MICROFLUCHIP · Microfluidic Chip

Microfluidic chip

This project determined designing strategies for manufacturing a microfluidic sensor / sorter, which is capable of measuring - merely electrically - aqueous droplets which enclose suspended microparticles, which evidently model erythrocyte cells and sort the droplets according to concentrations. We are worked on the functioning principles of this device. The manufactured device incorporates a fluidic microchannel, an impedance sensor and a separation mechanism. The fluidic architecture of this device was implemented in a way that satisfies requirements for measuring - electrically - sequence of aqueous droplets. The measuring sensor consists of an analog signal-conditioning circuit and a digital impedance analyser, which -both synchronised - are capable of analysing, electrically, the concentrations of the suspension enclosed in the aqueous droplet. Appropriate multisinewaves of preselected frequencies were plied for measuring the dielectric response of the droplets. Due to the lack of obtaining fast measurement rates, as well as complexity in synchronising measurements and separation processes, this project in the end was revised to only test the workability of the electrical impedance concept in the microfluidic scale, since the prototype device was unable to achieve functionality that is required for fast throughput. The core achievements of this project include: 1. a microfluidic mechanism that generates droplets by means of pumping two separate liquids, water and oil 2. manufacturing an impedance sensor which measures droplets electrically and 3. a droplet sorting mechanism which relies on electrode actuation switching. The manufactured device apparently enhances characterisation and separation of droplets which enclose microparticles or cells suspensions. Method: A test fixture was manufactured in a manner that is capable of performing impedimetric analysis of complex liquids samples. The electric signal is perturbed, due to dielectric polarisation changes of the liquid and its disparity is compared against the incident -reference- signal. A recording instrument, a digital scope or analyser, measures the dielectric response and compares its amplitude and phase against amplitude and phase of the reference signal. With this measurement setup the device measures the ionic current which flows through the measurand fluid, in conjunction with the voltage which is applied across the fluid and causes this current. Galvanic contact between fluid and electrodes improves measurement sensitivity because the impedance between the electrode and the fluid is measured low. However it was preferred measurements with electrode insulation which added capacitance, which greatly increased the electrode's impedance, however this capacitance was computed and deducted. Because the droplet should be transported across the surface of the microchannel without breaking up, the microchannel was intentionally passivated with alkysilane hydrophobic monolayers. The electrodes inside the microchannel were also passivated on top of their dielectric insulating film. Results: This project demonstrated the inline impedance measurement of the complex impedance of a droplet sequence. The device is of significance for measurement of the content of droplets that are used as microreactors in segmented flow in microfluidics. The frequency of the measurements ranged between some kHz and 10 MHz. In this range dispersions of microparticles were detected. Upon curve fitting and equivalent circuit, the capacity of single microparticle was determined within the range of µF/cm2 and nearly independent on the frequency. This is in the range of the reported, by authors, capacitance of erythrocyte membranes. Therefore this device is optimised for performing measurement of erythrocyte concentration in aqueous buffer solution. Of course, in the case of real erythrocyte measurement, statistical distribution, which would account for the size dispersion of the erythrocytes, should be performed extra. However this would increase the complication of such measurement and this project doesn't go that far, as it is been decided to only establish working principle for droplet based impedimetric cytometry. Based on the concentration content of the droplet, the same droplet was routed by means of electric actuation. This routing worked only under low driving pressure, due to the weak influence of the electroactuating force. Conclusions: The advancement and use of impedance spectroscopy in sensorics is leading to efficient and effective perceptions for the direct manipulation, separation and sorting of droplet microreactors on microfluidic devices. The dielectric measurement of microparticles, suspended in polar fluid and exposed to voltage signals of properly selected frequency and amplitude, determines the concentration of the particles within the specific droplet. Socioeconomic impact: The impact of this project affects bioelectronics and expends the possibility for advancing analyses of liquid samples. It is also of significance the impact in the technology of cytometers and microfluidic devices. This project is a step forward in the direction of developing devices that can analyse liquid samples in an alternative format than the present chromatographers or spectrometers, over which the analytical chemist gains a tool for modern analysis of liquid samples with automatic record of dielectric characteristics.

Data: CORDIS, © European Union