Coffee-ring effect-based simultaneous SERS substrate fabrication and analyte enrichment for trace analysis

Abstract

Based on the "coffee-ring effect", we developed a highly efficient SERS platform which integrates the fabrication of SERS-active substrates and the preconcentration of analytes into one step. The high sensitivity, robustness, reproducibility and simplicity make this platform ideal for on-site analysis of small volume samples at low concentrations in complex matrices.Since its invention in the 1970s, 1,2 surface-enhanced Raman spectroscopy (SERS) has been receiving growing interest in a variety of areas due to its inherent merits such as a high signalto-noise ratio, non-photobleaching features and the use of single photoexcitation. 3 These features make SERS one of the most powerful techniques for non-destructive, on-site and in vivo analysis of chemical and biological substances. 4 However, the utilization of SERS in determination of trace analytes is restricted by the sophisticated and expensive nanofabrication of highly SERS-active substrates, as well as its limited sensitivity and selectivity for trace substances in complex matrices due to the swamping of the analyte signal in background molecule signals. For example, while the concentrations of PAHs in the environment are commonly in the range of 10 À12 to 10 À9 g L À1 , the lowest detection limits available with a well-designed SERS substrate are in the range of 3 Â 10 À6 to 1.78 Â 10 À4 g L À1 . 5 To meet the requirements for analysis of trace analytes in complex matrices, metallic substrates were tailored to increase the signal strength, and analytes were preconcentrated before SERS analysis. As these two approaches are very complicated and timeconsuming, it is highly desired to develop a fast, simple and robust approach to simultaneously perform the self-assembling of SERS substrates and preconcentration of trace analytes.One technique that holds great promise in this regard is the "coffee-ring effect", which refers to the accumulation of a ringlike dense array on the border by evaporating a droplet of aqueous solution containing nonvolatile solutes such as organic small molecules, biomacromolecules, polymers, and nanoparticle microspheres on solid surfaces. In this process, the three-phase contact line among the atmosphere, droplet and solid substrate is pinned, and a remarkable capillary ow happens because of the evaporation of solvents, driving solutes to move outward from the inner side to the rim of the droplet. Consequently, solutes are highly concentrated along the original droplet edge. It was found that the coffee-ring effect is applicable for enriching both chemical and biological substances. 6-11 One example is its application in normal Raman spectrometry that is termed as drop coating deposition Raman (DCDR). 10 In recent years, the coffee-ring effect has become a powerful tool for self-structuring of nanomaterials. [12][13][14][15] Herein, we report the development of a novel SERS platform by integrating the generation of SERS substrates and the enrichment of analytes into one step. We demonstrate the benets of the coffee-ring effect in co...

Ultrasensitive SERS-Based Plasmonic Sensor with Analyte Enrichment System Produced by Direct Laser Writing

“…It is clearly seen that the approach presented in this work provides one of the best concentration factors, which is beneficial regarding fabrication cost. [43] and hydrophobic [43][44][45][46] surfaces, microtextured [42,47,48] and nanotextured [49][50][51][52] hydrophobic surfaces, hierarchical superhydrophobic [15,42,46,53,54] and superomniphobic [55][56][57] surfaces, slippery surface [17], as well as hierarchical nonuniform superhydrophobic surfaces [16,58,59]. The result obtained in this work is marked by the red star.…”

Leveraging coffee‐ring effect on plasmonic paper substrate for sensitive analyte detection using Raman spectroscopy

“…The direct deposition of the analytes on the plasmonic paper substrate also plays a role in reproducibility of the signals. It presents an entirely complementary method compared with the ones where the liquid phase consists of mobile nanoparticles, the analyte molecules and the external aggregating agents, a combination of which may result in variable hot spot formation . The single component liquid phase in case of the plasmonic paper method makes the deposition process relatively independent of the variation of sample pH or other external factors, thus ensuring uniform enhancement from preformed hot spots.…”

Ultrasensitive SERS-Based Plasmonic Sensor with Analyte Enrichment System Produced by Direct Laser Writing

“…When combined with their reduced reflectivity (which allows more efficient excitation), the strong broadband electromagnetic enhancement supported by the textures printed with double pulses makes these structures promising for SERS-based applications. the concentration factors calculated as a ratio between an initial volume of a water droplet V and the deposition area size S d according to previously reported data for the water droplets evaporating on surfaces with different wetting characteristics and morphology including flat hydrophilic [40] and hydrophobic [40][41][42][43] surfaces, microtextured [44][45][46] and nanotextured [47][48][49][50] hydrophobic surfaces, hierarchical superhydrophobic [15,43,44,51,52] and superomniphobic [53][54][55] surfaces, slippery surface [17] as well as hierarchical nonuniform superhydrophobic surfaces [16,56,57]. The result obtained in this work is marked by the red star.…”