This work develops a highly sensitive immunoassay sensor for use in graphene oxide sheet (GOS)-based surface plasmon resonance (SPR) chips. This sensing film, which is formed by chemically modifying a GOS surface, has covalent bonds that strongly interact with the bovine serum albumin (BSA), explaining why it has a higher sensitivity. This GOS film-based SPR chip has a BSA concentration detection limit that is 100 times higher than that of the conventional Au-film-based sensor. The affinity constants (KA) on the GOS film-based SPR chip and the conventional SPR chip for 100 μg/ml BSA are 80.82 × 106 M-1 and 15.67 × 106 M-1, respectively. Therefore, the affinity constant of the GOS film-based SPR chip is 5.2 times higher than that of the conventional chip. With respect to the protein-protein interaction, the SPR sensor capability to detect angle changes at a low concentration anti-BSA of 75.75 nM on the GOS film-based SPR chip and the conventional SPR chip is 36.1867 and 26.1759 mdeg, respectively. At a high concentration, anti-BSA of 378.78 nM on the GOS film-based SPR chip and the conventional SPR chip reveals two times increases in the SPR angle shift. Above results demonstrate that the GOS film is promising for highly sensitive clinical diagnostic applications.
In
this article, the excitation of dipolar localized surface plasmon
resonances (LSPRs) in both the far- and near-field regions is described
in terms of the relevant static, dynamic, and radiative depolarization
factors. This approach offers a direct relationship between the evolution
of the LSPR spectral line and the depolarization components in an
analogous sense to a harmonic oscillator. The static, dynamic, and
radiative terms reflect the coefficients of the “stiffness”,
effective mass, and damping in the oscillator system, respectively.
Hence, one can immediately perceive that the static part of the depolarization
factor is mainly responsible for the shifts in the resonant frequency,
and the radiative part is responsible for the change in bandwidth.
Additionally, the dynamic part behaves like an effective mass, acting
as an inertial weighting factor that decides how significant the changes
taking place in the system are. From this model, we can rationalize
that the qualitative behavior of the far-field efficiency primarily
depends on the shifting resonant frequencies, and the corresponding
near-field efficiency is highly sensitive to the presence of damping.
The model also clarifies the discrepancy in the resonant frequency
and bandwidth between the far- and near-field spectra, which is due
to the significant presence of the radiative component. These basic
descriptions can be used as a guiding principle for handling more
sophisticated structures and gaining more rationalized designs for
novel applications related to the LSPR mechanism.
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