Integrated Microfluidic Device with Carbon-Thread Microelectrodes for Electrochemical DNA Elemental Analysis

Cell counting and velocity algorithms for hydrodynamic study of unsteady biological flows in micro-channels

In this paper, the combination of two algorithms, a cell counting algorithm and a velocity algorithm based on a Digital Particle Image Velocimetry (DPIV) method, is presented to study the collective behavior of micro-particles in response to hydrodynamic stimuli. A wide experimental campaign was conducted using micro-particles of different natures and diameters (from 5 to 16 μ m ), such as living cells and silica beads. The biological fluids were injected at the inlet of a micro-channel with an external oscillating flow, and the process was monitored in an investigated area, simultaneously, through a CCD camera and a photo-detector. The proposed data analysis procedure is based on the DPIV-based algorithm to extrapolate the micro-particles velocities and a custom counting algorithm to obtain the instantaneous micro-particles number. The counting algorithm was easily integrated with the DPIV-based algorithm, to automatically run the analysis to different videos and to post-process the results in time and frequency domain. The performed experiments highlight the difference in the micro-particles hydrodynamic responses to external stimuli and the possibility to associate them with the micro-particles physical properties. Furthermore, in order to overcome the hardware and software requirements for the development of a real-time approach, it was also investigated the possibility to detect the flows by photo-detector signals as an alternative to camera acquisition. The photo-detector signals were compared with the velocity trends as a proof of concept for further simplification and speed-up of the data acquisition and analysis. The algorithm flexibility underlines the potential of the proposed methodology to be suitable for real-time detection in embedded systems.

Threads in tubing: an innovative approach towards improved electrochemical thread-based microfluidic devices

Thread-based microfluidic analytical devices have received growing attention since threads have some advantages over other materials. Compared to paper, threads are also capable of spontaneously transporting fluid due to capillary action, but they have superior mechanical strength and do not require hydrophobic barriers. Therefore, thread-based microfluidic devices can be inexpensively fabricated with no need for external pumps or sophisticated microfabrication apparatus. Despite these outstanding features, achieving a controlled and continuous flow rate is still a challenging task, mainly due to fluid evaporation. Here, we overcome this challenge by inserting a cotton thread into a polyethylene tube aiming to minimize fluid evaporation. Also, a cotton piece was inserted into the outlet reservoir to improve the wicking ability of the device. This strategy enabled the fabrication of an innovative electrochemical thread in a tubing microfluidic device that was capable to hold a consistent flow rate (0.38 μL s^-1) for prolonged periods, allowing up to 100 injections in a single device by simply replacing the cotton piece in the outlet reservoir. The proposed device displayed satisfactory analytical performance for selected model analytes (dopamine, hydrogen peroxide, and tert-butylhydroquinone), in addition to being successfully used for quantification of nitrite in spiked artificial saliva samples. Beyond the flow rate improvement, this "thread-in-tube" strategy ensured the protection of the fluid from external contamination while making it easier to connect the electrode array to the microchannels. Thus, we envision that the thread in a tube strategy could bring interesting improvements to thread-based microfluidic analytical devices.