Cindy Schaude

Novel colourimetric sensors are readily devised by combining multifunctional (nano)materials with miniature optoelectronic components. The demand to detect and monitor metal ions has resulted in the invention of new colourimetric sensing schemes, especially for use at the Point-of-Need (PoN). Nonetheless, the design of fully reversible optical materials for continuous real-time ion monitoring remains a bottleneck in the practical realisation of sensors. Magnesium ion is vital to physiological and environmental processes, but monitoring can be challenging, particularly in the presence of Ca²⁺ as a cross-sensitive interferent in real samples. In this work, a chromophore molecule Hyphan I (1-(2-hydroxy-5-ß-hydroxyethylsulfonyl-phenyl-azo)-2-naphthol) has been grafted onto a cellulose matrix with a simple one-pot vinylsulfonyl process, to form a transparent, biocompatible and highly flexible thin-film colourimetric magnesium ion sensing material (Cellulose Film with Hyphan-CFH). The CFH film has a pH response time of K_a1 = 5.8. The LOD and LOQ for Mg²⁺ at pH 8 are 0.089 mM and 0.318 mM, respectively, with an RSD = 0.93%. The CFH film exhibits negligible interference from alkaline and alkaline earth metals, but irreversibly binds certain transition metals (Fe³⁺, Cu²⁺ and Zn²⁺). The CFH material has a fast and fully reversible colourimetric response to pH and Mg²⁺ over physiologically relevant ranges without interference by Ca²⁺, demonstrating good potential for integration into microfluidic systems and wearable sensors for biofluid monitoring.

Novel colourimetric sensors are readily devised by combining multifunctional (nano)materials with miniature optoelectronic components. The demand to detect and monitor metal ions has resulted in the invention of new colourimetric sensing schemes, especially for use at the Point-of-Need (PoN). Nonetheless, the design of fully reversible optical materials for continuous real-time ion monitoring remains a bottleneck in the practical realisation of sensors. Magnesium ion is vital to physiological and environmental processes, but monitoring can be challenging, particularly in the presence of Ca2+ as a cross-sensitive interferent in real samples. In this work, a chromophore molecule Hyphan I (1-(2-hydroxy-5-ß-hydroxyethylsulfonyl-phenyl-azo)-2-naphthol) has been grafted onto a cellulose matrix with a simple one-pot vinylsulfonyl process, to form a transparent, biocompatible and highly flexible thin-film colourimetric magnesium ion sensing material (Cellulose Film with Hyphan - CFH). The CFH film has a pH response time of < 60s over the pH range 4 to 9, with a pKa = 5.8. The LOD and LOQ for Mg2+ at pH 8 are 0.089 mM and 0.318 mM, respectively, with an RSD = 0.93%. The CFH film exhibits negligible interference from alkaline and alkaline earth metals, but irreversibly binds certain transition metals (Fe3+, Cu2+ and Zn2+). The CFH material has a fast and fully reversible colourimetric response to pH and Mg2+ over physiologically relevant ranges without interference by Ca2+, demonstrating good potential for integration into microfluidic systems and wearable sensors for biofluid monitoring.

Indicator cotton swabs have been developed in order to enable faster, less expensive, and simpler information gathering of a wound status. Swabs are normally used for cleaning the wound, but here, they were covalently functionalized with indicator chemistry. Thus, they in principle enable simultaneous wound cleaning and wound pH detection. Using an indicator dye with a color change from yellow to red, combined with an inert dye of blue color, a traffic light color change from green to red is induced when pH increases. The indicator cotton swabs (ICSs) show a color change from green (appropriate wound pH) to red (elevated wound pH). This color change can be interpreted by the naked eye as well as by an optical color measurement device in order to obtain quantitative data based on the CIE L*a*b* color space. Two types of swabs have been developed—indicator cotton swabs ICS1 with a sensitive range from pH 5 to 7 and swabs ICS2 with a sensitive range from 6.5 to 8.5. The swabs are gamma-sterilized and the effect of sterilization on performance was found to be negligible. Furthermore, cytotoxicity testing shows cell viability and endotoxin levels to be within the allowable range.