Reliable Paper Surface Treatments for the Development of Inkjet‐Printed Electrochemical Sensors

Abstract

Inkjet printing (IJP) technology allows the digital deposition of functional materials in microscale dimensions on a wide range of substrates, simplifying iterative design changes during the initial development stages. It is a noncontact approach that allows the mask-less deposition of materials owing to the precise control of picoliter volumes and a reduction in the overall time and cost of fabrication. Furthermore, IJP permits customized geometries and is compatible with low temperature processes. [5] Although screen-printed sensors are nowadays the most reported ones, [3] recent advances have demonstrated that inkjet-printed and paper-based electrochemical sensors provide a reliable solution for many applications. [4,6] Paper has emerged as a strong competitive substrate for diagnostic devices due to its attractive properties, including flexibility and conformability, hydrophilicity and high mechanical strength. [7][8][9][10] These excellent characteristics give paper excellent performance properties in the fabrication of paper-based devices. In addition, it is environmentally friendly, reusable/recyclable, biodegradable and biocompatible. [9,[11][12][13] For these reasons, paper-based sensors are increasingly gaining attention due to the global trend and commitment to "green electronics." Accordingly, this paper presents a flexible, disposable, and low-cost solution to develop sensors by IJP technology.Paper-based analytical devices (PADs) are in the spotlight for the development of flexible, disposable, and simpler devices taking advantage of their microfluidic properties. [14][15][16] PADs typically include an arrangement of hydrophilic/hydrophobic microstructures patterned in the paper using techniques such as wax printing, photolithography or chemical vapor-phase deposition among others. [17] In 2009, Dungchai et al. [18] demonstrated how the combination of PADs with an electrochemical sensor (ePAD) led to more reliable measurements than single microelectrode detection or colorimetric PAD sensors. [19] Electrochemical detection is an attractive alternative detection scheme for paper-based microfluidics due to its small size, portability, low cost, high sensitivity, and high selectivity by proper choice of detection potential and/or electrode material. [20] Therefore, electrochemical detection is widely used in analytical measurements ranging from clinical diagnostics to environmental biosensing. [21][22][23][24][25] To date, different strategies have been used to integrate electrodes on paper substrate. [26][27][28][29] In 2007, Whitesides' group introduced wax-based electrochemical paper-based devices. [30] The need for disposable, simpler, and accurate paper-based analytical devices represents an open research field that is focused on simpler fabrication methods. To achieve this, four feasible methodologies are proposed for the direct printing of an electrochemical sensor on a biodegradable paper substrate using commercial gold and silver inks, which are compatible with inkjet printing technology. Four ...

An Electroactive and Self‐Assembling Bio‐Ink, based on Protein‐Stabilized Nanoclusters and Graphene, for the Manufacture of Fully Inkjet‐Printed Paper‐Based Analytical Devices

“…We used partially hydrophobic filter paper as a substrate, to ensure the permeability of the ink while preserving the printing definition. [ 75 ] The traces of the electrode were printed using an ink composed of commercial graphite, suspended in a mixture of water (80% v/v), t‐butanol (10% v/v), and propylene glycol (10% v/v). Two passes were required to achieve sufficient conductivity to guarantee the electrode functionality.…”

“…In fact, the pretreatment of paper with hydrophobic polymers is an effective strategy to improve the definition of the printing process. [ 75 ] Thanks to the presence of t‐butanol, a drop of ink in contact with the partially hydrophobic paper creates an angle of 34.97 ± 1.57°, much lower if compared to the angle formed by the active material in PBS (129.85 ± 0.76°, Figure S17, Supporting Information). Furthermore, while the electroactive material in a PBS solution takes several minutes to be absorbed in the substrate, the drop of ink soaks into the paper in less than a second, facilitating the fast drying of the ink.…”

“…[5] Among all, paper is particularly interesting for disposable sensors as it comprises several desirable qualities such as low cost, flexibility, biodegradability, recyclability, and biocompatibility. [6] In addition, it may impart special characteristics to the sensor device, such as the remotion of specific interferents, pre-concentration of the analyte, or support for specific reactants useful for analytical detection. [7] Due to the rising environmental consciousness, inks with a reduced ecological footprint are sought-after nowadays.…”

Controlling the Inkjet Printing Process for Electrochemical (Bio)Sensors

“…[5,14] However, this work is a fundamental study, systematically demonstrating the influence of the printing parameters on the electrical properties of the sensors, differing from other works previously reported. [5,[15][16][17][18] A commercially available Dimatix printer, which works with piezoelectric technology, was used to print the conductive tracks. Only the working electrodes were initially fabricated to evaluate the effect of the printing parameters.…”

Image Analysis Based Evaluation of Print Quality for Inkjet Printed Structures

“…An often-used method to influence wetting is to adjust the ink's properties, e.g., by adding solvents and surfactants and to determine their influence by contact angle measurements as conducted in [6,7] or [8]. To minimize testing efforts, [9] implemented a jetting prediction tool to improve jetting capabilities of newly formulated inks.…”