Topology Evolution and Gelation Mechanism of Agarose Gel

Xiong, Jun-Ying; Narayanan, Janaky; Liu, Xiang Yang; Chong, Tan Kok; Chen, Shing Bor; Chung, Tai‐Shung

doi:10.1021/jp044473u

Cited by 184 publications

(153 citation statements)

References 32 publications

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“…The gelation temperature of agar is primarily decided by the methoxy content of the material. Agar sols form thermo-reversible physical gels with the constituent unit being anti-symmetric double helices [22,23].…”

Section: Simple Coacervationmentioning

confidence: 99%

Coacervation in Biopolymers

Rawat¹

2014

J Phys Chem Biophys

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Polyelectrolyte charge; Ionic strength; Surface patch binding; Viscoelastic behavior and internal structure IntroductionCoacervation: Coacervation is a thermodynamic transition which allows a homogeneous solution of charged macroions to undergo liquidliquid phase separation, giving rise to a polymer-rich dense phase coexisting with its supernatant. These two liquid phases are immiscible but are thermodynamically compatible. The polymer-rich dense phase is often called the coacervate. Structurally it lies between the crystalline and liquid phases. Thus, it can bear intermediate range structural order and can be referred to as a mesophase. Coacervation has been mostly studied in aqueous solutions of charged synthetic or biological macromolecules in the past. In particular, protein-polysaccharide and protein-protein coacervates have attracted much attention because of their inherent potential in generating new biomaterials. In addition, such studies provide basic understanding of specific and non-specific interactions operating between complementary polyelectrolytes [1-6] or polyelectrolyte-polyampholyte [7][8][9][10][11][12][13][14][15] pairs. Normally, polysaccharides are strong polyelectrolytes whereas proteins, in addition, can be polyampholytes. Hence, the association problem reduces to that of the general study of interaction between polyelectrolyte (PE) and polyampholyte (PA) molecules [6,16]. A recent review encapsulates many of the anomalous as well as the salient features of protein-polyelectrolyte interactions [1] The phenomenon of protein based coacervates, formed of strong electrostatic interactions, has been reported for β-lactoglobulin-gum Arabic [7,8] [17]. The diversity of material properties associated with coacervates can be gauged from the fact that β-lactoglobulin-gum arabic coacervates were found to be associated with vescicular to sponge-like internal structure whereas whey protein-gum arabic coacervate was observed to be a highly concentrated (melt-like) phase. In contrast, *Corresponding author: Kamla Rawat, Special Center for Nanosciences, Jawaharlal Nehru University, New Delhi 110067, India, Tel: +91 11 2670 4699; Fax: +91 11 2674 1837; E-mail: kamla.jnu@gmail.com β-lactoglobulin-pectin coacervates were found to be a heterogeneous phase comprising of pectin networks with protein domains forming the junction points [17]. It has been shown that a polyelectrolyte, DNA and a polyampholyte, gelatin can undergo associative interaction and form complex coacervates with interesting thermal properties [15]. Further, it has been realized that in a class of systems coacervation transition is governed by surface selective patch binding even though both the polyions carry similar net charge [11,18,19]. In particular, in SPB interactions complementary polyions (normally a PA-PE pair) seek oppositely charged patches to bind overcoming the repulsion occurring between similarly charged surface patches. This is often referred to as binding on the wrong side of pH.The following provides a brief structural i...

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Section: Simple Coacervationmentioning

confidence: 99%

Coacervation in Biopolymers

Rawat¹

2014

J Phys Chem Biophys

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“…16 These nanochannels provide pathways that gold particles can occupy. The AFM image clearly shows that the number of particles is ϳ50 in a 200ϫ 200 nm 2 area, similar to the model of Maher et al 9 This turns out to be an optimal number of particles/area for an enhanced internal plasmon resonance to yield a high SERS activity.…”

Section: Fig 2 ͑A͒ Absorption Spectra Ofmentioning

confidence: 99%

Agarose-stabilized gold nanoparticles for surface-enhanced Raman spectroscopic detection of DNA nucleosides

