17 research outputs found
Programmable pH-Triggered DNA Nanoswitches
We have designed programmable DNA-based
nanoswitches whose closing/opening
can be triggered over specific different pH windows. These nanoswitches
form an intramolecular triplex DNA structure through pH-sensitive
parallel Hoogsteen interactions. We demonstrate that by simply changing
the relative content of TAT/CGC triplets in the switches, we can rationally
tune their pH dependence over more than 5 pH units. The ability to
design DNA-based switches with tunable pH dependence provides the
opportunity to engineer pH nanosensors with unprecedented wide sensitivity
to pH changes. For example, by mixing in the same solution three switches
with different pH sensitivity, we developed a pH nanosensor that can
precisely monitor pH variations over 5.5 units of pH. With their fast
response time (<200 ms) and high reversibility, these pH-triggered
nanoswitches appear particularly suitable for applications ranging
from the real-time monitoring of pH changes in vivo to the development
of pH sensitive smart nanomaterials
Programmable Quantitative DNA Nanothermometers
Developing molecules,
switches, probes or nanomaterials that are able to respond to specific
temperature changes should prove of utility for several applications
in nanotechnology. Here, we describe bioinspired strategies to design
DNA thermoswitches with programmable linear response ranges that can
provide either a precise ultrasensitive response over a desired, small
temperature interval (Ā±0.05 Ā°C) or an extended linear response
over a wide temperature range (e.g., from 25 to 90 Ā°C). Using
structural modifications or inexpensive DNA stabilizers, we show that
we can tune the transition midpoints of DNA thermometers from 30 to
85 Ā°C. Using multimeric switch architectures, we are able to
create ultrasensitive thermometers that display large quantitative
fluorescence gains within small temperature variation (e.g., >
700% over 10 Ā°C). Using a combination of thermoswitches of different
stabilities or a mix of stabilizers of various strengths, we can create
extended thermometers that respond linearly up to 50 Ā°C in temperature
range. Here, we demonstrate the reversibility, robustness, and efficiency
of these programmable DNA thermometers by monitoring temperature change
inside individual wells during polymerase chain reactions. We discuss
the potential applications of these programmable DNA thermoswitches
in various nanotechnology fields including cell imaging, nanofluidics,
nanomedecine, nanoelectronics, nanomaterial, and synthetic biology
Engineering Biosensors with Extended, Narrowed, or Arbitrarily Edited Dynamic Range
Biomolecular recognition has long been an important theme
in artificial
sensing technologies. A current limitation of protein- and nucleic
acid-based recognition, however, is that the useful dynamic range
of single-site binding typically spans an 81-fold change in target
concentration, an effect that limits the utility of biosensors in
applications calling for either great sensitivity (a steeper relationship
between target concentration and output signal) or the quantification
of more wide-ranging concentrations. In response, we have adapted
strategies employed by nature to modulate the inputāoutput
response of its biorecognition systems to rationally edit the useful
dynamic range of an artificial biosensor. By engineering a structure-switching
mechanism to tune the affinity of a receptor molecule, we first generated
a set of receptor variants displaying similar specificities but different
target affinities. Using combinations of these receptor variants (signaling
and nonsignaling), we then rationally extended (to 900000-fold), narrowed
(to 5-fold), and edited (three-state) the normally 81-fold dynamic
range of a representative biosensor. We believe that these strategies
may be widely applicable to technologies reliant on biorecognition
Biomolecular Steric Hindrance Effects Are Enhanced on Nanostructured Microelectrodes
The availability
of rapid approaches for quantitative detection
of biomarkers would drastically impact global health by enabling decentralized
disease diagnosis anywhere that patient care is administered. A promising
new approach, the electrochemical steric hindrance hybridization assay
(eSHHA) has been introduced for quantitative detection of large proteins
(e.g., antibodies) with a low nanomolar detection limit within 10
min. Here, we report the use of a nanostructured microelectrode (NME)
platform for eSHHA that improves the performance of this approach
by increasing the efficiency and kinetics of DNA hybridization. We
demonstrated that eSHHA on nanostructured microelectrodes leverages
three effects: (1) steric hindrance effects at the nanoscale, (2)
a size-dependent hybridization rate of DNA complexes, and (3) electrode
morphology-dependent blocking effects. As a proof of concept, we showed
that the sensitivity of eSHHA toward a model antibody is enhanced
using NMEs as scaffolds for this reaction. We improved the detection
limit of eSHHA, taking advantage of nanostructured surfaces to allow
the use of longer capture strands for detection of proteins. Finally,
we concluded that using the eSHHA approach in conjunction with nanostructured
microelectrodes is an advantageous alternative to conventional macroelectrodes
as the sensitivity and detection limits are enhanced
General Strategy to Introduce pH-Induced Allostery in DNA-Based Receptors to Achieve Controlled Release of Ligands
Inspired
by naturally occurring pH-regulated receptors, here we propose a rational
approach to introduce pH-induced allostery into a wide range of DNA-based
