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Metal/dendrimer nanocomposites (DNCs) uniquely combine the properties of metallic clusters and the biofriendly
polymer host in a nanosized hybrid particle. DNCs can biochemically target tissues and locally reduce femtosecond
optical breakdown thresholds, making highly precise and selective photodisruption possible. In this study, we have used
high-frequency acoustic monitoring of bubble production dynamics to investigate how DNC properties, solution
concentration, and optical parameters affect threshold reduction, actual waiting time, and mechanical characteristics of
breakdown. Breakdown is defined here as bubble production with an onset of less than 20 seconds after laser exposure.
DNC properties varied include metal content (silver, gold) and terminal group (amino-NH2, glycidol-OH, and carboxyl-
COOH) which determine pH values. Results indicate that DNC metal content markedly influences solution threshold
reduction, while DNC terminal group (and thus net surface charge) and solution concentration influence the details of
breakdown at these reduced threshold fluences. {Ag(0)} DNCs reduce breakdown threshold fluence 1-2 orders of
magnitude more than {Au(0)} DNCs. Furthermore, concentrated DNC solutions and DNCs carrying a net negative
charge (carboxyl terminal groups) increase bubble production up to four times and shorten waiting time for breakdown
from seconds to milliseconds. Increasing laser fluence for a given DNC solution concentration also shortens breakdown
waiting time. Lastly, utilizing the fluorescence properties of silver nanocomposites, we use confocal microscopy to
examine KB cell uptake of folate targeted silver DNCs. Cells incubated with folate targeted silver DNCs exhibit a
measurable increase of intracellular fluorescence compared to control cells (no DNC incubation). However, while we
observe a threshold reduction in KB cells incubated with 500nM folate-targeted DNC solution, there is no threshold
reduction in cells incubated with 50nM folate-targeted DNC solution. This suggests that a specific minimum DNC
concentration may be required for localized reduced-threshold breakdown to occur.
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