Do fats matter? Design of serum albumin bioreceptor for PFOA, from toxicological studies to biosensor applications

A better understanding of the interactions between perfluroocatanoic acid (PFOA) and human serum albumin (HSA) can improve the design of protein-based electrochemical biosensors for fluorinated environmental contaminants, namely per- and poly-fluoroalkyl substances (PFAS). In the last decade, the affinity of PFOA for fatted and defatted serum albumin was confirmed by numerous toxicological studies 1-3 . The results showed that PFOA can bind strongly to serum albumins, such as HAS, mimicking fatty acids binding and affecting the functions of these transport proteins. To transpose these findings in the design of bioreceptors, a multi-analytical study was carried out comparing directly the performances of fatted and defatted HSA in terms of stability, number of binding sites and affinity towards PFOA and other PFAS . Isothermal titration calorimetry (ITC) measurements allowed to define the stoichiometry and the affinity constants, while native nano-electronspray ionization MS (nESI-MS) provided additional information about the stability of the proteins and the protein-target complex. To identify the binding site and discriminate between fatted and defatted HSA, vapor diffusion crystallization was performed. All analysis confirmed the higher affinity of PFOA for the defatted HSA even though the fatted HSA showed an higher stability. Both types of HSA were immobilized on the graphite-screen printed electrodes modified with graphene oxide (GO) or electropolymerized o-phenylene diamine (oPD). Impedance electrochemical spectroscopy (EIS) and cyclic voltammetry (CV) were used to characterize the immobilization strategies performances. Also direct detection by EIS and indirect detection using a redox mediator were compared to evaluate the binding event between PFOA and HAS. The combination of toxicological data and electrochemistry allowed to devise a new detection strategy for environmental contaminants, mimicking a biological process happening in vivo for biosensing purposes.