It is challenging to routinely isolate and analyze high-purity exosomes in a clinical setting. Conventional methods face many disadvantages, such as low yield and/or purity, long processing time, high cost, and difficulty in standardization. Microfluidics integrates many separation and sensing functions, which can realize the separation, detection and analysis of exosomes. These new features are expected to promote basic research and pave the way for routine exosome-based liquid biopsy in personalized medicine.
What Are Exosomes?
Extracellular vesicles are goods secreted by cells to the surrounding environment. According to size and biogenesis, they can be roughly divided into three main subgroups: apoptotic bodies (>1000 nm), microvesicles (100~1000 nm) and exosomes (30~150 nm). Among different types of extracellular vesicles, exosomes have received more attention.
Fig.1 Exosomes represent a subset of extracellular vesicles. Emerging from endosome-multivesicular body (MVB) complexes within the cell, their surface protein markers and nucleic acid cargo play key roles in mediating intercellular communication. These signaling pathways are of intense interest as important new diagnostic and therapeutic targets for personalized medicine. (Contreras-Naranjo J. C, et al. 2017)
Exosomes mainly originate from the endosome-multivesicular body complex, which fuses with the plasma membrane and releases the exosomes into the extracellular environment. They are considered a means of communication and molecular transport between cells, which makes them ideal targets for therapeutic and diagnostic applications. For example, exosomes secreted from stem cells may be an effective source for repairing damaged tissues.
Microfluidics for Exosomes Research
The microfluidic chip consists of a microchannel and a microcavity, which is very suitable for processing micron and submicron particles and a small amount of samples. Many microfluidic device designs have been used to study exosomes. Compared with traditional methods, these exosomal microchips have shown a high level of purity and sensitivity as well as low cost and easy operation. Microfluidic chips used for exosome research can be divided into applications: isolation, detection and analysis.
Exosome Separation Based on Microfluidics
The separation methods that have been used for exosome analysis on microfluidic platforms include epidemic affinity, membrane-based filtration, trapping on nanowires, acoustic nanofiltration, and deterministic lateral displacement (DLD) sorting.
|Exosome Separation Method||Overview||Microfluidic Platforms|
|Immunoaffinity capture||Exosomes are specifically captured by antibodies immobilized on a solid surface. Mainly divided into: equipment with a modified inner surface; equipment using capture beads.||Functionalized (CD63) channel with herringbone groves |
iMER: Isolation using immunomagnetic (EGFR) microbeads
|Membrane filtration||The direct elimination of exosomes in complex biological fluids requires the elimination of any sample pretreatment, especially for microfluidic-enabled POC applications.||Pressure-driven filtration |
|Nanowire trapping||The use of nanowires to physically trap exosomes appears to be a promising method, especially due to its relatively high throughput and potentially high capture efficiency.||Vesicle trapping on array of ciliated (nanowires) micropillars|
|Acoustics||The acoustic standing field established in the fluid medium will produce different acoustic radiation forces according to the properties of the particles, which act on the particles immersed in the fluid. This principle has been used to acoustically capture particles on seed beads along the flow direction inside the capillary.||Continuous contact-free acoustic nanofilter|
|Lateral displacement||DLD is a continuous flow particle sorting technology implemented by embedding the geometry of the column array in the microfluidic device to determine the gradient of the critical diameter cutoff.||Nano-DLD sorting using pillar array|
|Viscoelastic flow||Another label-free passive microfluidic method used for EV classification is viscoelastic microfluidics, the particle separation of which is determined by the elastic lifting force acting on particles of different sizes in the viscoelastic medium.||Continuous viscoelasticity-based and field-free microfluidic sorting|
Exosome Detection and Analysis Based on Microfluidics
Microfluidic Detection of Exosomes
The microfeatures in the microfluidic device can be made so small that the micro-scale fluid flow can be controlled, making it possible to detect exosomes on the chip. Here are some methods for detecting exosomes embedded on microfluidic chips:
- Micro NMR
- Colorimetric detection
- Fluorescence detection
- Electric detection
- Magnetic Nanoparticle Immunolabeling
Fig.2 Examples of microfluidic approaches for exosome detection. (A) RInSE system leverages inertial focusing to perform isolation and fluorescence analysis via flow cytometry. (B) Enhanced immunocapture via electrohydrodynamic nanoshearing using on-chip electrodes enables colorimetric detection of exosomes. (C) μNMR-based detection using on-chip microcoil arrays is achieved by immunoaffinity labeling using magnetic nanoparticles. (D) An aptamer-based electrochemical approach enables label-free detection.. (Contreras-Naranjo J. C, et al. 2017)
Microfluidic Analysis of Exosomes
Microfluidic chips are modular, which allows them to be integrated to perform complex multi-step tasks. The chips can be connected to each other through pipes to minimize the preparation of samples outside the chip, thereby reducing cross-contamination. Microfluidics can be combined with a variety of methods for the on-chip analysis of exosomes. Below you can see some methods of using microfluidic chips for exosome analysis.
- Integrated analysis of exosomal mRNAs
- Integrated analysis of intravesicular proteins
- Integrated analysis of overall exosome levels
- Integrated detection of specific exosome subpopulations
If you need to purchase a custom microfluidic device for exosome research or want to know more about microfluidic exosome research, please let Alfa Chemistry know!
- Contreras-Naranjo J. C, et al. (2017). "Microfluidics for Exosome Isolation and Analysis: Enabling Liquid Biopsy for Personalized Medicine" Lab Chip. 17(21): 3558-3577.
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