Modulating the Kinetics of Nanoparticle Adsorption for Simple and High‐Yield Fabrication of Plasmonic Heterostructures as SERS Substrates

Abstract

This work reports scalable, low-cost, and simple fabrication of plasmonic heterostructures consisting of gold nanoparticles (NPs) of different sizes to generate intense hot-pots over large areas to serve as substrates for molecular sensing in SERS applications. Our approach involves assembly of massively-available colloidal gold NPs on substrates functionalized with end-grafted poly(ethylene glycol) (PEG) brushes without need for any sophisticated tools and post-modification of the particles and substrates. From real-time monitoring of the adsorption process by using a quartz crystal microbalance, we identified that the cyclic deposition of citrate-stabilized gold NPs on PEG brushes is an effective approach to modulate the kinetics of particle adsorption and greatly improves the surface coverage leading to reduced inter-particle distances. Cyclic deposition of NPs differing in size leads to placement of the small particles in close proximity of the large ones, yielding hot-spots as a consequence of the unique type of interaction between PEG chains and gold NPs. Assembly of heterostructures (60 nm+40 nm and 60 nm+20 nm) at optimized conditions resulted in strong SERS effects with enhancement factors as high as ≈2.0×10 and enabled detection of rhodamine 6G molecules in concentrations as low as 1 nm. The cyclic deposition of NPs also results in increase of the water contact angle without need for any post-modification of the substrate, resulting in ≈30 fold increase in the Raman intensity of aqueous molecules. The insights gained on the adsorption of gold NPs together with the simplicity of the presented approach show great promise for surface assembly of colloidal NPs for a broad range of applications.

Plasmonic assemblies of gold nanorods on nanoscale patterns of poly(ethylene glycol): Application in surface-enhanced Raman spectroscopy

“…The lowest concentration of the reporter molecule that could be clearly detected was 1 nM on the patterned NRs. This detection limit exceeds those obtained with surface-assemblies of gold nanostars [44], nanospheres [36], NRs [45], and core-shell nanoparticles [46]. Figure 5d compares the SERS intensity at 1365 cm -1 of the reporter molecule deposited on gold NRs immobilized on patterned and unpatterned PEG layers.…”

“…Silicon substrates were functionalized with PEG (M n = 35.0 kg/mol, PDI = 1.15, Polymer Source Inc.) by a grafting to approach as described in our previous studies [36]. Briefly, a ~120 nm film of PEG was deposited on the freshly cleaned (UV-Ozone for 20 min) silicon substrate via spincoating.…”

Chitosan Loses Innate Beneficial Properties after Being Dissolved in Acetic Acid: Supported by Detailed Molecular Modeling

“…53 It is known from previous studies that sharp edges, as well as close placement of metallic structures, result in improved SERS activity. 54,55 Two figures of merit are commonly used to evaluate the SERS performance of platforms. One is the limit of detection, which shows the lowest concentration that can be detected in the Raman spectroscopy over the substrate of interest.…”

Writing chemical patterns using electrospun fibers as nanoscale inkpots for directed assembly of colloidal nanocrystals

“…Third, PEG proved to be highly effective for directing the assembly of Au NCs. [66][67][68][69][70][71] PEO NF inkpots were written on Si substrates through the control of the diameter between 100 nm and 550 nm via adjusting NFES parameters, such as voltage bias (500 to 750 V) and tip-to collector distance (1 to 2 mm). As a result of the annealing and washing processes (Fig.…”