Fluctuations of the number of adsorbed molecules due to adsorption–desorption processes coupled with mass transfer and surface diffusion in bio/chemical MEMS sensors

• Theory of fluctuations of the number of adsorbed particles in sensors is devised.
• Adsorption–desorption, mass transfer and surface diffusion are considered.
• The fluctuations spectrum contains information about the adsorbed analyte.
• Novel detection methods based on the fluctuations spectrum analysis are proposed.
• Detection of various analytes using a single nonfunctionalized sensor is suggested.

In this study we have developed, for the first time, the comprehensive theoretical model of the fluctuations of the number of adsorbed molecules in MEMS chemical and biological sensors, taking into account the processes of mass transfer, adsorption and desorption, and surface diffusion of adsorbed molecules. It is observed that the shape of the fluctuations spectrum contains information about various parameters of the adsorbed analyte and that even the analytes with the same affinity for the same binding sites have different spectra. The numerical calculations performed using the derived theory show that the influence of surface diffusion on the fluctuations spectrum can be significant. The practical value of this work stems from the fact that the fluctuations of the number of adsorbed molecules can be a dominant noise component in affinity-based bio/chemical sensors. Therefore, the derived theory is useful for development of the methods for the detection of analytes based on frequency domain analysis of the measured fluctuations. The recognition of an adsorbed analyte using sensors with non-functionalized sensing surface will also be considered using the presented theory.

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