Undistorted cyclic voltammograms at scan rates up to 2.5 MV.s−1 through positive feedback compensation of Ohmic drop

One-step electrochemical sensor based on an integrated probe toward sub-ppt level Pb2+ detection by fast scan voltammetry

Herein, a one-step electrochemical sensor for selective and sensitive detection of lead ion Pb²⁺ was developed based on an integrated probe meso-tetra(4-carboxyphenyl) porphine (TCPP)-multi-walled carbon nanotubes (MWCNTs)@Fe₃O₄, which is TCPP-modified magnetic multi-walled carbon nanotubes. In the integrated probe, TCPP is a porphyrin with a specific cavity structure which could selectively chelate with Pb²⁺, MWCNTs with good electric conductivity provide a place to load TCPP and form a specific adsorption state of Pb²⁺ on the electrode surface, and Fe₃O₄ enables the rapid separation and one-step fabrication of the electrochemical sensor. Based on it, the sample pre-enrichment, separation and determination can be integrated, making the whole process very fast and simple. In addition, fast scan voltammetry (FSV) with a scan rate up to 200 V/s could be used to improve the detection sensitivity greatly, benefitting from the specific adsorption state formed. Under the optimal conditions obtained through orthogonal experiments including adsorption time, integrated probe dosage and solution pH, there was a good linear relationship between the peak current and Pb²⁺ concentration ranging from 2.0 × 10^-4 μg L^-1 to 2.0 × 10^-3 μg L^-1, with the limit of detection (LOD) being 6.7 × 10^-5 μg L^-1 (S/N = 3) i.e. 0.067 ppt. Analysis of actual water samples was successful. Therefore, being simple, fast, selective and sensitive, the one-step electrochemical sensor proposed has a good potential in practical applications.