Gold‐polymer nanocomposites: studies of their optical properties and their potential as SERS substrates

Abstract

Polymer-nanometallic-particle composites have demonstrated technological potential owing to their unique optical and electrical properties. In this article, we report on composites prepared via physical vapor deposition of gold metal onto pliable polydimethylsiloxane (PDMS) polymer. Rapid Au diffusion and nanometallic-particle formation in a phase-separated surface layer of the PDMS creates unique tunable sub-surface-based composites. The rate of deposition and average Au thickness can be manipulated to tune the optical properties, which are studied by visible wavelength optical extinction spectrometry and surfaceenhanced Raman scattering (SERS). DC conductivity measurements were made during Au deposition to study percolation conditions for the materials and depth profiling was performed by X-ray photoelectron spectrometry (XPS). This work presents the use of Au-PDMS nanocomposites in combination with a sample translation technique (STT) for the improved SERS qualitative and quantitative analysis. This translation approach considerably improves the reproducibility and the sensitivity of the technique by minimizing the thermal and photolytic effects inherent in SERS. The Au-PDMS nanocomposites exhibit an affinity for amine and nitro-based compounds that are biologically relevant and point toward the potential for being used as substrates for biologically based SERS experiments. Sample Raman spectra with the nanocomposite under STT-SERS conditions are included.

Analytical optimization of nanocomposite surface‐enhanced Raman spectroscopy/scattering detection in microfluidic separation devices

“…It should be noted that, with the 633 nm laser currently used for all Raman spectral collection, silver substrates offer enhancement of two-fold to an order of magnitude greater intensity than gold substrates, due to the agreement between irradiation wavelength and the enhancing metal's dielectric properties, size, shape, and interparticle arrangement. A compendium of such physical property comparisons is given in Table 1 and a more detailed description of the properties of these nanocomposites can be found in our prior reports [17,18]. The percolation threshold represents the point when millivolt applied potential results in microamperes of current as measured in situ during metal deposition onto elastomer.…”

“…To create gold nanocomposites, or gold-PDMS (Au-PDMS), the same procedure was followed exactly, except that the gold metal was physically vapor deposited to a nominal thickness of 25 nm at a rate of 0.2 A/s. These processes were carried out to create the metal-polymer nanocomposite SERS detection regions studied in earlier work [17,18].…”

Microsolidics: Fabrication of Three‐Dimensional Metallic Microstructures in Poly(dimethylsiloxane)

“…[19,20] A growing interest in flexible sensors and displays has fueled the development of polymer-metal composites. Research in this field includes composites of metal in PDMS with optical functions, [21] conductive PDMS-carbon nanotube composites, [22,23] substrates for surface-enhanced Raman spectroscopy, [24,25] spherically curved metal oxide semiconductor field-effect transistors, [26] and flexible gold-polymer nanocomposites as passive components. [27,28] In addition to materials with electrical functionality on curved or bendable surfaces, some groups have demonstrated stretchable electronics by patterning stiff materials on compliant polymer surfaces.…”

Applications, techniques, and microfluidic interfacing for nanoscale biosensing

“…Metal nanoparticles can also serve as functional materials for enhancing the performance of a microfluidic platform. For instance, metal nanoparticles have been directly incorporated into or coated onto the channel material (e.g., poly(dimethylsiloxane)(PDMS)) to serve as surfaceenhanced Raman scattering substrates (Giesfeldt et al 2005), to enhance electrophoretic performance , to bind bio-molecular recognition elements (Luo et al 2005), and to develop immobilized enzyme reactors (Zhang et al 2008b). Furthermore, gold nanoparticles self-assembled on a substrate have been demonstrated for coupling of localized surface plasmon energy for thermal mixing (Miao et al 2008) and manipulation of bio-particles (Miao and Lin 2007a, b).…”