Development of an immunoaffinity column and an indirect immunoassay with a biotin-streptavidin detection system for aflatoxin M1 in milk

Application of Biosensors Based on Lipid Membranes for the Rapid Detection of Toxins

Lipid assemblies in the form of two dimensional films have been used extensively as biosensing platforms. These films exhibit certain similarities with cell membranes, thus providing a suitable means for the immobilization of proteinaceous moieties and, further, a number of intrinsic signal amplification mechanisms. Their implementation in the detection of toxins yielded reliable and fast detectors for in field analyses of environmental and clinical samples. Some examples are presented herein, including aflatoxin and cholera toxin detection. The conditions and parameters that determine the analytical specifications of the lipid membrane sensors are discussed, advantages and technology bottlenecks are reviewed, and possible further developments are highlighted.

Immunoaffinity solid-phase extraction for the trace-analysis of low-molecular-mass analytes in complex sample matrices

Immunoaffinity solid-phase extraction (SPE) sorbents, so-called immunosorbents (ISs), are based upon molecular recognition using antibodies. Thanks to the high affinity and high selectivity of the antigen-antibody interaction, they allow a high degree of molecular selectivity and have shown to be a unique tool in the sample preparation area these last few years. Extraction and clean-up of complex biological and environmental aqueous samples are achieved in the same step and from large volumes when required. Their application to extracts from solid matrixes is solvent-free and more simple than any other clean-up procedure. Single analytes can be targeted, but since an antibody can also bind one or more analytes having structure similar to the one used for its preparation, ISs have been developed for targeting a single analyte and its metabolites. The cross-reactivity was also exploited for developing ISs that could selectively extract a whole class of structurally related compounds. This review describes the current technology used for the synthesis of the ISs, their properties and their field of application. The different parameters governing the antigen-antibody interactions and the solid-phase extraction process are discussed. Emphasis is given to the optimisation of the SPE sequence, especially to the desorption and regeneration steps. The importance of the capacity and its relationship with the analytes recovery and breakthrough volumes is highlighted for class-specific ISs. Multi-class-selective ISs are also presented. Validation studies are reviewed using various certified reference materials. Relevant examples, involving combination with chromatography in both off-line and on-line mode, illustrate the high selectivity provided in various complex matrixes. Miniaturisation is also described, since it allows high throughput of samples.

Flow injection monitoring of aflatoxin M1 in milk and milk preparations using filter-supported bilayer lipid membranes

This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring of aflatoxin M1 (AFM1) using stabilized systems of filter-supported bilayer lipid membranes (BLMs). Injections of AFM1 were made into flowing streams of a carrier electrolyte solution, and a transient current signal with a duration of seconds reproducibly appeared less than 10 s after exposure of the lipid membranes to the toxin. The magnitude of this signal was linearly related to the concentration of AFM1, with detection limits at the subnanomolar level. The mechanism of signal generation was investigated by differential scanning calorimetric experiments. The technique was applied for the rapid flow injection determination of AFM1 in milk and milk preparations. The effect of potent interferences such as proteins and lipids was investigated, and the results show that interferences from these milk constituents can be eliminated by modulation of the flow rate of the carrier solution so as not to allow adsorption of these compounds in BLMs. AFM1 could be determined in continuous flowing systems with a rate of at least 4 samples min-1. Repetitive cycles of injection of AFM1 showed no signal degradation during each cycle.