Biosensors. Introduced by Elena Neufeld Dec 8 th 2010

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1 Biosensors Introduced by Elena Neufeld Dec 8 th 2010

2 One of the first 'biosensors' To detect gas build-ups in coal mines, caged canaries were used because of their sensitivity towards methane. biological warning system for the workers in the time of the industrial revolution (end of 18 th - 19 th century)

3 Definitions In 1991 J.S. Schultz defined biosensors as follows: 'Biosensors are refined modern equivalents to the caged canary used in coal mines to warn miners of dangerous collections of methane (mine gas) and are based on vegetable or animal molecular building blocks. Official IUPAC definition: Biosensors are characterized by the direct coupling of an immobilized biological sensitive element connected to a transducer and an amplifier.

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5 Immobilization of the biosensitive elements: Physical methods: Adsorption on surface (e.g. antibodies on polystyrol) Attachment of enzymes inside pores of polymeric substances or hydrophobic gels often used matrices: gelatine, silicones, polyacrylamid Physical/chemical methods: Coupling of intact cells (e.g. neurons or microorganisms) Chemical methods: Covalent linkage of biosensitive elements via bifunctional agents by reactive groups on sensor surface

6 Examples of covalent linkages Protein H N C O Aminogroup Enzyme S Thiolgroup Antibody C O Carboxylic Group O Enzyme O Phenolpart of Tyrosine Protein N Imidazolegroup of Histidin N

7 Principles of detection: Amperometric: movement of electrons produced by a redox reaction Potentiometric: changes in the distribution of charges (ph-change) Calorimetric: heat output or absorbance Optical: light output or absorbance Piezoelectric: mass change of reactants or products

8 Example of an amperometric biosensor for glucose detection: The given potential of the electrode is changed by electroactive substances. Enzyme reaction (glucose oxidase): D-glucose + O 2 D-glucono-1,5-lactone + H 2 O 2 Pt anode: H 2 O 2 O H e - Ag cathode: 2 AgCl + 2 e - 2 Ag + 2 Cl -

9 Principle construction of an potentiometric biosensor: Reactions involve the release or absorption of ions and lead to ph-change: Construction: a) semi-permeable membrane b) biocatalyst c) active glass membrane d) ph probe e) electrical potential f) Ag/AgCl electrode g) dilute HCl h) external reference electrode Examples: Penicillinase: Pennicillin pennicilloic acid + H + Peroxidase: H 2 O H I - I H 2 O

10 Advantages and disadvantages of biological sensitive elements Advantages: High selectivity and specificity enzymes, receptors High sensitivity due to high affinity and/or enzymically recognition enzymes, antibodies, DNA Quantification of biological effects due to the amount of nutrients, mutagenity, allergenic effect and/or toxicity Disadvantages: Limited stability Complex preparation Coreactants Culture medium organelles, cells

11 Desirable characteristics of an successful biosensor: Highly specific recognition of an analyte with a large dynamic range by extremly low detection limits The accurate response should have a very short respose time Stable under normal storage conditions The recognition process should be independent of stirring, ph and temperature In clinical studies no toxic or antigenic effects must occur and the probe must be biocompatible and tiny Cheap, small, portable and userfriendly construction A profitable market should exist

12 Biosensors today Biosensors represent a rapidly expanding field 60 % estimated annual growth rate major impetus (Antrieb) from health-care industry Food quality control Environmental monitoring Estimated world analytical market: 12 billion USD per year (30% health care) Next developments are presented in World Congress on Biosensors 2012 in Mexico. examples:... DNA-Chips... Bionics... Biofuel... Nanobiosensors...

13 References: U. E. Spichiger-Keller,Chemical Sensors and Biosensors for Medical and Biological Applications, 1998, WILEY-VCH. W. Baltes, L. W. Kroh, Schnellmethoden zur Beurteilung von Lebensmitteln und ihren Rohstoffen, 2004, Behr's Verlag. A. O. Scott, Biosensors for food analysis,2000, Royal Society of Chemistry.