Surface enhanced Raman spectroscopy on a flat graphene surface

Abstract

Surface enhanced Raman spectroscopy (SERS) is an attractive analytical technique, which enables single-molecule sensitive detection and provides its special chemical fingerprints. During the past decades, researchers have made great efforts towards an ideal SERS substrate, mainly including pioneering works on the preparation of uniform metal nanostructure arrays by various nanoassembly and nanotailoring methods, which give better uniformity and reproducibility. Recently, nanoparticles coated with an inert shell were used to make the enhanced Raman signals cleaner. By depositing SERS-active metal nanoislands on an atomically flat graphene layer, here we designed a new kind of SERS substrate referred to as a graphene-mediated SERS (G-SERS) substrate. In the graphene/ metal combined structure, the electromagnetic "hot" spots (which is the origin of a huge SERS enhancement) created by the gapped metal nanoislands through the localized surface plasmon resonance effect are supposed to pass through the monolayer graphene, resulting in an atomically flat hot surface for Raman enhancement. Signals from a G-SERS substrate were also demonstrated to have interesting advantages over normal SERS, in terms of cleaner vibrational information free from various metal-molecule interactions and being more stable against photo-induced damage, but with a comparable enhancement factor. Furthermore, we demonstrate the use of a freestanding, transparent and flexible "G-SERS tape" (consisting of a polymer-layer-supported monolayer graphene with sandwiched metal nanoislands) to enable direct, real time and reliable detection of trace amounts of analytes in various systems, which imparts high efficiency and universality of analyses with G-SERS substrates.atomically smooth substrate | metal-molecule isolation | signal fluctuation | mediator | application F or almost all sorts of analytical methods, the dream to improve their sensitivity as well as their reproducibility and to optimize the analytical process (e.g., to simplify the sample preparation/ measurement procedures for quick analysis and to enable in situ and real time monitoring) is a long-term pursuit. Spectroscopic approaches based on fluorescence, infrared absorption and Raman scattering have been developed with rising importance for various sensing and imaging applications. Among them, Raman scattering provides more structural information (characteristic vibrational information of each chemical bond) over fluorescence, and higher spatial resolution (shorter excitation wavelength) over infrared absorption (1). However, as Raman scattering is an inelastic scattering process with a very low crosssection, it is not very sensitive and thus has limited analysis efficiency and applicability.Because of this, surface enhanced Raman spectroscopy (SERS) has been developed since the 1970s (2-4) to enable ultrasensitive characterization down to the single-molecule level (5, 6), comparable to single-molecule fluorescence spectroscopy (7). In a SERS experiment, a rough metal surface or colloid...

Label-Free SERS Selective Detection of Dopamine and Serotonin Using Graphene-Au Nanopyramid Heterostructure

“…Such preferential enhancement for ring related modes is believed to stem from chemical enhancement rendered by graphene. 32 The π−π interactions between graphene and ring structures in dopamine as well as serotonin are believed to be a major contributing factor. 33,34 As shown in Figure 6, when the concentration is reduced to 10 −10 M, the most easily recognized Raman peaks left are that of the 1482 cm −1 peak of dopamine and the 1423 and 1547 cm −1 peaks of serotonin.…”

Plasmon-driven reaction controlled by the number of graphene layers and localized surface plasmon distribution during optical excitation

“…A comparison between these two spectra of PATP on graphene and 1G-coated ABNA shows that PATP cannot covert to DMAB on chemically inert graphene without metal, even though a higher laser power is employed. Furthermore, Zhang's group reported the Raman spectra of a self-assembled monolayer of PATP on a flat Au and Ag surface by graphene-mediated SERS tapes 13 . Although PATP was anchored on the flat gold surface and had been isolated from the hot spot (Ag and Au nanoparticle gap) by graphene that was one atom thick, the weak and ignored characteristic Raman peaks of DMAB still emerged at approximately 1390 and 1430 cm 21 .…”

“…In a graphene-mediated SERS (G-SERS) substrate [13][14][15][16][17][18] ; the monolayer graphene (1G) provides an atomically flat surface for Raman enhancement. Because the graphene surface is chemically inert, signals from G-SERS substrates have great advantages over normal SERS by providing cleaner vibrational information free from various metal-molecule interactions (molecules cannot interact with the chemically active metal by graphene-mediated interactions) and being more stable against photo-induced damage 13 . Furthermore, the ultrasensitive graphene-plasmonic hybrid platform for label-free SERS detection is approaching single-molecule detection 18 .…”

Direct measurement of the Raman enhancement factor of rhodamine 6G on graphene under resonant excitation

“…Our results suggest that there are two kinds of GERS mechanisms, and they are able to increase and decrease the Raman cross-sections, respectively. Since R6G is a widely used Raman probe, a deeper understanding of the interaction of R6G and graphene gives us the opportunity to collect more reliable signals when using SERS on a flat graphene surface [27], which is a method that promises to provide cleaner and more reproducible Raman signals. Direct measurement of the Raman enhancement factor can be applied to a larger class of GERS and other chemical mechanismdominant Raman enhancement situations [28,29], which may involve high fluorescence quantum yield dyes.…”