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This paper describes a generative design methodology for a micro hydrodynamic single-RBC (red blood cell) trap for applications in microfluidics-based single-cell analysis. One key challenge in single-cell microfluidic traps is to achieve desired through-slit flowrates to trap cells under implicit constraints. In this work, the cell-trapping design with validation from experimental data has been developed by the generative design methodology with an evolutionary algorithm. L-shaped trapping slits have been generated iteratively for the optimal geometries to trap living-cells suspended in flow channels. Without using the generative design, the slits have low flow velocities incapable of trapping single cells. After a search with 30,000 solutions, the optimized geometry was found to increase the through-slit velocities by 49%. Fabricated and experimentally tested prototypes have achieved 4 out of 4 trapping efficiency of RBCs. This evolutionary algorithm and trapping design can be applied to cells of various sizes.

The coupling of the microfluidic chip to mass spectrometry (MS) has attracted considerable attention in the area of chemical and biological analysis. The most commonly used ionization technique in the chip–MS system is electrospray ionization (ESI). Traditional chip-based ESI devices mainly employ direct electrical contact between the electrode and the spray solvent. In this study, a microchip ESI source based on a novel polarization-splitting approach was developed. Specifically, the droplet in the microchannel is first polarized by the electric field and then split into two sub-droplets. In this process, the charge generated by polarization is retained in the liquid, resulting in the generation of two charged droplets with opposite polarities. Finally, when these charged droplets reach the emitter, the electrospray process is initiated and both positive and negative ions are formed from the same solution. Preliminary experimental results indicate that the coupling of this polarization-splitting ESI (PS-ESI) chip with a mass spectrometer enables conventional ESI-MS analysis of various analytes.

Increasing research efforts have been recently devoted to the coupling of microfluidic chip-integrated ionization sources to mass spectrometry (MS). Considering the limitations of microfluidic chips coupled with MS such as liquid spreading, dead volume, and manufacturing troubles, this paper proposed a new three-dimensional (3D) flow focusing (FF)-based microfluidic ionizing source. This source was fabricated by using the two-layer soft lithography method with the nozzle placed inside the chip. The proposed FF microfluidic chip can realize two-phase FF with liquid in air regardless of the viscosity ratio of the continuous and dispersed phases. MS results indicated that the proposed FF microfluidic chip can work as a typical electrical ionization source when supplied with high voltage and can serve as a sonic ionization source without high voltage. The electro-sonic FF ionization microfluidic chip is expected to have various applications, particularly in the integrated and portable applications of ionization sources coupling with portable MS in the future.

Simplifying tedious sample preparation procedures to improve analysis efficiency is a major challenge in contemporary analytical chemistry. Solid phase microextraction (SPME), a technology developed for rapid sample pretreatment, has flexibility in design, geometry, and calibration strategies, which makes it a useful tool in a variety of fields, especially environmental and life sciences. Therefore, it is important to study the coupling between the microfluidic electrospray ionization (ESI) chip integrated with the solid phase microextraction (SPME) module and the electrospray mass spectrometer (MS). In our previous work, we designed a solid phase microextraction (SPME) module on a microfluidic chip through geometric design. However, automation and calibration methods for the extraction process remain unresolved in the SPME on-chip domain, which will lead to faster and more accurate results. This paper discusses the necessity to design a micromixer structure that can produce different elution conditions on the microfluidic chip. By calculating the channel resistances, the microfluidic chip’s integrated module with the micromixer, SPME, and ESI emitters optimize the geometry structure. We propose the annular channel for SPME to perform the resistances balance of the entire chip. Finally, for SPME on a single chip, this work provides a quantitation calibration method to describe the distribution of the analytes between the sample and the extraction phase before reaching the adsorption equilibrium.

Microfluidic chips coupling with mass spectrometry (MS) will be of great significance to the development of relevant instruments involving chemical and bio-chemical analysis, drug detection, food and environmental applications and so on. In our previous works, we proposed two types of microfluidic electrospray ionization (ESI) chip coupling with MS: the two-phase flow focusing (FF) ESI microfluidic chip and the corner-integrated ESI emitter, respectively. However the pretreatment module integrated with these ESI emitters is still a challenging problem. In this paper, we concentrated on integrating the solid phase micro-extraction (SPME) module with our previous proposed on-chip ESI emitters; the fabrication processes of such SPME module are fully compatible with our previous proposed ESI emitters based on the multi-layer soft lithography. We optimized the structure of the integrated chip and characterized its performance using standard samples. Furthermore, we verified its abilities of salt removal, extraction of multiple analytes and separation through on-chip elution using mimic biological urine spiked with different drugs. The results indicated that our proposed integrated module with ESI emitters is practical and effective for real biological sample pretreatment and MS detection.

