Targeted MoSe2 Nanodots in Albumin Nanospheres: A Biocompatible Dual‑Modality Agent for Synergistic Photothermal Radiotherapy

Background

Breast cancer remains a leading cause of morbidity worldwide, with high rates of metastasis and recurrence. Conventional therapies—surgery, chemotherapy, and radiotherapy (RT)—often compromise healthy tissue and suffer from limited efficacy, especially in hypoxic tumor microenvironments. Recent advances in photothermal therapy (PTT) have demonstrated minimal invasiveness and high spatial specificity, yet PTT alone frequently fails to eradicate deep or inaccessible tumors. Notably, NIR‑induced hyperthermia can enhance tumor oxygenation, rendering cancer cells more susceptible to RT. Therefore, a combined PTT‑RT approach offers a compelling route to maximize therapeutic outcomes while mitigating collateral damage.

Two‑dimensional transition metal dichalcogenides (TMDs), including MoS₂, WS₂, and ReS₂, have emerged as potent NIR absorbers and radiosensitizers owing to their unique electronic properties. Molybdenum selenide (MoSe₂) specifically has shown strong photothermal conversion and high X‑ray attenuation, making it an attractive candidate for dual‑mode therapy. However, the inherent instability of MoSe₂ NDs in physiological conditions limits their clinical translation. Encapsulation within protein matrices such as BSA can stabilize these nanodots and confer biocompatibility, while FA conjugation provides tumor‑targeting capability via folate receptors overexpressed on many cancer cells.

Methods

Materials

FA‑PEG₅₀₀₀-NHS and CH₃-PEG₅₀₀₀-NHS (Shanghai Ponsure Biotech) were employed for FA attachment. Bulk MoSe₂ (Sigma‑Aldrich), BSA (≥98 % purity), and standard cell culture reagents (Corning) were used throughout.

Preparation of FA‑MoSe₂@BSA NSs

Bulk MoSe₂ (50 mg) was dispersed in 25 mL distilled water, sonicated (950 W, 25 kHz) for 12 h (2 s on/3 s off) to yield ultrafine NDs. Centrifugation (6000 rpm, 25 min; then 12 000 rpm, 30 min) collected the supernatant, containing MoSe₂ NDs. Adding 25 mg BSA and stirring for 6 h at 25 °C (pH 7.4) formed coacervates, which were cross‑linked with 0.5 % glutaraldehyde (250 µL). Dialysis (1 day) removed excess cross‑linker, producing MoSe₂@BSA NSs. For FA conjugation, 8 mg FA‑PEG₅₀₀₀-NHS was mixed with the NSs and stirred for 2 h; a parallel batch with CH₃-PEG₅₀₀₀-NHS (8 mg) served as a non‑targeted control. Dialysis completed purification, and UV–Vis spectroscopy quantified FA loading (280 nm), yielding an encapsulation efficiency of 10.5 ± 0.11 %.

Characterizations

Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) confirmed ultrasmall ND cores (≈3.8 nm) and spherical NS morphology (≈140 nm). Dynamic light scattering (DLS) showed stable hydrodynamic sizes in water, PBS, and cell medium. UV–Vis spectra displayed strong NIR absorption for both MoSe₂ NDs and FA‑MoSe₂@BSA NSs. X‑ray diffraction (XRD) revealed characteristic (002) peaks, indicating few‑layer MoSe₂ structures. Fourier‑transform infrared (FTIR) spectra confirmed the formation of amide bonds between FA and BSA. Photothermal stability was assessed over three laser cycles (808 nm, 1 W cm^‑2), showing no loss in temperature rise. Computed tomography (CT) imaging demonstrated concentration‑dependent Hounsfield unit (HU) values, confirming X‑ray attenuation capabilities.

Cellular Uptake & Biocompatibility

FITC‑labeling and confocal microscopy revealed enhanced uptake of FA‑conjugated NSs in 4T1 cells compared to non‑targeted NSs; blocking with excess free FA reduced uptake, confirming folate‑mediated endocytosis. Inductively coupled plasma–atomic emission spectroscopy (ICP‑AES) quantified Mo content, corroborating confocal findings. Hemolysis assays (0–400 µg mL^‑1) showed <5 % hemolysis, and CCK‑8 viability assays (0.01–0.4 mg mL^‑1) indicated >90 % cell survival after 24 h, demonstrating low cytotoxicity.

In Vitro Photothermal Radiotherapy

Under 808 nm irradiation (1 W cm^‑2, 5 min), FA‑MoSe₂@BSA NSs raised local temperature by ~41 °C (200 µg mL^‑1), while PBS increased only ~1.5 °C. Combined with X‑ray doses (0–5 Gy), FA‑conjugated NSs significantly reduced 4T1 viability, achieving 92.8 % cell death at 5 Gy with 1 W cm^‑2 NIR, surpassing non‑targeted NSs or single modalities.

In Vivo Biodistribution & Photothermal Effect

Fluorescence and ICP‑AES mapping in 4T1‑bearing Balb/c nude mice revealed peak tumor accumulation of FA‑MoSe₂@BSA NSs at 24 h post‑injection (10 mg kg^‑1). Blood half‑lives were 0.91 h (distribution) and 16.96 h (elimination). NIR irradiation (808 nm, 1 W cm^‑2, 5 min) at 24 h induced a ~22 °C rise in tumor temperature, confirming in vivo photothermal performance.

In Vivo Photothermal Radiotherapy

In a six‑group study (PBS, NIR, RT, MoSe₂@BSA + NIR + RT, FA‑MoSe₂@BSA + NIR, FA‑MoSe₂@BSA + NIR + RT), the FA‑conjugated dual‑mode group achieved the most pronounced tumor suppression (≥80 % volume reduction) over 30 days, with no significant weight loss or organ toxicity (H&E and complete blood counts within normal ranges).

Conclusions

We successfully fabricated FA‑conjugated MoSe₂ nanodots encapsulated in BSA nanospheres, achieving stable, tumor‑targeted, and biocompatible dual‑modality agents. Their strong NIR absorption and X‑ray attenuation enable synergistic photothermal and radiosensitizing effects, yielding superior in vitro and in vivo tumor ablation with minimal systemic toxicity. These multifunctional nanospheres represent a compelling platform for future clinical translation of combined photothermal‑radiotherapy.

Abbreviations

BSA:

Bovine serum albumin

FA:

Folic acid

MoSe₂:

Molybdenum selenide

NDs:

Nanodots

NIR:

Near infrared

NSs:

Nanospheres

PEG:

Polyethylene glycol

PTT:

Photothermal therapy

RT:

Radiotherapy