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Abstract3D printing provides a reliable approach for the manufacture of carbon thermoplastic composite electrochemical sensors. Many studies have explored the impact of printing parameters on the electrochemical activity of carbon thermoplastic electrodes but limited is known about the influence of instrument parameters, which have been shown to alter the structure and mechanical strength of 3D printed thermoplastics. We explored the impact of extruder temperature, nozzle diameter and heated bed temperature on the electrochemical activity of carbon black/poly-lactic acid (CB/PLA) electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were conducted using standard redox probes. The electrode surface and cross-section of the electrode was visualised using scanning electron microscopy. We found that using extruder temperatures of 230 °C and 240 °C improved the electrochemical activity of CB/PLA electrodes, due to an increase in surface roughness and a reduction in the number of voids in-between print layers. Nozzle diameter, heated bed temperature of different 3D printers did not impact the electrochemical activity of CB/PLA electrodes. However high-end printers provide improved batch reproducibility of electrodes. These findings highlight the key instrument parameters that need to be considered when manufacturing carbon thermoplastic composite electrochemical sensors when using 3D printing.

Material extrusion printing process can make electrodes and electronic components at any geometry and has provided a reproducible approach towards the fabrication of conductive carbon thermoplastic composite parts. Printing parameters can have a significant influence on the conductivity of the printed part, however limited studies have focused on understanding the impact of printing parameters. Our study explored the influence of printing speed on the electrochemical activity of 3D printed carbon black/polylactic acid (CB/PLA) electrodes. We made CB/PLA at print speeds ranging from 20 to 100 mm/s and evaluated the performance of these electrodes using cyclic voltammetry and through imaging. Electrodes made using 60 mm/s printing speed had the greatest current and electron transfer kinetics. Electrodes made using higher and lower printing speeds were more resistive. This study is the first to demonstrate the significant impact that printing speed can have on the electrochemical activity of 3D printed CB/PLA electrodes. The implications of this study are important when defining the 3D printing manufacturing process of electrodes and electronic components.

Falsified medicines and healthcare supplements provide a major risk to public health and thus early identification is critical. Although a host of analytical approaches have been used to date, they are limited, as they require extensive sample preparation, are semiquantitative and/or are inaccessible to low-and middle-income countries. Therefore, for the first time we report a simple total analysis system which can rapidly and accurately detect falsified medicines and healthcare supplements. We fabricated a poly-lactic acid (PLA) pestle and mortar and using a commercial 3D printer, then made carbon black/PLA (CB/PLA) electrodes in the base of the mortar using a 3D printing pen to make an electrochemical cell. The pestle and mortar were able to crush and grind the tablets into a fine powder to the same consistency as a standard laboratory pestle and mortar. Using 2 melatonin tablets to characterise the device, the 3D printed pestle and mortar was able to detect the concentration of melatonin in the presence of insoluble excipients. The calibration plot showed a linear response from 37.5 to 300 µg/mL, where the limit of detection was 7 µg/mL. Electrochemical treatment was able to regenerate the CB/PLA working electrode allowing for repeated use of the device. In a blinded study, the device was able to accurately determine falsified melatonin tablets with recovery percentages between 101 and 105 %. This was comparable to HPLC. Overall, these findings highlight that our 3D printed electrochemical pestle and mortar is an accessible and effective total analysis system that can have the ability to identify falsified medicines and healthcare supplements in remote locations.

Composite electrodes are an effective and cheap way to utilize a wide range of carbon materials to make electrodes. More recently, thermoplastics have been widely used as the binder to make carbon composite electrodes, as varying fabrication approaches, such as three-dimensional (3D) printing, can make highly reproducible electrodes. However, there is a clear need to understand how the electrochemical performance of different carbon allotrope materials varies when made into sensors. We accessed poly(lactic acid) (PLA) thermoplastic filaments containing carbon black, graphite, graphene, multiwall carbon nanotube (MWCNT), and carbon fiber using various electrochemical techniques. Graphite/PLA and graphene/PLA electrodes showed the best electron transfer kinetics. Graphene/PLA electrodes had the greatest sensitivity and lowest limit of detection for the measurement of serotonin. CB/PLA was least prone to electrode fouling from oxidative by-product generated from the oxidation of serotonin. 3D printing was used to make various carbon allotrope materials into complex shapes to evaluate the batch uniformity of the printed parts. Of all the materials explored, CB/PLA had the best resolution and batch uniformity when compared with PLA. Overall, our study highlights that the type of carbon allotrope has as much influence as the amount of carbon on the electrochemical performance of carbon thermoplastic electrodes. These findings will provide significant guidance on the appropriate choice of carbon thermoplastic composite materials when designing electrodes for a wide range of applications.