This paper proposes an electric power self-supply module for the wireless sensor network (WSN) sensor node. The module includes an electromagnetic vibration energy harvester based on micro-electro-mechanical system (MEMS) technology and a processing circuit. The vibration energy harvester presented in this paper is fabricated by an integrated microfabrication process and consists of four similar and relatively independent beam vibration elements. The main functions of the processing circuit are to convert the output of the harvester from unstable alternating current (AC) to stable direct current (DC), charge the super capacitor, and ensure the stable output of the super capacitor. The preliminary test results of the harvester chip show that the chip can output discontinuous pulse voltage, and the range of the voltage value is from tens to hundreds of millivolts in the vibration frequency range of 10–90 Hz. The maximum value that can be reached is 563 mV (at the vibration frequency of 18 Hz). The results of the test show that the harvester can output a relatively high voltage, which can meet the general electric power demand of a WSN sensor node.

Uniform droplets have significant potential in many biological applications due to their higher surface area to volume ratio. This paper proposed a semi-three-dimensional (sime-3D) flow-focusing microfluidic system, which was fabricated using the multi-layer soft lithography method. Based on the semi-3D structure, we focus on droplets formation modes and droplet uniformity at different bulk concentration of surfactant. The relationships between droplets uniformity, droplets breakup processes (jetting mode, dripping mode and tip-streaming mode) and surfactant concentration was investigated. It was found that three droplet generation modes occur through adjusting the pressure ratio in two inlet channels and the concentration of surfactant in continuous phase liquid. The jetting mode would transform to the dripping mode or the tip-streaming mode as the pressure ratio in different surfactant concentrations increased. Furthermore, the uniformity of droplets could be improved through the transition of jetting to dripping mode. We assumed that the uniformity declined through the transition of jetting to tip-streaming, and explored the specific transitions from jetting to dripping mode and tip-streaming mode. Dripping mode leads to high droplet uniformity, and generation frequency decreases with increasing pressure ratio. Tip-streaming mode is considered as an extreme state of jetting mode, leading to higher formation frequency and smaller droplet size at low uniformity.

Pulse wave monitoring is critical for the evaluation of human health. In this paper, a wearable multi-sensor pulse wave monitoring system is proposed and demonstrated. The monitoring system consists of a measuring unit and an analog circuit processing unit. The main part of the measuring unit is a flexible printed circuit board (PCB) with a thickness of 0.15 mm, which includes three micro-electromechanical system (MEMS) pressure sensors softly packaged by polydimethylsiloxane (PDMS), a blood oxygen detector and a MEMS three-axis accelerometer. The MEMS pressure sensors，the blood oxygen detector and the accelerometer are fixed on the expected locations of the flexible PCB. The analog circuit processing unit includes a power supply module, a filter and an amplifier. The pulse waves of two volunteers are detected by the monitoring system in this study. The output signals of the analog circuit processing module are processed and analyzed. In the preliminary test, the time delay of the three pressure pulse waves has been detected and the calculated pulse wave velocities (PWVs) are 12.50 and 11.36 m/s, respectively. The K value, related to the area of the pulse wave, can be obtained. Both the PWV and K value meet the health parameter standards.

Polydimethylsiloxane (PDMS) membranes have been widely used in the microfluidic community to achieve various functions such as control, sensing, filter, etc. In this paper, an experimental process was proposed to directly characterize the deformation of the on-chip PDMS membrane at large deformation based on the image processing method. High precision pressures were applied on the surface of the PDMS membrane with fixed edges and a series deformation of the PDMS membrane were captured by the imaging system. The Chan and Vese (CV) level set method was applied to segment the images of the deformed membrane. The volumes wrapped by the deformed membranes were obtained, and pressure-volumes relationships of the PDMS membranes with different geometry parameters were also calculated. Then the membrane capacitance can be derived by differentiating the curve of pressure-volumes. In addition, the theoretical estimation of the capacitance of the PDMS membrane at large deformation was also obtained through finite element simulation (FEM), which was in good agreement with the experimental results. These results are expected to be significant for designing and on-chip measuring of such PDMS membrane based microfluidic components in our future work.