Microfluidic Applications Based On Photoacoustic Microscopic Imaging System

Droplet-based microfluidic technology has the characteristics of low reagent dosage,high speed of analysis and excellent monodispersity.Because of that,it has been widely used in many fields,which require to produce droplets with suitable size and morphology.In addition,droplet-based high-throughput microfluidic technique allows thousands of drugs,genes,or chemical samples to be rapidly analyzed and processed in chip-based laboratory.Though the laser-induced fluorescence has become one of the most popular imaging techniques due to the high sensitivity and specificity,this method inevitably introduces pollution in the channel and has limited penetration depth.Therefore,novel imaging approach that enables monitoring the target samples such as droplets and cells in microfluidic channels without such drawbacks,is quite desirable.Photoacoustic imaging(PAI)is an emerging technique,which has many unique advantages,such as high sensitivity,high contrast,fast imaging speed and cost effective.In this paper,we propose an ultrafast and high-resolution PAI system for microfluidics application.By incorporating high-frequency lasers,high-speed galvanometer scanner and high-speed acquisition cards,the system can provide a high B-scan rate of up to2500 Hz with a lateral resolution of 1.7?m and an axial resolution of 36?m at the imaging plane,which are sufficient for the presentation of the details of contents such as droplets or cells in microfluidic channels.We expect that if the system is further optimized and integrated,it can also be applied in other applications.In this paper,we firstly evaluate the lateral resolution,the axial resolution,the resolution of the flow velocity direction,the scanning range and the signal-to-noise ratio in a testing experiment.To exploit the capabilities of the proposed system,a series of microfluidic experiments have been subsequently carried out.First,the droplets in the typical T-junction droplet generator have been imaged to detect the dynamic process of droplet generation,and the droplet morphology at different scanning frequencies have also been imaged respectively.Second,the migration process of magnetic nanoparticles subjected to heterogeneous magnetic fields in microchannels has been successfully monitored.Finally,the flow focusing devices that capable of producing minimal droplets at high speed is monitored,and the minimal droplets are also imaged in realtime.These results indicate that the proposed PAI system has sufficient temporal and spatial resolution to fulfill the needs in high-throughput microfluidics,droplet microfluidics and other applications.