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Immunomagnetic separation (IMS) using immunomagnetic beads (IMBs) or particles (IMPs) is useful for rapidly capturing and concentrating analytes such as bacteria, viruses, allergens, toxins, etc, prior to a detection stage.  Although powerful "rare earth" magnets are used to capture IMPs the rapid decrease of magnetic flux density with distance from a conventional magnet generally limits direct IMS to volumes of 1-10 mL (occasionally greater), which restricts the limit of detection of IMS-based techniques.

There are needs for lower limits of detection.  For example, if a regulation requires a bacterial pathogen to be absent in a 25g sample of food, the target cells will be dispersed in 250 mL by the time a suspension has been made.  Even if IMPs could trap every target cell, IMS based on a 10 or even 50 mL aliquot is unlikely to pull out the target - incubation will be required to increase cell density.  Similarly, there is a need to increase sample size in the detection of viral contamination in foods.  Just one commercial system (Pathatrix®) currently exists capable of handling 250 mL suspensions.

Workers in IMS will have noted a recent paper (Morton, et al, 2009) describing capture of Noroviruses from 250 mL suspensions using an apparatus called iCropTheBug.  This web page provides a little background about iCropTheBug.

In response to an idea by Dr. C. Bin Kingombe of Health Canada in Ottawa, Filtaflex Ltd used a creative magnetology to develop iCropTheBug for Health Canada.  The system permits IMPs to be rapidly captured directly from 250 mL volumes without need for specialised and costly consumables.

iCropTheBug handles suspensions in regular 500 mL conical (Erlenmeyer) flasks.  The system comprises three components:

- a "Settling Magnet" produces an upwardly "focused" magnetic field. The first step in capturing IMPs by iCropTheBug is to slide the flask around the top of the Settling Magnet a few times - IMPs sediment to the bottom of the flask in seconds.  The user then pushes the flask into the clamp of;

- a "Vibrating Table" which has a swing-away magnet.  In its "up" position this magnet pulls IMPs to the centre of the flask bottom.  The Table vibrates the flask to help the IMPs migrate - within 5-10 min IMPs coalesce into a pellet at the centre of its base.  The user swings the magnet down to reduce its influence and removes the IMP pellet from the flask using;

- a "Magnetic Pipet". This was a regular PickPen®, modified for Health Canada so that it could reach to the bottom of a 500 mL flask.  To permit easily stabbing the magnetic pipet into the IMP pellet through opaque suspensions, the Vibrating Table has LEDs and a mirror in its base so the user can see the pellet "from below".  Collecting IMPs on the pipet's tip takes just seconds and they can then be introduced to any desired analytical step.

The process of capturing IMPs from 250 mL suspensions by iCropTheBug thus requires 5-10 minutes.  iCropTheBug is subject to patent applications.