Nanoscale & Nanoscale Advances Blog

‘HOT’ article: Killing bacteria in broad daylight

Scientists have coated a TiO₂–InVO₄ film onto a glass layer and observed that the coating kills E. coli under ambient light.

Titanium oxide has been used by itself before, but it has to be activated with ultraviolet light. Adding InVO₄ – a stable narrow band gap semiconductor – ensures that the coating can absorb visible light. Now, the coating can be activated in daylight, increasing its potential applications in disinfecting surfaces.

 Read the ‘HOT’ Nanoscale article today:

Understanding bactericidal performance on ambient light activated TiO2-InVO4 nanostructured films
Z He, Q Xu and T T Y Tan,
Nanoscale, 2011
DOI: 10.1039/c1nr11126d

Inspired by the feeding tube of butterflies, US scientists have made a flexible and porous artificial proboscis that could be used to collect tiny liquid samples. The probe can be operated remotely to collect hazardous liquids.

Konstantin Kornev from Clemson University and his team wanted to find a way to sample miniscule amounts of liquid. They needed a probe that would be flexible and easy to manipulate. After seeing the effective way that butterflies and moths suck up their food using proboscises, they decided to make an artificial version.

‘A proboscis has two types of pores: very small to draw the liquid in and large, to transport the liquid as pipes would do,’ says Kornev. To mimic this system, the team made a bundle of porous polymer fibres and twisted them into a yarn using a new electrospinning technique. Electrospinning works by charging a liquid medium and accelerating it from a high electrical potential to a lower one to produce long fibres. The new part of the technique involves collecting the fibres with rolled brushes that act as arms. The arms are then spun in opposite directions to make a yarn. ‘Twisting these fibres into a yarn was a challenge,’ says Kornev. The yarn’s large interfibre pores provide rapid wicking and the small pores provide a strong capillary action.

Mimicking a butterfly proboscis: the diagram shows the artificial proboscis absorbing a droplet. The solid black fibre on the left is the artificial proboscis; the grey fibre on the right is a nylon yarn 

To manipulate the proboscis so it could be directed to its target – a droplet or even a single cell or gland – Kornev embedded magnetic particles into the porous polymer so that it could be controlled by applying an electric or magnetic field. With this flexibility, the proboscis can be attached to a microfluidic device for sampling hard to reach areas, in sensors or in forensic probes, or to sample hazardous substances. 

Joshua Edel, an expert in nanobiotechnology from Imperial College London, comments: ‘They are one of the first groups to develop nanoporous flexible probes that work as artificial proboscises. Assuming they can be made in a reproducible manner, I see no reason why this system would not have commercial implications.’  

‘We developed a special automated technique to make reproducible proboscises,’ says Kornev, who is now working on adding a sensing function to the proboscises in the hope of developing a probe that can sample and analyse minute amounts of fluids. 

Holly Sheahan

Read the paper from Nanoscale:

Nanoporous artificial proboscis for probing minute amount of liquids
Chen-Chih Tsai, Petr Mikes, Taras Andrukh, Edgar White, Daria Monaenkova, Oleksandr Burtovyy, Ruslan Burtovyy, Binyamin Rubin, David Lukas, Igor Luzinov, Jeffery R. Owens and Konstantin G. Kornev
Nanoscale, 2011
DOI: 10.1039/c1nr10773a

Scientists from China have created nanoparticles with dual mode colour for anti-counterfeiting ink, making it harder to imitate than current inks.

Lehui Lu and colleagues from the Chinese Academy of Sciences, Changchun, have designed dual mode fluorescent lanthanide doped nanocrystals to make the ink. The nanocrystals display upconversion, in which particles absorb light of one wavelength and emit light of a shorter wavelength, and downconversion, in which a high energy photon is split into two lower energy photons. These are triggered by near infrared and ultraviolet light, respectively, to produce different colours. The crystals would make the ink difficult to replicate if used on important documents as an anti-counterfeiting measure.

Traditional anti-counterfeiting materials only emit one colour so are more easily replicated. Including more colours involves mixing different nanocrystals, which could affect ink quality. Now, ‘colour tuning can be achieved from a single nanocrystal, avoiding a decrease in the ink’s quality’, says Lu.

