with column chromatography using silica gel (300–400 mesh). ¹H-NMR (400 MHz) and ¹³C-NMR (100 MHz) spectra were recorded with a Bruker AM-400BB spectrometer (Bruker, Karlsruhe, Germany) with TMS as the internal standard. Chemical shift values (δ) were listed in ppm and the coupling constant values (J) are in Hertz. The morphology of the freeze-dried hydrogel was observed by scanning electron microscope. The release properties were investigated by UV spectrophotometer.

The graphene was purchased from Nanjing XFNANO Materials Tech Co., Ltd. (Nanjing, China). Chitosan (CS, degree of deacetylation ≥ 95%,), β-TCP, maleic anhydride, and L-cysteine were obtained from Macklin Biochemical Technology Co., Ltd. (Shanghai, China). The α-minimum essential medium (α-MEM), fetal bovine serum (FBS), penicillin-streptomycin (P/S), and trypsin were purchased from Gibco (ThermoFisher, Shanghai, China). The ascorbic acid, dexamethasone, and β-glycerophosphate were purchased from Sigma Aldrich. All the reagents were used as received without further purification. Malt Sprague–Dawley (SD) rats were purchased from Silaike, Shanghai, China.

Gold chloride hydrate (HAuCl₄·4H₂O, 99.95%), potassium hexachloropalladate (K₂PdCl₆, 99%), L-Phenylalanine (99%) were purchased from Sigma-Aldrich. L-Cysteine (99%), L-Ribose (99%) and Bovine Serum Albumin (BSA, 96%) were obtained from Macklin, Accela and bidepharm, respectively. All other chemicals (99%) were provided by Sinopharm unless stated. Deionized (DI) water (from Millipore) was used for all the solution preparation. Au and Pt films with thickness of 70 nm were fabricated on Si substrate via thermal evaporation (JSD-400) or DC magnetron sputtering (Nexdep, Angstrom Engineering Inc.).

The dopamine (DA, 98%), uric acid (UA, 99%), ascorbic acid (AA, 99%), D-glucose monohydrate (99.5%), NaCl (99.9%), H₂O₂ (30%), KCl (99.5%), potassium ferricyanide (K₃[Fe(CN)₆], 99.5%), and L-cysteine (99%) were purchased from Macklin (Shanghai, China). All the reagents were analytically pure. The graphene oxide (GO) was bought from Ashine Advanced Carbon Materials Co., Ltd. (Changzhou, China). The MXene (Ti₃C₂) was obtained from Beike 2D Materials Co., Ltd. (Beijing, China). The Apiezon Wax W was bought from Madison Technology Co., Ltd. (Beijing, China). The isoflurane and brain stereotaxic instruments were bought from PWD Life Science Co., Ltd. (Shenzhen, China).