Per- and polyfluoroalkyl compounds (PFAS) are synthetic compounds recently classified as permanent and emerging chemicals, since their bioaccumulation in human and environment. Among the PFAS compounds, perfluorooctanoic acid (PFOA) are based on carbon-fluorine functional groups, which have been demonstrated resistant to degradation. Recent work on the accurate detection of PFOA in the range of 1.1 and 3.4 ng/mL in biological samples (plasma) uses the conventional HPLC/HRMS technique [1]. For the environmental concern, the level of PFOA in rainwater has been demonstrated to exceed the limits of EPA guidelines Here, PFOA concentrations were detected between 12.6 ng/L and 287 ng/L by UPLC-MS/MS [2]. Although HPLC/HRMS still remains an accurate analytical method able to detect a wide range of analytes, it suffers from practical drawbacks, high costs, user experiences in data treatment and interpretation, and so on. So, alternative methods in PFOA detection with addressed high sensitivity, simple operation, fast response time and transportability are currently gaining attention in research. In particular, the design of novel screening tools for the selective and sensitive quantification of PFAS compounds in water is highly desirable. Electrochemical sensors have been recently proposed for PFOA quantification in water [3,4], some of which reported the application of molecularly imprinted polymers (MIP) to selectively discriminate the analyte from matrix interferences.
MIP relies on artificial synthetic polymeric receptors intensively used in sensor development for water monitoring. Those are prepared through different synthetic techniques, in the presence of a polymerisation mixture comprising functional monomers and cross-linker agents that surround the analyte target complementary to its functionalities. Selective cavities are then formed onto a polymeric backbone through elution processes. In this work, we report a preliminary result on the solid-phase synthesis of MIPs in the form of nanoparticles (<150 nm) applied in sensor development for the highly sensitive and selective quantification of PFAS in water.
The solid phase polymerisation was carried out starting from an already available protocol [5] using silanized glass beads to selectively orientate the PFOA target. A polymerisation mixture was prepared by adding the functional monomers (itaconic acid, 2-hydroxyethyl methacrylate) and cross-linker agents. Here, a redox mediator, e.g. ferrocene methyl methacrylate was added to label a redox mediator to the high affinity nanoparticles. Finally, the UV-light polymerisation was carried out. To elute the target, a protocol involving several steps of temperature change was used, to finally elute the high affinity nanoMIP. The developed nanoparticles were characterised by dynamic light scattering (DLS), showing a size of 138 nm with a polydispersity index (PDI) below 0.3.
During sensor development, functionalized screen-printed platinum electrodes (SPPtE) and the nanoMIPs have been used as the transduction and the receptor element, respectively. Functionalization of SPPtE was optimised by using 0.5 % of APTES to be activated during nanoMIPs immobilization. The same were immobilised through EDC/NHS chemistry coupling. Each step of electrode modification was monitored by electrochemical methods, such as the cyclic voltammetry and differential pulse voltammetry. Results from CV/DPV measurement presented a reversible redox reaction due to the presence of the redox labelled nanoMIPs, that further facilitated the transferring of electrons from solution to the electrode surface. The developed sensors have been tested towards increasing concentration (1.5 – 100 ng/mL) of PFAS dissolved in PBS (50 mM pH 7.4), showing highly sensitive properties of the developed nanoMIPs. Optimisation and quality properties of the developed sensors, such as the selectivity and stability, are ongoing to be studied.