Single Particle Interferometric Reflectance Imaging Sensor (SP-IRIS)

SP-IRIS is a method for multiplex phenotyping and digitally counting of different populations of exosomes of size greater than 50 nm which are captured using microarray-based solid-phase chips. The IRIS signal depends on the fields interfering after reflecting from the SiO₂ layer. IRIS exhibits dual-modality consisting of label-free high-throughput measurement of biomass and high-magnification digital detection of single particles [88]. There are many tools used for exosome analysis and characterization, but they may not be very sensitive and the small size of exosomes can cause difficulty. Therefore, a plasmonic microscopy SP-IRIS could analyze the size and antibody interaction of a single exosome with higher sensitivity. Daaboul et al. demonstrated the characterization of exosomes in HEK 293 cell culture from human cerebrospinal fluid (hCSF). The method interferometric imaging could target nanoparticles with size compatibility with exosomes even from a 20 µL of hCSF volume using antibodies against tetraspanins. SP-IRIS could lead to improvements in disease diagnosis [89]. A study by Yang et al. demonstrated label-free imaging and real-time detection of exosomes using SP-IRIS. Exosomes were adsorbed on a chemically modified gold (Au) surface and then intensity of image and size distribution were calculated. The size distribution parameter determines the fusion activity taking place between exosomes and liposomes quantitatively. Antibody-exosome interaction and the behavior of adsorbed exosomes on a surface coated with antibody-coated surface were also monitored [129]. Using defocused images with such interferometric microscopy could improve the detection of nanoparticles such as exosomes and their detectable size limit. Aygun et al. proposed depth scanning correlation (DSC) interferometric microscopy which was able to detect and characterize exosomes over a few nanometers range [90]. Daaboul et al. proposed a label-free microarray imaging method using visible light that captures exosomes using a sensor functionalized by a membrane-specific array capture probe. Exosome populations from pancreatic cancer cell lines were studied by depositing antibodies against CD9, CD63, CD81, Epcam, Tissue Factor, EGFR, Mucin 1, MHC-1, and MHC-2. This technology was used to detect of exosomes from human plasma and it could improve exosome sample preparation standardization allowing liquid biopsy translation based on exosomes [130].