Recycled PETg embedded with graphene, multi-walled carbon nanotubes and carbon black for high-performance conductive additive manufacturing feedstock.

The first report of conductive recycled polyethylene terephthalate glycol (rPETg) for additive manufacturing and electrochemical applications is reported herein. Graphene nanoplatelets (GNP), multi-walled carbon nanotubes (MWCNT) and carbon black (CB) were embedded within a recycled feedstock to produce a filament with lower resistance than commercially available conductive polylactic acid (PLA). In addition to electrical conductivity, the rPETg was able to hold >10 wt% more conductive filler without the use of a plasticiser, showed enhanced temperature stability, had a higher modulus, improved chemical resistance, lowered levels of solution ingress, and could be sterilised in ethanol. Using a mix of carbon materials CB/MWCNT/GNP (25/2.5/2.5 wt%) the electrochemical performance of the rPETg filament was significantly enhanced, providing a heterogenous electrochemical rate constant, k0, equating to 0.88 (±0.01) × 10-3 cm s-1 compared to 0.46 (±0.02) × 10-3 cm s-1 for commercial conductive PLA. This work presents a paradigm shift within the use of additive manufacturing and electrochemistry, allowing the production of electrodes with enhanced electrical, chemical and mechanical properties, whilst improving the sustainability of the production through the use of recycled feedstock.

Multi-walled carbon nanotubes/carbon black/rPLA for high-performance conductive additive manufacturing filament and the simultaneous detection of acetaminophen and phenylephrine.

The combination of multi-walled carbon nanotubes (MWCNT) and carbon black (CB) is presented to produce a high-performance electrically conductive recycled additive manufacturing filament. The filament and subsequent additively manufactured electrodes were characterised by TGA, XPS, Raman, and SEM and showed excellent low-temperature flexibility. The MWCNT/CB filament exhibited an improved electrochemical performance compared to an identical in-house produced bespoke filament using only CB. A heterogeneous electrochemical rate constant, [Formula: see text] of 1.71 (± 0.19) × 10-3 cm s-1 was obtained, showing an almost six times improvement over the commonly used commercial conductive CB/PLA. The filament was successfully tested for the simultaneous determination of acetaminophen and phenylephrine, producing linear ranges of 5-60 and 5-200 µM, sensitivities of 0.05 µA µM-1 and 0.14 µA µM-1, and limits of detection of 0.04 µM and 0.38 µM, respectively. A print-at-home device is presented where a removable lid comprised of rPLA can be placed onto a drinking vessel and the working, counter, and reference components made from our bespoke MWCNT/CB filament. The print-at-home device was successfully used to determine both compounds within real pharmaceutical products, with recoveries between 87 and 120% over a range of three real samples. This work paves the way for fabricating new highly conductive filaments using a combination of carbon materials with different morphologies and physicochemical properties and their application to produce additively manufactured electrodes with greatly improved electrochemical performance.

Mixed Graphite/Carbon Black Recycled PLA Conductive Additive Manufacturing Filament for the Electrochemical Detection of Oxalate.

Mixing of graphite and carbon black (CB) alongside recycled poly(lactic acid) and castor oil to create an electrically conductive additive manufacturing filament without the use of solvents is reported herein. The additively manufactured electrodes (AMEs) were electrochemically benchmarked against a commercial conductive filament and a bespoke filament utilizing only CB. The graphite/CB produced a heterogeneous rate constant, k0, of 1.26 (±0.23) × 10-3 cm s-1 and resistance of only 155 ± 15 Ω, compared to 0.30 (±0.03) × 10-3 cm s-1 and 768 ± 96 Ω for the commercial AME. Including graphite within the filament reduced the cost of printing each AME from £0.09, with the CB-only filament, to £0.05. The additive manufacturing filament was successfully used to create an electroanalytical sensing platform for the detection of oxalate within a linear range of 10-500 µM, achieving a sensitivity of 0.0196 µA/µM, LOD of 5.7 µM and LOQ of 18.8 µM was obtained. Additionally, the cell was tested toward the detection of oxalate within a spiked synthetic urine sample, obtaining recoveries of 104%. This work highlights how, using mixed material composites, excellent electrochemical performance can be obtained at a reduced material cost, while also greatly improving the sustainability of the system.

Exploration of defined 2-dimensional working electrode shapes through additive manufacturing.

