Bioinspired Sensor Systems

This editorial summarizes and classifies the contributions presented by different authors to the special issue of the journal Sensors dedicated to Bioinspired Sensor Systems. From the coupling of sensor arrays or networks, plus computer processing abilities, new applications to mimic or to complement human senses are arising in the context of ambient intelligence. Principles used, and illustrative study cases have been presented permitting readers to grasp the current status of the field

Crown ether-modified electrodes for the simultaneous stripping voltammetric determination of Cd(II), Pb(II) and Cu(II)

This work describes the immobilization of 4-carboxybenzo-18-crown-6 (CB-18-crown-6) and 4-carboxybenzo-15-crown-5 (CB-15-crown-5) assisted by lysine on aryl diazonium salt monolayers anchored to the surface of graphite-epoxy composite electrodes (GEC), and their use for the simultaneous determination of Cd(II), Pb(II) and Cu(II) by differential pulse anodic stripping voltammetry (DPASV). These modified electrodes display a good repeatability and reproducibility with detection and quantification limits at levels of µg L(-1) (ppb), confirming their suitability for the determination of Cd(II), Pb(II) and Cu(II) ions in environmental samples. The overlapped nature of the multimetal stripping measurements was resolved by employing the two-sensor array CB-15-crown-5-GEC and CB-18-crown-6-GEC, since the metal complex selectivity exhibited by the considered ligands could add some discrimination power. For the processing of the voltammograms, Discrete Wavelet Transform and Causal Index were selected as preprocessing tools for data compression coupled with an artificial neural network for the modeling of the obtained responses, allowing the resolution of mixtures of these metals with good prediction of their concentrations (correlation with expected values for an external test subset better than 0.942)

Simultaneous voltammetric determination of acetaminophen, ascorbic acid and uric acid by use of integrated array of screen-printed electrodes and chemometric tools

In the present work, ternary mixtures of Acetaminophen, Ascorbic acid and Uric acid were resolved using the Electronic tongue (ET) principle and Cyclic voltammetry (CV) technique. The screen-printed integrated electrode array having differentiated response for the three oxidizable compounds was formed by Graphite, Prussian blue (PB), Cobalt (II) phthalocyanine (CoPc) and Copper oxide (II) (CuO) ink-modified carbon electrodes. A set of samples, ranging from 0 to 500 µmol·L, was prepared, using a tilted (3) factorial design in order to build the quantitative response model. Subsequently, the model performance was evaluated with an external subset of samples defined randomly along the experimental domain. Partial Least Squares Regression (PLS) was employed to construct the quantitative model. Finally, the model successfully predicted the concentration of the three compounds with a normalized root mean square error (NRMSE) of 1.00 and 0.99 for the training and test subsets, respectively, and R ≥ 0.762 for the obtained vs. expected comparison graphs. In this way, a screen-printed integrated electrode platform can be successfully used for voltammetric ET applications

Carbon based electrodes for the voltammetric determination of capsaicin in spicy samples

A voltammetric sensor based on the modification of a screen-printed carbon electrode with reduced graphene oxide (rGO-SPCE) is presented for the cyclic voltammetric determination of capsaicin in a wide range of concentrations. Special attention was given to factors affecting sensitivity and repeatability in order to overcome common reported issues related to the voltammetric determination of capsaicin. Fouling associated to the adsorption of capsaicin was minimized using a simple and effective washing step, allowing sensors to be reused for at least 10 measurements with a repeatable signal. The developed rGO-SPCE presented two well-defined linear ranges (from 1.1 to 25.0 and from 25.0 to 150.3 µmol L−1) and provided an increased sensitivity as compared to the unmodified electrode as well as to other modified electrodes based on carbon nanomaterials commercially available. Furthermore, a low limit of detection of 0.3 µmol L−1 was achieved and the accuracy of the method was demonstrated for the determination of capsaicin in chilli pepper, paprika samples and Tabasco sauce, obtaining comparable results to those achieved by liquid chromatography with UV-vis detection

