(251q) The Impact of Different Waveforms on Particle Trapping Efficiency When Using 3D Carbon-Electrode Dielectrophoresis 

Here we study the use of different waveforms when trapping latex particles on 3D carbon electrodes contained in a microfluidic channel using positive dielectrophoresis (DEP). DEP refers to motion induced on a targeted particle by a non-uniform electric field. The magnitude of such motion depends mainly on the particle size and the magnitude of the polarizing signal. The direction of the force, either towards as in positiveDEP or away from the field gradient in the case of negativeDEP, depends on the difference of electrical polarizability between the particle and the suspending media. Here we focus on assessing the potential advantages of optimizing the waveform of the polarizing signal to improve efficiency when extracting particles from a flow. Sinusoidal, square, and ramp signals of a given frequency and amplitude were characterized and compared based on their RMS voltage value (see table 1). The RMS value of the square signal is equal to its amplitude a, while the RMS values of the sinusoidal and ramp signal are only and of the signal amplitude respectively. Hence, the use of a square waveform is expected to induce the strongest electric field gradient of the three waveforms, and thus a higher degree of trapping. The goal of this work is to quantify the trapping latex particles when using different waveforms of varying frequencies.

Fluorescent latex particles, 1μm in diameter, were suspended in Distilled Water (DI) to obtain a concentration of 10⁷ particles/ml. The experimental protocol is similar to that previously presented by this group [1-4]. Briefly, the particles were flowed through an array of 3D carbon electrodes polarized by a specific waveform to trap targeted particles. Once trapped, the particles were washed with DI water. The field was then turned off to release the particles. The fluorescence intensity at the end of the electrode array was monitored throughout the experiment. Trapping efficiency was evaluated by comparing the difference in fluorescence intensity between the frame immediately before turning the field off and the area under the intensity curve obtained after turning the electric field off. Hence, a high area value means strong trapping. ImageJ software was used to obtain the levels of brightness in each frame of the recorded video. The data was plotted and the sums of the values under the curve were compared. The frequencies of interest ranged from 5 kHz to 50 kHz at an amplitude of 15 Vpp.

Initial results are shown in Figure 1. Using the square signal, the greatest amount of particles was released when the field was turned off compared to the sinusoidal and ramp signals at all frequencies above 5 kHz. This behavior suggests that trapping is most effective when using the square signal. The amount of particles trapped is proportional to the RMS value of each signal. Because the RMS value of the square signal is the greatest among the sinusoidal and ramp signals, it trapped the most particles on the electrodes. Likewise, the ramp signal, with the lowest RMS value, was the least effective at trapping particles on the carbon electrodes. Electrothermal effects begin to heat the media at low frequencies and cause the particles to waver between electrodes; thus, results below 5 kHz were inconclusive.

From these experiments the use of a square signal appears to be the most effective in trapping latex particles when compared with the sinusoidal and ramp signals. The results produced coincide with the values of the RMS value of each electrical signal.

Ongoing work is on characterizing trapping based on the energy delivered by each of the signals and the dynamics of particle accumulation in positiveDEP areas when using each of the waveforms. This will permit a better understanding on the phenomena induced when using different signals.

REFERENCES:

1. M. Islam, R. Natu, M. F. Larraga-Martinez and R. Martinez-Duarte â??Enrichment of diluted cell population from large sample volumes using 3D Carbon-electrode Dielectrophoresisâ? Biomicrofluidics, 10, 033107 (2016).
2. M. Elitas, R. Martinez-Duarte, N. Dhar, J. McKinney and P. Renaud, â??Dielectrophoresis-based purification of antibiotic-treated bacterial subpopulationsâ?. Lab on a Chip, 14, (11) 1850-1857 (2014).
3. M.C. Jaramillo, R. Martinez-Duarte, M. Hüttener, P. Renaud, E. Torrents and A. Juarez, â??Increasing PCR sensitivity by removal of Polymerase inhibitors in natural samples using Dielectrophoresisâ?. Biosensors and Bioelectronics, 43, 297-303 (2013).
4. R. Martinez-Duarte, F. Camacho-Alanis, P. Renaud and A. Ros, â??Dielectrophoresis of lambda-DNA using 3D carbon electrodesâ? Electrophoresis, 34, 1113-1122 (2013).