# Biodistribution of Tc-99m-Labeled Solid Lipid Nanoparticles and Evaluation of Their Possibility as a Radiopharmaceutical

## TL;DR

This study explores using radiolabeled solid lipid nanoparticles for imaging, showing they target the liver and spleen in rabbits.

## Contribution

The study demonstrates the potential of 99mTc-labeled SLNs as a novel radiopharmaceutical for liver–spleen imaging.

## Key findings

- 99mTc-labeled SLNs showed high radiolabeling efficiency (>95%) and were taken up mainly by the liver and spleen.
- Ex vivo analysis confirmed the in vivo findings, showing significant uptake in RES organs.
- Confocal microscopy supported the biodistribution results in liver and spleen tissues.

## Abstract

Solid lipid nanoparticles (SLNs) are submicron colloidal systems widely investigated as drug carriers; however, their intrinsic biodistribution properties are also critical when SLNs are considered for diagnostic imaging. In the present proof-of-concept study, drug-free SLNs were evaluated exclusively as a radiolabeled imaging agent rather than as a drug delivery system. SLNs were radiolabeled with Technetium-99m (99mTc), and their in vivo biodistribution was investigated using gamma camera imaging, ex vivo organ counting, and confocal microscopy. SLNs were prepared by a microemulsion–low-temperature solidification method and characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Radiolabeling efficiency was determined by instant thin-layer chromatography (ITLC) and exceeded 95%. Following intravenous administration in a rabbit model, dynamic scintigraphic imaging demonstrated predominant uptake in the liver and spleen. These findings were quantitatively confirmed by ex vivo biodistribution analysis at 4 h post-injection and qualitatively supported by confocal microscopy of liver and spleen tissues. The results indicate that 99mTc-labeled SLNs behave as RES-targeting radiocolloids and may serve as potential agents for liver–spleen scintigraphy.