Gold Nanostar Spatial Distribution Impacts the Surface-Enhanced Raman Scattering Detection of Uranyl on Amidoximated Polymers

Abstract

The plasmonic properties of carboxylated gold nanostars distributed on amidoximated polyacrylonitrile (AO PAN) electrospun polymer films scale with surface-enhanced Raman scattering (SERS) intensities for coordinated uranium­(VI) oxide (uranyl) species. This two-step plasmonic sensor first isolates uranyl from solution using functionalized polymers; then carboxylated gold nanostars are subsequently deposited for SERS. Spatially resolved localized surface plasmon resonance (LSPR) and SERS facilitate correlated nanostar optical density and uranyl quantification. To reduce sampling bias, gold nanostars are deposited in an inverted drop-coating geometry and measurements are conducted inside resulting nanoparticle coffee rings that form on the polymer substrates. This approach naturally preserves the plasmonic properties of gold nanostars while reducing the deposition of nanoparticle aggregates in active sensing regions, thereby maximizing both the accuracy and the precision of SERS measurements. Several advances are made. First, second-derivative analysis of LSPR spectra facilitates the quantification of local nanostar density across large regions of the sensor substrate by reducing background variations caused by the polymeric and gold materials. Second, local nanostar densities ranging from 140 to 200 pM·cm are shown to result in uranyl signals that are independent of nanostar concentration. Third, the Gibbs free energy of uranyl adsorption to carboxylated nanostars is estimated at 8.4 ± 0.2 kcal/mol. Finally, a linear dynamic range from ∼0.3 to 3.4 μg U/mg polymer is demonstrated. Signals vary by 10% or less. As such, the uniformity of the plasmonic activity of distributed gold nanostars and the employment of spatially resolved spectroscopic measurements on the composite nanomaterial sensor interface facilitate the quantitative detection of uranyl while also reducing the dependence on user expertise and the selected sampling region. These important advances are critical for the development of a user-friendly SERS-based sensor for uranyl.

Research progress of SERS on uranyl ions and uranyl compounds: a review

“…To eliminate SERS signal fluctuations derived from heterogeneous plasmonic distributions at coffee ring regions, A. J. Haes' group developed an inverted drop-coating geometry, making nanoparticle aggregates formed at the center of the droplet rather than at its edge. 45 Consequently, the linear dynamic range was from 0.3 to 3.4 mg U mg À1 polymer with signals varying less than 10% (Fig. 9b).…”

“…To further improve the adsorption selectivity of substrates for uranyl ions, A. J. Haes' group distributed gold nanostars functionalized with carboxyl-terminated alkanethiols on amidoximated polyacrylonitrile electrospun polymer films. 44,45 Herein, they utilized amidoximated polyacrylonitrile to selectively extract uranyl ions from the solution and gold nanostars to enhance Raman signals (Fig. 9a).…”

“…So far, a number of articles have focused on the trace analysis of uranyl ions and uranyl compounds based on the SERS technique since S. Dai et al first put forward the SERS effect of uranyl ions. 33 Most of the SERS substrates are gold or silver nanostructures, including silver-doped sol-gel films, 33,34 silver and gold nanoparticles, [35][36][37] surfacefunctionalized silver and gold nanoparticles, [38][39][40][41][42][43][44][45][46][47][48] nanofabricated ellipse-sphere dimer, 49 silver nanorods, 50,51 inert materialwrapped silver nanorods, 52,53 Ag 2 O aggregates, 54 and DNAmodified silver and gold nanostructures. [55][56][57][58][59] In order to improve the SERS intensity of uranyl ions as much as possible, it is essential to elucidate the SERS mechanisms of uranyl ions on gold and silver nanostructures.…”

“…Copyright 2018 American Chemical Society. (b) SERS signals for uranyl were plotted as a function of U uptake per mg polymer 45. Reproduced with permission.…”

Plasmonic Nanostars: Systematic Review of their Synthesis and Applications

“…AuNSts were also used to develop sensors for detecting and quantifying various other harmful analytes, from bisphenol A (BPA) and clenbuterol to the uranyl cation , in radioactive waste, as summarized in Table . These studies further highlighted the high performance and versatility of AuNSt-based sensors for the detection, quantification, and monitorization of many nonbioanalytes, which are harmful and toxic to human health and the environment.…”