Ultrasensitive Surface‐Enhanced Raman Spectroscopy Detection by Porous Silver Supraparticles from Self–Lubricating Drop Evaporation

Abstract

This work demonstrates an original and ultrasensitive approach for surface‐enhanced Raman spectroscopy (SERS) detection based on evaporation of self‐lubricating drops containing silver supraparticles. The developed method detects an extremely low concentration of analyte that is enriched and concentrated on sensitive SERS sites of the compact supraparticles formed from drop evaporation. A low limit of detection of 10−16 m is achieved for a model hydrophobic compound rhodamine 6G (R6G). The quantitative analysis of R6G concentration is obtained from 10−5 to 10−11 m. In addition, for a model micro‐pollutant in water triclosan, the detection limit of 10−6 m is achieved by using microliter sample solutions. The intensity of SERS detection in this approach is robust to the dispersity of the nanoparticles in the drop but became stronger after a longer drying time. The ultrasensitive detection mechanism is the sequential process of concentration, extraction, and absorption of the analyte during evaporation of self‐lubrication drop and hot spot generation for intensification of SERS signals. This novel approach for sample preparation in ultrasensitive SERS detection can be applied to the detection of chemical and biological signatures in areas such as environment monitoring, food safety, and biomedical diagnostics.

Determination of Trace Organic Contaminant Concentration via Machine Classification of Surface-Enhanced Raman Spectra

“…All spectral acquisitions were carried out with 0.1 W power, gratings of 1200 grooves/mm, exposure time of 10 s, and 10 acquisitions with the improved signal-to-noise ratio. 6,22 Machine Learning Techniques. In this work, we employed a supervised classification approach for the prediction of concentrations.…”

“…In the first set (Ouzo), reported by Dabodiya et al, aqueous samples containing R6G or TC were preconcentrated into a tiny droplet by the evaporating Ouzo method. 22 In the second set (Ag-NP), all three compounds were tested using Ag nanostructured Si substrate fabricated using a flow-based approach as reported by Kanike et al 6 Figure 3a provides an overview of the evaporating Ouzo technique, while Figure 3b shows the flow approach. The set of environmental spectra was collected using the methodology from Kanike et al, and its spectra are available in the Supporting Information, Figure S4.…”

“…SERS spectral data was obtained for three different organic compounds: rhodamine 6G (R6G), triclosan (TC), and chlorpyrifos (CP) from other works. , Sourcing for chemicals is as follows: R6G (Fisher Scientific), TC (TCI Chemicals, 98%), and CP (Sigma-Aldrich). Chemicals were selected for their compatibility with SERS and their relevance as municipal water pollutants.…”

“…R6G is a commonly used laser dye compound that is well-established in the SERS literature . Despite having minimal associated environmental concerns, it is an adequate model compound for SERS analysis purposes. , TC is a broad-spectrum antibiotic agent that is used in many household products and is seen as a municipal water pollutant. It has been linked to endocrine disruption in humans as well as acute toxicity in algae .…”

Three-Dimensional Deposits from Drying Particle-Laden Drops

“…This advective flow is caused by the liquid from the interior of the drop rushing toward the TPCL, with the TPCL remaining pinned, to replenish the liquid that is lost from the TPCL due to evaporation. − The ubiquitousness of the coffee ring formation has meant that the presence of such ring-like deposits at the TPCL, occurring during the evaporation of drop containing any type of particle, is generically denoted as the “coffee ring”. The inherent self-assembly process associated with the coffee ring formation has been extensively utilized to self-assemble different types of micro/nanoparticles and chemical species for applications, such as pre-concentrating chemical samples before their analyses, , sensitive detection of organic and biomolecules and their properties, − triggering size-dependent particle separation, and fabricating a variety of materials/structures/functional devices, such as immunoassays, photonic − and plasmonic crystals, conducting wires, − porous films, and scaffolds of different materials, and microcantilevers . At the same time, the “coffee ring” formation has also several disadvantages, such as the formation of nonuniform coating/patterning, formation of trench-like and raised ridge structures during three-dimensional (3D) printing with metal nanoparticle ink, , etc.…”