Abstract
Determining the characteristics and localization of nanoparticles inside cells is crucial for nanomedicine design for cancer therapy. Hyperspectral imaging is a fast, straightforward, reliable, and accurate method to study the interactions of nanoparticles and intracellular components. With a hyperspectral image, we could collect spectral information consisting of thousands of pixels in a short time. Using hyperspectral images, in this work, we developed a label-free technique to detect nanoparticles in different regions of the cell. This technique is based on plasmonic shifts taking place during the interaction of nanoparticles with the surrounding medium. The unique optical properties of gold nanoparticles, localized surface plasmon resonance bands, are influenced by their microenvironment. The LSPR properties of nanoparticles, hence, could provide information on regions in which nanoparticles are distributed. To examine the potential of this technique for intracellular detection, we used three different types of gold nanoparticles: nanospheres, nanostars and Swarna Bhasma (SB), an Indian Ayurvedic/Sidha medicine, in A549 (human non-small cell lung cancer) and HepG2 (human hepatocellular carcinoma) cells. All three types of particles exhibited broader and longer bands once they were inside cells; however, their plasmonic shifts could change depending on the size and morphology of particles. This technique, along with dark-field images, revealed the uniform distribution of nanospheres in cells and could provide more accurate information on their intracellular microenvironment compared to the other particles. The region-dependent optical responses of nanoparticles in cells highlight the potential application of this technique for subcellular diagnosis when particles with proper size and morphology are chosen to reflect the microenvironment effects properly.
Highlights
Nanoparticles (NPs) with different physicochemical properties are being developed for a wide range of biomedical applications
We showed how hyperspectral imaging and spectral measurements at the nanoscale enable us to approximate their localization in different subcellular regions and understand their interactions with subcellular compartments
There are various microenvironments, and gold particles localized in these regions exhibit different plasmonic shifts depending on the optical properties of their surrounding regions, as well as their physicochemical properties
Summary
Nanoparticles (NPs) with different physicochemical properties are being developed for a wide range of biomedical applications. Chen et al.[11] developed a superresolution fluorescence imaging technique with a spatial resolution of 10 nm, well below the light diffraction limit They used this technique to detect silica nanoparticles in HeLa cells, which they visualized in lysosomes and mitochondria. With the HSI technique, high-resolution spectral information consisting of thousands of pixels can be recorded in less than one hour With this technique, the localized surface plasmon resonance (LSPR) of gold and silver can be studied at the nanoscale to estimate their location and monitor their microenvironment in cells. The LSPR of gold particles is sensitive to the surrounding medium, and we measured changes in plasmonic shifts to estimate the intracellular location and characteristics of particles in cells (Fig. 1) With this system, we could confirm the presence of NPs in cells by considering their unique spectral signatures. The proposed subcellular detection method will help enhance our understanding of nanobio-interaction and develop nanomedicines for therapeutic and diagnostic applications
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