Determining intracellular temperature at single-cell level by a novel thermocouple method

A dual emission ratiometric nanothermometer for evaluating cell temperature during energy metabolism

ATP synthesis and thermogenesis are two key outputs of intracellular oxidative phosphorylation (OXPHOS), and simultaneous monitoring of changes in ATP and temperature will facilitate understanding of the energy metabolism mechanisms. Herein, a ratiometric probe was developed to measure temperature variations during ATP synthesis/hydrolysis. Firstly, poly(methyl methacrylate) (PMMA) copolymers with different types of charged groups (carboxylate, sulfonate and trimethylammonium) were prepared to obtain size-controllable nanoparticles by nanoprecipitation. The back energy transfer between excited state of Eu3+ and the ligand triplet state was sensitive to heat, so Eu3+ exhibited temperature-dependent emission behavior. Eu-complex-loaded polymer PMMA-trimethylammonium (PMMA-NMe3) nanoparticles (Eu@PMMA-NMe3 NPs) showed the strongest fluorescence and the smallest particle size, making them suitable as labels for cell imaging. Eu@PMMA-NMe3 NPs were subsequently doped with temperature-insensitive rhodamine dye to construct ratiometric temperature probes. The maximum relative thermal sensitivity of the temperature probe was 2.7 % °C-1 with a temperature resolution of 0.1-0.3 °C in the range of cell temperatures from 30.9 to 40.1 °C. Combining the temperature probe with an ATP indicator successfully monitored changes in temperature and ATP during OXPHOS and Ca2+ burst. When OXPHOS was inhibited, cell temperature increased by about 2.5 °C and ATP levels decreased by about 13 % within 360 s. The Ca2+ burst also induced a decrease in ATP levels and an increase in temperature attributed to the process of Ca2+ transport from the cytoplasm to the endoplasmic reticulum, which promoted ATP hydrolysis. These results have important implications for understanding energy conversion and metabolic pathways.

Simultaneous Detection of Neural Activity and Temperature in Photothermal Neural Stimulation

Photothermal neuromodulation is a promising non-electrical neural stimulation technology for treating brain diseases through optically induced cell membrane temperature changes. However, the technology faces limitations in understanding its mechanism and impact on cellular behavior due to the restriction of directly measuring temperature changes at the cell interface from a very close distance during optical stimulation of neural cells, necessitating advancements in high-precision temperature sensing and electrical recording without light interference. This challenge is addressed by developing ultrasensitive cell membrane interface temperature sensors integrated with low-noise electrical recording capabilities. Transparent resistive temperature detectors, composed of a 10 nm thickness of ultrathin Au film fabricated by polyelectrolyte seed layer-induced thermal evaporation, achieved precise measurement and control of temperature changes without significant light interference and self-heating. A transparent electrode composed of the same ultrathin Au layer shows low-noise electrical recordings of neural signals upon photothermal stimulation. Using this multifunctional system, it is demonstrated that an average increase of 2.34 °C at neuronal cell surfaces results in over 95% suppression of hippocampal neural spike activities. The approach provides unprecedented insights into the mechanisms of photothermal neuromodulation and its effects on cellular behavior, paving the way for advanced treatments of neurological disorders.

Non-Invasive Wide-Field Imaging of Chip Surface Temperature Distribution Based on Ensemble Diamond Nitrogen-Vacancy Centers

With the development of chip technology, the demand for device reliability in various electronic chip industries continues to grow. In recent years, with the advancement of quantum sensors, the solid-state spin (nitrogen-vacancy) NV center temperature measurement system has garnered attention due to its high sensitivity and spatial range. However, NV centers are not only affected by temperature but also by magnetic fields. This article analyzes the impact of magnetic fields on temperature detection. By combining the wide-field imaging platform of optically detected magnetic resonance (ODMR) with a temperature-sensitive structure of thin ensemble diamond overlaid on a quartz substrate, high-sensitivity temperature detection has been achieved. And obtains a sensitivity of approximately 10 mK/Hz1/2. By combining a CCD camera imaging system, it realizes a wide field of view of 500 μm2, a high spatial resolution of 1.3 μm. Ultimately, this study demonstrates the two-dimensional actual temperature distribution on the chip surface under different currents, achieving wide-field, non-contact, high-speed temperature imaging of the chip surface.

High-Precision Field- Effect Transistor Biosensor for Analyzing Differential Effects of Anti-Cancer Drugs on Cancerous and Non-Cancerous Cells

A high-precision biosensor technique is introduced, offering the capability to independently evaluate the effects of anti-cancer drugs on both cancerous (RAJI) and non-cancerous (WIL2S) cells. By analyzing and fitting current change curves and transfer characteristic curves under two drugs, camptothecin and doxorubicin, this technique quantifies both the magnitude of drug-induced current changes in cells and the rate of drug entry into cells. Flow cytometry was utilized to validate the entry rates of two drugs, camptothecin and doxorubicin, into the cells. The biosensor leverages the exceptional sensitivity of two-dimensional electron gas to detect proximal charge variations at ultralow concentrations, even in fluids with high ionic strength. The findings reveal that anti-cancer drugs have a more pronounced impact on tumor cells, with the effects and interaction speeds differing across normal cells and tumor cells. This innovative approach not only enhances our understanding of the specificity and action mechanisms of anti-cancer drugs but also provides a valuable tool for screening potential tumor anti-cancer drugs and advancing targeted cancer therapies.

Microbes, macrophages, and melanin: a unifying theory of disease as exemplified by cancer

It is widely accepted that cancer mostly arises from random spontaneous mutations triggered by environmental factors. Our theory challenges the idea of the random somatic mutation theory (SMT). The SMT does not fit well with Charles Darwin's theory of evolution in that the same relatively few mutations would occur so frequently and that these mutations would lead to death rather than survival of the fittest. However, it would fit well under the theory of evolution, if we were to look at it from the vantage point of pathogens and their supporting microbial communities colonizing humans and mutating host cells for their own benefit, as it does give them an evolutionary advantage and they are capable of selecting genes to mutate and of inserting their own DNA or RNA into hosts. In this article, we provide evidence that tumors are actually complex microbial communities composed of various microorganisms living within biofilms encapsulated by a hard matrix; that these microorganisms are what cause the genetic mutations seen in cancer and control angiogenesis; that these pathogens spread by hiding in tumor cells and M2 or M2-like macrophages and other phagocytic immune cells and traveling inside them to distant sites camouflaged by platelets, which they also reprogram, and prepare the distant site for metastasis; that risk factors for cancer are sources of energy that pathogens are able to utilize; and that, in accordance with our previous unifying theory of disease, pathogens utilize melanin for energy for building and sustaining tumors and metastasis. We propose a paradigm shift in our understanding of what cancer is, and, thereby, a different trajectory for avenues of treatment and prevention.

