Characterizing penetration depths of multi-wavelength surface plasmon resonance sensor using silica beads

A multi-wavelength surface plasmon resonance (Dr-SPR) sensor consisting of three excitation wavelengths at 665 nm, 980 nm, and 1480 nm has been demonstrated. The use of three excitation wavelengths not only provides three penetration depths of 186 nm, 570 nm, and 1395 nm but also enables depth-resolving capability. To verify its depth-resolving capability, three silica bead sizes of 150 nm, 540 nm, and 1860 nm were used to form bead monolayers with different thicknesses on the sensor chip surface. It is found that the Dr-SPR produces the maximum response when the bead size matches the penetration depth. The demonstration provides a unique technique to characterize penetration depths of SPR using multiple excitation wavelengths. It also opens a variety of applications in which particles can be used as a biomedical/biochemical marker and tracked by the Dr-SPR.