An Ultrasensitive Strand Displacement Signal Amplification-Assisted Synchronous Fluorescence Assay for Surface Proteins of Small Extracellular Vesicle Analysis and Cancer Identification

Shedding Light on Cellular Secrets: A Review of Advanced Optical Biosensing Techniques for Detecting Extracellular Vesicles with a Special Focus on Cancer Diagnosis

In the relentless pursuit of innovative diagnostic tools for cancer, this review illuminates the cutting-edge realm of extracellular vesicles (EVs) and their biomolecular cargo detection through advanced optical biosensing techniques with a primary emphasis on their significance in cancer diagnosis. From the sophisticated domain of nanomaterials to the precision of surface plasmon resonance, we herein examine the diverse universe of optical biosensors, emphasizing their specified applications in cancer diagnosis. Exploring and understanding the details of EVs, we present innovative applications of enhancing and blending signals, going beyond the limits to sharpen our ability to sense and distinguish with greater sensitivity and specificity. Our special focus on cancer diagnosis underscores the transformative potential of optical biosensors in early detection and personalized medicine. This review aims to help guide researchers, clinicians, and enthusiasts into the captivating domain where light meets cellular secrets, creating innovative opportunities in cancer diagnostics.

Simultaneous detection of breast cancer biomarkers circROBO1 and BRCA1 based on a CRISPR-Cas13a/Cas12a system

Breast cancer is reported to be one of the most lethal cancers in women, and its multi-target detection can help improve the accuracy of diagnosis. In this work, a cluster regularly interspaced short palindromic repeats (CRISPR)-Cas13a/Cas12a-based system was established for the simultaneous fluorescence detection of breast cancer biomarkers circROBO1 and BRCA1. CRISPR-Cas13a and CRISPR-Cas12a were directly activated by their respective targets, resulting in the cleavage of short RNA and DNA reporters, respectively, thus the signals of 6-carboxyfluorescein (FAM) and 6-carboxy-xrhodamine (ROX) were restored. As the fluorescence intensities of FAM and ROX were dependent on the concentrations of circROBO1 and BRCA1, respectively, synchronous fluorescence scanning could achieve one-step detection of circROBO1 and BRCA1 with detection limits of 0.013 pM and 0.26 pM, respectively. The system was highly sensitive and specific, holding high diagnostic potential for the detection of clinical samples. Furthermore, the competing endogenous RNA mechanism between circROBO1 and BRCA1 was also explored, providing a reliable basis for the intrinsic regulatory mechanism of breast cancer.

Tracking epithelial-mesenchymal transition in breast cancer cells based on a multiplex electrochemical immunosensor

Epithelial-mesenchymal transition (EMT) promotes tumor cell infiltration and metastasis. Tracking the progression of EMT could potentially indicate early cancer metastasis. A key characteristic of EMT is the dynamic alteration in the molecular levels of E-cadherin and N-cadherin. Traditional assays have limited sensitivity and multiplexing capabilities, relying heavily on cell lysis. Here, we developed a multiplex electrochemical biosensor to concurrently track the upregulation of N-cadherin expression and reduction of E-cadherin in breast cancer cells undergoing EMT. Small-sized gold nanoparticles (Au NPs) tagged with redox probes (thionin or amino ferrocene) and bound to two types of antibodies were used as distinguishable signal tags. These tags specifically recognized E-cadherin and N-cadherin proteins on the tumor cell surface without cross-reactivity. The diphenylalanine dipeptide (FF)/chitosan (CS)/Au NPs (FF-CS@Au) composites with high surface area and good biocompatibility were used as the sensing platforms for efficiently fixing cells and recording the dynamic changes in electrochemical signals of surface proteins. The electrochemical immunosensor allowed for simultaneous monitoring of E- and N-cadherins on breast cancer cell surfaces in a single run, enabling tracking of the EMT dynamic process for up to 60 h. Furthermore, the electrochemical detection results are consistent with Western blot analysis, confirming the reliability of the methodology. This present work provides an effective, rapid, and low-cost approach for tracking the EMT process, as well as valuable insights into early tumor metastasis.

