One-Step Determination of Alkaline Phosphatase in Human Serum Based on Manganese (IV) Dioxide/Manganese (II)-Mediated Nuclear Magnetic Resonance (NMR) Relaxation

Abstract

Alkaline phosphatase (ALP) is a significant biomarker of diseases, such as osteoblastic bone cancer, hepatitis, and myeloma, and hence its determination is essential and important. MnO₂/Mn²⁺ conversion-based magnetic relaxation sensing was developed to directly determine ALP in blood. In the presence of ALP, 2-phospho-L-ascorbic acid trisodium salt was catalyzed to produce ascorbic acid (AA), which reduced MnO₂ to Mn²⁺, causing transverse relaxation time (T₂) decay. A linear relationship of ALP from 5 mU·L⁻¹ to 500 mU·L⁻¹ with T₂ signal and a low limit of detection (LOD) of 3.32 mU·L⁻¹ were obtained using the optimized conditions of 200 µM of ascorbic acid-phosphate (AAP), 10 µg·mL⁻¹ of MnO₂, 37 °C, pH 7.4, and a 30 min reaction time. When directly measuring ALP in serum with the proposed method, the recoveries were from 99.2% to 101.3%, in accordance with values obtained by a commercial assay. In conclusion, a sensitive one-step method for ALP in complex samples was established which has potential for clinical applications.