Development and Surface Engineering of Nanomaterials for Cellular Uptake, Localized Targeting and Bioimaging Applications

During the past few decades, fluorescence microscopy has been a powerful technique in the field of cell biology for imaging cellular structures with single molecular sensitivity. However, the fluorescence signals do not provide detailed molecular information, and the photo-bleaching effect often limits their applications. A lot of research efforts have been carried out to synthesize new materials to overcome these limitations. Recently, sensitive optical imaging technology using metal nanoparticles has been extensively used for many cellular and biomedical applications. Recent advancements in molecular diagnosis, in vivo imaging and drug delivery are obtained by using nanoparticles such as plasmon resonant nanoparticles (gold (Au) and silver (Ag)), biodegradable nanoparticles, quantum dots and surface-enhanced Raman scattering (SERS) tags. Among different optical imaging technology, SERS is a versatile technique which enhances the intensity of the vibrational spectra of a molecule by several order of magnitude when the molecule is in close proximity with metallic nanoparticles made of gold or silver. These silver and gold nanoparticles-based SERS probe have overcome the limitation of fluorescence labeling and have been successfully applied for biomedical applications.
In view of this, we have successfully synthesized SERS-active nanoparticles-based probe for targeting and imaging applications using biological systems. Surface engineering of nanoparticle were performed by using bioconjugation protocols involving electrostatic attraction, ligand exchange and amide-bond linkage techniques.
Systematic improvement in the development of SERS-active nanoparticles-based probe was employed from the cellular level to animal model. At first, Silver nanoparticles-based probe was developed with added magnetic functionality for cellular sorting and imaging application. The developed probe comprises of silver-coated iron oxide nanoparticles to combine the magnetic property of iron oxide for sorting application and enhanced Raman scattering from metallic nanoparticles for in vitro optical imaging. Further functionalization of silver-coated iron oxide with benzenethiols of different halogen groups displayed clear and distinct Raman signature. When these functionalized SERS-active probe was incubated with 3T3 fibroblast cells, it was found that the cells could efficiently uptake the probe and due to the enhanced Raman signals, the probe can easily be observed through confocal imaging system.
Secondly, we further developed SERS-active Silver nanoparticles-based probe for lipid targeting and in vivo imaging in C.elegans. In this work, colloidal silver nanoparticles were conjugated non-covalently with lipid specific Nile red dye and the images of organism were subsequently monitored through confocal Raman and conventional confocal microscope. Additionally, the images obtained by Raman probes were very reproducible and no toxicity was observed during the experiment.
For in vivo targeting in higher animal models such as xenografts, the systematic development of SERS-active Gold nanorods-based probe for tumor targeting and in vivo imaging using CAL 27 xenografts was successfully performed. Based on our results, functionalized SERS-active probe can be promising tools for in vivo detection, drug delivery and photothermal-based applications.
Hence, we are able to develop SERS-active nanoparticle-based probes for in vitro and in vivo targeting and imaging applications, which can be a potential candidate for biomedical applications.