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Simple Solution to Create Fluorescent Quantum Defects

Researchers expect quantum computing and quantum cryptography to exhibit considerably higher potential compared to their classical equivalents.

A bright fluorescent quantum defect can be a tool to upgrade current biomedical imaging systems, looking at even smaller tumors through the defect emission. (Image credit: Belcher Lab)

For instance, a quantum system’s computation power may increase at a double exponential rate rather than a classical linear rate owing to the difference in nature of the basic unit—the qubit, or the quantum bit.

The unbreakable codes for secure communications are activated by entangled particles. The significance of these technologies inspired the U.S. government to enact the National Quantum Initiative Act, authorizing $1.2 billion over the following five years to develop quantum information science.

For such applications, single photons could be a vital qubit source. In order to realize practical utilization, it is necessary for the single photons to be in the telecommunication wavelengths, ranging from 1260 to 1675 nm. Moreover, the device must be functional at ambient temperature. Until now, only one fluorescent quantum defect in carbon nanotubes has both features at the same time.

However, the accurate production of these single defects has been hindered by preparation techniques that necessitate special reactants, are challenging to control, proceed gradually, create non-emissive defects, or are difficult to scale.

A study by Angela Belcher, head of the MIT Department of Biological Engineering, Koch Institute member, and the James Crafts Professor of Biological Engineering, and postdoc Ching-Wei Lin, reported online in Nature Communications, explains a simple solution to develop single-photon emitters based carbon nanotubes, called fluorescent quantum defects.

We can now quickly synthesize these fluorescent quantum defects within a minute, simply using household bleach and light. And we can produce them at large scale easily.

Ching-Wei Lin, Postdoctoral Fellow, MIT

By generating minimum non-fluorescent defects, Belcher’s lab has been able to demonstrate this incredibly simple method. First, carbon nanotubes were immersed in bleach and subsequently irradiated using ultraviolet light for less than a minute to generate the fluorescent quantum defects.

The fluorescent quantum defects provided by this technique has led to a considerable decrease in the barrier for converting fundamental studies into practical applications. At the same time, the nanotubes turn much brighter once these fluorescent defects are generated.

Moreover, the emission/excitation of these defect carbon nanotubes is moved to what is called the shortwave infrared region (900–1600 nm), an invisible optical window with somewhat longer wavelengths compared to the regular near-infrared.

Furthermore, operations carried out at longer wavelengths with brighter defect emitters enable scientists to observe through the tissue more deeply and clearly for optical imaging. Consequently, the optical probes based on defect carbon nanotubes (typically to conjugate the targeting materials to these defect carbon nanotubes) will considerably enhance the imaging performance, thus facilitating cancer detection and treatments, for example, early detection and image-guided surgery.

In 2017, cancers were the second-leading cause of death in the United States. Upon generalization, the figures come to around 500,000 people who die from cancer each year. The aim of the Belcher Lab is to create extremely bright probes that function at the optimal optical window for investigating very small tumors, mainly on brain and ovarian cancers.

According to statistics, the ability of doctors to detect the disease much earlier will considerably increase the survival rate. At present, the new bright fluorescent quantum defect could be the apt tool to modernize the existing imaging systems, analyzing even smaller tumors by means of the defect emission.

We have demonstrated a clear visualization of vasculature structure and lymphatic systems using 150 times less amount of probes compared to previous generation of imaging systems. This indicates that we have moved a step forward closer to cancer early detection.

Angela Belcher, Head, Department of Biological Engineering, MIT

In partnership with contributors from Rice University, for the first time, scientists can determine the quantum defects distribution in carbon nanotubes with the help of an innovative spectroscopy technique known as variance spectroscopy. This technique assisted the researchers to track the quality of the carbon nanotubes that contain quantum defects and find the accurate synthetic parameters easier.

Biological engineering graduate student Uyanga Tsedev, materials science and engineering graduate student Shengnan Huang, and Professor R. Bruce Weisman, Sergei Bachilo, and Zheng Yu of Rice University are other co-authors at MIT.

The study was supported by grants from the Marble Center for Cancer Nanomedicine, the Koch Institute Frontier Research Program, Frontier, the National Science Foundation, and the Welch Foundation.


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