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. 2020 Dec 16;10(12):208.
doi: 10.3390/bios10120208.

Interdigitated Sensor Optimization for Blood Sample Analysis

Julien Claudel  1 , Thanh-Tuan Ngo  1 , Djilali Kourtiche  1 , Mustapha Nadi  1
Affiliations

Interdigitated Sensor Optimization for Blood Sample Analysis

Julien Claudel et al. Biosensors (Basel). .

Abstract

Interdigitated (ITD) sensors are specially adapted for the bioimpedance analysis (BIA) of low-volume (microliter scale) biological samples. Impedance spectroscopy is a fast method involving simple and easy biological sample preparation. The geometry of an ITD sensor makes it easier to deposit a sample at the microscopic scale of the electrodes. At this scale, the electrode size induces an increase in the double-layer effect, which may completely limit interesting bandwidths in the impedance measurements. This work focuses on ITD sensor frequency band optimization via an original study of the impact of the metalization ratio α. An electrical sensor model was studied to determine the best α ratio. A ratio of 0.6 was able to improve the low-frequency cutoff by a factor of up to 2.5. This theoretical approach was confirmed by measurements of blood samples with three sensors. The optimized sensor was able to extract the intrinsic electrical properties of blood in the frequency band of interest.

Keywords: biosensors; blood analysis; impedance spectroscopy; interdigitated electrodes.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Geometric parameters of interdigitated sensors; (b) Electric current displacement between electrodes; (c) Electrical model of an interdigitated sensor and sample (an ionic solution).
Figure 2
Figure 2
Electrical equivalent circuit for the double-layer impedance of one electrode.
Figure 3
Figure 3
Typical complex conductivity and relative permittivity values for a blood sample.
Figure 4
Figure 4
Typical curve profiles for biological and electrolyte samples.
Figure 5
Figure 5
Low cutoff frequency as a function of α.
Figure 6
Figure 6
(a) Photograph of Sensors 1 with SU_8 well and blood sample, and (b) optical microscope image of different Sensor 1 digits.
Figure 7
Figure 7
Bode diagrams of the impedances for three different calibrated solutions measured with Sensor 1.
Figure 8
Figure 8
Bio impedance measurement setup.
Figure 9
Figure 9
Interdigital electrode sensors connected to the PCB circuit.
Figure 10
Figure 10
Bode diagrams for blood impedance characterizations (a) in modules, and (b) in phases.
See this image and copyright information in PMC

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