Meta-analysis study of small extracellular vesicle nursing application therapies for healing of wounds and skin regeneration

We designed and performed this meta-analysis to investigate the impact of the application of extracellular small vesicle therapies on regeneration of skin and wound healing. The findings of this study were computed using fixed or random effect models. The mean differences (MDs), and odds ratio (ORs) with their 95% confidence intervals (CIs) were calculated. In this study, 43 publications were included, encompassing 530 animals with artificial wounds. Small extracellular vesicle therapy had a significant greater rate of wound closure (MD, 24.0; 95% CI, 19.98-28.02, P < 0.001), lower scar width (MD, -191.33; 95%CI, -292.26--90.4, P < 0.001), and higher blood vessel density (MD,36.11; 95%CI, 19.02-53.20, P < 0.001) compared to placebo. Our data revealed that small extracellular vesicle therapy had a significantly higher regeneration of skin and healing of wounds based on the results of wound closure rate, lower scar width, and higher blood vessel density compared to placebo. Future studies with larger sample size are needed.

In Situ Array Microextraction and Metabolic Profiling of Small Extracellular Vesicles to Guide and Monitor Maternal Delivery

The advantages of small extracellular vesicles (sEV) in disease management have become increasingly prominent, with the main challenge lying in meeting the demands of large-scale extraction and high-throughput analysis, a crucial aspect in the realm of precision medicine. To overcome this challenge, an engineered on-plate aptamer array (16×24 spots) is developed for continuous scale-up microextraction of plasma sEV and their in situ metabolic analysis using mass spectrometry. With this integrated array strategy, metabolic profiles of sEV are acquired from the plasma of 274 antenatal or postpartum women, reducing analysis time by half (7.5 h) and sample volume by 95% (only 0.125 µL usage) compared to the traditional suspension method. Moreover, using machine learning algorithms on sEV metabolic profiles, a risk score system is constructed that accurately assesses the need for epidural analgesia during childbirth and the likelihood of post-administration fever. The system, based on admission samples, achieves an impressive 94% accuracy. Furthermore, post-administration fever can be identified from delivery samples, reaching an overall accuracy rate of 88%. This work offers real-time monitoring of the childbirth process that can provide timely guidance for maternal delivery, underscoring the significance of sEV detection in large-scale clinical samples for medicine innovation and advancement.

A highly sensitive and selective fluorescent biosensor for breast cancer derived exosomes using click reaction of azide-CD63 aptamer and alkyne-polymer dots

Exosomes have gained recognition as valuable reservoirs of biomarkers, holding immense potential for early cancer detection. Consequently, there is a pressing need for the development of an economical and highly sensitive exosome detection methodology. In this work, we present a fluorescence method for breast cancer-derived exosome detection based on Cu-triggered click reaction of azide-modified CD63 aptamer and alkyne functionalized Pdots. The detection threshold for the exosomes obtained from the breast cancer serum was determined to be 6.09 × 107 particles per μL, while the measurable range spanned from 6.50 × 107 to 1.30 × 109 particles per μL. The employed methodology achieved notable success in accurately distinguishing breast cancer patients from healthy individuals through serum analysis. The application of this method showcases the significant potential for early exosome analysis in the clinical diagnosis of breast cancer patients.

Monitoring of Medical Wastewater by Sensitive, Convenient, and Low-Cost Determination of Small Extracellular Vesicles Using a Glycosyl-Imprinted Sensor

The monitoring of small extracellular vesicles (sEVs) in medical waste is of great significance for the prevention of the spread of infectious diseases and the treatment of environmental pollutants in medical waste. Highly sensitive and selective detection methods are urgently needed due to the low content of sEVs in waste samples and the complex sample composition. Herein, a glycosyl-imprinted electrochemical sensor was constructed and a novel strategy for rapid, sensitive, and selective sEVs detection was proposed. The characteristic trisaccharide at the end of the glycosyl chain of the glycoprotein carried on the surface of the sEVs was used as the template molecule. The glycosyl-imprinted polymer films was then prepared by electropolymerization with o-phenylenediamine (o-PD) and 3-aminophenylboronic acid (m-APBA) as functional monomers. sEVs were captured by the imprinted cavities through the recognition and adsorption of glycosyl chains of glycoproteins on sEVs. The m-APBA molecule also acted as a signal probe and was then attached on the immobilized glycoprotein on the surface of sEVs by boric acid affinity. The electrochemical signal of m-APBA was amplificated due to the abundant glycoproteins on the surface of sEVs. The detection range of the sensor was 2.1 × 104 to 8.7 × 107 particles/mL, and the limit of detection was 1.7 × 104 particles/mL. The sensor was then applied to the determination of sEVs in medical wastewater and urine, which showed good selectivity, low detection cost, and good sensitivity.