A Nanothermometer with a Microwave Thermal Effect for Sensing Cell Membrane Temperature and Measuring Microwave-Induced Thermal Gradient Distribution

In microwave (MW) thermotherapy, it is challenging to regulate the temporal and spatial distribution of the temperature at the nanoscale. Herein, we report a nanothermometer for simultaneous MW heating and temperature distribution measurement. The nanothermometer was prepared by free radical polymerization with vinylbenzyl trimethylammonium chloride (VBTMACl) as the MW thermosensitizer and isopropylacrylamide (NIPAM) as the thermoresponsive unit, followed by anion exchange with fluorophore sodium 3-(4-(1,2,2-triphenylvinyl)phenoxy)propane-1-sulfonate (TPESO3Na). In aqueous medium, the nanothermometer self-assembles into micelles with TPESO3- as the hydrophobic core and thermoresponsive polymer P(NIPAM-co-VBTMACl) as the hydrophilic shell, thereby to exhibit aggregation-induced emission (AIE). By increasing the temperature, the conformational change of the thermoresponsive polymer drives TPESO3- to transfer from the core to the shell of the micelles, and the nanothermometer converts from an aggregate state to a dispersed state. As a result, the nanothermometer exhibits a superior temperature-dependent emission feature in the temperature range 25-41 °C, with a relative thermal sensitivity of 8.3% °C-1 at 37 °C. In addition, the nanothermometer possesses a positive charge and balanced hydrophilic-hydrophobic feature which prompts its anchoring to the cell membrane. Therefore, it realizes in situ temperature sensing of cell membranes during MW heating, as well as temperature distribution of the cell membrane.

Design, fabrication, and calibration of a micromachined thermocouple for biological applications in temperature monitoring

This paper presents a microneedle thermocouple probe designed for temperature measurements in biological samples, addressing a critical need in the field of biology. Fabricated on a Silicon-On-Insulator (SOI) wafer, the probe features a doped silicon (Si)/chrome (Cr)/gold (Au) junction, providing a high Seebeck coefficient, rapid response times, and excellent temperature resolution. The microfabrication process produces a microneedle with a triangular sensing junction. Finite Element Analysis (FEA) was employed to evaluate the thermal time constant and structural integrity in tissue, supporting the probe's suitability for biological applications. Experimental validation included temperature measurements in ex-vivo tissue and live Xenopus laevis oocytes. Notably, intracellular thermogenesis was detected by increasing extracellular potassium concentration to depolarize the oocyte membrane, resulting in a measurable temperature rise. These findings highlight the probe's potential as a robust tool for monitoring temperature variations in biological systems.

Exploring the Frontiers of Cell Temperature Measurement and Thermogenesis

The precise measurement of cell temperature and an in-depth understanding of thermogenic processes are critical in unraveling the complexities of cellular metabolism and its implications for health and disease. This review focuses on the mechanisms of local temperature generation within cells and the array of methods developed for accurate temperature assessment. The contact and noncontact techniques are introduced, including infrared thermography, fluorescence thermometry, and other innovative approaches to localized temperature measurement. The role of thermogenesis in cellular metabolism, highlighting the integral function of temperature regulation in cellular processes, environmental adaptation, and the implications of thermogenic dysregulation in diseases such as metabolic disorders and cancer are further discussed. The challenges and limitations in this field are critically analyzed while technological advancements and future directions are proposed to overcome these barriers. This review aims to provide a consolidated resource for current methodologies, stimulate discussion on the limitations and challenges, and inspire future innovations in the study of cellular thermodynamics.

Thermoelectric Materials and Devices for Advanced Biomedical Applications

Thermoelectrics (TEs), enabling the direct conversion between heat and electrical energy, have demonstrated extensive application potential in biomedical fields. Herein, the mechanism of the TE effect, recent developments in TE materials, and the biocompatibility assessment of TE materials are provided. In addition to the fundamentals of TEs, a timely and comprehensive review of the recent progress of advanced TE materials and their applications is presented, including wearable power generation, personal thermal management, and biosensing. In addition, the new-emerged medical applications of TE materials in wound healing, disease treatment, antimicrobial therapy, and anti-cancer therapy are thoroughly reviewed. Finally, the main challenges and future possibilities are outlined for TEs in biomedical fields, as well as their material selection criteria for specific application scenarios. Together, these advancements can provide innovative insights into the development of TEs for broader applications in biomedical fields.

Controllable Fabrication of Multifunctional Micro-thermocouples for Temperature Detection inside Single Suspended Droplets

Microdroplets have recently emerged as an exciting technological platform for wide applications. In this work, we developed a controllable fabrication approach to novel tungsten-platinum micro-thermocouples that function not only as a sensitive temperature sensor but also as a flexible suspender for individual microdroplet studies. The controllable fabrication hinges on the formation of tungsten tip apex nodes to make junctions with platinum, which was achieved through a unique combinational strategy, involving gradient coating with a complete insulating layer and subsequent targeted removal by tip electroporation. Benefiting from its coaxial structure, microspherical contact node end, hydrophobic surface, and thermoelectric performance, the as-fabricated micro-thermocouple was successfully employed for the microdroplet suspension and in situ temperature detection throughout the droplet evaporation cycle. It was observed that the temperature inside the suspended microdroplets was lower than that of the external environment, and there existed temperature discontinuity during droplet evaporation. By integrating the capabilities of temperature monitoring and droplet manipulation into a single micro-thermocouple, this work demonstrates its versatility and promising applications in expanded sensing for single microdroplets and other microsystems.

Multimodal analysis of traction forces and the temperature dynamics of living cells with a diamond-embedded substrate

Cells and tissues are constantly exposed to chemical and physical signals that regulate physiological and pathological processes. This study explores the integration of two biophysical methods: traction force microscopy (TFM) and optically detected magnetic resonance (ODMR) to concurrently assess cellular traction forces and the local relative temperature. We present a novel elastic substrate with embedded nitrogen-vacancy microdiamonds that facilitate ODMR-TFM measurements. Optimization efforts focused on minimizing sample illumination and experiment duration to mitigate biological perturbations. Our hybrid ODMR-TFM technique yields TFM maps and achieves approximately 1 K precision in relative temperature measurements. Our setup employs a simple wide-field fluorescence microscope with standard components, demonstrating the feasibility of the proposed technique in life science laboratories. By elucidating the physical aspects of cellular behavior beyond the existing methods, this approach opens avenues for a deeper understanding of cellular processes and may inspire the development of diverse biomedical applications.

