Abstract
Surface plasmon resonance (SPR) allows for real-time, label-free optical detection of many chemical and biological substances. Having emerged in the last two decades, it is a widely used technique due to its non-invasive nature, allowing for the ultra-sensitive detection of a number of analytes. This review article discusses the principles, providing examples and illustrating the utility of SPR within the frame of plasmonic nanobiosensing, while making comparisons with its successor, namely localized surface plasmon resonance (LSPR). In particular LSPR utilizes both metal nanoparticle arrays and single nanoparticles, as compared to a continuous film of gold as used in traditional SPR. LSPR, utilizes metal nanoparticle arrays or single nanoparticles that have smaller sizes than the wavelength of the incident light, measuring small changes in the wavelength of the absorbance position, rather than the angle as in SPR. We introduce LSPR nanobiosensing by describing the initial experiments performed, shift-enhancement methods, exploitation of the short electromagnetic field decay length, and single nanoparticle sensors are as pathways to further exploit the strengths of LSPR nanobiosensing. Coupling molecular identification to LSPR spectroscopy is also explored and thus examples from surface-enhanced Raman spectroscopy are provided. The unique characteristics of LSPR nanobiosensing are emphasized and the challenges using LSPR nanobiosensors for detection of biomolecules as a biomarker are discussed.
Highlights
In particular optical nanobiosensors are at the forefront of research measuring both catalytic and affinity reactions by utilizing a number of optical transduction routes,[2] such as absorption, fluorescence, phosphorescence, Raman, surface enhanced Raman spectroscopy (SERS) and dispersion spectroscopy measuring a number of property changes such as energy, polarization, decay time, phase and amplitude
Comparing surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) biosensing we note that the resonance conditions in LSPR can be achieved without the need for adaptive optics as in SPR reducing engineering challenges
It is evident that recent advances in nanotechnology have had a substantial impact in plasmonic nanobiosensing leading from the more conventional SPR biosensors which have been around since the 1990’s to novel LSPR designs based on the properties of metallic nanoparticles
Summary
T HE advancement of nanoscale materials over the last two decades has led to the introduction of nanobiosensors offering highly sensitive detection at the single molecular level as well as enabling the advancement of point of care diagnostics.[1,2,3,4,5,6,7] In particular optical nanobiosensors are at the forefront of research measuring both catalytic and affinity reactions by utilizing a number of optical transduction routes,[2] such as absorption, fluorescence, phosphorescence, Raman, surface enhanced Raman spectroscopy (SERS) and dispersion spectroscopy measuring a number of property changes such as energy, polarization, decay time, phase and amplitude. More specific the electric field of the incident light leads to collective excitations of the electrons in the conduction band resulting in ‘coherent localized plasmon oscillations with a resonant frequency depending on the composition, size, geometry, dielectric environment and separation distance of the NPs’.[31,32,33] Resonance in LSPR can be achieved without the need for adaptive optics as in SPR. As most LSPR methods involve ensembles of nanoparticles that can have different sizes, the signals obtained are average signals and can exhibit heterogeneous broadening (Figure 9), compared to the signal from each individual resonance of a single nanoparticle
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