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Matrix-Independent Surface-Enhanced Raman Scattering Detection of Uranyl Using Electrospun Amidoximated Polyacrylonitrile Mats and Gold Nanostars.

ABSTRACT: Reproducible detection of uranyl, an important biological and environmental contaminant, from complex matrixes by surface-enhanced Raman scattering (SERS) is successfully achieved using amidoximated-polyacrylonitrile (AO-PAN) mats and carboxylated gold (Au) nanostars. SERS detection of small molecules from a sample mixture is traditionally limited by nonspecific adsorption of nontarget species to the metal nanostructures and subsequent variations in both the vibrational frequencies and intensities. Herein, this challenge is overcome using AO-PAN mats to extract uranyl from matrixes ranging in complexity including HEPES buffer, Ca(NO3)2 and NaHCO3 solutions, and synthetic urine. Subsequently, Au nanostars functionalized with carboxyl-terminated alkanethiols are used to enhance the uranyl signal. The detected SERS signals scale with uranyl uptake as confirmed using liquid scintillation counting. SERS vibrational frequencies of uranyl on both hydrated and lyophilized polymer mats are largely independent of sample matrix, indicating less complexity in the uranyl species bound to the surface of the mats vs in solution. These results suggest that matrix effects, which commonly limit the use of SERS for complex sample analysis, are minimized for uranyl detection. The presented synergistic approach for isolating uranyl from complex sample matrixes and enhancing the signal using SERS is promising for real-world sample detection and eliminates the need of radioactive tracers and extensive sample pretreatment steps.

SUBMITTER: Lu G

PROVIDER: S-EPMC6354247 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Matrix-Independent Surface-Enhanced Raman Scattering Detection of Uranyl Using Electrospun Amidoximated Polyacrylonitrile Mats and Gold Nanostars.

Lu Grace G Johns Adam J AJ Neupane Binita B Phan Hoa T HT Cwiertny David M DM Forbes Tori Z TZ Haes Amanda J AJ

Analytical chemistry 20180517 11

Reproducible detection of uranyl, an important biological and environmental contaminant, from complex matrixes by surface-enhanced Raman scattering (SERS) is successfully achieved using amidoximated-polyacrylonitrile (AO-PAN) mats and carboxylated gold (Au) nanostars. SERS detection of small molecules from a sample mixture is traditionally limited by nonspecific adsorption of nontarget species to the metal nanostructures and subsequent variations in both the vibrational frequencies and intensiti ...[more]

PMID: 29741873

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Project description:Naturally occurring uranium is a widespread contaminant present in the water resources around the abandoned uranium mines in the southwest United States. A novel method for rapid uranium detection has been recently developed that relies on the sequestering of uranium by amidoximated polyacrylonitrile (AO-PAN) polymer mats and uses the Raman-active (ν1) symmetric stretch as the signal. The Raman signals obtained from uranium bearing AO-PAN were challenging to interpret due to an unknown uranyl speciation on the surface of the mats. Herein, we provide the synthesis and structural characterization of six model coordination compounds that contain acetamidoxime/benzamidoxime (AAO/BAO) coordinated to the uranyl cation: [UO2(η1-AAO)(NO3)2(H2O)] (1), [UO2(η1-AAO)2(NO3)2] (2), [UO2(η2-BAO)2(CH3OH)2] (3), [(UO2)3(η2-BAO)3(μ2-NO3)3] (4), [(UO2)4(μ3-O)2(μ2-BAO)4(η1-BAO)4(H2O)2](NO3)4 (5), and [(UO2)4(μ3-O)2(μ2-BAO)4(η1-BAO)6Na(NO3)2](NO3)3 (6). Solid-state Raman spectra of 1-6 showed dramatic differences in the uranyl ν1 symmetric stretch depending on the coordination of the amidoxime functional group. The assignments made from the solid-state Raman spectra were used to deconvolute the solution-state Raman spectra of uranyl-acetamidoxime/benzamidoxime methanol solutions at different metal to ligand molar ratios. At low molar ratios (1 U:1 AAO/BAO and 1 U:2 AAO/BAO) the dominant species is the uranyl coordinated via the η1-oxygen atom of the oxime group, while at high molar ratios (1 U:3 AAO/BAO and 1 U:4 AAO/BAO) the dominant species are a tetrameric uranyl-μ3-O-η1-amidoxime complex similar to compounds 5 and 6 and a uranyl-η2-amidoxime complex similar to compounds 3 and 4. Solid-state Raman spectra showed good agreement with Raman signals obtained from the uranyl-AO-PAN mats, demonstrating that binding motifs between uranyl and amidoxime in compounds 5 and 6 are the most representative of the uranyl species on the surface of the AO-PAN mats.

Project description: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.

Dataset Information

Matrix-Independent Surface-Enhanced Raman Scattering Detection of Uranyl Using Electrospun Amidoximated Polyacrylonitrile Mats and Gold Nanostars.

Publications

Matrix-Independent Surface-Enhanced Raman Scattering Detection of Uranyl Using Electrospun Amidoximated Polyacrylonitrile Mats and Gold Nanostars.

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