In this work, the electrochemical response of different morphologies (shapes) and dimensions of additively manufactured (3D-printing) carbon black (CB)/poly-lactic acid (PLA) electrodes are reported. The working electrodes (WE) are printed using standard non-conductive PLA based filament for the housing and commercial Protopasta (carbon black/PLA) filament for the electrode and connection parts. Discs, squares, equilateral triangles and six-point stars with varying working electrode (WE) widths from 2 to 10 mm are evaluated herein towards the well-known near-ideal outer sphere redox probe hexaamineruthenium(III) chloride (RuHex). The results obtained show that triangular and squared electrodes exhibit a faster heterogeneous electron transfer (HET) rate constant (k°) than those of discs and stars, the latter being the slowest one. The results reported here also show a trend between the WE dimension and the reversibility of the electrochemical reaction, which decreases as the WE size increases. It is also observed that the ratio of the geometrical and electroactive area (%realarea) decreases as the overall WE size increases. On the other hand, these four WE shapes were applied toward the well-known and benchmarking detection of ascorbic acid (AA), uric acid (UA), ß-nicotinamide adenine dinucleotide (NADH) and dopamine (DA). Moreover, electroanalytical detection of real acetaminophen (ACOP) samples is also showcased. The different designs for the working electrode proposed in this manuscript are easily changed to any other desired shapes thanks to the additive manufacturing methodology, these four shapes being just an example of what additive manufacturing can offer to experimentalists and to electrochemists in particular. Additive manufacturing is shown here as a versatile and rapid prototyping tool for the production of novel electrochemical sensing platforms, with scope for this work to be able to impact a wide variety of electroanalytical applications.

All-in-One Single-Print Additively Manufactured Electroanalytical Sensing Platforms.

This manuscript provides the first report of a fully additively manufactured (AM) electrochemical cell printed all-in-one, where all the electrodes and cell are printed as one, requiring no post-assembly or external electrodes. The three-electrode cell is printed using a standard non-conductive poly(lactic acid) (PLA)-based filament for the body and commercially available conductive carbon black/PLA (CB/PLA, ProtoPasta) for the three electrodes (working, counter, and reference; WE, CE, and RE, respectively). The electrochemical performance of the cell is evaluated first against the well-known near-ideal outer-sphere redox probe hexaamineruthenium(III) chloride (RuHex), showing that the cell performs well using an AM electrode as the pseudo-RE. Electrochemical activation of the WE via chronoamperometry and NaOH provides enhanced electrochemical performances toward outer-sphere probes and for electroanalytical performance. It is shown that this activation can be completed using either an external commercial Ag|AgCl RE or through simply using the internal AM CB/PLA pseudo-RE and CE. This all-in-one electrochemical cell (AIOEC) was applied toward the well-known detection of ascorbic acid (AA) and acetaminophen (ACOP), achieving linear trends with limits of detection (LODs) of 13.6 ± 1.9 and 4.5 ± 0.9 µM, respectively. The determination of AA and ACOP in real samples from over-the-counter effervescent tablets was explored, and when analyzed individually, recoveries of 102.9 and 100.6% were achieved against UV-vis standards, respectively. Simultaneous detection of both targets was also achieved through detection in the same sample exhibiting 149.75 and 81.35% recoveries for AA and ACOP, respectively. These values differing from the originals are likely due to electrode fouling due to the AA oxidation being a surface-controlled process. The cell design produced herein is easily tunable toward different sample volumes or container shapes for various applications among aqueous electroanalytical sensing; however, it is a simple example of the capabilities of this manufacturing method. This work illustrates the next step in research synergising AM and electrochemistry, producing operational electrochemical sensing platforms in a single print, with no assembly and no requirements for exterior or commercial electrodes. Due to the flexibility, low-waste, and rapid prototyping of AM, there is scope for this work to be able to span and impact a plethora of research areas.

Self-Powered Detection of Glucose by Enzymatic Glucose/Oxygen Fuel Cells on Printed Circuit Boards.

