A composite sensor array impedentiometric electronic tonguePart II. Discrimination of basic tastes

Critical View on the Qualification of Electronic Tongues Regarding Their Performance in the Development of Peroral Drug Formulations with Bitter Ingredients

In this review, we aim to highlight the advantages, challenges, and limitations of electronic tongues (e-tongues) in pharmaceutical drug development. The authors, therefore, critically evaluated the performance of e-tongues regarding their qualification to assess peroral formulations containing bitter active pharmaceutical ingredients. A literature search using the keywords 'electronic', 'tongue', 'bitter', and 'drug' in a Web of Science search was therefore initially conducted. Reviewing the publications of the past decade, and further literature where necessary, allowed the authors to discuss whether and how e-tongues perform as expected and whether they have the potential to become a standard tool in drug development. Specifically highlighted are the expectations an e-tongue should meet. Further, a brief insight into the technologies of the utilized e-tongues is given. Reliable protocols were found that enable (i) the qualified performance of e-tongue instruments from an analytical perspective, (ii) proper taste-masking assessments, and (iii) under certain circumstances, the evaluation of bitterness.

Establishment of a new cell-based assay to quantitatively evaluate the sweetness of sugar and sugar alcohol

Sweetness is a crucial indicator for identifying sweeteners used for flavor regulation and nutritional matching of foods. This study established a new quantitative sweetness evaluation method based on a combination of transiently transfected sweet taste receptor cells (STRs) and human sensory evaluation. Here, nine different sweeteners were evaluated and 10 sensory difference intensities and their corresponding concentrations were obtained through sensory evaluation. Using the same concentration solution as in the sensory evaluation, the dosage-response curve and EC50 of the nine sweeteners were obtained by analyzing the intracellular calcium signal fluctuation of STRs. Data analysis revealed that the calcium signal intensity and sweetness intensity under the same concentration of sweetener presented a strong linear correlation (R2 > 0.9). Additionally, we found a favorable correlation (R2 = 0.8746) between the relative sweetness and EC50. These findings indicate that the quantitative evaluation of sweetness based on STRs could be a potential alternative to human sensory evaluation.

Recent Advances in Bitterness-Sensing Systems

Bitterness is one of the basic tastes, and sensing bitterness plays a significant role in mammals recognizing toxic substances. The bitter taste of food and oral medicines may decrease consumer compliance. As a result, many efforts have been made to mask or decrease the bitterness in food and oral pharmaceutical products. The detection of bitterness is critical to evaluate how successful the taste-masking technology is, and many novel taste-sensing systems have been developed on the basis of various interaction mechanisms. In this review, we summarize the progress of bitterness response mechanisms and the development of novel sensors in detecting bitterness ranging from commercial electronic devices based on modified electrodes to micro-type sensors functionalized with taste cells, polymeric membranes, and other materials in the last two decades. The challenges and potential solutions to improve the taste sensor quality are also discussed.

E-Tongues/Noses Based on Conducting Polymers and Composite Materials: Expanding the Possibilities in Complex Analytical Sensing

Conducting polymers (CPs) are extensively studied due to their high versatility and electrical properties, as well as their high environmental stability. Based on the above, their applications as electronic devices are promoted and constitute an interesting matter of research. This review summarizes their application in common electronic devices and their implementation in electronic tongues and noses systems (E-tongues and E-noses, respectively). The monitoring of diverse factors with these devices by multivariate calibration methods for different applications is also included. Lastly, a critical discussion about the enclosed analytical potential of several conducting polymer-based devices in electronic systems reported in literature will be offered.

A Versatile Electronic Tongue Based on Surface Plasmon Resonance Imaging and Cross-Reactive Sensor Arrays-A Mini-Review

Nowadays, there is a strong demand for the development of new analytical devices with novel performances to improve the quality of our daily lives. In this context, multisensor systems such as electronic tongues (eTs) have emerged as promising alternatives. Recently, we have developed a new versatile eT system by coupling surface plasmon resonance imaging (SPRi) with cross-reactive sensor arrays. In order to largely simplify the preparation of sensing materials with a great diversity, an innovative combinatorial approach was proposed by combining and mixing a small number of easily accessible molecules displaying different physicochemical properties. The obtained eT was able to generate 2D continuous evolution profile (CEP) and 3D continuous evolution landscape (CEL), which is also called 3D image, with valuable kinetic information, for the discrimination and classification of samples. Here, diverse applications of such a versatile eT have been summarized. It is not only effective for pure protein analysis, capable of differentiating protein isoforms such as chemokines CXCL12α and CXCL12γ, but can also be generalized for the analysis of complex mixtures, such as milk samples, with promising potential for monitoring the deterioration of milk.

Sensing scaffolds to monitor cellular activity using impedance measurements

Scaffolds are cell adhesive matrices for the realisation of tissue constructs. Here we describe how scaffolds for tissue engineering can also be used as sensors for monitoring cellular activity such as adhesion and spreading. Carbon nanotube polymer composites were fabricated into membranes and scaffolds with electro-conductive properties. Impedance techniques were used to measure the effects of media and cell cultures on composite membranes and the results were analysed using lumped parameter models. We show that protein adhesion can be distinguished from cell adhesion as the impedance changes are much smaller for the latter (5%). In the presence of cells, impedance changes are of the order of 40% and can be correlated with adhesion, spreading and changes in cell density.

Review: highlights in recent applications of electronic tongues in food analysis

This paper examines the main features of modern electronic tongues (e-tongues) and their most important applications in food analysis in this new century. The components of an e-tongue (automatic sampler, array of chemical sensors, and data processing system) are described. Applications commented include process monitoring, freshness evaluation and shelf-life investigation, authenticity assessment, foodstuff recognition, quantitative analysis, and other quality control studies. Finally, some interesting remarks concerning the strengths and weaknesses of e-tongues in food analysis are also mentioned.

Conducting polymers in chemical sensors and arrays

The review covers main applications of conducting polymers in chemical sensors and biosensors. The first part is focused on intrinsic and induced receptor properties of conducting polymers, such as pH sensitivity, sensitivity to inorganic ions and organic molecules as well as sensitivity to gases. Induced receptor properties can be also formed by molecularly imprinted polymerization or by immobilization of biological receptors. Immobilization strategies are reviewed in the second part. The third part is focused on applications of conducting polymers as transducers and includes usual optical (fluorescence, SPR, etc.) and electrical (conductometric, amperometric, potentiometric, etc.) transducing techniques as well as organic chemosensitive semiconductor devices. An assembly of stable sensing structures requires strong binding of conducting polymers to solid supports. These aspects are discussed in the next part. Finally, an application of combinatorial synthesis and high-throughput analysis to the development and optimization of sensing materials is described.

Sensor arrays for liquid sensing--electronic tongue systems

Electronic tongue systems are multisensor devices dedicated to automatic analysis of complicated composition samples and to the recognition of their characteristic properties. Recently, the number of publications covering this topic has significantly increased. Many possible architectures of such devices were proposed: potentiometric, voltammetric, as well as approaches embracing mass- and optical-sensors. For the analysis of sensor array data, various pattern recognition systems were proposed. All of these topics are summarized in this review. Moreover, additional problems are considered: miniaturization of electronic tongues and hybrid systems for liquid sensing.