The paper discusses the detection of individual gas molecules adsorbed on graphene, a material with exceptional low-noise electronic properties. The authors demonstrate that micrometre-size graphene sensors can detect the adsorption and desorption of gas molecules, which changes the local carrier concentration in graphene by one electron, leading to step-like changes in resistance. This sensitivity is attributed to graphene's low-noise electronic properties, its two-dimensional nature, high conductivity, few crystal defects, and the ability to perform four-probe measurements. The study shows that graphene-based sensors can detect individual gas molecules with a detection limit of about 1 ppb, comparable to other highly sensitive gas sensors. The authors also explore the accumulation of chemical doping over time and the constant mobility of charge carriers with increasing chemical doping, challenging current theoretical estimates for scattering rates in graphene. They suggest that absorbed water may provide sufficient dielectric screening to explain the suppression of scattering by charged impurities.The paper discusses the detection of individual gas molecules adsorbed on graphene, a material with exceptional low-noise electronic properties. The authors demonstrate that micrometre-size graphene sensors can detect the adsorption and desorption of gas molecules, which changes the local carrier concentration in graphene by one electron, leading to step-like changes in resistance. This sensitivity is attributed to graphene's low-noise electronic properties, its two-dimensional nature, high conductivity, few crystal defects, and the ability to perform four-probe measurements. The study shows that graphene-based sensors can detect individual gas molecules with a detection limit of about 1 ppb, comparable to other highly sensitive gas sensors. The authors also explore the accumulation of chemical doping over time and the constant mobility of charge carriers with increasing chemical doping, challenging current theoretical estimates for scattering rates in graphene. They suggest that absorbed water may provide sufficient dielectric screening to explain the suppression of scattering by charged impurities.