Characterization of the Additional Pseudo‐Crossover Frequency of Nanoparticles in Low Frequency Dielectrophoresis Regime

Dielectrophoresis (DEP) is a powerful tool for manipulating particles using non-uniform electric fields. This study combines numerical simulations and experiments to investigate crossover frequencies (COFs) for micro- and nanoparticles in a 3D microfluidic device with circular traps. MATLAB simulations revealed an inverse relationship between particle size and COF. For microparticles with diameters of 1.03, 2.27, 4.42, and 6.83 µm, the COFs were calculated as 769.10, 352.76, 183.96, and 120.51 kHz, respectively. For nanoparticles measuring 50, 170, and 500 nm, the corresponding COFs were 15.6, 4.62, and 1.57 MHz. These results closely matched experimental data. Notably, additional low-frequency pseudo-COFs emerged in experiments for nanoparticles ranging from 2 to 8 kHz (50 nm), 10 to 50 kHz (170 nm), and 40 to 100 kHz (500 nm). These frequencies proportionally increased with nanoparticle size and corresponded to unexpected negative DEP (nDEP)-like behavior under positive DEP (pDEP) conditions. This effect is attributed to low-frequency alternating current electroosmosis (ACEO), which dominates the DEP response of the nanoparticles smaller than 1 µm. These findings demonstrate strong agreement between numerical simulations and experimental results while also revealing the limitations of traditional models in predicting nanoparticle behavior under DEP. We expect that these results can also be applied to the manipulation of various bioparticles.