Wrist-watch back cases, systems and methods for measuring biomarkers

A wristband for mounting a wearable device having a back case around a wrist of a user to place the back case in contact with the user's skin, the wristband comprising:

• a flexible layer having adjusting elements for adjusting the wristband to the user's wrist;
• coupling elements for coupling the flexible layer to the back case of the wearable device;
• a buckle coupled to an end of the flexible layer, the buckle having a frame and a pivoting prong coupled to the frame for selective engagement with the flexible layer adjusting elements;
• and
• a tightening mechanism arranged in the frame of the buckle for obtaining a predefined adjustment of the wristband around the user's wrist to thereby increase the contact of the back case with the user's skin, the tightening mechanism comprising a ratchet gear having locking teeth arranged at a periphery of the ratchet gear over a predetermined angular range, a pivoting strut configured for selective engagement with the locking teeth to place the tightening mechanism in a locked state, and a mechanism for pivoting the pivoting strut to disengage from the locking teeth to place the tightening mechanism in an unlocked state.