A Chromatic Sensor to Detect Free Radicals Using H2O2 as an Analyte withDTT and Au-NPs as Sensing Agents Microscopy

In this study, a simple chromatic biosensor for free radicals, which accumulate inside human bodies and can be identified as an essential sign of various diseases, is presented. Hydrogen peroxide (H2O2) was selected as a detection target as it is one of the main species of free radicals and owns longer life cycle than other species. Previous studies also showed that the cancer and cardiovascular disease were strongly correlated with the concentration of free radicals in urine greater than 10-4 M. Different concentrations of H2O2 were added into 1,4-dithiothreitol (DTT) solution for detection. The DTT could not only act as a common reductant reacting with H2O2 through redox reaction, but also cause the aggregation of gold-nanoparticles (Au-NPs), which resulted in color change of Au-NPs attributed to the effect of surface plasmon resonance (SPR). The H2O2 concentration is therefore can be detected from its correlation with the color change of H O /DTT/Au-NPs solutions, as more H 2O2 in solution will lead to more redox reaction and consequently less DTT to cause Au-NPs aggregation. Results show that the H2O2 concentrations ranged between 10-1 M to 10-6 M can be detected by naked eyes from color change. In additions, ultraviolet-visible (UV-Vis) absorption spectra were measured to further verify the correlation. Furthermore, liquid transmission electron microscopy (liquid-TEM) was also used to confirm the aggregation of Au-NPs in solutions. From above mentioned methods, the feasibility of using a chromatic biosensing system for free radical detection was demonstrated, showing the potential for future disease detection.