IEE proceedings. Nanobiotechnology最新文献

Measurements are reported of the main factors, namely the AC voltage frequency and magnitude, that were observed to influence the number of cells destroyed during dielectrophoresis (DEP) experiments on Jurkat T cells and HL60 leukemia cells. Microelectrodes of interdigitated and quadrupolar geometries were used. A field-frequency window has been identified that should be either avoided or utilised, depending on whether or not cell damage is to be minimised or is a desired objective. The width and location of this frequency window depends on the cell type, as defined by cell size, morphology and dielectric properties, and is bounded by two characteristic frequencies. These frequencies are the DEP cross-over frequency, where a cell makes the transition from negative to positive DEP, and a frequency determined by the time constant that controls the frequency dependence of the field induced across the cell membrane. When operating in this frequency window, and for the microelectrode designs used in this work, cell destruction can be minimised by ensuring that cells are not directed by positive DEP to electrode edges where fields exceeding 30-40 kV/m are generated. Alternatively, this field-frequency window can be exploited to selectively destroy specific cell types in a cell mixture.

A type of well-based assay that uses a laminated three-dimensional electrode design to characterise the effects of different drugs on red blood cells using dielectrophoresis is presented. The capability of the system to determine the effects of chemical agents on the electrophysiology of red blood cells is demonstrated using saponin and valinomycin as two examples of drugs that can penetrate the cell membrane and therefore change the dielectric properties of the cell. Light intensity changes are measured in the well over a period of time at various frequencies and the dielectric properties of the cells determined using an ellipsoidal multi-shell model. It is shown that the laminated electrode permits a high degree of automation and thus a high number of parallel experiments, which reduces both the time and effort needed to examine differences between populations of red blood cells. The technique is directly compatible with the industry-standard 1536 well-plate analysis technique.

Reverse miniemulsions, emulsions of droplets of size 200 nm-1 microm of a polar liquid dispersed in an apolar continuous liquid phase, exhibit strong electrokinetic responses in low-frequency electric fields. The electrokinetic behaviour of a reverse miniemulsion, previously developed for use as electronic paper, has been investigated under static and flow conditions, in uniform and non-uniform electric fields. Results reveal that when using frequencies lower than 10 Hz strong aggregation of the droplets occurs. In uniform electric fields, under static conditions, droplets reversibly aggregate into honeycomb-like or irregular aggregates. Under flow conditions, droplets aggregate into approximately equidistant streams. In non-uniform electric fields the droplets reversibly aggregate in high-field regions, and can be guided along regions of high field strength in a flow. The potential of the technique for the formation of structured materials is discussed.

Microsphere-based biosensors have been attracting the attention of the photonics community due to their high sensitivity, selectivity and implementation. Microspheres, with their high quality-factor (Q-factor) morphology dependent resonances, are very sensitive to refractive index and size changes. The perturbation of the microsphere morphology dependent resonances can be used for the detection of biomolecules. Adsorption of different biomolecules on the surface of microspheres causes a change of effective size and refractive index leading to the shift of resonance wavelengths. A biosensor, based on this phenomenon, can detect a single molecule sensitively depending on the configuration that needs to be designed and optimised. Silica with a refractive index of 1.5, which is very close to that of bimolecular agents, is a suitable photonic material to use for biosensing applications. The transverse electric and transverse magnetic elastic scattering spectra at 90 degrees and 0 degrees are calculated at 1.55 microm with the associated shifts after adding a layer on it. 90 degrees scattering is used to monitor the scattered signal, whereas 0 degrees scattering is used to monitor the transmission signal.

The effect of applying an external load to actin filaments moving in the in vitro motility assay is studied. Bead-tailed actin filaments were made by polymerising actin onto 2.8 microm diameter Dynabeads conjugated with gelsolin-G actin. These were introduced into a motility cell coated with 100 microg/ml rabbit fast skeletal myosin in the presence of ATP and 0.5% methylcellulose. The motility cell was inserted between the pole-pieces of an electromagnet and the fluorescent beads and filaments were observed. The force-current relationship of the electromagnet was determined from the velocity of free beads in viscous solution and Stokes' equation. The magnet produced up to 6 pN force on the Dynabeads at 1 A. Many bead-tailed actin filaments stuck to the surface, but the beads that did move moved at the same speed as unloaded f-actin in the same cell. Bead-tailed filaments slowed down under an increasing magnetic load, eventually stalled and then slid backward under increasing load before detaching from the surface. Single-filament force-velocity curves were constructed and a stalling force of about 0.6 pN/mm of actin filament estimated.

