3 research outputs found
A Proposed Mechanism of the Influence of Gold Nanoparticles on DNA Hybridization
A combination of gold nanoparticles (AuNPs) and nucleic acids has been used in biosensing applications. However, there is a poor fundamental understanding of how gold nanoparticle surfaces influence the DNA hybridization process. Here, we measured the rate constants of the hybridization and dehybridization of DNA on gold nanoparticle surfaces to enable the determination of activation parameters using transition state theory. We show that the target bases need to be detached from the gold nanoparticle surfaces before zipping. This causes a shift of the rate-limiting step of hybridization to the mismatch-sensitive zipping step. Furthermore, our results propose that the binding of gold nanoparticles to the single-stranded DNA segments (commonly known as bubbles) in the duplex DNA stabilizes the bubbles and accelerates the dehybridization process. We employ the proposed mechanism of DNA hybridization/dehybridization to explain the ability of 5 nm diameter gold nanoparticles to help discriminate between single base-pair mismatched DNA molecules when performed in a NanoBioArray chip. The mechanistic insight into the DNA–gold nanoparticle hybridization/dehybridization process should lead to the development of new biosensors
Dip-in Indicators for Visual Differentiation of Fuel Mixtures Based on Wettability of Fluoroalkylchlorosilane-Coated Inverse Opal Films
We have developed the dip-in indicator
based on the inverse opal
film (IOF) for visual differentiation of organic liquid mixtures,
such as oil/gasoline or ethanol/gasoline fuel mixtures. The IOF consists
of a three-dimensional porous structure with a highly ordered periodic
arrangement of nanopores. The specularly reflected light at the interface
of the nanopores and silica walls contributes to the structural color
of the IOF film. This color disappears when the nanopores are infiltrated
by a liquid with a similar refractive index to silica. The disappearance
of the structural color provides a means to differentiate various
liquid fuel mixtures based on their wettability of the nanopores in
the IOF-based indicators. For differentiation of various liquid mixtures,
we tune the wettability threshold of the indicator in such a way that
it is wetted (color disappears) by one liquid but is not wetted by
the other (color remains). Although colorimetric differentiation of
liquids based on IOF wettability has been reported, differentiation
of highly similar liquid mixtures require complicated readout approaches.
It is known that the IOF wettability is controlled by multiple surface
properties (e.g., oleophobicity) and structural properties (e.g.,
neck angle and film thickness) of the nanostructure. Therefore, we
aim to exploit the combined tuning of these properties for differentiation
of fuel mixtures with close compositions. In this study, we have demonstrated
that, for the first time, the IOF-based dip-in indicator is able to
detect a slight difference in the fuel mixture composition (i.e.,
0.4% of oil content). Moreover, the color/no-color differentiation
platform is simple, powerful, and easy-to-read. This platform makes
the dip-in indicator a promising tool for authentication and determination
of fuel composition at the point-of-purchase or point-of-use
Fotografia B221
The
front-line treatment for adult acute myeloid leukemia (AML)
is anthracycline-based combination chemotherapy. However, treatment
outcomes remain suboptimal with relapses frequently observed. Among
the mechanisms of treatment failure is multidrug resistance (MDR)
mediated by the ABCB1, ABCC1, and ABCG2 drug-efflux transporters.
Although genetic and phenotypic heterogeneity between leukemic blast
cells is a well-recognized phenomenon, there remains minimal data
on differences in MDR activity at the individual cell level. Specifically,
functional assays that can distinguish the variability in MDR activity
between individual leukemic blasts are lacking. Here, we outline a
new dielectrophoretic (DEP) chip-based assay. This assay permits measurement
of drug accumulation in single cells, termed same-single-cell analysis
in the accumulation mode (<i>SASCA-A</i>). Initially, the
assay was optimized in pretherapy samples from 20 adults with AML
whose leukemic blasts had MDR activity against the anthracyline daunorubicin
(DNR) tested using multiple MDR inhibitors. Parameters tested were
initial drug accumulation, time to achieve signal saturation, fold-increase
of DNR accumulation with MDR inhibition, ease of cell trapping, and
ease of maintaining the trapped cells stationary. This enabled categorization
into leukemic blast cells with MDR activity (MDR<sup>+</sup>) and
leukemic blast cells without MDR activity (MDR<sup>–ve</sup>). Leukemic blasts could also be distinguished from benign white
blood cells (notably these also lacked MDR activity). MDR<sup>–ve</sup> blasts were observed to be enriched in samples taken from patients
who went on to enter complete remission (CR), whereas MDR<sup>+</sup> blasts were frequently observed in patients who failed to achieve
CR following front-line chemotherapy. However, pronounced variability
in functional MDR activity between leukemic blasts was observed, with
MDR<sup>+</sup> cells not infrequently seen in some patients that
went on to achieve CR. Next, we tested MDR activity in two paired
AML patient samples. Pretherapy samples taken from patients that achieved
CR to front-line chemotherapy were compared with samples taken at
time of subsequent relapse. MDR<sup>+</sup> cells were frequently
observed in leukemic blast cells in both pretherapy and relapsed samples,
consistent with MDR as a mechanism of relapse in these patients. We
demonstrate the ability of a new DEP microfluidic chip-based assay
to identify heterogeneity in MDR activity in leukemic blasts. The
test provides a platform for future studies to characterize the mechanistic
basis for heterogeneity in MDR activity at the individual cell level