Quantitative surface acoustic wave detection based on colloidal gold nanoparticles and their bioconjugates

Area of Science:

• Materials Science
• Nanotechnology
• Sensor Technology

Background:

• Developing precise methods for immobilizing nanoparticles on sensor surfaces is crucial for advanced sensing applications.
• Surface Acoustic Wave (SAW) sensors offer high sensitivity for detecting mass changes, but require accurate calibration.
• Gold nanoparticles serve as ideal nanosized mass standards due to their uniform size and well-defined properties.

Purpose of the Study:

• To develop and validate a scheme for immobilizing monodispersed gold nanoparticles onto piezoelectric substrates for SAW sensors.
• To quantitatively correlate the frequency response of SAW sensors with the surface density of adsorbed gold nanoparticles.
• To demonstrate the utility of nanoparticle-enhanced SAW sensors for real-time mass monitoring in both gas and liquid environments.

Main Methods:

• Organosilane molecules were used as cross-linkers to immobilize 10-nm gold nanoparticles on lithium niobate and lithium tantalate substrates.
• High-resolution field-emission scanning electron microscopy and SAW sensors were employed for comparative measurements of nanoparticle adsorption kinetics.
• Rayleigh-SAW and guided shear horizontal-SAW (guided SH-SAW) sensors were utilized to monitor mass changes in gas and liquid phases, respectively.

Main Results:

• A quantitative correlation was established between SAW sensor frequency response and surface densities of adsorbed gold nanoparticles.
• Rayleigh-SAW sensors exhibited mass sensitivity over two orders of magnitude higher than conventional quartz crystal microbalance sensors.
• Guided SH-SAW sensors successfully demonstrated real-time monitoring of gold nanoparticle and DNA-gold nanoparticle conjugate adsorption in aqueous solutions.

Conclusions:

• Gold nanoparticles can be effectively immobilized on piezoelectric substrates, serving as reliable nanosized mass standards for SAW sensors.
• The developed nanoparticle-enhanced SAW sensors provide highly sensitive, real-time mass detection capabilities in both gas and liquid phases.
• This approach enables advanced applications in biosensing, such as determining the number of oligonucleotides bound per nanoparticle in real-time liquid-phase measurements.