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European Biopharmaceutical Review

Making Sense

Maria Minunni, Sara Tombelli and Marco Mascini at the Chemistry Department, and Anna Rita Bilia at the Pharmaceutical Science Department of Florence University break down the advantages of biosensors for natural product analysis

Analysis of the natural constituents of herbal drugs, herbal drug preparations and herbal medicinal products is generally carried out on a complex matrix where a target compound or target class of constituents (active principles or markers) must be evaluated. This evaluation is a crucial step both in quality control and stability testing, but it is also important in terms of chemical screening of bioactive constituents from plants in the search for new drugs.

Biosensors represent new analytical devices which appear to be an analyst’s dream. They are able to give rapid analysis responses; to operate, in many cases, directly on complex matrices; to be selective and sensitive enough for the required application; to be portable and sometimes also disposable; and to have fast analysis times (1).

Biosensors have mainly been applied for analytical purposes in environmental chemistry, clinical practice and analysis of food, but recently several examples dealing with natural compounds have also been reported in the literature. This article explores the main biosensor technologies, based on different transduction principles, and offers examples of their applications for natural product analysis. The different examples are grouped by target analytes in terms of their bioactivity, such as the ability to intercalate DNA or act as antioxidants. Some examples for single target detection are also reported.

BIOSENSORS

As defined by IUPAC in 1999, a biosensor is an integrated device able to give qualitative and quantitative or semiquantitative specific information through the use of a biological element of recognition in close spatial contact with a transducer. The biological element is responsible for the biological recognition of the target analyte and thus for the sensor specificity. The biomolecule is immobilised on a physical transducer that translates the biorecognition event into a useful electrical signal. Biosensors can be divided mainly into two categories: catalytic and affinity biosensors (2).

Catalytic biosensors involve a catalytic event in which a substrate is converted into a product. Catalysis occurs at the transducer interface, and substrate depletion or product formation is measured by a transducer. Only one enzyme can be immobilised, but it is also possible to use a set of enzymes, a whole organism (for example, a bacterial cell) or a tissue slice as the catalytic element.

In affinity biosensors, recognition of the analyte in solution by the immobilised biological element is based on an affinity reaction, such as an antigen-antibody binding, nucleic acid hybridisation, or receptor-ligand interaction. On the basis of these different interactions, the affinity biosensors can be divided into immunosensors, DNA sensors, aptasensors (3), and so on. The transduction principles used include electrochemical, optical and piezoelectric, thus the sensor surfaces can be electrodes, fibre optics, planar waveguides or quartz crystals. Table 1 shows some biological elements that could be used coupled to various forms of transducer.

Catalytic Biosensors: The Case of Polyphenols Detection
Catalytic sensors use enzymes which convert a substrate into a product that can be recognised and quantified. The selectivity and specificity of the system rely on the enzyme coupled to the transducer. Thus, by immobilising different enzymes on the sensing elements, a wide spectrum of analytes can be detected. The enzymes can respond only to a specific functional group rather than the whole molecule and therefore recognise a class of compounds (1).


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Professor Marco Mascini is Professor of Analytical Chemistry at the Faculty of Sciences at the University of Florence, Italy, and sits on the editorial board of several international journals, such as Analytical Letters, Biosensors & Bioelectronics and Talanta. He has coordinated and led participant units in several European projects of the past European Frameworks. He has authored of more than 300 papers on biosensor development and application. Marco was also one of the pioneers of biosensor technology. He realised several practical applications of biosensors in industrial prototypes for in vivo and in vitro applications in diagnostic medicine, environmental applications and for evaluating food quality and safety.

Anna Rita Bilia is Associate Professor of Pharmaceutical Technology and Phytochemistry at the Faculty of Pharmacy, University of Florence. She has had experience in Pharmacognosy since 1988, and has carried out research on the analytics and pharmaceutical technology of medicinal plants. Since 1997, she has been a member of the board of the Italian Society of Phytochemistry and the Italian delegate at the European Scientific Cooperative for Phytotherapy (ESCOP). Since 2006 she has been a member of the board of Gesellschaft für Arzneipflanzenforschung eV (GA) and, since 2007, she has been a member of the board of the Italian Society of University Teachers and Researchers in Legislation and Pharmaceutical technology (ADRITELF). She is the author of more than 100 scientific papers concerning studies on medicinal plants, herbal drug preparations and herbal medicinal products.

Dr Maria Minunni received the Laurea degree in Biology from Pisa University, Italy, in 1988, and a PhD in Environmental Sciences from the Italian Ministry of Science in 1994, with a thesis conducted at the Chemistry Department, University of Florence. She has been a visiting scientist at the Nestlè Research Centre, Lausanne, Switzerland, and at Pharmacia Biosensor AB, Uppsala, Sweden. She has been a postdoctoral researcher at the Technical University of Munich, Germany. Maria is currently a Senior Researcher at the Department of Chemistry, University of Florence, teaching Clinical Analytical Chemistry. She has been working in biosensor development since 1990, using various transduction principles. Her research interests have mainly covered the development of affinity sensors: immunosensing and nucleic acid-based sensors.

Sara Tombelli received an the Italian degree in Chemistry and a PhD in Environmental Sciences from the University of Florence, Italy, in 1996 and 2000, respectively. She also received a PhD in Biotechnology from Cranfield University, UK. She is currently a post-doctoral researcher at the Chemisty Department, University of Florence. Her research involves the development of biosensors based on nucleic acids with optical and piezoelectric transducers for applications in environmental, clinical and food analysis.

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Professor Marco Mascini
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Anna Rita Bilia
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Dr Maria Minunni
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Sara Tombelli
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