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Magnetite nanoparticles coated with quaternized poly(diethylamino)ethyl methacrylate (PDEAEMA) (PQDEA@MNP) and functionalized with bisphenol A (BPA)-specific peptide aptamer (CKSLENSYC) were synthesized and used as nano-adsorbents for selective adsorption with BPA. The polymer coated on the particles provided their good stability and dispersibility in water, and the aptamer provided selective adsorption with BPA targets. Fourier transformed infrared spectrophotometry (FTIR), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM) techniques confirmed the presence of the polymer on the particle surface. From transmission electron microscopy (TEM) study, the particle size was ca.6 - 10 nm in diameter with some nanoclustering (30 - 60 nm in diameter of the nanoclusters). The selective adsorption of BPA on the particles was predominant over the non-specific adsorption when performed in PBS buffer (pH 10) in the presence of NaCl and tween-20. The nano-adsorbents had a good linearity range for the detection of BPA between 0.04 and 0.20 ppm with limit of detection (LOD) of 0.0145 ppm. They retained good BPA adsorption efficiency even when other interfering molecules were present. This simple measurement with the use of these nano-adsorbents without molecular labelling might be promising solid supports for use in various applications with good tolerance towards interfering molecules. HIGHLIGHTS Magnetic nanoparticle was coated with cationic polymer and BPA-specific aptamer This label-free peptide aptamer allowed for the selective capture of BPA targets It showed high selectivity to BPA capture and good tolerance to interfering molecules GRAPHICAL ABSTRACT

Magnetite nanoparticles coated with poly(dimethyl aminoethyl methacrylate) (PDMAEMA@MNPs) and their quarternized form (PQDMAEMA@MNPs) were successfully synthesized and used as nano-adsorbents for bisphenol A (BPA). The particles were spherical with the average particle size between 10 and 20 nm in diameter with a moderate degree of nanoclustering (ca.150-200 particles/cluster). In terms of adsorption properties, the PDMAEMA@MNPs exhibited a higher BPA adsorption capacity (1.05 mg/g MNP at pH 9) than the quaternized form (0.50 mg/g MNP at pH 9). Equilibrium isotherm, kinetic, and thermodynamic characteristics of BPA adsorption on the PDMAEMA@MNPs were investigated. It was found that the BPA adsorption on the MNPs reached an equilibrium within 5 min and the maximum adsorption capacity (qe) was 9.88 mg/g. The adsorption isotherm study results indicated that the BPA adsorption process on PDMAEMA@MNPs exhibited the best fit with the Freundlich model, and the adsorption kinetics followed the pseudo-second order model with the R2 value of 1.00. The thermodynamic data exhibited a negative enthalpy change (ΔH◦ = -2585.571 J/mol), indicating exothermic BPA adsorption, and a negative Gibbs free energy (ΔG◦), implying a spontaneous BPA adsorption process.