Dual signal amplification for bioassays using ion release from nanolabels and ion-activated enzyme kinetics.

A dual signal amplification technique was developed for bioassays. The technique consists of zinc-ion release from ZnS nanoparticle labels and enzyme kinetics activated by the released zinc ions as cofactors. In the ion release process, each ZnS nanoparticle label liberates a high number of zinc ions by acidic dissolution. After the ion release, at appropriate pH levels, the released zinc ions are used as cofactors to trigger the enzymatic activity of carbonic anhydrase. The fluorescence produced from the activated enzyme kinetics is measured for bioassay signal quantification. A model bioassay on mouse IgG adopting this technique presents a detection limit around 0.5 pM and a detection range over at least two orders of magnitude. This technique was also successfully applied to the detection of human cardiac troponin I (cTnI) in human serum samples to demonstrate a clinical diagnosis application. The developed immunoassay is capable of distinguishing clinically critical levels of cTnI. This technique possesses a high detection resolution and offers the advantage of straightforward operation (simple preparation of ZnS nanoparticles and no enzyme immobilization).