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In clinical assay, enzymes are essential biomarkers for human disease diagnosis. In this work, a spectral-resolved single-particle detection (SPD) method is introduced to quantify alkaline phosphatase (ALP) activity in human serum with supraparticles (SPs) based on MnO2 modified gold nanoparticle (denoted as GNP@MnO2 SPs) as the probe. In the presence of ALP, 2-phospho-L-ascorbic acid trisodium salt (AA2P) can be hydrolyzed into L-ascorbic acid (AA), which serves as a good reduction agent to trigger the decomposition of MnO2 shell on GNPs surface. Given that trace amount of ALP exists, noticeable scattering color change can be detected at single-particle level due to the sensitive localized surface plasmon resonance (LSPR) effect from GNPs. With spectral-resolved dark-field optical microscopy (DFM), a linear dynamic range of 0.06-2.48 mU/mL (R2 = 0.99) and a very low limit of detection (LOD) 5.8 µU/mL for ALP assay is readily achieved, which is more sensitive over the methods based on ensemble sample measurement. As a consequence, this strategy opens a new avenue for the design of ultra-sensitive detection method for disease-correlated biomarker diagnosis in the future.
This article was published in the following journal.
Name: Analytical chemistry
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An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed.
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Methods used to measure the relative activity of a specific enzyme or its concentration in solution. Typically an enzyme substrate is added to a buffer solution containing enzyme and the rate of conversion of substrate to product is measured under controlled conditions. Many classical enzymatic assay methods involve the use of synthetic colorimetric substrates and measuring the reaction rates using a spectrophotometer.
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