Confocal microscopy uncovers toxic nanoparticles


Rebecca Pool

Monday, February 9, 2015 - 13:30
Confocal microscopy of a cell with silver nanoparticles [MPIKG]
Germany-based researchers have unveiled stunning confocal micoscopy images of cells incubated with silver nanoparticles as part of research into the toxicity of the materials.
The nanoparticles are being used in myriad applications, from drug delivery to disease diagnosis, yet researchers do not fully understand how the particles interact with cells.
With this in mind, Dr Guillermo Orts-Gil from the Max Planck Institute of Colloids and Interfaces, and colleagues, synthesized silver nanoparticles, coated with either glucose, galactose or mannose.
These carbohydrates are typically used during manufacture to functionalise the nanoparticle surface ready for use in disease diagnosis and treatment.
The researchers then incubated lab-grown cells with dilutions of the different nanoparticles, evaluating toxicity via a standard MTT assay.
They also used confocal microscopy and mass spectrometry to assess particle-cell interactions.
According to Orts-Gil, glucose-functionalised nanoparticles were found to be significantly more toxic towards the cells than those functionalised with galactose and mannose.
Crucially, confocal microscopy and mass spectrometry revealed that the least toxic of the nanoparticles - the galactose-functionalised nanoparticle - actually penetrated the cells the most, countering past nanoparticle research that related toxicity to cellular uptake.
Indeed, confocal microscopy showed galactose-functionalised nanoparticles clustering inside the cell cytoplasm while the more toxic glucose- and mannose-coated particles spread evenly through the cell.
Confocal microscopy images of cells incubated with nanoparticles; cell nuclei are stained in red while green dots represent fluorescently labelled nanoparticles. [Journal of Nanobiotechnology]
"We see that particles which are largely internalised into cells do not necessarily present the highest toxicity," says Orts-Gil. "Here, the glucose-capped nanoparticles present the highest toxicity... despite moderate cellular uptake, compared to the other nanoparticles."
"Intracellular oxidative stress, depending on particles coating was the deciding factor leading to toxicity," he adds. 
The researchers believe their latest findings provide new information for manufacturers of nanoparticles, on how bioactivity of silver nanoparticles can be altered, using different carbohydrate coatings.
Research is published in the Journal of Nanobiotechnology
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