Influence of silver-nanoparticle layer in a chiral sculptured thin film for surface-multiplasmonic sensing of analytes in aqueous solution

Abstract

Multiple surface-plasmon-polariton (SPP) waves at a single free-space wavelength can be guided by the interface of a metal and a chiral sculptured thin film (STF). Multilayers comprising a chiral STF of lanthanum fluoride deposited on an aluminum thin film deposited on a glass substrate were fabricated. In some chips, a 5-nm-thick layer of silver nanoparticles was deposited at one of two selected depths in the chiral STF. The chips were then deployed in a prism-coupled configuration in a custom-built machine for surface multiplasmonic resonance imaging (SMPRI), in order to observe the effects the silver-nanoparticle layer on the multiple SPP-wave modes. The angular locations of the SPP-wave modes were found to be not greatly dependent on whether the silver-nanoparticle layer was deposited after the first or the second period of a three-periods-thick chiral STF. With aqueous solutions of sucrose as infiltrant fluids, the angular shifts of the SPP-wave modes were determined as the refractive index of the infiltrant fluid increased. The use of a charge-coupled devices (CCD) camera and upgraded motion-control equipment for SMPRI was found to increase the sensitivity of the chip. The silver-nanoparticle layer was also found to enhance the sensitivity.

Hybrid Surface Plasmon Polariton Wave Generation and Modulation by Chiral-Graphene-Metal (CGM) Structure

“…The chiral material exhibits optical rotation phenomena and supports right circular polarization (RCP) and Left circular polarization (LCP) wave propagation, which means that the Transverse Magnetic (TM) and Transverse Electric (TE) modes cannot be studied independently, which is clear from the constitutive relationships i.e., D = ε E − jξ B and H = − jξ E + B / μ 24,25 . The following phasors that qualify all the characteristics of chiral material are given below; the E z and H z fields components in chiral components can be express as the superposition of the two given modes 28 where and are solutions to the wave equation that satisfy the wave equation when …”

Artificial neural network to estimate the refractive index of a liquid infiltrating a chiral sculptured thin film

“…Noting that most applications for biosensors involve small concentrations of analytes dispersed in solvents of refractive index close to that of water (n water = 1.333), we chose to calculate various R and R for n inf ∈ [1.3, 1.4] for equal increments ∆n inf = 0.0111 and ∆n inf ≈ 0.000503, respectively, as determined by J. All R and R were calculated for φ ∈ [−25 • , 24.8 • ] in steps of ∆φ = 0.2 • , which can be related [31] to θ by the standard law of refraction, yielding θ = 45 • + sin −1 n −1 prism sin φ for the prism with a 45 • -90 • -45 • triangle as its cross section. All data were computed using Mathematica R running on a laptop computer with a 4-core 2.4-GHz processor and 16 GB of RAM.…”

“…SPP-wave modes are capable of being excited by incident light of an arbitrary polarization state in the prism-coupled configuration when a periodically nonhomogeneous dielectric material is partnering a metal thin film [20]. However, experiments have shown that using p-polarized incident light results in a higher sensitivity over s-polarized incident light, based on the definition [31]…”

“…In order to evoke SPR in practice, many geometric configurations have been devised to couple incident light to the SPP wave guided by the metal/delectric interface. The most commonly implemented configuration is a prism-coupled configuration called the Turbadar-Kreschmann-Raether (TKR) configuration [22,23], wherein a metal film of thickness L met and a dielectric film of thickness L diel are successively deposited onto one face of a substrate, thus establishing a sensor chip [31]. The substrate has the same refractive index as a prism of refractive index n prism which exceeds n diel = √ ε diel , our assumption being that both n prism and n diel are real and positive.…”

“…The different SPP-wave modes have their peak field within the partnering dielectric material at different distances from the interface [20]. If the periodically nonhomogeneous dielectric material is porous and is infiltrated by a fluid of refractive index n inf , theory shows [29] and experiment has confirmed [30,31] that the locations of all SPP-wave modes in the graph of R vs. θ shift with n inf , thereby enabling optical-sensing applications.…”