Capturing efficacy assessment of antibodies against Xylella fastidiosa through Surface Plasmon Resonance

Xylella fastidiosa is among the most dangerous plant pathogenic bacteria, worldwide causing a variety of diseases with huge economic impact on agriculture and environment. A surveillance tool, ensuring the highest possible sensitivity enabling the early detection of X. fastidiosa outbreaks, would be of paramount importance. Fundamental to the development of such a detection system is the availability of high affinity and specific antibodies to the bacterium. So far, a variety of plant pathogen biomarkers were studied by means of Surface Plasmon Resonance (SPR), but none of them involves X. fastidiosa. In this study SPR has been proposed to assess the optimized biofunctionalization protocol of gold surfaces with anti-XF, validating their capturing efficacy against X. fastidiosa. Selectivity is guaranteed by bio-functionalizing the gold transducing interface with polyclonal antibodies for X. fastidiosa and it was assessed by means of a control experiment involving the non-binding Burkholderia phytofirmans bacterium. Remarkably, a limit of detection as low as 105 CFU/mL was achieved by transducing the direct interaction between the bacterium and its affinity antibody, which is comparable to the label-needing ELISA gold standard. Moreover, the binding-affinity between polyclonal antibodies and the X. fastidiosa bacteria has been also evaluated, obtaining an affinity constant of 3.5∙107 M-1, comparable with those given in the literature for bacteria detection against affinity antibodies. The study is therefore a preliminary development of a reliable cost-effective process to successfully bio-functionalize a gold surface, eventually suitable as gate electrode in wide-field bioelectronic sensors, for ultra-sensitive detection of X. fastidiosa.