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An electronic tongue formed by voltammetric sensors and biosensors containing phthalocyanines has been developed and used to analyze grapes of different varieties. The sensors are prepared using the carbon paste technique and have been chemically modified with different metallophthalocyanines. In turn, biosensors consist of carbon paste electrodes modified with phthalocyanines combined with tyrosinase or glucose oxidase. The response of the individual sensors towards model solutions of glucose and catechol have demonstrated that the voltammetric responses depend on the nature of the phthalocyanine, evidencing the important role of the electron mediator in the performance of the sensors. The capability of the system to discriminate grapes according to their sugar and their polyphenolic content has been evidenced using Principal Component Analysis. It has been demonstrated that the proposed array of sensors combines the advantages of classical phthalocyanine based sensors — that provide global information about the sample —, with the specificity of the enzyme substrate reaction typical of biosensors. For this reason, the selectivity of the multisensor system and its capability of discrimination is clearly improved when biosensors containing glucose oxidase or tyrosinase are included in the array.

Voltammetric sensors based on phthalocyanines have been used to detect a variety of compounds. In this paper, the state of the art of sensors prepared using classical techniques will be revised. Then, new strategies to improve the performance of the sensors will be described using as example sensors chemically modified with lutetium bisphthalocyanine (LuPc${}_2)$ dedicated to the detection of phenols of interest in the food industry. Classical LuPc₂ carbon paste electrodes can detect phenols such as catechol, caffeic acid or pyrogallol with limits of detection in the range of 10${}^{-4}$–10${}^{-5}$ M. The performance can be improved by using nanostructured Langmuir–Blodgett (LB) or Layer by Layer (LbL) films. The enhanced surface to volume ratio produce an increase in the sensitivity of the sensors. Limits of detection of 10${}^{-5}$–10${}^{-7}$ M are attained, which are one order of magnitude lower than those obtained using conventional carbon paste electrodes. Moreover, these techniques can be used to co-immobilize two electrocatalytic materials in the same device. The limits of detection obtained in LB sensors combining LuPc₂/AuNPs or LuPc₂/CNT are further improved. Finally, the LB technique has been used to prepare biosensors where a phenol oxydase (such as tyrosinase or lacasse) is immobilized in a biomimetic environment that preserves the enzymatic activity. Moreover, LuPc₂ can be co-immobilized with the enzyme in a lipidic film formed by arachidic acid (AA). LuPc₂ can act as an electron mediator facilitating the electron transfer. These biomimetic sensors formed by LuPc₂/AA/enzyme show Limits of detection of 10${}^{-8}$ M and an enhanced selectivity.

The electrodeposition of a film of reduced graphene oxide (ERGO) with well-dispersed on a glassy carbon electrode (GCE) was achieved using cyclic voltammetry (CV) in a graphene oxide (GO) colloidal solution. Using square wave adsorptive stripping voltammetry (SWASV), the ERGO film was applied for the first time, in developing a high-sensitive electrochemical sensor for detection of taxifolin. Compared with bare GCE, the resulting electrodes (ERGO/GCE) exhibited excellent response toward the oxidation of taxifolin by significantly enhancing the oxidation peak currents and the decreased peak-to-peak separation. Under selected conditions, the reduction peak currents had linear relationship with taxifolin concentration in the range of 5.0 × 10^-8 – 1.5 × 10^-6 mol L^-1, with detection limit of 4.0 × 10^-9 mol L^-1. Besides, the method was successfully applied to the quantitative determination of taxifolin in the Prince's-feather fruit with satisfactory results.

