During sports activities, monitoring hydration status before, during, and after exercise is essential for both performance and safety. Y. Zhou of Nanyang Technological University, Souhir Boujday of Sorbonne Universités in Paris, and their colleagues have now developed a gold nanoparticle-based colorimetric sensor that makes it possible to detect hydration balance and overhydration within minutes. They reported their work in the journal Materials & Design (DOI: 10.1016/j.matdes.2015.06.078).
The researchers used ascorbic acid-stabilized gold nanoparticles (AuNPs) in this work. To obtain a model mixture with the necessary concentration of the AuNPs, 100 µL of 100 g L−1 chloroauric acid (HAuCl4·3H2O) was mixed with 25 mL of de-ionized water and 1.5 mL of 21.2 g L−1 sodium carbonate solution. To complete the synthesis, 2 mL of 7 g L−1 ascorbic acid underwent vigorous stirring at 1000 rpm on a magnetic stirrer for 15 min. The mixed solution was chilled with ice at about 0–2°C. The designed mixture model had the concentration range of human body fluid.
Different colors were obtained at NaCl concentrations of 26.5 mM, 40 mM, and 47.9 mM, which indicate that the sensor can distinguish between hydration imbalance situations. As the concentration of NaCl increased from 26.5 mM to 40 mM and 47.9 mM, the A650/A520 ratio increased, indicating a decrease in dispersed particles and an increase in AuNP aggregates. The ratio of absorbance at 650–520 nm (A650/A520) is a good indicator of the aggregation state of the AuNPs. The particles’ aggregation/dispersion state occurred in the desired range of salt concentration.
The different color of AuNPs solution in the presence of different concentrations of NaCl. Credit: Materials & Design.
The researchers envision this type of sensor to be used for detection of hydration levels with many desirable properties, including simple detection display, high stability, and fast response time. Furthermore, this model of sensor may be useful in detecting small changes in biological substances in excreted fluids.
