MTL Annual Research Report 2011

Using suspended nanochannel resonators (SNRs), we demonstrate measurements of mass in solution with a resolution of 27 ag in a 1-kHz bandwidth, which represents a 100-fold improvement over existing suspended microchannel resonators and, to our knowledge, is the most precise mass measurement in liquid today ^[1] . As shown in Figure 1a,b, SNR consists of a cantilever that is 50 µm long, 10 µm wide, and 1.3 µm thick, with an embedded nanochannel that is 2 µm wide and 700 nm tall. The SNR has a resonance frequency near 630 kHz and exhibits a quality factor of approximately 8000 when dry and when filled with water. Figure 2 shows mass histograms corresponding to short- term (10 s, 1 kHz bandwidth) baseline frequency noise and the frequency shift measured from a population of 50-nm diameter gold nanoparticles in the flow-through mode, also at a 1-kHz bandwidth. The standard deviation of the baseline frequency noise is 38.6 ppb, and the mass sensitivity of 0.890 Hz/fg is deduced from the size specification of the nanoparticles and the density of gold. The average and standard deviation of the measured gold nanoparticles are 1.20 and 0.20 fg, respectively.  In addition, we introduce a new method that uses centrifugal force caused by vibration of the cantilever to trap particles at the free end. This approach eliminates the intrinsic position- dependent error of the SNR and also improves the mass resolution by increasing the averaging time for each particle.