Paper-based lateral flow immunoassays (LFIAs) are an interesting on site technique for detecting heavy metals. Pb(II) is one of the toxic heavy metals in polluted environmental water. This paper reports the synthesis and characterization of three Fe 3 O 4-based nanoadsorbents that show different performance to Pb(II), Cu(II), Cd(II), Hg(II), As(V), Zn(II), Fe(III), Ca(II), Mg(II), Mn(II), and Al(III) when a GO or an amino group is introduced. Compared with Fe 3 O 4 , Fe 3 O 4-GO showed higher adsorption percentage to many heavy metal ions under slightly acid condition. The negative surface on Fe 3 O 4 @NH 2 had favourable interactions for four main divalent metal ion adsorption, which followed the order: Pb(II) > Cu(II) > Hg(II) > Cd(II). Combined with antibody-functionalized AuNPs showed high affinity and specificity toward Pb(II), an Fe 3 O 4 @NH 2-based LFIA with five times greater sensitivity for detecting Pb(II) in lake water was developed. The cutoff value of this Fe 3 O 4 @NH 2-combined LFIA method for detection Pb(II) in lake water was 20 ng/mL and the detection result for 10 ng/mL Pb(II) was obviously observable by the naked eye or a strip reader machine. This detection strategy could be readily adapted for other small molecules or biomolecules as an ultrasensitive screening tool.

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