Self-Assembled Metal Colloid Films:  Two Approaches for Preparing New SERS Active Substrates

Abstract

In this paper, we propose two new approaches for preparing active substrates for surface-enhanced Raman scattering (SERS). In the first approach (method 1), one transfers AgI nanoparticles capped by negatively charged mercaptoacetic acid from a AgI colloid solution onto a quartz slide and then deoxidizes AgI to Ag nanoparticles on the substrate. The second approach (method 2) deoxidizes AgI to Ag nanoparticles in a colloid solution and then transfers the Ag nanoparticles capped by negatively charged mercaptoacetic acid onto a quartz slide. By transfer of the AgI/Ag nanoparticles from the colloid solutions to the solid substrates, the problem of instability of the colloid solutions can largely be overcome. The films thus prepared by both approaches retain the merits of metal colloid solutions while they discharge their shortcomings. Accordingly, the obtained Ag particle films are very suitable as SERS active substrates. SERS active substrates with different coverages can be formed in a layer-by-layer electrostatic assembly by exposing positively charged surfaces to the colloid solutions containing oppositely charged AgI/Ag nanoparticles. The SERS active substrates fabricated by the two novel methods have been characterized by means of atomic force microscopy (AFM) and ultraviolet−visible (UV−vis) spectroscopy. The results of AFM and UV−vis spectroscopy show that the Ag nanoparticles grow with the increase in the number of coverage and that most of them remain isolated even at high coverages. Consequently, the surface optical properties are dominated by the absorption due to the isolated Ag nanoparticles. The relationship between SERS intensity and surface morphology of the new active substrates has been investigated for Rhodamine 6G (R6G) adsorbed on them. It has been found that the SERS enhancement depends on the size and aggregation of the Ag particles on the substrates. Especially, we can obtain a stronger SERS signal from the substrate prepared by method 1, implying that for the metal nanoparticles capped with stabilizer molecules such as mercaptoacetic acid, the in situ deoxidization in the film is of great use in preparing SERS active substrates. Furthermore, we have found that the addition of Cl- into the AgI colloid solution changes the surface morphology of the SERS active substrates and favors stronger SERS enhancement.

An in situ reduction method for preparing novel surface‐enhanced Raman scattering substrates

“…28 Briefly, clean quartz slides were immersed in 0.5% PDDA solution for about 30 min and then rinsed with triply distilled water. The slides were immersed in the AgI colloid for about 20 min and then rinsed with triply distilled water.…”

“…This problem can be largely overcome by transferring the metal nanoparticles on to a solid substrate. In our previous studies, 28 we reported an in situ reduction method to prepare SERS substrates, in which AgI nanoparticles are transferred from the colloid and then reduced to Ag nanoparticles on the solid substrate. The SERS substrate thus obtained exhibited strong enhancement.…”

Peptide Mesocrystals as Templates to Create an Au Surface with Stronger Surface‐Enhanced Raman Spectroscopic Properties

“…These active films should also be stable, reproducibly prepared, inexpensive, and easy to make. [22][23][24][25] In reali-…”

Nanostructured and nanopatterned gold surfaces: application to the surface-enhanced Raman spectroscopy

“…In parallel, many approaches were proposed to optimize and control the surface-enhanced Raman scattering efficiency of colloidal AuNPs assembled on substrates into 2D nanostructures [9][10][11][12][13][14][15][16][17][18][19].…”