Flow Injection Monitoring of Aflatoxin M1 in Cheese Using Filter-Supported Bilayer Lipid Membranes with Incorporated DNA

Abstract

This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring of aflatoxin M1 (AFM1) in cheese samples. Stabilized filter-supported bilayer lipid membranes (BLMs) were used as detectors Single stranded DNA oligomers terminated with alkyl chains (dT20–C16) were incorporated into the membranes to control surface electrostatic properties. The incorporation of dT20–C16 in BLMs lowered the detection limit for the detection of this toxin by one to four orders of magnitude as compared with the detection limit obtained in the absence of DNA. Therefore, it is now possible to continuously monitor this toxin at concentrations that approached those that could be of interest as set by the U.S. Food and Drug Administration and most European countries. The work described herein takes a significant step towards development of a detector of greater practical potential by demonstrating that the incorporation of C16-ssDNA into lipid membranes results in a combination of properties that provides for a much more sensitive and robust detection system. Injections of AFM1 were made into flowing streams of a 0.1 M KCl electrolyte solution, and a transient current signal with duration of seconds reproducibly appeared in about 12 s after exposure of the detector element to the toxin. The magnitude of this signal was linearly related to the concentration of AFM1 with detection limits at subnanomolar level. The effect of interferents such as proteins and lipids was investigated. It was determined that interferences from proteins could be eliminated by adjustment of the flow rate of the carrier electrolyte solution. The technique was applied for the rapid flow injection determination of aflatoxin M1 in cheese samples. AFM1 could be determined in continuous flowing systems with a rate of at least 4 samples min–1. Repetitive cycles of injection of AFM1 have shown no signal degradation during each cycle for experiments that attempted over 30 cycles of detection.