Biosensor Introduction

    Sensing techniques form an integrated part of our modern life. We like to be accurately and constantly informed about the quality, security and composition of products that we consume or encounter in our daily life. Medical tests need to provide instantaneous answers on health parameters, blood values or presence of potential pathogenic organisms. Sensors come in thousand and more forms and shapes, principles and output. Future demand calls for further miniaturization, continuous sensing, rapidity, increased sensitivity or flexibility.
    One of the emerging domains in sensing technology is the use of living microbial cells or organisms(van der Meer and Belkin). A biosensor is a measurement device or system that is composed of a biological sensing component, which recognizes a chemical or physical change, coupled to a transducing element that produces a measurable signal in response to the environmental change(Daunert et al., 2000). It is only since the last twenty years that living cell-based sensing assays have gained impetus and developed into a scientific and technological area by itself.
    The question arises here is why one would use living cells and organisms for sensing? What are the specific purposes for basing sensing methods on living cells and what are the advantages that cellular-based sensing can have over other sensing techniques?
    Testing for toxic pollution such as heavy metals is commonly performed with chemical test kits of unsatisfying accuracy (Stocker et al., 2003). Normally, costly equipment is also needed. Instead, bacterial biosensors are easily produced low cost, simple, and highly accurate devices. For example, both laboratory and field studies have demonstrated arsenic detection limits in bacterial bioreporter assays of close to 5 nM, much lower than the drinking water standard of 10 ug, making these assays ideal for analysing large numbers of samples in developing countries facing arsenic contamination of their potable water sources. Some bioreporter assays (for example, for Hg or As) have excellent measurement accuracies and compound detection specificities, and some may even compete with chemical methods. Namely, bacterial sensor-reporters, which consist of living micro-organisms genetically engineered to produce specific output such as GFP fluorescence or colors that can be distinguished by naked eyes, offer an interesting alternative for heavy metal detection.

<img src="" align="left">Fig.1 Genetically engineered bacteria, tailored to respond by a quantifiable and easily recognizable signal to the presence of heavy metal, may serve as powerful tools for heavy metal detection and further assessment of the extent and the implications of environmental pollution.