Influence of Gold Nanoparticle Film Porosity on the Chemiresistive Sensing Performance

Abstract

The porosity of 1-hexanethiol-functionalised gold nanoparticle films was assessed and utilised as chemiresistor sensors. Electrochemical capacitance measurements showed that the accessibility of electrolytes of different ionic strengths into the pores depended on the thickness of the electric double layer formed. A large variation in capacitance was measured in 0.01-1000 mM NaClO 4 , implying a wide pore size distribution. The change in morphology of the nanoparticle films upon storage in air, water and ethanol for two weeks was investigated. There was a significant decrease in the electrochemical capacitance at high electrolyte concentrations for the ethanol-stored films compared to the freshly-prepared films suggesting a decrease in the number of small pores of radii in the range of 0.3-3 nm. This was further supported by optical topographical measurements where a decrease in the thickness of ethanolstored films was observed relative to the freshly-prepared films. The porous nature of the nanoparticle films was found to have an effect on the chemical sensing behaviour. When used as chemiresistor sensors, for the detection of heptane in water, the ethanol-stored films provided larger resistance changes and longer response times. This suggests that the more densely packed ethanol-stored films provided more sites that enabled film swelling, and that diffusion of the analyte occurred through the narrower water-filled pores. This demonstrates the effect of different storage conditions on film morphology and subsequently sensor response.

Gold nanoparticle superlattices: structure and cavities studied by GISAXS and PALS

“…7,36 Indeed, several studies indicated their inuence on the sensing properties. [37][38][39][40] For example, assemblies of thiol-stabilized cubic platinum nanoparticles, revealing a more compact structure than their spherical counterparts, showed considerably higher response amplitudes. 38 Further, the perforation of assemblies of thiol-stabilized GNPs has been shown to markedly alter the chemiresistive response.…”

“…39 For chemiresistive sensing in liquid phase using an assembly of thiol-stabilized GNPs it has been shown that reducing the number of cavities with diameters between 0.3 to 3 nm signicantly prolongs the response time and at the same time increases the response amplitudes. 40 The cavity sizes in that study were estimated using electrochemical capacitance measurements. A more widely used technique to study cavity sizes of nanoporous materials, such as zeolites, are gas adsorption (BET-) measurements.…”

Transistor‐Like Modulation of Gold Nanoparticle Film Conductivity Using Hydrophobic Ions

“…[ 8 ] Our group has expanded the potential utility of gold nanoparticle fi lms by showing that electrical resistance modulation can also occur in aqueous electrolyte solution. [ 4,[12][13][14][15][16][17][18] Following this, Lai et al [ 19 ] have shown that proteins can also modulate the resistance in biological samples. However, in all these cases, modulation of the nanoparticle fi lm resistance occurred via passive partitioning of a chemical species.…”

“…When the organic chemical species is positively charged, e.g. [ 4,[12][13][14][15][16][17][18] Following this, Lai et al [ 19 ] have shown that proteins can also modulate the resistance in biological samples. The positive gate voltage induces negative charges inside the nanoparticles which drives the positively charged ions (cetyl pyridinium) into the fi lm where the organic component of the species is believed to intercalate with the hexanethiolate coating and thereby increase the interparticle separation.…”

“…The ability of metal nanoparticle fi lms to passively change resistance in the presence of organic analytes has been exploited to develop chemiresistor sensors in the gas [6][7][8][9][10][11] and aqueous-phase [ 4,[12][13][14][15][16][17][18][19] for cancer, [ 9 ] environmental, [ 14,18 ] or microbial food spoilage [ 16 ] detection. Given the large number of charged biological, pharmaceutical, pesticide and herbicide molecules that are of interest for detection, the application of a gate potential could greatly broaden the development of sensor technology by enhancing their sensitivity.…”