Particle biology

FILTER-FEEDING bivalve molluscs, such as mussels, oysters, scallops and clams, are a useful and tasty source of protein. They can, though, also be harbingers of illness. A filter-feeder lives, as the name suggests, by trapping and consuming particles (mostly bacteria and single-celled algae) suspended in water it pumps through its body. If those particles are themselves toxic, they can seriously discomfort, and occasionally kill, a human who eats a mollusc that has been feeding on them.

The most common culprits are algae called dinoflagellates and diatoms, several species of which make potent toxins. These algae often multiply into spectacular blooms along coastlines. Even in the absence of such a bloom, though, they can be abundant enough to cause problems. For this reason, in most places in the rich world at least, bivalves intended for sale have to be tested before they go to market. That involves taking samples to a laboratory, which is cumbersome and time-consuming. What is needed is a simple test that can be carried out on-board a ship. And Waqass Jawaid, of Queen’s University in Belfast, thinks he has one.

One way of screening shellfish is pretty crude. This is to inject a mouse with a sample and see if it gets ill— a procedure no longer used in Europe, but still permitted in parts of America. The alternative, a mix of chromatography and mass spectrometry, is more sensitive, but requires expensive equipment and trained staff. Dr Jawaid’s method, which he and his colleagues report in the Journal of Agricultural and Food Chemistry, employs antibodies to create a system similar to a pregnancy test.

The system’s testing strip has three bands. The first is covered with the antibodies in question, which have a special affinity for okadaic acid, one of the most common algal toxins. These antibodies are loosely bound to the strip’s surface, so they will wash away if a sample is applied. Next to the antibody band is a band covered with molecules that have a special affinity for the antibody—but only if it is not bound to okadaic acid. Beyond these two bands is a third, which is peppered with similar molecules to the second, except that in their case they have an affinity for the antibody whether or not it is not bound to okadaic acid.

Crucially, the second and third bands turn red if their molecules bind to the antibody. This means that, if a sample containing okadaic acid is placed on the first band and allowed to diffuse along the strip, only the third band will turn red (because the antibodies picked up by the sample will be bound to okadaic acid). If the sample is okadaic acid-free, however, two red bands will form.

Prototypes of Dr Jawaid’s detector were indeed able to distinguish and reject all samples whose okadaic-acid levels exceeded established safety limits. They also threw up false positives, by rejecting some samples with highish levels of okadaic acid that did not actually breach these limits. But that is in contrast to mouse assays, which are subject to false negatives—ie, passing as safe samples that are not.

Compared with the mouse test, then, Dr Jawaid’s errs on the side of caution. It is also cheaper than the chromatography-mass spectrometry approach. But its greatest advantage may be that, because it can be done on-board ship for an instant result, it shortens the time it takes for shellfish to make it from the seabed to the table.