A new light-harvesting antenna complex could pave the way for making biologically based solar cells. Challa V. Kumar and his team at the University of Connecticut made the biodegradable antenna from DNA, modified bovine serum albumin (BSA), and four fluorescent dyes.

Kumar reported the research Monday at the American Chemical Society national meeting in Boston during a session sponsored by the Division of Analytical Chemistry.

The antenna is inexpensive to make because it doesn’t require complicated assembly procedures: The components arrange themselves. Each dye binds to a specific site on the DNA or protein. One dye binds to the minor groove of the DNA double helix; the other three bind to specific sites on the albumin. The dye-loaded protein in turn binds to the negatively charged DNA because the researchers chemically modified the albumin to be positively charged. The resulting DNA-protein matrix holds the dyes close enough, but not too close, for efficient energy transfer between the dyes.

DNA, bovine serum albumin (BSA), and four fluorescent donor and acceptor dyes self-assemble to form biodegradable light-harvesting artificial antennas. When researchers drop cast the material on a substrate, it forms floorboard-like structures on millimeter length scales (right). Credit: Challa V. Kumar.

DNA, bovine serum albumin (BSA), and four fluorescent donor and acceptor dyes self-assemble to form biodegradable light-harvesting artificial antennas. When researchers drop cast the material on a substrate, it forms floorboard-like structures on millimeter length scales (right). Credit: Challa V. Kumar.

In the resulting “bucket brigade,” the dyes transfer excitation energy from one to the next until it reaches the lowest energy acceptor dye. With the current set of dyes, the antenna absorbs blue light and then emits mostly red.

The overall efficiency of the antenna in converting blue to red photons is only 23%. But that efficiency is still remarkable for a system that involves energy transfer between four dye molecules and has a relatively inefficient final dye that sets an upper limit of 39% for the whole antenna, Kumar said. The team plans to find a more efficient final dye.

The complex acts as an antenna that amplifies energy capture relative to the final dye alone, which can absorb blue light and emit red. The multiple dyes allow the antenna to capture a wider range of wavelengths and thus more energy that can be funneled to the final dye. Excitation with blue light results in 2.3 times more red emission with the entire antenna than with the final dye alone, Kumar said.

The antenna also functions efficiently after exposure to 80 °C for more than 169 days, which mimics the harsh conditions under which solar cells operate.

“It’s a very intriguing idea to use DNA as a matrix for dye-associated BSA,” commented Ishita Mukerji, a professor of molecular biology and biochemistry at Wesleyan University who studies DNA-protein interactions. The complex “has a lot of promise for making an antenna for solar cells.”

Although the technology is far from commercialization, the UConn team is collaborating with an undisclosed company to test the complex as a solar collector on silicon solar cells, Kumar told C&EN.

By Celia Henry Arnaud

 

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