Functionalized Fe 3 O 4 /graphene oxide nanocomposites with hairpin aptamers for the separation and preconcentration of trace Pb 2+ from biological samples prior to determination by ICP MS.

Lead (Pb) as a topically poisonous metal represents a serious threat to the ecological environment and especially to human beings. Therefore, it is urgent to develop a rapid and reliable monitoring technique for this heavy metal in the environmental samples. In the present study, we have designed a selective and sensitive method for the determination of ultratrace contents of Pb ²⁺ in biological samples, based on the guanine (G)-quadruplex formed by the aptamer with hairpin structure and Pb ²⁺ . For this purpose, Pb ²⁺ specific aptamer serving as affinity probe to capture and separate trace amounts of the analyte, was covalently linked to Fe ₃ O ₄ /graphene oxide (GO) surface by using a suitable cross-linking agent. Then, the G-quadruplex complex was formed by the opening of the "neck- ring" of the hairpin structure of aptamer in the presence of Pb ²⁺ . Inductively coupled plasma mass spectrometry (ICP-MS) was used for determination of Pb ²⁺ in biological matrices. The analysis conditions were optimized and the performance of the proposed method was investigated. Under optimum conditions, the calibration curve was linear over the range of 0.3-867.5μgL ^-1 and an enrichment factor (EF) of 50 was obtained. The limit of detection (LOD) was 0.05μgL ^-1 and the relative standard deviation (RSD) for single-sorbent repeatability and sorbent-to-sorbent reproducibility were <4.7% and 8.8% (n=5), respectively. The accuracy of aptamer-based affinity purification method was confirmed by the analysis of quality control materials (QCMs, Seronorm™ Blood REF NO 201505 and Urine REF NO 2525).
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