What is piranah cleaning?
According to the Princton Chemical Safety website, piranha solution is a mixture of sulfuric acid and hydrogen peroxide. It likely gets the name from its corrosive and flammable nature. One common ratio is 4:1 (v/v) sulfuric acid with 30% hydrogen peroxide, as used in this study on the effect of various surface treatments. It effectively removes organic contaminants from glass surfaces, which makes it hydrophillic. Specifically, it hydroxylixes the surface by exposing silanol groups and Si-O- on the surface. Since hydrogen peroxide self-decomposes, piranha solution should be freshly mixed each time it is to be used to clean surfaces.
There is a closely-related solution, called "base piranha", which is commonly a 3:1 mixture of ammonium hydroxide and hydrogen peroxide.
For more info, see:
K. J. Seu, A. P. Pandey, F. Haque, E. A. Proctor, A. E. Ribbe and J. S. Hovis (2007). "Effect of Surface Treatment on Diffusion and Domain Formation in Supported Lipid Bilayers". Biophysical Journal 92 (7): 2445–2450. doi:10.1529/biophysj.106.099721. PMID 17218468.