Exponential Molecular Amplification by H₂ O₂ -Mediated Autocatalytic Deprotection of Boronic Ester Probes to Redox Cyclers

Herein, a new molecular autocatalytic reaction scheme based on a H₂ O₂ -mediated deprotection of a boronate ester probe into a redox cycling compound is described, generating an exponential signal gain in the presence of O₂ and a reducing agent or enzyme. For such a purpose, new chemosensing probes built around a naphthoquinone/naphthohydroquinone redox-active core, masked by a self-immolative boronic ester protecting group, were designed. With these probes, typical autocatalytic kinetic traces with characteristic lags and exponential phases were obtained by using either UV/Visible or fluorescence optical detection, or by using electrochemical monitoring. Detection of concentrations as low as 0.5 μm H₂ O₂ and 0.5 nm of a naphthoquinone derivative were achieved in a relatively short time (<1 h). From kinetic analysis of the two cross-activated catalytic loops associated with the autocatalysis, the key parameters governing the autocatalytic reaction network were determined, indirectly showing that the analytical performances are currently limited by the slow nonspecific self-deprotection of boronate probes. Collectively, the present results demonstrate the potential of this new exponential molecular amplification strategy, which, owing to its generic nature and modularity, is quite promising for coupling to a wide range of bioassays involving H₂ O₂ or redox cycling compounds, or for use as a new building block in the development of more complex chemical reaction networks.