A Simple Colorimetric Assay of Bleomycin‐Mediated DNA Cleavage Utilizing Double‐Stranded DNA‐Modified Gold Nanoparticles

A colorimetric assay of DNA cleavage by bleomycin (BLM) derivatives was developed utilizing high colloidal stability on double‐stranded (ds) DNA‐modified gold nanoparticles (dsDNA‐AuNPs) possessing a cleavage site. The assay was performed using dsDNA‐AuNPs treated with inactive BLM or activated BLM (Fe(II)⋅BLM). A 10‐min exposure in dsDNA‐AuNPs with inactive BLM treatment resulted in a rapid color change from red to purple because of salt‐induced non‐crosslinking aggregation of dsDNA‐AuNPs. In contrast, the addition of active Fe(II)⋅BLM retained the red color, probably because of the formation of protruding structures at the outermost phase of dsDNA‐AuNPs caused by BLM‐mediated DNA cleavage. Furthermore, the results of our model experiments indicate that oxidative base release and DNA‐cleavage pathways could be visually distinguished with color change. The present methodology was also applicable to model screening assays using several drugs with different mechanisms related to antitumor activity. These results strongly suggest that this assay with a rapid color change could lead to simple and efficient screening of potent antitumor agents.