Plasmonic Coupling in Silver Nanoparticle Aggregates and Their Polymer Composite Films for Near-Infrared Photothermal Biofilm Eradication

Abstract

Plasmonic nanoparticles with near-IR (NIR) light absorption are highly attractive in biomedicine for minimally invasive photothermal treatments. However, these optical properties are typically exhibited by plasmonic nanostructures with complex, nonspherical geometries that may prohibit their broad commercialization and further integration into photothermal devices. Herein, we present the single-step aerosol self-assembly of plasmonic nanoaggregates that consisted of spherical silver nanoparticles with tunable extinction from visible to NIR wavelengths. This tunable extinction was achieved by the addition of SiO 2 during the flame synthesis of the nanoparticles, which acted as a dielectric spacer between the spherical silver nanoparticles and was also computationally validated by simulating the extinction spectra of similar silver nanoaggregates. These plasmonic nanoaggregates were easily deposited on silicone polymeric surfaces and further encased with a top polymer layer, forming plasmonic photothermal nanocomposite films. The photothermal properties of the NIR nanocomposite films were utilized to eradicate the established biofilms of clinically relevant Escherichia coli and Staphylococcus aureus, with a relationship observed between the final surface temperature and biofilm eradication.

SERS Hotspot Engineering by Aerosol Self‐Assembly of Plasmonic Ag Nanoaggregates with Tunable Interparticle Distance

“…These images verify the formation of the Ag–SiO 2 (5 wt% nominal SiO 2 ‐content) core–shell morphology of the nanoaggregates in which the individual Ag spherical particles are separated by an amorphous SiO 2 layer (see high‐resolution TEM (HR‐TEM) images in Figure 1c ). [ 33 ] The TEM images here are primarily used to identify the morphology of the nanoparticles dispersed in suspension, however, the Raman tests are performed on deposited films.…”

“…The crystallinity of the Ag NPs can be seen in the BF (bright field) STEM image (Figure 1d , the second and third panels), Selected area electron diffraction (SAED, shown in panel 4 of Figure 1d ), and can also be verified by X‐ray diffraction (Figure S3 ). The formation of core–shell morphology was further investigated and confirmed with an elemental mapping technique known as hypermodal data fusion [ 33 , 47 , 48 ] that combines coregistered electron energy‐loss spectroscopy (EELS) and energy‐dispersive X‐ray spectroscopy (EDX) datasets (Figure 1d , the second row images). These maps show that the same crystalline Ag NPs from panels 2 and 3 are surrounded by an amorphous shell of Si and O.…”

“…To further understand the fundamental properties that dictate the SERS performance, we produced Ag–SiO 2 NP films varying their SiO 2 content (5 to 9 wt%, see Figure S10 , Supporting Information, for longer range 1.3 to 25 wt% SiO 2 , Figure S11 , Supporting Information, for the TEM images, and Figure S12 , Supporting Information, for STEM images and elemental mapping), and thus tuning their plasmonic coupling extinction. [ 33 ] Figure 4 a shows the extinction spectra of the deposited Ag–SiO 2 ( t d = 40 s) films for varying SiO 2 contents, in which the single mode plasmonic peak of Ag nanospheres appears at ≈390 nm [ 63 ] as well as their coupling extinction bands that largely extend to the near‐IR for all SiO 2 contents (the coupling extinction maximum wavelengths λ max are shown with dotted lines). Upon plotting the plasmonic coupling extinction λ max as a function of SiO 2 content (Figure 4b ), the λ max values monotonously decrease for increasing SiO 2 contents, in agreement with the literature.…”

“…[ 27 , 28 , 29 , 30 ] To overcome these limitations, coatings are often used to protect Ag NPs from degradation processes, and to introduce chemical, biological, and optical functionalities on their surface. [ 31 , 32 , 33 , 34 , 35 , 36 ]…”

Combating Drug-Resistant Bacteria Using Photothermally Active Nanomaterials: A Perspective Review

“…Similar results were observed in cerium oxide nanoparticles doped with tin (Sn-doped CeO 2 ) synthesized from Allophylus cobbe exhibiting concentration-dependent antibiofilm activity under visible light in Listeria monocytogenes and S. aureus at 512 mg/mL with a 2 log CFU reduction ( Naidi et al, 2021 ). In addition to Au nanocomposites, plasmonic silver nanocomposite films under NIR irradiation have been studied to photothermally eradicate biofilms in clinically relevant E. coli and S. aureus ( Merkl et al, 2021 ). Dai et al (2021) studied nanocomposites based on MSN (FITC Cu 2 –X SNPs MSNs) as combined NIR-activated photodynamic/PTT for the ablation of biofilms against P. aeruginosa and S. aureus (90% inhibition rate at a concentration of 160 μg/mL concentration).…”