Monitoring glucose levels in physiological fluids can help prevent severe complications associated with hypo- and hyper-glycemic events. Current glucose-monitoring systems require a three-electrode setup and a power source to function, which can hamper the system miniaturization to the patient discomfort. Enzymatic fuel cells (EFCs) offer the opportunity to develop self-powered and minimally invasive glucose sensors by eliminating the need for an external power source. Nevertheless, practical applications demand for cost-effective and mass-manufacturable EFCs compatible with integration strategies. In this study, we explore for the first time the use of gold electrodes on a printed circuit board (PCB) for the development of an EFC and demonstrate its application in saliva. To increase the specific surface area, the PCB gold-plated electrodes were modified with porous gold films. At the anode, glucose oxidase is immobilized with an osmium redox polymer that serves as an electron-transfer mediator. At the cathode, bilirubin oxidase is adsorbed onto the porous gold surface with a blocking agent that prevents parasitic reactions while maintaining the enzyme catalytic activity. The resulting EFC showed a linear response to glucose in phosphate buffer within the range 50 µM to 1 mM, with a sensitivity of 14.13 µA cm-2 mM-1. The sensor was further characterized in saliva, showing the linear range of detection of 0.75 to 2 mM, which is within the physiological range, and sensitivity of 21.5 µA cm-2 mM-1. Overall, this work demonstrates that PCBs are suitable platforms for EFCs, paving the way for the development of fully integrated systems in a seamless and miniaturized device.

Fast and direct amperometric analysis of polyphenols in beers using tyrosinase-modified screen-printed gold nanoparticles biosensors.

In this work it is explored a real applicability of miniaturised and portable biosensing technology for the estimation of total phenolic content in 15 different commercial beers by applying direct amperometry. Gold nanoparticles screen-printed electrodes were thoroughly modified with tyrosinase (Tyr-AuNPS-SPCEs), which was immobilised on the surface by crosslinking with glutaraldehyde. All chemical and instrumental variables involved in the electrochemical method were optimised to develop a reliable and powerful tool to estimate rapidly the content of phenolic compounds in complex beer samples. Catechol, phenol, caffeic acid and tyrosol were analysed individually using the proposed methodology and good analytical and kinetic performances were obtained. Total phenolic content in tested beers (high fermented, low fermented and non-alcoholic) were expressed as mg L-1 of tyrosol, which is one of the major phenolic compound reported in beer. Moreover, the developed amperometric methodology was successfully benchmarked against standardised Folin-Ciocalteau spectrophotometric method with a good Pearson correlation (r = 0.821, p < 0.01). Hierarchical Cluster Analysis (HCA) was also applied on electrochemical results and a good capability to group tested beers based on their tyrosol concentration was demonstrated.

The preparation of hydroxyapatite from unrefined calcite residues and its application for lead removal from aqueous solutions.

Calcite originating from waste treatment technologies was utilised for the chemical precipitation of hydroxyapatite (HAP). The physicochemical properties of the as-synthesised-HAP was fully characterised using FT-IR, BET, SEM and TEM, confirming its crystal structure and formation of high purity HAP by XRD. The product was employed for removal of lead from aqueous media at pH 5.0, achieving almost 80% of the adsorption in the first 5 min and a maximum adsorption capacity for Pb2+ of 224.4 mg g-1. A contact time of 40 min was required to achieve equilibrium with Pb2+ uptake of 98%. The kinetics of the cation exchange of HAP from calcite were predicted using integrated rate laws, revealing a pseudo-second order cation exchange process with a rate constant of 6.84 × 10-4 g (mg min)-1. All obtained results are benchmarked against a control HAP sample simultaneously derived from eggshells, which were demonstrated to offer slower kinetics of cation exchange (4.82 × 10-4 g (mg min)-1) and almost half the maximum adsorption capacity (129.1 mg g-1). The results showed that hydroxyapatite synthesised from calcite waste represents a low-cost material for the adsorption of hazardous Pb2+ in contaminated waters and a promising alternative for heavy metals remediation in aquatic environments.

Pencil It in: Exploring the Feasibility of Hand-Drawn Pencil Electrochemical Sensors and Their Direct Comparison to Screen-Printed Electrodes.

