In a bind with dirty water: Using CE to test water purification ability

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  • Published: Aug 15, 2011
  • Author: Jon Evans
  • Channels: Electrophoresis
thumbnail image: In a bind with dirty water: Using CE to test water purification ability

Magnetic nanoparticles

Using capillary electrophoresis (CE), Canadian chemists have explored the potential of using various different nanoparticles to remove environmental contaminants and pathogenic micro-organisms from water.

Their idea is to mix the nanoparticles with contaminated water, allow the contaminants to bind with the nanoparticles, and then remove the nanoparticles from the water. To aid with this removal process, the team of chemists from Carleton University in Ottawa, led by Edward Lai, turned to iron-based magnetic nanoparticles, which can easily be removed from water with a magnet. They then coated these nanoparticles with either polydopamine or polypyrrole, which are molecular adhesives that can bind with a wide variety of molecules, including many contaminants.

The only problem with this approach is that it's not very selective. Now this isn't really a problem if you just want to remove as many contaminants as possible, but it is a problem if you want to remove a specific contaminant. So Lai and his team also decided to investigate molecularly imprinted polymers (MIPs) made from polymethacrylic acid-co-ethylene glycol dimethacrylate (PolyMAA-co-EGDMA).

MIPs are produced by synthesising a polymer around a specific molecule and thus creating a nanoparticle with an imprint of that molecule in it. It's a molecular version of producing a copy of a key by pressing it into soft clay. When these nanoparticles are then mixed with a group of different molecules, only the specific molecule used as the template can fit in the imprint.

All bound up

To investigate how well these coated magnetic nanoparticles and MIPs would bind with environmental contaminants, Lai and his team turned to CE. They came up with a method that involved first injecting the nanoparticles into the capillary, followed by the contaminants. The fast-moving contaminants quickly catch up with the slower moving nanoparticles and bind with them, with any unbound contaminants overtaking the nanoparticles before reaching a UV detector.

Because the contaminants are present at known concentrations, the size of the peak produced by the unbound contaminants can be used to determine what proportion did bind to the nanoparticles, with smaller peaks meaning more binding. Using this method, Lai and his team tested how well the nanoparticles bound with three contaminants commonly found in water: bisphenol A, which is found in many plastics; naphthalene acetic acid (NAA), which is a plant hormone used as a pesticide; and the disinfectant proflavine.

Caught by the MIPs

They found that 90% of bisphenol A and 97% of proflavine would bind with magnetic nanoparticles covered in polydopamine. In contrast, although magnetic nanoparticles covered in polypyrrole were just as effective at binding proflavine (95%), they were less effective at binding bisphenol A (60%). Neither nanoparticle was particularly good at binding NAA, with just 20% binding to the polydopamine coating and 50% binding to the polpyrrole coating.

Unsurprisingly, the MIPs were very good at binding with their target contaminants, with 99% of bisphenol A and proflavine binding to their respective MIPs. Interestingly, however, it turned out that bisphenol A and proflavine would also bind with PolyMAA-co-EGDMA nanoparticles that lacked any imprint, with over 90% of both contaminants binding to the non-imprinted versions.

Lai and his team also tried out this approach on the bacteria Escherichia coli and found that 99% of E. coli cells would bind to magnetic nanoparticles coated with polydopamine. This all indicates that nanoparticles can offer an effective way to remove contaminants and pathogenic microorganisms from water.

The chemists are now testing this approach on other contaminants and pathogenic micro-organisms, including the neurotoxin-producing bacteria Clostridium botulinum.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

In a bind with dirty water: Using CE to test water purification ability

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