Environmentally Friendly Manufacturing of Flexible Graphite Electrodes for a Wearable Device Monitoring Zinc in Sweat

Abstract

Electrochemical sensors based on graphite and polymers have emerged as powerful analytical tools for bioanalytical applications. However, most of the fabrication processes are not environmentally friendly because they often involve the use of toxic reagents and generate waste. This study describes an alternative method to produce flexible electrodes in plastic substrates using graphite powder and thermal laminating sheets by solid−solid deposition through hot compression, without the use of hazardous chemical reagents. The electrodes developed through the proposed approach have successfully demonstrated flexibility, robustness, reproducibility (relative standard deviation around 6%), and versatility. The electrodes were thoroughly characterized by cyclic voltammetry, electrochemical impedance spectroscopy, Raman spectroscopy, and scanning electron microscopy. As a proof of concept, the electrode surfaces were modified with bismuth and used for zinc analysis in sweat. The modified electrodes presented linearity (R 2 = 0.996) for a wide zinc concentration range (50−2000 ppb) and low detection limit (4.31 ppb). The proposed electrodes were tested using real sweat samples and the achieved zinc concentrations did not differ statistically from the data obtained by atomic absorption spectroscopy. To allow wearable applications, a 3D-printed device was fabricated, integrated with the proposed electrochemical system, and fixed at the abdomen by using an elastic tape to collect, store, and analyze the sweat sample. The matrix effect test was performed, spiking the real sample with different zinc levels, and the recovery values varied between 85 and 106%, thus demonstrating adequate accuracy and robustness of the flexible electrodes developed based on the proposed fabrication method.

3D-printed electrochemical platform with multi-purpose carbon black sensing electrodes

“…Advances in 3D printing technology have contributed to the analytical chemistry including developments from sample preparation to detection [ 13 – 18 ]. Examples of miniaturized devices for solid-phase extraction [ 19 ], solution mixing [ 20 ], droplet generation [ 21 ], mass spectrometry interfacing [ 22 ], and analytical separations [ 23 , 24 ] as well as colorimetric [ 25 ] and electrochemical sensors [ 10 ] have been successfully reported in the last years.…”

A 3D Printer Guide for the Development and Application of Electrochemical Cells and Devices

“…The resolution is much higher than the FFF 3D-printed devices, however, longer time of fabrication, the need for post-treatment and curation, and the use of toxic resins are some drawbacks that make SLA less popular than FFF. Nevertheless, one of the first works on the Bismuth film electrodeposition 3D-printed wearable device containing the electrochemical device was fixed at the body using an elastic tape for zinc determination in sweat Dias et al (2019) Images reproduced with permission from American Chemical Society (Snowden et al, 2010;Richter et al, 2019;Sempionatto et al, 2017;Katseli et al, 2021;Dias et al, 2019), Italian Association of Chemical Engineering (Ponce de Leon et al, 2014), Elsevier (Dias et al, 2016;Cardoso et al, 2018;Mendonça et al, 2019;Cardoso et al, 2019;Silva et al, 2020;Escobar et al, 2020;Sibug-Torres et al, 2021;Cardoso et al, 2020c;Ferreira et al, 2021;O'Neil et al, 2019;Baltima et al, 2021); Brazilian Chemical Society (Cardoso et al, 2020a), Royal Society of Chemistry (Elbardisy et al, 2020) and Multidisciplinary Digital Publishing Institute (Vlachou et al, 2020).…”

“…Another interesting example of a wearable device enabled by 3D printing for sweat analysis was reported by Dias and coauthors (Dias et al, 2019). The 3D-printed device was fixed to the body of a volunteer and sweat was collected by a 3Dprinted reservoir at which a flexible thermal-printed electrode was placed.…”

Wearable and Biodegradable Sensors for Clinical and Environmental Applications

“…Most of these devices focus on monitoring organic compounds that are simultaneously found in body fluids such as glucose, , uric acid (UA), − lactate, , alcohol, , dopamine (DA), and ascorbic acid (AA), since a disorder in their concentration values could indicate an impact on individual health or some specific disease . Inorganic salt ions, such as H + (pH sensors), K + , Na + , Ca 2+ , Zn 2+ , Cl – , and NH 4 + , have also been monitored using wearable sensors, since they display a critical regulatory role in the human body. − Besides these, the fabrication of wearable sensors has been investigated for other biomarkers, such as tyrosine, antigen, and antibody, etc …”