Tuning the surface-enhanced Raman scattering effect to different molecular groups by switching the silver colloid...

Area of Science:

• Colloid and Surface Chemistry
• Spectroscopy
• Nanotechnology

Background:

• Surface-enhanced Raman scattering (SERS) is a powerful technique for molecular detection.
• The properties of silver colloids, such as size and surface chemistry, significantly influence SERS performance.
• Controlling these properties is crucial for optimizing SERS sensitivity and specificity.

Purpose of the Study:

• To investigate the role of hydroxylamine hydrochloride and solution pH in silver colloid formation.
• To examine the impact of pH on silver colloid dimensions and surface functional groups.
• To determine how pH affects SERS detection of various biological analytes and bacteria.

Main Methods:

• Synthesis of silver colloids using hydroxylamine hydrochloride.
• Characterization using Raman, FT-IR, UV-Vis spectroscopy, AFM, and zeta-size measurements.
• SERS analysis of biological molecules (RNA, albumin, etc.) and bacteria (P. aeruginosa, S. mutans) at varying pH.

Main Results:

• High pH values generally led to more pronounced SERS effects with sharper, higher spectral intensity.
• Low pH values resulted in protonation, aggregation, and altered surface chemistry, reducing SERS enhancement.
• pH-dependent SERS spectra were obtained from bacteria, allowing selective detection of different molecular groups, and the process was reversible.

Conclusions:

• Solution pH is a critical parameter for tuning silver colloid properties for SERS.
• pH control enables the production of site- or molecule-specific silver colloids.
• This approach allows for targeted enhancement of SERS signals for specific functional groups in analytes.