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Optical tweezers are widely used in materials assembly1, characterization2, biomechanical force sensing3,4 and the in vivo manipulation of cells5 and organs6. The trapping force has primarily been generated through the refractive index mismatch between a trapped object and its surrounding medium. This poses a fundamental challenge for the optical trapping of low-refractive-index nanoscale objects, including nanoparticles and intracellular organelles. Here, we report a technology that employs a resonance effect to enhance the permittivity and polarizability of nanocrystals, leading to enhanced optical trapping forces by orders of magnitude. This effectively bypasses the requirement of refractive index mismatch at the nanoscale. We show that under resonance conditions, highly doping lanthanide ions in NaYF4 nanocrystals makes the real part of the Clausius–Mossotti factor approach its asymptotic limit, thereby achieving a maximum optical trap stiffness of 0.086 pN μm–1 mW–1 for 23.3-nm-radius low-refractive-index (1.46) nanoparticles, that is, more than 30 times stronger than the reported value for gold nanoparticles of the same size. Our results suggest a new potential of lanthanide doping for the optical control of the refractive index of nanomaterials, developing the optical force tag for the intracellular manipulation of organelles and integrating optical tweezers with temperature sensing and laser cooling7 capabilities.The resonance of highly doping lanthanide ions in NaYF4 nanocrystals enhances the permittivity and polarizability of nanocrystals, leading to enhanced optical trapping forces by orders of magnitude, bypassing the trapping requirement of refractive index mismatch.

The intracellular metabolism of organelles, like lysosomes and mitochondria, is highly coordinated spatiotemporally and functionally. The activities of lysosomal enzymes significantly rely on the cytoplasmic temperature, and heat is constantly released by mitochondria as the byproduct of adenosine triphosphate (ATP) generation during active metabolism. Here, we developed temperature-sensitive LysoDots and MitoDots to monitor the in situ thermal dynamics of lysosomes and mitochondria. The design is based on upconversion nanoparticles (UCNPs) with high-density surface modifications to achieve the exceptionally high sensitivity of 2.7% K−1 and low uncertainty of 0.8 K for nanothermometry to be used in living cells. We show the measurement is independent of the ion concentrations and pH values. With Ca2+ ion shock, the temperatures of both lysosomes and mitochondria increased by ∼2 to 4°C. Intriguingly, with chloroquine (CQ) treatment, the lysosomal temperature was observed to decrease by up to ∼3 °C, while mitochondria remained relatively stable. Lastly, with oxidative phosphorylation inhibitor treatment, we observed an ∼3 to 7°C temperature increase and a thermal transition from mitochondria to lysosomes. These observations indicate different metabolic pathways and thermal transitions between lysosomes and mitochondria inside HeLa cells. The nanothermometry probes provide a powerful tool for multimodality functional imaging of subcellular organelles and interactions with high spatial, temporal, and thermal dynamics resolutions.

