Chemical Sensor Elaborated by Scientists on the Basis of Materials Possessing Molecular Memory

An electrochemical sensor has been elaborated by a team of scientists from the Faculty of Chemistry of the Lomonosov Moscow State University on the basis of polymers with molecular imprinting. This was done in order to detect saccharides and hydroxy acids. The results have been presented by the scientists in the journal Sensors and Actuators B: Chemical.

An enzyme-free sensor has been elaborated by chemists from the Electrochemical Methods Laboratory at the Lomonosov Moscow State University under the leadership of Professor Arkady Karyakin, Doctor of Chemistry, enabling measurement of lactic acid and glucose concentration.

The chemists from the Lomonosov Moscow State University work with alternative enzyme-free devices in their project. The sensor that has been elaborated by the scientists is an electrode customized by a thin polymer layer. Sensors of this type can be effortlessly produced and they are also considered to be more stable in storage and operation. Reagents for this production are extremely cheaper when compared to enzymes.

Many people have heard about glucose meters - devices, detecting glucose in blood. According to the operating principle most of them are electrochemical. This means that glucose concentration is measured in terms of current density, registered with the help of an enzyme electrode - biosensor, going with the device in the form of a testing strip. However, enzyme usage for chemical detection of substances of interest (for instance, the glucose oxidase enzyme is used in case of glucose) in such devices has its disadvantages. These disadvantages are mostly connected with low stability of enzymes and necessity to provide special storage and operating conditions and biosensor disposability.

Vita Nikitina, one of the project authors and a Junior Researcher at the Faculty of Chemistry of the Lomonosov Moscow State University

In the structure of polymer, synthesized by us on the surface of the electrode, there are functional groups, namely boronic acids, capable of detecting such common low-molecular compounds, like saccharides (glucose and fructose) and hydroxy acids (lactic and tartaric acids). In the project we've shown how our sensors could be used for detection of these substances. A signal, generated by the sensor, is registered by electrochemical means similar to enzyme electrodes. However, unlike amperometric glucose meters, our device is based on another principle - namely, the change of polymer conductivity.

project author

The generation of electrically conductive polymer coating on the surface of electrodes is indeed a significant task. This is the reason why elaboration and detailed optimization of parameters and conditions of electropolymerization have become a significant success of the scientists. Synthesization of polymers was carried out under the current action, passing through the working electrode arranged into an electrochemical cell containing monomer solution. This electrochemical process resulted in deposition of the water-insoluble polymer on the electrode surface.

A molecular imprinting method was used by the chemists to synthesize a polymer. It involves formation of special regions (imprints) in the material, and only those molecules that were used as templates during polymer synthesis were recognized by these regions. Materials with molecular memory could be used as a sensitive layer of chemical sensors in order to detect particular substances. Electrochemical polymerization of substituted aniline was performed in the presence of template molecules, such as saccharides and hydroxy acids. These molecules were removed from the polymer matrix after polymerization, but some spaces (so called molecular imprints) were left in its three-dimensional structure. These imprints in terms of the size, form and orientation of functional groups are complimentary to these template molecules. This effect, known as "molecular memory" of a polymer, enables the material to detect compounds, which have been employed as templates.

The scientists thus have a chemical sensor, developed from an electrode, and coated by substituted polyaniline with molecular imprints. The team tested the sensor by placing it into an electrochemical cell in which the analyzed sample is arranged. The presence of hydroxy acids or saccharides in the analyzed sample results in boronic acid groups of the polymer binding with them, leading to the growth of polymer conductivity, which has been registered by using an electrochemical impedance spectroscopy technique.

We've shown that it's possible to create multisensory systems on the basis of elaborated sensors with different selectivity. These systems allow the monitoring of concentration of various substances in biochemical processes. Such sensors could be used for detection of high-molecular substances and even whole cells, having structural fragments of saccharides or hydroxy acids.

Vita Nikitina