Signal Enhancement and Tuning of Surface Plasmon Resonance in Au Nanoparticle/Polyelectrolyte Ultrathin Films

Abstract

Investigations on optical and dielectric properties of hybrid ultrathin layer-by-layer (LbL) films of gold nanoparticles (AuNPs) and polyelectrolytes under different pH conditions resulted in surface plasmon resonance (SPR) signal enhancement under attenuated total reflection (ATR) spectroscopy conditions. Theoretical considerations on the basis of the Maxwell-Garnett theory were made to compare with experimental results. LbL films with different layer architectures were fabricated from AuNPs and two polyelectrolytes: poly-(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) on Au and Ag thin film substrates for ATR. UV-vis spectroscopy and SPR spectroscopy were applied to study LbL film growth and monitor SPR shift upon pH switching. The (PAH/AuNPs) x multilayers showed an interesting dual-responsive SPR change as a function of pH and distance between AuNP layers and metal film. The addition of (PAH/PSS) y layers was found to act as an effective cushion to enhance this SPR response due to the significant swelling/shrinking of the film. In the case of [(PAH/PSS) y + (PAH/AuNPs) x ], both theoretical calculations and experimental results showed that the SPR response can either (a) move toward lower incident angle with a sharp peak shape upon swelling in pH ) 2 or (b) shift to a higher angle with a broadened peak shape after contraction in pH ) 10. This effect was found to be opposite to what is expected from LbL films made up of the polyelectrolytes alone. Moreover, increasing the distance between AuNPs and the metal films also decouples this enhancement effect. A two-wavelength experiment (red and green lasers) was used to quantitatively demonstrate this SPR response to pH switching. Finally, SPR imaging was employed to monitor the SPR change with pH switching between 2 and 10 on the [(PAH/PSS) 4 + (PAH/AuNPs) 2 ] film. Thus, on the basis of the SPR spectroscopic and SPR imaging pH response, a reproducible and stable sensing system can be successfully fabricated with these films.

Preparation of Nanostructured Film Arrays for Transmission Localized Surface Plasmon Sensing

“…Surface plasmons (SPs) are coherent oscillations of free electrons that propagate along the surface of a metal when it is in contact with a dielectric interface [8][9][10][11][12][13]. SPs of the metal surface are greatly affected by adsorption and/or desorption events that occur at a metal/dielectric interface.…”

Patterning and Assembly of Single-Walled Carbon Nanotubes/Organic Semiconductor Composites

“…Another possibility is that the electrons are transferred from SWNT to methyl viologen inside the film, since such small molecules can exist inside LbL films in electrolyte solution. This is reasonable because LbL films usually contain electrolytes in aqueous solution (Jiang et al, 2007;Baba et al 2002). These results indicate that the TMPyP-SWNT/SCC-SWNT LbL multilayered film should have potential for effective photocurrent generation.…”

Stimulus‐Responsive Polymers as Intelligent Coatings for Biosensors: Architectures, Response Mechanisms, and Applications

“…Upon changing the pH from 5 to 2, the distance change between the AuNPs and the gold islands also changed the extent of interparticle coupling in LSPR, which resulted in a wavelength shift of the absorption peak maximum of 50 nm, as compared with only 6 nm in the absence of the NPs. Another example of enhanced LSPR sensing was reported by Jiang et al, 55 who modulated the packing of AuNP in a multilayer fi lm of pAH and pSS prepared by LBL deposition on gold by changes in pH. Using the planar SPR mode, they showed that pH -induced changes in the packing of the AuNPs strongly affected the SPR response.…”

“…26 To enhance the sensitivity, hybrid polymer coatings with AuNPs embedded in the polymer matrix are often used. 26,27,55 In addition to the change in the refractive index of the coating, the swelling/shrinking of the polymer changes the interparticle plasmon ) and nanoparticles, which generates a shift in the absorbance peak. Adapted with permission from references [17], [29], [67], [88], and [91] .…”