Silver nitrate solution

Fontana–Masson staining was carried out to visualize melanin content and distribution in irradiated dorsal skin as described previously [12 (link)]. Sections were deparaffinized and hydrated in water and placedinto a 2.5% silver nitrate solution (Sinopharm Chemical Reagent Co., Ltd, Beijing, China) for 4 h in a dark chamber. After rinsing in water, the slides were placed in 0.1% gold chloride (Sinopharm Chemical Reagent Co., Ltd, Beijing, China) for 1 min,rinsed again in water, and then in 5% sodium thiosulfate (Sinopharm Chemical Reagent Co., Ltd, Beijing, China) for an additional2 min. After a final rinse with water, the sections were counter-stained with eosin red.

Fresh Chinese flowering cabbage was purchased from a local supermarket (Wuxi, China). Indicators (bromocresol green, methyl red sodium salt, bromophenol blue, chlorophenol red, bromothymol blue sodium, and bromocresol purple), sodium hydroxide (NaOH), ethanol, phenolphthalein, sodium tetraborate decahydrate, potassium hexacyanoferrate (II) trihydrate, zinc acetate dihydrate, silver nitrate solution, and qualitative filter paper were bought from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). N–(1–Naphthyl) ethylenediamine dihydrochloride, t-butylammonium hydroxide (TBAH), and p-toluene sulfonic acid (TsOH) were obtained from Macklin Biochemical Co., Ltd. (Shanghai, China). 5,5–dithiobis (2–nitrobenzoic acid; DTNB) was bought from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China), and polyethylene glycol (PEG–400) was bought from Beijing InnoChem Science and Technology Co., Ltd. (Beijing, China). Man, Rogosa, and Sharpe (MRS) broth was purchased from Haibo Biotechnology Co., Ltd. (Qingdao, Shandong, China). Polyvinylidene fluoride (PVDF) membranes were purchased from Biosharp Biotechnology Co., Ltd. (Shanghai, China). All chemical reagents were of analytical grade and used as received.