muscle cells, and stem cells. [5][6][7][8][9][10][11][12] Although initially considered as membrane debris with no biological significance, the crucial roles of EVs in immune surveillance, viral infection, blood coagulation, tissue repair, and stem cell maintenance, have been sequentially identified since 1996. [6,[13][14][15][16][17][18][19] Additionally, biomolecular compositions inside EVs have also been closely associated with the pathology of various kinds of diseases such as cancers, musculoskeletal diseases, as well as degenerative neurological disorders. [20][21][22] As a result of the fundamental role of EVs in mediating cell-to-cell communications and regulating various tissue functions, there has been a critical need to develop novel therapeutics and diagnostics (or theranostics) using EVs and their associated biomolecules. [23] For example, cellfree therapy using EVs derived from mesenchymal stem cells (MSCs) has been exploited and is currently under clinical trials to enhance tissue regeneration after cardiac infarction. [6,7,17,18] Similarly, EVs capable of crossing the bloodbrain barrier (BBB) have been utilized for intranasal delivery of therapeutics for treating central nervous system (CNS) injuries. [24][25][26][27] Moreover, minimally invasive, highly sensitive/accurate diagnosis of cancer metastasis, viral infection, Prion diseases, Alzheimer's disease (AD), and Parkinson's disease (PD), has also been realized by analyzing the biomolecular formulation of EVs extracted from human body fluids. [28,29] Although the potential of using EVs for theranostic applications is enormous, their current clinical translation is still impeded by several critical barriers, which can be attributed mainly to the high heterogeneity of EVs. In general, there are four levels of heterogeneity of EVs, including size, composition, function, and source heterogeneities. [2,30] Specifically, most clinical applications often require a well-defined source of therapeutics. Sizes, compositions, functions, and sources have all been closely associated with the outcome of clinical treatment and diagnostic diseases. [30][31][32][33][34][35][36] Having the ability to isolate a specific population of EVs with well-defined sizes, biomolecular contents, disease-specific biological functions, and biodistributions would be crucial for the clinical application of EVs. Failing to achieve this can lead to compromised therapeutic effects and sometimes even adverse outcomes. For example, the multifaceted roles of EVs have been identified for regulating Extracellular vesicles (e.g., exosomes) carrying various biomolecules (e.g., proteins, lipids, and nucleic acids) have rapidly emerged as promising platforms for many biomedical applications. Despite their enormous potential, their heterogeneity in surfaces and sizes, the high complexity of cargo biomolecules, and the inefficient uptake by recipient cells remain critical barriers for their theranostic applications. To address these critical issues, multifunctional nanomaterials, such as magn...