Synthesis of a covalently linked bismuthene–graphene heterostructure loaded with mitomycin C for combined radio-thermo-chemotherapy of triple-negative breast cancer†

Fabricating innovative nanomaterials for cancer treatment is essential for reducing its morbidity. The present study focuses on synthesizing, evaluating, and utilizing a bismuth nanosheet–reduced graphene oxide (BiNS–rGO) heterostructure for cancer combination therapy. The successful fabrication of the heterostructure with regulated thickness and morphology was confirmed by structural characterization using Fourier transform infrared spectroscopy, scanning transmission electron microscopy, and X-ray diffraction. Atomic force microscopy indicated the heterostructure height of 1.3 ± 0.95 nm. Moreover, high-resolution TEM confirmed the heterostructure configuration of the nanoparticles with a bismuth nanosheet (BiNS) plane distance of 0.33 nm. Following the evaluation of the photothermal characteristics of the BiNS–rGO heterostructure, it was found that a light-to-heat conversion of η = 67.6% was efficient under laser irradiation (3 W cm⁻², 5 min, 50 μg mL⁻¹, 1064 nm) to increase the temperature from 25 °C to 42.5 °C. The heterostructure demonstrated excellent photothermal stability and recyclability, making it highly promising for photothermal treatment (PTT) applications. At pH 7.4, 30% and 70.5% drug release were observed in 24 h and 240 h, respectively. Both pH and photothermal effect considerably impact the drug release profile. Drug release was increased in an acidic environment (pH 5.0) as opposed to physiological pH (pH 7.4), suggesting pH-sensitive behavior. In particular, over 24 hours, 42% of the medication was released at pH 5.0, while only 30% was released at pH 7.4 during the same time frame. Due to photothermal heating, the release rate increased even more after exposure to one-time NIR laser radiation (3 W cm⁻², 1064 nm). Under the same irradiation settings, drug release reached 52% in 24 hours, much higher than the 42% release at pH 7.4 under light. This implies that quicker drug diffusion was made possible by structural alterations in BiNS–rGO brought about by heat. A BiNS–rGO band gap and flat band potential of 1.86 eV and −0.68 V (vs. Ag/AgCl), respectively, confirm the radiocatalytic ROS generation. Following 96 h of incubation, the IC₅₀ value of BiNS–rGO was determined to be 121.30 μg mL⁻¹via MTT assay. Combination therapy showed much lower values, with BiNS–rGO + RT showing 53.41 μg mL⁻¹ and BiNS–rGO + MitoC + PTT + RT showing 19.43 μg mL⁻¹. Regarding the flow cytometry data, PTT, RT, and MitoC + PTT + RT treatment has shown an apoptosis ratio (early and late) of 36, 71.4, and 97.5%, respectively. Furthermore, the elevation of the caspase-3 apoptotic gene up to 23-fold in combination therapy confirmed the apoptotic cancer cell death pathway. Overall, this research demonstrates the potential of the BiNS–rGO heterostructure as a versatile nano-platform for combination cancer therapy that combines radiation, controlled drug delivery, and photothermal therapy with maximum efficacy and minimal side effects. This research study creates new opportunities for the development of sophisticated nanomaterials for targeted cancer therapy.