Bi-Modal Nonlinear Optical Contrast from Si Nanoparticles for Cancer Theranostics

Presenting a safe alternative to conventional compound quantum dots and other functional nanostructures, nanosilicon can offer a series of breakthrough hyperthermia-based therapies under near-infrared, radiofrequency, ultrasound, etc., excitation, but the size range to sensitize these therapies is typically too large (>10 nm) to enable efficient imaging functionality based on photoluminescence properties of quantum-confined excitonic states. Here, it is shown that large Si nanoparticles (NPs) are capable of providing two-photon excited luminescence (TPEL) and second harmonic generation (SHG) responses, much exceeding that of smaller Si NPs, which promises their use as probes for bi-modal nonlinear optical bioimaging. It is finally demonstrated that the combination of TPEL and SHG channels makes possible efficient tracing of both separated Si NPs and their aggregations in different cell compartments, while the resolution of such an approach is enough to obtain 3D images. The obtained bi-modal contrast provides lacking imaging functionality for large Si NPs and promises the development of novel cancer theranostic modalities on their basis.