A novel microfluidic chip integrated with Pt micro-thermometer for temperature measurement at the single-cell level

Noninvasive and sensitive thermometry of a single cell during the normal physiological process is crucial for analyzing fundamental cellular metabolism and applications to cancer treatment. However, current thermometers generally sense the average temperature variation for many cells, thereby failing to obtain real-time and continuous data of an individual cell. In this study, we employed platinum (Pt) electrodes to construct an integrated microfluidic chip as a single-cell thermometer. The single-cell isolation unit in the microchip consisted of a main channel, which was connected to the inlet and outlet of a single-cell capture funnel. A single cell can be trapped in the funnel and the remaining cells can bypass and flow along the main channel to the outlet. The best capture ratio of a single MCF7 cell at a single-cell isolation unit was 90 % under optimal condition. The thermometer in the micro-chip had a temperature resolution of 0.007 °C and showed a good linear relationship in the range of 20-40 °C (R2 = 0.9999). Slight temperature increment of different single tumor cell (MCF7 cell, H1975 cell, and HepG2 cell) cultured on the chip was continuously recorded under normal physiological condition. In addition, the temperature variation of single MCF7 cell in-situ after exposure to a stimulus (4 % paraformaldehyde treatment) was also monitored, showing an amplitude of temperature fluctuations gradually decreased over time. Taken together, this integrated microchip is a practical tool for detecting the change in the temperature of a single cell in real-time, thereby offering valuable information for the drug screening, diagnosis, and treatment of cancer.

Recent advances of nanopore technique in single cell analysis

Single cells and their dynamic behavior are closely related to biological research. Monitoring their dynamic behavior is of great significance for disease prevention. How to achieve rapid and non-destructive monitoring of single cells is a major issue that needs to be solved urgently. As an emerging technology, nanopores have been proven to enable non-destructive and label-free detection of single cells. The structural properties of nanopores enable a high degree of sensitivity and accuracy during analysis. In this article, we summarize and classify the different types of solid-state nanopores that can be used for single-cell detection and illustrate their specific applications depending on the size of the analyte. In addition, their research progress in material transport and microenvironment monitoring is also highlighted. Finally, a brief summary of existing research challenges and future trends in nanopore single-cell analysis is tentatively provided.

Warm Cells, Hot Mitochondria: Achievements and Problems of Ultralocal Thermometry

Temperature is a crucial regulator of the rate and direction of biochemical reactions and cell processes. The recent data indicating the presence of local thermal gradients associated with the sites of high-rate thermogenesis, on the one hand, demonstrate the possibility for the existence of "thermal signaling" in a cell and, on the other, are criticized on the basis of thermodynamic calculations and models. Here, we review the main thermometric techniques and sensors developed for the determination of temperature inside living cells and diverse intracellular compartments. A comparative analysis is conducted of the results obtained using these methods for the cytosol, nucleus, endo-/sarcoplasmic reticulum, and mitochondria, as well as their biological consistency. Special attention is given to the limitations, possible sources of errors and ambiguities of the sensor's responses. The issue of biological temperature limits in cells and organelles is considered. It is concluded that the elaboration of experimental protocols for ultralocal temperature measurements that take into account both the characteristics of biological systems, as well as the properties and limitations of each type of sensor is of critical importance for the generation of reliable results and further progress in this field.

Thermoelectric Nanofluidics Probing Thermal Heterogeneity inside Single Cells

Accurate temperature measurement in one living cell is of great significance for understanding biological functions and regulation. Here, a nanopipet electric thermometer (NET) is established for real-time intracellular temperature measurement. Based on the temperature-controlled ion migration, the temperature change in solution results in altered ion mobilities and ion distributions, which can be converted to the thermoelectric responses of NET in a galvanostatic configuration. The exponential relationship between the voltage and the temperature promises highly sensitive thermoelectric responses up to 11.1 mV K-1, which is over an order of magnitude higher than previous thermoelectric thermometry. Moreover, the NET exhibits superior thermal resolution of 25 mK and spatiotemporal resolution of 100 nm and 0.9 ms as well as excellent stability and reproducibility. Benefiting from these unique features, both thermal fluctuations in steady-state cells and heat generation and dissipation upon drug administration can be successfully monitored, which are hardly achieved by current methods. By using NET, thermal heterogeneities of single cancer cells during immunotherapy were reported first in this work, in which the increased intracellular temperature was demonstrated to be associated with the survival benefit and resistance of cancer cells in immunotherapy. This work not only provides a reliable method for microscopic temperature monitoring but also gains new insights to elucidate the mechanism of immune evasion and therapeutic resistance.

Additive Manufacturing of Thermoelectric Microdevices for 4D Thermometry

Thermometry, the process of measuring temperature, is one of the most fundamental tasks not only for understanding the thermodynamics of basic physical, chemical, and biological processes but also for thermal management of microelectronics. However, it is a challenge to acquire microscale temperature fields in both space and time. Here, a 3D printed micro-thermoelectric device that enables direct 4D (3D Space + Time) thermometry at the microscale is reported. The device is composed of freestanding thermocouple probe networks, fabricated by bi-metal 3D printing with an outstanding spatial resolution of a few µm. It shows that the developed 4D thermometry can explore dynamics of Joule heating or evaporative cooling on microscale subjects of interest such as a microelectrode or a water meniscus. The utilization of 3D printing further opens up the possibility to freely realize a wide range of on-chip, freestanding microsensors or microelectronic devices without the design restrictions by manufacturing processes.

Measurement of cellular thermal properties and their temperature dependence based on frequency spectra via an on-chip-integrated microthermistor

To understand the mechanism of intracellular thermal transport, thermal properties must be elucidated, particularly thermal conductivity and specific heat capacity. However, these properties have not been extensively studied. In this study, we developed a cellular temperature measurement device with a high temperature resolution of 1.17 m °C under wet conditions and with the ability to introduce intracellular local heating using a focused infrared laser to cultured cells on the device surface. Using this device, we evaluated the thermal properties of single cells based on their temperature signals and responses. Measurements were taken using on-chip-integrated microthermistors with high temperature resolution at varying surrounding temperatures and frequencies of local infrared irradiation on cells prepared on the sensors. Frequency spectra were used to determine the intensities of the temperature signals with respect to heating times. Signal intensities at 37 °C and a frequency lower than 2 Hz were larger than those at 25 °C, which were similar to those of water. The apparent thermal conductivity and specific heat capacity, which were determined at different surrounding temperatures and local heating frequencies, were lower than and similar to those of water at 37 °C and 25 °C, respectively. Our results indicate that the thermal properties of cells depend on both temperatures and physiological activities in addition to local heating frequencies.

Single-cell thermometry with a nanothermocouple probe

Herein, a nanopipette-based thermocouple probe that possesses high temperature resolution, rapid response, good reversibility and stability was constructed and successfully applied for single-cell temperature sensing. Different intracellular temperatures were observed in diverse types of cells, which reveals differences in their metabolism levels. Temperature responses of cancer and normal cells against various exogenous drugs were also demonstrated. The spatially resolved temperature sensing of three-dimensional cell culture models unveils the existence of their inner temperature gradients. This work would facilitate drug screening and disease diagnosis.

