ABSTRACT
Electrochemical sensing techniques rely on redox reactions taking place at the electrode surface. The configuration of this surface is of the utmost importance in the advancement of electrochemical sensors. The majority of previous electrode manufacturing methods, including 3D printing have produced electrodes with flat surfaces. There is a distinct potential for 3D printing to create intricate and distinctive electrode surface shapes. In the proposed work, 3D printed carbon black polylactic acid electrodes with nine different surface morphologies were made. These were compared to a flat surface electrode. To evaluate the performance of the electrodes, measurements were conducted in three different redox probes (ferrocene methanol, ferricyanide, and dopamine). Our findings highlighted that when electrodes were normalised for the geometric surface area of the electrode, the surface pattern of the electrode surface can impact the observed current and electron transfer kinetics. Electrodes that had a dome and flag pattern on the electrode surface showed the highest oxidation currents and had lower values for the difference between the anodic and cathodic peak current (ΔE). However, designs with rings had lower current values and higher ΔE values. These differences are most likely due to variations in the accessibility of conductive sites on the electrode surface due to the varying surface roughness of different patterned designs. Our findings highlight that when making electrodes using 3D printing, surface patterning of the electrode surface can be used as an effective approach to enhance the performance of the sensor for varying applications.
ABSTRACT
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 semi-quantitative 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 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 measurements. 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.
