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Nanoelectromechanical systems (NEMS) enable mass sensing with unprecedented sensitivity and mass dynamic range. Previous works have relied on statistical analysis of multiple landing events to assemble mass spectra. Here we demonstrate the utility of using multiple modes of the NEMS device in determining the mass of individual molecules landing on the NEMS. Analyte particles in vapor form are produced using matrix assisted laser desorption ionization. Resonant frequencies of the first two modes of a single NEMS device, placed in close proximity to the analyte source, are tracked using parallel phase locked loops. Each analyte molecule landing on the NEMS generates a distinct frequency shift in the two modes. These time correlated frequency jumps are used to evaluate the mass of each analyte particle landing on the NEMS and thus generate mass spectra. We present the latest experimental results …