The measurement of electrical bioimpedance is a non-invasive detection approach similar to microfluidic cell detection, although it focuses on tissue rather than on individual cells. The technique is widely used for medical purposes, and is complementary to physicochemical and biochemical methods. Applications include bioelectrical impedance analysis (BIA), electrocardiography (ECG), electrical impedance tomography (EIT), and electrical impedance myography (EIM). In these applications, a weak AC voltage or current signal is applied to the body tissue, which comprises resistive body water and capacitive cell membrane. The resulting current or voltage signal is measured with a phase-sensitive technique to quantify the complex electrical impedance of the tissue.
An LCR meter is often used to measure bioimpedance at one or several fixed frequencies typically ranging between 10 Hz and 100 kHz, but no equivalent circuit model can be confirmed based on such a limited dataset. This range of frequencies is also insufficient to capture the full picture of the tissue's impedance, and it is neither suitable for penetrating the cell membrane (which requires frequencies above 1 MHz) nor to distinguish low-frequency signals from heartbeats or breathing (on the order of 1 Hz or below).
The MFIA Impedance Analyzer and the HF2LI Lock-in Amplifier give access to broad frequency ranges going from 1 mHz to 5 MHz and 50 MHz, respectively, and offer both 2-terminal and 4-terminal configurations (also known as 2-wire or 4-wire configurations). In particular, the advantage of the 4-terminal arrangement (see Figure 1) is to mitigate the effect of the contact resistance between the electrodes and the tissue. If the contact resistance itself is the parameter of interest, it can be determined by measuring in 2-terminal and 4-terminal configurations sequentially. In addition to frequency-domain sweeps of impedance and related parameters (see Figure 2), time-domain measurements make it possible to study the time evolution of impedance, as in the case of a fast change in a neuron network or a small change due to a subtle muscle movement (as shown in Figure 3).
The Benefits of Choosing Zurich Instruments
- Determine your equivalent circuit model thanks to impedance sweeps over a wide frequency range including the low-frequency regime.
- Tracking fast impedance and phase changes with high precision and at high speed only requires the LabOne Plotter or Data Acquisition modules – no external digitizer card is needed.
- Save time by performing more measurements in parallel: probing the frequency-dependent impedance at multiple frequencies simultaneously is possible with the MF-MD or HF2LI-MF options.
- Workflow automation becomes straightforward thanks to the included LabOne APIs for Python, C, MATLAB®, LabVIEW™ and .NET.
Please note: The MFIA is suitable for laboratory research use only and should not be used for diagnostic procedures.