Recent Development of Fluorescent Nanodiamonds for Optical Biosensing and Disease Diagnosis

The ability to precisely monitor the intracellular temperature directly contributes to the essential understanding of biological metabolism, intracellular signaling, thermogenesis, and respiration. The intracellular heat generation and its measurement can also assist in the prediction of the pathogenesis of chronic diseases. However, intracellular thermometry without altering the biochemical reactions and cellular membrane damage is challenging, requiring appropriately biocompatible, nontoxic, and efficient biosensors. Bright, photostable, and functionalized fluorescent nanodiamonds (FNDs) have emerged as excellent probes for intracellular thermometry and magnetometry with the spatial resolution on a nanometer scale. The temperature and magnetic field-dependent luminescence of naturally occurring defects in diamonds are key to high-sensitivity biosensing applications. Alterations in the surface chemistry of FNDs and conjugation with polymer, metallic, and magnetic nanoparticles have opened vast possibilities for drug delivery, diagnosis, nanomedicine, and magnetic hyperthermia. This study covers some recently reported research focusing on intracellular thermometry, magnetic sensing, and emerging applications of artificial intelligence (AI) in biomedical imaging. We extend the application of FNDs as biosensors toward disease diagnosis by using intracellular, stationary, and time-dependent information. Furthermore, the potential of machine learning (ML) and AI algorithms for developing biosensors can revolutionize any future outbreak.

Combined Cellular Thermometry Reveals That Salmonella typhimurium Warms Macrophages by Inducing a Pyroptosis-like Phenotype

The attenuated Salmonella typhimurium VNP20009, enriched in tumors, is known to have antitumor effects and recruit macrophages. Little is known, however, about whether VNP will lead to specific changes in macrophages, e.g., cell temperature. Here, using a real-time wireless multicell thermometry system, we reported for the first time that VNP20009 increases the macrophage temperature by 0.2 °C. Nigericin, recognized as an inducer of pyroptosis, was found to induce macrophage warming. Moreover, the ΔsipD-VNP20009 strain failed to induce macrophage pyroptosis and simultaneously failed to warm macrophages, and the Gsdmd^-/- macrophages that were unable to achieve pyroptosis were no longer warmed following VNP20009 induction. These results suggested that the occurrence of macrophage pyroptosis is the key to VNP20009-mediated cell warming. With the aid of a single-cell thermometry system, it was further confirmed that cell warming occurred in pyroptosis-like macrophages. Cellular warming was not detected after the induction of pyroptosis in macrophages with loss of mitochondrial biological function, suggesting a critical role of mitochondria in warming. Moreover, we found that VNP20009 caused local tumor temperature increases. The local tumor warming induced by VNP20009 was significantly reduced after macrophage clearance. Notably, this temperature increase contributed to M1-type polarization. These findings expanded our knowledge of the cellular biological changes induced by the strain on macrophages, as well as the biochemical phenomena accompanying pyroptosis, and provide a reference for the study of biochemical signals transduced to biothermal signals with a combined cell-level temperature detector.

Thermal Probing Techniques for a Single Live Cell

Temperature is a significant factor in determining and characterizing cellular metabolism and other biochemical activities. In this study, we provide a brief overview of two important technologies used to monitor the local temperatures of individual living cells: fluorescence nano-thermometry and an array of micro-/nano-sized thin-film thermocouples. We explain some key technical issues that must be addressed and optimised for further practical applications, such as in cell biology, drug selection, and novel antitumor therapy. We also offer a method for combining them into a hybrid measuring system.

Raman Thermometry Nanopipettes in Cancer Photothermal Therapy

Raman thermometry based on surface-enhanced Raman scattering has been developed using nanopipettes in cancer cell photothermal therapy (PTT). Gold nanorods (AuNRs) are robustly epoxied on glass pipettes with a high surface coverage of ∼95% and less than 10 nm-wide nanogaps for intracellular thermometry and photothermal cancer therapy. The temperature changes could be estimated from the N≡C band shifts of 4-fluorophenyl isocyanide (FPNC)-adsorbed AuNRs on the Raman thermometry nanopipette (RTN) surfaces. An intracellular temperature change of ∼2.7 °C produced by altering the [Ca²⁺] in A431 cells was detected using the RTN in vitro, as checked from fura-2 acetoxymethyl ester (fura-2 AM) fluorescence images. For in vivo experiments, local temperature rises of ∼19.2 °C were observed in the mouse skin, whereas infrared camera images could not tract due to spatial resolution. In addition, a tumor growth suppression was observed in the PTT processes after an administration of the three AuNR-coated nanopipettes combined with a 671 nm laser irradiation for 5 min in 30 days. These results demonstrate not only the localized temperature sensing ability of FPNC-tagged AuNR nanopipettes in cell biology but also anti-cancer effects in photothermal cancer therapy.

Fast wide-field upconversion luminescence lifetime thermometry enabled by single-shot compressed ultrahigh-speed imaging

Photoluminescence lifetime imaging of upconverting nanoparticles is increasingly featured in recent progress in optical thermometry. Despite remarkable advances in photoluminescent temperature indicators, existing optical instruments lack the ability of wide-field photoluminescence lifetime imaging in real time, thus falling short in dynamic temperature mapping. Here, we report video-rate upconversion temperature sensing in wide field using single-shot photoluminescence lifetime imaging thermometry (SPLIT). Developed from a compressed-sensing ultrahigh-speed imaging paradigm, SPLIT first records wide-field luminescence intensity decay compressively in two views in a single exposure. Then, an algorithm, built upon the plug-and-play alternating direction method of multipliers, is used to reconstruct the video, from which the extracted lifetime distribution is converted to a temperature map. Using the core/shell NaGdF4:Er3+,Yb3+/NaGdF4 upconverting nanoparticles as the lifetime-based temperature indicators, we apply SPLIT in longitudinal wide-field temperature monitoring beneath a thin scattering medium. SPLIT also enables video-rate temperature mapping of a moving biological sample at single-cell resolution.

Diamond quantum thermometry: from foundations to applications

Diamond quantum thermometry exploits the optical and electrical spin properties of colour defect centres in diamonds and, acts as a quantum sensing method exhibiting ultrahigh precision and robustness. Compared to the existing luminescent nanothermometry techniques, a diamond quantum thermometer can be operated over a wide temperature range and a sensor spatial scale ranging from nanometres to micrometres. Further, diamond quantum thermometry is employed in several applications, including electronics and biology, to explore these fields with nanoscale temperature measurements. This review covers the operational principles of diamond quantum thermometry for spin-based and all-optical methods, material development of diamonds with a focus on thermometry, and examples of applications in electrical and biological systems with demand-based technological requirements.

