Recent advances in optical-based and force-based single nucleic acid imaging

Re-engineering Electrochemical Aptamer-Based Biosensors to Tune Their Useful Dynamic Range via Distal-Site Mutation and Allosteric Inhibition

Electrochemical aptamer-based (E-AB) sensors, exploiting binding-induced changes in biomolecular conformation, are rapid, specific, and selective and perform well even in a complex matrix, such as directly in whole blood and even in vivo. However, like all sensors employing biomolecular recognitions, E-AB sensors suffer from an inherent limitation of single-site binding, i.e., its fixed dose-response curve. To circumvent this, we employ here distal-site mutation and allosteric inhibition to rationally tune the dynamic range of E-AB sensors, achieving sets of sensors with a significantly varied target affinity (∼3 orders of magnitude). Using their combination, we recreate several approaches to narrow (down to 5-fold) or extend (up to 2000-fold) the dynamic range of biological receptors. The thermodynamic consequences of aptamer-surface interactions are estimated via the free-energy difference in solution-phase and surface-bound biosensors employing the same aptamer as a recognition element, revealing that an allostery strategy provides a more predictable and efficient means to finely control the target affinity and dynamic range. Such an ability to rationally modulate the affinity of biomolecule receptors would open the door to applications including cancer therapy, bioelectronics, and many other fields employing biomolecule recognition.

Reversible Ratiometric Probe Combined with the Time-Gated Method for Accurate In Vivo Gastrointestinal pH Sensing

Fluorescence sensing has the advantages of being real time, noninvasive, and convenient and having a low impact on the original environment for in vivo detection. Here, a reversible time-gated ratiometric in vivo detection method that could eliminate the interferences from probe amount, photon scattering, and absorption is proposed. Correspondingly, the composite probe must be able to reversibly respond to changes in the microenvironment and emit two luminescence signals at the same working wavelength but different lifetimes. Benefitting from the reversible detection mechanism, the probes could be used to monitor a dynamic biological process and the ratio signal value could be determined only by the concentration of analytes, independent of the probe concentration. Furthermore, benefitting from the same working wavelength, the read-out errors from photon absorption and scattering could be minimized. This method is very suitable for in vivo detection in which the probe distribution and depth are unknown and variable. As a typical model, different pH values in the gastrointestinal area and pH changes caused by drugs and fasting are successfully monitored.