Analyte-Responsive Metal–Organic Frameworks of Polymer-Stabilized Silver Nanoparticles for Gas Sensors: A Comparative Study Using Surface Plasmon Resonance and Quartz Crystal Microbalance Techniques

Composite nanostructures stabilized by responsive polymers are of undoubted interest for chemical sensors. The combination of a heavy metal core with polymer functionality creates a smart nanobot in which the inertial mass of the nanoparticle enhances the initial adsorption effect of an analyte-sensitive organic nanoactuator. In this report, we discuss advanced QCM sensors in which the informative signal is due to a change in the structural organization, the triggering factor for activation of which is the adsorption of the analyte. Silver nanoparticles of a 60 nm diameter stabilized by a branched polyethyleneimine polymer (BPEI) and low-molecular-weight citric acid (CIT) were used as a sensing coating for SPR and QCM transducers (10 MHz) tested on water and ethyl alcohol vapor. SPR spectroscopy showed the behavior typical of organic sensing layers, whereas the BPEI-coated QCM sensor showed a response of the opposite sign for water and ethanol vapor. The anti-Sauerbrey behavior with an increasing loading of QCM sensors results from changes in the contacts of nanoparticles with the surface and with each other. The dynamic relaxations of the sensor architecture under alternating accelerations, initiated by adsorption on sensitive polymer nanoactuators and enhanced by the presence of “heavy” metal nanoparticles with a high inert mass open the possibility of formulating a fundamentally different approach to the detection of specific analytes than the traditional loading-based approach.