Abstract
Measuring pH has become a major key for determining health conditions, and food safety. The traditional pH assessment approaches are costly and offer low sensitivity. Here, a novel pH sensor based on a pH-responsive hydrogel has been developed. A Fresnel lens pattern was replicated on the surface of the pH-responsive hydrogel using the replica mould method. The pH sensors were tested in a pH range of 4–7. Introducing various pH solutions to the pH sensor led to volumetric shifts as the hydrogel swelled with pH. Consequently, the dimensions of the replicated Fresnel lens changed, modifying the focal length and the focus efficiency of the optical sensor. As a result, the measured optical power at a fixed distance from the sensor changed with pH. The optical sensor showed the best performance in the acidic region when pH changed from 4.5 to 5.5, in which the recorded power increased by 13%. The sensor exhibited high sensitivity to pH changes with a short respond time in a reversible manner. The developed pH optical sensor may have applications in medical point-of-care diagnostics and wearable continuous pH detection devices.
Highlights
Heart disease is a chronic condition that continues to be the primary cause of death in Europe [1]
Introducing different pH solutions in the pH range of 4.5–7.0 to the sensor led to changes in the recoded optical signals, and the maximum detected optical power increased with pH levels (Figure 2A)
The sensor showed the highest sensitivity in the pH range of 4.5–5.5 as the power increased to a value of 45 μW, which represents 7% of the reference power, and the sensitivity decreased to 6.5% and to 2.6% in the pH ranges of 5.5–6.0 and 6.5–7.0, respectively
Summary
Heart disease is a chronic condition that continues to be the primary cause of death in Europe [1]. Improved treatment methods for such disorders have been under review. PH has become a major signal for determining health conditions, and food safety. In food-quality applications, variations in pH are generally correlated with bacteria growth and colonisation. An increase in the pH level beyond the normal range (7.35–7.45) is related to degenerative diseases, and a decrease in the pH level is related to lower blood flow due to excessive acid adhering to the vessel [4,5,6]. The pH determination is necessary in a variety of applications in many fields such as chemistry and medical research [7]
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