Biosensors for the analysis of microbiological and chemical contaminants in food.

Increases in food production and the ever-present threat of food contamination from microbiological and chemical sources have led the food industry and regulators to pursue rapid, inexpensive methods of analysis to safeguard the health and safety of the consumer. Although sophisticated techniques such as chromatography and spectrometry provide more accurate and conclusive results, screening tests allow a much higher throughput of samples at a lower cost and with less operator training, so larger numbers of samples can be analysed. Biosensors combine a biological recognition element (enzyme, antibody, receptor) with a transducer to produce a measurable signal proportional to the extent of interaction between the recognition element and the analyte. The different uses of the biosensing instrumentation available today are extremely varied, with food analysis as an emerging and growing application. The advantages offered by biosensors over other screening methods such as radioimmunoassay, enzyme-linked immunosorbent assay, fluorescence immunoassay and luminescence immunoassay, with respect to food analysis, include automation, improved reproducibility, speed of analysis and real-time analysis. This article will provide a brief footing in history before reviewing the latest developments in biosensor applications for analysis of food contaminants (January 2007 to December 2010), focusing on the detection of pathogens, toxins, pesticides and veterinary drug residues by biosensors, with emphasis on articles showing data in food matrices. The main areas of development common to these groups of contaminants include multiplexing, the ability to simultaneously analyse a sample for more than one contaminant and portability. Biosensors currently have an important role in food safety; further advances in the technology, reagents and sample handling will surely reinforce this position.

Comparison of porcine urine and bile as matrices to screen for the residues of two sulfonamides using a semi-automated enzyme immunoassay.

Porcine urine enzyme immunoassays for sulfamethazine and sulfadiazine have previously been employed as screening tests to predict the concentrations of the drugs in the corresponding tissues (kidneys). If a urine was found positive (> 800 ng ml-1) the corresponding kidney was then analysed by an enzyme immunoassay and, if found positive, a confirmatory analysis by HPLC was performed. Urine was chosen as the screening matrix since sulfonamides are mainly eliminated through this body fluid. However, after obtaining a number of false positive predictions, an investigation was carried out to assess the possibility of using an alternative body fluid which would act as a superior indicator of the presence of sulfonamides in porcine kidney. An initial study indicated that serum, plasma- and bile could all be used as screening matrices. From these, bile was chosen as the preferred sample matrix and an extensive study followed to compare the efficiencies of sulfonamide positive bile and urine at predicting sulphonamide positive kidneys. Bile was found to be 17 times more efficient than urine at predicting a sulfamethazine positive kidney and 11 times more efficient at predicting a sulfadiazine positive kidney. With this enhanced performance of the initial screening test, the need for the costly and time consuming kidney enzyme immunoassay, prior to HPLC analysis, was eliminated.

Rapid screening for monensin residues in poultry plasma by a dry reagent dissociation enhanced lanthanide fluoroimmunoassay.

Monensin, a carboxylic acid ionophore, is commonly fed to poultry to control coccidiosis. A method for rapid analysis of unextracted poultry plasma samples has been developed based on a novel immunoassay format: one-step all-in-one dry reagent time resolved fluorimetry. All assay specific components were pre-dried onto microtitration plate wells. Only addition of the serum sample diluted in assay buffer was required to perform analysis. Results were available one hour after sample addition. The limit of detection (mean +/- 3s) of the assay calculated from the analysis of 23 known negative samples was 14.2 ng ml-1. Intra- and inter-assay RSD were determined as 15.2 and 7.4%, respectively, using a plasma sample fortified with 50 mg ml-1 monensin. Eight broiler chickens were fed monensin at a dose rate of 120 mg kg-1 feed for one week, blood sampled then slaughtered without drug withdrawal. Plasma monensin concentrations, as determined by the fluoroimmunoassay ranged from 101-297 ng ml-1. This compared with monensin liver concentrations, determined by LC-MS, which ranged from 13-41 ng g-1. The fluoroimmunoassay described is extremely user friendly, gives particularly rapid results and is suitable for the detection and quantification of plasma monensin residues. Data from medicated poultry suggest that analysis of plasma may be useful in predicting the extent of monensin liver residues.