An Electrochemiluminescent Sensor Based on Glycosyl Imprinting and Aptamer for the Detection of Cancer-Related Extracellular Vesicles

Cancer-related extracellular vesicles (EVs) are considered important biomarkers for cancer diagnosis because they can convey a large amount of information about tumor cells. In order to detect cancer-related EVs efficiently, an electrochemiluminescence (ECL) sensor for the specific identification and highly sensitive detection of EVs in the plasma of cancer patients was constructed based on dual recognitions by glycosyl-imprinted polymer (GIP) and aptamer. The characteristic glycosyl Neu5Ac-α-(2,6)-Gal-β-(1-4)-GlcNAc trisaccharide on the surface of EVs was used as a template molecule and 3-aminophenylboronic acid as a functional monomer to form a glycosyl-imprinted polymer by electropolymerization. After glycosyl elution, the imprinted film specifically recognized and adsorbed the EVs in the sample, and then the CD63 aptamer-bipyridine ruthenium (Aptamer-Ru(bpy)) was added to combine with the CD63 glycoprotein on the extracellular vesicle's surface, thus providing secondary recognition of the EVs. Finally, the EVs were quantitatively detected according to the ECL signal produced by the labeled bipyridine ruthenium. When more EVs were captured by the imprinted film, more probes were obtained after incubation, and the ECL signal was stronger. Under the optimized conditions, the ECL signal showed a good linear relationship with the concentration of EVs in the range of 9.5 × 102 to 9.5 × 107 particles/mL, and the limit of detection was 641 particles/mL. The GIP sensor can discriminate between the EV contents of cancer patients and healthy controls with high accuracy. Because of its affordability, high sensitivity, and ease of use, it is anticipated to be employed for cancer early detection and diagnosis.

Microfluidic Device-Based In Vivo Detection of PD-L1-Positive Small Extracellular Vesicles and Its Application for Tumor Monitoring

Liquid biopsy is of great significance in tumor early diagnosis and treatment stratification. PD-L1-positive small extracellular vesicles (PD-L1+ sEVs) are closely related to tumor growth and immunotherapy response, which are considered valuable liquid biopsy biomarkers. In contrast to conventional in vitro detection, in vivo detection has the ability to improve the detection efficiency and enable continuous or real-time dynamic monitoring. However, in vivo detection of PD-L1+ sEVs has multiple difficulties, such as high cell background, complex blood environments, and lack of a specific and stable detection method. Herein, the in vivo detection of PD-L1+ sEVs method was constructed, which efficiently separated sEVs based on the microfluidic device and quantitatively analyzed PD-L1+ sEVs by aptamer recognition and hybridization chain reaction. The concentration of PD-L1+ sEVs was continuously monitored, and significant differences at different stages of tumor as well as a correlation with tumor volume were found. Diseased and healthy individuals could also be effectively distinguished based on the concentration of PD-L1+ sEVs. The method with good stability, biocompatibility, and detection performance provided a powerful means for in vivo detection of PD-L1+ sEVs, contributing to the clinical diagnosis and treatment of tumor.

Ultrasensitive determination of surface proteins on tumor-derived small extracellular vesicles for breast cancer identification based on lanthanide-activated signal amplification strategy

Small extracellular vesicles (sEVs) carrying multiple tumor-associated proteins inherited from parental cells play crucial roles in noninvasive breast cancer (BC) diagnosis. However, it is challenging to assess the subtle variations of surface proteins on sEV membranes due to the highly heterogeneous BC. Therefore, a simple and ultrasensitive assay based on lanthanide (Ln3+)-activated luminescence signal amplification was developed to detect multiple surface proteins on BC-derived sEVs. Multiple protein biomarkers on sEVs can be well identified with high sensitivity and specificity through dissolution-amplified luminescence of the NaEuF4 nanoparticle-based nanoprobe. We employ linear discriminant analysis to successfully discriminate triple negative BC cell (MDA-MB-231 cell) derived sEVs from other breast cell lines (MCF-7, SK-BR-3, BT474 and MCF-10A cell). Furthermore, the strategy enables high accuracy for districting the progression stages of BC patients and healthy donors. The simple and sensitive signal amplification strategy exhibits great potential for early clinic diagnosis by precise protein profiling of sEVs.