Toward Quantitative Bio-sensing with Nitrogen-Vacancy Center in Diamond

The long-dreamed-of capability of monitoring the molecular machinery in living systems has not been realized yet, mainly due to the technical limitations of current sensing technologies. However, recently emerging quantum sensors are showing great promise for molecular detection and imaging. One of such sensing qubits is the nitrogen-vacancy (NV) center, a photoluminescent impurity in a diamond lattice with unique room-temperature optical and spin properties. This atomic-sized quantum emitter has the ability to quantitatively measure nanoscale electromagnetic fields via optical means at ambient conditions. Moreover, the unlimited photostability of NV centers, combined with the excellent diamond biocompatibility and the possibility of diamond nanoparticles internalization into the living cells, makes NV-based sensors one of the most promising and versatile platforms for various life-science applications. In this review, we will summarize the latest developments of NV-based quantum sensing with a focus on biomedical applications, including measurements of magnetic biomaterials, intracellular temperature, localized physiological species, action potentials, and electronic and nuclear spins. We will also outline the main unresolved challenges and provide future perspectives of many promising aspects of NV-based bio-sensing.

Cellular Thermometry Considerations for Probing Biochemical Pathways

Temperature is a fundamental thermodynamic property that can serve as a probe of biochemical reactions. Extracellular thermometry has previously been used to probe cancer metabolism and thermoregulation, with measured temperature changes of ~1-2 K in tissues, consistent with theoretical predictions. In contrast, previous intracellular thermometry studies remain disputed due to reports of >1 K intracellular temperature rises over 5 min or more that are inconsistent with theory. Thus, the origins of such anomalous temperature rises remain unclear. An improved quantitative understanding of intracellular thermometry is necessary to provide a clearer perspective for future measurements. Here, we develop a generalizable framework for modeling cellular heat diffusion over a range of subcellular-to-tissue length scales. Our model shows that local intracellular temperature changes reach measurable limits (>0.1 K) only when exogenously stimulated. On the other hand, extracellular temperatures can be measurable (>0.1 K) in tissues even from endogenous biochemical pathways. Using these insights, we provide a comprehensive approach to choosing an appropriate cellular thermometry technique by analyzing thermogenic reactions of different heat rates and time constants across length scales ranging from subcellular to tissues. Our work provides clarity on cellular heat diffusion modeling and on the required thermometry approach for probing thermogenic biochemical pathways.

A Micromachined Picocalorimeter Sensor for Liquid Samples with Application to Chemical Reactions and Biochemistry

Calorimetry has long been used to probe the physical state of a system by measuring the heat exchanged with the environment as a result of chemical reactions or phase transitions. Application of calorimetry to microscale biological samples, however, is hampered by insufficient sensitivity and the difficulty of handling liquid samples at this scale. Here, a micromachined calorimeter sensor that is capable of resolving picowatt levels of power is described. The sensor consists of low-noise thermopiles on a thin silicon nitride membrane that allow direct differential temperature measurements between a sample and four coplanar references, which significantly reduces thermal drift. The partial pressure of water in the ambient around the sample is maintained at saturation level using a small hydrogel-lined enclosure. The materials used in the sensor and its geometry are optimized to minimize the noise equivalent power generated by the sensor in response to the temperature field that develops around a typical sample. The experimental response of the sensor is characterized as a function of thermopile dimensions and sample volume, and its capability is demonstrated by measuring the heat dissipated during an enzymatically catalyzed biochemical reaction in a microliter-sized liquid droplet. The sensor offers particular promise for quantitative measurements on biological systems.

Hybrid 0D Antimony Halides as Air-Stable Luminophores for High-Spatial-Resolution Remote Thermography

Luminescent organic-inorganic low-dimensional ns2 metal halides are of rising interest as thermographic phosphors. The intrinsic nature of the excitonic self-trapping provides for reliable temperature sensing due to the existence of a temperature range, typically 50-100 K wide, in which the luminescence lifetimes (and quantum yields) are steeply temperature-dependent. This sensitivity range can be adjusted from cryogenic temperatures to above room temperature by structural engineering, thus enabling diverse thermometric and thermographic applications ranging from protein crystallography to diagnostics in microelectronics. Owing to the stable oxidation state of Sb3+ , Sb(III)-based halides are far more attractive than all major non-heavy-metal alternatives (Sn-, Ge-, Bi-based halides). In this work, the relationship between the luminescence characteristics and crystal structure and microstructure of TPP2 SbBr5 (TPP = tetraphenylphosphonium) is established, and then its potential is showcased as environmentally stable and robust phosphor for remote thermography. The material is easily processable into thin films, which is highly beneficial for high-spatial-resolution remote thermography. In particular, a compelling combination of high spatial resolution (1 µm) and high thermometric precision (high specific sensitivities of 0.03-0.04 K-1 ) is demonstrated by fluorescence-lifetime imaging of a heated resistive pattern on a flat substrate, covered with a solution-spun film of TPP2 SbBr5 .

Cell Temperature Measurement for Biometabolism Monitoring

Temperature is an important factor in the process of life, as thermal energy transfer participates in all biological events in organisms. Due to technical limitations, there is still a lot more information to be explored regarding the correlation between life activities and temperature changes. In recent years, the emergence of a variety of new temperature measurement methods has facilitated further research in this field. Here, we introduce the latest advances in temperature sensors for biological detection and their related applications in metabolic research. Various technologies are discussed in terms of their advantages and shortcomings, and future prospects are presented.

Upconversion Nanoparticle Decorated Spider Silks as Single-Cell Thermometers

Noninvasive and sensitive thermometry of a single living cell is crucial to the analysis of fundamental cellular processes and applications to cancer diagnosis. Optical fibers decorated with temperature-sensitive nanomaterials have become widely used instruments for biosensing temperature. However, current silica fibers exhibit low compatibility and degradability in biosystems. In this work, we employ spider silks as natural optical fibers to construct biocompatible thermometers. The spider silks were drawn directly from Araneus ventricosus and were decorated with core-shell upconversion nanoparticles (UCNPs) via a photophoretic effect. By measuring the fluorescence spectra of the UCNPs on the spider silks, the membrane temperature of a single breast cancer cell was obtained with absolute and relative sensitivities ranging from 3.3 to 4.5 × 10^-3 K^-1 and 0.2 to 0.8% K^-1, respectively. Additionally, the temperature variation during apoptosis was monitored by the thermometer in real time. This work provides a biocompatible tool for precise biosensing and single-cell analysis.

A high-precision thermometry microfluidic chip for real-time monitoring of the physiological process of live tumour cells

Temperature changes in cells are generally accompanied by physiological processes. Cellular temperature measurements can provide important information to fully understand cellular mechanisms. However, temperature measurements with conventional methods, such as fluorescent polymeric thermometers and thermocouples, have limitations of low sensitivity or cell state disturbance. We developed a microfluidic chip integrating a high-precision platinum (Pt) thermo-sensor that can culture cells and monitor the cellular temperature in situ. During detection, a constant temperature system with a stability of 0.015 °C was applied. The temperature coefficient of resistance of the Pt thermo-sensor was 2090 ppm/°C, giving a temperature resolution of the sensor of less than 0.008 °C. This microchip showed a good linear correlation between the temperature and resistance of the Pt sensor at 20-40 °C (R² = 0.999). Lung and liver cancer cells on the microchip grew normally and continuously. The maximum temperature fluctuation of H1975 (0.924 °C) was larger than that of HepG2 (0.250 °C). However, the temperature of adherent HepG2 cells changed over time, showing susceptibility to the environment most of the time compared to H1975. Moreover, the temperature increment of non-cancerous cells, such as hepatic stellate cells, was monitored in response to the stimulus of paraformaldehyde, showing the process of cell death. Therefore, this thermometric microchip integrated with cell culture could be a non-disposable and label-free tool for monitoring cellular temperature applied to the study of physiology and pathology.

