Given the intricate relationship between metal ions and reproductive biology, there is aneed to develop new metal ion sensors that can provide rapid/real-time information, arereusable and capable of continuous or repeated measurements. In this context, sensorswith ‘photoswitchable’ properties where ion sensing can be turned ‘On’ and ‘Off’ withdifferent wavelengths of light, would allow for multiple measurements to be made on asingle sample without the need to change the probe. This is a highly desirable property inbiological experiments, where sample availability and volumes often limit the number ofexperiments that can be performed.This talk highlights the recent advances made by our group in developing nanoliter-scaleregenerable ion sensors based on microstructured optical fiber (MOF). Here, the air holesof the MOF are functionalized with a specific photochromic molecule, to yield a switchablesensor that can detect metal ions such as zinc and calcium, down to nanoliter-scalevolumes, where ion binding is turned on and off on upon irradiation with light. Unboundions are readily flushed from the fiber in the ‘off’ state to allow the sensor to be reused.The integration of an ionophore into the sensor paves the way for the development ofhighly specific light-based sensing platforms that are readily adaptable to sense aparticular ion. This work represents advances in both fiber sensing technology and indeveloping new tools for answering biologically related questions, particularly in the areasof reproductive health.