Wooden Tongue Depressor Multiplex Saliva Biosensor Fabricated via Diode Laser Engraving.

Since wood is a renewable, biodegradable naturally occurring material, the development of conductive patterns on wood substrates is a new and innovative chapter in sustainable electronics and sensors. Herein, we describe the first wooden (bio)sensing device fabricated via diode laser-induced graphitization. For this purpose, a wooden tongue depressor (WTD) is laser-treated and converted to an electrochemical multiplex biosensing device for oral fluid analysis. A low-cost laser engraver, equipped with a low-power (0.5 W) diode laser, programmably irradiates the surface of the WTD, forming two mini electrochemical cells (e-cells). The two e-cells consist of four graphite electrodes: two working electrodes, a common counter, and a common reference electrode. The two e-cells are spatially separated via programmable pen-plotting, using a commercial hydrophobic marker pen. Proof-of-principle for biosensing is demonstrated for the simultaneous determination of glucose and nitrite in artificial saliva. This wooden electrochemical biodevice is an easy-to-fabricate disposable point-of-care chip with a wide scope of applicability to other bioassays, while it paves the way for the low-cost and straightforward production of wooden electrochemical platforms.

AChE-based electrochemical biosensor for pesticide detection in vegetable oils: matrix effects and synergistic inhibition of the immobilized enzyme.

Enzyme-based electrochemical biosensors have been widely deployed for the detection of a range of contaminants in different food products due to their significant advantages over other (bio)sensing techniques. Nevertheless, their performance is greatly affected by the sample matrix itself or by the matrix they are presented with in pretreated samples, both of which can impact the accuracy as well as the sensitivity of the measurements. Therefore, and in order to acquire reliable and accurate measurements, matrix effects and their influence on sensor performance should be taken into consideration. Herein, acetylcholinesterase (AChE)-modified electrochemical sensors were employed for the detection of pesticides in vegetable oils. Sensor interrogation with pretreated oil samples, spiked with carbofuran, revealed the inhibitory potential of the extracted matrix varies between different types of vegetable oil and their fatty acid content. In addition, synergies between the extracted matrix from different types of vegetable oils and the carbamate pesticide, carbofuran, were observed, which led to significant deviations of the sensor's performance from its anticipated behavior in buffered solution. Taking the aforementioned into consideration, appropriate calibration curves for each type of vegetable oil were drafted, which allowed for the highly reproducible determination of different pesticide concentrations in pretreated real samples. Collectively, a better understanding of AChE inhibition by single or multiple contaminants present in vegetable oils was gained, which can find many applications in numerous fields, ranging from sensor development to the design of new pesticides and medicinal products.

Plot-on-demand integrated paper-based sensors for drop-volume voltammetric monitoring of Pb(II) and Cd(II) using a bismuth nanoparticle-modified electrode.

The fabrication of fully ink-drawn fluidic electrochemical paper-based analytical devices (ePADs) is reported for the determination of trace Pb(II) and Cd(II) by differential pulse anodic stripping voltammetry (DPASV). The fluidic pattern was formed on the paper substrate using an inexpensive computer-controlled x-y plotter and a commercial hydrophobic marker pen. Then, electrodes were deposited on the devices using a second x-y plotting step with a commercial technical pen filled with a graphite-based conductive ink prepared in house. The fabrication parameters of the ePADs were studied by cyclic voltammetry using the ferro/ferri couple as a probe and by scanning electron microscopy. The ePADs, featuring a bismuth nanoparticle-modified working electrode, were applied to the determination of Pb(II) and Cd(II) by DPASV. The chemical and instrumental conditions were studied. The limits of detection were 3.1 µg L-1 for Cd(II) and 4.5 µg L-1 for Pb(II) whereas the between-device reproducibility (expressed as the % relative standard deviation of the response at 6 different ePADs) was < 14%. Each ePAD requires 120 s to fabricate and costs less than 0.15 € in terms of consumables. The ePADs are suitable for the on-site determination of Pb(II) and Cd(II) in environmental and food samples.

