Ultrasensitive second harmonic generation nanoprobes via plasmonic coreshell structures

As a new mechanism of contrast for biomedical imaging, second harmonic generation (SHG) possesses unique advantages over fluorescence, such as non-bleaching, non-blinking, and narrow emission bandwidth. SHG has also shown great potential for three-dimensional microscopy [1, 2]. It was shown in theory that the nonlinear susceptibility of composite nanostructures can be greatly increased at resonance [3]. Recently silica-core Au nanoshells were demonstrated with engineered resonance [4]. Here we show, for the first time to our knowledge, that when we encapsulate a core material that is not centrosymmetric (BaTiO
3
) in a plasmonic shell (Au), the SHG response is strongly enhanced at resonance. In theory, the enhancement can reach 900 times based on a 100 nm diameter BaTiO
3
core and a 10 nm Au shell. Experimentally, we measured a 741 times enhancement of the SH scattering efficiency. Such composite nanostructures potentially provide a class of ultrasensitive SHG biomarkers.