LAUSR

Background To take advantages, such as multiplex capacity, non-photobleaching property, and high sensitivity, of surface-enhanced Raman scattering (SERS)-based in vivo imaging, development of highly enhanced SERS nanoprobes in near-infrared (NIR) region is needed. A well-controlled morphology and biocompatibility are essential features of NIR SERS nanoprobes. Gold (Au)-assembled nanostructures with controllable nanogaps with highly enhanced SERS signals within multiple hotspots could be a breakthrough. Results Au-assembled silica (SiO 2 ) nanoparticles (NPs) (SiO 2 @Au@Au NPs) as NIR SERS nanoprobes are synthesized using the seed-mediated growth method. SiO 2 @Au@Au NPs using six different sizes of Au NPs (SiO 2 @Au@Au 50 –SiO 2 @Au@Au 500 ) were prepared by controlling the concentration of Au precursor in the growth step. The nanogaps between Au NPs on the SiO 2 surface could be controlled from 4.16 to 0.98 nm by adjusting the concentration of Au precursor (hence increasing Au NP sizes), which resulted in the formation of effective SERS hotspots. SiO 2 @Au@Au 500 NPs with a 0.98-nm gap showed a high SERS enhancement factor of approximately 3.8 × 10 6 under 785-nm photoexcitation. SiO 2 @Au@Au 500 nanoprobes showed detectable in vivo SERS signals at a concentration of 16 μg/mL in animal tissue specimen at a depth of 7 mm. SiO 2 @Au@Au 500 NPs with 14 different Raman label compounds exhibited distinct SERS signals upon subcutaneous injection into nude mice. Conclusions SiO 2 @Au@Au NPs showed high potential for in vivo applications as multiplex nanoprobes with high SERS sensitivity in the NIR region. Graphical Abstract