Immobilization-free dual-aptamer-based photoelectrochemical platform for ultrasensitive exosome assay

Exosomes, involved in cancer-specific biological processes, are promising noninvasive biomarkers for early diagnosis of cancer. Herein, an immobilization-free dual-aptamer-based photoelectrochemical (PEC) biosensor was proposed for the enrichment and quantification of cancer exosome based on photoactive bismuch oxyiodide/gold/cadmium sulfide (BiOI/Au/CdS) composites, nucleic acid-based recognition and signal amplification. In this biosensor, the recognition of exosome by two aptamers would trigger the deoxyribonucleotidyl transferase (TdT) enzyme-aided polymerization, leading to the enrichment of alkaline phosphatase (ALP) on Fe3O4 surface. After magnetic separation, ALP could catalyze the generation of ascorbic acid (AA) as electron donor and initiate the following redox cycle reaction for further signal amplification. Furthermore, all the above processes were performed in solution, the recognition and signal amplification efficiency would be superior than the heterogeneous strategy owing to the avoidance of steric hindrance effect. As a result, the proposed PEC biosensor was capable of enriching and detecting of cancer exosomes with high sensitivity and selectivity. The linear range of the biosensor was from 1.0 × 102 particles·μL-1 to 1.0 × 106 particles·μL-1 and the detection limit was estimated to be 21 particles·μL-1. Therefore, the proposed PEC biosensor holds great promise in quantifying tumor exosome for nondestructive early clinical cancer diagnosis and various other bioassay applications.

Simultaneous subset tracing and miRNA profiling of tumor-derived exosomes via dual-surface-protein orthogonal barcoding

The clinical potential of miRNA-based liquid biopsy has been largely limited by the heterogeneous sources in plasma and tedious assay processes. Here, we develop a precise and robust one-pot assay called dual-surface-protein-guided orthogonal recognition of tumor-derived exosomes and in situ profiling of microRNAs (SORTER) to detect tumor-derived exosomal miRNAs and enhance the diagnostic accuracy of prostate cancer (PCa). The SORTER uses two allosteric aptamers against exosomal marker CD63 and tumor marker EpCAM to create an orthogonal labeling barcode and achieve selective sorting of tumor-specific exosome subtypes. Furthermore, the labeled barcode on tumor-derived exosomes initiated targeted membrane fusion with liposome probes to import miRNA detection reagents, enabling in situ sensitive profiling of tumor-derived exosomal miRNAs. With a signature of six miRNAs, SORTER differentiated PCa and benign prostatic hyperplasia with an accuracy of 100%. Notably, the diagnostic accuracy reached 90.6% in the classification of metastatic and nonmetastatic PCa. We envision that the SORTER will promote the clinical adaptability of miRNA-based liquid biopsy.

Recent progress in quantitative technologies for the analysis of cancer-related exosome proteins

Exosomes are a kind of extracellular vesicles, which play a significant role in intercellular communication and molecular exchange. Cancer-derived exosomes are potential and ideal biomarkers for the early diagnosis and treatment monitoring of cancers because of their abundant biological information and contribution to the interaction between cancer cells and the tumor microenvironment. However, there are a number of drawbacks, such as low sensitivity and tedious steps, in conventional detection techniques. Furthermore, exosome quantification is not enough to accurately distinguish cancer patients from healthy individuals. Therefore, developing efficient, accurate, and inexpensive exosome surface protein analysis techniques is necessary and critical. In recent years, a considerable number of researchers have presented novel detection strategies in this field. This review summarizes the recent progress in quantitative technologies for the analysis of cancer-related exosome proteins, mainly including the detection methods based on aptamers, nanomaterials, and antibodies, discusses a roadmap for future developments, and aims to offer an innovative perspective of exosome research.

Polymerase-Driven Logic Signal Amplification for the Detection of Small Extracellular Vesicle Surface Proteins and the Identification of Breast Cancer

Small extracellular vesicles (sEVs) derived from tumors contain a vast amount of cellular information and are regarded as a potential diagnostic biomarker for noninvasive cancer diagnosis. Nevertheless, it remains challenging to accurately measure sEVs from clinical samples due to the low abundance of these vesicles as well as their phenotypic heterogeneity. Herein, a polymerase-driven logic signal amplification system (PLSAS) was developed for the high-sensitivity detection of sEV surface proteins and breast cancer (BC) identification. Aptamers were introduced to serve as sensing modules to specifically recognize target proteins. By changing the input DNA sequences, two polymerase-driven primer exchange reaction systems were rationally designed for DNA logic computing. This allows for autonomous targeting of a limited number of targets using "OR" and "AND" logic, leading to a significant increase in fluorescence signals and enabling the specific and ultrasensitive detection of sEV surface proteins. In this work, we investigated surface proteins of mucin 1 (MUC1) and the epithelial cell adhesion molecule (EpCAM) as model proteins. When MUC1 or EpCAM proteins were used as single signal input in the "OR" DNA logic system, the detection limit of sEVs was 24 or 58 particles/μL, respectively. And MUC1 and EpCAM proteins of sEVs can be simultaneously detected in the AND logic method, which can significantly reduce the effect of phenotypic heterogeneity of sEVs to distinguish the source of sEVs derived from various mammary cell lines, such as MCF-7, MDA MB 231, SKBR3, and MCF-10A. The approach has achieved high discrimination in serologically tested positive BC samples (AUC 98.1%) and holds significant potential in advancing the early diagnosis and prognostic assessments of BC.

