Thermometry
in biological objects

Variations in temperature often signal pathological changes, including inflammation, cancer, or infections. Examining how quickly temperature changes after the disease onset can offer valuable insights into the body's physiological responses. For successful clinical implementation of thermometry approaches, precise real‐time temperature measurements are required with high spatial resolution, sensitivity, and accuracy, particularly in deeper tissues. This necessity has stimulated advances in optical nanothermometry, which employs light‐responsive agents that alter their optical properties in response to temperature variations. This review examines recent progress in optical nanothermometry as a diagnostic tool for detecting pathological conditions, particularly cancer, inflammation, and disorders of the muscles, heart, and brain. The fundamental principles and techniques of optical thermometry are outlined, and the challenges and limitations of temperature measurements in biological systems are addressed.

Hyperthermia plays a significant role in cancer treatment by inducing cell damage through temperature elevation, often used alongside other treatment modalities. During hyperthermia therapy, temperature control is crucial. Here, we report on a simple synthesis route of hybrid plasmonic nanodiamonds either completely wrapped with an Au shell (NV@Au) or densely covered with Au NPs (NV@SiO2 @Au). Such integration of nanodiamonds with Au NPs is advantageous both for heating and precise thermometry at nanoscale. After structural and optical investigations, heating abilities of the obtained plasmonic nanodiamonds were thoroughly inspected on glass, in association with living cells, and in tissue slices ex vivo, revealing their effective heat generation under excitation with light using a single excitation source. The developed hybrid plasmonic nanodiamonds were finally applied for local photothermal therapy of melanoma in vivo, demonstrating their efficacy in eradicating cancer cells and monitoring temperature during the process.

Heat is a well-known treatment method for a wide range of diseases. Hyperthermia treatment or intentional overheating of cells is a rapidly developing therapeutic strategy in cancer treatment. All-dielectric nanophotonics has established itself in optical applications, including nanothermometry and optical heating; generally, it involves Mie resonances in nonplasmonic nanoparticles (NPs). However, such nanomaterials do not always provide sufficient heating due to their nonoptimal size distribution after fabrication by nonlithographic approaches. To overcome this limitation, additional steps, such as size-separation of NPs, are required. Another strategy for efficient heating is intelligent integration of plasmonic and all-dielectric nanostructures to develop hybrid nanomaterials with outstanding optical performances, e.g., efficient nanoheaters and nanothermometers. Taking this into account, we report on a simple and accessible approach for the fabrication of hybrid silicon–gold NPs. Their heating abilities are further compared with those of pristine monodispersed Si NPs inside and outside B16–F10 melanoma cells and confirmed by simultaneous nanoscale thermometry. The obtained results show that the obtained hybrid nanomaterials are more efficient nanoheaters even in biological environments, where cell inhomogeneity and deviations of NP sizes make it difficult to exactly meet the critical coupling conditions.

Nanostructures enabling light manipulation in response to external stimuli offer unprecedented opportunities for efficient control over optomechanical systems at the nanoscale. The integration of stimuli‐responsive materials in such systems is an important milestone in the creation of miniaturized and smart nano‐ and micromechanical systems. In this article, a thermally sensitive mechanically driven platform based on pNIPAM microspheres modified with high refractive index dielectric silicon (Si) and plasmonic gold (Au) nanoparticles is presented to probe the temperature‐dependent reversible mechanical transformations through the second‐harmonic generation signal switching. The second‐harmonic generation process is investigated theoretically and experimentally depending on the applied temperature and pNIPAM phase. It is found that the change of the interparticle distance in the system during the phase transition provokes generation of optically induced static electric field probed by the second‐harmonic generation signal. The obtained results can become the foundation in the creation of nanophotonic devices based on thermo‐sensitive polymers, as they combine reversible tuning of optical signals with the opportunity of local probing of mechanical changes.

Real-time temperature monitoring within biological objects is a key fundamental issue for understanding the heating process and performing remote-controlled release of bioactive compounds upon laser irradiation. The lack of accurate thermal control significantly limits the translation of optical laser techniques into nanomedicine. Here, we design and develop hybrid (complex) carriers based on multilayered capsules combined with nanodiamonds (NV centers) as nanothermometers and gold nanoparticles (Au NPs) as nanoheaters to estimate an effective laser-induced temperature rise required for capsule rupture and further release of cargo molecules outside and inside cancerous (B16-F10) cells. We integrate both elements (NV centers and Au NPs) in the capsule structure using two strategies: (i) loading inside the capsule’s cavity (CORE) and incorporating them inside the capsule’s wall (WALL). Theoretically and experimentally, we show the highest and lowest heat release from capsule samples (CORE or WALL) under laser irradiation depending on the Au NP arrangement within the capsule. Applying NV centers, we measure the local temperature of capsule rupture inside and outside the cells, which is determined to be 128 ± 1.12 °C. Finally, the developed hybrid containers can be used to perform the photoinduced release of cargo molecules with simultaneous real-time temperature monitoring inside the cells.