A recent study published in the journal Materials Science in Semiconductor Processing describes an efficient method for constructing novel surface-enhanced Raman scattering (SERS) substrates based on functionalized single-walled carbon nanotubes (SWCNTs) to detect heavy metal ions.
Study: ZnO nanoparticles functionalized SWCNTs as highly sensitive SERS substrate for heavy metal ions detection. Image Credit: Rattiya Thongdumhyu/Shutterstock.com
Lead (Pb): A Toxic Heavy Metal Pollutant
Due to rapidly evolving technology, our ecosystem is becoming more contaminated, resulting in significant issues for developing a green environment. Heavy metal ions, which come from industrial, medical, and agricultural wastes, are by far the most dangerous environmental contaminants. This is due to the ease with which these metal ions combine in water, land, and air.
Lead (Pb) is a very hazardous heavy metal ion that causes major health issues in humans through the food system and drinkable water. Pb metallic ions are not biodegradable, and small levels of Pb can cause severe harm to human body functions and components owing to long-term build-up.
As a result, there is a rising need to form new and suitable technology for sensitive monitoring of Pb2+ ions.
Emerging Spectroscopy Techniques for Lead Detection
Several spectroscopic methods have been established for efficient sensing of heavy metallic ions, including inductively coupled plasma mass spectrometry (ICP-MS), fluorescence spectroscopy, and ultraviolet (UV) spectroscopy. However, the primary need is the rapid and extremely sensitive monitoring of heavy metallic ions at relatively small concentrations.
Surface-enhanced Raman scattering (SERS) is now considered one of the most sensitive developing spectroscopic methods. It is instrumental in environmental investigations since it generates vibrating spectroscopic imprints for specific solutes such as heavy metallic contaminants.
SERS is a surface-sensitive technology that improves Raman dispersion by adsorbing molecules onto carefully formulated rough metal surfaces. The major benefit of this approach is that it can detect particles at very low concentrations, even at a single-molecule level. Raman spectroscopy produces a signal as soon as a solitary molecule of substance makes contact with the medium.
Plasmonic Nanomaterials Like SWCNTs as SERS Based Sensors
Various kinds of plasmonic nanoparticles are frequently employed in the development of SERS-based detectors. Plasmonic nanoparticles exhibit aggregate plasmonic oscillations of conducting electrons via resonance in the visual or near-infrared (IR) range. These nanomaterials' optical sensitivity can be modified by modifying their size, structure, and content from UV to visible to IR range.
Carbon-based nanoparticles like carbon nanotubes (CNTs) and monolayer graphene are future interface plasmon enhancers that will provide a new level to SERS-based sensing. Because of its large surface area, robust chemical sensitivity, long-term durability, and intense light scattering qualities, single-wall carbon nanotubes have excellent sensing capabilities.
Novel ZnO Nanoparticles-based SWCNTs for Lead Detection
In this study, the researchers created a flexible sensing substrate by functionalizing SWCNTs with ZnO nanoparticles for extremely sensitive monitoring of Pb2+ ions in aquatic media. The produced substrates were characterized using several methods such as the Field Emission Scanning Electron Microscope (FESEM), X-Ray Diffraction (XRD), and Raman spectrometry.
At low temperatures, single-walled carbon nanotubes (SWCNTs) were created using the plasma-enhanced chemical vapor deposition (PECVD) process. The interface of SWCNTs was then synthesized and characterized with zinc oxide nanoparticles (ZnO NPs) through thermal evaporation to produce a ZnO@SWCNTs nanocomposite sheet as a SERS substrate.
Important Findings of the Study
The presented SERS substrate, ZnO@ SWCNTs, was shown to have great accuracy and sensitivity for the detection of Pb2+ ions, with a lower limit of detection of 0.225 nM and long-term durability and reproducibility. The existence of ZnO NPs, which amplify the local electric fields, results in this high sensitivity.
More significantly, the SERS substrate of extremely sensitive and stable ZnO@SWCNTs may offer a diverse foundation for metal ion monitoring in an aquatic solution. The SERS substrate's stability and repeatability analysis revealed that the Raman intensity readings are repeatable in the Pb2+ metallic ion solution.
It is expected that creating this sophisticated SERS substrate would pave the way for a new research sector dedicated to discovering solutions for a sustainable and green ecosystem.
Parveen, S. et al. (2022). ZnO nanoparticles functionalized SWCNTs as highly sensitive SERS substrates for heavy metal ions detection. Materials Science in Semiconductor Processing. Available at: https://www.sciencedirect.com/science/article/pii/S1369800122003900?via%3Dihub