Single-Use Fluidic Electrochemical Paper-Based Analytical Devices Fabricated by Pen Plotting and Screen-Printing for On-Site Rapid Voltammetric Monitoring of Pb(II) and Cd(II).

This work reports the fabrication of integrated electrochemical fluidic paper-based analytical devices (ePADs) using a marker pen drawing and screen-printing. Electrodes were deposited on paper using screen-printing with conductive carbon ink. Then, the desired fluidic patterns were formed on the paper substrate by drawing with a commercial hydrophobic marker pen using an inexpensive computer-controlled x-y plotter. The working electrode was characterized by cyclic voltammetry and scanning electron microscopy. The analytical utility of the electrochemical PADs is demonstrated through electrochemical determination of Pb(II) and Cd(II) by anodic stripping voltammetry. For this purpose, the sample was mixed with a buffer solution and a Bi(III) solution, applied to the test zone of the PAD, the metals were preconcentrated as a bismuth alloy on the electrode surface and oxidized by applying an anodic potential scan. The proposed manufacturing approach enables the large-scale fabrication of fit-for-purpose disposable PADs at low cost which can be used for rapid on-site environmental monitoring.

Facile and Low-Cost SPE Modification Towards Ultra-Sensitive Organophosphorus and Carbamate Pesticide Detection in Olive Oil.

Despite the fact that a considerable amount of effort has been invested in the development of biosensors for the detection of pesticides, there is still a lack of a simple and low-cost platform that can reliably and sensitively detect their presence in real samples. Herein, an enzyme-based biosensor for the determination of both carbamate and organophosphorus pesticides is presented that is based on acetylcholinesterase (AChE) immobilized on commercially available screen-printed carbon electrodes (SPEs) modified with carbon black (CB), as a means to enhance their conductivity. Most interestingly, two different methodologies to deposit the enzyme onto the sensor surfaces were followed; strikingly different results were obtained depending on the family of pesticides under investigation. Furthermore, and towards the uniform application of the functionalization layer onto the SPEs' surfaces, the laser induced forward transfer (LIFT) technique was employed in conjunction with CB functionalization, which allowed a considerable improvement of the sensor's performance. Under the optimized conditions, the fabricated sensors can effectively detect carbofuran in a linear range from 1.1 × 10-9 to 2.3 × 10-8 mol/L, with a limit of detection equal to 0.6 × 10-9 mol/L and chlorpyrifos in a linear range from 0.7 × 10-9 up to 1.4 × 10-8 mol/L and a limit of detection 0.4 × 10-9 mol/L in buffer. The developed biosensor was also interrogated with olive oil samples, and was able to detect both pesticides at concentrations below 10 ppb, which is the maximum residue limit permitted by the European Food Safety Authority.

On-line microfluidic immobilized-enzyme reactors: A new tool for characterizing synthetic polymers.

Biodegradable polymeric materials may eventually replace biostable materials for medical applications, including therapeutic devices, scaffolds for tissue engineering, and drug-delivery vehicles. To further develop such materials, a more fundamental understanding is necessary to correlate parameters including chemical-composition distribution within a macromolecular structure with the final properties of the material, including particle-size. A wide variety of analytical techniques have been applied for the characterization of polymer materials, including hyphenated techniques such as comprehensive two-dimensional liquid chromatography (LC × LC). In this context, we have investigated enzymatic degradation of polyester-based nanoparticles, both in-solution and by the use of an immobilized-enzyme reactor (IMER). We have demonstrated for the first time the implementation of such an IMER in a size-exclusion chromatography system for on-line degradation and subsequent analysis of the polymer degradation products. The effect of residence times ranging from 12 s to 4 min on polymer degradation was assessed. IMER-assisted degradation is much faster compared to in-solution degradation, which requires several hours to days, and opens the possibility to use such reactors in LC × LC modulation interfaces.