Localized Surface Plasmon Resonance Theory

Localized Surface Plasmon Resonance vs. Surface Plasmon Resonance

How is LSPR Different from SPR?

Localized surface plasmon resonance is generated by metal nanoparticles, typically gold and silver, as compared to a continuous film of gold as used in traditional SPR.

OpenSPR is similar in many ways to traditional SPR, and provides the same data using the same experimental conditions and procedures. To the user, everything would seem the same between other SPR instruments and OpenSPR. However, OpenSPR uses what is known as localized surface plasmon resonance (LSPR).
Localized surface plasmon resonance is generated by metal nanoparticles, typically gold and silver, as compared to a continuous film of gold as used in traditional SPR. LSPR produces a strong resonance absorbance peak in the visible range of light, with its position being highly sensitive to the local refractive index surrounding the particle. Therefore, OpenSPR measures small changes in the wavelength of the absorbance position, rather than the angle as in traditional SPR.
localized surface plasmon resonance theory
Using LSPR instead of SPR has a number of significant advantages:
  • The optical hardware needed for LSPR is much less complex since no prism is needed to couple the light, so the instrument can be made smaller and more affordable
  • Since the angle is not important, the instrument is much more robust against vibration and mechanical noise
  • LSPR is not as sensitive to bulk refractive index changes, which causes errors in experimental data, because it has a much shorter electromagnetic field decay length
  • No strict temperature control is needed, simplifying the instrument
  • The sensor chips can be manufactured at a much more affordable price
  • Easier to use and maintain
Although SPR sensors have a much higher refractive index sensitivity (m or RIS) than LSPR sensors,  their sensitivity towards biomolecular binding events is similar. This is due to the much shorter electromagnetic decay length (ld) of nanoparticles compared to gold films, which confines the response to a smaller sensing volume. An LSPR’s sensor response (R) to an absorbed layer can be modeled with the following equation:
localized surface plasmon resonance theory
Where ∆n is the difference in refractive index between the absorbed layer and the surrounding medium, and d is the thickness of the absorbed layer.

The smaller decay length of SPR versus LSPR is illustrated in the image below. This smaller sensing volume means that LSPR is more sensitive to molecular binding and less sensitive to bulk effects. The smaller decay length and sensitivity associated with LSPR reduces artifacts caused by external variables such as temperature drift or buffer refractive index changes.

localized surface plasmon resonance theory