Magnetic Nanoparticle
Mediated Enhancement of Localized
Surface Plasmon Resonance for Ultrasensitive Bioanalytical Assay in
Human Blood Plasma
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Abstract
We demonstrate that Fe<sub>3</sub>O<sub>4</sub> magnetic
nanoparticle
(MNP) can greatly enhance the localized surface plasmon resonance
(LSPR) of metal nanoparticle. The high refractive index and molecular
weight of the Fe<sub>3</sub>O<sub>4</sub> MNPs make them a powerful
enhancer for plasmonic response to biological binding events, thereby
enabling a significant improvement in the sensitivity, reliability,
dynamic range, and calibration linearity for LSPR assay of small molecules
in a trace amount. Rather than using fluorescence spectroscopy or
magnetic resonance imaging, this study marks the first use of the
label-free LSPR nanosensor for a disease biomarker in physiological
solutions, providing a low cost, clinical-oriented detection. This
facile and ultrasensitive nanosensor with an extremely light, robust,
and low-cost instrument is attractive for miniaturization on a lab-on-a-chip
system to deliver point-of-care medical diagnostics. To further evaluate
the practical application of Fe<sub>3</sub>O<sub>4</sub> MNPs in the
enhancement of LSPR assay, cardiac troponin I (cTnI) for myocardial
infarction diagnosis was used as a model protein to be detected by
a gold nanorod (GNR) bioprobe. MNP-captured cTnI molecules resulted
in spectral responses up to 6-fold higher than direct cTnI adsorption
on the GNR sensor. The detection limit (LOD) was lowered to ca. 30
pM for plasma samples which is 3 orders lower than a comparable study.
To the best of our knowledge, this marks the lowest LOD for a real
plasma protein detection based on label-free LSPR shift without complicated
instrumentation. The observed LSPR sensing enhancement by Fe<sub>3</sub>O<sub>4</sub> MNPs is independent of nonspecific binding