Magnetic Biotransport for Gene Therapy
Magnetic nanoparticles are finding increasing use in bioapplications, primarily as carrier particles for biomaterials such as cells, proteins and DNA. In this paper we present a model for predicting the transport and targeting of biofunctional magnetic nanoparticles for the magnetofection process. In magnetofection, magnetic carrier particles with surface-bound gene vectors are magnetically attracted towards host cells for transfection (delivery of the transported DNA into the host cell). In in vitro magnetofection, the carrier particles/DNA are introduced into a host cell culture, where they experience a magnetic transport force, which is produced by a rare-earth magnetic element positioned beneath the culture. Magnetofection has significant advantages over traditional transfection methods: the process time is dramatically reduced, e.g., peak transfection levels can be achieved with a particle/cell incubation time on the order of 10 minutes, as compared to 2-4 hours for standard methods, high transfection rates can be obtained with significantly lower vector doses; an increase in the gene transfer efficiency of up to 5 orders of magnitude can be realized, and gene delivery can be achieved with non-permissive cells. The model developed in this paper provides a fundamental understanding of nanoscale magnetic biotransport, and enables the development and optimization of novel magnetofection systems for in vitro applications.
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LQ11849
See the kinetics of self-assembly of molecules on surfaces
It has been well-known that ammonia molecules on Si surfaces are
self-assembled. The self-assembly has been tentatively or rigorously from
the quantum mechanical calculations considered as a result of the H-bond
interaction between the molecules. However, the atomic structure of the
molecules self-assembled on the surface has been highly controversial to the
surface scientists; the H-bonded linear chain structure is the lowest in
energy, but the zigzag chain structure is more preferential in experiments,
which consists of surprisingly no H-bond. In this paper, we show explicitly
that not only the H-bond but the covalent coordinate bond between the
ammonia molecule and the surface Si atom plays an essential role in the
self-assembly of the molecules. Surface chemical reactions on reactive
surfaces are typically irreversible and thus easily form an in-equilibrium
state. Therefore, searching for the low energy configuration sometimes
conducts us to a wrong conclusion. In order to see the kinetics of the
self-assembly, we investigated the detailed potential energy surfaces from
first-principles, and the experimentally observed zigzag feature is found to
be well described by the kinetics consideration.
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EF10322
Elimination of biosensor fouling using acoustically driven flow field
All transducers used in biological sensing suffer from fouling resulting from non-specific binding of protein molecules to the device surface. Our research group at the Sensors Research Laboratory at University of South Florida has successfully identified a phenomenon which can potentially eliminate biofouling and increase the sensitivity of biosensors. Biosensors typically operate in liquid media for detection of biomarkers. In the current work, using a novel numerical technique as well as experiments, we have identified that fluid motion induced by high intensity sound waves, such as those propagating in these sensors, can lead to the removal of the non-specifically bound proteins thereby eliminating sensor fouling (Figures attached). This phenomenon, known as acoustic streaming, allows sensor re-use while also increasing its sensitivity and reducing the signal-to-noise ratio. We present a computational and experimental study of the acoustic-streaming phenomenon induced biofouling elimination by surface-acoustic-waves (SAWs). The transient solutions generated from the developed coupled-field fluid solid interaction model were utilized to predict trends in acoustic-streaming velocity for varying design parameters such as voltage intensity, device frequency, fluid viscosity and density. The model predictions were utilized to compute the various interaction forces involved and thereby identify the possible mechanisms for removal of non-specifically-bound proteins. Our study indicates that the SAW body force overcomes the adhesive forces of the fouling proteins to the device surface and the fluid-induced drag and lift forces prevent its re-attachment. The streaming velocity fields computed using the finite-element models in conjunction with the proposed mechanism were used to identify the conditions leading to improved removal efficiency. Our research findings have significant implications in designing reusable and highly sensitive biosensors.
