Liquid biopsy for determining the presence of cancer
and the underlying
tissue of origin is crucial to overcome the limitations of existing
tissue biopsy and imaging-based techniques by capturing critical information
from the dynamic tumor heterogeneity. A newly emerging liquid biopsy
with extracellular vesicles (EVs) is gaining momentum, but its clinical
relevance is in question due to the biological and technical challenges
posed by existing technologies. The biological barriers of existing
technologies include the inability to generate fundamental details
of molecular structure, chemical composition as well as functional
variations in EVs by gathering simultaneous information on multiple
intra-EV molecules, unavailability of holistic qualitative analysis,
in addition to the inability to identify tissue of origin. Technological
barriers include reliance on EV isolation with a few labeled biomarkers,
resulting in the inability to generate comprehensive information on
the disease. A more favorable approach would be to generate holistic
information on the disease without the use of labels. Such a marker-free
diagnosis is impossible with the existing liquid biopsy due to the
unavailability clinically validated cancer stem cells (CSC)-specific
markers and dependence of existing technologies on EV isolation, undermining
the clinical relevance of EV-based liquid biopsy. Here, CSC EVs were
employed as an independent liquid biopsy modality. We hypothesize
that tracking the signals of CSCs in peripheral blood with CSC EVs
will provide a reliable solution for accurate cancer diagnosis, as
CSC are the originators of tumor contributing to tumor heterogeneity.
We report nanoengineered 3D sensors of extremely small nano-scaled
probes self-functionalized for SERS, enabling integrative molecular
and functional profiling of otherwise undetectable CSC EVs. A substantially
enhanced SERS and ultralow limit of detection (10 EVs per 10 μL)
were achieved. This was attributed to the efficient probe–EV
interaction due to the 3D networks of nanoprobes, ensuring simultaneous
detection of multiple EV signals. We experimentally demonstrate the
crucial role of CSC EVs in cancer diagnosis. We then completed a pilot
validation of this modality for cancer detection as well as for identification
of the tissue of origin. An artificial neural network distinguished
cancer from noncancer with 100% sensitivity and 100% specificity for
three hard to detect cancers (breast, lung, and colorectal cancer).
Binary classification to distinguish one tissue of origin against
all other achieved 100% accuracy, while simultaneous identification
of all three tissues of origin with multiclass classification achieved
up to 79% accuracy. This noninvasive tool may complement existing
cancer diagnostics, treatment monitoring as well as longitudinal disease
monitoring by validation with a large cohort of clinical samples.