Inkjet-printed Ag micro-/nanostructure clusters on Cu substrates for in-situ pre-concentration and surface-enhanced Raman scattering

Abstract

Effective surface-enhanced Raman scattering (SERS) detection requires substrates that are typically fabricated using expensive, low-throughput and time-consuming micro-/nanofabrication processes such as photolithography, electron-beam lithography and template- assisted methods Here, a novel micro-/nanofabrication technique for fabricating SERS substrates with hydrophobicity gradients is demonstrated. An inkjet printer enables injecting an AgNO3 solution onto a thiol-functionalized superhydrophobic Cu surface, upon which Ag micro/nanostructures are generated via replacement reactions in the droplet-injected areas. When a mixed solution of target analytes and Au-nanoparticles (Au-NPs) are placed on this substrate, the contact area decreases over time due to the evaporation of the solution and the hydrophobicity of the substrate. As a result, the analyte molecules and Au-NPs are delivered to the Ag micro-/nanostructure clusters, upon which the analyte and Au-NPs are simply and easily concentrated in situ. With the cooperation of Ag nanoplates and Au-NPs, two antibiotics at very low concentrations (e.g., 100 pM 6-aminopenicillanic acid and 50 pM penicillin G sodium) were successfully detected, confirming the higher SERS activity than that of Ag-nanoplate-assembled nanotube arrays or an Ag-NPs decorated graphene electrophoretic pre-concentration device. Hence, this rapid design-to-prototype method for substrates with adjustable wetting properties can be very useful for a SERS platform to detect various target analytes in biosamples.