SERS detection of uranyl using functionalized gold nanostars promoted by nanoparticle shape and size

Abstract

The radius of curvature of gold (Au) nanostar tips but not the overall particle dimensions can be used for understanding the large and quantitative surface-enhanced Raman scattering (SERS) signal of the uranyl (UO2)(2+) moiety. The engineered roughness of the Au nanostar architecture and the distance between the gold surface and uranyl cations are promoted using carboxylic acid terminated alkanethiols containing 2, 5, and 10 methylene groups. By systematically varying the self-assembled monolayer (SAM) thickness with these molecules, the localized surface plasmon resonance (LSPR) spectral properties are used to quantify the SAM layer thickness and to promote uranyl coordination to the Au nanostars in neutral aqueous solutions. Successful uranyl detection is demonstrated for all three functionalized Au nanostar samples as indicated by enhanced signals and red-shifts in the symmetric U(vi)-O stretch. Quantitative uranyl detection is achieved by evaluating the integrated area of these bands in the uranyl fingerprint window. By varying the concentration of uranyl, similar free energies of adsorption are observed for the three carboxylic acid terminated functionalized Au nanostar samples indicating similar coordination to uranyl, but the SERS signals scale inversely with the alkanethiol layer thickness. This distance dependence follows previously established models assuming that roughness features associated with the radius of curvature of the tips are considered. These results indicate that SERS signals using functionalized Au nanostar substrates can provide quantitative detection of small molecules and that the tip architecture plays an important role in understanding the resulting SERS intensities.

Ultrasensitive and reproducible SERS platform of coupled Ag grating with multibranched Au nanoparticles

“…nanoparticles with the star or urchinlike symmetry. 20,21 Application of these nanoparticles and their assembly 22,23 was reported for the detection of the various molecules in both medical 24,25 and safety 26 fields. However, utilization of gold nanostars is limited by the inhomogeneity of the hot spot distribution, thus making it impossible to predict the enhancement factor along the SERS-active substrate.…”

Review of SERS Substrates for Chemical Sensing

“…Functionalizing the SERS substrates has also been explored to increase specificity and selectivity [2,3,4,5,8,9,10,11,12,14,15,16,17,18,19,21,22,23,24,26,27,30,33,44,48,50,79,139,140,141,142,143,144,145,146]. A PDMS coating over an Au nanoparticle monolayer film (PDMS-Au MLF) composite substrate was fabricated to detect aromatic molecules in aqueous and air samples [5].…”

“…From changes in the spectral peaks of MPY, it was possible to differentiate the two species of mercury as well as to quantify them. SERS has also been used to detect and quantify polyatomic cationic species such as uranyl (UO 2 + ) [21,139]. (Aminomethyl)phosphonic acid (AMA)-modified gold nanoparticles were used to detect uranyl [21].…”

SERS Nanotags and Their Applications in Biosensing and Bioimaging

“…These plasmonic properties can be tuned by changing the physical properties such as shape [44][45][46][47], size [48][49][50][51] and dimensionality (2D and 3D) [52][53][54] of the plasmonic nanostructures. Over the last 3 decades, researchers have made great progress in the development of SERS plasmonic nanostructures to maximize enhancement factors (EFs).…”