## 3 Immunolabeling Approach
The potential of the immunocomplex for detection of clinical samples was also demonstrated. [PERSON] et al. developed a SERS method for the identification of several sorts of exosomes simultaneously using magnetic beads as a captured substrate and gold nanoparticles decorated with specific aptamers as a SERS probe (Figure 10). SERS probes were also comprised of three types of Raman reporters providing spectral separation of the SERS signals. HER2 aptamers bind to the HER2 protein, which is a biomarker for SKBR3 breast cancer cells, in the same way PSMA and CEA  
Figure 8: Selective exosome binding to metallic nanoparticles and SERS detection. Reproduced with permission from [104], John Wiley and Sons, Inc. Copyright © 2000 by John Wiley Sons, Inc, 2017. Figure 9: Mechanisms of (**a**) AuNS®4-MBA®Au SERS nanoprobe fabrication; (**b**) exosome detection. Reproduced with permission from [105], The Royal Society of Chemistry, 2018.  
aptamers recognize LNCaPP prostate and T84 colorectal cancer cells, respectively. Gold nanoparticles functionalized with DTNB Raman reporter (strong peak at 1326 cm\({}^{-1}\)) and HER2 aptamer, 2 NAT Raman reporter (one of strong peaks at 1378 cm\({}^{-1}\)) and PSMA aptamer, and MMC Raman reporter (strong peak at 1170 cm\({}^{-1}\)) and CEA aptamer allowed simultaneous observation of several sorts of cancerous exosomes in the assay spectrum without spectroscopic overlapping. Upon forming of apta-immunocomplex between magnetic beads, exosomes, and SERS probes, a magnet is applied to collect the pellet followed by SERS measurements of the supernatant. The limit of detection (LOD) of three types of exosomes was found to be 32 SKBR3, 73 T84, and 203 LNCaPP exosomes per microliter, respectively. The addition of one exosome sort to the mixture of SERS probes and magnetic beads decreased the SERS intensity of the corresponding probe. The same trend was observed upon the addition of two or three types of exosomes to the mixture. This approach was successfully tested for detection of exosomes derived from blood samples of three patients suffering from/diagnosed with breast, colorectal, and prostate cancers [106]. [PERSON] et al. used a 3D-printed array template and AuNR to implement a simple, cheap, highly efficient, and miniaturized array device. It captures exosomes in a target-specific manner on the antibody array template situated on standard glass microscopy slides coated with silver. Figure 11a demonstrates the measurement sequence: First, the antibody array preparation; then, labeling the captured exosomes by AuNR; and finally, exosome detection. SERS nanotags represent AuNR with the QSY21 Raman reporter incorporated in the cetyltrimethylammonium bromide (CTAB) bilayer. AuNRs attach to exosome lipid membranes due to their opposite charges. Their interaction with the exosome lipid membrane is illustrated in Figure 11b,c. Protein profiling (CD9, CD44, CD 63, EGFR, CD81, EpCAM, HER2, IGF1R) of cancerous and non-cancerous exosomes (derived from breast cancer MM231, MM468, SKBR3, and normal MCF12A cells) demonstrated that exosomes from different cell lines are related to different surface marker profiles. Proteins CD9, CD63, CD81 are present in all  
Figure 10: A scheme of multiple exosome detectionReproduced with permission from [106], The Royal Society of Chemistry, 2018.  
considered cell lines. Within breast cancer patients' serum assays, CD44 was not able to distinguish probes from cancer patients and controls, while EpCAM and HER2 succeeded in this task. Thus, the device provides a quantitative detection of the target proteins and this process has no significant nonspecific interference. The productivity is 80 purified samples per 2 h. The developed method is meant for initially isolated exosomes, but in future it is proposed to allow direct exosome detection in plasma [107]. A high-sensitivity approach for early diagnosis, classification, and metastasis monitoring of pancreatic cancer was developed by [PERSON] et al.