All-nanofiber-based analytical device for colorimetric detection of hexavalent chromium in water samples

Paper-based analytical devices have emerged as a powerful alternative for colorimetric assays due to their portability, ease of handling, and global affordability. However, these devices may suffer from some issues, including inconsistent flow rates and low color uniformity. In this regard, replacing paper with nanofibrous membranes (NFMs) is a promising alternative, as the key properties of NFMs can be easily tuned while offering superior chemical resistance. To demonstrate the feasibility of this concept, we propose a novel, disposable, and leak-proof all-nanofiber-based analytical device (NAD) for the detection of Cr(VI). The device, consisting of a trilayer asymmetric NFM, was fabricated through the sequential layer-by-layer electrospinning of a polylactic acid (PLA) NFM as the hydrophobic layer, a PLA/poly(ethylene oxide) (PEO)@1,5-diphenylcarbazide (DPC) NFM as the reaction layer, and a PLA/PEO NFM as the sealing layer. The NAD was applied for Cr(VI) detection using digital image colorimetry. Three image capture devices were employed to evaluate the impact of image acquisition methods on the analytical response. Using the USB digital microscope, the NAD exhibited a linear response in the range of 12.5-100 μmol L^-1, a limit of detection of 0.02 μmol L^-1 (1.0 μg L^-1), and high selectivity against common ions present in water samples. The NAD was employed to analyze actual water samples, yielding recoveries ranging from 92.0 to 106 %. Moreover, the good adhesion between layers and homogeneous DPC distribution ensure excellent repeatability and reproducibility. These achievements highlight that using electrospinning to develop analytical devices represents an innovative solution for environmental monitoring.