Nanoparticle-based indicator-displacement assay for pyrophosphate

Silica nanoparticles functionalized with a Zn(II) -dipicolylamine derivative are used as the receptor component of a sensing ensemble for an indicator-displacement assay. The nano-ensemble system, constructed with pyrocatechol violet as an indicator, selectively senses pyrophosphate over other anions including hydrogen phosphate, thus showing a visible blue-to-yellow color change and the corresponding absorption spectral changes in a buffer solution of pH 7. A distinct recognition behavior--the nano-ensemble does not sense hydrogen phosphate that was sensed by the traditional ensemble with the same molecular receptor--is explained by an incomplete-displacement model in the case of the integrated receptor system. The present work demonstrates that the nanoparticle-based competition assay is as effective as the traditional approach with molecular receptors. Furthermore, such an integrated receptor system can provide distinct recognition behavior from its molecular receptor.