Molecular sensor for detecting methane and/or carbon dioxide dissolved in a liquid

Disclosed is a molecular sensor for detecting molecules dissolved in liquid, the molecular sensor comprising: a sensor housing, a measurement chamber comprised in the sensor housing and being fluidly coupled to an exterior of the sensor housing, and a quartz crystal microbalance (QCM). A quartz crystal resonator comprised in the QCM is functionalised with a metal-organic framework (MOF) which can reversibly adsorb methane and/or reversibly adsorb carbon dioxide, and the molecular sensor is configured such that liquid which enters the measurement chamber can come in direct contact with a surface of the MOF. Also disclosed is a method of detecting and/or quantifying molecules dissolved in a liquid, the method comprising the steps of: providing a molecular sensor comprising a quartz crystal microbalance (QCM), the QCM comprising a quartz crystal resonator, the QCM being functionalised with a metal-organic framework (MOF) which can reversibly adsorb methane and/or reversibly adsorb carbon dioxide; providing the liquid to a functionalised surface of the QCM such that the liquid directly contacts the functionalised surface.