A deep study of two-dimensional transition metal chalcogenides

Two-dimensional materials, like transition metal dichalcogenide, have applications in public health because of their large surface area and high surface sensitivities, along with their unique electrical, optical, and electrochemical properties. A research team has undertaken a review study of methods used to modulate the properties of two-dimensional transition metal dichalcogenide (TMD). These methods have important biomedical applications, including biosensing.

The team's work is published in the journal Nano Research Energy.

The team's goal is to present a comprehensive summarization of this promising field and show challenges and opportunities available in this research area.

"In this review, we focus on the state-of-the-art methods to modulate properties of two-dimensional TMD and their applications in biosensing. In particular, we thoroughly discuss the structure, intrinsic properties, property modulation methods, and biosensing applications of TMD," said Yu Lei, an assistant professor at the Institute of Materials Research, Shenzhen International Graduate School, Tsinghua University.

Since graphene was discovered in 2004, two-dimensional materials, such as TMD, have attracted significant attention. Because of its unique properties, two-dimensional TMD can serve as the atomically thin platforms for energy storage and conversion, photoelectric conversion, catalysis, and biosensing. TMD also displays a wide band structure and has unusual optical properties. Yet another benefit of two-dimensional TMD is that it can be produced in large quantities at a low cost.

In public health, reliable and affordable in vitro and in vivo detection of biomolecules is essential for disease prevention and diagnosis. Especially during the COVID-19 pandemic, people have suffered not only from the physical disease, but also from the psychological problems related to extensive exposure to stress.

Extensive stress can result in abnormal levels in biomarkers such as serotonin, dopamine, cortisol, and epinephrine. So, it is essential that scientists find non-invasive ways to monitor these biomarkers in body fluids, such as sweat, tears, and saliva. In order for health care professionals to quickly and accurately assess a person's stress and diagnose psychological disease, biosensors are of significant importance in the diagnostics, environmental monitoring, and forensic industries.

The team reviewed the use of two-dimensional TMD as the functional material for biosensing, the approaches to modulate the properties of TMD, and different types of TMD-based biosensors including electric, optical, and electrochemical sensors.

"Public health study is always a major task in preventing, diagnosing, and fighting off the diseases. Developing ultrasensitive and selective biosensors is critical for diseases prevention and diagnosing," said Bilu Liu, an associate professor and a principal investigator at Shenzhen Geim Graphene Center, Shenzhen International Graduate School, Tsinghua University.

Two-dimensional TMD is a very sensitive platform for biosensing. These two-dimensional TMD based electrical/optical/electrochemical sensors have been readily used for biosensors ranging from small ions and molecules, such as Ca²⁺, H⁺, H₂O₂, NO₂, NH₃, to biomolecules such as dopamine and cortisol, that are related to central nervous disease, and all the way to molecule complexities, such as bacteria, virus, and protein.

The research team determined that despite the remarkable potentials, many challenges related to TMD-based biosensors still need to be solved before they can make a real impact. They suggest several possible research directions. The team recommends that the feedback loop assisted by machine learning be used to reduce the testing time needed to build the database needed for finding the proper biomolecules and TMD pairs.

Their second recommendation is the use of a feedback loop assisted by machine learning to achieve the on-demand property modulation and biomolecules/TMD database. Knowing that TMD-based composites exhibit excellent performance when constructed into devices, their third recommendation is that surface modifications, such as defects and vacancies, be adopted to improve the activity of the TMD-based composites.

Their last recommendation is that low-cost manufacturing methods at low temperature be developed to prepare TMD. The current chemical vapor deposition method used to prepare TMD can lead to cracks and wrinkles. A low-cost, low-temperature method would improve the quality of the films. "As the key technical issues are solved, the devices based on two-dimensional TMD will be the overarching candidates for the new healthcare technologies," said Lei.