Effects of Physiological-Scale Variation in Cations,\npH, and Temperature on the Calibration of Electrochemical Aptamer-Based\nSensors

Electrochemical\naptamer-based (EAB) sensors are the first technology\nsupporting high-frequency, real-time, in vivo molecular measurements\nthat is independent of the chemical reactivity of its targets, rendering\nit easily generalizable. As is true for all biosensors, however, EAB\nsensor performance is affected by the measurement environment, potentially\nreducing accuracy when this environment deviates from the conditions\nunder which the sensor was calibrated. Here, we address this question\nby measuring the extent to which physiological-scale environmental\nfluctuations reduce the accuracy of a representative set of EAB sensors\nand explore the means of correcting these effects. To do so, we first\ncalibrated sensors against vancomycin, phenylalanine, and tryptophan\nunder conditions that match the average ionic strength, cation composition,\npH, and temperature of healthy human plasma. We then assessed their\naccuracy in samples for which the ionic composition, pH, and temperature\nwere at the lower and upper ends of their physiological ranges. Doing\nso, we find that physiologically relevant fluctuations in ionic strength,\ncation composition, and pH do not significantly harm EAB sensor accuracy.\nSpecifically, all 3 of our test-bed sensors achieve clinically significant\nmean relative accuracy (i.e., better than 20%) over the clinically\nor physiologically relevant concentration ranges of their target molecules.\nIn contrast, physiologically plausible variations away from the temperature\nused for calibration induce more substantial errors. With knowledge\nof the temperature in hand, however, these errors are easily ameliorated.\nIt thus appears that physiologically induced changes in the sensing\nenvironment are likely not a major impediment to clinical application\nof this in vivo molecular monitoring technology.