Plasmon-Enhanced Single Extracellular Vesicle Analysis for Cholangiocarcinoma Diagnosis

Advances in exosome plasmonic sensing: Device integration strategies and AI-aided diagnosis

Exosomes, as next-generation biomarkers, has great potential in tracking cancer progression. They face many detection limitations in cancer diagnosis. Plasmonic biosensors have attracted considerable attention at the forefront of exosome detection, due to their label-free, real-time, and high-sensitivity features. Their advantages in multiplex immunoassays of minimal liquid samples establish the leading position in various diagnostic studies. This review delineates the application principles of plasmonic sensing technologies, highlighting the importance of exosomes-based spectrum and image signals in disease diagnostics. It also introduces advancements in miniaturizing plasmonic biosensing platforms of exosomes, which can facilitate point-of-care testing for future healthcare. Nowadays, inspired by the surge of artificial intelligence (AI) for science and technology, more and more AI algorithms are being adopted to process the exosome spectrum and image data from plasmonic detection. Using representative algorithms of machine learning has become a mainstream trend in plasmonic biosensing research for exosome liquid biopsy. Typically, these algorithms process complex exosome datasets efficiently and establish powerful predictive models for precise diagnosis. This review further discusses critical strategies of AI algorithm selection in exosome-based diagnosis. Particularly, we categorize the AI algorithms into the interpretable and uninterpretable groups for exosome plasmonic detection applications. The interpretable AI enhances the transparency and reliability of diagnosis by elucidating the decision-making process, while the uninterpretable AI provides high diagnostic accuracy with robust data processing by a "black-box" working mode. We believe that AI will continue to promote significant progress of exosome plasmonic detection and mobile healthcare in the near future.

A cavity induced mode hybridization plasmonic sensor for portable detection of exosomes

Exosomes have been considered as promising biomarkers for cancer diagnosis due to their abundant information from originating cells. However, sensitive and reliable detection of exosomes is still facing technically challenges due to the lack of a sensing platform with high sensitivity and reproducibility. To address the challenges, here we propose a portable surface plasmon resonance (SPR) sensing of exosomes with a three-layer Au mirror/SiO2 spacer/Au nanohole sensor, fabricated by an economical polystyrene nanosphere self-assembly method. The SiO2 spacer can act as an optical cavity and induce mode hybridization, leading to excellent optimization of both sensitivity and full width at half maximum compared with normal single layer Au nanohole sensors. When modified with CD63 or EpCAM aptamers, a detection of limit (LOD) of as low as 600 particles/μL was achieved. The sensors showed good capability to distinguish between non-tumor derived L02 exosomes and tumor derived HepG2 exosomes. Additionally, high reproducibility was also achieved in detection of artificial serum samples with RSD as low as 2%, making it feasible for clinical applications. This mode hybridization plasmonic sensor provides an effective approach to optimize the detection sensitivity of exosomes, pushing SPR sensing one step further towards cancer diagnosis.

In Situ, Fusion-Free, Multiplexed Detection of Small Extracellular Vesicle miRNAs for Cancer Diagnostics

Tumor-derived small extracellular vesicle (sEV) microRNAs (miRNAs) are emerging biomarkers for cancer diagnostics. Conventional sEV miRNA detection methods necessitate the lysis of sEVs, rendering them laborious and time-consuming and potentially leading to damage or loss of miRNAs. Membrane fusion-based in situ detection of sEV miRNAs involves the preparation of probe-loaded vesicles (e.g., liposomes or cellular vesicles), which are typically sophisticated and require specialist equipment. Membrane perforation methods employ chemical treatments that can induce severe miRNA degradation or leaks. Inspired by previous studies that loaded nucleic acids into EVs or cells using hydrophobic tethers for therapeutic applications, herein, we repurposed this strategy by conjugating a hydrophobic tether onto molecular beacons to aid their transportation into sEVs, allowing for in situ detection of miRNAs in a fusion-free and multiplexing manner. This method enables simultaneous detection of multiple miRNA species within serum-derived sEVs for the diagnosis of prostate cancer, breast cancer, and gastric cancer with an accuracy of 83.3%, 81.8%, and 100%, respectively, in a cohort of 66 individuals, indicating that it holds a high application potential in clinical diagnostics.

