Tuning the Interfacial Chemistry of Nanoparticle Assemblies via Spin-Coating: From Single Sensors to Monolithic Sensor Arrays

Sensor arrays based on gold nanoparticle (GNP) films are promising candidates for numerous applications, including medical diagnosis and health monitoring. Their economic fabrication, however, remains challenging. This study presents a facile route to GNP chemiresistors with tunable properties via layer-by-layer spin-coating (LbL-SC). Key steps involve the alternating deposition of dodecylamine-stabilized GNPs and mixtures of monothiols (MTs) with 1,9-nonanedithiol (9DT). The 9DT molecules serve to reinforce the growing film via GNP cross-linking while the MT ligands are used to tune the interfacial chemistry of the GNP assembly. Hence, by employing differently functionalized MTs the sensors' chemical selectivity can easily be adjusted. Further, by varying the MT-9DT ratio and adjusting the size of the MT ligands the sensitivity can be tuned along with the conductivity and optical properties of the films. In general, decreasing the 9DT fraction significantly enhances the sensitivity while the response isotherms change from Langmuir-Henry to Henry type. Finally, the cross-linked GNP films are robust enough to be patterned via photolithography. Hence, this study demonstrates the fabrication and application of monolithic sensor arrays. Different features of the responses to numerous analytes are used as input data for linear discriminant analyses (LDA), revealing that very similar analytes can be distinguished. Using various monothiol-dithiol mixtures and amine-stabilized gold nanoparticles, chemiresistors with tunable selectivity, enhanced sensitivity, and linear response isotherms are fabricated via facile layer-by-layer spin-coating. Combining this approach with photolithography allows for the fabrication of monolithic sensor arrays which enable the classification and discrimination of very similar volatile analytes. image