Bioenzyme-free colorimetric assay for creatinine determination based on Mn 3 O 4 nanoparticles catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine.

Mn 3 O 4 nanozyme with good oxidase-like activity was successfully synthesized. The prepared Mn 3 O 4 nanozyme can directly and effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate green-blue-colored ox-TMB. Creatinine exhibits distinct inhibition effect on Mn 3 O 4 nanozyme-catalyzed TMB colorimetric reaction system, leading to obvious color fading and absorbance intensity decrease of the reaction system. Furthermore, interference from uric acid can be effectively eliminated by regulating the pH of TMB-Mn 3 O 4 colorimetric reaction system to pH 2.0. Then, a simple and bioenzyme-free colorimetric assay for the determination of creatinine was developed based on TMB-Mn 3 O 4 colorimetric reaction. The linear detection range is from 100 to 800 μM and from 1 to 20 mM. The lowest limit of detection is 35.3 μM. Satisfied results are obtained for the determination of creatinine in real urine and sweat samples. This work provides the synthesis of a good oxidase-like nanozyme Mn 3 O 4 and presents the fabrication of an effective nanozyme-based bioenzyme-free colorimetric assay for the determination of creatinine.