5.1 Background
The mechanical properties of biological fluids, such as viscosity and surface tension, are valuable indicators for the early detection of diseases, reflecting subtle physiological and pathological changes. However, conventional technologies often suffer from slow detection speeds and low throughput, limiting their effectiveness in clinical applications. Optical microcavities with ultrahigh Q-factors offer enhanced light–matter interactions and hold promise for biomechanical sensing. In this study, researchers present a laser-emission vibrational microscopy technique based on whispering-gallery-mode (WGM) microcavities, which overcomes the limitations of traditional optical cavities in probing fluid mechanics. By applying ultrasound to stimulate microdroplet lasers and detecting the resulting mechanical vibrations through WGM laser emission, the method enables high-throughput measurement of fluid viscosity. The approach demonstrated strong potential for rapid and large-scale screening of hyperlipidemia.
5.2 Research Innovation
5.2.1 Coupling mechanism of ultrasound and WGM microcavity laser
The research team printed dye-doped microdroplets onto a superhydrophobic surface. These microdroplets, with their smooth interfaces, support WGMs with ultrahigh Q-factors, enabling strong laser emission. Ultrasound was applied to the droplets using a piezoelectric transducer, inducing periodic mechanical deformation of the microdroplets (Fig. 1a). To investigate the coupling between ultrasound and the microdroplet laser, the researchers monitored the temporal evolution of the spectral images. As shown in Fig. 1b, the spectra exhibited distinct orientation changes at different time points, attributed to the periodic vibrations induced by the acoustic stimulation. The team quantified the mechanical vibrations by analyzing the temporal relative correlation of the spectral patterns (Fig. 1c), and established a calibration curve relating the standard deviation of the relative correlation to the viscosity (Fig. 1d), enabling accurate measurement of fluid mechanical properties.
5.2.2 Rapid scanning of mechanical properties
The team employed laser-emission vibrational microscopy to rapidly assess the viscosity of microdroplets. A large-scale microdroplet array was generated using an inkjet printer (Fig. 2a), and stage scanning was implemented to enable high-throughput mapping of viscosity across the droplets (Fig. 2b). As shown in Fig. 2c, the resulting viscosity map accurately reflects the mechanical properties of individual droplets. The experiment demonstrated that the viscosity of over 5,400 microdroplets within a 4.8 mm × 1.8 mm area could be measured in just 90 minutes, highlighting the method’s strong potential for large-scale mechanical properties measurement.
5.2.3 High-throughput screening of hyperlipidemia
To validate the sensor's performance in real and complex biological fluids, the research team applied the technique to hyperlipidemia screening. Within just 25 minutes, high-throughput analysis of over 2,000 serum microdroplets was successfully completed. Serum samples from four individuals were tested, with their viscosities clearly classified into four stages: normal, mild, moderate, and severe. The measured viscosity showed a strong correlation with total blood cholesterol levels. Owing to the ultra-small volume of each microdroplet (~4.2 pL), a single drop of blood (~30 μL) can support over seven million individual measurements. This study highlights laser-emission vibrational microscopy as a powerful, high-throughput platform for rapid, label-free measurement of the intrinsic mechanical properties of biological fluids, offering promising prospects for mechanical biomarker discovery and low-cost clinical diagnostics.
5.3 Conclusions
The research team proposed laser-emission vibrational microscopy, which can realize high-throughput and rapid quantitative analysis of the intrinsic mechanical properties of biological fluids, overcoming the limitations of traditional optical cavities in probing intrinsic mechanical properties. The technology provides a novel tool for high-throughput, large-scale cardiovascular risk screening.
Light Science & Applications
Laser-emission vibrational microscopy of microdroplet arrays for high-throughput screening of hyperlipidemia