Early diagnosis of lung cancer by breath analysis using gold nanoparticle sensors

Gold nanoparticles based sensors array in combination with pattern recognition method provide an effective diagnostic tool for lung cancer. This system can distinguish between the order prints of non-small cell lung cancer (NSCLC) and negative control with 100% accuracy. Among other advantages over conventional diagonistic method like GC-MS based systems, this is non-invasive, inexpensive scheme which do not need any preconcentrator and high expertise to use.

Scientists have designed an array of 18 chemiresistors based on functionalized Gold NPs for detecting headspace of NSCLC and the control medium. Each sensor is widely responsive to variety of odorants. Hence, each analyte yields a distinct signature from the array of broadly cross-reactive sensors.Sensors of Gold NPs mostly coated with hydrophobic functionalities that are almost insensitive to water and hence perticularly suitable for breath testing, since exhaled breath contains ~ 80% relative humidity. This journal article further establish that AuNPs sensors can also be used as highly sensitive, simple-to-use tool for understanding the biochemical background of endogenous compound appearing in exhaled breath.

For details, please refer to Small, 2009, 5, No. 22, 2618-2624

Palladium Nanorods with Magnetic Properties

Palladium as free atom has all filled atomic orbitals, hence diamagnetic behavior is observed based on Hund's rule. However, in confined nanoscale systems, more localized electronic states as well as narrower bands are usually supposed to increase the densities of states and lead to the exotic magnetic behavior.

These magnetic behavior can be controlled by changing the shape and size of nano-particles. Studies based on the feasibility of tuning the magnetic property of Pd at the nanoscale is facilitating, both the understanding of fundamental magnetism and the future application of spintronic technology.

Despite all the efforts put by scientific community in this field, it remains a great challenge to achieve shape-controlled synthesis of single crystalline palladium nanostructures in a large scale, particularly the 1D structure.

In a recently published scientific article, authors have successfully demonstrated the synthetic approach toward single crystalline Pd nanorods with a controlled aspect ratio in large quantities via a simple one-pot solution method.They have observed the ferromagnetic properties of Pd nanorods at room temperature, and proved that the onset of ferromagnetic behavior to be highly related to the unique 1D growth behavior.

In a simple solution phase chemistry, through tuning the molar ratio of two surfactants, cetyltrimethylammonium bromide (CTAB) and poly(vinyl pyrrolidone) (PVP), single crystalline palladium nanorods with different aspect ratios have been synthesized in large quantities.

The introduction of cosurfactant CTAB is critical to the growth of palladium nanorods. Its headgroup CTA+ and counterion Br- anion act as stabilizing species and etchant, respectively.

Compared with PVP-capped Pd nanoparticles, the Pd nanorods show a ferromagnetism behavior at 5 and 300 K. Pd nanorods at different temperatures were measured by SQUID. It has been concluded that a permanent magnetic moment is an intrinsic property of a Pd nanorod based on EELS study and M-H curve of PVP.

Although the detailed mechanism is still elusive, the morphology- related magnetism is believed to be meaningful in the exploration of novel magnetism in other nonmagnetic metals at nanoscale.

Ref: J. Phys. Chem. C, 2009, 113 (31), 13466–13469

Magnetic nanoribbons!

Owing to their nanoscale spintronic applications, doping of semiconductor nanocrystals by transition-metal ions has attracted tremendous attention . However, such doping is difficult to achieve in low-dimensional strongly quantum confined nanostructures by conventional growth procedures. In a recent report in Nature materials, researchers from korea in collaboration with american researchers have demonstrate that the incorporation of manganese ions up to 10% into CdSe quantum nanoribbons can be readily achieved by a nucleation-controlled doping process.

The cation-exchange reaction of (CdSe)13 clusters with Mn2+ ions governs the Mn2+ incorporation during the nucleation stage. This highly efficient Mn2+ doping of the CdSe quantum nanoribbons results in giant exciton Zeeman splitting with an effective g-factor of ~600, the largest value seen so far in diluted magnetic semiconductor nanocrystals. The sign of the s–d exchange is inverted to negative owing to the exceptionally strong quantum confinement in our nanoribbons. figure on the right show the theoretical investigation of Mn2+ doping of CdSe clusters.

This novel nucleation-controlled doping strategy opens the possibility of doping various strongly quantum confined nanocrystals for diverse applications.

Ref: Nature Materials 9, 47 - 53 (2009)

Photoluminescent Silicon Quantum Dots : Chromophore for Biological Imaging

Due to their strong luminescence,Quantum dots of group II/VI such as CdSe quantum dots are well-known, and substantial research has been conducted on these systems .There have, however, been concerns over the toxicity of these quantum dots in the human body. It has been reported in past that cell damage could be caused by an uncoated CdSe core under UV excitation. Because of their low toxicity and also inexpensive nature, silicon nanoparticles emerges as an ideal candidate for biological fluorescence imaging. In a recent article in JACS, researchers from New Zealand and Japan suggested the synthesis of amino-terminated silicon quantum dots made in reverse micelle system and capped with allylamine using a platinum catalyst. Their newly developed technique of surface modification is multistepped based on the chemistry of the terminal double bond on the surface to achieve the target functionalities. Thus formed Silicon quantum dots were characterized by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The capping of the silicon quantum dots has been fully characterized using nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The results from cytotoxicity studies indicate that toxicity is dependent on the surface functionality and that the silicon quantum dots as prepared have potential in biological applications such as bioimaging. In summary, silicon quantum dots opens new doors in the field of biological imaging.
Ref: J. Am. Chem. Soc., Article ASAP, DOI: 10.1021/ja906501v

Single Molecule detection by SERS active Gold-Silver-Core-Shell Nanodumbbells

Detection methods using plasmonic nanostructures based on Surface-enhanced Raman scattering (SERS) have been widely investigated for imaging and sensing applications.However, SERS-based single-molecule detection generally faces a problem with structural reproducibility, as particle structure and interparticle distance can markedly affect Raman signals and constructing robust SERS-active nanostructures still remain a challenge.

