ABSTRACT
Extracellular vesicles (EVs) represent a next generation drug delivery system that combines nanoparticle size with extraordinary ability to cross biological barriers, reduced immunogenicity, and low offsite toxicity profiles. A successful application of this natural way of delivering biological compounds requires deep understanding EVs intrinsic properties inherited from their parent cells. Herein, we evaluated EVs released by cells of different origin, with respect to drug delivery to the brain for treatment of neurodegenerative disorders. The morphology, size, and zeta potential of EVs secreted by primary macrophages (mEVs), neurons (nEVs), and astrocytes (aEVs) were examined by nanoparticle NTA, DLS, cryoTEM, and AFM. Spherical nanoparticles with average size 110-130 nm and zeta potential around -20 mV were identified for all EVs types. mEVs showed the highest levels of tetraspanins and integrins compared to nEVs and aEVs, suggesting superior adhesion and targeting to the inflamed tissues by mEVs. Strikingly, aEVs were preferentially taken up by neuronal cells in vitro, followed by mEVs and nEVs. Nevertheless, the brain accumulation levels of mEVs in a transgenic mouse model of Parkinson's disease were significantly higher than those of nEVs or aEVs. Therefore, mEVs were suggested as the most promising nanocarrier system for drug delivery to the brain.
ABSTRACT
Tip-enhanced Raman spectroscopy (TERS) is a promising technique for structural studies of biological systems and biomolecules, owing to its ability to provide a chemical fingerprint with sub-diffraction-limit spatial resolution. This application of TERS has thus far been limited, due to difficulties in generating high field enhancements while maintaining biocompatibility. The high sensitivity achievable through TERS arises from the excitation of a localized surface plasmon resonance in a noble metal atomic force microscope (AFM) tip, which in combination with a metallic surface can produce huge enhancements in the local optical field. However, metals have poor biocompatibility, potentially introducing difficulties in characterizing native structure and conformation in biomolecules, whereas biocompatible surfaces have weak optical field enhancements. Herein, a novel, biocompatible, highly enhancing surface is designed and fabricated based on few-monolayer mica flakes, mechanically exfoliated on a metal surface. These surfaces allow the formation of coupled plasmon enhancements for TERS imaging, while maintaining the biocompatibility and atomic flatness of the mica surface for high resolution AFM. The capability of these substrates for TERS is confirmed numerically and experimentally. We demonstrate up to five orders of magnitude improvement in TERS signals over conventional mica surfaces, expanding the sensitivity of TERS to a wide range of non-resonant biomolecules with weak Raman cross-sections. The increase in sensitivity obtained through this approach also enables the collection of nanoscale spectra with short integration times, improving hyperspectral mapping for these applications. These mica/metal surfaces therefore have the potential to revolutionize spectromicroscopy of complex, heterogeneous biological systems such as DNA and protein complexes.
