Amperometric cell for subcutaneous detection of hydrogen sulfide in anesthetized experimental animals

Hydrogen sulfide (H2S) is a toxic gas. It has been recognized that H2S evolving in biochemical reactions in living organisms has an important role in different physiologic processes. Nowadays, H2S is known as an endogenous messenger molecule. Natural sulfurous spring water has been proved beneficial in the therapy of diseases of the skin and other organs (Boros et al 2013). In vivo real-time detection of local H2S concentration is an important but challenging task.We developed a two-electrode amperometric cell for selective subcutaneous detection of H2S in anesthetized mice. The cell is a small size implantable gas sensor containing a platinum disc anode and a silver cathode. The selectivity is provided by a membrane permeable only by gases. There is a buffered reversible electrochemical mediator solution in an oxidized form inside the cell. As gaseous H2S penetrates into the cell the mediator is reduced, and +0.4 V versus the reference is employed on the platinum working electrode. The reduced mediator is oxidized on the anode surface. The current provides an analytical signal representing the concentration of H2S.Appropriate shape, size and membrane material were selected, and optimal working parameters--such as mediator concentration, pH and cell voltage--were determined in vitro. The lower limit of detection in the stirred sample solution at pH = 5.5 was as small as 9.4 × 10(-7) M and a dynamic concentration range of 0-6 × 10(-4) M could be achieved.The detecting surfaces of the cell were covered with freshly dissected mouse skin to test dermal H2S permeability. In other experiments, the cell was implanted subcutaneously in an anesthetized mouse and the animal was submerged in a buffer solution containing different concentrations of H2S so that the skin surface over the sensor was covered by the solution. Measurements of subcutaneous H2S concentration were taken. The experiments clearly proved that H2S diffuses through the skin of the live mouse.