Recently, in a article in Nature Materials, researchers have reported a high-yield synthetic strategy to obtain gap-tailorable gold–silver core–shell nanodumbbells (GSNDs) and subsequent hot SERS-based single-molecule detection with structurally reproducible dimetric nanostructures.

Gold nanoparticle heterodimers were successfully synthesized in a relatively high yield by means of a single-target-DNA hybridization (displayed in the figure). A single Raman-active Cy3 dye molecule is located between two DNA-tethered particles. In another step, Ag shells were formed on the surface of the dimeric Au nanoparticles, and the Ag shell thickness was controlled on the nanometre scale to generate gap-engineerable, DNA-embedded GSNDs. To detect a Raman signal from each single-DNA-captured GSND, atomic force microscope (AFM)-coupled nano-Raman spectroscopy was used.

To prove that single-DNA detection is possible from a single GSND structure, several characterization experiments were suggested in the article.It has been demonstrated that as formed Raman-active GSNDs have single-molecule sensitivity with high structural reproducibility. This research is important because of following reasons:

- opens new opportunities in the high-yield synthesis of specific nanostructures for materials science and bio-detection applications..

- unlike the conventional strong electrolyte-induced nonspecific nanoparticle aggregation, this synthesis method can be easily scalable to produce targeted SERS-active nanoprobes.

- the nanogap-engineering of GSNDs allows for exploring hot SERS structures in an efficient and straightforward fashion

To summarize, these SERS-active GSNDs could be further modified by other biomolecules (such as proteins) and used as both in vitroand in vivo bio-labelling probes with ultrahigh sensitivity, quantification potential and multiplexing capability.

reference: Nature Materials (13 December 2009) doi:10.1038/nmat2596

Flexible Floating-gate Transistor

Traditionally, high-temperature manufacturing methods are employed for fabricated electronic device using inorganic semiconductors and rigid substrates . Organic semiconductors on the other hand can be processed at low temperatures and on large-area polymeric substrates. This has allowed for the development of a variety of electronic devices on flexible plastic substrates, including solar cells.Most of the organic memory transistors reported to date exploit the electric field–induced remnant polarization in ferroelectric polymer films . A considerable limitation of ferroelectric polymer memory transistors is that the coercive field required to reverse the macroscopic polarization increases with decreasing film thickness, which makes it difficult to obtain a large enough memory window with program and erase voltages below about 20 V. Also, due to the substantial surface roughness of the ferroelectric polymer films, the carrier field-effect mobility in these transistors is usually quite low.

Although silicon floating-gate transistors are excellent for high-density data storage, flexible organic floating-gate transistors are potentially useful for large-area sensors and actuators with integrated nonvolatile memory capability.

Using organic transistors with a floating gate embedded in hybrid dielectrics that comprise a 2-nanometer-thick molecular self-assembled monolayer and a 4-nanometer-thick plasma-grown metal oxide, nonvolatile memory arrays on flexible plastic substrates is realized . The small thickness of the dielectrics allows very small program and erase voltages (6 volts) to produce a large, nonvolatile, reversible threshold-voltage shift. The transistors endure more than 1000 program and erase cycles, which is within two orders of magnitude of silicon-based floating-gate transistors widely employed in flash memory. By integrating a flexible array of organic floating-gate transistors with a pressure-sensitive rubber sheet, a sensor matrix that detects the spatial distribution of applied mechanical pressure and stores the analog sensor input as a two-dimensional image over long periods of time has been created.

Ref: Science 11 December 2009: Vol. 326. no. 5959, pp. 1516 - 1519

Bamboo like Carbon Nanorods fabricated by Non-catalytic Approach

Since their discovery in 1990s, Carbon nanotubes (CNTs) are continuously of great interest in both fundamental research and practical applications. As an important member of carbon material family, bamboo-like carbon nanotubes (BCNTs) have been explored extensively due to their unique properties resulting from their hollow compartments inside nanotubes. BCNTs are expected to exhibit excellent electrochemical performances for their high percentage of edge sites along inner wall, compared with the common straight CNTs. For there synthesis, the catalyst is usually used and left inside the final carbon nanotubes, which needs further purification before their applications.

A novel approach for non-catalytic fabrication of BCNT has been suggested by Scientist from China in their recent article in Material Letters. The preparation procedures involve synthesis of monodispersed core–shell structured polymer spheres and the pyrolysis in an argon atmosphere.

The carbon nanotubes with bamboo-like structures are formed via the pyrolysis of PMMA@PDVB core–shell structured spheres. The typical SEM image reveals the one dimensional (1D) twisted nanostructures of BCNTs, which are up to several tens of micrometers in length. The compartments inside the nanotubes are observed from representative TEM images. The wall thickness of the BCNTs is between 20 and 30 nm and the inner diameter is around 200 nm. High-resolution TEM image reveals the lattice fringes with the space of 0.357 nm, which corresponds with the (002) plane lattice parameter of graphitic carbon. X-ray powder diffraction (XRD), Raman spectroscopy and energy dispersive spectroscopy (EDS) measurements were performed to get insight into the structure of BCNTs. Also, the possible mechanism for fabrication has been proposed in the report.