A biosensor is an analytical device containing a biological recognition element immobilized on a solid surface and a transduction element which converts analyte binding events into a measurable signal . There are various transducers including optical, magnetic, electrochemical, radioactive, piezoelectric, micromechanical, and mass spectrometric .
Optical transducers are highly sensitive to biomolecular targets, insensitive to electromagnetic interference, and present real time response to biomolecular interactions. Main optical methods employed in biosensors include fluorescence spectroscopy, interferometry, and surface plasmon resonance.
Nano-structured plasmonic sensors are emerging sensing platforms permitting low-cost, miniaturized, on-chip biosensing without requiring bulky prism-coupling configuration in conventional surface plasmon resonance (SPR) sensors . While these new sensing platforms have significant advantages, the main drawback of the existing plasmonic sensors is their relatively low sensitivity and high detection limit as compared to the conventional SPR technique. As a result, recently, there is wide spread interest in developing novel plasmonic sensing platforms with enhanced sensing performance.
Surface Plasmon Resonance (SPR) or Localized Surface Plasmon Resonance (LSPR) works on evanescent electromagnetic fields. It can monitor a wide range of analyte surface binding interactions such as absorption of small molecules, proteins, antibody antigen, DNA and RNA hybridization. Both SPR and LSPR methods are label free sensing methods and do not require labeling of the target molecules with different types of reagents, such as fluorescent dyes.
Surface enhanced Raman scattering (SERS) has been used as a signal transduction mechanism in biological and chemical sensing. Examples are trace analysis of pesticides anthrax, prostate-specific antigen, glucose, and nuclear waste. SERS has also been implemented for identification of bacteria, genetic diagnostics, and immunoassay labelling. A miniaturized and inexpensive SERS device can be used in clinics, field, and urban settings.
Various biomolecular interactions have been exploited in SPR and LSPR biosensors including antigen-antibody, receptor-ligand, hormone-receptor, streptatividin-biotin, protein-protein, protein-DNA, even detection of conformational changes in an immobilized protein.
Extracted and edited from “Nano-plasmonic Biosensors: A Review” by “Daryoush Mortazavi, Abbas Z. Kouzani, Akif Kaynakand Wei Duan, 2011”