Surface Plasmon Resonance in Living Cell Sensing

Surface plasmon resonance (SPR) is a label free technique to study surface interactions. It is based on photon-plasmon coupling. Laser light is directed through a prism and reflects form a metal surface, often gold. At certain conditions, photons turn into plasmons, which then propagate on the metal surface. The refractive index (RI) of the medium close to the metal surface alters the conditions when plasmons can be generated. By changing the incident angle of the light, photon-plasmon coupling can be matched. Thus, change in the SPR sensogram peak angular position (PAP) indicates change in the RI of the sample. Traditionally, SPR has been used to investigate biomolecule dissociation / association kinetics. Recently, it has gained popularity in living cell sensing. Exosomes are 30-100 nm size lipid bilayer structured vesicles, which are excreted by nearly all cells. They play a role in cell-cell communications. Exosomes carry selected cargo from the cells of origin, including mRNA, miRNA, dsDNA and proteins, and they are directed to specific cells, which internalize them. This initiates responses in the recipient cells. The aim of the study was to harvest exosomes from prostate cancer (LNCaP) cells and use SPR as a novel method to detect exosome internalization by these cells. Adhesion proteins were tested in their efficiency to promote confluent cell monolayer formation on SPR gold substrate sensor surface. Nanoparticle tracking analysis (NTA) showed that exosome purification by ultracentrifugation was successful. It was also found that gold substrate supports confluent LNCaP cell monolayer formation. Adhesion proteins did not shorten the incubation time on gold substrate, but helped the cells remain on the sensor during the SPR experiment. Prostate and platelet exosomes were tested on whether they are internalized by LNCaP cells. Control samples with plain medium and PEI/DNA nanoparticles were used. PEI/DNA particles are nonviral gene delivery vectors, which are known to permeate into cells. The SPR results showed RI increase caused 0.9 ° change in the SPR sensogram with the PEI/DNA sample and no change with the medium sample. Exosomes showed more complex responses, both increasing the PAP approximately 0.1 °. Prostate exosome sensogram returned to baseline after sample rinsing, which did not occur with platelet exosomes. It was concluded that SPR shows a response in cell-exosome interactions, which is most likely because of exosome internalization.

Publication year: 2014
Authors: Teemu Suutari

University of Helsinki, Faculty of Pharmacy, Helsinki, Finland

Published in: Master's Thesis


cell monolayer exosome (lipid vesicle) interaction PEI/DNA nanoparticles interactions prostate cancer cells


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