Abstract
A new DEP spectroscopy method and supporting theoretical model is developed to systematically quantify the dielectric properties of nanoparticles using continuously pulsed DEP collection rates. Initial DEP collection rates, that are dependent on the nanoparticle dielectric properties, are an attractive alternative to the crossover frequency method for determining dielectric properties. The new method introduces dual-cycle amplitude modulated and frequency-switched DEP (dual-cycle DEP) where the first collection rate with a fixed frequency acts as a control, and the second collection rate frequency is switched to a chosen value, such that, it can effectively probe the dielectric properties of the nanoparticles. The application of the control means that measurement variation between DEP collection experiments is reduced so that the frequency-switched probe collection is more effective. A mathematical model of the dual-cycle method is developed that simulates the temporal dynamics of the dual-cycle DEP nanoparticle collection system. A new statistical method is also developed that enables systematic bivariate fitting of the multifrequency DEP collection rates to the Clausius–Mossotti function, and is instrumental for determining dielectric properties. A Monte-Carlo simulation validates that collection rates improve estimation of the dielectric properties, compared with the crossover method, by exploiting a larger number of independent samples. Experiments using 200 nm diameter latex nanospheres suspended in 0.2 mS/m KCl buffer yield a nanoparticle conductivity of 26 mS/m that lies within 8% of the expected value. The results show that the dual-frequency method has considerable promise particularly for automated DEP investigations and associated technologies.
Highlights
DEP is an important electrokinetic technique for micromanipulating and transporting micro- and nanoscale biological particles suspended in aqueous media [1,2,3]
The dual frequency collection rates comprised of a control collection pulse set at, f1 = 0.7 MHz and a probe pulse that ranged in carrier frequency from f2 = 1.0 to 4.0 MHz
The application of a control positive DEP (pDEP) collection cycle, preceding the probe cycle acts to mitigate against experimental variations that arise from fluctuations in localized nanoparticle concentrations
Summary
Before switching on the DEP force at the start of the collection phase of the cycle t < tc, Fig. 2A(i), the nanoparticles are uniformly distributed with the initial number of nanoparticles close to the array, nci (the subscripts “c” and “i” denote “collection” phase of cycle and “initial” time-point). Switching off the alternating current potential at t = tr initiates the release phase since there is no longer any pDEP force to trap the nanoparticles, and they diffuse into the bulk medium, Fig. 2A(iv), eventually reaching release SS (release (phase) steady state (RS)) at t = trs. In the scheme where on-off switch period times are sufficiently long for the system to reach SS in each of the phases, the difference between the collection SS and the initial nanoparticle number close to the array, is the initial to CS transition, ⌬ns = ncs − nci.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
