Massive use of herbicides in agriculture over the last few decades has become a serious environmental problem. The residual concentration of these compounds frequently exceeds the maximum admissible concentration in drinking water for human consumption and is a real environmental risk for the aquatic ecosystem. Herbicides inhibiting photosynthesis via targeting photosystem II function still represent the basic means of weed control. A multibiosensor was constructed for detecting herbicides using as biosensing elements photosynthetic preparations coupled to an optical fluorescence transduction system (Giardi et al. EU patent EP1134585, 01830148.1-2204); this paper is about its application in the detection of herbicide subclasses in river water. Photosynthetic material was immobilized on a silicio septum inside a series of flow cells, close to diodes so as to activate photosystem II (PSII) fluorescence. The principle of the detection was based on the factthat herbicides selectively modify PSII fluorescence activity. The multibiosensor has the original feature of being able to distinguish the subclasses of the photosynthetic herbicides by using specific immobilized biomediators isolated from mutated organisms. This setup resulted in a reusable, portable multibiosensor for the detection of herbicide subclasses with a half-life of 54 h for spinach thylakoids and limit of detection of 3 x 10(-9) M for herbicides present in river water.
A miniaturized biosensor-based optical instrument has been designed and fabricated for multiarray
fluorescence measurements of several biomediators in series, with applications in environmental
monitoring and agrofood analysis. It is a multicell system featuring two arrays of five static cells
(1 × 1 × 2 cm3)
which are sealed to avoid contamination. Every cell is made up by two modular sections:
the bottom compartment with optical LED light excitations and a photodiode
detector for fluorescence emission capture, and the top biocompatible compartment
where the biosample is deposited. The system (0.250 kg without batteries and case,
100 × 100 × 150 mm3
internal case dimensions) is equipped with electronic control boards, a flash memory card
for automatic data storage, and internal batteries, thus being portable and versatile. The
instrument allows one to perform simultaneous and multiparametric analyses and offers a
large applicability in biosensor technology. The first prototype has been implemented with
genetically modified oxygenic photosynthetic algae that were employed in the instrument
experimental testing by monitoring pesticide pollution in water. Pesticides modify the
photosystem II (PSII) activity in terms of fluorescence quenching. The PSII complex
features a natural nanostructure and can be considered a sophisticated molecular device.
Results from measurements employing several PSII mutants and six different
pesticides at increasing concentrations and incubation times are presented and
discussed.
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