Lab-on-cloth integrated with gravity/capillary flow chemiluminescence (GCF-CL): towards simple, inexpensive, portable, flow system for measuring trivalent chromium in water

Flow chemiluminescence (CL) is widely applied for detection of heavy metal ions in environment, but it is seldom used in economical, practical, or affordable settings because non- and minimally instrumented flow driving is difficult to achieve. Here, we first report a gravity and capillary force-driven flow CL (GCF-CL) lab-on-cloth device, toward development of low-cost, easy-to-use, portable, minimally-instrumented platform for determination of trivalent chromium [Cr(III)] in water, where a difference in height between two zones on cloth creates a fast flow of CL trigger solution. Wax screen-printing was used to fabricate ultra-low-cost cloth-based devices, and the light emitted from the Cr(III)-catalysed oxidation of luminol by H 2 O 2 was imaged using an inexpensive portable CCD camera. Under optical conditions, Cr(III) could be determined over the range of 0.01–100   mg/L, with a detection limit of 6.2   μg/L, an analysis time of less than 30   s per sample, and RSDs of 6.2%, 3.1% and 1.7% for 0.05, 0.5 and 5   mg/L Cr(III) (n   =   5). The proposed GCF-CL lab-on-cloth was successfully applied for measuring Cr(III) in water samples, with recoveries of 100.67-111.70% and RSDs of 4.73–6.88%. Thus, the presented method should have the potential for portable field applications in environmental and public health fields.