Synthesis and preclinical validation of 5HT_1A receptor-targeted carbon dots functionalized with Gd³⁺ and ^99mTc as a...

We report a novel 5HT_1A receptor-targeted multimodal imaging probe developed by functionalizing biocompatible nitrogen doped carbon quantum dots (CD_MPP-DTPA). The carbon quantum dots were hydrothermally synthesized using methoxyphenyl piperazine (MPP) for neuro receptor targeting and diethylenetriaminepentaacetic acid (DTPA) for metal chelation. Subsequent loading with Gd³⁺ and radiolabeling with ^99mTc (efficiency: 95.5% ± 0.5) enabled MRI-optical and SPECT-optical imaging, respectively. Subsequent to Gd³⁺ loading, CD_MPP-DTPA continued to exhibit excellent fluorescence characteristics at 360-380 nm. A bright contrast of the 5HT_1A rich hippocampal region was observed in T₁-weighted MRI scans using Gd-CD_MPP-DTPA, with a longitudinal relaxivity (r₁) of 9.983 mM^-1 s^-1 and a transverse relaxivity (r₂) of 15.262 mM^-1 s^-1. In vitro assays confirmed the biocompatibility of the resulting probes, which were evaluated using an MTT cytotoxicity assay with HEK cells, and a haemolysis assay. Histopathological analysis confirmed the nontoxic nature of the probes. In vivo T₁-weighted MRI and SPECT scans in mice demonstrated significant brain permeability and indicated early brain uptake. Region of interest (ROI) analysis corroborated the invasive organ biodistribution pattern, and a brain uptake of approximately 3.24% ID g^-1 (injected dose per gram of tissue) was evident, along with the hepato-biliary and renal clearance pathways. These findings establish the functionalized carbon quantum dots as a promising multimodal imaging nanoplatform for the noninvasive mapping of 5HT_1A receptors, particularly relevant in the diagnosis and longitudinal monitoring of neurological conditions.