Measurement of Time-dependent Change of Metal Nanoparticles

Importance of the Topic

Metal nanoparticles such as gold and silver exhibit unique optical properties driven by surface plasmon resonance (SPR). This phenomenon underpins applications ranging from biosensing to antibacterial coatings. Monitoring time‐dependent spectral changes upon environmental triggers is essential for ensuring nanoparticle stability and functionality.

Objectives and Study Overview

This application note evaluates the Shimadzu UV‐1900 UV–Vis spectrophotometer’s ability to rapidly record absorption spectra of gold and silver nanoparticles. The study correlates particle size with SPR peak position and investigates aggregation kinetics induced by salt addition.

Used Instrumentation

• Spectrophotometer: Shimadzu UV‐1900
• Wavelength range: 300–1000 nm for gold, 300–700 nm for silver
• Scan speed: “Survey” mode (~29 000 nm/min)
• Sampling interval: 1.0 nm

Methodology

Commercial gold and silver nanoparticles (10, 30, 50 nm nominal diameter) were prepared at 0.02 mg/mL (gold) and 0.01 mg/mL (silver). Absorption spectra were acquired under the specified conditions. To induce aggregation, 600 µL of 25 wt.% NaCl solution was added to 3 mL of nanoparticle dispersion. Spectra were recorded at 0 s, 30 s, 1 min, 2 min, 4 min and up to 10 min post‐addition.

Main Results and Discussion

• Size‐dependent SPR: Both gold and silver nanoparticles exhibited red‐shifts in SPR peak wavelength as particle diameter increased, confirming theoretical predictions.
• Aggregation effects: Salt‐induced clustering caused decreased SPR band intensity and a concurrent rise in absorbance at longer wavelengths (700–800 nm for gold, 500–600 nm for silver), consistent with nanoparticle agglomeration.
• Instrument performance: The “Survey” scan mode delivered full‐range spectral data within seconds, capturing rapid optical changes during aggregation.

Benefits and Practical Applications

• Rapid formulation screening: Enables quick assessment of nanoparticle stability in research and development.
• Quality assurance: Early detection of aggregation supports product optimization in pharmaceuticals, coatings and diagnostics.
• Fundamental research: Facilitates detailed studies of plasmonic behavior in diverse colloidal systems.

Future Trends and Potential Applications

Future developments may focus on automated, high‐throughput nanoparticle characterization integrating flow cells and real‐time data analysis. Machine learning algorithms applied to rapid spectral datasets could enable predictive monitoring of nanoparticle behavior under varying conditions.

Conclusion

The Shimadzu UV‐1900 spectrophotometer, with its ultrafast “Survey” scanning capability, provides both high‐speed and high‐sensitivity measurements of gold and silver nanoparticle dispersions. It effectively captures static SPR properties and dynamic aggregation phenomena, offering a versatile tool for analytical and quality control laboratories.