The binding of the sensor's target to this recognition element reduces the efficiency with which the attached redox reporter approaches the electrode (analogous to the change in tumbling seen in fluorescence polarization), producing an easily measured change in electron transfer efficiency (analogous to a change in fluorescence polarization). Specifically, we show here that the simultaneous optimization of square-wave frequency and amplitude produces large (often more than two-fold) increases in the signal gain of a wide range of E-DNA-type sensors. Here we show that, because it alters the driving force of the redox reaction and thus electron transfer kinetics, signal gain in this class of sensors is also strongly dependent on the amplitude of the square-wave potential pulse. Because signalling in this class of sensors relies on binding-induced changes in electron transfer rate, the signal gain of such sensors (change in signal upon the addition of saturating target) is dependent on the frequency of the square-wave potential pulse used to interrogate them, with the optimal square-wave frequency depending on the structure of the probe, the nature of the redox reporter, and other features of the sensor. In these sensors a binding-induced conformational change in an electrode-bound "probe" (a target-binding nucleic acid or nucleic-acid-peptide chimera) alters the location of an attached redox reporter, leading to a change in electron transfer that is typically monitored using square-wave voltammetry. Sensors for both targets are sensitive (detection limits in the low nanomolar range), rapid (minutes), reusable, and selective enough to function directly in complex matrices including blood serum, soil, and foodstuffs.Įlectrochemical DNA (E-DNA) sensors have emerged as a promising class of biosensors capable of detecting a wide range of molecular analytes (nucleic acids, proteins, small molecules, inorganic ions) without the need for exogenous reagents or wash steps.
We generated streptavidin sensors exhibiting both signal-on (target binding increases the faradaic current) and signal-off behavior, of which only the signal-off approach was generalizable to the detection of antibodies. We optimized the scaffold using a biotin recognition element and streptavidin as a target to determine the variables that define sensor performance before then applying the approach to detection of anti-digoxigenin antibodies using the steroid as the recognition element. The binding of a protein to the small molecule recognition element alters the dynamics of the scaffold, increasing or decreasing the efficiency with which the redox tag collides with the electrode and thus altering the observed faradaic current.
Our electrochemical approach utilizes a redox-tagged DNA signaling scaffold that is conjugated to a small molecule recognition element and is covalently attached to an interrogating electrode. Here we have demonstrated a general, sensitive, and selective approach for the detection of macromolecules that bind to specific small molecule recognition elements.
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