Luminescent substance for safer diagnostic imaging

Spanish researchers have designed a fluid that works like a luminous ink to obtain very sharp images of damaged tissues, organs and cartilages in diagnostic tests.

This new compound, still in the laboratory phase, reduces adverse effects on the human body because it allows lower amounts to be injected and the dose to be targeted only at the affected area. It has been described in the Journal of Colloid and Interface Science.

Substances that serve to ‘light up’ and allow better observation of damaged organs, tissues or cartilages are called contrast agents, and act like an ink to better define the parts of the anatomy that need to be viewed through diagnostic imaging techniques. These substances are used in various tests that provide 3D images of organs and tissues of the human body, such as computed tomography (CT) — which is used to observe damaged organs through X-rays — or magnetic resonance imaging (MRI), a diagnostic test based on a machine that uses a very powerful magnet. They are also used for photoluminescent imaging, a technique that works like an X-ray in which the damaged area is illuminated. The latter, being more harmful, is only used in laboratories for tests on mice.

The patient ingests or is injected with a contrast agent when the images taken using these techniques are not sharp enough, for example when a tumour cannot be distinguished from the surrounding area. Each diagnostic test requires a different contrast agent, and sometimes the patient must ingest or be injected with two types of substances so that the image of the body part photographed looks more defined. Furthermore, there is some toxicity in some of the substances used today.

Researchers from the Institute of Materials Science of Seville (a CSIC–University of Seville joint centre), in collaboration with the Institute of Materials Science of Aragon, the Andalusian Centre of Medicine and Biotechnology (BIONAND) and the National Accelerator Centre (CNA), developed a contrast agent based on nanoparticles consisting of 80 nm spheres with luminescent properties that were coated with molecules called ligands. These molecules work as a magnet that is attracted to the area of interest, preventing them from spreading to other parts of the body, as is the case with commonly used contrast agents. Their function is to simulate the zoom of a camera: the nanoparticles are concentrated in a single area of interest and help to focus it better.

“We have designed this contrast agent to be effective in both MRI and CT scans,” said study co-author Ana Isabel Becerro, from the Institute of Materials Science of Seville. “This makes it possible to reduce the dose injected into the vein and to reduce the potential toxic or adverse effects of this substance on the body. In addition, it enables luminescent images of cells and tissues to be taken for in vitro studies.”

The use of nanoparticles in medicine requires them to be uniform in order for their properties to be replicated: all spheres must emit the same amount of light and always have the same size. As noted by Becerro, “They are injected intravenously, so they must not exceed 100 nm, they must be dispersed so as not to produce thrombi or clots, and they must be harmless to the organism.”

In addition to these properties, the researchers’ nanoparticles have an architecture known as core-shell, which means that they have a luminous nucleus that makes them useful for luminescent imaging, with an intermediate layer that shields the light emitted by the nucleus and an outer shell made of a material visible under MRI. Furthermore, their chemical composition makes them equally effective for CT scans.

Once ingested or injected, the nanoparticles become visible when exposed to ultraviolet light; the scientists are now looking to ensure that the luminescence of the nucleus of the nanoparticles persists after ultraviolet light is removed. This would mean the substance could be activated before being introduced into the body, enabling in vivo applications without exposing the patient to ultraviolet radiation.

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