Whole-cell detection

The distinction between chemical sensors and biosensors is more complex. Many authors attempt to define a sensor based on the nature of the analyte detected. This approach can be misleading since nearly all analytes measured by a chemical or biosensor are chemicals or Wochemicals, the exception being sensors which detect whole cells. Other authors attempt to define a chemical of biosensor by the nature of the reaction which leads to the detection event. Again, this is confusing since all reactions at chemical and biosensor surfaces are chemical (or biochemical) reactions. 

EAPs have proved to be effective at detection of small quantities of biomolecules, specifically in cancer detection and real-time monitoring of blood-borne analytes such as glucose and nucleic acids (383-389). These sensors employ EAPs containing natural biomolecular recognition units sometimes referred to as biosensors. These biosensor moieties can be ligands, single strands of DNA, enzymes, antibodies, or synthetic proteins that can detect whole cells or individual proteins (390-392). 

It is well known that arsenic is one of the most dangerous elements in terms of its potential impacts to both to human and ecosystem health. Therefore the problem of As detection at ppb level remains very important from the point of environmental hazard investigation. The goal of the present work is the developing of very simple and inexpensive assay for arsenite and arsenate determination in environmental samples using whole-cell bacterial biosensors. 

Corbisier, R, van der Lelie, D., Borremans, B., Provoost, A., de Lorenzo, V., Brown, N., Lloyd, J.R., Hobman, J.L., Csoregi, E., Johansson, G., and Mattiasson, B., Whole cell- and protein-based biosensors for the detection of bioavailable heavy metals in environmental samples, Anal Chim Acta, 387 (3), 235-244, 1999. 

Lebaron, P. Catala, P. Fajon, C. Joux, F. Baudart, J. Bernard, L. A new sensitive, whole-cell hybridization technique for detection of bacteria involving a biotinylated oligonucleotide probe targeting rRNA and tyramide signal amplification. Appl. Environ. Microbiol. 1997, 63, 3274-3278. 

As noted above, whole-cell MALDI-TOF MS was intended for rapid taxonomic identification of bacteria. Neither the analysis of specific targeted bacterial proteins, nor the discovery of new proteins, was envisioned as a routine application for which whole cells would be used. An unknown or target protein might not have the abundance or proton affinity to facilitate its detection from such a complex mixture containing literally thousands of other proteins. Thus, for many applications, the analysis of proteins from chromatographically separated fractions remains a more productive approach. From a historical perspective, whole-cell MALDI is a logical extension of MALDI analysis of isolated cellular proteins. After all, purified proteins can be obtained from bacteria after different levels of purification. Differences in method often reflect how much purification is done prior to analysis. With whole-cell MALDI the answer is literally none. Some methods attempt to combine the benefits of the rapid whole cell approach with a minimal level of sample preparation, often based on the analysis of crude fractions rather... 

The most common criticism of whole-cell MALDI is that the method requires a relatively large number of cells, usually obtained directly from culture media. In principle, an analysis of even a few unknown bacteria (a colony-forming unit) is possible after a culture step. More important is the number of bacteria needed in a sample or on the sample probe for successful analysis. Detection of a very small number of bacteria could eliminate the need for a preliminary culture step. This would be a considerable asset for environmental analysis (unless to many bacteria were detected) and for the detection of a bioterrorism-related release of bacteria. 

Notwithstanding the aforementioned difficulty in detecting specific target proteins other than the types normally observed in the taxonomic fingerprints from whole bacteria MALDI spectra (i.e., ribosomal proteins), some other target proteins and protein-like materials have been studied directly from whole cells. For example, Lantibiotics, antimicrobial peptides secreted by Gram-positive bacteria have been detected directly from whole bacteria by MALDI-TOF MS.51 The lantibiotics nisin and lacticin 481 were detected from whole cells and crude supernatants. Surprisingly, better results were reported from whole cells than the supernatants. In this study the presence of variants... 

Madonna, A. I Basile, F. Imma, I. Meetani, A. M. Rees, J. C. Voorhees, K. J. On-probe sample pretreatment for the detection of proteins above 15 KDa from whole cell bacteria by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Rapid Comm. Mass Spectrom. 2000,14, 2220-2229. 

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