Micromachined ultrasonic droplet generator based on a liquid horn structure

Meacham, J. Mark; Ejimofor, C.; Kumar, Sanjay; Degertekin, F. Levent; Fedorov, Andrei G.

doi:10.1063/1.1711187

Cited by 44 publications

(35 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Continued efforts to model and simulate droplet and ion transport in the air amplifier will enable improved designs and device implementation to further enhance ion transmission efficiency and lower limits of detection. The improvements shown in this work for standard ESI-MS should be also of great value to other emerging ambient ionization techniques such as DESI [21,22], MALDESI [23,24], and AMUSE [25,26].…”

Section: Resultsmentioning

confidence: 99%

Probing the mechanisms of an air amplifier using a LTQ-FT-ICR-MS and fluorescence spectroscopy

Dixon

Muddiman

Hawkridge

et al. 2007

J. Am. Soc. Mass Spectrom.

Self Cite

View full text Add to dashboard Cite

We report the first quantitative assessment of electrosprayed droplet/ion focusing enabled by the use of a voltage-assisted air amplifier between an electrospray ionization emitter and a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer (ESI-LTQ-FT-ICR-MS). A solution of fluorescent dye was electrosprayed with a stainless steel mesh screen placed in front of the MS inlet capillary acting as a gas-permeable imaging plate for fluorescence spectroscopy. Without use of the air amplifier, no detectable FT-ICR signal was observed, as well as no detectable fluorescence on the screen upon imaging using a fluorescence scanner. When the air amplifier was turned ON while electrospraying the fluorescent dye, FT-ICR mass spectra with high signal to noise ratio were obtained with an average ion injection time of 21 ms for an AGC target value of 5 ϫ 10 5 . Imaging of the screen using a fluorescence scanner produced a distinct spot of cross-sectional area ϳ33.5 mm 2 in front of the MS inlet capillary. These experimental results provide direct evidence of aerodynamic focusing of electrosprayed droplets/ions enabled by an air amplifier, resulting in improved electrospray droplet/ion capture efficiency and reduced ion injection time. A second set of experiments was carried out to explore whether the air amplifier assists in desolvation. By electrospraying a mix of quaternary amines, ratios of increasingly hydrophobic molecules were obtained. Observation of the solvophobic effect associated with electrospray ionization resulted in a higher abundance of the hydrophobic molecule. This bias was eliminated when the air amplifier was turned ON and a response indicative of the respective component concentrations of the molecules in the bulk solution was observed. (J Am Soc Mass Spectrom 2007, 18, 1909 -1913) © 2007 American Society for Mass Spectrometry I t is well known that electrospray ionization is a soft ionization technique that enables the study of biological samples by mass spectrometry [1]. However, it is estimated that 99.9% or more of the electrosprayed ions are lost in transport to the detector [2-6]. A recent publication indicates that significant sampling efficiency is obtained with a short emitter to capillary distance, at the expense of lower ionization efficiency [7]. At longer distances, less sample is captured, but there is improved ionization due to more efficient sample desolvation. Based on the results presented herein, along with previous reports, the air amplifier has the capabilities to improve capture efficiency and sample desolvation. Devices such as the ion funnel [8 -10], high-field asymmetric ion mobility spectrometry (FAIMS) [11][12][13], the air amplifier [14 -16], and an interface plate [17] have been reported to improve ion abundance. To translate current technology into future advances in mass spectrometry, systematic investigations of devices such as the air amplifier are necessary to improve instrument performance and subsequently the study of biological systems. The ...

show abstract

Section: Resultsmentioning

confidence: 99%

Probing the mechanisms of an air amplifier using a LTQ-FT-ICR-MS and fluorescence spectroscopy

Dixon

Muddiman

Hawkridge

et al. 2007

J. Am. Soc. Mass Spectrom.

Self Cite

View full text Add to dashboard Cite

show abstract

“…[15][16][17] One of the vibrators, an ultrasonic, can generate typical size of droplets. 18,19 However, the task of rapidly generating droplets in cell structures is not easy.…”

Section: -5mentioning

confidence: 99%

Novel method of generating water-in-oil(W/O) droplets in a microchannel with grooved walls

