Physics – Ceri Brenner
The movie Babe is about a pig that befriends some sheep and ends up as a prize-winning sheepdog (oops, plot spoiler). When he’s quiet, the sheep stay in the pen and hardly move. When he growls like the dogs they scatter and waste energy running around but are still stuck in the pen. It’s only when he uses the secret sheep code “baa ram ewe” that he can get them to move calmly out of the pen and around the circuit of the sheep-herding contest trail.
Semiconductor materials act like this when light shines onto them. For each material there a certain colour acts as the “baa ram ewe” secret code that energises the electrons (the sheep) to flow out of the atomic structure (the pen) and along the surface. Solar cells are semiconductors that optimise this process to generate electricity. If the light gives too much energy, then the electrons whizz about before losing their energy as heat and retreating back to the atomic structure. These excess energy electrons are called hot electrons. A paper in Nature Communications describes the observation that light-energised hot electrons from a tin-based semiconductor stay hot for longer than in a lead-based equivalent. They exist as hot electrons for thousands of times longer – billionths of a second (nanoseconds) rather than trillionths of a second (picoseconds). This is exciting as it offers enough time to intercept the hot electrons and harvest their excess energy for additional electricity rather than it being wasted as heat.
This special material is a type of semiconductor with a specific structure called a hybrid organic-inorganic perovskite. Researchers are studying these because they’re ideal candidates for making cheap and efficient solar cells. The most common version explored until now was a lead-based perovskite but this can’t work for large-scale use as lead is toxic. This latest discovery that formamidinium tin tri-iodide (what a name!) not only works as a lead-free alternative but has this long-life hot electron effect is pointing towards big gains in solar cell efficiency in the coming years. A tin roof of sorts that we can all look forward to.
Ceri Brenner is a physicist who works for the Science and Technology Facilities Council
Chemistry – Mark Lorch
Natural and artificial additives play a wide range of roles in the processed foods and drinks we regularly consume. Sugars and other flavourings enhance the taste, preservatives (from salt to vitamin C) lengthen shelf lives, and colours improve the foods’ presentation. And some compounds are added to foods to help with the manufacturing process. One such additive is the natural sugar trehalose (commonly found in honey, mushrooms and seed).
Trehalose isn’t as sweet as other sugars but it does have other advantages. Most notably it doesn’t react at high temperatures with proteins in the food. This process, known as the Maillard reaction, is responsible for the browning (and the flavour that goes with it) of your cakes, breads and seared steaks. And whilst you might like a nicely browned loaf, there are situations when the colour and taste that result from the Maillard reaction are not desirable. So where the manufacturing process involves high temperatures, trehalose is a good sugar to use.
Trehalose was first approved for use in foods at the turn of the century. Around the same time, there was an increasing number of cases of the potentially dangerous bacterium and stomach bug Clostridium difficile. A correlation does not necessarily imply a causative link, but is often worth investigating. Which is exactly what a team from Baylor College of Medicine in Texas did. Their work (published in Nature in January) looked at two strains of C. difficile that caused outbreaks between 2001 and 2006. They found that in both cases the C. difficile had evolved to produce higher levels of an enzyme that allowed the bacterium to feed on the trehalose sugar, making the sugar a viable energy source allowing it to breed more rapidly in the gut.
The work seems to support a link between C. difficile and trehalose, and, according to Mark Wilcox from Public Health England, trehalose “may be one part of the jigsaw explaining why these [C. difficile infections] became more common.” Nevertheless the lead authors of the paper do suggest that hospitals suffering from C. difficile infections may consider cutting trehalose from their patients’ diet.
Mark Lorch lectures in chemistry at Hull University
Biology – Lydia Leon
Millions of people are born with degenerative loss-of-sight disorders that culminate in total blindness by childhood or adolescence. Until now, effective treatments to halt or reverse this deterioration have been largely non-existent. However, in December the US Food and Drugs Administration (FDA) approved the marketing of a new gene-therapy, Luxturna, targeted at a specific group of these disorders caused by mutations in the RPE65 gene.
RPE65 is a key component of the visual cycle: the process of chemical reactions that convert photons of light from the environment into electrical signals transmitted to our brain. Dozens of different mutations within the RPE65 gene can reduce the amount of protein in the eye or limit its capacity to function normally. The clinical trial was conducted at the Children’s Hospital of Philadelphia. The treatment works by injecting working copies of the RPE65 gene into patient’s eyes, providing patients with the capacity to produce normal, functional copies of the key protein. Twenty-one patients with a specific congenital disorder received the treatment, while 10 were given a placebo. Those treated with Luxturna showed a substantial improvement in a specialised obstacle course designed to test visual capacity at different light levels. Those who received the placebo showed no improvement at all. Researchers are hopeful that the treatment will also be effective on other RPE65 visual disorders Eye tissue is particularly suited to gene-therapy due to its size and accessibility. The production of this treatment is the culmination of decades of clinical research and millions of dollars of investment. After substantial setbacks due to safety concerns in the 1990s, gene-therapy research is having something of a comeback in recent years.
The most recent announcement in the Luxturna story is that the drug will be priced at $425,000 per eye: a huge sum under debate by healthcare legislators in the US. Luxturna is currently under review by the European Medicines Agency, which is a prerequisite for UK approval.
Lydia Leon is a research associate in women’s health at Kings College London and University College London
