Retraction Note to: A Comparative Study of the Toxicity of Polyethylene Glycol–Coated Cobalt Ferrite Nanospheres and Nanoparticles. - Akhtar, Shahnaz; Khan, Qasim; Anwar, Shahzad; Ali, Ghafar; Maqbool, Muhammad; Khan, Maaz; Karim, Shafqat; Gao, Lan (Nanoscale Research Letters, 2020)