Fourier transform infrared spectroscopy was used to characterise magnetic nanoparticles that might one day be used to treat lead poisoning, but could have more immediate applications in diagnostics, biomedical research and environmental science.

Lead is one of the most dangerous heavy metals. Lead(II) ions accumulate in the body and have been linked to various problems including muscle paralysis, mental confusion, memory loss, and anaemia. It is especially toxic to children damaging neuronal connections, causing brain and blood disorders. Evidence suggests that lead(II) ions affect multiple targets including the calcium- and zinc-binding proteins involved in cell signalling and gene expression.

Safe and effective detoxification processes are not readily unavailable. Now, researchers in Korea have developed a highly promising approach that uses a fluorescence receptor that selectively and strongly binds to lead(II) ions to allow lead ions to be extracted using magnetic nanoparticles.

Won Seok Han and Jong Hwa Jung and colleagues Hye Young Lee, Doo Ri Bae of the Department of Chemistry and Research Institute of Natural Sciences and Environmental Biotechnology National Core Research Center, Gyeongsang National University, in Jinju and Ji Chan Park and Hyunjoon Song of the Department of Chemistry and School of Molecular Science Korea Advanced Institute of Science and Technology, in Daejeon, describe details of their approach in the international chemistry journal Angewandte Chemie

Han and Jung point out that various methods for metal ion recovery from aqueous solutions have been developed, including chemical precipitation, membrane filtration, ion exchange, and liquid extraction. However, no such practical means for lead removal from blood has yet been developed.

Bing Xu and colleagues at The Hong Kong University of Science & Technology, reported the use of bisphosphate-modified magnetic nanoparticles for the removal of radioactive uranium ions with high efficiency from blood. Their nanoparticles could remove almost three quarters of the initial 100 ppm UO₂²⁺. At the time, they also suggested that such functionalized, biocompatible magnetic nanoparticles might work in vivo.

This result inspired Han and Jung to investigate the possibility of removing lead ions from blood using related magnetic nanoparticles to which a fluorescent probe could be added.

"In this work, a new 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivative was selected as a signal-transducing unit because it absorbs and emits in the visible region with high excitation coefficients, high fluorescent quantum yields, and high photostability," the team explains. The team used transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), FTIR spectroscopy, time-of-flight second ion mass spectroscopy (TOF-SIMS), and fluorophotometric methods to characterise the functionalised magnetic nanoparticles.

"The new class of BODIPY-functionalized magnetic silica nanoparticles could therefore be an ideal candidate for the removal or recovery of lead(II) ions with high efficiency from water or human blood," they say. One crucial aspect of such a technology is that it has to be highly selective for lead(II) only otherwise it could strip essential metals, such as calcium and zinc from the blood.

To address this point, and having demonstrated extraction efficacy spectroscopically, the team tested selectivity when competitive ions were added to their samples including Li⁺, Na⁺, Mg²⁺, K+ ,Ca²⁺, Cu²⁺, Zn²⁺, Ag+, Cd²⁺, and Hg²⁺, all of which are of biological or environmental relevance. The extractant displayed a large effect only with lead(II) ions and the team saw minimal or no changes with other metal ions.

Detoxification could theoretically work like the process of hemodialysis used for patients with kidney failure. The blood would be diverted out of the body and into a special chamber containing the biocompatible magnetic particles. The lead ions would bind to the selective anchors on the particles and a magnetic field used to remove the lead-encrusted particles. The purified blood would then be reintroduced into the patient's system.

The highly selective nature of the BODIPY nanoparticles is in sharp contrast to conventional chelation therapy, as no vital minerals or trace elements would be removed from the body in this process. Additional research is now required to test efficacy as well as to determine whether or not related ligands might be used with magnetic nanoparticles to extract different toxic metals from biological and environmental samples.

Related links:

• Angew Chem Int Edn, 2009, 48, 1239-1243

Article by David Bradley