All Publications

  • Opportunities and challenges in the diagnostic utility of dermal interstitial fluid. Nature biomedical engineering Friedel, M., Thompson, I. A., Kasting, G., Polsky, R., Cunningham, D., Soh, H. T., Heikenfeld, J. 2023


    The volume of interstitial fluid (ISF) in the human body is three times that of blood. Yet, collecting diagnostically useful ISF is more challenging than collecting blood because the extraction of dermal ISF disrupts the delicate balance of pressure between ISF, blood and lymph, and because the triggered local inflammation further skews the concentrations of many analytes in the extracted fluid. In this Perspective, we overview the most meaningful differences in the make-up of ISF and blood, and discuss why ISF cannot be viewed generally as a diagnostically useful proxy for blood. We also argue that continuous sensing of small-molecule analytes in dermal ISF via rapid assays compatible with nanolitre sample volumes or via miniaturized sensors inserted into the dermis can offer clinically advantageous utility, particularly for the monitoring of therapeutic drugs and of the status of the immune system.

    View details for DOI 10.1038/s41551-022-00998-9

    View details for PubMedID 36658344

  • Pre-equilibrium biosensors as an approach towards rapid and continuous molecular measurements. Nature communications Maganzini, N., Thompson, I., Wilson, B., Soh, H. T. 2022; 13 (1): 7072


    Almost all biosensors that use ligand-receptor binding operate under equilibrium conditions. However, at low ligand concentrations, the equilibration with the receptor (e.g., antibodies and aptamers) becomes slow and thus equilibrium-based biosensors are inherently limited in making measurements that are both rapid and sensitive. In this work, we provide a theoretical foundation for a method through which biosensors can quantitatively measure ligand concentration before reaching equilibrium. Rather than only measuring receptor binding at a single time-point, the pre-equilibrium approach leverages the receptor's kinetic response to instantaneously quantify the changing ligand concentration. Importantly,by analyzing the biosensor output in frequency domain, rather than in the time domain, we show the degree to which noise in the biosensor affects the accuracy of the pre-equilibrium approach. Through this analysis, we provide the conditions under which the signal-to-noise ratio of the biosensor can be maximized for a given target concentration range and rate of change. As a model, we apply our theoretical analysis to continuous insulin measurement and show that with a properly selected antibody, the pre-equilibrium approach could make the continuous tracking of physiological insulin fluctuations possible.

    View details for DOI 10.1038/s41467-022-34778-5

    View details for PubMedID 36400792

  • A Photoresponsive Intramolecular Triplex Motif That Enables Rapid and Reversible Control of Aptamer Binding Activity. ACS nano Trinh, T., Thompson, I. A., Clark, F., Remington, J. M., Eisenstein, M., Li, J., Soh, H. T. 2022


    DNA switches that can change conformation in response to certain wavelengths of light could enable rapid and noninvasive control of chemical processes for a wide range of applications. However, most current photoresponsive DNA switches are limited by either irreversible switching or reversible switching with impractically slow kinetics. Here, we report the design of an intramolecular triplex photoswitch (TPS) design based on single-stranded DNA that undergoes rapid and reversible photoswitching between folded and unfolded states through isomerization of internal azobenzene modifications. After optimizing the performance of our photoswitch design, we used molecular dynamics simulations to reveal how individual azobenzenes contribute to the stabilization or destabilization of the triplex depending on their photoisomerization state. By coupling our TPS to an existing aptamer, we can reversibly modulate its binding affinity with less than 15 s of UV light exposure. We further demonstrate reproducible shifting in affinity over multiple cycles of UV and blue light irradiation without substantial photobleaching.

    View details for DOI 10.1021/acsnano.2c05010

    View details for PubMedID 36094303

  • Rational design of aptamer switches with programmable pH response. Nature communications Thompson, I. A., Zheng, L., Eisenstein, M., Soh, H. T. 2020; 11 (1): 2946


    Aptamer switches that respond sensitively to pH could enhance control over molecular devices, improving their diagnostic and therapeutic efficacy. Previous designs have inserted pH-sensitive DNA motifs into aptamer sequences. Unfortunately, their performance was limited by the motifs' intrinsic pH-responses and could not be tuned to operate across arbitrary pH ranges. Here, we present a methodology for converting virtually any aptamer into a molecular switch with pH-selective binding properties - in acidic, neutral, or alkaline conditions. Our design inserts two orthogonal motifs that can be manipulated in parallel to tune pH-sensitivity without altering the aptamer sequence itself. From a single ATP aptamer, we engineer pH-controlled target binding under diverse conditions, achieving pH-induced selectivity in affinity of up to 1,000-fold. Importantly, we demonstrate the design of tightly regulated aptamers with strong target affinity over only a narrow pH range. Our approach offers a highly generalizable strategy for integrating pH-responsiveness into molecular devices.

    View details for DOI 10.1038/s41467-020-16808-2

    View details for PubMedID 32522989

  • Independent control of the thermodynamic and kinetic properties of aptamer switches. Nature communications Wilson, B. D., Hariri, A. A., Thompson, I. A., Eisenstein, M. n., Soh, H. T. 2019; 10 (1): 5079


    Molecular switches that change their conformation upon target binding offer powerful capabilities for biotechnology and synthetic biology. Aptamers are useful as molecular switches because they offer excellent binding properties, undergo reversible folding, and can be engineered into many nanostructures. Unfortunately, the thermodynamic and kinetic properties of the aptamer switches developed to date are intrinsically coupled, such that high temporal resolution can only be achieved at the cost of lower sensitivity or high background. Here, we describe a design strategy that decouples and enables independent control over the thermodynamics and kinetics of aptamer switches. Starting from a single aptamer, we create an array of aptamer switches with effective dissociation constants ranging from 10 μM to 40 mM and binding kinetics ranging from 170 ms to 3 s. Our strategy is broadly applicable to other aptamers, enabling the development of switches suitable for a diverse range of biotechnology applications.

    View details for DOI 10.1038/s41467-019-13137-x

    View details for PubMedID 31699984