4 mercaptobenzoic acid

Amyloid β Protein Fragment 1–40 (Aβ₄₀) peptides powder (≥90%), chloroauric acid (HAuCl₄·3H₂O, 99.999%), L-cysteine (≥97%), cysteamine (≥98%), 4-mercaptobenzoic acid (≥99%), mercaptopropionic acid (≥99%), glutathione (≥98%), N-isobutyryl-L-cysteine (≥97%) and 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium sodium salt (CCK-8) were purchased from Sigma-Aldrich Co. Ltd. (NJ, USA). Sodium borohydride (NaBH₄, ≥96.0%), DMEM, hydrochloric acid, anhydrous ethanol, anhydrous methanol, sodium hydroxide, glacial acetic acid and sulfuric acid were analytical grade and all from Innochem (China). Cys-Arg (97%) was purchased from ChinaPeptides (Shanghai, China). The ultrapure water used was from the Millipore Milli-Q ultrapure water system. All the reaction vessels were soaked in aqua regia (volume ratio = 3:1, HCl/HNO₃) for 24 h, washed thoroughly with ultrapure water several times and dried in an oven before use. The PC-12 cell line was purchased from the Cell Bank of Chinese Academy of Sciences (Beijing). APPswe/PSdE9 double transgenic mice (APP/PS1 Tg mice, 35 weeks of age) and C57BL/6 wild-type mice (9 weeks of age) were obtained from the Model Animal Research Center of Nanjing University (China). All animal experiments were approved by the Animal Ethics Committee, Wuhan University of Technology.

Anodic aluminum oxide (AAO) membranes with pore size of 0.2 μm and thickness of 60 μm were obtained from Whatman Corporation (Anodisc 25, catalog No. 6809-6022; UK). Gold sputtering target was from Quorum Technologies Ltd., USA. An electrochemical cell were custom made with Teflon cylinder (1.25 cm inner diameter) and stainless steel plate (W = 5 cm, L = 5 cm, H = 0.5 cm). The reference and counter electrodes were Ag/AgCl and 0.5 mm-diameter platinum wire, respectively.
All chemicals were purchased from a commercial source and used without further purification. Deionized (DI) water used in all experiments was obtained from Thermo scientific water purification system with an electronic resistance 18.2 MΩ. Gold plating solution (Orotemp 24 RTU RACK) and silver plating solution (1025 RTU @4.5 troy/gallon) were purchased from Technic (Cranston, RI, USA). Alloy plating solution was prepared by mixing gold and silver plating solutions with volume ratio of 70:30. nitric acid for etching process was diluted from 65% nitric acid obtained from CARLO ERBA, France. A Raman probe, 4-mercaptobenzoic acid (catalog no. 706329), was purchased from Sigma-Aldrich, USA. Adhesive glue used for substrate preparation is cyanoacrylate adhesive (catalog no. Z105902) from Sigma Aldrich, USA.

Gold and silver substrates were purchased from Silmeco (SERStrate). Ultrapure water (18.2 MΩ cm) was obtained from a Barnstead Genpure system. 4-Mercaptobenzoic acid (MBA), cysteamine, and riboflavin were purchased from Sigma-Aldrich. Phosphate buffered saline (PBS) 1× was purchased from Gibco. Orange tough resin was purchased from Prusa. Isopropanol (IPA), sodium hydroxide, hydrochloric acid, nitric acid, and PTFE tubing (i.d. = 1/32 in) were purchased from Fisher scientific. Carboxylated polystyrene beads (100 nm) were purchased from Interfacial Dynamics Corp. Silver shot was purchased from Kurt J. Lesker. Anodized aluminum oxide filters (AAO) (0.2 μm pores) were purchased from Cytiva. Loctite EA 9017 and Gorilla glue was purchased from McMaster-Carr. Coverslips were purchased from VWR. Clear nail polish was purchased from LA Colors. PTFE thread seal tape was purchased from Lowes.

Gold(III) chloride trihydrate (~30 wt.% in HCl 99.99%), sodium borohydride (98%), L-ascorbic acid (AA) (≥ 99%), silver nitrate (99.8%), sodium citrate (≥ 99%), hydrochloric acid (≥ 37%), nitric acid (≥ 65%), sulfuric acid (95%), hydrogen peroxide (30 wt.%), ethanol (≥ 99.7%), toluen (≥ 99.7%)N-Dodecyl-N,N-dimethyl-3-ammoniun-1-propansulfunate (LSB; ≥ 99.7%), (3-aminopropyl)trimethoxysilane (APTES; ≥ 98.0%), L-glutathione, reduced (99%), 1-dodecanthiol (≥ 98%), 4-mercaptophenylboronic acid (≥ 99.7%), 4-mercaptobenzoic acid (99%) and 7-Mercapto-4-methylcoumarin (≥ 97%) were purchased from purchased from Sigma-Aldrich (St. Louis, MO, USA). Microscopy cover glass slides 21 mm × 6 mm were purchased from DEL Chimica (Milano, Italy).. All reagents were used as received. All the preparations were made with bidistilled water.
Tryptone Soya Broth (TSB) and Tryptone Soya Agar (TSA) for bacteria culture were purchased from Oxoid, Basingstoke, Hampshire, UK. S. aureus ATCC 6538 and Escherichia coli ATCC 10536 bacterial strains were used.