Magnetic-nanowaxberry-based microfluidic ExoSIC for affinity and continuous separation of circulating exosomes towards cancer diagnosis

Exosomes are seen as promising biomarkers for minimally invasive liquid biopsies and disease surveillance. However, the complexity of body fluids, inherent heterogeneity, and tiny size of exosomes impede their extraction, consequently restricting their clinical application. In this study, in order to efficiently isolate exosomes from clinical samples, an irregular serpentine channel microfluidic chip (ExoSIC) was designed to continuously separate exosomes from plasma based on a magnetic-nanowaxberry (MNWB). In the ExoSIC, irregular serpentine microchannels are utilized to increase fluid chaotic mixing, hence improving exosome capture efficiency. In comparison to commonly used spherical magnetic particles, the designed MNWB can not only enhance the capture efficiency of exosomes, but also possess a size-exclusion effect to improve exosome purity. Consequently, the ExoSIC exhibited a large yield (24 times higher than differential centrifugation), optimum purity (greater than precipitation and similar to differential centrifugation), and high specificity. Furthermore, the ExoSIC was utilized for plasma-based cancer diagnosis by multiplex monitoring of five exosomal biomarkers (exosomal concentration, EGFR, EpCAM, SAA1 and FV), and the AUC reached 0.791. This work provides a comprehensive framework for exosome-based cancer diagnostics in order to meet clinical requirements for exosome isolation and downstream analysis.

A review of sensors for classification and subtype discrimination of cancer: Insights into circulating tumor cells and tumor-derived extracellular vesicles

Liquid biopsy can reflect the state of tumors in vivo non-invasively, thus providing a strong basis for the early diagnosis, individualized treatment monitoring and prognosis of tumors. Circulating tumor cells (CTCs) and tumor-derived extracellular vesicles (tdEVs) contain information-rich components, such as nucleic acids and proteins, and they are essential markers for liquid biopsies. Their capture and analysis are of great importance for the study of disease occurrence and development and, consequently, have been the subject of many reviews. However, both CTCs and tdEVs carry the biological characteristics of their original tissue, and few reviews have focused on their function in the staging and classification of cancer. In this review, we focus on state-of-the-art sensors based on the simultaneous detection of multiple biomarkers within CTCs and tdEVs, with clinical applications centered on cancer classification and subtyping. We also provide a thorough discussion of the current challenges and prospects for novel sensors with the ultimate goal of cancer classification and staging. It is hoped that these most advanced technologies will bring new insights into the clinical practice of cancer screening and diagnosis.

Highly Sensitive Aptasensor for Detecting Cancerous Exosomes Based on Clover-like Gold Nanoclusters

Exosome-based liquid biopsy technologies play an increasingly prominent role in tumor diagnosis. However, the simple and sensitive method for counting exosomes still faces considerable challenges. In this work, the CD63 aptamer-modified DNA tetrahedrons on the gold electrode were used as recognition elements for the specific capture of exosomes. Partially complementary DNA probes act as bridges linking trapped exosomes and three AuNP-DNA signal probes. This clover-like structure can tackle the recognition and sensitivity issues arising from the undesired AuNP aggregation event. When cancerous exosomes are present in the system, the high accumulation of methylene blue molecules from DNA-AuNP nanocomposites on the surface of the electrode leads to an intense current signal. According to the results, the aptasensor responds to MCF-7 cell-derived exosomes in the concentration range from 1.0 × 10³ to 1.0 × 10⁸ particles·μL^-1, with the detection limit of 158 particles·μL^-1. Furthermore, the aptasensor has been extended to serum samples from breast cancer patients and exhibited excellent specificity. To sum it up, the aptasensor is sensitive, straightforward, less expensive, and fully capable of receiving widespread application in clinics for tumor monitoring.

