Bismuth nanoparticles (Bi Nps) exhibit strong X-ray attenuation due to bismuth's high atomic number (Z = 83) and present lower bulk cost than gold or platinum. Bi Nps show improved biocompatibility relative to iodinated contrast agents (ICA) and can be functionalized for tissue-specific targeting, such as with anti-contactin-2 antibodies for cardiac conduction system (CCS) imaging.

Bi Nps were synthesized by reducing bismuth(III) nitrate pentahydrate in 1,2-propanediol with borane and glucose. Particles underwent layer-by-layer functionalization with poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), followed by PEGylation with mPEG-NH₂ via EDC chemistry. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and ζ-potential was used to characterize structure, hydrodynamic diameter, and surface charge. DLS and FT-IR spectroscopy confirmed PEGylation. Bi Nps were functionalized with either IgG Ab (control) or anti-contactin-2 (Cntn2 Ab), an antibody targeting CCS membrane proteins. Nano differential scanning fluorimetry (NanoDSF) confirmed antibody conjugation and monitored protein stability of nanoparticle-bound antibodies.

Bi Nps exhibited a hydrodynamic diameter of 105.1 ± 0.64 nm with a polydispersity index of 0.19 ± 0.006. TEM confirmed a large inorganic core (65.6 ± 9.6 nm). ζ-potential was −25.6 ± 0.88 mV, supporting colloidal stability. PEGylation was validated by a 41 nm diameter increase and the presence of C–O–C and C=O peaks at 1100 cm^-1 and ~1650 cm^-1, respectively. X-ray attenuation exceeded that of ICAs. Long-term studies showed stable size and charge, underscoring circulation suitability. NanoDSF confirmed antibody presence on Bi Nps by detecting protein unfolding at 70.11 ± 0.43 °C. Antibody functionalization enables targeted imaging for diagnosis and therapy. These findings support Bi Nps for in vitro and in vivo precision imaging.

Figure 1. Bi Nps conjugation: A) Schematic, B) TEM image, C) ζ-potential, D) FTIR spectra, and E) NanoDSF highlighting changes in protein intrinsic fluorescence as a function of temperature. *Not to scale

Blake Fallon

Houston Methodist Academic Institute

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