The Indian Institute of Science team used a 2D material to design what they call a non-linear optical mirror stack to increase or up-convert the frequency of short infrared light to the visible range, combined with widefield imaging capability.
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Researchers at the Indian Institute of Science (IISc) have fabricated a device to increase or up-convert the frequency of short infrared light to the visible range. This up-conversion of light has diverse applications, especially in defence and optical communications, said IISc.

“The human eye can only see light at certain frequencies (called the visible spectrum), the lowest of which constitutes red light. Infrared light, which we can’t see, has an even lower frequency than red light. IISc researchers have now fabricated a device to increase or up-convert the frequency of short infrared light to the visible range,” IISc said.

2D material used

The institute added that in a first, the IISc team used a 2D material to design what they call a non-linear optical mirror stack to achieve this up-conversion, combined with widefield imaging capability. The stack consists of multilayered gallium selenide fixed to the top of a gold reflective surface, with a silicon dioxide layer sandwiched in between.

It said that traditional infrared imaging uses exotic low-energy bandgap semiconductors or micro-bolometer arrays, which usually pick up heat or absorption signatures from the object being studied.

However, existing infrared sensors are bulky and not very efficient. They are also export-restricted because of their utility in defence. There is, therefore, a critical need to develop indigenous and efficient devices.

The method used by the IISc team involves feeding an input infrared signal along with a pump beam onto the mirror stack. The nonlinear optical properties of the material constituting the stack result in a mixing of the frequencies, leading to an output beam of increased (up-converted) frequency, but with the rest of the properties intact. Using this method, they were able to up-convert infrared light of a wavelength of around 1,550 nm to 622 nm visible light. The output light wave can be detected using traditional silicon-based cameras.

Going forward, the researchers plan to extend their work to up-convert light of longer wavelengths. They are also trying to improve the efficiency of the device by exploring other stack geometries.

Worldwide interest

“There is a lot of interest worldwide in doing infrared imaging without using infrared sensors. Our work could be a game-changer for those applications,” said Varun Raghunathan, associate professor, Department of Electrical Communication Engineering.

Indian Institute of Science, Bengaluru

Researchers at the Department of Biochemistry, Indian Institute of Science, have developed a novel method for the production of recombinant proteins.

According to IISc, mass production of recombinant proteins using yeast cell factories needs methanol, a compound that requires safe handling, carries the risk of catching fire, and sometimes produces harmful byproducts. However, researchers have now developed an alternative, safer process that instead relies on a common food additive called monosodium glutamate (MSG).

Recombinant proteins, such as vaccine antigens, insulin and monoclonal antibodies, are mass-produced by growing modified bacterial, viral or mammalian cells in large bioreactors. The most widely used organism is the yeast Pichia pastoris (now called Komagataella phaffii).

A unique promoter

“It contains a unique promoter – a specific gene region which can be activated by methanol. This promoter codes for an enzyme called alcohol oxidase (AOX),” IISc said.

To mass-produce a recombinant protein, the gene coding for that protein is spliced into the yeast genome right next to the AOX promoter. The yeast cells are then fed glycerol or glucose as the carbon source. Once enough cells have formed, methanol is added, which activates the AOX promoter, and the cells start producing the recombinant protein in copious amounts.

“Most industries use this methanol-induced process for producing recombinant proteins. However, methanol is highly flammable and hazardous, requiring stringent safety precautions. Methanol is also metabolized to form hydrogen peroxide which can induce oxidative stress in the yeast cells or damage the recombinant proteins,” said Prof P.N. Rangarajan, corresponding author of the study published in Microbial Cell Factories.

Role of MSG

To solve this problem, Trishna Dey, a former PhD student at the Department of Biochemistry, started looking for alternatives. After an extensive search, the team found that monosodium glutamate (MSG), a USFDA-approved food additive, can activate a different promoter in the yeast genome that codes for an enzyme called phosphoenolpyruvate carboxykinase (PEPCK). Activating this promoter with MSG led to protein production similar to methanol activation of the AOX promoter.

The researchers hope that this novel and indigenous expression system can be used in biotech industries to mass-produce valuable proteins, including milk and egg proteins, baby food supplements, and nutraceuticals, as well as therapeutic molecules.

The Indian Institute of Science, Bengaluru

An interdisciplinary team of researchers from the Indian Institute of Science have uncovered how the stiffness of a cell’s microenvironment influences its form and function. The findings are expected to provide a better understanding of what happens to tissues during healing of wounds.

Scar formation

“Inefficient wound healing results in tissue fibrosis, a process that can cause scar formation and may even lead to conditions like cardiac arrest. Changes in the mechanical properties of tissues like stiffness also happen in diseases like cancer,” IISc said.

The research team was led by Prof. Namrata Gundiah from the Department of Mechanical Engineering and Prof. Paturu Kondaiah from the Department of Developmental Biology and Genetics.

Change in stiffness

In the study, published in Bioengineering, the team cultured fibroblast cells, the building blocks of our body’s connective tissue, on a polymer substrate called PDMS with varying degrees of stiffness.

They found that a change in the stiffness altered the cell structure and function. Fibroblast cells are involved in extensive remodelling of the extracellular matrix (ECM) surrounding biological cells.

The ECM, in turn, provides the mechanical tension that cells feel inside the body. The team found that fibroblasts cultured on substrates that had lower stiffness were rounder and showed accompanying changes in the levels of cytoskeleton proteins such as actin and tubulin. Moreover, fibroblasts grown on such substrates showed cell cycle arrest, lower rates of cell growth and cell death.

Regulator that drives changes

To pinpoint the master regulator that drives changes in the cell when substrate stiffness changes, the team focused their attention on an important signalling protein called Transforming Growth Factor-β (TGF-β). Previous work has shown that the activity of fibroblasts and the downstream ECM architecture is regulated by TGF-β.

“The thing is, people talk about the chemical changes but not about biomechanical changes. For example, while the TGF-β signalling cascade has been studied extensively in cancer, the influence of mechanical forces such as substrate stiffness has not been studied so far,” said Brijesh Kumar Verma, first author of the study. In the future, the researchers seek to understand how other mechanical factors, such as surface properties and cell stretch, can also influence TGF-β activity.