Performance Investigation of Micromixer with Spiral Pattern on the Cylindrical Chamber Side Wall.

In this paper, a sequence of passive micromixers with spiral patterns on the side wall of cylindrical chambers are designed, optimized, prepared and tested. The simulation studies show that the vortex magnitude and continuity in the mixing chamber are the most important factors to determine mixing performance, while the inlet position and structural parameters are secondary influences on their performance. According to the above principles, the performance of a micromixer with a continuous sidewall spiral finally wins out. The total mixing length is only 14 mm, but when Re = 5, the mixing index can reach 99.81%. The multi-view visual tests of these mixer chips prepared by 3D printing are consistent with the simulation results. This paper provides a new idea for optimizing the micromixer with spiral patterns on the side wall and the problems of floor area and pressure loss are significantly improved compared to the conventional spiral structure.

A Genosensor Based on the Modification of a Microcantilever: A Review.

When the free end of a microcantilever is modified by a genetic probe, this sensor can be used for a wider range of applications, such as for chemical analysis, biological testing, pharmaceutical screening, and environmental monitoring. In this paper, to clarify the preparation and detection process of a microcantilever sensor with genetic probe modification, the core procedures, such as probe immobilization, complementary hybridization, and signal extraction and processing, are combined and compared. Then, to reveal the microcantilever's detection mechanism and analysis, the influencing factors of testing results, the theoretical research, including the deflection principle, the establishment and verification of a detection model, as well as environmental influencing factors are summarized. Next, to demonstrate the application results of the genetic-probe-modified sensors, based on the classification of detection targets, the application status of other substances except nucleic acid, virus, bacteria and cells is not introduced. Finally, by enumerating the application results of a genetic-probe-modified microcantilever combined with a microfluidic chip, the future development direction of this technology is surveyed. It is hoped that this review will contribute to the future design of a genetic-probe-modified microcantilever, with further exploration of the sensitive mechanism, optimization of the design and processing methods, expansion of the application fields, and promotion of practical application.

The Influence of the Unit Junction on the Performance of a Repetitive Structure Micromixer.

In order to investigate the influence of the unit junction on the micromixer performance, a repetitive structure micromixer with a total length of 12.3 mm was proposed. This micromixer consists of a T-shape inlet channel and six cubic mixing units, as well as junctions between them. Numerical simulations show that, when the junctions are all located at the geometric center of the cubic mixing unit, the outlet mixing index is 72.12%. At the same flow velocity, the best mixing index achieved 97.15% and was increased by 34.68% when the junctions were located at different corners of the cubic mixing unit. The improvement in the mixing index illustrated that the non-equilibrium vortexes generated by changing the junction location to utilize the restricted diffusion by the mixing unit's side wall could promote mixing. Visual tests of the micromixer chip prepared by 3D printing were consistent with the simulation results, also indicating that the junction location had a significant influence on the mixer's performance. This article provides a new idea for optimizing the structural design and improving the performance of micromixers.

Overload performance study and fabrication of the capacitive pressure-sensitive chip with linkage film.

In order to satisfy the demands of pressure measurement under high overload conditions, the overload characteristics of the capacitive pressure-sensitive chip with linkage film are studied. Through the simulation and analysis for the stress distribution of this sensitive structure and in light of the dimension effect of the tensile strength of monocrystalline silicon, the influence of sizes of the sensitive structure on the overload pressure is expounded. The simulated results illustrate that the maximum overload pressure can exceed 200 times the full-scale (FS) when appropriately adjusting the sizes of the sensitive structure. The proposed chip is fabricated using SOI wafers combined with bonding technology. Our experimental results show that the sample chip has a linear response in the pressure range of 25-100 kPa, and its overload pressure is 4.5 MPa, reaching 45 times the full-scale.

Chaotic Micromixer Based on 3D Horseshoe Transformation.

To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the 3D HT, which was calculated based on a symbolic dynamic system, proved the chaotic enhancement. Based on the 3D HT, a micromixer with a mixing length of 12 mm containing six mixing units was obtained by sequentially applying "squeeze", "stretch", "twice fold", "inverse transformation", and "intersection" operations. Numerical simulation and Peclet Number (Pe) calculations indicated that when the squeeze amplitude 0 < α < 1/2, 0 < ß < 1/2, the stretch amplitude γ > 4, and Re ≥ 1, the mass transfer in the mixer was dominated by convective diffusion induced by chaotic flow. When Re = 10, at the outlet of the mixing chamber, the simulated mixing index was 96.4%, which was far less than the value at Re = 0.1 (σ = 0.041). Microscope images of the mixing chamber and the curve trend of pH buffer solutions obtained from a mixing experiment were both consistent with the results of the simulation. When Re = 10, the average mixing index of the pH buffer solutions was 91.75%, which proved the excellent mixing efficiency of the mixer based on the 3D HT.

Design, Preparation and Performance Study of On-Chip Flow-Through Amperometric Sensors with an Integrated Ag/AgCl Reference Electrode.

To improve the reference potential stability of on-chip amperometric sensors, we propose a novel integrated Ag/AgCl reference electrode structure. This structure can refresh the saturated potassium chloride filling solution surrounding the Ag/AgCl electrode. We then designed a flow-through amperometric sensor and a multilayer microfluidic chip based on the integrated reference electrode. In order to improve the detection signal strength of the flow-through sensor, a numerical simulation model was established. The simulation results showed that a combination of (1) using a step-type detection cell structure that maintains micro-channel width while reducing micro-channel height, and (2) controlling the sample flow rate to limit the mass transfer of the sensor surface effectively, improves the detection signal strength. The step-type detection cell structure had dimensions of 200 µm × 200 µm × 100 µm (length × width × height), and the electroosmotic flow driving voltage was 120 V/cm. Finally, successful trace detection of Mg2+ and Pb2+ in the water was achieved using the amperometric sensor and microfluidic chip: detection limits were 5 µmol/L and 84 µmol/L. The preparation of an on-chip flow-through amperometric sensor with an integrated Ag/AgCl reference electrode will facilitate improved portability of microfluidic detection technology.

Piezoresistive sensitivity, linearity and resistance time drift of polysilicon nanofilms with different deposition temperatures.

Our previous research work indicated that highly boron doped polysilicon nanofilms (≤100 nm in thickness) have higher gauge factor (the maximum is ∼34 for 80 nm-thick films) and better temperature stability than common polysilicon films (≥ 200nm in thickness) at the same doping levels. Therefore, in order to further analyze the influence of deposition temperature on the film structure and piezoresistance performance, the piezoresistive sensitivity, piezoresistive linearity (PRL) and resistance time drift (RTD) of 80 nm-thick highly boron doped polysilicon nanofilms (PSNFs) with different deposition temperatures were studied here. The tunneling piezoresistive model was established to explain the relationship between the measured gauge factors (GFs) and deposition temperature. It was seen that the piezoresistance coefficient (PRC) of composite grain boundaries is higher than that of grains and the magnitude of GF is dependent on the resistivity of grain boundary (GB) barriers and the weight of the resistivity of composite GBs in the film resistivity. In the investigations on PRL and RTD, the interstitial-vacancy (IV) model was established to model GBs as the accumulation of IV pairs. And the recrystallization of metastable IV pairs caused by material deformation or current excitation is considered as the prime reason for piezoresistive nonlinearity (PRNL) and RTD. Finally, the optimal deposition temperature for the improvement of film performance and reliability is about 620 °C and the high temperature annealing is not very effective in improving the piezoresistive performance of PSNFs deposited at lower temperatures.