Exploring the 'cold/hot' properties of traditional Chinese medicine by cell temperature measurement

Context: It is common sense that chewing a mint leaf can cause a cooling feeling, while chewing ginger root will produce a burning feeling. In Traditional Chinese Medicine (TCM), this phenomenon is referred to as 'cold/hot' properties of herbs. Herein, it is reported that TCM with different "cold/hot" properties have different effects on the variation of cells.Objective: To explore the intrinsic 'cold/hot' properties of TCM from the perspective of cellular and molecular biology.Materials and methods: A375 cells were selected using Cancer Cell Line Encyclopaedia (CCLE) analysis and western blots. Hypaconitine and baicalin were selected by structural similarity analysis from 56 and 140 compounds, respectively. A wireless thermometry system was used to measure cellular temperature change induced by different compounds. Alteration of intracellular calcium influx was investigated by means of calcium imaging.Results: The IC₅₀ values of GSK1016790A, HC067047, hypaconitine, and baicalin for A375 cells are 8.363 nM, 816.4 μM, 286.4 μM and 29.84 μM, respectively. And, 8 μM hypaconitine induced obvious calcium influx while 8 μM baicalin inhibited calcium influx induced by TRPV4 activation. Cellular temperature elevated significantly when treated with GSK1016790A or hypaconitine, while the results were reversed when cells were treated with HC067047 or baicalin.Discussion and conclusions: The changes in cellular temperature are speculated to be caused by the alteration of intracellular calcium influx mediated by TRPV4. In addition, the 'cold/hot' properties of compounds in TCM can be classified by using cellular temperature detection.

The conundrum of hot mitochondria

The mitochondrion is often referred as the cellular powerhouse because the organelle oxidizes organic acids and NADH derived from nutriments, converting around 40% of the Gibbs free energy change of these reactions into ATP, the major energy currency of cell metabolism. Mitochondria are thus microscopic furnaces that inevitably release heat as a by-product of these reactions, and this contributes to body warming, especially in endotherms like birds and mammals. Over the last decade, the idea has emerged that mitochondria could be warmer than the cytosol, because of their intense energy metabolism. It has even been suggested that our own mitochondria could operate under normal conditions at a temperature close to 50 °C, something difficult to reconcile with the laws of thermal physics. Here, using our combined expertise in biology and physics, we exhaustively review the reports that led to the concept of a hot mitochondrion, which is essentially based on the development and use of a variety of molecular thermosensors whose intrinsic fluorescence is modified by temperature. Then, we discuss the physical concepts of heat diffusion, including mechanisms like phonons scattering, which occur in the nanoscale range. Although most of approaches with thermosensors studies present relatively sparse data and lack absolute temperature calibration, overall, they do support the hypothesis of hot mitochondria. However, there is no convincing physical explanation that would allow the organelle to maintain a higher temperature than its surroundings. We nevertheless proposed some research directions, mainly biological, that might help throw light on this intriguing conundrum.

Advances and challenges for fluorescence nanothermometry

Fluorescent nanothermometers can probe changes in local temperature in living cells and in vivo and reveal fundamental insights into biological properties. This field has attracted global efforts in developing both temperature-responsive materials and detection procedures to achieve sub-degree temperature resolution in biosystems. Recent generations of nanothermometers show superior performance to earlier ones and also offer multifunctionality, enabling state-of-the-art functional imaging with improved spatial, temporal and temperature resolutions for monitoring the metabolism of intracellular organelles and internal organs. Although progress in this field has been rapid, it has not been without controversy, as recent studies have shown possible biased sensing during fluorescence-based detection. Here, we introduce the design principles and advances in fluorescence nanothermometry, highlight application achievements, discuss scenarios that may lead to biased sensing, analyze the challenges ahead in terms of both fundamental issues and practical implementations, and point to new directions for improving this interdisciplinary field.

Single-cell temperature mapping with fluorescent thermometer nanosheets

Recent studies using intracellular thermometers have shown that the temperature inside cultured single cells varies heterogeneously on the order of 1°C. However, the reliability of intracellular thermometry has been challenged both experimentally and theoretically because it is, in principle, exceedingly difficult to exclude the effects of nonthermal factors on the thermometers. To accurately measure cellular temperatures from outside of cells, we developed novel thermometry with fluorescent thermometer nanosheets, allowing for noninvasive global temperature mapping of cultured single cells. Various types of cells, i.e., HeLa/HEK293 cells, brown adipocytes, cardiomyocytes, and neurons, were cultured on nanosheets containing the temperature-sensitive fluorescent dye europium (III) thenoyltrifluoroacetonate trihydrate. First, we found that the difference in temperature on the nanosheet between nonexcitable HeLa/HEK293 cells and the culture medium was less than 0.2°C. The expression of mutated type 1 ryanodine receptors (R164C or Y523S) in HEK293 cells that cause Ca²⁺ leak from the endoplasmic reticulum did not change the cellular temperature greater than 0.1°C. Yet intracellular thermometry detected an increase in temperature of greater than ∼2°C at the endoplasmic reticulum in HeLa cells upon ionomycin-induced intracellular Ca²⁺ burst; global cellular temperature remained nearly constant within ±0.2°C. When rat neonatal cardiomyocytes or brown adipocytes were stimulated by a mitochondrial uncoupling reagent, the temperature was nearly unchanged within ±0.1°C. In cardiomyocytes, the temperature was stable within ±0.01°C during contractions when electrically stimulated at 2 Hz. Similarly, when rat hippocampal neurons were electrically stimulated at 0.25 Hz, the temperature was stable within ±0.03°C. The present findings with nonexcitable and excitable cells demonstrate that heat produced upon activation in single cells does not uniformly increase cellular temperature on a global basis, but merely forms a local temperature gradient on the order of ∼1°C just proximal to a heat source, such as the endoplasmic/sarcoplasmic reticulum ATPase.