Tumor-associated macrophages: orchestrators of cholangiocarcinoma progression

Cholangiocarcinoma (CCA) is a rare but highly invasive cancer, with its incidence rising in recent years. Currently, surgery remains the most definitive therapeutic option for CCA. However, similar to other malignancies, most CCA patients are not eligible for surgical intervention at the time of diagnosis. The chemotherapeutic regimen of gemcitabine combined with cisplatin is the standard treatment for advanced CCA, but its effectiveness is often hampered by therapeutic resistance. Recent research highlights the remarkable plasticity of tumor-associated macrophages (TAMs) within the tumor microenvironment (TME). TAMs play a crucial dual role in either promoting or suppressing tumor development, depending on the factors that polarize them toward pro-tumorigenic or anti-tumorigenic phenotypes, as well as their interactions with cancer cells and other stromal components. In this review, we critically examine recent studies on TAMs in CCA, detailing the expression patterns and prognostic significance of different TAM subtypes in CCA, the mechanisms by which TAMs influence CCA progression and immune evasion, and the potential for reprogramming TAMs to enhance anticancer therapies. This review aims to provide a framework for deeper future research.

Studying the small extracellular vesicle capture efficiency of magnetic beads coated with tannic acid

The isolation of small extracellular vesicles (sEVs), including those secreted by pathological cells, with high efficiency and purity is highly demanded for research studies and practical applications. Conventional sEV isolation methods suffer from low yield, presence of contaminants, long-term operation and high costs. Bead-assisted platforms are considered to be effective for trapping sEVs with high recovery yield and sufficient purity for further molecular profiling. In this study, magnetically responsive beads made of calcium carbonate (CaCO3) particles impregnated with iron oxide (Fe3O4) nanoparticles are fabricated using a freezing-induced loading (FIL) method. The developed magnetic beads demonstrate sufficient magnetization and can be collected by a permanent magnet, ensuring their rapid and gentle capture from an aqueous solution. The tannic acid on the surface of magnetic beads is formed by a layer-by-layer (LbL) method and is used to induce coupling of sEVs with the surface of magnetic beads. These tannic acid coated magnetic beads (TAMB) were applied to capture sEVs derived from MCF7 and HCT116 cell lines. Quantitative data derived from nanoparticle tracking analysis (NTA) and BCA methods revealed the capture efficiency and recovery yield of about 60%. High-resolution transmission electron microscopy (HRTEM) imaging of sEVs on the surface of TAMBs indicated their structural integrity. Compared with the size exclusion chromatography (SEC) method, the proposed approach demonstrated comparable efficiency in terms of recovery yield and purity, while offering a relatively short operation time. These results highlight the high potential of the TAMB approach for the enrichment of sEVs from biological fluids, such as cell culture media.

Colocalization of protein and microRNA markers reveals unique extracellular vesicle subpopulations for early cancer detection

Extracellular vesicles (EVs) play important roles in cell-cell communication but are highly heterogeneous, and each vesicle has dimensions smaller than 200 nm with very limited amounts of cargos encapsulated. The technique of NanOstirBar (NOB)-EnabLed Single Particle Analysis (NOBEL-SPA) reported in the present work permits rapid inspection of single EV with high confidence by confocal fluorescence microscopy, thus enables colocalization assessment for selected protein and microRNA (miRNA) markers in the EVs produced by various cell lines, or present in clinical sera samples. EV subpopulations marked by the colocalization of unique protein and miRNA combinations were discovered to be able to detect early-stage (stage I or II) breast cancer (BC). NOBEL-SPA can be adapted to analyze other types of cargo molecules or other small submicron biological particles. Study of the sorting of specific cargos to heterogeneous vesicles under different physiological conditions can help discover distinct vesicle subpopulations valuable in clinical examination and therapeutics development and gain better understanding of their biogenesis.

Precise Identification and Profiling of Surface Proteins of Ultra Rare Tumor Specific Extracellular Vesicle with Dynamic Quantitative Plasmonic Imaging

Specific detection of tumor-derived EVs (tEVs) in plasma is complicated by nontumor EVs and non-EV particles. To accurately identify tEVs and profile their surface protein expression at single tEV resolution directly with clinical plasma is still an unmet need. Here, we present a Dynamic Immunoassay for Single tEV surface protein Profiling (DISEP), a kinetic assay based on surface plasmon resonance microscopy (SPRM) for specific single tEV profiling. DISEP adopts a pair of low-affinity oligonucleotide probes to respectively label EV surface proteins and functionalize an SPRM biosensor interface. tEVs labeled with the oligonucleotide probes possess distinctive binding kinetics from nonspecific particles in plasma, which permits accurate digital plasmonic counting of single EVs. We demonstrate DISEP for recognizing target EVs among 350-fold background plasma particles with high sensitivity (4677 EVs per μL). Clinical plasma samples were analyzed to discriminate between pancreatic cancer patients (n = 40) and healthy donors (n = 45). With a panel of biomarker signatures (EpCAM, HER2, and GPC1), DISEP only requires 10 μL primary sample from each donor to classify tumor patients with an area under the curve of 0.98. DISEP provides a highly specific EV detection and surface protein profiling strategy for early cancer diagnosis.

