A portable impedance microflow cytometer for measuring cellular response to hypoxia

Next generation microfluidics: fulfilling the promise of lab-on-a-chip technologies

Microfluidic lab-on-a-chip technologies enable the analysis and manipulation of small fluid volumes and particles at small scales and the control of fluid flow and transport processes at the microscale, leading to the development of new methods to address a broad range of scientific and medical challenges. Microfluidic and lab-on-a-chip technologies have made a noteworthy impact in basic, preclinical, and clinical research, especially in hematology and vascular biology due to the inherent ability of microfluidics to mimic physiologic flow conditions in blood vessels and capillaries. With the potential to significantly impact translational research and clinical diagnostics, technical issues and incentive mismatches have stymied microfluidics from fulfilling this promise. We describe how accessibility, usability, and manufacturability of microfluidic technologies should be improved and how a shift in mindset and incentives within the field is also needed to address these issues. In this report, we discuss the state of the microfluidic field regarding current limitations and propose future directions and new approaches for the field to advance microfluidic technologies closer to translation and clinical use. While our report focuses on using blood as the prototypical biofluid sample, the proposed ideas and research directions can be extrapolated to other areas of hematology, oncology, biology, and medicine.

Adhesion measurement of living cells based on electrical impedance

BACKGROUND

Cells adherence provides specific information about physiology and pathology, the adhesion measurement between living cells and nanostructures can be measured by atomic force microscopy, but this detection technique is difficult to operate and costly. The adhesion height and effective contact area between cells and substrates are also the key factors affecting measurement value of the overall impedance. These factors change with structural parameters of the substrates, so the adhesion measurement between living cells and substrate can be indirectly reflected by the impedance value.

OBJECTIVE

To establish a mapping relationship between the impedance measurement and the adhesion measurement of living cells. The possibility of dynamic measurement of adhesion is realized by this method, and the experimental process is simplified.

METHODS

Laser interference technology was used to prepare nanoarray structures with different periods on the surface of silicon wafers for cells culture. Under the same experimental conditions, the impedance of living cells on the substrates of different cycle sizes were measured. The adhesion between cells and different substrates were analyzed by measuring impedance after the interaction between cells and substrate.

RESULTS

The adhesion of living cells on the substrates of different sizes be analyzed, and the mapping relationship between the impedance and the adhesion measurement was established. The results showed that, the larger the impedance value between cells and substrate, the larger the effective contact area and the smaller the gap between them.

CONCLUSION

The difference of adhesion height and effective adhesion area between living cells and substrates were obtained. This paper, a new method to measure the adhesion properties of living cells is presented, which provides theoretical basis for the related research.

Rapid electrical impedance detection of sickle cell vaso-occlusion in microfluidic device

Sickle cell disease is characterized by painful vaso-occlusive crises, in which poorly deformable sickle cells play an important role in the complex vascular obstruction process. Existing techniques are mainly based on optical microscopy and video processing of sickle blood flow under normoxic condition, for measuring vaso-occlusion by a small fraction of dense sickle cells of intrinsic rigidity but not the vaso-occlusion by the rigid, sickled cells due to deoxygenation. Thus, these techniques are not suitable for rapid, point-of-care testing. Here, we integrate electrical impedance sensing and Polydimethylsiloxane-microvascular mimics with controlled oxygen level into a single microfluidic chip, for quantification of vaso-occlusion by rigid, sickled cells within 1 min. Electrical impedance measurements provided a label-free, real-time detection of different sickle cell flow behaviors, including steady flow, vaso-occlusion, and flow recovery in response to the deoxygenation-reoxygenation process that are validated by microscopic videos. Sensitivity of the real part and imaginary part of the impedance signals to the blood flow conditions in both natural sickle cell blood and simulants at four electrical frequencies (10, 50, 100, and 500 kHz) are compared. The results show that the sensitivity of the sensor in detection of vaso-occlusion decreases as electrical frequency increases, while the higher frequencies are preferable in measurement of steady flow behavior. Additional testing using sickle cell simulants, chemically crosslinked normal red blood cells, shows same high sensitivity in detection of vaso-occlusion as sickle cell vaso-occlusion under deoxygenation. This work enables point-of-care testing potentials in rapid, accurate detection of steady flow and sickle cell vaso-occlusion from microliter volume blood specimens. Quantification of sickle cell rheology in response to hypoxia, may provide useful indications for not only the kinetics of cell sickling, but also the altered hemodynamics as obseved at the microcirculatory level.