Abstract
Here we report a low-cost synthetic approach for the direct fabrication of large-area Au nanourchin arrays on indium tin oxide (ITO) via a facile galvanic-cell-reaction-driven deposition in an aqueous solution of chloroauric acid and poly(vinyl pyrrolidone) (PVP). The homogeneous Au nanourchins are composed of abundant sharp nanotips, which can served as nanoantennas and increase the local electromagnetic field enhancement dramatically. Finite element theoretical calculations confirm the strong electromagnetic field can be created around the sharp nanotips and located in the nanogaps between adjacent tips of the Au nanourchins. In addition, the interparticle nanogaps between the neighboring Au nanourchins may create additional hotspots, which can induce the higher electromagnetic field intensity. By using rhodamine 6G as a test molecule, the large-area Au nanourchin arrays on ITO exhibit active, uniform, and reproducible surface-enhanced Raman scattering (SERS) effect. To trial their practical application, the Au nanourchin arrays are utilized as SERS substrates to detect 3,3’,4,4’-tetrachlorobiphenyl (PCB-77) one congener of polychlorinated biphenyls (PCBs) as a notorious class of persistent organic pollutants. The characteristic Raman peaks can be still identified when the concentration of PCB-77 is down to 5 × 10−6 M.
Highlights
After the galvanic-cell-reaction-driven deposition had proceeded for 5 h, large-scale homogeneous Au nanourchin arrays are achieved on the indium tin oxide (ITO) wafer, as shown in the top-view scanning electron microscope (SEM) images (Figure 2a,b)
The enlarged-view SEM image (Figure 2b) reveals that flocky Au nanourchins with an average diameter of ~650 nm are uniformly deposited on the ITO
The lattice spacing is estimated to be 0.24 nm, which is in good accordance with the distance of the (111) crystal plane of the face-centered cubic Au crystals, demonstrating that the growth of the Au nanotips preferentially occurs in the (111) directions
Summary
Gold (Au) nanostructures have received widespread research interests, due to their fascinating size- and shape-dependent physicochemical properties [1,2,3,4,5,6], and their various promising applications in catalysis [7,8], chemical sensing [9,10,11,12], plasmonics [13], and surface-enhanced Raman scattering (SERS) [14,15,16,17,18,19,20,21,22]. The individual nanourchin is composed of many sharp nanotips serving as nanoantennas, where localized surface plasmons (LSPs) can be excited by the incident light to enhance. Nanomaterials 2018, 8, 265 many sharp nanotips serving as nanoantennas, where localized surface plasmons (LSPs) can be excited by the incident light to enhance the local electromagnetic (EM) field intensity by 2–5 orders tohfemloagcanliteuledcetr[o3m5].aTghneertiecfo(EreM, i)t ficaenldbienetexnpseictytebdyth2a–t5thoredcehresmoifcmalaignnerittuAdue n[3a5n]o. HHoowweevveerr,, AAuu nnaannoouurrcchhiinnss aacchhiieevveedd bbyy the colloidal ssttrraatteeggyy aarree nnoott tthhee ooppttiimmaall ooppttiioonn ffoorr wwaaffeerr--bbaasseedd aapppplliiccaattiioonnss,, iinncclluuddiinngg ooppttiiccss,, eelleeccttrrooccaattaallyyssiiss,, chemical//bbiioocchheemmical sseennssiinngg,,aannddSESERRSSsusbusbtrsatrtaeste. SScchheemmaattiicc iilllluussttrraattiioonn ffoorr tthhee ffoorrmmaattiioonn ooff AAuu nnaannoouurrcchhiinn aarrrraayyss oonn iinnddiiuumm ttiinn ooxxiiddee ((IITTOO)) tthhrroouugghh ggaallvvaanniicc--cceellll--rreeaaccttiioonn--ddrriivveenn ddeeppoossiittiioonn
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