Semiconducting single-walled carbon nanotubes (SWCNTs)
are versatile
near-infrared (NIR) fluorophores. They are noncovalently modified
to create sensors that change their fluorescence when interacting
with biomolecules. However, noncovalent chemistry has several limitations
and prevents a consistent way to molecular recognition and reliable
signal transduction. Here, we introduce a widely applicable covalent
approach to create molecular sensors without impairing the fluorescence
in the NIR (>1000 nm). For this purpose, we attach single-stranded
DNA (ssDNA) via guanine quantum defects as anchors to the SWCNT surface.
A connected sequence without guanines acts as flexible capture probe
allowing hybridization with complementary nucleic acids. Hybridization
modulates the SWCNT fluorescence and the magnitude increases with
the length of the capture sequence (20 > 10 ≫ 6 bases).
The
incorporation of additional recognition units via this sequence enables a generic route to NIR fluorescent biosensors
with improved stability. To demonstrate the potential, we design sensors
for bacterial siderophores and the SARS CoV-2 spike protein. In summary,
we introduce covalent guanine quantum defect chemistry as rational
design concept for biosensors.
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