Recently we reported surface acoustic wave nebulization (SAWN) (S. Heron et al. Anal. Chem. 2010) as a novel approach for the generation of multiply-charged ions for mass spectrometry from a planar surface. For various reasons including the lack of an applied voltage, SAWN has been shown to produce ions of lower energy than electrospray ionization (Huang et al. JASMS 2012). SAWN is also easily integrated with both digital microfluidics (DMF) and molded microfluidics due to its planar nature. While the initial report used progressive wave (PW) interdigitated electrodes (IDT), standing wave (SW) IDTs have been shown (Ju et al. Sensors and Actuators A: Physical. 2008) to produce aerosolized droplets of smaller diameter. We tested the hypothesis that smaller aerosolized droplets would decrease limit of detection (LOD) by mass spectrometry by virtue of better desolvation of smaller than larger PW generated droplets. As a result of these experiments using SW SAWN chips to interface to MS ion detection sensitivity improved 3-orders of magnitude and pushed detection of peptides nebulized by SW IDTs down to low femtomoles on chip. Theory also predicts that aerosolized droplet diameter is inversely proportional to the applied IDT frequency. Based on our existing data and this theory, we should be able to tailor aerosolized droplets diameter for the desired application. Here, we report on the effects of high frequency (HF) SW SAWN chips operating at a frequency of 20 and 30 MHz to further improve SAWN sensitivity. We are now analyzing the effects of higher operational frequencies to see if this will affect the pinch off on the droplet surface in a way that will further reduce the size of the droplets and lead to an even greater increase in sensitivity.

Development of a surface acoustic wave nebulization source for mass spectrometry

248th National Meeting (2014)

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