Crosslinked zwitterionic polymeric ionic liquid-functionalized nitinol wires for fiber-in-tube solid-phase microextraction and UHPLC-MS/MS as an amyloid beta peptide binding protein assay in biological fluids

Abstract

Alzheimer disease (AD) is a neurodegenerative disorder characterized by extracellular accumulation of amyloid-β peptide (Aβ) in the brain interstitium. Human serum albumin (HSA) highly binds to Aβ in blood plasma and is thought to inhibit plaque formation in peripheral tissue. Thus, the evaluation of albumin binding to Aβ is an important key to understand the dynamics of these molecules in the biological system of patients with AD. In this work, a fiber-in-tube solid-phase microextraction (fiber-in-tube SPME) and ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed to estimate Aβ fraction binding to HSA in cerebrospinal fluid (CSF) and plasma samples. Crosslinked zwitterionic polymeric ionic liquid (zwitterionic PIL)-coated nitinol wires were developed and packed into a polyether ether ketone (PEEK) capillary for a fiber-in-tube SPME and UHPLC-MS/MS method. Zwitterionic PIL sorbent was synthetized from 1-vinyl-3-(butanesulfonate)imidazolium ([VIm⁺C₄SO₃^-]) and 1,12-di(3-vinylimidazolium)dodecane dibromide ([(VIm)₂C₁₂]2[Br]) monomers by in-situ thermally-initiated polymerization. Morphological characterization by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed a decrease in the surface roughness of the nitinol wires from ∼17 nm to 1 nm after the in-situ polymerization. The zwitterionic PIL sorbent selectively preconcentrates Aβ through a two-pronged interaction mechanism. The fiber-in-tube SPME and UHPLC-MS/MS method presented lower limits of quantification (LLOQ) of 0.4 ng mL^-1 for Aβ38 and 0.3 ng mL^-1 for Aβ40 and Aβ42, a linear range from LLOQ values to 15 ng mL^-1 with coefficients of determination higher than 0.99, precision with coefficient of variation (CV) values ranging from 2.1 to 7.3% and accuracy with relative standard deviation (RSD) values from -0.3 to 7.4. This method was successfully applied to evaluate the binding of HSA to Aβ in cerebrospinal fluid (CSF) and plasma samples.

Keywords: Amyloid beta peptide; Fiber-in-tube SPME; Protein binding; UHPLC-MS/MS; Zwitterionic ionic liquids.