Controlled synthesis of Mn3(PO4)2 hollow spheres as biomimetic enzymes for selective detection of superoxide anions released by living cells

The authors have synthesized nanostructured manganese(II) phosphate hollow spheres [Mn 3 (PO 4 ) 2 HS] with tunable pore structure by using a micro-emulsion method. These, if deposited on a glassy carbon electrode (GCE), are shown to be a viable material for electrochemical sensing of superoxide (radical) anion (O 2 ˙ − ) at a typical working voltage of 0.7 V (vs. SCE). Hence, they act as biomimetic enzymes that allow for the determination of O 2 ˙ − with a very low detection limit (1.35 nM), wide linear range (5 nM to 0.4 mM), and good long-term stability. The modified GCE was applied in-situ to the electrochemical determination of O 2 − that is released from human malignant melanoma cells and normal keratinocyte, and it showed excellent real time analytical capability. In our perception, the use of this material offers exciting opportunities in terms of implementing nanoscale transition metal phosphates as biomimetic enzymes in enzyme-free diagnostic sensors. Conceivably, these will offer higher sensitivity and longer durability than assays based on the use of natural enzymes. Micro-emulsion method-derived nanostructured manganese(II) phosphate hollow spheres [Mn 3 (PO 4 ) 2 HS] as biomimetic enzymes to sensitively detect superoxide anions released by living cells.