Enhancing the Capabilities of Electrochemical Sensor Arrays Using Nanomaterials and Nanostructured Films
Authors: Rodriguez-Mendez Maria Luz 
Published: September 2023

In the last years electronic tongues (ET) based on electrochemical sensors coupled to a pattern recognition system, have been developed and applied to the analysis of a variety of foods [1]. Nowadays it is evident that improvements in the field involve the development of instruments dedicated to a specific application. This requires the search of sensors specifically designed to analyze an specific target, using the appropriate sensing materials and transduction methods adapted to a specific problem.
Important advances in the field of electrochemical sensors are linked to the use of techniques and materials coming from the field of nanoscience. On one hand, incorporating nanomaterials in the sensing layers can enhance the sensitivity thanks to their excellent electrocatalytic properties. On the other hand, using nanostructured sensing layers can offer opportunities to increase the number of active sites at the surface and to develop structures similar to that of the cellular membranes that can host enzymes or other biologic receptors in a biomimetic environment. Here, the new strategies based on potentiometric and voltammetric sensors will be presented, paying special attention to the new developments based on nanobiosensors and the combinations of enzymes with nanomaterials.
The developments of our group in the field of multisensor systems based on potentiometric sensors and biosensors applied to the analysis of milk are based on PVC membranes where different additives and plasticizers are added. The different compositions give rise to membranes with different porosity and hydrophilicity and hence an array of sensors with cross-sensitivity can be constructed. Such an array can discriminate main components of milk such as galactose, lactose, lactic acid or urea. The capability of the array is drastically enhanced when the membranes are modified with combinations of nanoparticles and enzymes specific to components present in milk such as galactose oxydase, lactose dehydrogenase or urease [2].
Voltammetric sensors can be used to analyze liquid mixtures containing electroactive substances. The example shown here is the wine, which is an hydroalcoholic solution rich in antioxidants such as the polyphenols and sugars such as glucose.
In arrays of voltammetric sensors, electrodes are chemically modified with electrocatalytic materials that increase the intensity of the signals while reducing the oxidation potential of the phenols. Classic materials such as phthalocyanines or conducting polymers are excellent electrocatalytic materials that facilitate the electron transfer between the phenols or sugars and the electrode. Metal nanoparticles and nanocarbons are also excellent electron mediators [3].
Nanostructured Sensing layers prepared using de Layer by Layer (LbL) or the Langmuir-Blodgett (LB) technique can further increase the intensity of the signals due to the high surface-to-volume ratio. In addition, these techniques facilitate the preparation of films made of different materials with different functionalities. For instance, the combination of nanoparticles with phthalocyanines have synergistic effects that increase even further the intensity of the signals.
Enzymes such as glucose oxydase or galactose oxydase (specific for the detection of sugars) or tyrosinase or laccase (specific for the detection of phenols) have been introduced in nanostructured films based on phospholipids that create a biomimetic environment enhancing the performance of the sensors.
The biosensors described above have been combined to develop bioelectronic tongues (bio-ETs) that have been successfully used to discriminate and classify milk and wine samples.

References

Rodríguez-Méndez, M.L., Electronic noses and tongues in the food industry. Elsevier-Academic press, 2016

Perez-Gonzalez et al., Food Control, 145, 109425 (2023)

Medina-Plaza et. Al. Biosens. Bioelectronics, 57, 276-286 (2015)