pH-responsive metal nanoparticles as high contrast theranostic agents for selective imaging and synergistic cancer therapy

The low signal-to-noise ratio (S/N) and single functionality of fluorescence imaging agents have limited their practical applications. Bright two-photon excitation (2PE) imaging probes are highly desirable in vivo with larger imaging depth, minor autofluorescence background, and less photodamage. Herein, we developed responsive aggregated gold nanoparticles (Au NPs) as high contrast 2PE imaging agents, capable of emitting red fluorescence upon excitation of near-infrared (NIR) laser and possessing a high signal-to-noise ratio (S/N of 2,475). By forming aggregates in situ inside tumor tissue, doxorubicin hydrochloride (DOX)-loaded mix-charged gold nanoparticles (DOX-MC-Au NPs) were utilized to act as selective fluorescence imaging probes and precise therapy agents. These high-contrast theranostic agents offer a promising potential for precise cancer imaging and therapy, which might open a new venue to multifunctional and noninvasive theranostics.