| Abstract
| - The immobilization scheme of monodispersed gold nanoparticles (10-nm diameter) on piezoelectric substratesurfaces using organosilane molecules as cross-linkershas been developed for lithium niobate (LiNbO3) andsilicon oxide (SiO2)/gold-covered lithium tantalate (LiTaO3)of Rayleigh and guided shear horizontal- (guided SH)surface acoustic wave (SAW) sensors. In this study,comparative measurements of gold nanoparticle adsorption kinetics using high-resolution field-emission scanningelectron microscopy and SAW sensors allow the frequencyresponses of SAW sensors to be quantitatively correlatedwith surface densities of adsorbed nanoparticles. Usingthis approach, gold nanoparticles are used as the “nanosized mass standards” to scale the mass loading in a widedynamical range. Rayleigh-SAW and guided SH-SAWsensors are employed here to monitor the surface masschanges on the device surfaces in gas and liquid phases,respectively. The mass sensitivity (∼20 Hz·cm2/ng) ofRayleigh-SAW device (fundamental oscillation frequencyof 113.3 MHz in air) is more than 2 orders of magnitudehigher than that of conventional 9-MHz quartz crystalmicrobalance sensors. Furthermore, in situ (aqueoussolutions), real-time measurements of adsorption kineticsfor both citrate-stabilized gold nanoparticles and DNA−gold nanoparticle conjugates are also demonstrated byguided SH-SAW (fundamental oscillation frequency of121.3 MHz). By comparing frequency shifts between theadsorption cases of gold nanoparticles and DNA−goldnanoparticle conjugates, the average number of boundoligonucleotides per gold nanoparticle can also be determined. The high mass sensitivity (∼6 Hz·cm2/ng) ofguided SH-SAW sensors and successful detection ofDNA−gold nanoparticle conjugates paves the way for real-time biosensing in liquids using nanoparticle-enhancedSAW devices.
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