Active Gap SERS for the Sensitive Detection of Biomacromolecules with Plasmonic Nanostructures on Hydrogels

Abstract

COMMUNICATIONnanoparticle distance using stimuli-responsive polymers, [ 25,26 ] elastomers, [ 27 ] and DNA [ 28,29 ] have been developed. However, the structures formed using these approaches differ from that of the ideal SERS substrate, which has an extensive regular structure, as described above. Although there is a report on SERS substrates in which gap distance can uniformly change, it did not show the enhancement of trapping effi ciency of large molecules by active gap control. [ 30 ] To address this issue, we have fabricated tunable plasmonic nanostructures with a highly ordered structure through the combination of the self-assembled gold nanoparticles (GNPs) and the use of a hydrogel as a substrate. In our previous report, we demonstrated the transfer of gold dot patterns, fabricated by photolithography and electron-beam lithography, and confi rmed changes in the interval between dots by volume change in the gel. [ 31 ] This result indicates that the gap distance in the GNP-assembled fi lm can be controlled on the gel. Our approach in this study is shown in Scheme 1 . Here, we demonstrate that active gap distance control using tunable plasmonic substrates can signifi cantly intensify the SERS signals of proteins. Therefore, we propose the use of an open-to-closed system for active gap distance control for the sensitive detection of biomacromolecules by SERS.Highly ordered GNP thin fi lm was prepared using the cast method following our previous report. [ 32 ] GNPs (diameter: 20 nm) coated with fl uorinated tetraethylene glycol (FTEG) ligand were cast on piranha-cleaned glass or silicon substrates and dried under ambient conditions. The solvent quickly evaporated and a thin blue-colored fi lm was formed from a redcolored colloidal solution ( Figure 1 B-i, Figure S1A, Supporting Information). This color change resulted from the plasmon coupling effect due to the close proximity of the GNPs. The extinction spectra of this colloidal solution and thin fi lm showed a plasmonic peak shift of ≈90 nm ( Figure S1B, Supporting Information). Atomic force microscopic (AFM) images of the GNP thin fi lm showed that GNPs formed a well-packed, mostly mono-layered, structure with minimum defects on the solid substrates ( Figure S1C, Supporting Information). Scanning electron microscope (SEM) observation of the GNP fi lm prepared on a supported carbon membrane for transmission electron microscopy gave a clear image showing that the interparticle (center-to-center) distance and the gap distance were ≈20.5 nm and ≈1.5 nm, respectively ( Figure S1D, Supporting Information).Transfer of the GNP thin fi lms onto gels was performed by in situ polymerization on the substrates (Figure 1 A). [ 31 ] Molds A surface plasmon resonance is a coherent oscillation of the surface conduction electrons excited by electromagnetic radiation. Research on such light-metal interactions, which are known as plasmonics, has attracted a great deal of attention due to their potential applications in optical or photonic devices and sensors. [1][2][3][4] In...

DNA Brush-Directed Vertical Alignment of Extensive Gold Nanorod Arrays with Controlled Density

“…Metal nanoparticles have an array of attractive electronic, optical, and thermal properties, which have a variety of applications in sensing, 1−3 drug delivery, 4,5 and catalysis. 6,7 To harness these unique properties, their self-assembly into ordered structures is of strategic importance.…”

Reversible changes in the orientation of gold nanorod arrays on polymer brushes

“…Thus, the latter approach, such as embedding into or attachment onto so materials such as elastomers and gels as a supporting matrix, is promising as it allows their distances to be tuned through stretching or compressing the matrices by mechanical forces [30][31][32] or the changing of the matrix volume through variations in the swelling conditions. [33][34][35] These changes in the matrix shape were also applied to actively change the GNR orientations. 36 From the viewpoint of applications, arrays on solid substrates are more preferable.…”

“…To date, a number of actively tunable plasmonic arrays based on changes in the nanoparticle distance on polymer brushes have been reported. 34,[37][38][39][40] However, there are no reports of the active control of GNR orientation using polymer brushes on solid substrates, despite their obvious importance.…”

Nanoscale uniformity in the active tuning of a plasmonic array by polymer gel volume change

“…In any case, the plasmonic peaks were actively tuned by the change in the salt concentration as shown in our previous report using gold nanoparticle assembled lms. 47 There is no doubt that the gold nanodot patterns were actively changed by the volume change in the hydrogels. However, their actual structures in this active tuning remain unclear.…”