Gold nanorod-seeded synthesis of Au@Ag/Au nanospheres with broad and intense near-infrared absorption for photothermal cancer therapy.As a widely-adopted agent for photothermal therapy (PTT), gold nanorods (Au NRs) remain problematic due to the cytotoxicity derived from cetyltrimethylammonium bromide (CTAB) and the comparatively weak and narrow near-infrared (NIR) absorption band.  Remarkably, the optimum Au@Ag/Au nanospheres (NSs) with a diameter of ∼40 nm were revealed to have a broad and intense absorption cross section from 400 to 1100 nm, a ∼4.7 times higher hyperthermic effect than Au NRs, and low dark-cytotoxicity. 
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