Encapsulation of Dual Emitting Giant Quantum Dots in Silica Nanoparticles for Optical Ratiometric Temperature Nanosensors

Accurate temperature measurements with a high spatial resolution for application in the biomedical fields demand novel nanosized thermometers with new advanced properties. Here, a water dispersible ratiometric temperature sensor is fabricated by encapsulating in silica nanoparticles, organic capped PbS@CdS@CdS “giant” quantum dots (GQDs), characterized by dual emission in the visible and near infrared spectral range, already assessed as efficient fluorescent nanothermometers. The chemical stability, easy surface functionalization, limited toxicity and transparency of the silica coating represent advantageous features for the realization of a nanoscale heterostructure suitable for temperature sensing. However, the strong dependence of the optical properties on the morphology of the final core–shell nanoparticle requires an accurate control of the encapsulation process. We carried out a systematic investigation of the synthetic conditions to achieve, by the microemulsion method, uniform and single core silica coated GQD (GQD@SiO2) nanoparticles and subsequently recorded temperature-dependent fluorescent spectra in the 281-313 K temperature range, suited for biological systems. The ratiometric response—the ratio between the two integrated PbS and CdS emission bands—is found to monotonically decrease with the temperature, showing a sensitivity comparable to bare GQDs, and thus confirming the effectiveness of the functionalization strategy and the potential of GQD@SiO2 in future biomedical applications.

A Multi-Channel System for Temperature Sensing of Neural Stem Cells in Adherent Culture

Neural stem cells (NSCs) can gradually proliferate or differentiate during adherent culture. It is found that stem cells have different temperature characteristics in different physiological states. In order to detect the temperature of NSCs during adherent culture, in this study, we have designed a temperature monitoring system, in which a thin-film platinum resistor was used as the sensor. The NSCs were seeded on the sensor, and the data acquisition device was connected to the host computer via Bluetooth. Results indicate that there are about 5000 cells attached on the surface of each sensor, and the cell viability is maintained at about 90% after 24 h culture. An electrostatic force microscope (EFM) result proves that there is no electric field on the sensor surface to influence the activity of NSCs. This system can work continuously for more than 24 h with 0.05 °C detection sensitivity. Furthermore, the significant temperature change of NSCs is observed when stimulated by different concentrations of thyroid hormone, which demonstrates that the temperature change related to cell activity. Therefore, by detecting the temperature of the cell population, the fabricated system can provide reference information for studying the metabolic state of NSCs, as well as physiological responses of cells under various conditions in biomedical applications.

Modeling of an Optically Heated MEMS-Based Micromechanical Bimaterial Sensor for Heat Capacitance Measurements of Single Biological Cells

Detection of thermal activities of biological cells is important for biomedical and pharmaceutical applications because these activities are closely associated with the conformational change processes. Calorimetric measurements of biological systems using bimaterial microcantilevers (BMC) have increasingly been reported with the ultimate goal of developing highly sensitive and inexpensive techniques with real-time measurement capability techniques for the characterization of dynamic thermal properties of biological cells. BMCs have been established as highly sensitive calorimeters for the thermal analysis of cells and liquids. In this paper, we present a simulation model using COMSOL Multiphysics and a mathematical method to estimate the heat capacity of objects (treated here as a biological cell) placed on the surface of a microcantilever. By measuring the thermal time constant, which is obtained from the deflection curve of a BMC, the heat capacity of a sample can be evaluated. With this model, we can estimate the heat capacity of single biological cells using a BMC, which can potentially be used for the thermal characterization of different biological samples.

Cell-specific frequency as a new hallmark to early detection of cancer and efficient therapy: Recording of cancer voice as a new horizon

Early detection is the most important strategy for controlling and management of cancer, which can significantly increase the survival rate by detecting disease in the early stages and rapid treating and preventing the progression of the disease. There are a number of methods to differentiate the normal and cancerous cells including pH changes, temperature change, variation in electrical properties and also preliminary evidence on specific frequency of some cancer cells which are reviewed in this work. The results obtained in cancer treatment using the amplitude-modulated electromagnetic fields indicate that each type of cell has a specific response to the emitted frequencies. Also, the results reveal that the recorded frequencies of prostate and breast cancers are lower compared to the normal cells associated with these tissues. There are more evidences for the existence of specific cell frequencies in the form of the response of each cell to its own specific frequency and the difference between normal and tumor cell frequency levels. Based on these evidences, it can be introduced as a hallmark with the ability to the distinction between normal and tumor cells for cancer detection. Our suggestion is to hear the voice of cancer, by designing and developing a non-invasive, biocompatible, affordable and miniaturized tools, such as nano-antennas and implantable biosensors that able to detect and record cell-specific frequencies. Designing transducers to convert the cell-specific frequency to a sound or other measurable signal will accomplish the job. To the best of our knowledge, this is the first time that the cell-specific frequency measurement, which is derived from cell activity, is introduced as a biomarker for early detection of cancer. The development of studies aimed at expanding research and designing instruments for detection of the frequency with the goal of establishing a comparative library of cell-specific frequency for all cell types, especially non-communicable diseases such as cancer. The main goal of the project is to plan the idea of developing modern tools and hallmark for early detection of cancer as one of the most important global strategies for managing the disease by introducing new parameters with a high-accuracy and in proportion and direct relationship with the activity and functioning of the body, without any affecting exogenous interferer.

Transient heat release during induced mitochondrial proton uncoupling

Non-shivering thermogenesis through mitochondrial proton uncoupling is one of the dominant thermoregulatory mechanisms crucial for normal cellular functions. The metabolic pathway for intracellular temperature rise has widely been considered as steady-state substrate oxidation. Here, we show that a transient proton motive force (pmf) dissipation is more dominant than steady-state substrate oxidation in stimulated thermogenesis. Using transient intracellular thermometry during stimulated proton uncoupling in neurons of Aplysia californica, we observe temperature spikes of ~7.5 K that decay over two time scales: a rapid decay of ~4.8 K over ~1 s followed by a slower decay over ~17 s. The rapid decay correlates well in time with transient electrical heating from proton transport across the mitochondrial inner membrane. Beyond ~33 s, we do not observe any heating from intracellular sources, including substrate oxidation and pmf dissipation. Our measurements demonstrate the utility of transient thermometry in better understanding the thermochemistry of mitochondrial metabolism.