In this study, a film of electrochemically reduced graphene oxide (ERGO) deposited onto a glassy carbon electrode (GCE) was prepared through the pulse potential method (PPM). The as-prepared film was characterized via scanning electron microscopy (SEM) and cyclic voltammetry (CV). The ERGO film was applied for the first time to develop a highly sensitive electrochemical sensor for imidacloprid determination. Results revealed that the ERGO film can effectively increase response towards imidacloprid reduction by significantly enhancing the reduction peak currents and decreasing the over potential of imidacloprid. Under optimum conditions, the modified electrode showed a linear voltammetric response to imidacloprid at concentrations ranging from $3.0\times 10^{-8}$ mol L${}^{-1}$ to $1.1\times 10^{-6}$mol L${}^{-1}$, with a detection limit of $1.0\times 10^{-8}$ mol L${}^{-1}$. The developed electrode is potentially a good candidate for imidacloprid determination. The proposed method provides a good recovery rate of imidacloprid in spiked practical samples, such as lake water and tap water.

In this work, a novel electrochemical sensor was presented for Tanshinone IIA determination. The as-prepared electrode was prepared by electrodepositing a reduced graphene oxide film onto a carbon paste electrode modified with gold nanoparticles, which combined the advantages of both gold nanoparticles and electrochemically reduced graphene oxide. It was characterized with scanning electron microscopy and cyclic voltammetry. The electrochemical behavior of Tanshinone IIA at the modified electrode was investigated for the first time. Results revealed that the modified electrode can effectively increase response toward Tanshinone IIA by significantly enhancing the redox peak currents and decreasing the peak-to-peak separation. Under the optimized conditions, the modified electrode showed a linear voltammetric response to Tanshinone IIA at concentrations ranging from $5.0\times 10^{-8}$mol L${}^{-1}$ to $1.0\times 10^{-5}$mol L${}^{-1}$, with a detection limit of $1.0\times 10^{-8}$mol L${}^{-1}$ ($S∕N=3$). The proposed method was successfully applied in determination of Tanshinone IIA in pharmaceutical samples with satisfactory results.

The electrodeposition of reduced graphene oxide (rGO) film with preferred vertical orientation was fabricated on a glassy carbon electrode by using pulse potential method in a graphene oxide solution. The rGO film was applied in developing a high-sensitive electrochemical sensor for detection of levodopa (L-dopa). The new electrochemical sensor displayed a significant response to L-dopa because of its excellent electric conductivity and large specific surface area. Moreover, the determination of L-dopa on this modified electrode was not interfered by the coexistence of ascorbic acid (AA) and uric acid (UA). Under the selective conditions, the modified electrode showed a linear voltammetric response to L-dopa within a certain concentration ranging from $5.0\times 10^{-7}$$-1.5\times 10^{-4}$ mol L${}^{-1}$, with the detection limit of $1.0\times 10^{-7}$ mol L${}^{-1}$. Besides, the modified electrode also exhibited an excellent selectivity, stability, reproducibility and repeatability.

In this work, one-step fabrication of electrochemical reduced graphene oxide-carboxyl functionalized multi-walled carbon nanotubes (ErGO-$c$MWCNTs) was successfully presented using potentiostatic method (PM). Characteristics of nanocomposite film were studied by using scanning electron microscopic (SEM) and electrochemical experiments. Furthermore, nanocomposite film of ErGO-$c$MWCNTs was presented to develop a sensitive voltammetric sensor for detection of clopidogrel bisulphate (CLP). Electrochemical tests showed that nanocomposite film of ErGO-$c$MWCNTs modified electrode can effectively increase currents to the oxidation of CLP due to the large accessible surface area as well as its excellent conductivity. Under optimum conditions, response peak currents were linear related to CLP in the range of $8.0\times 10^{-7}\mathrm{\text{mol}}{\mathrm{\text{L}}}^{-1}$ to $4.0\times 10^{-5}\mathrm{\text{mol}}{\mathrm{\text{L}}}^{-1}$ with a lower detection limits of $1.0\times 10^{-7}\mathrm{\text{mol}}{\mathrm{\text{L}}}^{-1}$ ($S/N=3$). Moreover, the proposed method exhibited an excellent selectivity, stability, reproducibility and was applied successfully for determination of CLP content in tablet dosage form with acceptable recovery values.