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in vivo capture microenvironments 114,115 . As comprehensively documented in Table 5,

these engineered platforms demonstrate remarkable specificity and efficiency in

isolating three critical classes of oncological biomarkers: CTCs, exosomes, and protein
markers. Contemporary technological advances have yielded microfluidic designs that

incorporate (1) biomimetic surface topographies for enhanced cellular interactions, (2)

tunable fluidic parameters for size-based exosome sorting, and (3) nanostructured

interfaces for ultrasensitive protein detection - collectively representing a paradigm

shift in liquid biopsy technologies 116 .

5.1 Microfluidic Isolation and Detection of CTCs

CTCs are tumor cells found in circulation, shed from malignancies to enter the

bloodstream and migrate to distant organs forming metastases 117 . Dissemination from

primary tumors initiates metastasis and is a major cause of cancer mortality. CTCs are

extremely rare versus blood cells, making their separation from circulation or tumor

cells from body fluids significant for diagnosis, monitoring, and metastasis

understanding. In metastatic patients, peripheral blood CTC concentration is typically
extremely low (< 10 cells/mL). Efficient recovery of highly pure, viable single CTCs

or clusters from large blood volumes (> 5 mL) poses the core technological challenge.

Early strategies relied on CTC-specific surface markers like epithelial cell adhesion

molecule (EpCAM), exemplified by the antibody-based "CTC-chip". However,

affinity-based capture applicability is limited for non-epithelial tumors (e.g., melanoma)

and CTCs undergoing epithelial-mesenchymal transition (EMT) with downregulated

EpCAM 118 . Sorting technologies based on physical properties (size, density,

deformability, electrical impedance, acoustics) have advanced rapidly to address this.

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Notably, Fachin et al. developed a microfluidic device called CTC-iChip to separate
CTCs based on cell size and EpCAM expression heterogeneity, overcoming CTC

heterogeneity challenges (Figure 6A).

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