A simple, low-cost and new all-optical photoacoustic droplet microfluidic detection system is proposed by combining the pure optical photoacoustic detection technology based on polarized light reflection with droplet microfluidic chip technology. In this work, we first use Matlab and Comsol to carry out theoretical calculation and simulation of polarized light reflection, the theory and simulation results are highly consistent. In the experiment, a simple and practical microfluidic chip was prepared by the molding method, and the application range of the polarization based pure light photoacoustic microfluidic detection technology was expanded. Firstly, the photoacoustic signals of black tape in microfluidic chips with different pipe heights are tested to verify the feasibility of our system. Then the suitable flow rate and the flow rate ratio of the two-phase flow were adjusted, and a large number of homogeneous droplets were generated. Methylene blue as one of the samples, the photoacoustic signal of methylene blue droplets was detected. The results show that the polarized light based total internal reflection optical system combined with microfluidic chips has great application potential in microfluidic detection.
Gallium-based liquid metals (LMs), including elemental gallium and associated alloy metals, are notable for their liquid state at room temperature. These LMs have gained attention due to their safety, non-toxicity, and exceptional physical and chemical properties. They exhibit optical resonance in the UV-VIS-IR spectral range, making them potential alternatives to expensive precious metals like gold and silver. However, the optical properties of gallium-based LMs have not been fully explored, especially their photoacoustic property. Photoacoustic detection is a label free method based on photoacoustic effect, detecting the optical absorption contrast of samples through photoacoustic waves. Photoacoustic detection has the advantages of non-contact, highs sensitivity, good contrast and etc. Using the photoacoustic detection method, we can avoid the influence of light scattering on the metal surface and thus obtain the optical absorption of gallium-based LMs directly. In this paper, we report a photoacoustic detection system based on intensity modulated high repetition supercontinuum laser to explore the light absorption properties of EGaIn LM.
Photoacoustic microfluidics emerges as a promising method for particle or droplet analysis. Here we propose a microfluidic chip design based on laser polarization-dependent reflection from the interface of an optical prism and the liquid, which can detect photoacoustic signal without the need of the bulky ultrasonic transducer. This design will reduce the structure complexity and also the cost. As demonstration, we made such chips and detected moving microspheres by analyzing the photoacoustic signal from the black tape fixed underneath the flow channel.
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