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AR10309
A Step Forward
Entanglement is a subtle and eluding property of quantum systems
comprising many parts. Entanglement induces correlations between the
measurable properties of different parts of a quantum system which cannot
be reproduced by any procedure involving only the local operations (LO)
and classical communication (CC) between various parts of any system.
In consonance with this, entanglement in a quantum system cannot increase
(or be created) via LOCC. This principle is connected to another
intriguing property of entanglement: a multipartite quantum system can
get entangled in various inequivalent ways, which cannot be transformed
into each other via LOCC. However, the most intimidating aspect of
entanglement is that it cannot be `built in parts¡|, that is, the
entanglement of N parts is not a sum or a simple function of the
entanglement of M (< N) partite subsystems.
In order to understand and use entanglement and its role in various
quantum phenomena involving many particle systems (eg. quantum phase
transitions, BE condensates etc.) we must be able to say how much
entangled a given quantum system is. In other words, we need a measure for
entanglement in a given system. Such a measure must respect non-increase
of entanglement under LOCC, apart from many other properties. Further, the
computation of entanglement measure should not be formidable. Such a
`good¡| entanglement measure is known only for bipartite pure states and
thanks to Wooters, for all two qubit states. Finally, a good entanglement
measure is expected to be determined experimentally, without prior
knowledge of the system¡|s state. A detailed specification of the state of
a quantum system is a formidable task unless you already know the state.
It is very unlikely that in an actual application, eg. quantum
communication, the intermediate states of the quantum system could be
specified in detail.
In this paper we have proposed a measure of entanglement for N-qubit pure
states (N ¿d 2), which can be experimentally determined, without prior
knowledge of the state. We have proved that this measure has all the
properties expected of a ¡¥good¡| entanglement measure including the above
properties. We have computed this measure for important classes of N-qubit
states like GHZ states, W states and their superposition, as well as for
physical application like 1-D spin chain. We use this measure to follow
the entanglement dynamics of Grover¡|s quantum search algorithm. We hope
that this measure will prove to be useful in quantitative analysis of
entanglement in various applications.
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LL11013E
Chromosomes meeting in the dark
At the onset of meiosis - the specialized cell division required
in sexual reproduction - homologous chromosomes in the cell nucleus
recognize each other at a distance and come in physical contact.
Such a step is crucial for preventing fertility problems, birth
defects and cancer. Yet, the mechanisms of self-recognition and
colocalization remain deeply mysterious.
In this paper, we propose a model describing how DNA binding
molecules guide the long distance interaction of special
chromosome sequences: if molecule concentration exceeds a critical
threshold, they induce a spontaneous recognition and colocalization
of chromosomes, otherwise independently diffusing. By acting on such
a switch, having a thermodynamic origin, the cell can actively
control pair formation and release.
The issue can have also a broader relevance as many other essential
cell processes involve the organization of chromosomes in nuclear
space. The new stochastic regulatory mechanism here described could
be important to those cases as well.
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LQ11849
See the kinetics of self-assembly of molecules on surfaces
It has been well-known that ammonia molecules on Si surfaces are self-assembled. The self-assembly has been tentatively or rigorously from the quantum mechanical calculations considered as a result of the H-bond interaction between the molecules. However, the atomic structure of the molecules self-assembled on the surface has been highly controversial to the surface scientists; the H-bonded linear chain structure is the lowest in energy, but the zigzag chain structure is more preferential in experiments, which consists of surprisingly no H-bond. In this paper, we show explicitly that not only the H-bond but the covalent coordinate bond between the ammonia molecule and the surface Si atom plays an essential role in the self-assembly of the molecules. Surface chemical reactions on reactive surfaces are typically irreversible and thus easily form an in-equilibrium state. Therefore, searching for the low energy configuration sometimes conducts us to a wrong conclusion. In order to see the kinetics of the self-assembly, we investigated the detailed potential energy surfaces from first-principles, and the experimentally observed zigzag feature is found to be well described by the kinetics consideration.
