A multitude of imaging modalities and contrast agents have been devised to improve detection, dynamics, and resolution. Whether imaging low copy number proteins in cells or detecting small pathologies in vivo, materials and detection schemes must be specifically tailored to visualize weak signals buried within high backgrounds. Working toward real-world applications, we have tailored bright Ag cluster chromophores and ultrasensitive optical spectroscopies for their selective visualization, even when buried deep within highly absorptive/emissive and highly scattering tissue. Our few-atom Ag nanocluster fluorophores exhibit extremely bright and stable fluorescence, but it is their very long-wavelength absorbing dark states that enable ground state populations to be optically modulated. By optically shifting steady-state population between dark and bright state manifolds, we marry molecular modulation schemes characteristic of absorption spectroscopy with both multi-label fluorescence imaging and photoacoustic detection, to recover only Ag cluster signals without interfering background. Such modulated optical contrast has enabled signal recovery from metal clusters buried multiple cm within tissue-mimicking phantoms. Finite element computational models nicely match experimental results giving predictive insight for future studies and for potential medical applications.

Optically modulated Ag cluster contrast agents

247th National Meeting (2014)

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