Acidosis, cystic fibrosis, tumor metastasis, microbial infection, and other pathophysiological conditions can all be detected by changes in the pH of biofluids like urine, sweat, and blood. Monitoring pH may therefore shed light on those patho-physiological alterations. Sweat analysis offers non-invasive way to monitor personal health. Atopic dermatitis, fungal infections, and cystic fibrosis can all be detected by changes in sweat pH. Therefore, measuring the pH of sweat could help to precisely identify some health issues. Although there are many ways to measure the pH of a solution, including electrochemical, colorimetric, and fluorescence methods, optical pH measurements have become more common in recent years due to the availability of a wide range of materials and advancements in imaging technology. Due to their exceptional photophysical properties, such as photo-stable near-infrared (nIR) fluorescence and sensitive molecular recognition, semiconducting single-walled carbon nanotubes (SWCNTs) are emerging molecular optical probes and sensors. Here, we report that pH changes in a model biofluid —artificial sweat — can be accurately detected by SWCNT-based optical sensors. Through changes in the nIR fluorescence, the sensor demonstrated significant responses within biologically relevant pH ranges within minutes. Development of optical pH sensors for use in chemistry, bioengineering, environmental sciences, and healthcare is made possible by the nanotubes' optical response to pH changes.

Optical nanosensors for pH measurements in model biofluids

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