Kattumuri

Chandrasekhar

Guha

et al. 2006

Applied Physics Letters

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We present surface-enhanced Raman scattering ͑SERS͒ studies of DNA nucleosides using biologically benign agarose-stabilized gold nanoparticles ͑AAuNP͒. We compare the SERS activity of nucleosides with AAuNP to that of commercially obtained citrate-stabilized gold nanoparticles and find the SERS activity to be an order of magnitude higher with AAuNP. The higher SERS activity is explained in terms of the agarose matrix, which provides pathways for the gold nanoparticles to have distinct arrangements that result in stronger internal plasmon resonances. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2192573͔ Nanoparticle research is at the leading edge of a rapidly growing technology in nanoscale, medical, and biological sciences. Advances in the preparation of gold and silver nanoparticles have rekindled interest in surface-enhanced Raman scattering ͑SERS͒ as a means to detect single molecules and to identify their chemical structure; SERS now provides a potential for label-free detection of biomolecules. 1 Significant efforts focus on the binding of oligonucleosides to metal surfaces and colloids for applications that include multiplexed DNA detection technology, 2 rapid sequencers based on SERS from single DNA bases, 3 and real-time DNA detection methodology. 4 In this work we use biologically benign agarosestabilized gold nanoparticles for the detection of micromolar concentrations of DNA nucleosides using SERS. This process for gold nanoparticle production allows for systematic variation in nanoparticulate size via changes in the stoichiometry of the precursors. Agarose-stabilized gold nanoϽ-?Ͼ particles have several advantages over the conventional citrate reduction technique of preparing nanoparticles; agarose, which is a biologically benign medium, ensures nondegradation of probe molecules. Furthermore, its gelation properties facilitate easy film formation for on-chip biosensing applications.Although the relative importance of various mechanisms for SERS is still debated, electromagnetic enhancement due to the local field of surface plasmons excited by the incident light is considered to have a major contribution. 3 A major enhancement occurs for aggregated colloidal silver or gold nanoparticles ͑induced by halide ions͒, where plasmon resonances can result in a strong confinement of the optical fields between the aggregated particles. 3 Another mechanism involves dynamical charge transfer between a nanoparticle and a molecule, or a resonance Raman effect due to a chargetransfer electronic transition. The magnitudes of such chemical enhancement have been estimated to reach factors only of the order of 10-100. 5 It was pointed out by Haslett et al. that a chemical contribution to SERS almost always exists for chemisorbed molecules but that alone cannot explain the existence of SERS. 6 Estimates of enhancement factors based on the comparison of SERS intensity with normal Raman intensity are usually tricky since the number of target molecules that contribute to the SERS signal is usually unknown. The lar...

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“…[8][9][10][11] There have also been studies on the rheological evolution of agarose 10,11 where its rheological changes have been linked with the micro/meso-scale network properties of the gel by analyzing the correlation length or the hydrodynamic mesh size. 8,9 However, studies that link structural changes at the molecular level to the rheological response have not been thoroughly pursued and, as a result, a mechanistic understanding of this macroscopic behavior from a molecular point of view is very limited.…”

Section: Introductionmentioning

confidence: 99%

“…12 Monitoring changes in the structure of water during gelation in agarose systems has been illustrated previously 12 where the high frequency (2700-3800 cm −1 ) region was observed for intramolecular O-H stretching vibrations. However, limited studies have been carried out on exploring effects on the timescale of picoseconds 9,11 which is relevant for intermolecular modes of a hydrogen bonded water network and is the time scale of hydrogen bond formation and cleavage. 13,14 To explore these processes at this timescale, analysis of the low-frequency region (50-300 cm −1 ) of the spectrum is required but has been difficult to obtain due to historic limitations in instrumentation that resulted from measuring Raman spectra close to the exciting line.…”

Section: Introductionmentioning

confidence: 99%

A novel combination of DLS-optical microrheology and low frequency Raman spectroscopy to reveal underlying biopolymer self-assembly and gelation mechanisms

Amin¹,

Blake²,

Kenyon³

et al. 2014

The Journal of Chemical Physics

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The connectivity between gelation and increasing water confinement and structuring within nanopores of a thermally induced gel is demonstrated for the first time through low frequency Raman spectroscopy and optical microrheology measurements. Specifically, the work confirms that increased ordering of individual water molecules can be observed during the gelation of agarose upon cooling. More importantly, it illustrates the ability of the two techniques to provide new insights and a more direct link between intermolecular interactions/microstructure and evolving rheological response in gelling systems.

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Topology Evolution and Gelation Mechanism of Agarose Gel

Cited by 184 publications

References 32 publications

Coacervation in Biopolymers

Coacervation in Biopolymers

Agarose-stabilized gold nanoparticles for surface-enhanced Raman spectroscopic detection of DNA nucleosides

A novel combination of DLS-optical microrheology and low frequency Raman spectroscopy to reveal underlying biopolymer self-assembly and gelation mechanisms

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