Real-time detection of chlorpyrifos at part per trillion levels in ground, surface and drinking water samples by a portable surface plasmon resonance immunosensor

Continuous monitoring of the organophosphate pesticide chlorpyrifos in real water samples has been performed using a portable surface plasmon resonance (SPR) immunosensor. The immunoassay was based on a binding inhibition test by using the covalent immobilization of an analyte derivative onto the gold-coated sensing surface. Sensor reusability was assured through the formation of alkanethiol self-assembled monolayers (SAMs). In this format, the biosensor surface remained stable over 190 measurements including regeneration cycles. The reproducibility and precision of SPR measurements were evaluated by performing independent immunoassays for three replicates of each sample. The batch-assay variability was also estimated using three different gold-coated sensor surfaces. The assay provided a highly sensitive detection of chlorpyrifos at nanogram per litre levels (55 ng L−1) in laboratory buffer. No significant matrix effects were found for ground, river and drinking water samples, where the limits of detection ranged from 45 to 64 ng L−1 and the recovery values were between 80 and 120%. The validation of chlorpyrifos immunoassay was performed using conventional chromatographic methods (GC–MS). The correlation between both techniques was proved by the good correlation coefficient (r2 = 0.995) obtained. Chlorpyrifos immunoassays were developed using the β-SPR sensor system commercialised by the company SENSIA, S.L. (Spain). Rapid analysis of samples, without previous extraction or clean-up, was accomplished in only 20 min, including the regeneration cycle. The high sensitivity, low-time of response and portability of the β-SPR biosensor platform, would allow its application as a field analytical method for environmental waters.