During recent decades, extensive industrialisation and farming associated with improper waste management policies have led to the release of a wide range of toxic compounds into aquatic ecosystems, causing a rapid decrease of world freshwater resources and thus requiring urgent implementation of suitable legislation to define water remediation and protection strategies. In Europe, the Water Framework Directive aims to restore good qualitative and quantitative status to all water bodies by 2015. To achieve that, extensive monitoring programmes will be required, calling for rapid, reliable and cost-effective analytical methods for monitoring and toxicological impact assessment of water pollutants. In this context, whole cell biosensors appear as excellent alternatives to or techniques complementary to conventional chemical methods. Cells are easy to cultivate and manipulate, host many enzymes able to catalyse a wide range of biological reactions and can be coupled to various types of transducers. In addition, they are able to provide information about the bioavailability and the toxicity of the pollutants towards eukaryotic or prokaryotic cells. In this article, we present an overview of the use of whole cells, mainly bacteria, yeasts and algae, as sensing elements in electrochemical biosensors with respect to their practical applications in water quality monitoring, with particular emphasis on new trends and future perspectives. In contrast to optical detection, electrochemical transduction is not sensitive to light, can be used for analysis of turbid samples and does not require labelling. In some cases, it is also possible to achieve higher selectivities, even without cell modification, by operating at specific potentials where interferences are limited.

Cell-based electrochemical biosensors for water quality assessment

We report the fabrication of an amperometric whole-cell herbicide biosensor based on magnetic retention of living cells functionalised with magnetic nanoparticles (MNPs) on the surface of a screen-printed electrode. We demonstrate that Chlorella pyrenoidosa microalgae cells coated with biocompatible MNPs and retained on the electrode with a permanent magnet act as a sensing element for the fast detection of herbicides. The magnetic functionalisation does not affect the viability and photosynthesis activity-mediated triazine herbicide recognition in microalgae. The current of ferricyanide ion was recorded during alternating illumination periods and biosensor fabricated was used to detect atrazine (from 0.9 to 74 µM) and propazine (from 0.6 to 120 µM) (the limits of detection 0.7 and 0.4 µM, respectively). We believe that the methodology presented here can be widely used in fabrication of a number of whole cell biosensors since it allows for efficient and reversible cells immobilisation and does not affect the cellular metabolism.

A whole-cell amperometric herbicide biosensor based on magnetically functionalised microalgae and screen-printed electrodes

Oxygen demands: COD- Biochemical Oxygen Demand BOD- Total organic carbon - TOC- Dissolved oxygen- pH Measurements- Metals- Non-Metal Inorganic Ions and Molecules- Electroanalysis and Speciation- Nanoparticles-emerging contaminants- Pharmaceuticals and Personal Care Products- Surfactants- Aromatic Hydrocarbons and their Derivatives- Nitrated Compounds: Explosives- Pesticides- Volatile organic compounds- Sulphur Compounds (H2S, S-oxides)- Ammonia and Nitrogen Oxides- Carbon Oxides

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Environmental analysis by electrochemical sensors and biosensors

Green algae are a promising platform for the development of biosensors and bioelectronic devices. Here we report a reliable single-step technique for the functionalisation of living unicellular green algae Chlorella pyrenoidosa with biocompatible 15 nm superparamagnetic nanoparticles stabilised with poly(allylamine hydrochloride). The magnetised algae cells can be manipulated and immobilised using external permanent magnets. The distribution of the nanoparticles on the cell walls of C. pyrenoidosa was studied by optical and fluorescence microscopy, TEM, SEM and EDX spectroscopy. The viability and the magnetic properties of the magnetised algae are studied in comparison with the native cells. The technique may find a number of potential applications in biotechnology and bioelectronics.

Interfacing living unicellular algae cells with biocompatible polyelectrolyte-stabilised magnetic nanoparticles.

International Journal of Current Microbiology and Applied Sciences ISSN:2319-7692(Print), ISSN:2319-7706(Online)  is a multidisciplinary peer-reviewed journal with reputable academics and experts as members of its Editorial Board. The Current Microbiology aims to publish all the latest and outstanding research articles. Review and letters in all areas of major importance to techniques of microbiology and applied research with publishes high quality of review and research articles on novel aspects of  Microbiology including Environmental, Food, Agricultural, Medical, Pharmaceutical, Veterinary, Soil, Water and Biodeterioration. The Applied Sciences aims to publish Research articles in Biological Sciences, Biodiversity, Biotechnology, Clinical Sciences, Agricultural Sciences, Chemical Sciences, and Environmental Sciences.

International Journal of Current Microbiology and Applied Sciences

A whole-cell environmental biosensor was fabricated on a diamond electrode. Unicellular microalgae Chlorella vulgaris was entrapped in the bovine serum albumin (BSA) membrane and immobilized directly onto the surface of a diamond electrode for heavy metal detection. We found that the unique surface properties of diamond reduce the electrode fouling problem commonly encountered with metal electrodes. The cell-based diamond biosensor can attain a detection limit of 0.1 ppb for Zn2+ and Cd2+, and exhibits higher detection sensitivity and stability compared to platinum electrodes.

Kailian Ang

Papers

Whole cell environmental biosensor on diamond