Blood coagulation
is a critical defense mechanism against bleeding
that results in the conversion of liquid blood into a solid clot through
a complicated cascade, which involves multiple clotting factors. One
of the final steps in the coagulation pathway is the conversion of
fibrinogen to insoluble fibrin mediated by thrombin. Because coagulation
disorders can be life-threatening, the development of novel methods
for monitoring the coagulation cascade dynamics is of high importance.
Here, we use near-infrared (NIR)-fluorescent single-walled carbon
nanotubes (SWCNTs) to image and monitor fibrin clotting in real time.
Following the binding of fibrinogen to a tailored SWCNT platform,
thrombin transforms the fibrinogen into fibrin monomers, which start
to polymerize. The SWCNTs are incorporated within the clot and can
be clearly visualized in the NIR-fluorescent channel, where the signal-to-noise
ratio is improved compared to bright-field imaging in the visible
range. Moreover, the diffusion of individual SWCNTs within the fibrin
clot gradually slows down after the addition of thrombin, manifesting
a coagulation rate that depends on both fibrinogen and thrombin concentrations.
Our platform can open new opportunities for coagulation disorder diagnostics
and allow for real-time monitoring of the coagulation cascade with
a NIR optical signal output in the biological transparency window.