Ultra trace analysis of small molecule by label-free impedimetric immunosensor using multilayer modified electrode

A multilayer electrode modified with a self-assembled thiourea monolayer (SATUM) followed by gold nanoparticles (AuNPs), mercaptosuccinic acid (MSA) and antibody was investigated for the detection of ultra trace amount of a small molecule (chloramphenicol) in an impedimetric system. The formation of the antibody–antigen complex at the electrode surface caused the impedance to increase. Under optimum conditions three modified electrodes were compared the SATUM/AuNPs/MSA electrode provided a wide linear range (0.50–10) × 10−16 M, and a very low determination limit of 1.0 × 10−16 M. This determination limit was much lower than the SATUM/AuNPs electrode, 1.0 × 10−15 M, and SATUM electrode, 4.7 × 10−14 M. The modified electrode provided good selectivity for chloramphenicol detection and can be reused up to 45 times with a relative standard deviation of lower than 4%. When applied to determine chloramphenicol in shrimp samples, the results agreed well with those obtained by the high-performance liquid chromatography coupled with a photo diode array detector (P > 0.05). The developed system can be applied to detect other small molecules using appropriate affinity binding pairs.