Gold Nanorod Array-Bridged Internal-Standard SERS Tags: From Ultrasensitivity to Multifunctionality

Abstract

Bimetallic gold core−silver shell (Au@Ag) surfaceenhanced Raman scattering (SERS) tags draw broad interest in the fields of biological and environmental analysis. In reported tags, silver coating tended to smooth the surface and merge the original hotspot of Au cores, which was disadvantageous to signal enhancement from the aspect of surface topography. Herein, we developed gold nanorod (AuNR)-bridged Au@Ag SERS tags with uniform three-dimensional (3D) topography for the first time. This unique structure was achieved by selecting waxberry-like Au nanoparticles (NPs) as cores, which were capped by vertically oriented AuNR arrays. Upon selective surface blocking with thiol− ligands, Ag NPs were controlled to anisotropically grow on the tips of the AuNRs, producing high-density homo-(Ag−Ag) and hetero-(Au−Ag) hotspots in a single NP. The 3D hotspots rendered this NP extraordinary SERS enhancement ability (an analytical enhancement factor of 3.4 × 10 6) 30 times higher than the counterpart with a smooth surface, realizing signal detection from a single NP. More importantly, multiplexing signals ("blank" or multiplex "internal standard") can be achieved by simply changing thiol−ligands, as exemplified in the synthesis of NPs with 8 signatures. Furthermore, the multifunctionality has been demonstrated in living cell/in vivo imaging, photothermal therapy, and SERS substrates for ratiometric quantitative analysis, relying on the inherent internal standard signal. The prepared Au@Ag NPs have great potential as standard tools in many SERS-related fields.

Towards practical and sustainable SERS: a review of recent developments in the construction of multifunctional enhancing substrates

“…The most widely used strategy to introduce self-calibration functionality in SERS substrates is to modify the enhancing surface with a self-assembled monolayer of Raman tag molecules. [197][198][199][200] Typical examples of Raman tag molecules include 4-mercaptobenzoic acid (MBA) and 5,5-dithio-bis-(2nitrobenzoic acid) (DTNB, also known as "Ellman's Reagent") which adsorb strongly to Ag/Au surfaces to generate intense and distinct Raman vibration bands that could be compared against the SERS signals of analytes to improve the accuracy of quantitative detection. 94,201 However, a problem with these conventional Raman tag molecules is that their signature peaks often lie within the Raman fingerprint region and therefore overlaps with the SERS signals of the analyte, which make data analysis difficult.…”

Tunable LSPR of silver/gold bimetallic nanoframes and their SERS activity for methyl red detection

“…10 Various kinds of SERS substrates have been designed, such as Au@Ag coreshell nanorods, gold nanorods, Ag/Au nanospheres, Ag-Au hollow nanocubes, Au-Cu nanorods, and so on. [10][11][12][13][14] In the SERS imaging technique, SERS substrates are responsible for the generation of an optical signal and typically consist of noble metallic nanoparticles and specic Raman reporter molecules coated on a materials surface for producing characteristic scattering signals. 12 Nanoplate or nanoframe structures can enhance electromagnetic eld due to their localized surface plasmon resonance (LSPR) properties, which can improve the sensitivity of the SERS signal.…”

Optimum fabrication parameters for preparing high performance SERS substrates based on Si pyramid structure and silver nanoparticles

“…Some authors have shown that strong localized surface plasmon resonance (LSPR) occurs at the nanoscale of noble metals, which can greatly improve the SERS signal (SERS hot spots). [4][5][6][7][8][9][10][11][12][13][14][15][16][17] There are two mechanisms for increasing SERS signal widely accepted. Those are electromagnetic (EM) enhancement and chemical enhancement.…”