posted on 2022-01-18, 14:36authored byCongnyu Che, Ruiyang Xue, Nantao Li, Prashant Gupta, Xiaojing Wang, Bin Zhao, Srikanth Singamaneni, Shuming Nie, Brian T. Cunningham
Rapid,
ultrasensitive, and selective quantification of circulating
microRNA (miRNA) biomarkers in body fluids is increasingly deployed
in early cancer diagnosis, prognosis, and therapy monitoring. While
nanoparticle tags enable detection of nucleic acid or protein biomarkers
with digital resolution and subfemtomolar detection limits without
enzymatic amplification, the response time of these assays is typically
dominated by diffusion-limited transport of the analytes or nanotags
to the biosensor surface. Here, we present a magnetic activate capture
and digital counting (mAC+DC) approach that utilizes magneto-plasmonic
nanoparticles (MPNPs) to accelerate single-molecule sensing, demonstrated
by miRNA detection via toehold-mediated strand displacement.
Spiky Fe3O4@Au MPNPs with immobilized target-specific
probes are “activated” by binding with miRNA targets,
followed by magnetically driven transport through the bulk fluid toward
nanoparticle capture probes on a photonic crystal (PC). By spectrally
matching the localized surface plasmon resonance of the MPNPs to the
PC-guided resonance, each captured MPNP locally quenches the PC reflection
efficiency, thus enabling captured MPNPs to be individually visualized
with high contrast for counting. We demonstrate quantification of
the miR-375 cancer biomarker directly from unprocessed human serum
with a 1 min response time, a detection limit of 61.9 aM, a broad
dynamic range (100 aM to 10 pM), and a single-base mismatch selectivity.
The approach is well-suited for minimally invasive biomarker quantification,
enabling potential applications in point-of-care testing with short
sample-to-answer time.