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Tuesday 25 April 2017

Chemical Sensors for Biology

 

A. Kuhn, V. Ravaine, N. Sojic, S. Arbault, V. Lapeyre, B. Goudeau

This field of research deals with the development of sensing systems that are designed to detect selectively or specifically molecules of biological interest :
1. Bioelectrodes with complex architectures
2. Glucose-responsive nanogels as sensors and insulin delivery systems
3. Synthetic biosystems
This involves two main aspects that we are pursuing in parallel. First, engineering chemical systems in order to allow a molecular recognition event. Secondly, the detection part which consists in transducing the recognition event into a recordable signal.

1. Bioelectrodes with complex hierarchical architectures

In recent years we have elaborated new approaches to design electrodes with a highly ordered porosity. The internal surface of these electrodes can be subsequently modified with redox-mediators, coenzymes and enzymes for applications in biosensing, biofuel cells or bioelectrosynthesis.

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(A) Side view of a macroporous polypyrrole electrode with a porosity gradient obtained with the Langmuir Blodgett technique (B) 3D reconstitution of a porous gold electrode characterized by FIB-SEM.

This structuration at the sub-micrometer scale is of particular interest for electrodes with very small dimensions (microelectrodes) as they show normally very small currents. This can be compensated by using porous microelectrodes, thus increasing the active surface area and the current by up to two orders of magnitude. When such porous electrodes are partially or completely filled with a matrix containing enzyme a significant increase in current can be observed.

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(A) TEM picture of an electrodeposited Resydrol matrix in the pores of the macroporous electrode (B) Comparison of the electroenzymatic D-sorbitol oxidation when the biocatalytic system is deposited on a flat gold electrode (b), and on a gold electrode with three half pore layers filled with Resydrol (c).

In fine we use these porous electrodes not only to design biosensors with better detection limits (see also Electrochemistry of biosystems), but also for novel bioelectrochemical reactors with an increased production efficiency and biofuel cells with an optimized power output.

2. Glucose-responsive nanogels as sensors and insulin delivery systems

Nanogels are colloidal particles made of swollen cross-linked polymers. These soft particles, functionalized with a ligand of glucose such as phenylboronic acid, undergo swelling transitions in response to changes in glucose concentration. Our group explores the application of such particles in the treatment of diabetes: firstly as sensors to measure glucose concentration level, secondly as containers for closed-loop insulin delivery. In this area, we focus on the design of biocompatible materials made of polysaccharides. This project involves collaborative work with pharmacists and practitioner.

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3. Synthetic Biosystems

A strong interest for artificial systems mimicking single living cells has aroused over the last decade. In this context, we designed giant unilamellar vesicles (GUV, 10-100 µm), prepared from natural or synthetic phospholipids, because this system represents a convenient biomimetic setup of the closed lipid matrix of cell membranes. Challenging applications of GUVs include gene expression and enzymatic synthesis of active species inside a vesicle with the ultimate goal of constructing a dynamic artificial system with essential features of living cells. Our project aims at developing GUV, in which enzymatic reactions (ex. Glucose Oxidase, NO Synthase) can be established under quantitative and time-resolved control (micro-injection, liposome fusion). Enzymatic products (H2O2, NO°, ONOO-) can be monitored in situ and simultaneously by fluorescence microscopy (ex. Amplex Red) and electrochemistry (Ultramicroelectrode), in order to decipher the nature of species generating nitro-oxidative stress processes in living systems (see also the section Electrochemistry of biosystems).

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Left: principle of a biomimetic system based on a single liposome (Giant Unilamellar Vesicle). An enzymatic reaction (E) is achieved within, following the micro-injection of a substrate (S), the formed product (P) being detected in situ owing to Electrochemistry (microelectrode) or Fluorescence (dye F). Right: an example of a single GUV (Egg-phosphatidylcholine lipids) in which hydrogen peroxide formed by Glucose oxidase is detected with a fluorescence dye (Amplex Red).

Références

Chemically-controlled closed-loop insulin delivery
Journal of Controlled Release 2008132, 2-11.

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