Microfluidic Particle Separation and Detection System Based on Standing Surface Acoustic Wave and Lensless Imaging

Objective: Separation and detection of micro-particles or cells from bio-samples by point-of-care (POC) systems are critical for biomedical and healthcare diagnostic applications. Among various microfluidic separation techniques, acoustophoresis-based technique has the advantages of label-free and good biocompatibility. However, most of the existing separation techniques are bulky and require additional equipment for analysis. Methods: We proposed a platform, which integrates an acoustophoresis-based separation device and a lensless imaging sensor into a compact standalone system to tackle this challenge. Standing Surface Acoustic Wave (SSAW) is utilized for label-free particle separation, while lensless imaging is employed for seamless particle detection and counting using self-developed dual-threshold motion detection algorithms. In particular, we specially optimized the design of microfluidic channel and interdigital transducers (IDTs) for higher performance bioparticle separation, designed a heat dissipation system for the suppression of fluid temperature, and proposed a novel frequency-temperature-curve based method to determine the appropriate signal driving frequency for IDTs. Results: At 2 μL/min flow rate, separation efficiency of 93.52% and purity of 94.29% for 15 μm microbead were achieved in mixed 5μm and 15μm microbead solution at a 25 dBm RF driving power, and similar results for mixed 10 μm and 15 μm microbead solution. Conclusions: The results showed that the integrated platform has an excellent capability to seamlessly separate, distinguish, and count microbeads of different sizes. Significance: Such a platform and the design methodologies offer a promising POC solution for label-free cell separation and detection in biomedical diagnostics.

I. Introduction

Separation and detection of micro-particles or cells from bio-samples by point-of-care (POC) systems are of great importance for biomedical and healthcare diagnostic applications, such as circulating tumor cells (CTCs) detection, antimicrobial resistance study, and drug screening, etc [1], [2]. Particles and cells can be separated based on their distinct biochemical or physical properties. Biochemical properties usually include surface molecular marker and antibody binding, while physical properties include size, weight, deformability, impedance, etc. Based on the differences in these properties, many technologies have been successfully developed over the years for micro-particle and cell separation, such as optical method [3], magnetophoresis [4], dielectrophoresis [5], acoustophoresis [6]–[8].