A simple thermometer-based photothermometric assay for alkaline phosphatase activity based on target-induced nanoprobe generation

Developing more portable point-of-care testing tools has attracted great attention in clinical diagnostics. Though great advances have been made in the color readout-based colorimetric field, there are some limitations, due to the lower color resolution of the most naked-eye-detectable color signal. We herein propose a useful strategy for simply achieving a visually detectable temperature readout-based photothermometric assay for sensing the target analyte of alkaline phosphatase (ALP), which is based on the analyte-induced in situ generation of Prussian blue nanoparticles (PB NPs) as both colorimetric and photothermometric nanoprobe. In our design, ascorbic acid 2-phosphate is enzymatically hydrolyzed by target ALP to produce ascorbic acid in the solution reaction system, which then reduces Fe3+ to Fe2+ and further leads to the in situ formation of PB NPs via a specific reaction between potassium ferricyanide and the in situ generated Fe2+. As both colorimetric and photothermometric nanoprobe, such in situ generated PB NPs not only exhibit sensitive color change but also demonstrate a distinct temperature response that is closely dependent on the ALP content. More significantly, the limitation of low color resolution in the colorimetric system for ALP detection was successfully overcome by the proposed photothermometric method with a simple temperature readout and higher sensitivity. This approach provides a general concept with good universality, considerable simplicity and flexibility for realizing a simple thermometer-based photothermometric assay.