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.

Intracellular thermometry provides important information about the physiological activity of single cells and has been implemented using diverse temperature‐sensitive materials as nanoprobes. However, measuring the temperature of specific organelles or subcellular structures is challenging because it requires precise positioning of the nanoprobes. Here, it is shown that dispersed fluorescent nanodiamonds (FNDs) endocytosed in living cells can be aggregated into microspheres using optical forces and used as intracellular temperature probes. The aggregation of the FNDs and electromagnetic resonance between individual nanodiamonds in the microspheres lead to a sevenfold intensity enhancement of 546‐nm laser excitation. With the assistance of a scanning optical tweezing system, the FND microspheres can be precisely patterned and positioned within the cells. By measuring the fluorescence spectra of the microspheres, the temperatures at different locations within the cells are detected. The method provides an approach to the constructing and positioning of nanoprobes in an intracellular manner, which has potential applications in high‐precision and flexible single‐cell analysis.

We developed adjustable and movable droplet microlenses consisting of a liquid with a high refractive index. The microlenses were prepared via ultrasonic shaking in deionized water, and the diameter of the microlenses ranged from 1 to 50 μm. By stretching the microlenses, the focal length can be adjusted from 13 to 25 μm. With the assistance of an optical tweezer, controllable assembly and movement of microlens arrays were also realized. The results showed that an imaging system combined with droplet microlenses could image 80 nm beads under white light illumination. Using the droplet microlenses, fluorescence emission at 550 nm from CdSe@ZnS quantum dots was efficiently excited and collected. Moreover, Raman scattering signals from a silicon wafer were enhanced by ∼ 19 times. The presented droplet microlenses may offer new opportunities for flexible liquid devices in subwavelength imaging and detection.

Using a single biological element as a photonic component with well-defined features has become a new intriguing paradigm in biophotonics. Here we show that endogenous lipid droplets in the mature adipose cells can behave as fully biocompatible microlenses to strengthen the ability of microscopic imaging as well as detecting intra- and extracellular signals. By the assistance of biolenses made of the lipid droplets, enhanced fluorescence imaging of cytoskeleton, lysosomes, and adenoviruses has been achieved. At the same time, we demonstrated that the required excitation power can be reduced by up to 73%. The lipidic microlenses are finely manipulated by optical tweezers in order to address targets and perform their real-time imaging inside the cells. An efficient detecting of fluorescence signal of cancer cells in extracellular fluid was accomplished due to the focusing effect of incident light by the lipid droplets. The lipid droplets acting as endogenous intracellular microlenses open the intriguing route for a multifunctional biocompatible optics tool for biosensing, endoscopic imaging, and single-cell diagnosis.

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