## 3 Results
### Lead Adsorption Using Peptide-Linked Magnetic Bead  
To determine the contact time for lead adsorption, the time profile of lead adsorption onto the peptide-linked (TNTLSNN) bead was monitored, and the results are shown in Figure 2. A contact time within approximately 30 min was required for the peptide bead to be saturated with lead. The increase in lead adsorption was not significant after 1 h, so the time for each of the following adsorption experiments was determined to be 1 h, if not specifically mentioned otherwise. Previous research has shown that the experimental pH can affect the adsorptive uptake of lead ion [29; 30; 31]. For example,  
Figure 1: Pb(II) adsorption onto bare bead (mg Pb(II)/g bead): © Dynabeads® M-270 Carboxylic Acid; © AccuBeadTM COOH magnetic bead; © Cytodiagnostic ZeptoTM Mag Carboxyl Microspheres; and © BChagTM long-arm carboxy-terminated magnetic bead. lead can precipitate at pH values equal to or greater than 7, due to the formation of Pb(OH)2 in the solution. Meanwhile, the extent of protonation from sorbent materials interacting electrostatically with Pb(II) ion is determined by the solution pH. The adsorptive uptake of lead decreased at lower pH due to the protonation of sorbents. For the polymeric adsorbent [31], the adsorption in distilled water led to the highest adsorption amount of Pb(II) ion. In this study, the pH effect was not examined in detail (pH around 5-6 provided similar results; data not shown). Each metal nitrate was solubilized in distilled water without any further pH adjustment. **To further explore the contribution of peptide on the lead binding, three kinds of bead were compared: activated bare bead for EDC/NHS reaction, albumin(BSA)-coated bead using the activated bare bead, and peptide-linked bead using the activated bare bead (Figure 3). ** Bovine serum albumin is frequently used as a blocking agent, to prevent the nonspecific binding of antibodies in biological research. Compared to the lead binding capacity of the peptide bead, the albumin bead showed significantly lower lead binding (3.5 mg lead/g bead). A slight increase in lead binding, as compared to that of bare bead, may be caused by the exposed functional group of albumin surface interacting with lead. Thus, it can be presumed that the specific lead-binding capacity was substantially enhanced by the function of the lead-binding peptide. Figure 3: Comparison of lead adsorption capacity: 1 bare bead, 2 albumin-coated bead, and 3 peptide-linked bead. Figure 2: Effect of contact time on Pb(II) adsorption onto peptide-linked bead. To characterize the lead adsorption by the peptide bead, adsorption isotherm experiments were conducted. The experimental data shown in Figure 4a comprise an L-shaped isotherm, meaning that the peptide bead is expected to have a high affinity toward lead. The representative model for this type of adsorption is the Langmuir model (Equation (1)), which describes the homogeneous distribution of the adsorbate onto the uniform surface of the adsorbent. To analyze the model parameter, the linearized model (Equation (2)) was applied (Figure 4b). \[q_{e}=\frac{q_{max}K_{L}C_{e}}{1+K_{L}C_{e}} \tag{1}\]  
\[\frac{C_{e}}{q_{e}}=\frac{1}{q_{max}}C_{e}+\frac{1}{q_{max}K_{L}} \tag{2}\]  
where \(q_{e}\) (mg/g of adsorbent) is the equilibrium lead-adsorption capacity of the peptide bead and \(C_{e}\) (mg/L) is the equilibrium lead concentration in solution. The two empirical parameters of \(q_{max}\) (mg/g) and \(K_{L}\) (L/mg) represent the theoretical maximum adsorption capacities of the adsorbent and the affinity constant, respectively. Based on the linear regression analysis (R\({}^{2}\) = 0.997) presented in Figure 4b, \(q_{max}\) was determined to be 70.4 mg/g, while \(K_{L}\) was 0.03 L/mg. The Freundlich model (Equation (3)) known to describe multilayer adsorption behavior on the heterogeneous surface was also fitted to the experimental data.