Application Cases

Experiment Name: The Application of Power Amplifiers in Non-Contact Manipulation of Droplets on Superhydrophobic Surfaces and High-Throughput Surface-Enhanced Raman Scattering Measurements

Experiment Content:In this study, we introduce an innovative non-contact acoustic tweezer (CAT) for manipulating droplets on superhydrophobic surfaces. This technology achieves non-contact droplet manipulation by forming ultrasonic standing waves between the ultrasonic transducer and the superhydrophobic substrate. We demonstrate that even tiny droplets with volumes less than 20 microliters can be manipulated in three dimensions in mid-air, while larger droplets with volumes up to 500 microliters can be captured and manipulated in-plane. The experimental results confirm that CAT can effectively manipulate droplets of different compositions and volumes on various superhydrophobic substrates, providing an efficient, universal, and contamination-free liquid handling solution for high-throughput surface-enhanced Raman scattering (SERS) applications.

Research Direction: Ultrasonic Levitation

Testing Equipment:ATA-1220D power amplifier, signal generator, ultrasonic transducer, etc.

Figure 1: Schematic Diagram of the Experimental Setup

Figure 2: High-Throughput Surface-Enhanced Raman Scattering Experiment

Experimental Process:

All droplet manipulation experiments were conducted using a custom platform equipped with a manual xyz stage, as shown in Figure 1. A set of 3D-printed molds were used to fix a 10 mm diameter, 38 kHz resonant frequency ultrasonic transducer to the z-axis of the stage. To power the ultrasonic transducer, we used a 38 kHz sine signal generated by a function generator and amplified by a power amplifier. The superhydrophobic surface was placed on top of the xy stage, allowing us to manually adjust the distance between the ultrasonic transducer and the superhydrophobic surface to generate standing waves for reliable droplet manipulation. Figure 2 illustrates the process of the high-throughput SERS experiment, where droplets carrying highly diluted aqueous analytes interact with carbon and silver nanoparticles. Under the controlled movement of the acoustic tweezers, the nanoparticles are separated from the substrate, and the sensitivity of Raman measurements is enhanced due to the plasmonic properties of the silver nanoparticles. After measurement, the first droplet is moved away, and then a second droplet is manipulated to the desired detection point using the acoustic tweezers, enabling the analysis of different droplets.

Experimental Results:

Figure 3: Manipulation of Multiple Droplets on Superhydrophobic Paper

Figure 4: Raman Signals of Two Droplets Containing 10 μM and 1 mM Rhodamine 6G (R6G)

Figure 3 demonstrates the manipulation of multiple droplets on superhydrophobic paper, highlighting the precise and selective droplet manipulation capabilities of CAT. (A) Formation of a pattern of three droplets on a superhydrophobic surface using non-contact ultrasound. (B) Selective transportation of a red droplet surrounded by six green droplets. (C) Merging two droplets with ultrasound enhances mixing. (D) Continuous transportation and merging of multiple droplets. (E) Sequential coalescence of three droplets with vinegar, litmus, and sodium carbonate using CAT. Figure 4 shows the Raman signals of two droplets containing 10 μM and 1 mM rhodamine 6G (R6G). The second droplet with a concentration of 1 mM R6G exhibits distinct R6G peaks in the SERS spectrum. However, the first droplet with a concentration of 10 μM R6G produces relatively low spectral noise, making it difficult to detect typical R6G peaks. Additionally, the blank substrate signal obtained after removing these two droplets (as shown by the black line in Figure 4B) indicates that no residual material remains on the superhydrophobic surface once the droplets are manipulated by the acoustic tweezers. The entire detection process is completed within 1 minute. This result demonstrates the successful application of acoustic tweezers on superhydrophobic substrates for droplet-based SERS, enabling high-throughput measurements.

Power Amplifier Recommendation: ATA-1220E Broadband Amplifier

Figure: Performance Parameters of the ATA-1220E Broadband Amplifier

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