Cryogenically Deposited Plasmonic Au Nanoparticle Films for Photothermal Treatment of Lung Cancer Cells

Abstract In this study, Au nanoparticle-coated glass substrates were fabricated by a cryogenic nonequilibrium deposition method at substrate temperatures of 300 and 230 K for plasmonic photothermal therapy applications. Field-emission scanning electron microscopy analysis revealed that the Au films deposited at 300 and 230 K consisted of nanoparticle assemblies with size distributions of approximately 7–17 nm and 8–10 nm, respectively. The significantly narrower particle size distribution observed at 230 K could be attributed to the emergence of a morphology consistent with the proposed soliton-mediated nonequilibrium growth mechanism characteristic of cryogenic deposition conditions. Atomic force microscopy measurements demonstrated that the average surface roughness decreased from 5.27 nm for the 300 K sample to 1.55 nm for the 230 K sample, confirming the formation of a more homogeneous nanoparticle architecture under cryogenic growth conditions. Optical characterization showed that both Au nanoparticle films exhibited surface plasmon resonance near 600 nm. However, the cryogenically fabricated film produced at 230 K displayed a substantially stronger plasmonic response, which was attributed to its enhanced structural uniformity and improved interparticle plasmonic coupling. To evaluate their photothermal performance, human lung adenocarcinoma A549 cells and normal bronchial epithelial BEAS-2B cells were cultured on bare-glass and Au nanoparticle-coated substrates and subsequently exposed to ∼600 nm irradiation using a 450 mW light source. Morphological and fluorescence-based analyses revealed pronounced photothermal-induced cytotoxicity in A549 cells cultured on Au-coated surfaces, including reduced cell density, disruption of cell–cell interactions, membrane damage, and loss of cellular organization. In contrast, BEAS-2B cells largely preserved their morphology, adhesion behavior, and membrane integrity under identical treatment conditions. The strongest cytotoxic response was observed for the Au nanoparticle films fabricated at 230 K. These findings suggest that cryogenic nonequilibrium deposition can improve nanoparticle uniformity and plasmonic performance, with the 230 K Au nanoparticle films producing the most pronounced photothermal response under the investigated conditions. In the preliminary biological evaluation, A549 cells exhibited a greater photothermal response than BEAS-2B cells under identical experimental conditions. These proof-of-concept findings highlight the potential of cryogenically fabricated plasmonic nanostructures for further investigation in photothermal biomedical applications.