Folic Acid-Conjugated Albumin-Stabilized Gold–Terbium Nanoparticles for SPCCT/MRI Imaging: An in vitro Cellular and Phantom Study

Abstract

Introduction Triple-negative breast cancer (TNBC) remains challenging to image because of its biological heterogeneity and the limitations of single-modality imaging. Multifunctional nanoparticles may provide complementary contrast for spectral photon-counting CT (SPCCT) and MRI, potentially improving multimodal tumor imaging. Methods Folic acid-conjugated, albumin-stabilized gold-terbium nanoparticles (BSA@Au/Tb-FA) were synthesized and characterized using TEM, XRD, FTIR, XPS, and DLS. In vitro cellular uptake, cytotoxicity, and hemocompatibility were evaluated using MDA-MB-231 cells using confocal microscopy and flow cytometry. SPCCT and MRI performance were assessed in phantom models. Results The BSA@Au/Tb-FA nanoparticles exhibited a spherical-like morphology, with a mean particle size of ~10.68 ± 1.69 nm (n = 55). Cell viability remained >80% up to 250 µg/mL, with an IC50 of 352 µg/mL. The hemocompatibility was good, with hemolysis values below the ASTM safety threshold of 5% at 200 µg/mL. The materials demonstrated concentration-dependent cellular uptake at 25, 50, and 100 µg/mL, with BSA@Au/Tb-FA nanoparticles exhibiting higher uptake than the non-FA-conjugated nanoparticles, BSA@Au/Tb (p < 0.05). SPCCT showed an attenuation efficiency of 38.35 HU·mL·mg⁻1 for BSA@Au/Tb-FA, attributable to the strong X-ray attenuation of Au and Tb components near their K-edge energies. Material decomposition showed strong agreement between measured and experimental concentrations (R2 = 0.98). MRI phantom studies revealed relaxivity values of r1 = 1.42 mM⁻1s⁻1 and r2 = 13.82 mM⁻1s⁻1, indicating a dominant transverse relaxation effect and T2-weighted contrast capability. Conclusion BSA@Au/Tb-FA exhibited favorable in vitro hemocompatibility and biocompatibility, with enhanced cellular uptake in MDA-MB-231 and complementary enhanced SPCCT/MRI contrast under phantom conditions, supporting its potential as a bimodal imaging agent. However, because cellular evaluation was limited to MDA-MB-231 cells without a receptor-blocking study, the enhanced uptake should not be interpreted as confirmed folate-receptor-mediated targeting. Further preclinical and in vivo studies are required to establish targeting specificity, safety, and imaging performance.