Single-Cell Photothermal Analysis Induced by MoS2 Nanoparticles by Raman Spectroscopy

Abstract

Two-dimensional nanomaterials, such as MoS2 nanosheets, have been attracting increasing attention in cancer diagnosis and treatment, thanks to their peculiar physical and chemical properties. Although the mechanisms which regulate the interaction between these nanomaterials and cells are not yet completely understood, many studies have proved their efficient use in the photothermal treatment of cancer, and the response to MoS2 nanosheets at the single-cell level is less investigated. Clearly, this information can help in shedding light on the subtle cellular mechanisms ruling the interaction of this 2D material with cells and, eventually, to its cytotoxicity. In this study, we use confocal micro-Raman spectroscopy to reconstruct the thermal map of single cells targeted with MoS2 under continuous laser irradiation. The experiment is performed by analyzing the water O-H stretching band around 3,400 cm−1 whose tetrahedral structure is sensitive to the molecular environment and temperature. Compared to fluorescence-based approaches, this Raman-based strategy for temperature measurement does not suffer fluorophore instability, which can be significant under continuous laser irradiation. We demonstrate that irradiation of human breast cancer MCF7 cells targeted with MoS2 nanosheets causes a relevant photothermal effect, which is particularly high in the presence of MoS2 nanosheet aggregates. Laser-induced heating is strongly localized near such particles which, in turn, tend to accumulate near the cytoplasmic membrane. Globally, our experimental outcomes are expected to be important for tuning the nanosheet fabrication process.

Genesis of Active Phase and Support Effect in Ultradispersed Mo Sulfide Catalysts

“…UV–vis DRS spectra were recorded only for the oxide-supported samples because carbon-supported samples are black. In bulk MoS 2 , direct electronic transitions between the conduction band and valence band result in two absorption peaks around 610 and 670 nm. , For the MoS 2 catalysts supported on alumina, silica, and titania, the UV–vis peaks of MoS 2 were observed and easily distinguished from those of the corresponding supports even in air. − In our spectra, beside the absorption bands of supports, several broad peaks centered around 420, 470, and 570 nm were observed, but no bands were present above 600 nm (Figure S3). This difference might be explained by the ultradispersion of MoS x species, leading to the modification of their electronic properties, or due to the partial oxidation of MoS 2 nanoclusters in air .…”

“…In bulk MoS 2 , direct electronic transitions between the conduction band and valence band result in two absorption peaks around 610 and 670 nm. 50,51 For the MoS 2 catalysts supported on alumina, silica, and titania, the UV−vis peaks of MoS 2 were observed and easily distinguished from those of the corresponding supports even in air. 52−55 In our spectra, beside the absorption bands of supports, several broad peaks centered around 420, 470, and 570 nm were observed, but no bands were present above 600 nm (Figure S3).…”

The Effectiveness of Cyrene as a Solvent in Exfoliating 2D TMDs Nanosheets

“…This also means that the final dispersion will contain 2D NSs of varied thicknesses, which can be separated in accordance with their size and thickness upon liquid cascade centrifugation. In this context, the acquisition of UV–Vis spectra is a quick approach to evaluate the average number of layers <N>, average size <L> and average concentration <C> for the exfoliated dispersion [ 38 , 39 , 40 , 41 ]. Indeed, within one sample/dispersion, UV spectra show characteristic, size-dependent spectral changes originating mostly from the absorbance and scattering components of the extinction, as the optical extinction spectra of small and large nanosheets include contributions from both the edge and basal plane effects, respectively [ 42 , 43 ].…”

“…Bulk MoS 2 exhibits high hydrophobicity and, upon exfoliation, the contact angle of the bulk material decreases; after further centrifugation steps, the angle is reduced further and the material will transform from a hydrophobic material to a hydrophilic material in a given solvent [ 71 ]. Normally, when exfoliated in pure water, MoS 2 and WS 2 NSs exhibit surface charges in the range of −26 mV to −32 mV, which provides a stable dispersion and sufficient electrostatic repulsive forces to avoid the aggregation of dispersed 2D TMDs [ 38 , 41 , 68 ]. Interestingly, we found that the ς-potential values were significantly more negative in cyrene than those obtained with water for both materials, WS 2 being significantly more negative than MoS 2 with values of −86.5 ± 1.5 and −50 ± 3, respectively.…”

“…Sci. 2023, 24, x FOR PEER REVIEW 4 of 20 average concentration <C> for the exfoliated dispersion [38][39][40][41]. Indeed, within one sample/dispersion, UV spectra show characteristic, size-dependent spectral changes originating mostly from the absorbance and scattering components of the extinction, as the optical extinction spectra of small and large nanosheets include contributions from both the edge and basal plane effects, respectively [42,43].…”