Innovative microfluidic thread electroanalytical device with automated injector: A simple, green and upgraded analytical platform for the fast and sensitive analysis of ferrous ions

Abstract

Cotton thread-based microfluidic devices are attractive for analytical procedures due to advantages that include affordable cost, low consumption of reagents and minimal production of waste. The coupling of cotton-based devices to electrochemical detection, known as microfluidic thread electroanalytical device (µTED), has demonstrated vast potential. However, some aspects in the µTED concept can still be improved, such as sample injection, which, until now, has been performed exclusively with manual micropipettes. This conventional injection has some deficiencies that include the variability in the aspiration/dispensing rates and inconstancy in the position of the pipette during injections, which can impair the measurements. Here we propose a new approach to improve the injection step in µTEDs by using electronic pipettes, which we named as automated injection. This novel injection mode overcomes the aforementioned disadvantages of manual injection. Electronic pipettes control aspiration and dispensing volumes/rates electronically and offer better ergonomics. We developed a new 3D-printed platform that allows to attach the electronic pipette to the µTED and always perform injections at a fixed position, increasing reproducibility of measurements. To demonstrate the practical applicability, this approach was first utilized for analysis of ferrous ion in pharmaceutical supplements and environmental samples. The method presented a wide linear range (0.7 to 200 μmolL–1), low limit of detection (0.21 μmolL–1), good accuracy (recoveries between 96 and 103 %) and excellent precision (relative standard deviation (RSD) ≤ 3.3 %). Thus, automated injection can be a great advance and change the state-of-the-art regarding µTEDs.