A diffusion limited sorption-desorption noise model for polymer coated SAW chemical sensors

作者：Yadava R D S^*; Verma Vivek K

来源：Sensors and Actuators B: Chemical , 2014, 195: 590-602.

DOI：10.1016/j.snb.2014.01.067

• SAW chemical sensor
• Sorption-desorption noise
• Chemical detection sensitivity
• Minimum limit of detection
• Concentration resolution
• Stochastic resonance

The paper presents a new model for the sorption-desorption noise in polymer-coated SAW chemical sensors. The model visualizes the sorption and desorption phenomena in polymer coatings similar to the activated gaseous adsorption and desorption on solid surfaces, however, the interpretations of the activation energy and the attempt frequency in the two cases are fundamentally different. In the case of gaseous adsorption/desorption on the solid surfaces the activation energies are associated with discrete surface sites (or traps) having potential well or barrier like character for the adsorbates. The adsorption is modeled as a succession of discrete random events of entrapment for the gas molecules striking the surface, and the desorption as a thermally activated escape from the traps by overcoming the potential barrier. The stochastic nature of these processes generates instantaneous fluctuation in the gaseous load on the surface. In contrast, the present model visualizes the change in free energy associated with the partitioning of analytes from the vapor phase into the polymer coating as the activation energy for both the sorption and desorption processes. The attempt frequency for desorption is determined by the analyte diffusion time across the polymer coating thickness. In equilibrium, the average rates for sorption and desorption are equal. The instantaneous fluctuation of the vapor load in the polymer coating generates noise in the sensor response. The model predicts an exponential autocorrelation function for the polymer mass density fluctuation with variance in proportion to the average mass loading. This results in Lorentzian phase noise spectrum for the SAW sensor oscillators with bandwidth determined by the inverse diffusion time. The paper presents some numerical results for the analyte concentration resolution and limit of detection and the phase noise spectrum by assuming typical sensing conditions. A possibility for enhancing sensor performance by stochastic resonance is also proposed by utilizing nonlinear interaction between sorption-desorption noise and a modulating signal generated by modulation of vapor concentration.

• 出版日期2014-5