Since 2014, strict regulations have governed the sale, transport, use, and waste disposal of uranyl acetate, a contrast agent in electron microscopy for over 40 years, due to its toxicity. These constraints have compelled many researchers to seek less toxic alternatives. Nowadays, numerous non-toxic and non-radioactive contrasting agents, such as UAR, Uranyless, and OTE, are readily available.<\/p>\n
OTE, an alternative derived from Oolong tea extract, acts as a tannin, enabling the completion of etching through a lead citrate post-contrast process. Additionally, OTE, used as a beverage extract in Asia, falls between green tea (non-oxidized) and black tea (fully oxidized).<\/p>\n
Our Oolong tea extract boasts a high tannin content, ensuring exceptional purity and maximum efficiency during contrasts.<\/p>\n
To prepare the OTE solution, dissolve the OTE powder in 70\u00b0C water at a concentration of 0.2% using a magnetic stirrer. Complete dissolution, achieved within 15 to 30 minutes under agitation, requires filtering the solution at 0.45\u00b5 or preferably at 0.22\u00b5. To maintain its quality, store the solution in a small Eppendorf tube or an AirLess Black bottle in the refrigerator, ensuring darkness at 4\u00b0C. Always allow the solution to return to room temperature before use.<\/p>\n
When contrasting grids with OTE, immerse them in the solution for 15 to 20 minutes at room temperature in darkness. After contrast, drain the grids without rinsing or with a very brief wash (1 to 2 seconds). For post-staining, treat the samples with lead citrate according to Reynolds (Ref # 11300) for 1 to 2 minutes. Subsequently, drain, rinse briefly, dry the samples, and they are ready for observation.<\/p>\n
The prepared aqueous OTE solution has a slightly acidic pH of 6, which can be adjusted by replacing water with a phosphate or cacodylate Na buffer.<\/p>\n