Upconverting nanoparticles (UCNPs) exhibit a unique nonlinear optical response, where the emission intensity in the UV/blue range increases non-linearly with the excitation intensity of a continuous-wave (CW) laser in the NIR range. This property can provide inherent three-dimensional (3D) capabilities for various applications. As a demonstration, we illustrate that 3D fluorescence imaging is achievable without the need for a pinhole or ultrafast pulsed lasers, allowing us to image mouse cerebrovascular networks up to the depth of around 700 μm through opaque brain tissues. Additionally, we demonstrate that co-dispersing UCNPs with photosensitizers enables depth-targeted photodynamic therapy with reduced damage to superficial cells. The nonlinear optical properties of UCNPs hold promise for providing 3D capabilities across a wide range of applications.
Porous silicon nanoparticles (PSiNPs) have attracted increasing interest for imaging and treatment of diseases due to biocompatibility, large specific capacity for drug loading, non-toxic degradation products, and intrinsic photoluminescence (PL). In particular, the PL lifetime is typically on the order of microseconds, significantly longer than the nanosecond lifetimes exhibited by fluorescent molecules naturally presented in cells and tissues, thus allows discrimination of the silicon nanoparticle from the tissue autofluorescence. Herein, the long-lived PL is employed to monitor the status of drug payload elution, associated with biodegradation of the silicon nanocarriers, and demonstrated as a “self-reporting” system. Dissolution of the silicon matrix in physiological environment triggers drug release, along with decreasing intensity and blue shift of the PL spectra. Furthermore, by tracking the PL lifetime, the drug releasing status and the residual lifespan of the silicon nanocarriers are correspondingly acquired. The PL lifetime is a physically intensive property that can report only the inherent characteristics of the PSiNPs regardless of surrounding noise while the intensity-based reporting is substantially affected by many unwanted factors. We investigate a unique means to inform the lifespan of the PSiNPs as a biodegradable drug nanocarrier in vivo. This study presents a promising potential of the photoluminescent PSiNPs toward advanced drug delivery systems for translational medical platform including theranostics and visualized drug delivery tracking.
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