Non-faradaic impedance characterization of an evaporating droplet for microfluidic and biosensing applications

Abstract

We develop a general numerical/analytic theory of non-faradaic impedance of an evaporating droplet, and validate the model by experiments involving droplets of various analyte concentrations deposited on a surface defined by coplanar electrodes. The impedance of the droplet Z(n0, t, f) is analyzed as a function of concentration (n0) of the ions in the solution, the measurement frequency (f) and the evaporation time (t). We illustrate the versatility of the model by determining the sensitivity enhancement α(t) of the droplet-based impedimetric nano-biosensor under different regimes of operation. The model should have broad applications in characterization/optimization of droplet-based systems, especially lab-on-chip components involving digital microfluidics.

Highly Sensitive and Practical Detection of Plant Viruses via Electrical Impedance of Droplets on Textured Silicon-Based Devices

“…Similar tests on flat silicon or gold surfaces were unsuccessful since the untreated surfaces were only partially and in-homogenously hydrophobic. The inhomogeneous surface causes droplets to have varying or low contact angles onto the surfaces i.e., the geometrical capacitance would be varying depending on droplet positions onto the supports [18]. Therefore, these surfaces could not allow the determination of a set of impedance data suitable for an unambiguous extraction of a calibration curve, depending solely on the virus concentration [18].…”

“…The resulting artificial cell membrane system was suitable for ion channel study and drug screening [17]. Furthermore, numerical/analytical theory have been developed for studying the impedance evolution of droplets involving various analyte concentrations when deposited on a surface defined by coplanar electrodes [18]. An attomolar (aM) scale limit was achieved in DNA hybridization by using microliter droplet in distilled water on a nanotextured superhydrophobic electrode array [19].…”

Evaporation-induced stimulation of bacterial osmoregulation for electrical assessment of cell viability

“…In addition, as a reference, we analyzed another group of cells that lost their osmoregulation ability due to heat treatment and therefore, are "osmoregulatory dead" (defined as "dead" throughout this work). Overall, we find that the droplet-based impedance sensors (25)(26)(27)(28) can selectively differentiate live vs. dead E. coli cells with 10-15% accuracy (comparable with the colony counting method) in less than 20 min.…”

“…(B) ρ tot * vs. ρ tot is shown for five different samples, where ρ tot * is calculated by using the algorithm described in A; ρ tot and α of S#1-S#5 are ∼ 8.65 × 10 4 , ∼ 8.65 × 10 4 , ∼ 8.65 × 10 4 , ∼ 8.65 × 10 5 , and ∼ 8.65 × 10 5 cells per milliliter, respectively, and 70%, 25%, 75%, 50%, and 70%, respectively. circuit model and conductance formulation can be found elsewhere (26).…”

“…Fabrication procedure of superhydrophobic nickel microelectrodes is explained in detail in our previous papers (25,26,28). The biosensor has a two-electrode configuration, with each electrode being an array of electroplated nickel fins (microscale structures) with width of a = 10 μm, height of H = 10 μm, spacing of b = 20 μm, and inplane length of H z = 4 mm patterned and deposited on a glass substrate.…”