Exposing film stamped with the ink to near infrared light caused a green emission, while under ultraviolet light, a colour change from green to blue was seen

The team bound the nanocrystals to oleic acid, which stabilises them in organic solvents so that they can be applied to paper. They tested the crystals by stamping the ink onto a transparent film. In daylight, the effect was invisible. However, when they shone infrared light on the film the stamped section was clearly seen, with a bright green upconversion emission. When they changed to ultraviolet light, the colour changed to blue because of the downconversion.

The nanocrystals could also be developed for use in biological imaging, as Yadong Li, an expert in lanthanide-doped nanocrystals from Tsinghua University, P. R. China, points out. ‘The near infrared emission is suitable for in vivo imaging, owing to the weak autofluorescence background and deeper penetration,’ he says.

The next step for Lu is to increase the nanocrystals’ quantum yield by increasing the number of molecules participating in the process. ‘Compared to traditional organic dyes,’ explains Lu, ‘the quantum yield of oleic acid-stabilised lanthanide doped fluoride nanocrystals is relatively low. Improving the quantum yield is a big challenge.’

Rachel Cooper

Read the paper from Nanoscale:

Designing lanthanide-doped nanocrystals with both up- and down-conversion luminescence for anti-counterfeiting
Yanlan Liu, Kelong Ai and Lehui Lu
Nanoscale, 2011
DOI: 10.1039/c1nr10752f

Novel Zn-Sn-O nanocactus films, synthesized by a simple hydrothermal method, display overall power conversion efficiencies (PCEs) of 2.21 per cent when used as the photoanode of dye-sensitised solar cells. After treatment with TiCl₄ the PCE rises to 6.62 per cent, comparing favourably with P25 DSSCs (6.97 per cent).

The authors suggest that such materials could have excellent prospects for use as photoanodes in DSSCs.

For full details on this exciting work read this HOT Nanoscale article today:

Novel Zn–Sn–O nanocactus with excellent transport properties as photoanode material for high performance dye-sensitized solar cells
Xincun Dou, Nripan Mathews, Qing Wang, Stevin Snellius Pramana, Yeng Ming Lam and Subodh Mhaisalkar
Nanoscale, 2011
DOI: 10.1039/C1NR11083G

Scientists in Ireland have developed a method to convert perpendicularly aligned  CdS and CdSe nanorods to their silver and copper chalcogenide equivalents. The nanorod dimensions and superlattice order remain unchanged during the process.

Such nanorods have potential applications in solar cells. The authors envisage that this new technique can be extended to other material systems.

Read the full HOT Nanoscale communication to find out more:

A facile spin-cast route for cation exchange of multilayer perpendicularly-aligned nanorod assemblies
Dervla Kelly, Ajay Singh, Christopher A. Barrett, Catriona O’Sullivan, Claudia Coughlan, Fathima R. Laffir, Colm O’Dwyer and Kevin M. Ryan
Nanoscale, 2011
DOI: 10.1039/C1NR11031D

Graphene-based materials have many applications due to their interesting electronic and mechanical properties. Part of the typical process used to prepare graphene is the reduction of graphene oxide (GO), often using toxic and unstable hydrazine derivatives.

Now Boukherroub and co-workers report a method for the production of graphene nanosheets whereby GO is reduced by UV irradiation in aqueous solution. This was most successful in the presence of silicon nanowire arrays decorated with copper nanoparticles which act as photocatalysts.

The graphene nanosheets produced were free of contaminants and the authors believe the scalability of this process will be an advantage.

Read this HOT Nanoscale article in full:

Silicon nanowire arrays-induced graphene oxide reduction under UV irradiation
Ouarda Fellahi, Manash R. Das, Yannick Coffinier, Sabine Szunerits, Toufik Hadjersi, Mustapha Maamache and Rabah Boukherroub
Nanoscale, 2011
DOI: 10.1039/C1NR10970G

Scientists from India have made blood compatible “hybrid quantum clusters” (HQCs) by combining fluorescent gold clusters with iron-containing superparamagnetic nanoparticles.

They found that the HQCs were capable of selective separation of cancer cells in blood or saline using an external magnet. The fact that the clusters are fluorescent means they can be imaged.

The authors hope their system could one day be used for a dialysis-type set up for cancer therapy.

Read this HOT Nanoscale article in full:

Fluorescent and superparamagnetic hybrid quantum clusters for magnetic separation and imaging of cancer cells from blood
C. V. Durgadas, Chandra P. Sharma and K. Sreenivasan
Nanoscale, 2011
DOI: 10.1039/C1NR10900F