receptors. To demonstrate this we re-engineered two model DNA-based
probes, a molecular beacon and a cocaine-binding aptamer, by introducing
in their sequence a pH-dependent domain. We demonstrate here that
we can finely tune the affinity of these model receptors and control
the load/release of their specific target molecule by a simple pH
change
General Strategy to Introduce pH-Induced Allostery in DNA-Based Receptors to Achieve Controlled Release of Ligands
Inspired
by naturally occurring pH-regulated receptors, here we propose a rational
approach to introduce pH-induced allostery into a wide range of DNA-based
receptors. To demonstrate this we re-engineered two model DNA-based
probes, a molecular beacon and a cocaine-binding aptamer, by introducing
in their sequence a pH-dependent domain. We demonstrate here that
we can finely tune the affinity of these model receptors and control
the load/release of their specific target molecule by a simple pH
change
Thermodynamic Basis for Engineering High-Affinity, High-Specificity Binding-Induced DNA Clamp Nanoswitches
Naturally occurring chemoreceptors almost invariably employ structure-switching mechanisms, an observation that has inspired the use of biomolecular switches in a wide range of artificial technologies in the areas of diagnostics, imaging, and synthetic biology. In one mechanism for generating such behavior, clamp-based switching, binding occurs <i>via</i> the clamplike embrace of two recognition elements onto a single target molecule. In addition to coupling recognition with a large conformational change, this mechanism offers a second advantage: it improves both affinity and specificity simultaneously. To explore the physics of such switches we have dissected here the thermodynamics of a clamp-switch that recognizes a target DNA sequence through both WatsonāCrick base pairing and triplex-forming Hoogsteen interactions. When compared to the equivalent linear DNA probe (which relies solely on WatsonāCrick interactions), the extra Hoogsteen interactions in the DNA clamp-switch increase the probeās affinity for its target by ā¼0.29 Ā± 0.02 kcal/mol/base. The Hoogsteen interactions of the clamp-switch likewise provide an additional specificity check that increases the discrimination efficiency toward a single-base mismatch by 1.2 Ā± 0.2 kcal/mol. This, in turn, leads to a 10-fold improvement in the width of the āspecificity windowā of this probe relative to that of the equivalent linear probe. Given these attributes, clamp-switches should be of utility not only for sensing applications but also, in the specific field of DNA nanotechnology, for applications calling for a better control over the building of nanostructures and nanomachines
A Highly Selective Electrochemical DNA-Based Sensor That Employs Steric Hindrance Effects to Detect Proteins Directly in Whole Blood
Here
we describe a highly selective DNA-based electrochemical sensor that
utilizes steric hindrance effects to signal the presence of large
macromolecules in a single-step procedure. We first show that a large
macromolecule, such as a protein, when bound to a signaling DNA strand
generates steric hindrance effects, which limits the ability of this
DNA to hybridize to a surface-attached complementary strand. We demonstrate
that the efficiency of hybridization of this signaling DNA is inversely
correlated with the size of the molecule attached to it, following
a semilogarithmic relationship. Using this steric hindrance hybridization
assay in an electrochemical format (eSHHA), we demonstrate the multiplexed,
quantitative, one-step detection of various macromolecules in the
low nanomolar range, in <10 min directly in whole blood. We discuss
the potential applications of this novel signaling mechanism in the
field of point-of-care diagnostic sensors
Electrochemical DNA-Based Immunoassay That Employs Steric Hindrance To Detect Small Molecules Directly in Whole Blood
The
development of
a universal sensing mechanism for the rapid
and quantitative detection of small molecules directly in whole blood
would drastically impact global health by enabling disease diagnostics,
monitoring, and treatment at home. We have previously shown that hybridization
between a free DNA strand and its complementary surface-bound strand
can be sterically hindered when the former is bound to large antibodies.
Here, we exploit this effect to design a competitive antibody-based
electrochemical assay, called CeSHHA, that enables the quantitative
detection of small molecules directly in complex matrices, such as
whole blood or soil. We discuss the importance of this inexpensive
assay for point-of-care diagnosis and for treatment monitoring applications
Allosterically Tunable, DNA-Based Switches Triggered by Heavy Metals
Here we demonstrate the rational
design of allosterically controllable,
metal-ion-triggered molecular switches. Specifically, we designed
DNA sequences that adopt two low energy conformations, one of which
does not bind to the target ion and the other of which contains mismatch
sites serving as specific recognition elements for mercuryĀ(II) or
silverĀ(I) ions. Both switches contain multiple metal binding sites
and thus exhibit <i>homotropic allosteric</i> (cooperative)
responses. As <i>heterotropic</i> allosteric effectors we
employ single-stranded DNA sequences that either stabilize or destabilize
the nonbinding state, enabling dynamic range tuning over several orders
of magnitude. The ability to rationally introduce these effects into
target-responsive switches could be of value in improving the functionality
of DNA-based nanomachines