Novel Ti4+-Chelated Polyoxometalate/Polydopamine Composite Microspheres for Highly Selective Isolation and Enrichment of Phosphoproteins

Selective isolation and enrichment of phosphoproteins play critical roles for identification of biomarkers in biological applications. Herein, a kind of polyoxometalate (P5W30)/polydopamine (PDA) composite microspheres is readily synthesized via an in situ polymerization way, followed by immobilization of Ti4+ on the surface of the microspheres to obtain P5W30/PDA-Ti4+. Due to metal affinity and π stacking interaction, this novel material exhibits high selectivity to β-casein (β-ca), and the theoretical maximum adsorption capacity is as high as 1250 mg g-1, fitting well with the Langmuir model. The captured β-ca can be collected by using Britton-Robinson (B-R) buffer at pH 7.0, and a recovery of 81.5% is acquired. The enrichment factor is over 150 at a mass ratio of BSA/β-ca = 100:1, indicating that phosphoproteins can be purified by P5W30/PDA-Ti4+. Moreover, the application of P5W30/PDA-Ti4+ as sorbent in real biological samples has been investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, and the consequences show that this kind of material is able to selectively isolate phosphoproteins from complex samples such as drinking milk and chicken egg white.