Optical Detection of Intracellular Quantities Using Nanoscale Technologies

Optical probes that can be used to measure certain quantities with subcellular resolution give us access to a new level of information at which physics, chemistry, life sciences, and medicine become strongly intertwined. The emergence of these new technologies is owed to great advances in the physical sciences. However, evaluating and improving these methods to new standards requires a joint effort with life sciences and clinical practice. In this Account, we give an overview of the probes that have been developed for measuring a few highly relevant parameters at the subcellular scale: temperature, pH, oxygen, free radicals, inorganic ions, genetic material, and biomarkers. Luminescent probes are available in many varieties, which can be used for measuring temperature, pH, and oxygen. Since they are influenced by virtually any metabolic process in the healthy or diseased cell, these quantities are extremely useful to understand intracellular processes. Probes for them can roughly be divided into molecular dyes with a parameter dependent fluorescence or phosphorescence and nanoparticle platforms. Nanoparticle probes can provide enhanced photostability, measurement quality, and potential for multiple functionalities. Embedding into coatings can improve biocompatibility or prevent nonspecific interactions between the probe and the cellular environment. These qualities need to be matched however with good uptake properties, colloidal properties and eventually intracellular targeting to optimize their practical applicability. Inorganic ions constitute a broad class of compounds or elements, some of which play specific roles in signaling, while others are toxic. Their detection is often difficult due to the cross-talk with similar ions, as well as other parameters. The detection of free radicals, DNA, and biomarkers at extremely low levels has significant potential for biomedical applications. Their presence is linked more directly to physiological and clinical manifestations. Since existing methods for free radical detection are generally poor in sensitivity and spatiotemporal resolution, new reliable methods that are generally applicable can contribute greatly to advancing this topic in biology. Optical methods that detect DNA or RNA and protein biomarkers exist for intracellular applications, but are mostly relevant for the development of rapid point-of-care sample testing. To elucidate the inner workings of cells, focused multidisciplinary research is required to define the validity and limitations of a nanoparticle probe, in both physical and biological terms. Multifunctional platforms and those that are easily made compatible with conventional research equipment have an edge over other techniques in growing the body of research evidencing their versatility.

A new approach of electrochemical etching fabrication based on drop-off-delay control

W-Pt micro-nano-thermocouple is a brand new sensor for intracellular temperature measurement. As a nanodevice, it is based on the electrochemical etching method of which the shape is directly related to the performance. Although much research has been done on how to control the shape of the tungsten tip through electrochemical etching method, preparing different shapes requires different fabrication methods. In this article, we proposed a flexible and general control method which can fit all the fabrication methods by merely modifying the software. Moreover, this method based on drop-off-delay time control is capable of controlling the duration of the electrochemical reaction during the final formation of the tungsten tip. Based on this method, the cone angle can be set to any value from 5° to 30° with the radius of curvature maintaining from 2 nm to 5 nm. Additionally, the sophisticated fabrication of W-Pt micro-nano-thermocouple was designed to be automatically completed by three workshops in batches. The efficiency and uniformity of W-Pt micro-nano-thermocouple fabrication were well improved.

Cell-line characterization by infrared-induced pyroelectric effect

Evaluation of cellular thermodynamics has recently received a high interest because of its implication in many mechanisms related with function, structure and health of cells. Recent literature reported significant efforts to provide affordable intracellular thermal components of absorption, such as thermal conductivity, to overcome the lack of experimental data. Herein, we provide lines of evidence towards the fabrication of an electronic system, using a rapid thermoelectric technique based on infrared-induced pyroelectric effect for in-vitro cell model characterization. Results demonstrated that the assessment of the average single cell thermal conductivity, sample concentration, and information on cell viability is possible over a wide concentration range. The proposed electronic system establishes a different analysis paradigm if compared to those reported in the literature, with consistent results, demonstrating that the adopted technique can provide cell-specific information and knowledge, closely linked to cell viability and its vital functions.

Microscale direct measurement of localized photothermal heating in tissue-mimetic hydrogels

Photothermal hyperthermia is proven to be an effective diagnostic tool for cancer therapy. The efficacy of this method directly relies on understanding the localization of the photothermal effect in the targeted region. Realizing the safe and effective concentration of nano-particles and the irradiation intensity and time requires spatiotemporal temperature monitoring during and after laser irradiation. Due to uniformities of the nanoparticle distribution and the complexities of the microenvironment, a direct temperature measurement in micro-scale is crucial for achieving precise thermal dose control. In this study, a 50 nm thin film nickel resistive temperature sensor was fabricated on a 300 nm SiN membrane to directly measure the local temperature variations of a hydrogel-GNR mixture under laser exposure with 2 mK temperature resolution. The chip-scale approach developed here is an effective tool to investigate localization of photothermal heating for hyperthermia applications for in-vitro and ex-vivo models. Considering the connection between thermal properties, porosity and the matrix stiffness in hydrogels, we present our results using the interplay between matrix stiffness of the hydrogel and its thermal properties: the stiffer the hydrogel, the higher the thermal conductivity resulting in lower photothermal heating. We measured 8.1, 7.4, and 5.6 °C temperature changes (from the room temperature, 20 °C) in hydrogel models with stiffness levels corresponding to adipose (4 kPa), muscle (13 kPa) and osteoid (30 kPa) tissues respectively by exposing them to 2 W/cm² laser (808 nm) intensity for 150 seconds.

High-performance flexible metal-on-silicon thermocouple

We have demonstrated metal-on-silicon thermocouples with a noticeably high Seebeck coefficient and an excellent temperature-sensing resolution. Fabrication of the thermocouples involved only simple photolithography and metal-liftoff procedures on a silicon substrate. The experimentally measured Seebeck coefficient of our thermocouple was 9.17 × 10-4 V/°K, which is 30 times larger than those reported for standard metal thin-film thermocouples and comparable to the values of alloy-based thin-film thermocouples that require sophisticated and costly fabrication processes. The temperature-voltage measurements between 20 to 80 °C were highly linear with a linearity coefficient of 1, and the experimentally demonstrated temperature-sensing resolution was 0.01 °K which could be further improved up to a theoretical limit of 0.00055 °K. Finally, we applied this approach to demonstrate a flexible metal-on-silicon thermocouple with enhanced thermal sensitivity. The outstanding performance of our thermocouple combined with an extremely thin profile, bending flexibility, and simple, highly-compatible fabrication will proliferate its use in diverse applications such as micro-/nanoscale biometrics, energy management, and nanoscale thermography.

Penetrating effect of high-intensity infrared laser pulses through body tissue

Researchers have utilized infrared (IR) lasers as energy sources in laser therapy for curing skin diseases and skin injuries with remarkable effects. Preliminary experiments have also shown that high-intensity IR laser pulses could penetrate thick body tissues, resulting in remarkable effects for recovery from injuries in deep muscles and cartilage tissues. However, for deep-level IR laser therapy, it is unclear how much of the laser power density penetrates the body tissues at certain depths and which of the three major effects of laser irradiation, namely, laser-induced photo-chemical effect, photo-thermal effect and mechanical dragging effect, play a key role in the curing process. Thus, in this study, we developed micro-sized thin-film thermocouple (TFTC) arrays on freestanding Si₃N₄ thin-film windows as sensors for laser power density and local temperature. These devices showed excellent linear responses in output voltage to laser power density with wavelengths in the range of 325-1064 nm, and also indicated the local temperature at the laser spot. We systematically measured the penetrating effect and thermal effect through thick porcine tissues for high-intensity IR pulses with a laser system used in clinical treatment and subtracted the attenuation parameters for the porcine skin, fat and muscle tissue from the experimental data. The results offered reliable quantitative references for safe irradiation doses of high-intensity IR laser pulses in practical laser therapy.