CRISPR/Cas13a-Based MicroRNA Detection in Tumor-Derived Extracellular Vesicles

MicroRNAs (miRNAs) in extracellular vesicles (EVs) play essential roles in cancer initiation and progression. Quantitative measurements of EV miRNAs are critical for cancer diagnosis and longitudinal monitoring. Traditional PCR-based methods, however, require multi-step procedures and remain as bulk analysis. Here, the authors introduce an amplification-free and extraction-free EV miRNA detection method using a CRISPR/Cas13a sensing system. CRISPR/Cas13a sensing components are encapsulated in liposomes and delivered them into EVs through liposome-EV fusion. This allows for accurately quantify specific miRNA-positive EV counts using 1 × 108  EVs. The authors show that miR-21-5p-positive EV counts are in the range of 2%-10% in ovarian cancer EVs, which is significantly higher than the positive EV counts from the benign cells (<0.65%). The result show an excellent correlation between bulk analysis with the gold-standard method, RT-qPCR. The authors also demonstrate multiplexed protein-miRNA analysis in tumor-derived EVs by capturing EpCAM-positive EVs and quantifying miR-21-5p-positive ones in the subpopulation, which show significantly higher counts in the plasma of cancer patients than healthy controls. The developed EV miRNA sensing system provides the specific miRNA detection method in intact EVs without RNA extraction and opens up the possibility of multiplexed single EV analysis for protein and RNA markers.

Fluorescence labeling of extracellular vesicles for diverse bio-applications in vitro and in vivo

Extracellular vesicles (EVs) are nanosized vesicles enclosed in a lipid membrane that are sustainably released by nearly all cell types. EVs have been deemed as valuable biomarkers for diagnostics and effective drug carriers, owing to the physiological function of transporting biomolecules for intercellular communication. To investigate their biological properties, efficient labeling strategies have been constructed for EV research, among which fluorescence labeling exerts a powerful function due to the capability of visualizing the nanovesicles with high sensitivity both in vitro and in vivo. In one aspect, with the help of functional fluorescence tags, EVs could be differentiated and categorized in vitro by various analytical techniques, which exert vital roles in disease diagnosis, prognosis, and treatment monitoring. Additionally, innovative EV reporters have been utilized for visualizing EVs, in combination with powerful microscopy techniques, which provide potential tools for investigating the dynamic events of EV release and intercellular communication in suitable animal models. In this feature article, we survey the latest advances regarding EV fluorescence labeling strategies and their application in biomedical application and in vivo biology investigation, highlighting the progresses in individual EV imaging. Finally, the challenges and future perspectives in unravelling EV physiological properties and further biomedical application are discussed.

Colocalization of Protein and microRNA Markers Reveals Unique Extracellular Vesicle Sub-Populations for Early Cancer Detection

Extracellular vesicles (EVs) play important roles in cell-cell communication but they are highly heterogeneous, and each vesicle has dimensions smaller than 200 nm thus encapsulates very limited amounts of cargos. We report the technique of NanOstirBar (NOB)-EnabLed Single Particle Analysis (NOBEL-SPA) that utilizes NOBs, which are superparamagnetic nanorods easily handled by a magnet or a rotating magnetic field, to act as isolated "islands" for EV immobilization and cargo confinement. NOBEL-SPA permits rapid inspection of single EV with high confidence by confocal fluorescence microscopy, and can assess the colocalization of selected protein/microRNA (miRNA) pairs in the EVs produced by various cell lines or present in clinical sera samples. Specific EV sub-populations marked by the colocalization of unique protein and miRNA combinations have been revealed by the present work, which can differentiate the EVs by their cells or origin, as well as to detect early-stage breast cancer (BC). We believe NOBEL-SPA can be expanded to analyze the co-localization of other types of cargo molecules, and will be a powerful tool to study EV cargo loading and functions under different physiological conditions, and help discover distinct EV subgroups valuable in clinical examination and therapeutics development.