We explore the fabrication, physicochemical characterisation (SEM, Raman, EDX and XPS) and electrochemical application of hand-drawn pencil electrodes (PDEs) upon an ultra-flexible polyester substrate; investigating the number of draws (used for their fabrication), the pencil grade utilised (HB to 9B) and the electrochemical properties of an array of batches (i.e, pencil boxes). Electrochemical characterisation of the PDEs, using different batches of HB grade pencils, is undertaken using several inner- and outer-sphere redox probes and is critically compared to screen-printed electrodes (SPEs). Proof-of-concept is demonstrated for the electrochemical sensing of dopamine and acetaminophen using PDEs, which are found to exhibit competitive limits of detection (3σ) upon comparison to SPEs. Nonetheless, it is important to note that a clear lack of reproducibility was demonstrated when utilising these PDEs fabricated using the HB pencils from different batches. We also explore the suitability and feasibility of a pencil-drawn reference electrode compared to screen-printed alternatives, to see if one can draw the entire sensing platform. This article reports a critical assessment of these PDEs against that of its screen-printed competitors, questioning the overall feasibility of PDEs' implementation as a sensing platform.

Pencil it in: pencil drawn electrochemical sensing platforms.

Inspired by recent reports concerning the utilisation of hand drawn pencil macroelectrodes (PDEs), we report the fabrication, characterisation (physicochemical and electrochemical) and implementation (electrochemical sensing) of various PDEs drawn upon a flexible polyester substrate. Electrochemical characterisation reveals that there are no quantifiable electrochemical responses upon utilising these PDEs with an electroactive analyte that requires an electrochemical oxidation step first, therefore the PDEs have been examined towards the electroactive redox probes hexaammineruthenium(iii) chloride, potassium ferricyanide and ammonium iron(ii) sulfate. For the first time, characterisation of the number of drawn pencil layers and the grade of pencil are examined; these parameters are commonly overlooked when utilising PDEs. It is demonstrated that a PDE drawn ten times with a 6B pencil presented the most advantageous electrochemical platform, in terms of electrochemical reversibility and peak height/analytical signal. In consideration of the aforementioned limitation, analytes requiring an electrochemical reduction as the first process were solely analysed. We demonstrate the beneficial electroanalytical capabilities of these PDEs towards p-benzoquinone and the simultaneous detection of heavy metals, namely lead(ii) and cadmium(ii), all of which are explored for the first time utilising PDEs. Initially, the detection limits of this system were higher than desired for electroanalytical platforms, however upon implementation of the PDEs in a back-to-back configuration (in which two PDEs are placed back-to-back sharing a single connection to the potentiostat), the detection limits for lead(ii) and cadmium(ii) correspond to 10 µg L(-1) and 98 µg L(-1) respectively within model aqueous (0.1 M HCl) solutions.

Utilising copper screen-printed electrodes (CuSPE) for the electroanalytical sensing of sulfide.

A mediatorless sulfide electrochemical sensing platform utilising a novel nanocopper-oxide screen-printed electrodes (CuSPE) is reported for the first time. The state-of-the-art screen-printed electrochemical sensors demonstrate their capability to quantify sulfide within both the presence and absence of an array of interferents with good levels of sensitivity and repeatability. The direct sensing (using linear sweep voltammetry) of sulfide utilising the CuSPEs provides a mediatorless approach for the detection of sulfide, yielding useful analytical signatures that can be successfully quantified. The proposed novel protocol using the CuSPEs is successfully applied to the sensing of sulfide within drinking water exhibiting a high level of recovery.

Long-term assessment of ecological risk from deposition of elemental pollutants in the vicinity of the industrial area of Puchuncaví-Ventanas, central Chile.

The present work investigates soil pollution by elemental contaminants and compares ecological risk indexes related to industrial activities for the case study of Puchuncaví-Ventanas: a relevant industrial zone located in central Chile. Selected elements (As, Pb, Cd, Ni, Hg, V, Mn, Zn, Sr, Sb, Cr, Co, Cu, K, and Ba) were analyzed during a long-term period (yearly sampling campaigns during 2007-2011), at 5 sampling stations representing different degrees of impact. PCA and cluster analysis allowed identifying a copper smelter and a coal-fired power plant complex as major pollution sources. Geoaccumulation index (I geo), enrichment factor (EF), contamination factor (Cf), contamination degree (C deg), and integrated pollution index (IPI) are critically discussed for quantitative ecological risk assessment. I geo, EF and Cf indexes are producing comparable environmental information, showing moderate to high pollution risks in the area that demands further monitoring and adoption of prevention and remediation measures. CAPSULE: Long term assessment of elemental pollution around an industrial area. New insight on ecological risk indexes for trace element pollution in soils, by critical comparison among them.