Carlos Jacinto (Universidade federal de Alagoas, Brazil)

Optical Nanothermometry for Non-invasive Temperature Monitoring in Acoustofluidic Chip

Three-dimensional (3D) cell culture platforms are increasingly used for drug testing and personalized medicine because they replicate the physiological microenvironment more accurately than 2D systems. Acoustofluidic chips, which use ultrasonic standing waves to levitate and aggregate cells into spheroids, are particularly attractive for high-throughput assays [1–4]. However, the piezoelectric transducer (PZT) that generates these standing waves is also a significant source of localized heating, potentially creating temperature gradients inside the microcavity. Precise thermal control is critical, as deviations from 37 ± 1 °C can compromise cell viability and spheroid morphology. Conventional infrared (IR) thermography measures only the chip’s outer surface temperature and cannot resolve thermal conditions at the levitation plane where cells are cultured. To overcome this limitation, we are developing an in situ temperature sensing method using rare-earth doped dielectric nanoparticles dispersed in the culture medium and analyzed by Raman/optical spectroscopy. These upconversion/downconversion nanoparticles exhibit temperature-dependent Raman/optical spectra, enabling accurate thermal mapping directly within the levitation zone (~300 µm above the cavity bottom) [5,6]. Calibration experiments were performed to correlate luminescence peaks with controlled temperature variations, with expected excellent thermal resolution. Our results reveal temperature increases induced by the PZT during acoustic trapping, with spatial gradients undetectable by IR methods. This approach provides real-time, non-invasive thermal monitoring of acoustofluidic systems, offering valuable insights for optimizing acoustic power and ensuring stable physiological conditions during long-term 3D culture. The method holds promise for improving the reliability of acoustofluidic platforms in drug discovery, toxicological studies, and patient-derived cell assays.

I would like to thank CAPES, FINPE, CNPq, and FAPEAL for the financial support of the work. 

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[2]       2. E. Cesewski et al., Lab Chip 18 (2018) 2087–2098. https://doi.org/10.1039/C8LC00427G.

[3]       3. V.O. Baron et al., Commun Biol 3 (2020) 236. https://doi.org/10.1038/s42003-020-0915-3.

[4]       4. U. Rocha et al., Appl Phys Lett 123 (2023) 034105. https://doi.org/10.1063/5.0145565.

[5]       5. A.C.C. Soares et al., Nanoscale Adv 5 (2023) 3664–3670. https://doi.org/10.1039/D2NA00941B.

[6]       6. C. Jacinto et al., J. Mater Chem B 1 (2025) 54–102. https://doi.org/10.1039/D4TB01416B.