Aggregation-induced color-coded imaging for HOCl detection in living cells with dark-field microscopy

In this work, we develop a nanoprobe for the detection of hypochlorous acid (HOCl), a key reactive oxygen species, utilizing dark-field microscopy (DFM). The nanoprobe is constructed by covalently attaching PEG-SH and an HOCl-sensitive molecule, FD, to gold nanoparticles (GNPs-FD-PEG). This probe detects HOCl by observing a color shift from green to red due to the aggregation of GNPs, which is triggered by HOCl-induced the cleavage of FD molecule. This aggregation occurs primarily due to electrostatic interactions between the differently charged particles following the cleavage. By recording the scattering signal changes of the GNPs-FD-PEG nanoprobe, we have achieved quantitative detection of HOCl, with a linear response range of 0.5-50 μM and a detection limit of 0.16 μM. By integrating the high-resolution capabilities of DFM imaging with the distinct color change due to electrostatic-induced nanoparticle aggregation, the constructed nanoprobe effectively monitors HOCl in live cells.