An optical immunosensor based on White Light Reflectance Spectroscopy is described for the determination of the herbicide glyphosate in drinking water samples. The biosensor allows for the label-free real-time monitoring of biomolecular interactions taking place onto a SiO2/Si chip by transforming the shift in the reflected interference spectrum caused by the immunoreaction to effective biomolecular adlayer thickness. Glyphosate determination is accomplished by functionalizing the chip with a protein conjugate of the herbicide followed by a competitive immunoassay format. Prior to the assay, glyphosate derivatization in the calibrators and/or the samples was performed through reaction with succinic anhydride. Under the optimized assay protocol, a detection limit of 10 pg mL-1 was achieved. Recovery values ranging from 90.0 to 110% were determined in spiked bottled and tap water samples, demonstrating the accuracy of the method. In addition, the sensor could be regenerated and re-used for at least 14 times without statistically significant effect on the assay sensitivity and accuracy. The excellent analytical performance and short analysis time (approx. 25 min), combined with the small sensor size, should be helpful for the fast on-site determination of glyphosate in drinking water samples.
Keywords: Drinking water; Glyphosate; Label-free immunosensor; White light reflectance spectroscopy.
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