Sensitivity Tuning through Additive Heterogeneous Plasmon Coupling between 3D Assembled Plasmonic Nanoparticle and Nanocup Arrays

Abstract

Plasmonic substrates have fixed sensitivity once the geometry of the structure is defined. In order to improve the sensitivity, significant research effort has been focused on designing new plasmonic structures, which involves high fabrication costs; however, a method is reported for improving sensitivity not by redesigning the structure but by simply assembling plasmonic nanoparticles (NPs) near the evanescent field of the underlying 3D plasmonic nanostructure. Here, a nanoscale Lycurgus cup array (nanoLCA) is employed as a base colorimetric plasmonic substrate and an assembly template. Compared to the nanoLCA, the NP assembled nanoLCA (NP-nanoLCA) exhibits much higher sensitivity for both bulk refractive index sensing and biotin-streptavidin binding detection. The limit of detection of the NP-nanoLCA is at least ten times smaller when detecting biotin-streptavidin conjugation. The numerical calculations confirm the importance of the additive plasmon coupling between the NPs and the nanoLCA for a denser and stronger electric field in the same 3D volumetric space. Tunable sensitivity is accomplished by controlling the number of NPs in each nanocup, or the number density of the hot spots. This simple yet scalable and cost-effective method of using additive heterogeneous plasmon coupling effects will benefit various chemical, medical, and environmental plasmon-based sensors.

3D Plasmon Coupling Assisted Sers on Nanoparticle-Nanocup Array Hybrids

“…The NP-nanoLCA substrate was prepared after fabricating the nanoLCA. Cysteamine, which has both amine and thiol functional groups at each end, was chosen as a linker molecule in order to electrostatically attract negatively charged NPs to the nanoLCA surface 20 , 25 . After treating the nanoLCA surface with cysteamine, 50 nm Au NPs were assembled by incubating for 24 hours.…”

“…After treating the nanoLCA surface with cysteamine, 50 nm Au NPs were assembled by incubating for 24 hours. This resulted in self-assembled monolayer (SAM) of NPs on the nanoLCA substrate, forming the NP-nanoLCA 20 . The SEM image of the NP-nanoLCA in Fig.…”

“…The shifted resonance wavelength when measured in water (i.e., 592 nm), on the other hand, was not exactly the same as the excitation wavelength (i.e, 632 nm). Since the resonance wavelength of the nanoLCA or the NP-nanoLCA linearly red-shifts with increasing surrounding RI 20 , the plasmonic response with varying concentration of glycerol solution (0%, 20%, 40%, 60%, and 100%) on the NP-nanoLCA was tracked. As Fig.…”

Biocompatible Cup‐Shaped Nanocrystal with Ultrahigh Photothermal Efficiency as Tumor Therapeutic Agent

“…The Au nanocup (Au NC), which displays unique optical properties, including efficient light bending and scattering, has drawn attention in recent years, but the fabrication of Au NC with a gentle method is still difficult, hindering its further investigation. The conventional procedure for fabricating Au NC is tedious and expensive, so a new method of preparing Au NC is highly desirable . Using a simple wet chemistry method, Au NC with a controllable plasmonic spectrum was synthesized by the selective overgrowth of Au on lead sulfide, facilitating the bioapplication of these particles.…”

Current achievements of nanoparticle applications in developing optical sensing and imaging techniques

“…Recently, Chang et al developed a plasmon-enhanced SERS colorimetric sensor consisting of a nanostructured Lycurgus cup and nanoparticles in the cup, as illustrated in Fig. 8 , and the feasibility of extraordinary transmission-based SERS ultrasensitive sensing applications was suggested [ 137 , 138 ]. The possibility of enhanced Raman sensors using plasmonic electromagnetic enhancements based on the combination of a stochastic metallic nanostructure substrate and metallic nanoparticles was also recently reported [ 139 ].…”