Fabrication of folate functionalized polyoxometalate nanoparticle to simultaneously detect H₂O₂ and sarcosine in colorimetry

The colorimetric detection of sarcosine, a possible biomarker of prostate cancer (PCa), is long-standing research interest and challenge. Folate functionalized polyoxometalate (FA-PMo₄V₈) was designed and found to detect H₂O₂ and sarcosine without using peroxidase and sarcosine oxidase (SOD) in 3,3,5,5-tetramethylbezidine (TMB) colorimetric reaction. At optimal condition, FA-PMo₄V₈ exhibited excellent peroxidase-like activity and catalyzed the oxidation of TMB during detection of H₂O₂ concentrations in the linear range of 0.007 to 4 μM at limit of detection of 0.012 μM. Also, FA-PMo₄V₈ was found to mimic SOD by reacting with sarcosine in the presence of oxygen to generate H₂O₂, glycine and formaldehyde. Sarcosine concentrations were indirectly detected by FA-PMo₄V₈ with the linear range of 0.2–500 μM at limit of detection of 0.311 μM. FA-PMo₄V₈ was easily fabricated and exhibited good selectivity, reproducible and sensitivity for detecting H₂O₂ and sarcosine in broader pH range. FA-PMo₄V₈ further discriminated PCa patients and healthy persons based on urinary sarcosine concentrations. This study demonstrated that FA-PMo₄V₈ is simply designed and accurate in colorimetric detection of urinary sarcosine, which could be useful for clinical applications.