Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

BIOSENSOR-BASED TECHNOLOGIES 435
structurally diverse aflatoxins have been reported, aflatoxins B 1 ,B 2 ,G 1 and G 2 , and M represent
the greatest danger to human health (Keller et al., 2005). All of these compounds may
be assembled in Aspergillus parasiticus, while Aspergillus flavu can synthesize aflatoxins
B 1 and B 2 independently (Yu et al., 2004).
Due to the agricultural importance of these mycotoxins, several biosensor-based platforms
have been developed to permit the detection of trace levels of different aflatoxins
(Lacy et al., 2006). Several of these protocols have been carried out in our laboratory and
have focused on aflatoxin B 1 (AFB 1 ). Daly et al. (2000) used a rabbit-derived polyclonal
antibody to detect AFB 1 , which was conjugated to BSA and immobilized onto a CM5 Biacore
chip. A competition assay between free and bound AFB 1 permitted a linear range of
detection of trace levels (3–98 ng/mL). Daly et al. (2002) subsequently generated murine
scFvs against AFB 1 by using a phage-display format and incorporated these antibodies into
a Biacore-based inhibition assay. Dunne et al. (2005) developed a unique SPR-based inhibition
assay that incorporated monomeric and dimeric scFv antibody fragments that could
detect AFB 1 immobilized on a CM5 Biacore chip. Monomeric scFvs could detect between
390 and 12,000 ppb, while the dimeric scFv was more sensitive, detecting between 190 and
24,000 ppb.
Several other research groups have developed similar rapid analytical biosensor-based
platforms for aflatoxin detection. Carlson et al. (2000) developed a handheld biosensor to
detect minute traces of aflatoxins at concentrations of between 0.1 and 50 ppb. In another
elaborate experiment, Sapsford et al. (2006) developed an indirect competitive immunoassay
on a fluorescence-based biosensor that permitted rapid detection of AFB 1 in spiked
corn (cornflakes, cornmeal) and nut (peanuts, peanut butter) products. Mouse monoclonal
antibodies were labeled with the fluorescent dye CY5, with detectable signals inversely
proportional to the concentration of AFB 1 present. Limits of detection for nut and corn
products were 0.6–1.4 and 1.5–5.1 ng/g, respectively. Adanyi et al. (2007) also recently
described a unique protocol for permitting aflatoxin detection by using optical wavelength
light mode spectroscopy (abbreviated to OWLS). Integrated optical wavelength sensors
were selected for use in this experiment with the sensitive detection range for a competitive
assay being between 0.5 and 10 ng/mL. An indirect screening protocol was subsequently
applied to wheat and barley that permitted the detection of AFB 1 and ochratoxin A.
20.6 Legislation
This chapter has discussed a variety of different biosensor-based platforms that may be
used to detect a range of different molecules such as pesticides, herbicides, and mycotoxins.
It is important to consider the legislation associated with the monitoring of agricultural
produce. The Food and Agriculture Organization of the United Nations (FAOSTAT)
(http://faostat.fao.org/) is an international body whose overall aim is to protect the health of
consumers. FAOSTAT has an online database (The Codex Alimentarius: Pesticide Residues
in Food Maximum Residue Limits, see additional websites of interest), which details the
maximum residue limits (MRLs) for pesticides in commodities such as fruit and vegetables.
The establishment of an MRL (usually expressed as mg/kg) is dependent on good agricultural
practice for pesticides. This relates to where the highest detectable residues anticipated
(when a pesticide-containing product is applied to a commodity to remove contaminants)
are intended to be toxicologically acceptable. Under these arrangements, the important