Temperature plays a key role in regulating intracellular activities. Accurate measurements of temperature inside living cells at the nanoscale can tell if the cells are under their healthy physiological status or in dysfunctional diseases. As the energy factory and metabolism center, mitochondria constantly release heat during ATP production, which greatly impacts the intracellular organelles’ temperature. A direct visualization platform with probes that can sense the in situ temperature dynamics of mitochondria, and map the temperature-related interactions among intercellular organelles, will facilitate our understanding of mitochondria-related diseases towards better therapy. Upconversion nanoparticles (UCNPs), being excited by near-infrared (NIR) light to generate visible light, have been widely applied in the fields of single-molecule bioassays, super-resolution microscopy, and recently non-contact thermometers, due to their unique optical properties, including their exceptional photo-stability against photo-bleaching or photo-blinking, tunable multi-wavelength emissions for multiplexing assays, anti-Stokes’ emissions to suppress autofluorescence background, near infrared excitation and emissions allowing deep-tissue penetration depth, and most importantly, temperature-dependent ratiometric luminescence for thermometry application. However, the chemical stability of hydrophilic UCNPs has limited their developments in biomedical applications. To obtain the hydrophilic UCNPs (NaYF4: 20%Yb3+, 2%Er3+) with excellent stability and dispersibility in aqueous physiological buffers, five different functionalization strategies have been systematically evaluated (chapter 2). To study the temperature dynamics of mitochondria, I developed a mitochondria-targeting UCNPs-based thermometer with a sensing sensitivity of 3.2% K-1 to monitor the temperature variations through the chemical stimulations. The cells displayed distinct response time and temperature dynamic profiles (chapter 3). To further study the interaction between lysosomes and mitochondria, I updated the design of UCNPs-based thermometer by optimizing the surface functionalization of UCNPs, which resulted in an enhanced reliability with the relative temperature sensing sensitivity of 2.7% K-1 and temperature uncertainty of 0.8 K in HeLa cells. The new probes can cascade target lysosomes and mitochondria, respectively (chapter 4). Chapter 5 concludes this thesis by providing a thermometry platform to study the temperature dynamics of mitochondria and organelles’ functional interactions under the physiological or pathological status. Combined with other state-of-the-art technologies, such as sequential labelling of mtDNA, super-resolution imaging, UCNPs-based thermometer will become a powerful multimodal probe for imaging, sensing, and therapy.

Light scattering from nanoparticles is significant in nanoscale imaging, photon confinement. and biosensing. However, engineering the scattering spectrum, traditionally by modifying the geometric feature of particles, requires synthesis and fabrication with nanometre accuracy. Here it is reported that doping lanthanide ions can engineer the scattering properties of low‐refractive‐index nanoparticles. When the excitation wavelength matches the ion resonance frequency of lanthanide ions, the polarizability and the resulted scattering cross‐section of nanoparticles are dramatically enhanced. It is demonstrated that these purposely engineered nanoparticles can be used for interferometric scattering (iSCAT) microscopy. Conceptually, a dual‐modality iSCAT microscopy is further developed to identify different nanoparticle types in living HeLa cells. The work provides insight into engineering the scattering features by doping elements in nanomaterials, further inspiring exploration of the geometry‐independent scattering modulation strategy. Benefitting from the enhanced resonance of lanthanide ions, the geometry dependence of Rayleigh scattering engineering is broken through by adjusting the ion types in nanoparticles, which results in an efficient and dual‐modality nanoprobe for scattering‐based microscopy.

Interferometric Scattering Microscopy Rayleigh scattering of the nanoparticles can be engineered by doping lanthanide ions, which is based on the enhanced polarizability of the nanoparticles when the excitation wavelength matches the ion resonance frequency of the lanthanide ions. More details can be found in article number 2203354 by Baolei Liu, Chaohao Chen, Xiaoxue Xu, Fan Wang, and co‐workers.

Non-functional pancreatic neuroendocrine tumors (NF-PanNETs) account for the majority of neuroendocrine neoplasms arising in the pancreas and exhibit substantial clinical and biological heterogeneity, yet their epigenetic regulation and spatial architecture remain poorly understood. Here, we present an integrative study of NF-PanNETs across multiple tumor grades using single-nucleus ATAC-seq (snATAC-seq) and spatial ATAC-seq. snATAC-seq delineates the chromatin accessibility landscapes of distinct tumor subtypes, immune cells, and cancer-associated fibroblasts (CAFs), revealing key transcription factor (TF) programs that drive tumor progression and shape microenvironmental interactions. Spatial ATAC-seq further identifies two distinct tumor-stroma ecological niches: a proliferative niche marked by MYC and FOX family, and an invasive niche enriched for Snail family TFs and KRAS pathway activity. These findings demonstrate that cellular behavior in NF-PanNETs is governed not only by intrinsic epigenetic states but also by spatial context. Together, our study provides a spatially resolved epigenomic framework for dissecting NF-PanNET heterogeneity and evolution, offering new biomarkers and regulatory axes for molecular stratification and precision therapy.

