Using Ambient Ion Beams to Write Nanostructured Patterns for Surface Enhanced Raman Spectroscopy

Abstract

Electrolytic spray deposition was used to pattern surfaces with 2D metallic nanostructures. Spots that contain silver nanoparticles (AgNP) were created by landing solvated silver ions at desired locations using electrically floated masks to focus the metal ions to an area as little as 20 mm in diameter. The AgNPs formed are unprotected and their aggregates can be used for surface-enhanced Raman spectroscopy (SERS). The morphology and SERS activity of the NP structures were controlled by the surface coverage of landed silver ions. The NP structures created could be used as substrates onto which SERS samples were deposited or prepared directly on top of predeposited samples of interest. The evenly distributed hot spots in the micron-sized aggregates had an average SERS enhancement factor of 10 8 . The surfaces showed SERS activity when using lasers of different wavelengths (532, 633, and 785 nm) and were stable in air.Metallic nanoparticles have attractive properties in catalysis, photonics, and chemical sensing. [1] Raman spectroscopy is a powerful nondestructive technique, [2] the sensitivity of which can be significantly improved through surfaceenhanced or tip-enhanced methods. [3] The enhancement arises from the proximity of the analytes to intense localized fields created by nanoscale objects. [4] The capability to modify, coat, and pattern surfaces with nanostructures is important for SERS and also for a wider range of nanomaterials applications. [5] Conventionally, modified surfaces are constructed by delivering intact nanoparticles to target locations through dropcasting or spin coating. [6] However, the difficulty in positioning discrete particles with control over orientation, position, and degree of aggregation means that drop casting of nanoparticles has not been widely used in the highthroughput preparation of SERS substrates. Immobilized and shell-isolated nanosystems [5b, 6c, 7] address these issues, but the necessary vacuum preparation procedures significantly increase the complexity of such approaches.Ion/surface collisions including ion soft-landing have been used to fabricate surface structures under vacuum. [8] Recently an electrolytic spray ionization method [9] has been developed that is capable of generating noble metal ions directly from their solids under ambient conditions as precursors for nanoparticle synthesis. Herein, we report the in situ fabrication of SERS-active spots and micro-scale patterns by landing ionized silver at desired locations where spontaneous cathodic reduction takes place, allowing the creation of nanostructure assemblies.Silver is a widely used SERS material [10] and the plasmon resonance of silver nanostructures is tunable through the visible to mid-infrared regions of the electromagnetic spectrum. [11] Electrolytic spray deposition readily creates spots of approximately 3 mm in diameter composed of silver particles (AgNP) at desired locations, both on top of previously deposited analyte as well as prior to analyte deposition (Figure 1). Both the NP-on-top and ...

From Isolated Ions to Multilayer Functional Materials Using Ion Soft Landing

“…This development has important implications for the preparation of metal clusters and nanoparticles for catalysts and optical sensors, including species that are not readily synthesized in solution. For example, ambient ion beams combined with nonconductive masks were used to prepare structured patterns of Ag nanoparticles for surface‐enhanced Raman spectroscopy (SERS) with substantial enhancement factors of up to 10 8 . In another study, soft landing was used to create 2D nano‐networks of molecules on graphite under ambient conditions.…”

On‐Demand Ambient Ionization of Picoliter Samples Using Charge Pulses

“…Because it is isolated from the sample solutions, the primary electrospray ionization source also provides opportunities for versatile chemistries 20. As one example, noble metal ions from electrolytic spray ionization of silver21 and gold16b, 17 in the primary ion source were used as cationization reagents22 for the soft ionization of olefins and alkynes in steroids, vitamin D3, and 3‐octyne (Figures 2 c, S9 and S10).…”

Recent Advances of In‐Source Electrochemical Mass Spectrometry

“…[48] Van Berkel utilized a photodiode array detector to explore the electrolytic induced corrosion of a stainless-steel emitter in ESI. [49] In addition to iron and zinc, [48][49][50] electro-corrosion of other transition metals like copper, silver and gold [51][52][53] was also observed in nanoESI. Cooks group found that the electrolysis of copper, silver and gold wires in anhydrous acetonitrile in nanoESI can generate monovalent metal species (free metal and metal clusters with water and acetonitrile).…”