2011

View full text Add to dashboard Cite

We present a novel method of generating and retrieving droplets stored in microfluidic grooves or cavity structures. First we designed and fabricated polydimethylsiloxane microchannels with grooves on the walls and then produced a two-phase flow of oil and aqueous phases to form aqueous phase droplets in an oil state. We propose the following three mechanisms of droplet generation: the contact line on the groove wall continues moving along the wall and descends to the bottom of the cavity, confining the aqueous phase in the cavity; once the interface between the oil and aqueous phases moves into the cavity, the interface contacts the top of the neighboring groove; and a spherical droplet forms at the corner in the cavity due to surface tension. The viscosity of the oil phase and the surface tension of the interface determine whether a droplet can be generated. Then, we could adjust the velocity of the interface and the aspect ratio of the cavity to achieve the optimal conditions for generating the single droplet. We observed that the largest droplet is stably generated without a daughter droplet at typical values of free-stream velocity ͑10 l / min͒ and groove pitch 110 m for all three cases with different oil phases ͑20, 50, and 84 cP͒. This technique is expected to serve as a platform for dropletbased reaction systems, particularly with regard to monitoring cell behavior, in vitro expression, and possibly even micropolymerase chain reaction chambers.

show abstract

“…Details of the device operation and microfabrication processes are described elsewhere. 33 Characterization of the droplet formation and ejection physics, using stroboscopic visualization and scaling analysis has previously been conducted. 34 Finally, the AMUSE has recently been demonstrated as a "soft" ion source for bioanalytical mass spectrometry, 15,20,21 including investigations into charge separation 18 and droplet charging under static and dynamic electric fields.…”

Section: Experimental Charge Measurementsmentioning

confidence: 99%

“…33,34 Again, an electric field in the region of droplet pinch-off is used to control the transport of charge into a forming droplet. 17,18 In these applications, precise control over droplet charging is imperative.…”

Section: Introductionmentioning

confidence: 99%

Droplet charging regimes for ultrasonic atomization of a liquid electrolyte in an external electric field

2011

View full text Add to dashboard Cite

Distinct regimes of droplet charging, determined by the dominant charge transport process, are identified for an ultrasonic droplet ejector using electrohydrodynamic computational simulations, a fundamental scale analysis, and experimental measurements. The regimes of droplet charging are determined by the relative magnitudes of the dimensionless Strouhal and electric Reynolds numbers, which are a function of the process ͑pressure forcing͒, advection, and charge relaxation time scales for charge transport. Optimal ͑net maximum͒ droplet charging has been identified to exist for conditions in which the electric Reynolds number is of the order of the inverse Strouhal number, i.e., the charge relaxation time is on the order of the pressure forcing ͑droplet formation͒ time scale. The conditions necessary for optimal droplet charging have been identified as a function of the dimensionless Debye number ͑i.e., liquid conductivity͒, external electric field ͑magnitude and duration͒, and atomization drive signal ͑frequency and amplitude͒. The specific regime of droplet charging also determines the functional relationship between droplet charge and charging electric field strength. The commonly expected linear relationship between droplet charge and external electric field strength is only found when either the inverse of the Strouhal number is less than the electric Reynolds number, i.e., the charge relaxation is slower than both the advection and external pressure forcing, or in the electrostatic limit, i.e., when charge relaxation is much faster than all other processes. The analysis provides a basic understanding of the dominant physics of droplet charging with implications to many important applications, such as electrospray mass spectrometry, ink jet printing, and drop-on-demand manufacturing.

show abstract

Micromachined ultrasonic droplet generator based on a liquid horn structure

Cited by 44 publications

References 13 publications

Probing the mechanisms of an air amplifier using a LTQ-FT-ICR-MS and fluorescence spectroscopy

Probing the mechanisms of an air amplifier using a LTQ-FT-ICR-MS and fluorescence spectroscopy

Novel method of generating water-in-oil(W/O) droplets in a microchannel with grooved walls

Droplet charging regimes for ultrasonic atomization of a liquid electrolyte in an external electric field

Contact Info

Product

Resources

About