Surface plasmon resonance microscopy (SPRM), also called surface plasmon resonance imaging (SPRI), is a label free analytical tool that combines the surface plasmon resonance of metallic surfaces with imaging of the metallic surface. The heterogeneity of the refractive index of the metallic surface imparts high contrast images, caused by the shift in the resonance angle. SPRM can achieve a sub-nanometer thickness sensitivity and lateral resolution achieves values of micrometer scale. SPRM is used to characterize surfaces such as self-assembled monolayers, multilayer films, metal nanoparticles, oligonucleotide arrays, and binding and reduction reactions. Surface plasmon polaritons are surface electromagnetic waves coupled to oscillating free electrons of a metallic surface that propagate along a metal/dielectric interface. Since polaritons are highly sensitive to small changes in the refractive index of the metallic material, it can be used as a biosensing tool that does not require labeling. SPRM measurements can be made in real-time, such as measuring binding kinetics of membrane proteins in single cells, or DNA hybridization.

The concept of classical SPR has been since 1968 but the SPR imaging technique was introduced in 1988 by Rothenhäusler and Knoll. Capturing a high resolution image of low contrast samples for optical measuring techniques is a near impossible task until the introduction of SPRM technique that came into existence in the year 1988. In SPRM technique, plasmon surface polariton (PSP) waves are used for illumination. In simple words, SPRI technology is an advanced version of classical SPR analysis, where the sample is monitored without label through the use of a CCD camera. The SPRI technology with the aid of CCD camera gives advantage of recording the sensograms and SPR images, and simultaneously analyzes hundreds of interactions.

Surface plasmons or surface plasmon polaritons are generated by coupling of electrical field with free electrons in a metal. SPR waves propagate along the interface between dielectrics and a conducting layer rich in free electrons.

As shown in Figure 2, when light passes from a medium of high refractive index to a second medium with a lower refractive index, the light is totally reflected under certain conditions.

In order to get total internal reflection (TIR), the θ₁ and θ₂ should be within a certain range that can be explained through the Snell's law. When light passes through a high refractive index media to a lower refractive media, it is reflected at an angle θ₂, which is defined in Equation 1.^{[citation needed]}

In the TIR process some portion of the reflected light leaks a small portion of electrical field intensity into medium 2 (η₁ > η₂). The light leaked into the medium 2 penetrates as an evanescent wave. The intensity and penetration depth of the evanescent wave can be calculated according to Equations 2 and 3, respectively.

Figure 3 shows a schematic representation of surface plasmons coupled to electron density oscillations. The light wave is trapped on the surface of the metal layer by collective coupling to the electrons of the metal surface. When the electron's plasma and the electric field of the wave light couple their frequency oscillations they enters into resonance.

Recently, the leakage light inside of the metal surface had been imaged. Radiation of different wavelengths (green, red and blue) was converted into surface plasmon polaritons, through the interaction of the photons at the metal/dielectric interface. Two different metal surfaces were used; gold and silver. The propagation length of the SPP along the x-y plane (metal plane) in each metal and photon wavelength were compared. The propagation length is defined as the distance traveled by the SPP along the metal before its intensity decreases by a factor of 1/e, as defined in Equation 4.^{[citation needed]}