Steve has used a modified colorimeter along with a acetylcholinesterase inhibition assay to determine whether there was any detectable difference in the levels of pesticides found in store-bought organic versus conventional raspberries.
The acetylcholinesterase (AChE) inhibition assay works as follows: Activity of AChE produces thiocholine which reacts with Ellman's Reagent (DNTB: 5,5'-dithio-bis-[2-nitrobenzoic acid) to produce a 412nm absorbing product. The product is measured with a colorimeter or spectrophotometer at 412nm to determine AChE activity. Pesticides in food (mainly Carbamate and Organophosphate) inhibit AChE activity thereby also inhibiting the production of the 412nm product in the assay tube.
For this pesticide assay, Steve used a commercially available kit, the Rapid Pesticide Detection Test Kit from RenekaBio, Cat # 003RT. With this kit AChE activity (and consequent production of the 412nm product) converts the assay reaction from an initial pink color to a dark orange color. Extracts prepared from food (typically fruits and vegetables) are introduced into the assay to determine their inhibitory affect on the enzyme. If there is no AChE inhibition (i.e. no detectable pesticides in the extract) the reaction turns orange. Conversely, if there is pesticides in the food extract, the reaction stays pink. The kit includes a visual color guide for the end-user. After a 5 minute incubation the color of the reaction is examined and food extract is classified as "strongly unsafe" for pink, "unsafe" for a pink/orange color and "safe" for a dark-orange color.
Interestingly, Steve also made use of the Public Lab Spectrometer, a project we were happy to back on Kickstarter. Using these two open source instruments in a complimentary way is an excellent idea and has inspired us to also use our spectrometer in more of our own experiments. You can also follow Steves research on his Wiki page on the public lab website.