Classification and authentication of spices and aromatic herbs by means of HPLC-UV and chemometrics

Recent increase in the adulteration of spices and aromatic herbs in food industry constitutes a problem that requires exhaustive quality control. As every spice has a different composition with characteristic biomarkers, chromatographic profiles are especially valuable to authenticate these products. Thus, in this work a new high performance liquid chromatography (HPLC) method with UV-vis detection was developed for the characterization, identification and authentication of cinnamon, oregano, thyme, sesame, bay leaf, clove, cumin, and vanilla. Chromatographic separation was optimized based on the separation of six characteristic biomarkers (sesamol, eugenol, thymol, carvacrol, salicylaldehyde and vainillin) and was performed using a C18 reversed-phase column under a 35 min gradient elution based on 0.1% (v/v) formic aqueous solution and methanol by means of UV-Vis detection at 280 nm. 87 samples, purchased in local supermarkets, were analyzed and the obtained profiles were processed by chemometric techniques. First, data treatment was evaluated by principal component analysis (PCA); next soft independent modelling by class analogy (SIMCA) and partial least squares discriminant analysis (PLS-DA) were carried out in order to verify if classification according to their biomarkers was possible. The study concluded that PLS-DA (0.14-0.75% global error) classifies better the types of spice or aromatic herb than SIMCA (0.82-3.67% global error)

Simultaneous voltammetric determination of heavy metals by use of crown ether-modified electrodes and chemometrics

A three‐sensor array consisting of a graphite‐epoxy composite electrode (GEC), 4‐carboxybenzo‐18‐crown‐6‐GEC and 4‐carboxybenzo‐15‐crown‐5‐GEC was employed for the simultaneous determination of Cd(II), Pb(II) and Hg(II) by differential pulse anodic stripping voltammetry (DPASV). Sensors were firstly studied for the determination of Hg(II); secondly, peak current responses confirmed that all sensors showed differentiated response for the three considered metals. A response model was developed to resolve mixtures of Cd(II), Pb(II) and Hg(II) at the µg L−1 level; Discrete Wavelet Transform was selected as preprocessing tool and artificial neural network used for the modelling of the obtained responses

Potentiometric Electronic Tongue to Resolve Mixtures of Sulfide and Perchlorate Anions

This work describes the use of an array of potentiometric sensors and an artificial neural network response model to determine perchlorate and sulfide ions in polluted waters, by what is known as an electronic tongue. Sensors used have been all-solid-state PVC membrane selective electrodes, where their ionophores were different metal-phtalocyanine complexes with specific and anion generic responses. The study case illustrates the potential use of electronic tongues in the quantification of mixtures when interfering effects need to be counterbalanced: relative errors in determination of individual ions can be decreased typically from 25% to less than 5%, if compared to the use of a single proposed ion-selective electrode

A Reusable Impedimetric Aptasensor for Detection of Thrombin Employing a Graphite-Epoxy Composite Electrode

Here, we report the application of a label-free electrochemical aptasensor based on a graphite-epoxy composite electrode for the detection of thrombin; in this work, aptamers were immobilized onto the electrodes surface using wet physical adsorption. The detection principle is based on the changes of the interfacial properties of the electrode; these were probed in the presence of the reversible redox couple [Fe(CN)6]3−/[Fe(CN)6]4− using impedance measurements. The electrode surface was partially blocked due to formation of aptamer-thrombin complex, resulting in an increase of the interfacial electron-transfer resistance detected by Electrochemical Impedance Spectroscopy (EIS). The aptasensor showed a linear response for thrombin in the range of 7.5 pM to 75 pM and a detection limit of 4.5 pM. The aptasensor was regenerated by breaking the complex formed between the aptamer and thrombin using 2.0 M NaCl solution at 42 °C, showing its operation for different cycles. The interference response caused by main proteins in serum has been characterized