Foldable displays. Bioimaging. Photo-induced therapeutics. Each one of these has something in common – carbon nanodots. And spectroscopy plays a large role in developing these technologies.
Carbon nanodots are tiny particles made of carbon on the nanometer scale. Scientists can make it from various sources, such as bulk carbon or carbohydrates. They can even make it from biomass, or organic matter. These particles are easy to synthesize, making the cost of preparation low.
Scientists produce carbon nanodots as stacks of a few graphene layers. It is arranged in a continuous two-dimensional carbon honeycomb. Due to the confined size, carbon nanodots have a finite band-gap that can absorb and emit light.
Graphene in its larger state does not fluoresce, since it’s a metallic substance. It has high electrical conductivity, though, useful in many applications. But when the size of the graphene becomes smaller, it becomes semi-conductive and can emit strong fluorescence.
Carbon nanodots are important because of its photoluminescence properties. Scientists can tune the color of the fluorescence from carbon nanodots by modifying its size and surface chemistry.
Researchers use spectrofluorometers to measure the characteristics of the nanodots and photoluminescence of these materials.
Doo-Young Kim, Ph.D. is an Associate Professor of Chemistry at the University of Kentucky. Kim studies how the size and structure of carbon nanodots influence fluorescence and other properties. These properties in turn affect the performance of the nanodots in its ultimate application.
Kim uses an extended version of the HORIBA FluoroxMax®-C spectrofluorometer for his research on carbon nanodots. It can do several things: measure steady-state fluorescence intensity and spectrum in a wide spectral range, from visual to near-infrared wavelengths. It can determine the accurate efficiency of the fluorescence process. And the time-correlated single photon counting (TCSPC) unit of the FluoroMax-C can measure the time-resolved fluorescence lifetime of emitting materials. All this information fuels the knowledge of the properties of the carbon nanodots.
There are several applications for carbon nanodots. Practitioners introduce these nano-sized materials into biological cells to color the cells and track biological components. Researchers can track the component’s locations and movements with specific and predetermined carbon nanodots, which fluoresce at different colors.
Carbon nanodots are also used in cancer treatment. If you excite certain carbon nanodots with a specific light source, it generates toxic chemicals locally, such as singlet oxygen species. Researchers have identified certain singlet oxygen species as being able to damage a cancer cell. Fluorescence spectroscopy for chemical analysis reveals information on the biological samples. This area, called photodynamic therapy, is being studied intensively.
Perhaps the most commercially interesting application of carbon nanodots, and least developed, is its use in display devices.
Known as organic light emitting diodes, or OLEDs, engineers take advantage of the carbon nanodots’ fluorescing properties. Carbon nanodots can emit strong fluorescent light, and the color of its emission can be tuned from ultraviolet to red. OLEDs are being used for displays in televisions, monitors, and smartphones.
The advantages of OLEDs include a lower cost to produce and the flexibility of the material. Manufacturers can make OLED-based displays in a curved shape, but durability and its vulnerability to the environment have been problematic.
OLEDs are a potential replacement for LEDs, light emitting diode displays. LEDs use more expensive silicon to manufacture and require a more sophisticated optimization than OLEDs.
Researchers believe in the next few years, scientists will learn how to construct carbon nanodots in a way that allows for foldable displays. One that you can collapse and put into your pocket. Imagine the possibilities.
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