Improving the performance and versatility of microfluidic thread electroanalytical devices by automated injection with electronic pipettes: a new and powerful 3D-printed analytical platform.

Microfluidic cotton thread-based electroanalytical devices (µTEDs) are analytical systems with attractive features such as spontaneous passive flow, low cost, minimal waste production, and good sensitivity. Currently, sample injection in µTEDs is performed by hand using manual micropipettes, which have drawbacks such as inconstant speed and position, dependence of skilled analysts, and need of physical effort of operator during prolonged times, leading to poor reproducibility and risk of strain injury. As an alternative to these inconveniences, we propose, for the first time, the use of electronic micropipettes to carry out automated injections in µTEDs. This new approach avoids all disadvantages of manual injections, while also improving the performance, experience, and versatility of µTEDs. The platform developed here is composed by three 3D-printed electrodes (detector) attached to a 3D-printed platform containing an adjustable holder that keeps the electronic pipette in the same x/y/z position. As a proof-of-concept, both injection modes (manual and electronic) were compared using three model analytes (nitrite, paracetamol, and 5-hydroxytryptophan) on µTED with amperometric detection. As result, improved analytical performance (limits of detection between 2.5- and 5-fold lower) was obtained when using electronic injections, as well as better repeatability/reproducibility and higher analytical frequencies. In addition, the determination of paracetamol in urine samples suggested better precision and accuracy for automated injection. Thus, electronic injection is a great advance and changes the state-of-art of µTEDs, mainly considering the use of more modern and versatile electronic pipettes (wider range of pre-programmed modes), which can lead to the development of even more automated systems.

Electrochemical study and forensic electroanalysis of fungicide benzovindiflupyr using disposable graphite pencil electrode.

Nowadays, the use of pesticides in world agriculture is fundamental. However, it leads to an increase in the illegal sale and smuggling of these products in various parts of the world, mainly in Brazil. Therefore, the development of new analytical methods for screening and analysis of these kind of substances is a relevant issue. We present in this work, for the first time, an electrochemical study and a novel electroanalytical method for determination of fungicide benzovindiflupyr (BENZO). According to our knowledge, the electrochemical behavior of BENZO, as well as its voltammetric determination, have never been reported before. The sensors used here consisted of disposable pencil graphite electrodes (PGEs). On this electrode surface and at optimal pH, BENZO behaved according to a quasi-reversible system and showed two voltammetric peaks, one anodic at Ep = +0.59 V and another cathodic at Ep = +0.43 V. The analytical studies utilized BENZO anodic sweep and square-wave adsorptive stripping voltammetry (SWAdSV). All experimental and instrumental parameters were fully investigated and optimized. Under the best conditions, a calibration plot was obtained in the concentration range from 0.10 to 12.5 µmol L-1. The limits of detection (LOD) and quantification (LOQ) achieved were 0.023 and 0.076 µmol L-1, respectively. An electrochemical mechanism for BENZO oxidation was also proposed. The method developed here was successfully employed for the qualitative and quantitative forensic analysis of BENZO in smuggled products, showing good accuracy (recoveries ca. 104%) and precision (relative standard deviation < 5%). These data attest the potential for use of this method in forensic area.

A novel all-3D-printed thread-based microfluidic device with an embedded electrochemical detector: first application in environmental analysis of nitrite.

A microfluidic thread electroanalytical device (µTED) containing an embedded electrochemical detector is presented for the first time in this work. This novel device was entirely produced in an automated way using the fused deposition modeling (FDM) 3D printing technique. The main platform was fabricated with acrylonitrile butadiene styrene (ABS) filament, while the integrated electrochemical detector was produced using a commercial conductive filament composed of carbon black and polylactic acid (CB/PLA). The microfluidic channels consisted of cotton threads, which act as passive pumps, and the µTED was used for microflow injection analysis (µFIA). As a proof of concept, this µFIA system was utilized for the amperometric sensing of nitrite in natural waters. This is the first report on the use of both µTEDs and 3D-printed CB/PLA electrodes to determine this species. This fully 3D-printed µTED was characterized and all experimental and instrumental parameters related to the method were studied and optimized. Using the best conditions, the proposed approach showed a linear response in the concentration range from 8 to 200 µmol L-1 and a limit of detection (LOD) of 2.39 µmol L-1. The LOD obtained here was ca. ten-fold lower than the maximum contaminant level for nitrite in drinking water established by the Brazilian and US legislation. Moreover, the platform presented good repeatability and reproducibility (relative standard deviations (RSDs) were 2.1% and 2.5%, respectively). Lastly, the 3D-printed µTED was applied for the quantification of nitrite in well water samples and the results obtained showed good precision (RSD < 3%) and excellent concordance (relative error was ca.±3%) with those achieved by ion chromatography, used for validation.