A DNA aptamer platform for target-responsive photoacoustic sensing via ICG assembly

Photoacoustic imaging enables deep-tissue visualization using optical absorption contrast; however, most molecular photoacoustic probes rely on static or irreversible signal changes. Here, we present a switchable aptamer sensor platform that converts molecular binding into a reversible, wavelength-encoded photoacoustic contrast mechanism by exploiting proximity-induced dimerization of indocyanine green (ICG). Complementary ICG-labeled DNA strands form a duplex that drives ICG dimerization, producing a distinct absorption peak at 715 nm. Target binding induces strand displacement, restoring the monomeric absorption peak at 780 nm. We validate this switching behavior using absorbance and fluorescence spectroscopy and demonstrate robust, ratiometric photoacoustic contrast in tissue-mimicking phantoms. This approach reframes dye aggregation as a functional transduction mechanism for molecular photoacoustic sensing and establishes a modular platform for wavelength-resolved imaging in scattering media.