Real time and spatiotemporal quantification of pH and H2O2 imbalances with a multiplex SERS nanosensor

Abstract Oxidative stress is involved in many aging-related pathological disorders and is the result of a defective cellular management of redox reactions. Particularly, hydrogen peroxide, H2O2 is a major byproduct and a common oxidative stress biomarker. Monitoring H2O2 dynamics and a direct correlation to diseases remain still a challenge due to the complexity of redox reactions. Sensitivity and specificity are a major drawback for H2O2 sensors regardless their readout. Luminiscent boronate-based probes such as 4-MPBA are emerging as the most effective quantitation tool due to their specificity and sensitivity. Problems associated to these probes are limited intracellular sensing, water solubility, selectivity, and quenching. We have synthesized a boronate-based nanosensor with a SERS readout to solve these challenges. Furthermore, we found out that environmental pH gradients, as found in biological samples, affect the sensitivity of boronate-based sensors. When the sensor is in an alkaline environment, the oxidation promoted by H2O2 is more favored than in an acidic environment. This leads to different H2O2 measurements depending on pH. To solve this issue, we synthesized a multiplex nanosensor able to concomitantly quantify pH and H2O2. Our nanosensor first measures the local pH and based on this value, provide the amount of H2O2. It seems that this pH-dependent sensitivity effect applies to all boronic acid-based probes. We tested the multiplexing ability by quantitatively measuring intra-and extra-cellularly pH and H2O2 dynamics under physiological and pathological conditions on healthy cells and cells which H + and/or H2O2 homeostasis has been altered.