Single-beam super-resolution microscopy, also known as superlinear microscopy, exploits the nonlinear response of fluorescent probes in confocal microscopy. The technique requires no complex purpose-built system, light field modulation, or beam shaping. Here, we present a strategy to enhance spatial resolution of superlinear microscopy by modulating excitation intensity during image acquisition. This modulation induces dynamic optical nonlinearity in upconversion nanoparticles (UCNPs), resulting in variations of higher spatial-frequency information in the obtained images. The high-order information can be extracted with a proposed weighted finite difference imaging algorithm from raw fluorescence images, to generate an image with a higher resolution than superlinear microscopy images. We apply this approach to resolve two adjacent nanoparticles within a diffraction-limited area, improving the resolution to 130 nm. This work suggests a new scope for developing dynamic nonlinear fluorescent probes in super-resolution nanoscopy.

Video-rate super-resolution imaging through biological tissue can visualize and track biomolecule interplays and transportations inside cellular organisms. Structured illumination microscopy allows for wide-field super resolution observation of biological samples but is limited by the strong absorption and scattering of light by biological tissues, which degrades its imaging resolution. Here we report a photon upconversion scheme using lanthanide-doped nanoparticles for wide-field super-resolution imaging through the biological transparent window, featured by near-infrared and low-irradiance nonlinear structured illumination. We demonstrate that the 976 nm excitation and 800 nm up-converted emission can mitigate the aberration. We found that the nonlinear response of upconversion emissions from single nanoparticles can effectively generate the required high spatial frequency components in Fourier domain. These strategies lead to a new modality in microscopy with a resolution of 130 nm, 1/7th of the excitation wavelength, and a frame rate of 1 fps.

The intracellular metabolism of organelles, like lysosomes and mitochondria, are highly coordinated spatiotemporally and functionally. The activities of lysosomal enzymes significantly rely on the cytoplasmic temperature, and heat is constantly released by mitochondria as the byproduct of ATP generation during active metabolism. Here, we develop temperature-sensitive LysoDots and MitoDots to monitor the in situ thermodynamics of lysosomes and mitochondria. The design is based on upconversion nanoparticles (UCNPs) with high-density surface modifications to achieve the exceptionally high sensitivity of 2.7% K-1 and accuracy of 0.8 K for nanothermometry to be used in living cells. We show the measurement is independent of the intracellular ion concentrations- and pH values. With Ca2+ ion shock, the temperatures of both lysosomes and mitochondria increased by 2~4 C. Intriguingly, with Chloroquine treatment, the lysosomal temperature was observed to decrease by up to ~3 C, while mitochondria remained relatively stable. Lastly, with oxidative phosphorylation inhibitor treatment, we observed a 3~7 C thermal increase and transition from mitochondria to lysosomes. These observations indicate different metabolic pathways and thermal transitions between lysosomes and mitochondria inside HeLa cells. The nanothermometry probes provide a powerful tool for multi-modality functional imaging of subcellular organelles and interactions with high spatial, temporal and thermal dynamics resolutions. Competing Interest Statement The authors have declared no competing interest.

Abstract Temperature dynamics reflect the physiological conditions of cells and organisms. Mitochondria regulates temperature dynamics in living cells, as they oxidize the respiratory substrates and synthesize ATP, with heat being released as a by-product of active metabolism. Here, we report an upconversion nanoparticles based thermometer that allows in situ thermal dynamics monitoring of mitochondria in living cells. We demonstrate that the upconversion nanothermometers can efficiently target mitochondria and the temperature responsive feature is independent of probe concentration and medium conditions. The relative sensing sensitivity of 3.2% K−1 in HeLa cells allows us to measure the mitochondrial temperature difference through the stimulations of high glucose, lipid, Ca2+ shock and the inhibitor of oxidative phosphorylation. Moreover, cells display distinct response time and thermal dynamic profiles under different stimulations, which highlights the potential applications of this thermometer to study in situ vital processes related to mitochondrial metabolism pathways and interactions between organelles. Competing Interest Statement The authors have declared no competing interest.