3 research outputs found
Amplifying the Macromolecular Crowding Effect Using Nanoparticles
The melting temperature (<i>T</i><sub>m</sub>) of DNA
is affected not only by salt but also by the presence of high molecular
weight (MW) solutes, such as polyethylene glycol (PEG), acting as
a crowding agent. For short DNAs in a solution of low MW PEGs, however,
the change of excluded volume upon melting is very small, leading
to no increase in <i>T</i><sub>m</sub>. We demonstrate herein
that by attaching 12-mer DNAs to gold nanoparticles, the excluded
volume change was significantly increased upon melting, leading to
increased <i>T</i><sub>m</sub> even with PEG 200. Larger
AuNPs, higher MW PEGs, and higher PEG concentrations show even larger
effects in stabilizing the DNA. This study reveals a unique and fundamental
feature at nanoscale due to geometric effects. It also suggests that
weak interactions can be stabilized by a combination of polyvalent
binding and the enhanced macromolecular crowding effect using nanoparticles
Aptamer-Functionalized Hydrogel Microparticles for Fast Visual Detection of Mercury(II) and Adenosine
With a low optical background, high loading capacity,
and good
biocompatibility, hydrogels are ideal materials for immobilization
of biopolymers to develop optical biosensors. We recently immobilized
mercury and lead binding DNAs within a monolithic gel and demonstrated
ultrasensitive visual detection of these heavy metals. The high sensitivity
was attributed to the enrichment of the analytes into the gels. The
signaling kinetics was slow, however, taking about 1 h to obtain a
stable optical signal because of a long diffusion distance. In this
work, we aim to understand the analyte enrichment process and improve
the signaling kinetics by preparing hydrogel microparticles. DNA-functionalized
gel beads were synthesized using an emulsion polymerization technique
and most of the beads were between 10 and 50 μm. Acrydite-modified
DNA was incorporated by copolymerization. Visual detection of 10 nM
Hg<sup>2+</sup> was still achieved and a stable signal was obtained
in just 2 min. The gel beads could be spotted to form a microarray
and dried for storage. A new visual sensor for adenosine was designed
and immobilized within the gel beads. The adenosine aptamer binds
its target about 1000-fold less tightly compared to the mercury binding
DNA, allowing a comparison to be made on analyte enrichment by aptamer-functionalized
hydrogels
Instantaneous Attachment of an Ultrahigh Density of Nonthiolated DNA to Gold Nanoparticles and Its Applications
The last 16 years have witnessed the landmark development
of polyvalent
thiolated DNA-functionalized gold nanoparticles (AuNP's) possessing
striking properties within the emerging field of nanobiotechnology.
Many novel properties of this hybrid nanomaterial are attributed to
the dense DNA shell. However, the question of whether nonthiolated
polyvalent DNA–AuNP could be fabricated with a high DNA density
and properties similar to those of its thiolated counterpart has not
been explored in detail. Herein, we report that by simply tuning the
pH of the DNA–AuNP mixture an ultrahigh capacity of nonthiolated
DNA can be conjugated to AuNP's in a few minutes, resulting in polyvalent
DNA–AuNP conjugates with cooperative melting behavior, a typical
property of polyvalent thiolated DNA-functionalized AuNP's. With this
method, large AuNP's (e.g., 50 nm) can be functionalized to achieve
the colorimetric detection of sub-nanometer DNA. Furthermore, this
fast, stable DNA loading was employed to separate AuNP's of different
sizes. We propose that a large fraction of the attached DNAs are adsorbed
via one or a few terminal bases to afford the high loading capacity
and the ability to hybridize with the complementary DNA. This discovery
not only offers a time- and cost-effective way to functionalize AuNP's
with a high density of nonthiolated DNA but also provides new insights
into the fundamental understanding of how DNA strands with different
sequences interact with AuNP's