A sensor structure, comprising: a storage compartment (300, 1540) configured to retain a storage medium (322, 1542) therein; a sensing element (200, 1520) extending through an aperture in the compartment (300, 1540) and comprising a sensing structure (210, 1522), a distal end of the sensing structure located proximal a distal end of the sensing element (200, 1520), the sensing element (200, 1520) movable between a first position in which the sensing structure (210, 1522) is in fluid communication within the storage compartment (300, 1540) and a second position in which the sensing structure is not in fluid communication with the storage compartment (300, 1540), a proximal portion of the sensing element (200, 1520) or of a movable component connected to the sensing element (200, 1520) being located proximal and outside of the storage compartment (300, 1540) when the sensing element (200, 1520) is in the first position and the proximal portion located within the storage compartment (300, 1540) when the sensing element (200, 1520) is in the second position; a sealing element (310b, 1512) disposed at least partially within the aperture and configured to engage a surface of the sensing element (200, 1520) to provide a seal inhibiting fluid flow in or out of storage compartment (300, 1540) through the aperture; a plug defining a proximal end of the storage compartment, the plug configured to allow longitudinal translation of the proximal portion through the plug; and a sterilizable and compressible bellows structure proximal the plug and configured to retain the proximal portion when the sensing element is in the first position to maintain the sterility of the storage compartment when the proximal portion is moved into and out of the storage compartment. a storage compartment (300, 1540) configured to retain a storage medium (322, 1542) therein; a sensing element (200, 1520) extending through an aperture in the compartment (300, 1540) and comprising a sensing structure (210, 1522), a distal end of the sensing structure located proximal a distal end of the sensing element (200, 1520), the sensing element (200, 1520) movable between a first position in which the sensing structure (210, 1522) is in fluid communication within the storage compartment (300, 1540) and a second position in which the sensing structure is not in fluid communication with the storage compartment (300, 1540), a proximal portion of the sensing element (200, 1520) or of a movable component connected to the sensing element (200, 1520) being located proximal and outside of the storage compartment (300, 1540) when the sensing element (200, 1520) is in the first position and the proximal portion located within the storage compartment (300, 1540) when the sensing element (200, 1520) is in the second position; a sealing element (310b, 1512) disposed at least partially within the aperture and configured to engage a surface of the sensing element (200, 1520) to provide a seal inhibiting fluid flow in or out of storage compartment (300, 1540) through the aperture; a plug defining a proximal end of the storage compartment, the plug configured to allow longitudinal translation of the proximal portion through the plug; and a sterilizable and compressible bellows structure proximal the plug and configured to retain the proximal portion when the sensing element is in the first position to maintain the sterility of the storage compartment when the proximal portion is moved into and out of the storage compartment.