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The need to deliver high performant and miniaturised electrochemical sensors has boosted the use of carbon nanomaterials as smart modifiers of working electrode surface. Among the carbon nanomaterials, the common and cost-effective carbon black has recently attracted the attention from the scientific community for its outstanding features as electrode nanomodifier for analyte detection. Herein, we report the structural and morphological characterisation of several types of carbon blacks, namely HP 160, HS20, MTN 990, N115, N220, N375, N660, PL6, Super P, and XE2B, by means of Raman spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses. Furthermore, the electrochemical characterisation of screen-printed electrodes modified with these carbon blacks was carried out by cyclic voltammetry and electrochemical impedance spectroscopy with ferro/ferricyanide as redox probe, highlighting the advantage to use carbon black as nanomodifier in respect to the bare electrode. Among several tested carbon black types, the lowest peak-to-peak separation and resistance to electron transfer values were achieved using screen-printed electrodes modified with CB N115, N375, HP 160 and PL6. The electrodes modified with these types of CB were successively tested in cyclic voltammetry towards epinephrine, benzoquinone, ascorbic acid, cysteine, catechol, and caffeic acid, observing a remarkable improvement of electrochemical performances in respect to the bare electrode, even when the amperometric mode was used. The results obtained demonstrated that several types of CB can remarkably improve the electrochemical performances of the sensors in terms of the decrease of applied potential or peak-to-peak separation, the improvement of the peak intensity, and the decrease of the resistance of the electron transfer due to several key features, including nanodimensions, the onion-like carbon structure, and the high number of defect sites. Image 1 [ABSTRACT FROM AUTHOR]

3D-printing of conductive carbon materials in sensing applications and energy storage devices has significant potential, however high resistivity of 3D-printed filaments poses a challenge. Strategies to enhance sensors post printing are time consuming and can reduce structural integrity. In this work, we investigated the effects different printing layer thickness and orientation can have on the electron transfer kinetics and resistivity of conductive materials. The response of these electrodes was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and imaging. Electrodes printed with the lowest layer thickness of 0.1 mm in a vertical orientation had the greatest conductivity. With increasing print layer thickness and printing in a horizontal orientation, the electrode was more resistive. This work is the first to demonstrate the significant impact 3D-printing parameters can have on the electron transfer kinetics of carbon conductive electrodes. The implications of this study are important in defining the manufacturing process of electrodes for all applications. Electron transfer in 3D-printed electrodes: 3d-printed electrodes are printed in vertical and horizontal orientation with thickness ranging from 0.1 to 0.4 mm. Electron transfer kinetics are enhanced in vertical orientation at lower print layer thickness due to the formation of less air voids and more conductive pathways. Image 1 [ABSTRACT FROM AUTHOR]

This work shows that the electrochemical activity of a 3D-printed electrode fabricated using a conductive composite of polylactic acid (PLA) containing carbon black (CB) can be substantially improved through a simple and fast chemical/electrochemical pretreatment in 0.5 mol L−1 NaOH. Scanning electron microscopy and infrared spectroscopy data showed that the pretreatment process promotes the removal of the non-conductive PLA material, providing greater exposure of the conductive particles. Cyclic voltammetry of the redox probe ferricyanide/ferrocyanide indicated faster electron transfer on the treated 3D-printed surface and increase in electroactive area. Moreover, electrochemical impedance spectroscopic results also confirmed faster electron transfer after surface pretreatment. As a proof-of-concept, a low-cost and sensitive method for the determination of cadmium and lead in real urine and saliva samples by square-wave anodic stripping voltammetry was developed. The chemical/electrochemical treatment provided an impressive 30-fold current increase in the detection of both metals. Acceptable limits of detection (2.9 μg L−1 for Cd2+ and 2.6 μg L−1 for Pb2+), wide linear ranges for both metals (30 μg L−1 to 270 μg L−1; R = 0.997), high stability (RSD lower than 4.5%; n = 10), and adequate recovery values (between 93% and 112%) for the analysis of spiked samples were achieved. Additionally, interday (n = 3), intra-day (n = 3), inter-electrode (n = 2) and inter-treatment (n = 2) experiments revealed RSD values lower than 6.5%, which indicates high reproducibility of the proposed treated 3D-printed electrode. The strategy here proposed opens up new applications for 3D-printed electrode in analytical electrochemistry with improved electrochemical sensing properties in comparison to screen-printed electrodes. [ABSTRACT FROM AUTHOR]