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A low cost colorimetric microfluidic paper-based analytical device (µPAD) for the determination of nitrite in real samples with improved precision has been fabricated and its performance has been evaluated. The µPAD was fabricated by laser cutting and patterning on the paper and the nitrite concentration measurement is based on the modified Griess assay. In this assay, tartaric acid was used as an antioxidant reagent to increase Griess reagent stability. A novel geometrical design was used to achieve better color gradient over µPAD detection zone for improving the precision of the measurements. The results of measurement indicate that the fabricated device could successfully detect and quantify the nitrite concentration in real samples with the limit of detection of 15 μM. The results are in good accordance with the results of spectrophotometry. The fabricated sensor has the potential to be applied for monitoring of the trace level of nitrite in drinking water and environmental applications.

Thin-layer gelatin nanofiber mats were fabricated as a biodegradable scaffold for proliferating human retinal pigment epithelium. Together with MTT assay, the glucose consumption rate, lactate formation, and lactate dehydrogenase activity of the human retinal pigment epithelium cells-on the gelatin nanofibers-were analyzed as indicators for cell growth and viability. The results showed that gelatin nanofiber did not make any toxic effect on the cells and the growth rate was comparable to the tissue culture plates. Using the fabricated thin-layer nanofibers let the by-product to leave which in turn cause less adverse effect on the cells. The biodegradability and stability of the gelatin nanofibers were optimized as a function of reaction time.