Abstract
The unique attributes of surface enhanced Raman spectroscopy (SERS) make it well suited to address the challenges associated with portable diagnostics. However, despite the remarkable progress in this field, where the instrumentation has made great strides forward providing a route to the miniaturization of sensing devices, to date producing three-dimensional low-cost SERS substrates which simultaneously fulfill the multitude of criteria of high sensitivity, reproducibility, tunability, multiplexity, and integratability for rapid sensing has not yet been accomplished. Successful implementation of SERS requires readily fine-tuned nanostructures, which create a high enhancement. Here, an advanced electrofluidynamic patterning (EFDP) technique enables rapid fabrication of SERS active topographic morphologies with high throughput and at a nanoresolution via the spatial and lateral modulation of the dielectric discontinuity due to the high electric field generated across the polymer nanofilm and air gap. The subsequent formation of displacement charges within the nanofilm by coupling to the electric field yield a destabilizing electrostatic pressure and amplification of EFDP instabilities enabling the controllable pattern formation. The top of each gold coated EFDP fabricated pillar generates controllable high SERS enhancement by coupling of surface plasmon modes on top of the pillar, with each nanostructure acting as an individual sensing unit. The absolute enhancement factor depends on the topology as well as the tunable dimensions of the nanostructured units, and these are optimized in the design and engineering of the dedicated EFDP apparatus for reproducible, low-cost fabrication of the three-dimensional nanoarchitectures on macrosurfaces, rendering them for easy integration in further lab-on-a-chip devices. This unique combination of nanomaterials and nanospectroscopic systems lay the platform for a variety of applications in chemical and biological sensing.
Highlights
Surface enhanced Raman spectroscopy (SERS) has been undergoing a renaissance in the past decade, on a trajectory to become the best-positioned analytical technique to posture significant impact on portable sensing
We have previously demonstrated the use of the combination of the electric field and the hydrodynamics for lithography by patterning dielectric materials, conductive and crystalline materials, superapolar lotus-to-rose hierarchical nanosurfaces, with controllable alignment of the internal nanomorphologies.[19−23] Building upon these principles, in this study we systematically explore the localized plasmons in different nanogeometries, delivering an intuitive guidance for appropriate nanostructure design and introducing intelligent engineering of a novel nanolithographic device, which is further exploited to fabricate and control the metallic nanomorphologies with an inherent nanoroughness for tunable surface enhanced Raman spectroscopy
A thin polymer film with an initial thickness, h (h = 80−100 ± 21 nm) is deposited on a bottom electrode, and a second top planar electrode is placed at a controllable distance, d (d = 150−800 ± 53 nm), leaving a certain air gap, which can be adjusted to micronanometer levels of precision (Figure 1a)
Summary
Surface enhanced Raman spectroscopy (SERS) has been undergoing a renaissance in the past decade, on a trajectory to become the best-positioned analytical technique to posture significant impact on portable sensing. SERS, due to its distinctive attributes of rapid detection, high-sensitivity heightened with the capability of detection down to single molecule levels[1−7] as well as multiplexing, all while requiring no complex sample preparation, can be deployed for a breadth of applications ranging from homeland security through to medical diagnostics and biochemical sensors and onto food pathogenesis. Any imperfections in substrates have a significant effect on the definitive response, SERS-active platforms are often plagued by irreproducibility, instability, and a lack of tunability toward specific molecules. SERS substrates with tunable localized surface plasmon resonances (LSPR) which can be interfaced externally (e.g., in electrochemical devices) or Received: May 1, 2020 Accepted: June 22, 2020 Published: June 22, 2020
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