A General Strategy to Make an On-Demand Library of Structurally and Functionally Diverse SERS Substrates

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for sensing molecules proximal to suitable coinage metal surfaces. The physical structure of the SERS-active metal layer and its support is a key design parameter inspiring considerable, and frequently specialized, efforts in substrate fabrication. The necessary gold film structure can arise from both the metallization process and the underlying support structure, and the structure of the support can deliver additional functions including analytical capabilities such as physical filtering. We used electroless plating as a general approach to create a library of SERS substrates: SERS-active gold films on a range of supports made from a variety of materials, made with a mixture of simple and complex fabrication histories, and offering a selection of structurally-derived functions. The result was that supports with existing functions had their capabilities enhanced by the addition of SERS sensing. Electroless plating thus offers a host of beneficial characteristics 3 for nanofabricating multifunctional SERS substrates, including: tolerance to substrate composition and form factor; low equipment overhead requirements; process chemistry flexibility—including compatibility with conventional top-down nanofabrication; and a lengthy history of commercial application as a simple metallization technique. We gold-plated standard nanofabrication-compatible silicon nitride support surfaces with planar and porous architectures, and with native and polymer-grafted surface chemistries. We used the same plating chemistry to form SERS-active gold films on cellulose fibers arrayed in commercial filter paper and formed into nanocellulose paper. In a functional sense, we used electroless plating to augment nanoporous filters, chromatography platforms, and nanofabrication building blocks with SERS capability

Surveying silicon nitride nanopores for glycomics and heparin quality assurance

Polysaccharides have key biological functions and can be harnessed for therapeutic roles, such as the anticoagulant heparin. Their complexity—e.g., \u3e100 monosaccharides with variety in linkage and branching structure—significantly complicates analysis compared to other biopolymers such as DNA and proteins. More, and improved, analysis tools have been called for, and here we demonstrate that solid-state silicon nitride nanopore sensors and tuned sensing conditions can be used to reliably detect native polysaccharides and enzymatic digestion products, differentiate between different polysaccharides in straightforward assays, provide new experimental insights into nanopore electrokinetics, and uncover polysaccharide properties. We show that nanopore sensing allows us to easily differentiate between a clinical heparin sample and one spiked with the contaminant that caused deaths in 2008 when its presence went undetected by conventional assays. The work reported here lays a foundation to further explore polysaccharide characterization and develop assays using thin-film solidstate nanopore sensors

Solution-Based Photo-Patterned Gold Film Formation on Silicon Nitride

Silicon nitride fabricated by low-pressure chemical vapor deposition (LPCVD) to be silicon-rich (SiNx), is a ubiquitous insulating thin film in the microelectronics industry, and an exceptional structural material for nanofabrication. Free-standingcompelling, particularly when used to deliver forefront molecular sensing capabilities in nanofluidic devices. We developed an accessible, gentle, and solution-based photo-directed surface metallization approach well-suited to forming patterned metal films as integral structural and functional features in thin-membrane-based SiNx devices—for use as electrodes or surface chemical functionalization platforms, for example—augmenting existing device capabilities and properties for a wide range of applications

Electroless Plating of Thin Gold Films Directly onto Silicon Nitride Thin Films and into Micropores

A method to directly electrolessly plate silicon-rich silicon nitride with thin gold films was developed and characterized. Films with thicknesses \u3c100nm were grown at 3 and 10°C between 0.5 and 3 hours, with mean grain sizes between ~20-30nm. The method is compatible with plating free-standing ultrathin silicon nitride membranes, and we successfully plated the interior walls of micropore arrays in 200nm-thick silicon nitride membranes. The method is thus amenable to coating planar, curved, and line-of-sight-obscured silicon nitride surfaces

A Simple and Cost-Effective Nanopore Fabrication Platform with Microcontroller Technology

With growing interest in solid-state nanopore sensing—a single molecule technique capable of profiling a host of analyte classes—establishing facile and scalable approaches for fabricating molecular size pores is gaining considerable traction. The introduction of nanopore fabrication by controlled breakdown (CBD) has transformed the economics and accessibility of nanopore fabrication. Here, we present an Arduinobased, portable CBD device, with an estimated cost of less than 120 USD (≳10x cheaper than most laboratory implementations), to fabricate pores of less than 5 nm in diameter. Using this device, 40 pores with sizes between ~2.5 nm and ~12.6 nm diameter were fabricated. The device is constructed with offthe-shelf readily available components, powered through the same cable used for data transmission, and controlled using a highly customizable MATLAB application, which has capabilities encompassing pore fabrication, pore enlargement, and current-voltage acquisition for pore size estimation. This creates a holistically portable sensing platform when coupled with portable amplifiers: a critical step towards onfield solid-state nanopore sensing applications

“Lights, Camera, Questions and Answers!”: Talking About Science on Camera

Three video packages taken from on-camera interviews, discussion a range of topics from motivations for choosing careers in science, to discussions of the societal implications of scientific research

Electroless Plating of Thin Gold Films Directly onto Silicon Nitride Thin Films and into Micropores

A method to directly electrolessly plate silicon-rich silicon nitride with thin gold films was developed and characterized. Films with thicknesses <100 nm were grown at 3 and 10 °C between 0.5 and 3 h, with mean grain sizes between ∼20 and 30 nm. The method is compatible with plating free-standing ultrathin silicon nitride membranes, and we successfully plated the interior walls of micropore arrays in 200 nm thick silicon nitride membranes. The method is thus amenable to coating planar, curved, and line-of-sight-obscured silicon nitride surfaces