ClotChip: A Microfluidic Dielectric Sensor for Point-of-Care Assessment of Hemostasis

Abstract

This paper describes the design, fabrication, and testing of a microfluidic sensor for dielectric spectroscopy of human whole blood during coagulation. The sensor, termed ClotChip, employs a three-dimensional, parallel-plate, capacitive sensing structure with a floating electrode integrated into a microfluidic channel. Interfaced with an impedance analyzer, the ClotChip measures the complex relative dielectric permittivity, ϵ_r , of human whole blood in the frequency range of 40 Hz to 100 MHz. The temporal variation in the real part of the blood dielectric permittivity at 1 MHz features a time to reach a permittivity peak, , as well as a maximum change in permittivity after the peak, , as two distinct parameters of ClotChip readout. The ClotChip performance was benchmarked against rotational thromboelastometry (ROTEM) to evaluate the clinical utility of its readout parameters in capturing the clotting dynamics arising from coagulation factors and platelet activity. exhibited a very strong positive correlation ( r = 0.99, p < 0.0001) with the ROTEM clotting time parameter, whereas exhibited a strong positive correlation (r = 0.85, p < 0.001) with the ROTEM maximum clot firmness parameter. This paper demonstrates the ClotChip potential as a point-of-care platform to assess the complete hemostatic process using <10 μL of human whole blood.

Fig. 1

Conceptual illustration of a POC dielectric coagulometer utilizing the proposed ClotChip microfluidic sensor.

Fig. 2

Illustration of the ClotChip design and fabrication steps along with the experimental setup. A) Cross-sectional and top views of the ClotChip. B) ClotChip fabrication and assembly procedure. C) Photograph of the fabricated ClotChip loaded with human whole blood as the MUT. D) Photograph of the testing setup.

Fig. 3

Variation in ${\epsilon }_r^{\text{'}}$ of blood during coagulation. A) Surface plot of the variation in ${\epsilon }_r^{\text{'}}$ of human whole blood versus time and frequency. B) Histogram plot of the peak frequency for all tested blood samples. C) 2D slice of the surface plot showing variation in ${\epsilon }_r^{\text{'}}$ versus time at 1MHz. D) 2D slice of the surface plot showing variation in ${\epsilon }_r^{\text{'}}$ versus frequency at 5 minutes.

Fig. 4

Time course of variation in ${\epsilon }_r^{\text{'}}$ at 1MHz for human whole blood without (black square) and with (blue diamond) coagulation initiated by the addition of CaCl₂ to a citrated (anticoagulated) blood sample [32].

Fig. 5

Variation in coagulation time induced by a change in temperature. A) Time course of variation in ${\epsilon }_r^{\text{'}}$ at 1MHz for CaCl₂-treated human whole blood at various temperatures. B) Bar graph comparing the ClotChip readout parameter T_peak versus visual observation-based readings of the coagulation time for various temperatures. Horizontal lines indicate statistically significant difference in coagulation time at different temperatures (p < 0.05). C) Fitted curve to the ClotChip readout parameter T_peak showing a power relationship between the coagulation time and temperature (R² = 0.8876). Error bars represent the standard deviation of measurements run in triplicate for each temperature.

Fig. 6

Variation in coagulation time induced by changes in CaCl₂ concentration. A) Bar graph comparing the ClotChip readout parameter T_peak versus visual observation-based readings of the coagulation time for various CaCl₂ concentrations. Horizontal lines indicate statistically significant difference in coagulation time at different concentrations (p < 0.05). B) Fitted curve to the ClotChip readout parameter T_peak showing a power relationship between the coagulation time and CaCl₂ concentration (R² = 0.8344). Error bars represent the standard deviation of measurements run in triplicate for each CaCl₂ concentration.

Fig. 7

Comparison of ClotChip T_peak and ROTEM CT parameters. A) Time course of variation in ${\epsilon }_r^{\text{'}}$ at 1MHz for an untreated whole blood sample and for the same sample treated with anti-thrombin as well as thrombin. B) ROTEM profiles obtained for the three blood samples used in Fig. 7A. The arrow shows the clotting time (CT) of the anti-thrombin-treated blood sample, defined as the time taken for the ROTEM profile to reach an amplitude of 2mm. C) A very strong positive correlation (r = 0.99, p < 0.0001, n = 9) was observed between the ClotChip T_peak and ROTEM CT parameters. For all plots, error bars indicate duplicate measurements and are presented as mean ± standard error of the mean (SEM).

Fig. 8

Comparison of ClotChip Δε_r,max and ROTEM MCF parameters. A) Time course of variation in ${\epsilon }_r^{\text{'}}$ at 1MHz for an untreated whole blood sample (CyD concentration of 0μM) and for the same sample treated with CyD concentrations of 2.5μM and 10μM. B) ROTEM profiles obtained for the three blood samples used in Fig. 8A. The arrows show the maximum clot firmness (MCF) of the 10μM-CyD-treated blood sample. C) A strong positive correlation (r = 0.85, p < 0.001, n = 13) was observed between the ClotChip Δε_r,max and ROTEM MCF parameters. For all plots, error bars indicate duplicate measurements and are presented as mean ± SEM.