Multimodal Imaging Probes Based on Carbon Dots

Carbon dots are quasi-spherical nanometre-sized particles composed predominantly of carbon, often functionalised or doped with heteroatoms and metals to confer additional imaging and therapeutic capabilities. Their intrinsic fluorescence combined with favourable biocompatibility, water solubility and facile surface modification renders them ideal for multimodal imaging. By incorporating paramagnetic ions such as gadolinium or manganese, carbon dots can serve simultaneously as fluorescence markers and magnetic resonance imaging contrast agents. Emerging strategies encompass microwave-assisted and hydrothermal syntheses to yield uniform particles with high photoluminescence quantum yield and enhanced relaxivity. Advanced designs integrate photosensitising or photothermal functionalities, enabling image-guided therapy and real-time monitoring of treatment efficacy. Such multifunctional probes hold promise for early detection of tumours, pH-responsive imaging of pathological microenvironments and targeted delivery of therapeutic payloads. Their modular architecture supports conjugation to targeting ligands, offering precise localisation and reduced off-target effects. The global significance of these innovations spans oncology, neurology and cardiovascular diagnostics, signalling a shift towards integrated diagnosis and therapy within a single nanoplatform.

Research from Nature Portfolio

Recent studies have demonstrated the synthesis of gadolinium-doped carbon quantum dots via a hydrothermal method using renewable starch precursors. The resulting 2–8 nm probes exhibit excitation-dependent photoluminescence with a quantum yield exceeding 13 per cent, while retaining exceptional thermal and ionic stability. Measurement of longitudinal and transverse relaxivities revealed values exceeding 200 mM⁻¹ s⁻¹, surpassing many clinical contrast agents. In vitro fluorescence imaging confirmed cytoplasmic distribution in fibroblast cells, and in vivo magnetic resonance imaging showed pronounced T₁ signal enhancement in murine liver and spleen. This work underscores the capacity of carbon-based quantum dots to integrate robust optical and paramagnetic properties for dual-modality biomedical imaging.

Research from all publishers

A one-step microwave-assisted strategy yielded gadolinium/ruthenium co-doped carbon dots with a narrow size distribution around 4 nm. These probes combine red-emitting fluorescence with tunable MRI contrast and efficient reactive oxygen species generation, enabling light-induced tumour suppression in murine models. In vivo studies confirmed non-invasive fluorescence and magnetic resonance bimodal imaging during treatment.

Alternative approaches have focused on stringent purification criteria to eliminate artefacts in gadolinium-doped carbon nanodots. The purified 7–10 nm particles display homogeneous morphology, stable photoluminescence and a longitudinal relaxivity of approximately 5 mM⁻¹ s⁻¹. Cellular assays and murine MRI studies demonstrated clear contrast enhancement in liver and kidney, validating their potential as dual-function probes.

Further innovation has explored gadolinium-doped carbon nanodots acting as both photothermal agents and MRI contrast media. These nanodots exhibit pH-sensitive emission and relaxivity, allowing ratiometric monitoring of tumour microenvironments. Upon near-infrared irradiation, they generate heat for image-guided photothermal therapy, achieving selective apoptosis of cancer cells while preserving healthy tissue viability.

Multimodal Imaging Probes Based on Carbon Dots publication trend

The graph below shows the total number of articles in multimodal imaging probes based on carbon dots across all publications each year (not limited to Nature Index journals).

Technical terms

Carbon Dots: Nanoscale carbonaceous particles with intrinsic fluorescence and surface tunability.

Photoluminescence Quantum Yield: Ratio of emitted to absorbed photons, indicating fluorescence efficiency.

Relaxivity (r₁, r₂): Efficiency of a contrast agent in enhancing longitudinal (r₁) or transverse (r₂) relaxation rates in MRI.

Bimodal Imaging Probe: Nanoparticle capable of providing contrast in two distinct imaging modalities simultaneously.

Theranostics: Integration of diagnostic imaging and therapeutic functions within a single agent.

Hydrothermal Synthesis: High-pressure, high-temperature method for nanoparticle formation in aqueous solutions.

Microwave-Assisted Synthesis: Rapid, uniform heating technique to produce nanoparticles with controlled size and composition.

Reactive Oxygen Species (ROS): Chemically reactive molecules derived from oxygen, used for photodynamic therapy.

References

1. Gadolinium-doped fluorescent carbon quantum dots as MRI contrast agents and fluorescent probes. Scientific Reports (2022).
2. Facile synthesis of Gd/Ru-doped fluorescent carbon dots for fluorescent/MR bimodal imaging and tumor therapy. Journal of Nanobiotechnology (2024).
3. Luminescent Carbon Nanodots Doped with Gadolinium (III): Purification Criteria, Chemical and Biological Characterization of a New Dual Fluorescence/MR Imaging Agent. Small (2023).
4. Gadolinium-Doped Carbon Nanodots as Potential Anticancer Tools for Multimodal Image-Guided Photothermal Therapy and Tumor Monitoring. ACS Applied Nano Materials (2023).