Provided herein are methods and devices for measuring pH and for amplifying a pH signal to obtain ultrasensitive detection of changes in pH. This is achieved by providing a sensor and a transducer, wherein the sensor transconductance is sensitive to changes in pH and the transducer transconductance is not affected by pH change. The transducer instead compensates for changes in the sensor transconductance arising from pH change. The unique configuration of the sensor and transducer with respect to each other provides substantial increases in a pH amplification factor, thereby providing pH sensing devices with a giant Nernst response and, therefore, effectively increased pH sensitivity.