RSC Advances Blog

Silver is commonly used both in ionic form and in nanoparticulate form as a bactericidal agent. This is generally ascribed to a higher toxicity towards prokaryotic cells than towards mammalian cells.

Scientists in Germany have carried out studies to compare silver ions (such as silver acetate) and polyvinylpyrrolidone (PVP)-stabilised silver nanoparticles (70 nm). They found that silver’s toxic effect occurs in a similar concentration range for Escherichia coli, Staphylococcus aureus, human mesenchymal stem cells and peripheral blood mononuclear cells (0.5 to 5ppm for silver ions and 12.5 to 50ppm for silver nanoparticles).

For a better comparison, the team cultivated bacteria in Lysogeny broth medium and in Roswell Park Memorial Institute medium/10% fetal calf serum medium, as the state of silver ions and silver nanoparticles may be different owing to the presence of salts and biomolecules such as proteins. They found that the effective toxic concentration of silver towards bacteria and human cells is almost the same.

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The toxic effect of silver ions and silver nanoparticles towards bacteria and human cells occurs in the same concentration range

Christina Greulich,  Dieter Braun,  Alexander Peetsch,  Jörg Diendorf,  Bettina Siebers,  Matthias Epple and Manfred Köller
RSC Adv., 2012, 2, 6981-6987

Schematic drawings of (A) different designs of assay probes for cocaine detection: (left) monolithic aptamer (MA), (middle) double-fragment aptamer (DFA), and (right) triple-fragment aptamer (TFA); (B) gold nanoparticle based optical cocaine detection using TFA. The same oligonucletide sequences were drawn in the same colors.

Chinese scientists have developed a  colorimetric sensor consisting of a triple-fragment aptamer (TFA) that is able to assemble in the presence of cocaine. Xinhui Lou and Yueying Liu and co-workers at the Capital Normal University in Beijing, showed that the aptasensor was specific for cocaine and worked equally well in complex urine samples containing 100 μM cocaine or filtered serum containing cocaine.   

This new type of aptamer probe design showed a gradual colour change from red to blue when the concentrations of cocaine was increased from 0 to 200 μM . “TFA broadens the repertoire of probe designs and provides good opportunities for the future development of novel detection approaches and for nanostructure constructions,” says Liu et al. 

Even though the assays need to be conducted at low temperature (4 °C), the authors believe that the detection method can be further improved by increasing the stem length. 

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Highly specific triple-fragment aptamer for optical detection of cocaine
Ruxing Zou ,  Xinhui Lou ,  Huichao Ou ,  Ying Zhang ,  Wenjie Wang ,  Min Yuan ,  Ming Guan ,  Zhaofeng Luo and Yueying Liu 

RSC Adv., 2012,2, 4636-4638
DOI: 10.1039/C2RA20307C

SEM image of an ordered array of MnSO4 bowls obtained after calcination of the MnSO4–PVP composite film at 550 °C for 5 h.

Scientists at the  Jawaharlal Nehru Centre for Advanced Scientific Research, in Bangalore, India, report a simple method for the “spontaneous formation of ordered, mesoscale structures made up of inorganic salt bowls”. These tiny bowls are said to be generating a lot of interest due to their unique application as ‘containers’ to hold ultra-low volumes.

The team led by Eswaramoorthy showed that when manganese sulfate is heated with the water soluble polymer PVP, the mix spontaneously forms arrays of tiny water-soluble bowls of the manganese sulfate salt. The beautiful structures are the result of the salt crystallising around the PVP as it bubbles and evaporates. The salt bowl were coated in gold, before the salt is washed away leaving some of the tiniest gold bowls ever made.

Scheme showing formation process of different MnSO4 morphologies through gas-bubble template method, Scheme A: Bowls, Scheme B: Ball-in-bowl shaped structures, Scheme C: Ring shaped structures (for convenience, all morphologies are shown to be evolved from the same film).

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Shaping up: spontaneous formation of ordered mesoscopic salt bowls

Katla Sai Krishna, Bosukonda V. V. S. Pavan Kumar and Muthusamy Eswaramoorthy
RSC Adv., 2012, Advance Article
DOI: 10.1039/C2RA20596C, Communication