The Mn3O4 microspheres of about 800 nm in size could be prepared through a hydrothermal method, and we found that the as-prepared Mn3O4 microspheres could quickly oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to its oxidized form (TMBox) in the absence of H2O2.  Furthermore, this assay possessed high selectivity specificity, which made it possible to detect GSH in human serum samples. 
THERM