Assembly of Mid-Nanometer-Sized Gold Particles Capped with Mixed Alkanethiolate SAMs into High-Coverage Colloidal Films

Abstract

We investigated the influence of the mixed n-alkanethiolate self-assembled monolayer (SAM) formed on gold nanoparticles (AuNPs: 50.0 ± 3.2 nm in diameter) on their assembly into colloidal films. Dodecanethiol and octadecanethiol were selected as the short- and long-chain alkanethiols, respectively. The mixed SAMs were formed by immersing AuNPs in a mixed alkanethiol solution at different molar ratios. Au colloidal films were fabricated on indium tin oxide substrates by our previously reported hybrid method. The composition of the two alkanethiolates in the SAM was deduced from the intensity ratio of two Raman bands at 1080 and 1105 cm(-1). The surface coverage of the colloidal films increased by forming equimolar or dodecanethiolate-dominant mixed SAMs on AuNPs instead of a pure dodecanethiolate or octadecanethiolate SAM. The highest coverage exceeded 80%. This improvement is attributed to the high dispersion stability of AuNPs covered with equimolar or dodecanethiolate-dominant mixed SAMs.

Formation of Uniform and High-Coverage Monolayer Colloidal Films of Midnanometer-Sized Gold Particles over the Entire Surfaces of 1.5-in. Substrates

“…This red shift suggests the reduction of the interparticle gap distance. In our previous work, we found that the peak wavelength of the LSPR band increased with increasing mole fraction (χ C12 sol ) of DDT in the mixed alkanethiol (DDT and ODT) solution used for exchanging the capping molecules of AuNPs. In particular, the peak wavelength increased rapidly in the range of 0.8 < χ C12 sol < 1.0, indicating that a rapid reduction of the interparticle gap distance occurred in this χ C12 sol range.…”

“…Then, the AuNPs were capped with a mixed alkanethiol self-assembled monolayer (SAM). This surface modification was conducted using a mixed solution with ODT/DDT = 1:6 (molar ratio) in acetone, according to the procedure described in our previous work . In the final preparation step, alkanethiol-capped AuNPs were dried in a nitrogen atmosphere, producing stable black flakes.…”

“…In this method, three elemental technologies were used: surface modification of Au nanoparticles (AuNPs) and conductive substrates with alkanethiols and thiol-terminating agents, respectively; deposition under a constant applied voltage; and solvent evaporation. − The stability of the colloidal films was ensured by Au–S bond formation between the AuNPs and the thiol-terminated conductive substrate. Large-area colloidal Au films with high surface coverage could be fabricated by functionalizing the AuNP surfaces with one type of alkanethiol for AuNPs smaller than 10 nm in size , or a mixture of long- and short-chain alkanthiols for midnanometer-sized AuNPs (>10 nm). ,, This hybrid method had two drawbacks: no applicability to nonconductive substrates and time-consuming process. In our recipe, ,,− the solvent evaporation process for 10-mm square substrates takes about 5 h. Recently, the first problem was solved by improving the experimental conditions.…”

“…Large-area colloidal Au films with high surface coverage could be fabricated by functionalizing the AuNP surfaces with one type of alkanethiol for AuNPs smaller than 10 nm in size , or a mixture of long- and short-chain alkanthiols for midnanometer-sized AuNPs (>10 nm). ,, This hybrid method had two drawbacks: no applicability to nonconductive substrates and time-consuming process. In our recipe, ,,− the solvent evaporation process for 10-mm square substrates takes about 5 h. Recently, the first problem was solved by improving the experimental conditions. We found that the application of a voltage is not needed if high-purity water is used for washing labware and the AuNP synthesis and self-assembly of the AuNPs are performed in a dry nitrogen atmosphere.…”

Extrinsic surface-enhanced Raman scattering detection of influenza A virus enhanced by two-dimensional gold@silver core–shell nanoparticle arrays

“…Additionally considering the feasibility of narrow size distribution and shape uniformity of Au@Ag NPs, the Au core diameter and the Ag shell thickness were determined to be 40 nm and 5 nm, respectively. 16 Alkanethiolate-capped Au@Ag NPs were synthesized according to the procedure reported previously, 16 except for using a mixed solution of octadecanethiol : dodecanethiol ¼ 1 : 6 (molar ratio) in acetone 21 for the mixed self-assembled monolayer (SAM) formation on the Au@Ag NP surface. The details of Au@Ag NP synthesis were described in ESI.…”