Microcalorimetric Detection of Creatinine in Urine

In this work, we demonstrate the quantification of creatinine in human urine samples using a micro-calorimetric sensing system. The calorimetric sensor is based on an array of microfabricated Y-cut quartz resonators. The piezoelectric quartz is etched down to a thickness of 10 μm and exhibits a bulk acoustic resonance of 166 MHz. The temperature sensitivity of this high-frequency quartz resonator is 14,600 Hz/K due to the high phenomenological sensitivity of quartz. The sensing resonator structure is thermally isolated from the bulk quartz by fabricating a plate-like cantilevered structure from the etched quartz using focused ion beam etching. Importantly, the quartz sensors and fluidics are decoupled providing a significantly more robust calorimetric sensing system than directly contacted thermopile based chip calorimeters. We employ alginate entrapped creatinine deiminase to transduce urinary creatinine into temperature signatures allowing for the quantification. Ultimately, we envision the development of a handheld calorimetric device similar to that of the glucose meter but with the capability of detecting a much wider range of biomolecules due to the near universality of calorimetric sensing.