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Acid and disperse dyes are two well‐known synthetic materials that are primarily used for dyeing of nylon 6 fibres. Despite their good performance, several negative impacts on the environment, including air and water pollution, are major concerns to researchers. An alternative ecofriendly approach to the dyeing of nylon 6 is the use of natural dyes, given their abundant natural sources, biocompatibility, biodegradability, non‐toxicity, non‐allergic responses, and non‐carcinogenic effects on human life. Based on these advantages, we extracted polyphenolic dyes from henna leaves, pomegranate rind, and Pterocarya fraxinifolia leaves and studied the dyeability on nylon 6 fabric using three compounds of aluminium sulfate, tannic acid, and tin chloride as toxic and non‐toxic mordants before dyeing. Fourier transform infrared spectra of the nylon 6 fabric confirmed the coordination complexes and π–π bonding between the mordants and the dyes. Colorimetric and fastness results showed that the mordants increased the colour strength and improved the fastness properties of the fibres. Our results suggest that tin chloride and aluminium sulfate as metal mordants can be successfully replaced with tannic acid as a biomordant in the natural dyeing of nylon 6. Also, cost assay showed that dyeing of nylon 6 with extracted natural dyes from waste leaves could be a sustainable and economical substitute for synthetic dyeing.

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A microfluidic platform with a fluorescent nanoparticle-based sensor is demonstrated for real-time, ratiometric pH imaging of biofilms. Sensing is accomplished by a thin patterned layer of covalently bonded Ag@SiO2+FiTC nanoparticles on an embedded planar glass substrate. The system is designed to be sensitive, responsive and give sufficient spatial resolution to enable new micro-scale studies of the dynamic response of oral biofilms to well-controlled chemical and hydrodynamic stimulation. Performance under challenging operational conditions is demonstrated, which include long-duration exposure to sheer stresses, photoexcitation and pH sensor biofouling. After comprehensive validation, the device was used to monitor pH changes at the attachment surface of a biofilm of the oral bacteria, Streptococcus salivarius. By controlling flow and chemical concentration conditions in the microchannel, biochemical and mass transport contributions to the Stephan curve could be probed individually. This opens the way for the analysis of separate contributions to dental caries due to localized acidification directly at the biofilm tooth interface.