Carbon Nanotubes Press-Transferred on PMMA Substrates as Exclusive Transducers for Electrochemical Microfluidic Sensing

Abstract

Novel single-walled carbon nanotube press-transfer electrodes (SW-PTEs) for microfluidic sensing are proposed. In this approach, carbon nanotubes are press-transferred on poly- (methyl methacrylate) (PMMA) substrates and are easily coupled to microfluidic chips and act as the exclusive transducer in electrochemical sensing. The detector design consisted of a presstransferred SW film (7 mm × 1 mm) positioned and centered on the PMMA substrate (33 mm × 9 mm). The analytical performance of the SW-PTEs was deeply evaluated using two commercial SWs sources and employing a mixture of dopamine and catechol as model analytes. Analyte detection was influenced by the volume of commercial SW dispersion used in the fabrication of SW-PTEs, with 5 mL taken from a dispersion of 0.5 mg/100 mL being the most favorable volume. In addition, excellent repeatability (relative standard deviation (RSD) of ≤7%, n = 5), interelectrodes reproducibility (RSD ≤ 9%, n = 5), and an extreme resistance to fouling were obtained even after 1 h of microchip analysis with RSD values of ≤4% and ≤9% (n = 15) for migration times and peak heights, respectively. Good sensitivity, remarkable signal-to-noise characteristics, and a well-defined linear concentration dependence (r ≥ 0.990) was also obtained, which allowed these novel detectors to be considered as valuable tools for quantitative analysis. Analytical characterization of the SW-PTEs by field-emission scanning electron microscopy (FESEM) revealed individual bundles of SWs that were highly ordered over the PMMA at the background where the SW bundles were embedded on the PMMA substrate, giving the electrode a high stability. Furthermore, the laboratory-fabricated SW-PTEs can be afforded in any laboratory since they do not require clean-room facilities and are highly compatible with microfluidic scale, mass production, and disposability. In addition, the proposed approach draws new and exciting horizons for electrochemical microfluidic sensing, such as the use of other pure or hybrid nanomaterials and also the possibilities to incorporate biomolecules for highly selective sensing