Polyester resin and graphite flakes: turning conductive ink to a voltammetric sensor for paracetamol sensing

Simple graphite/PVC ink-designed paper-based electrodes integrated with a 3D-printed electrochemical device for affordable analyses

A simple and cost-effective methodology for manufacturing a portable electroanalytical device is reported. The device is based on a graphite/polyvinyl chloride (PVC) paper-based electrode coupled to a miniaturized 3D-printed electrochemical cell (3DEC). The 3DEC was designed to ensure the reproducibility of the system by delimitating the paper-based graphite electrode (PGE) area. The disposable PGE was fabricated by paint-brushing a conductive ink based on graphite powder and toluene-free PVC glue, onto a kraft paper. Different weight proportions (wt%) of graphite/PVC were evaluated regarding mechanical stability and electrochemical behavior. Cyclic voltammetric (CV) analysis in the presence of the [Fe(CN)6]3-/4- redox probe has shown that as the wt% of graphite in the ink increased from 50 to 90%, a clear decrease in peak potential separation (ΔEp) and increase in current are observed, indicating an improvement in charge transfer kinetics. However, 90 wt% graphite electrodes have shown poor adhesion to the substrate and easy leaching due to the small amount of PVC (binder). Therefore, the best PGE was achieved using 80:20 wt% graphite/PVC ink (PGE8020). Moreover, scanning electron microscopy (SEM) images and energy dispersive spectroscopy (EDS) mapping revealed a rugous and more uniform deposition of the conductive ink containing 80 wt% graphite. As a proof of concept, the graphite/PVC ink-based disposable electrodes were employed for the detection of 3-nitro-L-tyrosine (3-NLT) in synthetic urine samples, showing a detection limit of 2.85 μmol L-1, and %recovery in synthetic urine between 97 and 109%, highlighting the reliability and applicability of the proposed approach.

Screen-Printing vs Additive Manufacturing Approaches: Recent Aspects and Trends Involving the Fabrication of Electrochemical Sensors

A few decades ago, the technological boom revolutionized access to information, ushering in a new era of research possibilities. Electrochemical devices have recently emerged as a key scientific advancement utilizing electrochemistry principles to detect various chemical species. These versatile electrodes find applications in diverse fields, such as healthcare diagnostics and environmental monitoring. Modern designs have given rise to innovative manufacturing protocols, including screen and additive printing methods, for creating sophisticated 2D and 3D electrochemical devices. This perspective provides a comprehensive overview of the screen-printing and additive-printing protocols for constructing electrochemical devices. It is also informed that screen-printed sensors offer cost-effectiveness and ease of fabrication, although they may pose challenges due to the use of toxic volatile inks and limited design flexibility. On the other hand, additive manufacturing, especially the fused filament fabrication (or fused deposition modeling) strategies, allows for intricate three-dimensional sensor designs and rapid prototyping of customized equipment. However, the post-treatment processes and material selection can affect production costs. Despite their unique advantages and limitations, both printing techniques show promise for various applications, driving innovation in the field toward more advanced sensor designs. Finally, these advancements pave the way for improved sensor performance and expand possibilities for academic, environmental, and industrial applications. The future is full of exciting opportunities for state-of-the-art sensor technologies that will further improve our ability to detect and determine various substances in a wide range of environments as researchers continue to explore the many possibilities of electrochemical devices.

Fabrication of paper-based analytical devices using stencil-printed glass varnish barriers for colorimetric detection of salivary α-amylase

BACKGROUND

Developing disposable paper-based devices has positively impacted analytical science, particularly in developing countries. Some benefits of those devices include their versatility, affordability, environmentally friendly, and the possibility of being integrated with portable electrochemical or colorimetric detectors. Paper-based analytical devices (PADs) comprising circular zones and microfluidic networks have been successfully employed in the analytical chemistry reign. However, the combination of the stencil-printing method and alternative binder has not been satisfactorily explored for fabricating colorimetric paper devices.

RESULTS

We developed PADs exploring the stencil printing approach and glass varnish as the hydrophobic chemical agent. As a proof-of-concept, the colorimetric assay of salivary α-amylase (sAA) was performed in saliva samples. Through the scanning electron microscopy measurements, it was possible to indicate satisfactory definitions between native fibers and barrier, and that the measured values for the channel width revealed suitable fidelity (R2 = 0.99) with the nominal widths (ranging from 400 to 5000 μm). The proposed hydrophobic barrier exhibited excellent chemical resistance. The analytical applicability for detecting sAA revealed linear behavior in the range from 2 to 12 U mL-1 (R2 = 0.99), limit of detection of 0.75 U mL-1, reproducibility (RSD ≤2.4%), recovery experiments ranged from 89 to 108% and AGREE response (0.86). In addition, the colorimetric analysis of sAA in four different saliva samples demonstrated levels ranging from 202 to 2080 U mL-1, which enabled monitoring the absence and presence of periodontitis.

SIGNIFICANCE

This report has presented the first use of a self-adhesive mask and glass varnish for creating circular zones and microfluidic architectures on paper without using thermic or UV curing treatments. Also, the proposed analytical methodology for detecting sAA exhibited suitable ecological impact considering the AGREE tool. We believe the proposed fabrication of paper devices emerges as a novel, simple, high-fidelity microfluidic channel and portable analytical approach for colorimetric sensing.