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.