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

The 3D printing is described of a complete and portable system comprising a batch injection analysis (BIA) cell and an electrochemical platform with eight sensing electrodes. Both BIA and electrochemical cells were printed within 3.4 h using a multimaterial printer equipped with insulating, flexible, and conductive filaments at cost of ca. ~ U$ 1.2 per unit, and their integration was based on a threadable assembling without commercial component requirements. Printed electrodes were exposed to electrochemical/Fenton pre-treatments to improve the sensitivity. Scanning electron microscopy and electrochemical impedance spectroscopy measurements upon printed materials revealed high-fidelity 3D features (90 to 98%) and fast heterogeneous rate constants ((1.5 ± 0.1) × 10-3 cm s-1). Operational parameters of BIA cell were optimized using a redox probe composed of [Fe(CN)6]4-/3- under stirring and the best analytical performance was achieved using a dispensing rate of 9.0 µL s-1 and an injection volume of 2.0 µL. The proof of concept of the printed device for bioanalytical applications was evaluated using adrenaline (ADR) as target analyte and its redox activities were carefully evaluated through different voltammetric techniques upon multiple 3D-printed electrodes. The coupling of BIA system with amperometric detection ensured fast responses with well-defined peak width related to the oxidation of ADR applying a potential of 0.4 V vs Ag. The fully 3D-printed system provided suitable analytical performance in terms of repeatability and reproducibility (RSD ≤ 6%), linear concentration range (5 to 40 µmol L-1; R2 = 0.99), limit of detection (0.61 µmol L-1), and high analytical frequency (494 ± 13 h-1). Lastly, artificial urine samples were spiked with ADR solutions at three different concentration levels and the obtained recovery values ranged from 87 to 118%, thus demonstrating potentiality for biological fluid analysis. Based on the analytical performance, the complete device fully printed through additive manufacturing technology emerges as powerful, inexpensive, and portable tool for electroanalytical applications involving biologically relevant compounds.

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

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 (R2 = 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.

Batch injection analysis towards auxiliary diagnosis of periodontal diseases based on indirect amperometric detection of salivary α-amylase on a cupric oxide electrode.

This study describes, for the first time, the use of a batch injection analysis system with amperometric detection (BIA-AD) to indirectly determine salivary α-amylase (sAA) levels in saliva samples for chronic periodontitis diagnosis. A chemical/thermal treatment was explored to generate a CuO film on a Cu electrode surface. This procedure offered good stability (RSD = 0.3%), good repeatability (RSD < 1.3%) and excellent reproducibility (RSD < 1.5%). The sAA concentration levels were determined based on the detection of maltose produced by enzymatic hydrolysis of starch. The analytical performance was investigated, and a linear correlation was observed for a maltose concentration range between 0.5 and 6.0 mmol L-1 with a correlation coefficient equal to 0.999. The analytical sensitivity and the limit of detection were 48.8 µA/(mmol L-1) and 0.05 mmol L-1, respectively. In addition, the proposed system provided an excellent analytical frequency (120 analysis h-1). The clinical feasibility of the proposed method was investigated by the determination of sAA levels in four saliva samples (two from healthy control persons (C1 and C2) and two from patients with chronic periodontitis (P1 and P2)). The accuracy provided by the BIA-AD system ranged from 93 to 98%. The sAA concentration levels achieved for each sample were compared to the values found by spectrophotometry and there was no statistically significant difference between them at a confidence level of 95%. Finally, the method reported herein emerges as a simple, low cost and promising tool for assisting periodontal diseases diagnosis.

Determination of Ascorbic Acid in Commercial Tablets Using Pencil Drawn Electrochemical Paper-based Analytical Devices.

This study describes the use of electrochemical paper-based analytical devices (ePADs) drawn with graphite pencil for the determination of ascorbic acid (AA) in commercial tablets. ePADs were fabricated using vegetal paper and graphite pencil. First, the three-electrode electrochemical cell drawn using a graphical software and toner lines were laser printed on the vegetal paper surface to delimit the electrode areas. Then, the electrode regions were manually painted with graphite pencil. Afterwards, the pseudo-reference electrode was defined with the deposition of silver ink over the graphite surface. Cyclic voltammetry and square wave voltammetry (SWV) experiments were performed to optimize the electroanalytical parameters as well as to quantitatively determine the AA concentration in two commercial tables. ePADs exhibited linear behavior for a concentration range between 0.5 and 3.0 mmol L-1. The achieved limit of detection and sensitivity were 70 µmol L-1 and 0.47 µA/mmol L-1, respectively. The AA concentration levels found by SWV experiments in both CenevitTM and Energil CTM were 2.80 ± 0.02 and 3.10 ± 0.01 mmol L-1, respectively. The accuracy of the proposed devices was investigated through recovery experiments in three concentration levels and it presented values between 95 and 115%.