Dual-mode surface plasmon resonance sensor chip using a grating 3D-printed prism

Abstract

The method for fabricating a grating prism surface plasmon resonance (SPR) sensor chip was developed. The grating prism was 3D-printed by a stereolithography 3D printer and subsequently created a grating pattern by soft lithography. A gold film was thermally evaporated on the grating prism. Moreover, a liquid cell was 3D-printed and assembled into a gold-coated grating prism. To make the sensor chip compact and practical, a compatible prism holder was 3D-printed by a fused deposition model 3D printer. The SPR sensor chip was mounted on the rotation stage and the SPR spectrum was recorded by spectrometer. The SPR excitation of the sensor chip can be extended to the near-infrared region by creating a grating pattern on the prism surface. A gold-coated grating prism exhibited dual modes of SPR excitations, namely, prism-coupling SPR (PC-SPR) and grating-coupling SPR (GC-SPR). The dual-mode SPR excitation was observed at the incident angles of 45°-80°. When the incident angle increased, the SPR excitation of the PC-SPR mode exhibited a blue shift in the wavelength region of 480-690 nm, whereas the GC-SPR mode exhibited a red shift in the wavelength region of 670-770 nm. The surface plasmon (SP) dispersion obtained from the dual-mode SPR configuration confirmed observable PC-SPR (which corresponded to + SP⁰ of the gold-resin interface) and GC-SPR (which corresponded to -SP⁺¹ of the gold-air interface), which could be excited from the developed substrate. The refractive index sensitivities of the PC-SPR and GC-SPR modes were 2924.4 and 414.9 nm RIU^-1, respectively. The SPR excitations of the sensor chip exhibited a simultaneous shift when the local refractive index of the materials adjacent to the gold-coated grating prism surface was changed, especially the material that had overlapping light absorption at the SPR excitation wavelength. Using this fabrication process, the prism is designed and then printed; moreover, the grating pattern on the prism surface can be employed to tune the SPR excitation wavelength of the sensor chip for the versatility and broad perspective of the optical sensing-based SPR.

Keywords: 3D printing; Grating; Polymeric prism; Soft lithography; Surface plasmon resonance.