This minireview describes the main developments of electronic tongues (e-tongues) and taste sensors in recent years, with a summary of the principles of detection and materials used in the sensing units. E-tongues are sensor arrays capable of distinguishing very similar liquids employing the concept of global selectivity, where the difference in the electrical response of different materials serves as a fingerprint for the analysed sample. They have been widely used for the analysis of wines, fruit juices, coffee, milk and beverages, in addition to the detection of trace amounts of impurities or pollutants in waters. Among the various principles of detection, electrochemical measurements and impedance spectroscopy are the most prominent. With regard to the materials for the sensing units, in most cases use is made of ultrathin films produced in a layer-by-layer fashion to yield higher sensitivity with the advantage of control of the film molecular architecture. The concept of e-tongues has been extended to biosensing by using sensing units capable of molecular recognition, as in films with immobilized antigens or enzymes with specific recognition for clinical diagnosis. Because the identification of samples is basically a classification task, there has been a trend to use artificial intelligence and information visualization methods to enhance the performance of e-tongues.

Surface plasmon resonance (SPR) biosensing is based on the detection of small changes in the refractive index on a gold surface modified with molecular recognition materials, thus being mostly limited to detecting large molecules. In this paper, we report on a SPR biosensing platform suitable to detect small molecules by making use of the mediator-type enzyme microperoxidase-11 (MP11) in layer-by-layer films. By depositing a top layer of glucose oxidase or uricase, we were able to detect glucose or uric acid with limits of detection of 3.4 and 0.27 μ mol l ⁻¹ , respectively. Measurable SPR signals could be achieved because of the changes in polarizability of MP11, as it is oxidized upon interaction with the analyte. Confirmation of this hypothesis was obtained with finite difference time domain simulations, which also allowed us to discard the possible effects from film roughness changes observed in atomic force microscopy images. The main advantage of this mediator-type enzyme approach is in the simplicity of the experimental method that does not require an external potential, unlike similar approaches for SPR biosensing of small molecules. The detection limits reported here were achieved without optimizing the film architecture, and therefore the performance can in principle be further enhanced, while the proposed SPR platform may be extended to any system where hydrogen peroxide is generated in enzymatic reactions.

Lab-on-a-Disc (LoaD) biosensors are increasingly a promising solution for many biosensing applications. In the search for a perfect match between point-of-care (PoC) microfluidic devices and biosensors, the LoaD platform has the potential to be reliable, sensitive, low-cost, and easy-to-use. The present global pandemic draws attention to the importance of rapid sample-to-answer PoC devices for minimising manual intervention and sample manipulation, thus increasing the safety of the health professional while minimising the chances of sample contamination. A biosensor is defined by its ability to measure an analyte by converting a biological binding event to tangible analytical data. With evolving manufacturing processes for both LoaDs and biosensors, it is becoming more feasible to embed biosensors within the platform and/or to pair the microfluidic cartridges with low-cost detection systems. This review considers the basics of the centrifugal microfluidics and describes recent developments in common biosensing methods and novel technologies for fluidic control and automation. Finally, an overview of current devices on the market is provided. This review will guide scientists who want to initiate research in LoaD PoC devices as well as providing valuable reference material to researchers active in the field.