Low-noise fluorescent detection of cardiac troponin I in human serum based on surface acoustic wave separation.

Acute myocardial infarction (AMI) is a life-threatening disease when sudden blockage of coronary artery occurs. As the most specific biomarker, cardiac troponin I (cTnI) is usually checked separately to diagnose or eliminate AMI, and achieving the accurate detection of cTnI is of great significance to patients' life and health. Compared with other methods, fluorescent detection has the advantages of simple operation, high sensitivity and wide applicability. However, due to the strong fluorescence interference of biological molecules in body fluids, it is often difficult to obtain high sensitivity. In order to solve this problem, in this study, surface acoustic wave separation is designed to purify the target to achieve more sensitive detection performance of fluorescent detection. Specifically, the interference of background noise is almost completely removed on a microfluidic chip by isolating microbeads through acoustic radiation force, on which the biomarkers are captured by the immobilized detection probe. And then, the concentration of cTnI in human serum is detected by the fluorescence intensity change of the isolated functionalized beads. By this way, the detection limit of our biosensor calculated by 3σ/K method is 44 pg/mL and 0.34 ng/mL in PBS buffer and human serum respectively. Finally, the reliability of this method has been validated by comparison with clinical tests from the nephelometric analyzer in hospital.

Characterization of Residual Stress in SOI Wafers by Using MEMS Cantilever Beams.

Silicon-on-insulator (SOI) wafers are crucial raw materials in the manufacturing process of microelectromechanical systems (MEMS). Residual stresses generated inside the wafers during the fabrication process can seriously affect the performance, reliability, and yield of MEMS devices. In this paper, a low-cost method based on mechanical modeling is proposed to characterize the residual stresses in SOI wafers in order to calculate the residual stress values based on the deformation of the beams. Based on this method, the residual strain of the MEMS beam, and thus the residual stress in the SOI wafer, were experimentally determined. The results were also compared with the residual stress results calculated from the deflection of the rotating beam to demonstrate the validity of the results obtained by this method. This method provides valuable theoretical reference and data support for the design and optimization of devices based on SOI-MEMS technology. It provides a lower-cost solution for the residual stress measurement technique, making it available for a wide range of applications.

Analysis of Acousto-Optic Phenomenon in SAW Acoustofluidic Chip and Its Application in Light Refocusing.

This paper describes and analyzes a common acousto-optic phenomenon in surface acoustic wave (SAW) microfluidic chips and accomplishes some imaging experiments based on these analyses. This phenomenon in acoustofluidic chips includes the appearance of bright and dark stripes and image distortion. This article analyzes the three-dimensional acoustic pressure field and refractive index field distribution induced by focused acoustic fields and completes an analysis of the light path in an uneven refractive index medium. Based on the analysis of microfluidic devices, a SAW device based on a solid medium is further proposed. This MEMS SAW device can refocus the light beam and adjust the sharpness of the micrograph. The focal length can be controlled by changing the voltage. Moreover, the chip is also proven to be capable of forming a refractive index field in scattering media, such as tissue phantom and pig subcutaneous fat layer. This chip has the potential to be used as a planar microscale optical component that is easy to integrate and further optimize and provides a new concept about tunable imaging devices that can be attached directly to the skin or tissue.

Acoustic valves in microfluidic channels for droplet manipulation.

A novel concept of using acoustic valves in microfluidic channels is reported in this work for the first time. An acoustic valve is a controllable virtual barrier constructed with focused acoustic fields, which can control droplets into different branch channels or block and then release them to specific target channels. Compared with other droplet sorting devices using a surface acoustic wave, acoustic valves do not use an acoustic field to drive droplets but only block branch channels. Compared with other sorting methods, such as using dielectric and magnetic forces, acoustic valves do not need a high voltage or target sample modification. As a non-contact and low-damage manipulation method with minimal requirements for target samples, the use of acoustic valve is suitable for microfluidic applications like sorting and manipulation in biochemical experiments, especially those involving optical observation, fluorescence testing, and chemical reactions.

Intra-droplet particle enrichment in a focused acoustic field.

Particle enrichment is an important preparation or collection process in biomedical and biochemical experiments, but the enrichment process in droplets is harder to realize than in continuous fluid. Here we demonstrate an on-chip, label-free and controllable intra-droplet particle enrichment realized in a focused acoustic field. In this process, droplets containing microparticles are trapped, merged together and split off in the focused acoustic region, resulting in droplets with particles of high concentration. By changing the experimental conditions, the degree of enrichment of this method can be tuned up to 26 times, which enables it to meet requirements for sample preparation in various applications.