A Washing-Free and Easy-to-Operate Fluorescent Biosensor for Highly Efficient Detection of Breast Cancer-Derived Exosomes

"One suction and one extrusion" mode-based wash-free platform for determination of breast cancer cell-derived exosomes

A simple and wash-free POCT platform based on microcapillary was developed, using breast cancer cell-derived exosomes as a model. This method adopted the "one suction and one extrusion" mode. The hybridized complex of epithelial cell adhesion molecule (EpCAM) aptamer and complementary DNA-horseradish peroxidase conjugate (CDNA-HRP) was pre-modified on the microcapillary's inner surface. "One suction" meant inhaling the sample into the functionalized microcapillary. The exosomes could specifically bind with the EpCAM aptamer on the microcapillary's inner wall, and then the CDNA-HRP complex was released. "One extrusion" referred to squeezing the shedding CDNA-HRP into the 3,3',5,5'-tetramethylbenzidine (TMB)/H₂O₂ solution, and then the enzyme-catalyzed reaction would occur to make the solution yellow using sulfuric acid as the terminator. Therefore, exosome detection could be realized. The limit of detection was 2.69 × 10⁴ particles mL^-1 and the signal value had excellent linearity in the concentration range from 2.75 × 10⁴ to 2.75 × 10⁸ particles⋅mL^-1 exosomes. In addition, the wash-free POCT platform also displayed a favorable reproducibility (RSD = 2.9%) in exosome detection. This method could effectively differentiate breast cancer patients from healthy donors. This work provided an easy-to-operate method for detecting cancer-derived exosomes without complex cleaning steps, which is expected to be applied to breast cancer screening.

Paper-based biosensors as point-of-care diagnostic devices for the detection of cancers: a review of innovative techniques and clinical applications

The development and rapid progression of cancer are major social problems. Medical diagnostic techniques and smooth clinical care of cancer are new necessities that must be supported by innovative diagnostic methods and technologies. Current molecular diagnostic tools based on the detection of blood protein markers are the most common tools for cancer diagnosis. Biosensors have already proven to be a cost-effective and accessible diagnostic tool that can be used where conventional laboratory methods are not readily available. Paper-based biosensors offer a new look at the world of analytical techniques by overcoming limitations through the creation of a simple device with significant advantages such as adaptability, biocompatibility, biodegradability, ease of use, large surface-to-volume ratio, and cost-effectiveness. In this review, we covered the characteristics of exosomes and their role in tumor growth and clinical diagnosis, followed by a discussion of various paper-based biosensors for exosome detection, such as dipsticks, lateral flow assays (LFA), and microfluidic paper-based devices (µPADs). We also discussed the various clinical studies on paper-based biosensors for exosome detection.

Recent developments in isolating methods for exosomes

Exosomes are the smallest extracellular vesicles that can be released by practically all cell types, and range in size from 30 nm to 150 nm. As the major marker of liquid biopsies, exosomes have great potential for disease diagnosis, therapy, and prognosis. However, their inherent heterogeneity, the complexity of biological fluids, and the presence of nanoscale contaminants make the isolation of exosomes a great challenge. Traditional isolation methods of exosomes are cumbersome and challenging with complex and time-consuming operations. In recent years, the emergence of microfluidic chips, nanolithography, electro-deposition, and other technologies has promoted the combination and innovation of the isolation methods. The application of these methods has brought very considerable benefits to the isolation of exosomes such as ultra-fast, portable integration, and low loss. There are significant functional improvements in isolation yield, isolation purity, and clinical applications. In this review, a series of methods for the isolation of exosomes are summarized, with emphasis on the emerging methods, and in-depth comparison and analysis of each method are provided, including their principles, merits, and demerits.

A light-activated magnetic bead strategy utilized in spatio-temporal controllable exosomes isolation

Tumor-derived exosomes are considered as a key biomarker in the field of liquid biopsy. However, conventional separation techniques such as ultracentrifugation, co-precipitation and column chromatography cannot isolate samples with high throughput, while traditional immunomagnetic separation techniques, due to steric effect of magnetic beads, reducing sensitivity of exosomes optical detection. Herein, we provide a novel and simple nanoplatform for spatiotemporally controlling extraction and elution of exosomes via magnetic separation and light-activated cargo release. In this system, magnetic beads are co-modified by photoresponsive groups -nitrobenzyl group and aptamers that are compatible with CD63-a highly expressed exosomal surface-specific protein. Through exosomes extracted from cell model and nude mice xenograft tumor model morphological characterization and proteomic analysis, results showed that our novel magnetic bead system outperformed current ultracentrifugation in serum exosome extraction in terms of extraction time, yield, and proportion of populations with high CD63 expression. This strategy may be a powerful tool for exosome isolation in clinical liquid biopsies of cancer disease.