An in situ exosomal miRNA sensing biochip based on multi-branched localized catalytic hairpin assembly and photonic crystals

Exosomal microRNAs (miRNAs) are emerging as attractive non-invasive and reliable biomarkers for disease diagnosis. In situ exosomal miRNA detection can avoid laborious and time-consuming exosome lysis, RNA extraction and effectively improve the accuracy. However, in situ exosomal miRNA detection is hampered by the low abundance of the targets and low permeability of the probes. Herein, an in situ exosomal miRNA sensing biochip based on multi-branched localized catalytic hairpin assembly (MLCHA) and photonic crystals (PCs) was proposed. The MLCHA probes could penetrate into the exosomes nondestructively due to its rigidity and generate amplified fluorescence signal upon recognizing the target miRNA. And then, the fluorescence signal was further enhanced by PCs to improve the sensitivity. The developed biosensor can not only detect exosomal miRNA in a concentration-dependent manner but also distinguish samples from cancer state and healthy state, which is potential for non-invasive clinical diagnostics.

Nucleic acid and nanomaterial-assisted signal-amplified strategies in fluorescent analysis of circulating tumor cells and small extracellular vesicles

As two main types of liquid biopsy markers, both circulating tumor cells (CTCs) and small extracellular vesicles (sEVs) play important roles in the diagnosis and prognosis of cancers. CTCs are malignant cells that detach from the original tumor tissue and enter the circulation of body fluids. sEVs are nanoscale vesicles secreted by normal cells or pathological cells. However, CTCs and sEVs in body fluids are scarce, leading to great difficulties in the accurate analysis of related diseases. For the sensitive detection of CTCs and sEVs in body fluids, various types of nucleic acid and nanomaterial-assisted signal amplification strategies have been developed. In this review, we summarize the recent advances in fluorescent detection of CTCs and sEVs in liquid biopsy based on nucleic acid and nanomaterial-assisted signal amplification strategies. We also discuss their advantages, challenges, and future prospects.

A novel DNA detection using spherical identification probe and strand displacement reaction-initiated silver nanocluster switch

Herein, we developed a novel fluorescent assay using spherical identification probes and toehold-mediated strand displacement reaction-initiated silver nanoclusters (AgNCs) "on-off" signal switch. In this strategy, the target was captured by the spherical probes to induce the activity of exonuclease III (Exo III), catalyzing the cyclic cleavage of substrates to produce a mass of trigger strands. After magnetic bead separation, the intermediates in the supernatant activated downstream toehold-mediated strand displacement reaction to change the structure of silver nanocluster templates, leading to fluorescence intensity reduction. Furthermore, it is demonstrated that the application of spherical identification probes could reduce the signal leakage and the limit of detection. In addition, AgNCs with perfect optical property were ingeniously combined to realize signal output, which reduced the cost and time of synthesis. Under the optimal conditions, the sensing method displayed a good linear range from 250 pM to 25 nM with a detectable minimum concentration of 250 pM. And the practical application potential in complex biological matrices was also evaluated. Considering these advantages, this constructed strategy opens a new path for nucleic acid detection with better performance. A simple, label- and hairpin-free fluorescent system based on spherical identification probe and toehold-mediated strand displacement reaction-initiated silver nanoclusters (AgNCs) "on-off" signal switch was successfully constructed to detect target DNA.

Isolation of circulating exosomes and identification of exosomal PD-L1 for predicting immunotherapy response

Exosomes, a subgroup of extracellular vesicles secreted by multiple cells, have great potential as cancer biomarkers in clinical applications. However, enrichment and detection of exosomes from complex media remain a huge challenge due to their small size. Herein, we used iodixanol density gradient centrifugation for the isolation and purification of exosomes and label-free detection of exosomal PD-L1 using a biochip based on surface plasmon resonance (SPR-Exo_PD-L1). The obtained exosomes are lipid-bilayer vesicles and the classical exosome markers CD9, CD63 and CD81 are highly enriched. Besides, PD-L1 is specifically expressed on exosomes instead of non-vesicular components or large extracellular vesicles. Compared with enzyme-linked immunosorbent assays, the SPR-Exo_PD-L1 assay could better distinguish exosomes derived from melanoma cells with different levels of PD-L1. Accurate measurement of exosomal PD-L1 could provide critical clinical information for cancer diagnosis and personalized immunotherapy of cancer.