Enhancing in vitro photothermal therapy using plasmonic gold nanorod decorated multiwalled carbon nanotubes

Photothermal therapy (PTT) is a promising approach for cancer treatment that selectively heats malignant cells while sparing healthy cells. Here, the light-to-heat conversion efficiency of multiwalled carbon nanotubes (MWCNTs) within the near-infrared biological transmission window is enhanced by decorating them with plasmonic gold nanorods (GNRs). The results reveal a significant photothermal enhancement of hybrid MWCNTs-GNRs compared to bare MWCNTs, displaying a 4.9 enhancement factor per unit mass. The enhanced plasmonic PTT properties of MWCNTs-GNRs are also investigated in vitro using PC3 prostate cancer cell lines, demonstrating a potent ablation efficiency. These findings advance innovative hybrid plasmonic nanostructures for clinical applications.


Contents
Table S1.The zeta potentials of MWCNTs at different stages during the covalent bonding process.The near-field optical properties of the nanostructures were solved numerically in the frequency domain using the scattering field formulation in a commercially available FEM package (COMSOL Multiphysics 5.6 with the RF module).The 3D simulation space was composed of a nanostructure, an embedded spherical medium, and a perfectly matched layer (PML) spherical domain with a scattering boundary condition, as shown in Fig. 2(c).The embedded medium was water, with a refractive index of n = 1.33.The dielectric permittivity of gold and carbon nanotube components were obtained from Johnson and Christy [1], and Djurišić [2], respectively.To conduct the simulation, we employed a free tetrahedral meshing algorithm from COMSOL with a tetrahedral element.The simulation was performed in the visible and near-infrared wavelength ranges of 200 nm and 1200 nm, respectively, with a spectral resolution of 10 nm using a parametric sweep.The Helmholtz equation is used to describe the electromagnetic interaction between the laser and nanostructure in an aqueous environment, as follows:

Samples
where   is the relative permeability of the particle, E is the sum of the electric fields, which consists of the incident and scattered fields,  =   +   ,   is the wave propagation vector, and  is the dielectric permittivity of gold, which is composed of both the real and imaginary parts.When solving the scattered field, the incident light for a plane wave polarized along the x-axis and propagated along the z-axis is defined as, where   is the amplitude wave [V/m], n is the refractive index of the medium,  and is the wavelength [nm].

Section S6. Calculation of the photothermal conversion efficiency
The figure of merit (η) determines the heating efficiency of the incident power transduced by the nanoparticles to generate heat that causes cell death.The optical absorbance of the hybrid nanoparticles was investigated using a UV-Vis-NIR spectrometer.Using this spectrometer tool, we extracted the optical density (A λ ) at different nanoparticle concentrations, with a focus on the NIR wavelength (808 nm).Based on the total energy balance equation for the system [4]: where  and   are the mass and heat capacity of the sample solution, respectively. is the temperature of the solution, and the   is the energy input by the nanoparticles, and   is the baseline energy input by the solvent (i.e., deionized water), and   is the outgoing energy, which is the energy dissipated from the system to the surroundings.The term   is defined as the laser-induced heat input, as follows: where  is the incident laser power in W•cm -2 , A λ is the absorbance of the nanoparticles at a given wavelength λ (i.e., 808 nm).The term   is the heat dissipation linear to the temperature of the system, defined as where ℎ is the heat transfer coefficient, A is the exposed surface area of the cuvette,   is the maximum temperature reached by the nanoparticles,   is the surrounding temperature.When the temperature reaches equilibrium,   ,   = 0, and Equation (S6.1) becomes: When the laser is off, the heat input terms become zero, and Equation (S6.1) becomes.
Rearranging it, it would give: And with integration, it would give: And the system time constant is defined as: The term   is determined by the linear regression of the time versus the negative natural logarithm of , which is defined as:  =  -    -  (S6.9)Thus, the time is defined as:  = -  () (S6.10) The term ℎ is determined by measuring the rate of temperature drop when the laser is off, then, Thus, the photothermal conversion efficiency is defined as: Where T sur is the ambient room temperature, T max is the equilibrium temperature, Q diss is the energy input by the aqueous solution and the sample cell without the nanoparticles, h is the heat-transfer coefficient, A is the surface area for radiative heat transfer, I is the laser power (2 W•cm -2 at a spot diameter of 5 mm), and A λ is the optical density of the nanoparticle solution at the laser wavelength λ.Table S2.Experimental parameters associated with the calculation of the photothermal conversion efficiency of each tested sample.Since hybridization with MWCNTs does not modify absorption at 250 nm, one can use DF to determine the final concentration of MWCNTs in the as-prepared hybrid composite:

Samples
The mass of MWCNT is involved in the photothermal process by dividing the PCE by the mass of MWCNT present in each sample solution; thus, one will obtain the PCE per unit mass of MWCNT.This represents the efficiency of photothermal conversion with respect to the mass of MWCNT in the near-infrared region.
Therefore, the   of MWCNTs-GNRs is approximately 4.9 times greater than the bare MWCNT.Where C GNR is the concentration of GNRs [nanoparticles/mL] equal to N GNR , defined as the number concentration of nanoparticles in unit of particles/mL,  808 is the measured optical absorption at 808 nm [a.u.], which is 1.859, C abs is the extracted absorption cross-section [m -2 ] of GNRs, which is 1.74e-15 m -2 , and l is the cuvette path length [cm], which is 1 cm.

Section S10. Photothermal conversion efficiency of several carbon-based PTT agents
Nanoparticle concentration in molar concentration (molarity):  =   6.02 × 10 23 where N GNR is the number concentration of nanoparticles in units of particles/mL, and the denominator is Avogadro's number.
Fig. S3.(a) TEM images of MWCNTs-GNRs at 200 nm scale.Statistical analysis of 120 GNRs based on TEM image to determine (b) the length, (c) the diameter, and (d) the aspect ratio.

Fig. S7 .
Fig. S7.(a) The relative viability of PC3 cells incubated with different concentrations of MWCNTs-GNRs after 24, 48, and 72 hours of incubation.(b) The relative viability of PC3 cells incubated with MWCNTs-GNRs and exposed at different irradiation times.A two-paired student t-test was used to evaluate the statistical significance; * = p < 0.05.

Table S3 .
Experimental parameters associated with PCE per unit MWCNT mass at 808 nm.Cell viability of PC3 cells incubated with MWCNTs-GNRs over several days, and cell viability of PC3 cells irradiated with MWCNTs-GNRs, GNRs, and MWCNTs