Iain Larmour, web science writer – Page 3 – Chemical Communications Blog

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Overcoat makes carbon quantum dots biocompatible

22 Aug 2012

Quantum dots are currently being developed for a variety of applications, including as sensors and cellular tags. Semiconductor quantum dots are attractive for their high fluorescence quantum yields but the toxicity of some of the metals involved, such as cadmium, pose a problem for biological applications.

Carbon quantum dots (CQDs) offer an alternative however when transferred into aqueous solution they possess low quantum yields. The problem is how do you harness the higher fluorescence of CQDs prepared in an organic solvent for biological applications?

To answer this question John Callan and his team have employed an amphiphilic polymer to act as an overcoat and transfer agent for the CQDs. Surprisingly they found that the transfer actually improved the quantum yield rather than the normally expected repression when ligand exchange is used. These aqueous carbon quantum dots were taken up into cells and were found to be non-toxic.

The development of inexpensive and biocompatible quantum dots with an improved quantum yield holds great potential for a wide range of future biological applications.

To find out more, download the ChemComm article today (free to access for a limited period).

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Luminogenic materials have a bright future

30 Jul 2012

Luminogenic materials are a hot topic of research due to their potential applications in biotechnology and memory systems. But most luminogenic materials undergo aggregation-caused quenching (ACQ) in the solid state. This is when the dye molecules near each other aggregate and form species that weaken the material’s emission.

Ben Zhong Tang and his team have been researching materials that instead exhibit aggregation-induced emission (AIE). This makes the preparation of solid state luminogens much simpler as aggregation increases the activity. Unfortunately, there are few AIE-active emitters in the longer wavelength region, which is of interest for biotechnology applications.

Tang’s team have addressed this oversight by developing a novel luminogen which couples the AIE property of tetraphenylethene and the longer wavelength activity of a hemicyanine dye. The emission properties of the resultant crystals can be readily tuned by the solvent molecules in the solution they are grown from.

: Crystochromism of the novel luminogen

Most interestingly, the prepared luminogen shows crystochromism: a strong yellow emission in its thermodynamically stable crystalline form and a red colour in its metastable amorphous form. These changes are fully reversible, with grinding, heating or fuming causing the change in the luminogen’s crystallinity.

To find out more, download the ChemComm article today.

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Nanoscopic electrochemical cells probe forests

16 May 2012

3D carbon nanotube forests are of particular interest in the electrochemical arenas of sensing and energy applications. Some researchers have suggested that it is necessary to use open-ended carbon nanotubes and carry out a pre-treatment or activation step to support fast electrochemistry, but is this always the case?

Patrick Unwin and co-workers set out to investigate. They prepared carbon nanotube forests using a chemical vapour deposition growth method. To probe the local electrochemical response of the forests, they used a nanoscopic double barrelled pipette tip, filled with supporting electrolyte and redox species. This allowed the team to interrogate the sidewalls and closed ends of the nanotubes that made up the forest with high spatial resolution.

Both sidewalls and the closed tube ends were capable of fast electron transfer proving that single walled carbon nanotubes do not require open ends for fast electrochemistry with outer sphere redox couples. This overturns the current consensus, based on averaged macro-sized measurements, that open ends dominate nanotube forest electrochemistry.

Without the requirement for pre-treatment or activation, electrochemical nanotube forest applications will be easier to achieve.

To find out more, download the ChemComm article today.

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Ambient pressure XPS on the cheap

21 Mar 2012

X-ray photoelectron spectroscopy (XPS) is capable of characterising the surface composition, oxidation state and electron state of materials. Unfortunately, it uses electrons and so common XPS machines must work at vacuum pressures. But how could you use XPS under ambient pressure?

One option would be to use public synchrotron facilities but access is through proposal review and available time is restricted so it is not feasible for day-to-day studies. Another option would be to follow the lead of Franklin Tao and build an inexpensive, ambient pressure XPS machine in-house.

Such a machine is ideal for catalytic studies. Previously scientists investigated catalysts with conventional vacuum XPS before and after experiments. Tao’s machine enables him to investigate catalyst surface changes during reaction conditions, something that required synchrotron facilities until now. The machine’s novel reaction cell allows XPS measurements to be carried out at up to 25-50 Torr using an inexpensive bench top X-ray source.

: external view of the reaction cell

In addition to the ambient pressure XPS functionality, an on-line mass spectrometer allows correlation between catalytic performance and surface chemistry. Tao has demonstrated this novel machine by investigating the oxidation and reduction of ceria under real reaction conditions.

With day-to-day ambient pressure XPS now within reach of every research group, catalytic studies under reaction conditions have received a significant boost.

To find out more, download the ChemComm article today.

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Chemical Communications Blog

Author Archive

Overcoat makes carbon quantum dots biocompatible

Luminogenic materials have a bright future

Nanoscopic electrochemical cells probe forests

Ambient pressure XPS on the cheap

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