Electronic tongue systems are traditionally used to analyse: food products, water samples and taste masking technologies for pharmaceuticals. In principle, their applications are almost limitless, as they are able to almost completely reduce the impact of interferents and can be applied to distinguish samples of extreme complexity as for example broths from different stages of fermentation. Nevertheless, their applications outside the three principal sample types are, in comparison, rather scarce. In this review, we would like to take a closer look on what are real capabilities of electronic tongue systems, what can be achieved using mixed sensor arrays and by introduction of biosensors or molecularly imprinted polymers in the matrix. We will discuss future directions both in the sense of applications as well as system development in the ever-growing trend of low cost analysis.

The electrocatalytic oxidation of neurotransmitters on the electrodes modified with oppositely charged carbon nanoparticles has been investigated. These nanoparticles were deposited at the electrode from the aqueous suspensions via a layer-by-layer method. The electrocatalytic response was evaluated by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. The modified electrode exhibited good electrocatalytic properties towards not only dopamine oxidation, but also for epinephrine and serotonin oxidation. This allows us to separate their voltammetric signals from the signals of interfering substances such as ascorbic acid or uric acid. The obtained calibration curves are in the range 0.4–350 μM, 1–49 μM and 0.8–100 μM with detection limits of 0.4 μM, 1.0 μM and 0.8 μM for dopamine, epinephrine and serotonin, respectively. In addition these carbon nanoparticulate electrodes showed excellent sample to sample reproducibility (the relative standard deviations for n = 7 equal 0.7%) and, maintained 94% of electrochemical signal corresponding to dopamine oxidation after 18 month storage.

We present an electrochemical, microfluidic system with a working electrode based on an ordered 3D array of pencil leads. The electrode array was integrated into a plexiglass/PDMS channel. We tested the setup using a simple redox probe and compared the results with computer simulations. As a proof of concept application of the device we showed that the setup can be used for determination of dopamine concentration in physiological pH and ultrasensitive, although only qualitative, detection of p-nitrophenol with a limit of detection below 1 nmol L⁻¹. The observed limit of detection for p-nitrophenol is not only much lower than achieved with similar methods but also sufficient for evaluation of exposure to pesticides such as methyl parathion through urinalysis. This low cost setup can be fabricated without the need for clean room facilities and in the future, due to the ordered structure of the electrode could be used to better understand the process of electroanalysis and electrode functionalization. To the best of our knowledge it is the first application of pencil leads as 3D electrochemical sensor in a microfluidic channel.

In this work, we explore generation–collection electrochemistry in a rotating droplet hydrodynamic system, where a 70 μL droplet containing a redox active species (ferrocyanide) is sandwiched between an upper rotating rod and bottom nonmoving generator and collector planar electrodes. In such a system, we studied the effect of the counter electrode reaction on the recorded generator current, and the effect of the generator–collector distance (ranging from 3 to ca. 500 μm) on the collection efficiencies obtained at rotation rates ranging from 50 to 1100 rpm. We found that the counter electrode reaction competes with the collector reaction for the regeneration of the electroactive species; thus, collection efficiencies of 100% are probably impossible to obtain with this system geometry. We found that the collection efficiency increases with the droplet rotation rate and decreases with the generator–collector distance. The highest collection efficiency we obtained is 62% for the generator–collector distance of 3 μm, which is more than two times higher than that for typical bulk experiments with a commercial rotating ring disk electrode. We show that the increased collection efficiency can be successfully used in epinephrine detection for filtering out signals from ascorbic acid and uric acid interferents.