8.4 Surface Plasmon Resonance (SPR)
SPR spectroscopy is a quantitative technique for studying antigen-antibody, DNA-DNA,
DNA-protein, protein-protein, receptor-ligand, peptide-membrane, and protein-membrane
interactions. SPR is a real-time label-free technique for disease diagnosis on a molecular
basis, monitoring of disease development and therapy [18]. In SPR, electron charges os
cillate at the metal-dielectric interface and are termed surface plasmons [19]. It quantifies
the adsorption strength and determines the biological content adsorbed on the gold surface.
It is thus a multiplexed sensing technique used to analyze hundreds to thousands of in
teractions on the metal surface [20].
Alzheimer’s disease (AD) is an age-related neurodegenerative disorder leading to de
mentia and reducing the life expectancy to 50%. Cognitive tests, magnetic resonance
imaging (MRI), and computed tomography (CT) scan are the tools used in diagnosing
AD. Cerebrospinal fluid (CSF) indicates changes in biochemical parameters of AD pa
tients and thus discriminates the patients from healthy individuals. Amyloid beta-peptide
and tau protein are the AD biomarkers. Amyloid beta-peptide causes mitochondrial
dysfunction and neuronal death by binding with 17β-HSD10 enzyme present in the mi
tochondria. In a study conducted by Hegnerová, K. et al., a SPR-based sensor was de
veloped to clinically diagnose AD. The authors immobilized the polyclonal antibody
against 17β-HSD10 through alkyl-thiolates and amino coupling chemistry. SPR-based
biosensor detected 17β-HSD10 enzyme in ng/mL quantity [18,21].
Carcinoma antigen 125 (CA-125) is the ovarian cancer biomarker used in epithelial
ovarian carcinoma. It affects the female reproductive system. This tumor marker has hy
drophilic and lubricating properties. In ovarian cancer, it is expressed in units/mL, unlike
FIGURE 8.1
Dual QD-based FLISA detection of C-reactive protein and serum amyloid A. Adapted with permission [ 17],
Copyright (2019), Elsevier.
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