Highly Sensitive Detection of Caspase‑3 Activities
via a Nonconjugated Gold Nanoparticle–Quantum Dot Pair Mediated
by an Inner-Filter Effect
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Abstract
We describe here a simple fluorometric
assay for the highly sensitive detection of caspase-3 activities on
the basis of the inner-filter effect of gold nanoparticles (AuNPs)
on CdTe quantum dots (QDs). The method takes advantage of the high
molar absorptivity of the plasmon band of gold nanoparticles as well
as the large absorption band shift from 520 to 680 nm upon nanoparticle
aggregation. When labeled with a peptide possessing the caspase-3
cleavage sequence (DEVD), the monodispersed Au-Ps (peptide-modified
AuNPs) exhibited a tendency to aggregate when exposed to caspase-3,
which induced the absorption band transition from 520 to 680 nm and
turned on the fluorescence of the CdTe QDs for caspase-3 sensing.
Under optimum conditions, a high sensitivity towards caspase-3 was
achieved with a detection limit as low as 18 pM, which was much lower
than the corresponding assays based on absorbance or other approaches.
Overall, we demonstrated a facile and sensitive approach for caspase-3
detection, and we expected that this method could be potentially generalized
to design more fluorescent assays for sensing other bioactive entities