Fast On-Site Speciation and High Spatial Resolution Imaging of Labile Arsenic in Freshwater and Sediment Using the...

Area of Science:

• Environmental Science
• Analytical Chemistry
• Materials Science

Background:

• Diffusive Gradients in Thin Films (DGT) is effective for passive sampling but not rapid on-site analysis.
• Surface-Enhanced Raman Spectroscopy (SERS) offers ultrasensitive on-site detection but struggles with complex matrices.
• Existing methods lack simultaneous speciation and imaging capabilities for contaminants in complex environmental samples.

Purpose of the Study:

• To develop an integrated DGT-SERS sensor for simultaneous, on-site speciation and imaging of arsenic species.
• To overcome the limitations of DGT in rapid analysis and SERS in complex sample matrices.
• To demonstrate the sensor's applicability in real-world environmental conditions, including sediment-water interfaces.

Main Methods:

• Fabrication of a hierarchical nanostructure (PAM/Ag mirror/AgNPs) within a polyacrylamide hydrogel DGT device.
• Integration of the nanostructure as both the DGT binding phase and the SERS substrate.
• Utilizing size exclusion within the DGT diffusive layer to prevent matrix interference with SERS hotspots.

Main Results:

• The DGT-SERS sensor achieved simultaneous detection of As(III) and As(V) at low μg L⁻¹ levels (0.9 and 0.8 μg L⁻¹, respectively).
• Rapid on-site Raman analysis took only 2 seconds using a portable spectrometer without DGT disassembly.
• The sensor successfully produced the first 2D micron-scale images of As(III) and As(V) distribution at the sediment-water interface.

Conclusions:

• The developed DGT-SERS sensor provides a powerful tool for rapid, on-site speciation and imaging of contaminants in complex environmental matrices.
• This technology mitigates matrix effects and enables sensitive detection, paving the way for next-generation DGT devices.
• The study highlights the potential of integrating passive sampling with advanced spectroscopic techniques for environmental monitoring.