Regulars Soundbite
Scratch and sniff to detect crime
Patrick Walter finds out how the public can help catch criminals with their nose
The game is afoot! UK charity
Crimestoppers is enlisting the
help of the Great British public to
sniff out cannabis farms. To aid
the public in their undercover
work they’ve been handing out
scratch and sniff panels. These
give people an idea of what
living, growing, cannabis smells
like – Crimestoppers describes
it as a sickly, sweet smell, as
opposed to the more acrid aroma
when it’s smoked.
What’s the problem?
The charity is working with the
police to try to tackle the increase
in residential farms, where
people often grow the plants
hydroponically in attics using
heat lamps and high intensity
lighting. The police claim that
cannabis cultivation is fuelling
organised crime, while the UK’s
energy regulator says that the cost
of electricity stolen by these farms
may be costing the economy as
much as £400 million each year.
Lucy Reid, campaign manager
at Crimestoppers, explains that
the Dutch police ran a similar
campaign and as a result there
was a 45% rise in cannabis farms
sniffed out in Amsterdam. She
points out that the scratch and
sniff panel doesn’t contain any
tetrahydrocannabinol (THC) –
the psychoactive compound
in cannabis.
Recreating smell
To try to find out more, I spoke
with JanCees Neef at the Edge
Factory in the Netherlands, whose
company produces the scratch
and sniff cannabis panels. Dutch
police deliver cannabis plants
to them and that they quickly
process them to extract an oil
from the plants. This cannabis
oil is then microencapsulated
and printed onto cards – this
technology can preserve the smell
for a couple of years.
To capture a smell
There are many ways of
microencapsulating compounds
and most have been developed
by the cosmetics industry.
Scratch and sniff panels often use
polymers like polyoxymethylene
urea. The oil and polymer are
mixed together at high speed to
produce droplets of oil 15–20 µm
in size, suspended in the polymer
solution. A catalyst is then added
to crosslink the polymers, sealing
the oil inside the microcapsules.
The microencapsulated oil
droplets are washed to remove
leftover polymer and oil,
and then processed to form
a slurry for printing. The
printed microcapsules burst
when scratched, releasing
whatever smelly compound the
manufacturer desires.
As it’s a company secret, Neef
couldn’t tell us which of the
volatiles produced the distinctive
fresh cannabis smell. However,
cannabis’ smell is the product
of more than 100 terpenoids,
including eucalyptol, linalool and
pinene. What’s also interesting is
Reid’s insistence that the scratch
and sniff panels don’t contain any
THC, but obviously still contain
enough of the smelly terpenoids
to provide a rough approximation
of the odour of growing cannabis.
Education in Chemistry | July 2013 | www.rsc.org/eic | 9