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3D printing has attracted the interest of researchers due to its creative freedom, low cost, and ease of operation. Because of these features, this technology has produced different types of electroanalytical platforms. Despite their popularity, the thermoplastic composites used for electrode fabrication typically have high electrical resistance, resulting in devices with poor electrochemical performance. Herein, we propose a new strategy to improve the electrochemical performance of 3D-printed electrodes and to gain chemical selectivity towards glucose detection. The approach involves synthesising a nanostructured gold film using an infrared laser source directly on the surface of low-contact resistance 3D-printed electrodes. The laser parameters, such as power, focal distance, and beam scan rate, were carefully optimised for the modification steps. Scanning electronic microscopy and energy-dispersive X-ray spectroscopy confirmed the morphology and composition of the nanostructured gold film. After modification, the resulting electrodes were able to selectively detect glucose, encouraging their use for sensing applications. When compared with a gold disc electrode, the gold-modified 3D-printed electrode provided a 44-fold current increase for glucose oxidation. As proof of concept, the devices were utilised for the non-enzymatic catalytic determination of glucose in drink samples, demonstrating the gold film's catalytic nature and confirming the analytical applicability with more precise results than commercial glucometers. [ABSTRACT FROM AUTHOR]

Paper-based analytical devices (PADs) are powerful platforms for point-of-need testing since they are inexpensive devices fabricated in different shapes and miniaturized sizes, ensuring better portability. Additionally, the readout and detection systems can be accomplished with portable devices, allying with the features of both systems. These devices have been introduced as promising analytical platforms to meet critical demands involving rapid, reliable, and simple testing. They have been applied to monitor species related to environmental, health, and food issues. Herein, an outline of chronological events involving PADs is first reported. This work also introduces insights into fundamental parameters to engineer new analytical platforms, including the paper type and device operation. The discussions involve the main analytical techniques used as detection systems, such as colorimetry, fluorescence, and electrochemistry. It also showed recent advances involving PADs, especially combining optical and electrochemical detection into a single device. Dual/combined detection systems can overcome individual barriers of the analytical techniques, making possible simultaneous determinations, or enhancing the devices' sensitivity and/or selectivity. In addition, this review reports on distance-based detection, which is also considered a trend in analytical chemistry. Distance-based detection offers instrument-free analyses and avoids user interpretation errors, which are outstanding features for analyses at the point of need, especially for resource-limited regions. Finally, this review provides a critical overview of the practical specifications of the recent analytical platforms involving PADs, demonstrating their challenges. Therefore, this work can be a highly useful reference for new research and innovation. [ABSTRACT FROM AUTHOR]

The combination of CO2 laser ablation and electrochemical surface treatments is demonstrated to improve the electrochemical performance of carbon black/polylactic acid (CB/PLA) 3D-printed electrodes through the growth of flower-like Na2O nanostructures on their surface. Scanning electron microscopy images revealed that the combination of treatments ablated the electrode's polymeric layer, exposing a porous surface where Na2O flower-like nanostructures were formed. The electrochemical performance of the fabricated electrodes was measured by the reversibility of the ferri/ferrocyanide redox couple presenting a significantly improved performance compared with electrodes treated by only one of the steps. Electrodes treated by the combined method also showed a better electrochemical response for tyrosine oxidation. These electrodes were used as a non-enzymatic tyrosine sensor for quantification in human urine samples. Two fortified urine samples were analyzed, and the recovery values were 106 and 109%. The LOD and LOQ for tyrosine determination were 0.25 and 0.83 μmol L−1, respectively, demonstrating that the proposed devices are suitable sensors for analyses of biological samples, even at low analyte concentrations. [ABSTRACT FROM AUTHOR]

The limiting aspects in the voltammetric response of 3D printed electrodes is thoroughly investigated with numerical simulations and new 3D printed electrode designs. Severe diffusion limitations, resulting from a recessed electrode geometry, is found in a commonly used 3D printed electrode and electrochemical cell design, impeding the investigation of electron transfer kinetics at these electrodes by classical methods, such as Nicholson's, widely used on this and similarly mass transport-limited designs. A new 3D printed electrode design, an inlaid disk (non-recessed) geometry, is used to investigate the voltammetric response of printed electrodes in bulk solution, i.e., without mass transport limitations. At this condition, it is clear that the voltammetric response is limited by contact resistance, arising from the printed material low electrical conductivity. Gold modified electrodes, deliberately designed with different contact resistances, highlight the resistive behavior, with quasi-reversible voltammetric profiles. This contrasts with the common assumption of a voltammetric response limited by finite electron kinetics. Electron transfer rate constants (k0) and transfer coefficients (α) for electrodes with and without surface modifications are calculated from experimental data using a modified Butler-Volmer equation, incorporating ohmic losses. The reported k0 and α values are independent of electrode geometry or printing parameters, unlike the observable rate constant usually reported for 3D printed electrodes. By accounting for contact resistance and finite electron transfer kinetics, cathodic and anodic peak potentials and currents of voltammograms recorded with 3D printed electrodes are predicted before printing, allowing electrode designs to be optimized in the virtual space. [Display omitted] [ABSTRACT FROM AUTHOR]