Macroscopical monolayer films of ordered arrays of gold nanoparticles as SERS substrates for in situ quantitative detection in aqueous solutions

Abstract

In this work, macroscopical monolayer films of ordered arrays of gold nanoparticles (MMF-OA-Au NPs) are successfully prepared at the interfaces of toluene-diethylene glycol (DEG) with a water volume fraction of...

Large-Area Monolayer Films of Hexagonal Close-Packed Au@Ag Nanoparticles as Substrates for SERS-Based Quantitative Determination

“…Due to the poor solubility of citrate ions in the DEG phase, the remaining citrate ions can quickly transfer from the oil phase into the DEG phase containing a proper amount of water (10% v/v) during the interfacial self-assembly to reduce the residual negative charges among NPs (Scheme 1d). 37 Therefore, high- quality LAMFs of Au@Ag NPs can be fabricated at the interface of toluene−DEG containing a proper amount of water. Three types of high-quality LAMF-HCP-Au 5.5 @Ag m NPs (Figures 3, S5 and S6) were successfully fabricated by our improved self-assembly method, 37 in which the ligands on the surfaces of these as-prepared Au 5.5 @Ag 5.25 NPs have to be exchanged from citrate into OLA using the phase transfer technology.…”

“…37 Therefore, high- quality LAMFs of Au@Ag NPs can be fabricated at the interface of toluene−DEG containing a proper amount of water. Three types of high-quality LAMF-HCP-Au 5.5 @Ag m NPs (Figures 3, S5 and S6) were successfully fabricated by our improved self-assembly method, 37 in which the ligands on the surfaces of these as-prepared Au 5.5 @Ag 5.25 NPs have to be exchanged from citrate into OLA using the phase transfer technology. It is found that the resulting LAMF-HCP-Au 5.5 @ Ag 5.25 NPs on the surface of the DEG phase show a fuchsia color and their area can be up to 30 cm 2 , as shown in the optical photograph (Figure 3a).…”

“…7,8 Moreover, both citrate ions and OLA ligands hardly have any SERS signals during the SERS detection, which have been widely reported in previous works. 37,43,47 Thus, the presence of citrate ions and OLA ligands in the LAMFs will not affect their performance as SERS substrates. Furthermore, LAMF-HCP-Au@Ag NP@PDMS substrates could be easily obtained by transferring the resulting LAMF-HCP-Au@Ag NPs onto PDMS substrates (insets in Figures 3f, S5f and S6f, respectively), in which PDMS has good flexibility and hardly impacts on the SERS signals.…”

“…The SERS performance of LAMF-HCP-Au 5.5 @ Ag 5.25 NP@PDMS as SERS substrates was further investigated (Figure 5) for comparison with that of LAMF-HCP-Au 16 NP@ PDMS (Figures S11 and S12) composed of Au NPs with comparable size (16 nm), which has been reported in our recent work. 37 Figure 5 shows the representative spectra of CV (Figure 5a) and 4-ATP probes (Figure 5b) adsorbed on LAMF-HCP-Au 16 NP@PDMS and LAMF-HCP-Au 5.5 @Ag 5.25 NP@PDMS. It can be clearly seen that the intensity (Table S3) of the SERS peak at 1617 cm −1 measured on LAMF-HCP-Au 5.5 @Ag 5.25 NP@PDMS is much stronger (red curve in Figure 5a), which is about 9 times stronger than that of LAMF-HCP-Au 16 NP@ PDMS (black curve in Figure 5a).…”

“…36 Therefore, quasi-spherical Au-NP-based SERS substrates were widely fabricated into LAMFs because of easy preparation of citrate-stabilized Au NPs with narrow distributions in size and shape. 37 Since Ag NPs as SERS substrates can have a better SERS performance than Au NPs of comparable size, 38−40 However, the aqueous dispersion of quasi-spherically, smallsized, citrate-stabilized Ag NPs with the narrow distribution in size and shape is hard to prepare by current synthetic methods. 41,42 As the interaction with light is dominated by the outermost shell in bimetallic core−shell structured (CS) NPs, 38,39 CS Au@Ag NPs with Ag shells of controlled thicknesses can be used to replace small-sized pure Ag NPs, Thus, quasi-spherically, small-sized, citrate-stabilized CS Au@ Ag NPs with a narrow distribution in size and shape are prepared for the fabrication of LAMFs with ordered arrays, instead of pure Ag NPs.…”