## 1 Introduction  
Heavy metal pollution in water environments has become a severe problem, since metals are generally refractory components and some are highly hazardous to the ecosystem, even at low concentrations [1]. Lead, which is principally discharged from industrial sources, has also been reported to be harmful to human health [2]. Various technologies (i.e., precipitation, filtration, ion exchange, and extraction) for removing heavy metals from aqueous effluents have been suggested, but many of those are only appropriate for the treatment of effluent, including high concentrations of metals [3; 4; 5]. Moreover, their removal efficiencies are not high enough to reduce the metal concentration down to the level of the water quality standard [6]. Therefore, a process capable of lowering the metal concentration from dilute solution is required. Adsorption is a relatively simple process for efficiently removing metals from dilute solution [7]. A wide range of adsorbents originating from various chemical to biological sources (i.e., activated carbon, cellulose, graphene oxide, and chitosan) has been explored as metal adsorbents [8; 9; 10; 11]. However, most of the adsorbents explored have not shown the selective binding property for specific metal in complex environmental matrices. This means that excessive doses of the adsorbents need to be used for the removal of the target metal coexisting with a relatively greater amount of interfering pollutants. A specific peptide sequence, an oligomer of amino acids, has been reported to have selective binding affinity for various inorganic materials, such as metal oxides, metal sulfides, and metals [12; 13; 14]. Therefore, peptides with an affinity to specific metals can be used as metal binding moieties from aqueous solution [15; 16]. Various peptide sequences possessing an affinity to metals, such as nickel and cobalt, are summarized, where amino acid composition and theoretical pI was analyzed [15]. In a previous study, a lead-binding peptide sequence (TNTLSNN) was screened by chromatographic biopanning [17]. The 7-mer peptide showed a selective affinity to Pb(II) while displaying low binding affinities to different divalent metal ions, such as Ni(II), Cu(II), Co(II), and Fe(II). Moreover, there are nearly unlimited target materials (i.e., most options other than lead) that can be chosen from, and a peptide with affinity to a specific target can be identified through a biopanning procedure [15]. Therefore, the peptide-based adsorbent can potentially be applied for the selective removal of various target materials. Meanwhile, considering the high cost of synthesizing the peptide, it would be beneficial to construct a reusable adsorbent. To date, various frameworks for constructing reusable adsorbents for pollutant removal have been investigated [18; 19; 20], and it appears to be difficult to collect the adsorbent from an aqueous system. Magnetic particles have attracted substantial interest for this purpose, since solid-liquid separation can be facilely enabled by magnetic assistance [21]. To date, magnetic adsorbents for the removal of heavy metals have been developed as a composite of iron oxide and other compounds (i.e., biochar, chitosan, cellulose, graphene oxide, and titanate) [9; 10; 22; 23; 24]. Among them, only a few materials, such as magnetic ion-imprinted polymer and magnetic biomaterial coated with amino siloxane, have been reported as selective adsorbents for lead [25; 26]. Here, the magnetic bead linked with a specific peptide is investigated as another promising reusable adsorbent with selective removal capability. We constructed a magnetic bead incorporating lead-binding peptide via covalent bonding on the bead's surface. Then, the peptide bead was evaluated as a reusable adsorbent for the removal of lead under various aqueous conditions. In particular, its selective binding performance to lead was demonstrated in the presence of interfering substances like different metal ions (i.e., Ni(II), Cu(II), and Co(II)) and artificial wastewater.