Featured Application: An electrochemical reader developed with the aim to create a low-cost disposable, maintenance-free and user-friendly point-of-need sensing system. Abstract:The work presented details the manufacturing of a low-cost hybrid inkjet-printed paper-based potentiostat, with the aim of creating a low-cost sensing system for rapid water quality monitoring. Potentiostats exhibit high sensitivities and can be used for a variety of applications. The results highlight the functionality of a paper-based potentiostat compared to a potentiostat manufactured on a printed circuit board (PCB), an LMP91000EVM development board and a laboratory-based Metrohm Autolab potentiostat. Cyclic voltammetry was performed using an 80 µL sample of 5 mM ferri-ferrocyanide dropped onto a commercial screen-printed electrode from DropSens. The miniaturized paper-based potentiostat is small enough to be stored in a wallet and therefore easy to transport. Furthermore, a cost analysis shows that the potentiostat is 10 times lower in cost than the commercially available handheld potentiostat, taking the costs of man hours into account. This technology enables electrochemistry experiments to be performed on-site using the portable, disposable and low-cost solution and can be applied to a variety of fields including healthcare, wearables and environmental monitoring.

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The development of low-cost, disposable electrode materials has been at the forefront of sensor technology in recent decades. Paper, offers possibilities for multi-functional, disposable and economically friendly sensing capabilities and has proved to be a suitable reagent storage and substrate material in paper-based analytical devices (PADs). In this work, we report a simple inkjet printing procedure on photographic paper for the fabrication of single analyte electrochemical sensors. A three-electrode system, consisting of a 3 mm diameter working electrode (WE), a counter electrode (CE) and a reference electrode (RE) were prepared by inkjet printing of silver conductive inks for comparison to common commercial screen printed electrode (SPE) brands. In a second step, carbon coating and modification of the working electrode surface with an electrochemically reduced graphene oxide, gold nanoparticle (ERGO-AuNP) film, to improve electrode sensitivity and selectivity was employed. Improved electron-transfer kinetics, increased active surface area and enhanced catalytic properties were achieved due to the ERGO-AuNP layer inclusion. Electrical and topographical characterization of the printed layers was performed in the fabrication process. Printing of AgÀ NP ink showed good resistivity (1.8-6.3 Ω) on photographic paper. The prepared printed paper-based electrodes (PPE) offer a quantitative analysis of Ni(II), based on the accumulation of Ni(dmgH) 2 complexes at the modified electrode surface by squarewave adsorptive cathodic stripping voltammetry (SW-AdCSV). This study offers the first investigation on the feasibility of adsorptive electrochemical sensing methods at porous cellulose paper-based substrates. Instrumental parameters including deposition potential and deposition time were optimized for both electrochemical sensors. Improved sensitivities were achieved at the modified integrated electrodes over the unmodified derivate with a limit of detection (LOD) of 32.19 μg L À 1 achieved for the ERGO-AuNPÀ CCÀ AgÀ PPE. This is well below the EPA and WHO standards of 0.1 mg L À 1 or 0.1 ppm for Ni 2 + in drinking water.

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Electrochemical detection of metal cations at paper-based sensors has been suggested as an attractive alternative to current spectroscopic and chromatographic detection techniques due to the ease of fabrication, disposable nature, and low cost. Herein, a novel carbon black (CB), dimethylglyoxime (DMG) ink is designed as an electrode modifier in conjunction with 3-electrode inkjet-printed paper substrates for use in the adsorptive stripping voltammetric electroanalysis of nickel cations in water samples. The developed method provides a novel, low-cost, rapid, and portable adsorptive stripping detection approach towards metal analysis in the absence of the commonly used toxic metallic films. The study demonstrated a novel approach to nickel detection at paper-based sensors and builds on previous work in the field of paper-based metal analysis by limiting the use of toxic metal films. The device sensitivity is improved by increasing the active surface area, electron transfer kinetics, and catalytic effects associated with non-conductive dimethylglyoxime films through CB nanoparticles for the first time and confirmed by electroanalysis. The first use of the CB-DMG ink allows for the selective preconcentration of analyte at the electrode surface without the use of toxic Mercury or Bismuth metallic films. Compared to similarly reported paper-based sensors, improved limits of detection (48 µg L-1), selectivity, and intermetallic interferences were achieved. The method was applied to the detection of nickel in water samples well below World Health Organization (WHO) standards.

This work details manufacturing processes developed to integrate an unpackaged silicon die onto a paper substrate, as part of constructing a hybrid inkjet-printed paper-based circuit. This integration between rigid components and flexible substrates is beneficial in low-cost applications and capitalises on the advantages of both the well-established integrated circuit technology and the emerging paper-based electronics platforms. A superglue incline at the chip edge formed a ramp for printing the silver interconnects between the paper-based circuit and the chip pads. Two printing protocols are compared, the first a single layer using 5 μm drop spacing, and the second using a 35 μm drop spacing for three layers. An unpackaged RFID tag die is successfully integrated and is presented as proof of concept.