An Allosteric Transcription Factor-Based Electrochemical Progesterone Sensor

There is an immense potential for using biosensors in medical diagnostics as well as industries like pharmaceutical, food, beverages, environmental, and agricultural. Today, there remains a significant challenge to meet low levels of detection without compromising simplicity and affordability. Hormone measurements play a central role in family planning programs benefiting millions of women, and in monitoring endocrine disorders. Progesterone is a steroid hormone secreted by the corpus luteum and tracking progesterone levels during an ovulation cycle is beneficial for increasing fertility odds. Furthermore, during pregnancy, progesterone balance helps nurture and develop the fetus. Currently, there are no convenient and cost effective point-of-care (POC) devices to detect progesterone: antibody based approaches are used for progesterone sensing but their use is limited by high cost, production duration, and unreliability. This work has led to the development of in vitro biosensors based on bacterial allosteric transcription factors (aTFs). Like antibodies, aTFs recognize analytes with high sensitivity and specificity. In contrast to antibodies, aTFs respond to analyte binding by changing their affinity for a cognate DNA sequence. Using a novel progesterone-specific aTF, and its binding affinity to a specific DNA sequence provides an intrinsic electrochemical transduction mechanism for the development of novel progesterone biosensor. An electrochemical transduction method offers higher sensitivity and specificity at low cost. The biosensor surface includes a gold electrode with a surface immobilized DNA-aTF complex. During electrochemical measurements using a negative redox mediator (ferrocyanide/ferricyanide complex), in the absence of progesterone the overall negative charge of DNA-aTF complex blocks the negative mediator, prevents exchange of electrons with gold electrode, and generates lower current output. Addition of analyte or progesterone alters the affinity binding of DNA-aTF, releases the aTF from the surface, and enables the mediator to reach the surface, thereby resulting in an amplified current output. Preliminary results using our biosensor yielded a limit of detection of 33 nM over a physiologically relevant range of 0-10 µM progesterone in buffer, and 44 nM in presence of interferents in artificial urine.