First, the LSPR λ max of bare Au nanoshells was measured to be 830 nm. The LSPR λ max after incubation to the BSA solution
was measured to be 885 nm, corresponding to an additional 55-nm red shift, which was a wavelength shift two times larger than that of the reported nanohole substrate as a femtomole-level LSPR sensor [18]. Also, we confirmed that this peak position was not shifted after immersion in water. Furthermore, since the BSA molecule has no selective adsorption, this peak shift was attributed to the LSPR response to the changing of the local refractive index with the adsorption of BSA, which physically adsorbed to the gold surface of nanoshells and the substrate at the gap of nanoshells. It is indicated that we can improve the detection Temozolomide ic50 efficiency by localizing learn more the adsorption area of the target molecule without gold film directly laminated on the glass substrate. After immersion in water for 24 h, it is found that the λ max of nanoshell arrays returned to 834 nm. It is revealed that the
red shift of peak position was due to the physical adsorption of BSA proteins. Additionally, it is indicated that the LSPR peak did not return to its initial position because of the incomplete removal of BSA only with immersion in water. For application to bio/chemical detection devices, it should be noted that the signal transduction Chorioepithelioma mechanism in this nanosensor is a reliably measured wavelength shift in the NIR region. Figure 4 LSPR spectra of nanoshells before/after BSA attachment in (a) Au and (b) Cu nanoshell arrays. All spectra were collected in the air. Figure 4b shows the change
of LSPR properties taken from Cu nanoshell arrays before/after incubation to the BSA solution. In the air, the LSPR λ max of the bare Cu nanoshell arrays was measured to be 914 nm. Exposure to the BSA solution resulted in LSPR λ max = 944 nm, corresponding to an additional 30-nm red shift. In the case of Cu nanoshells, they exhibited a not so low sensitivity to the adsorption of molecule relative to Au. While Cu nanoshell arrays have problems to solve about their oxide layer and chemical stability, it is possible for inexpensive Cu to substitute for Au because of its sensitivity to the adsorption of biomolecule. We could evaluate the difference in LSPR sensing performance by changing the metal materials in the experiment. Conclusion In summary, we successfully fabricated uniform metal nanoshell arrays in a large area (30 × 60 mm2) on glass substrates and characterized the geometry and the optical properties based on the LSPR of the Au, Ag, and Cu nanoshell arrays. The LSPR λ max of Au and Cu were at longer wavelengths than that of Ag nanoshell arrays of similar structural parameters. This result indicates that Au and Cu are superior to Ag as materials for NIR light-responsive plasmonic sensors.