Surfactant-coated amorphous titania nanospheres have been synthesised using templating 'water-in-supercritical carbon dioxide' emulsion droplets; the process represents a clean and controlled method for the manufacture of high-purity nanoparticles.

A novel polymer-coated adsorbent (subtractive adsorbent) has been manufactured and evaluated for the recovery of nanoparticle bioproducts. The core principle was to coat inert macroporous polymers (e.g. agarose) upon adsorbent beads of varied ligands. Here BSA nanoparticles, with an average nanoparticle diameter 95 nm, were fabricated and selected as feedstock for the demonstration of the principle. The adsorption of a mixture of fluorescently labelled BSA solution and BSA nanoparticles was investigated in a batch binding experiment upon polymer-coated Streamline DEAE and visualised by laser scanning confocal microscopy. The mechanistic design of such adsorbents and their basic application for the recovery of target nano-bioproducts from complex feedstock is strongly indicated.

The encapsulation of molecular species has received considerable attention in recent years. Polymers, dendrimers and microemulsions along with other systems have been used as precursors for the synthesis of encapsulating agents. Especially important in this field is the core-shell architecture. This structure offers the encapsulated species an extra level of protection due to the presence of a shell, covering the interior of a capsule. Dyes, porphyrines, drugs, cells and other active agents have been successfully encapsulated, and the host-guest interaction has been studied by various experimental techniques. A review is new provided of the progress made in this field in the last several years is presented. Different classes of synthetic approaches are presented and resulting encapsulation studies are summarised. An approach to the encapsulation of dansyl chloride dye in core-shell nanoparticles is also presented.

The synthesis of poly(ethylene glycol)-b-poly(2-N,N-dimethylaminoethylmethacrylate) processing an acetal group at the PEG chain end (acetal-PEGPAMA) is reported. The obtained acetal-PEGPAMA block copolymer was found to reduce tetrachloroauric acid at room temperature to produce gold nanoparticles. The size of these nanoparticles was controllable in the range of 6 to 13 nm by changing the initial Au3+: polymer ratio. In addition to the reduction of tetrachloroauric acid, acetal-PEGPAMA bonds on the surface of the obtained gold nanoparticles to improve their dispersion stability in an aqueous medium even at a salt concentration as high as two. Biotinyl-PEGPAMA-anchored gold nanoparticles undergo specific aggregation in the presence of streptavidin thereby revealing their promising utility as colloidal sensing systems for use in biological systems. Biotin-PEGPAMA can also be utilised for the preparation of a functionally PEGylated quantum dot (QD). When CdCl2 and Na2S were mixed in aqueous media in the presence of the biotin-PEGPAMA, a CdS QD with an approximately 5 nm size was prepared. The polyamine segment was anchored onto the surface of the formed CdS nanoparticle, whereas the PEG segment was tethered onto the surface to form a hydrophilic palisade, thus improving the dispersion stability in aqueous media even under a high salt concentration condition. An effective fluorescent resonance energy transfer (FRET) was observed by the specific interaction of the biotin-PEGPAMA stabilised CdS QD with TexasRed-labelled streptavidin with the physiological ionic strength of 0.15 M. The extent of the energy transfer was in proportion to the concentration of the TexasRed-streptavidin. This FRET system using the PEGylated CdS QD coupled with fluorescent-labelled protein can be utilised as a highly sensitive bioanalytical system.

The development of up-converting phosphor reporter particles has added a powerful tool to modern detection technologies. Carefully constructed phosphor reporters have core-shell structures with surface functional groups suitable for standard bio-conjugations. These reporters are chemically stable, possess the unique property of infrared up-conversion, and are readily detected. In contrast to conventional fluorescent reporters, up-converting phosphor particles do not bleach and allow permanent excitation with simultaneous signal integration. A large anti-Stokes shift (up to 500 nm) separates discrete emission peaks from the infrared excitation source. Along with the unmatched contrast in biological specimens due to the absence of autofluorescence upon infrared excitation, up-converting phosphor technology (UPT) has unique properties for highly-sensitive particle-based assays. The production and characteristics of UPT reporter particles as well as their application in various bioassays is reviewed.