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Time-temperature indicators (TTIs) with the capability to visually reflect the accumulated time and temperature effect for real time are of substantial significance for securing the safety and quality of perishable products, such as foods and medical products. Herein, we design a novel TTI with high accuracy and low cost based on a ratiometric fluorescent nanosensor capable of self-calibration. The nanosensor was fabricated via the co-assembly of amphiphilic block copolymer and a responsive triplet-triplet annihilation upconversion (TTA-UC) system. The pH responsiveness of the triplet-sensitized nanomicelle was well investigated experimentally and theoretically. A linear relationship between the intensity ratio (of the integrated upconversion emission to the integrated phosphorescence emission) and pH was revealed for the ratiometric fluorescent nanomicelle. The TTA-UC functionalized nanomicelle turned out to be an extraordinary nanosensor with excellent sensitivity, reliability, and anti-reference. Subsequently, the nanomicelle was firstly applied for enzymatic time-temperature indicators (TTIs). Comprehensive kinetic study of the TTI prototype and the released total volatile basic nitrogen during meat storage was conducted under isothermal and non-isothermal conditions, which demonstrated remarkable correlation between the TTI response and the food spoilage. The activation energy of the TTI prototype could be readily modified to satisfy diverse food products including meat, diary, and aquatic products. The TTI based on triplet-sensitized ratiometric fluorescent nanosensor could be employed for visual monitoring food quality with low cost, high accuracy, and good reliability. [Display omitted] • A novel TTI prototype is designed for monitoring food quality for real time. • The TTI is fabricated with a ratiometric fluorescent nanosensor based on triplet-triplet annihilation upconversion. • It shows self-calibration and superior accuracy more than excellent sensitivity, reliability, and anti-reference ability. • Comprehensive kinetic study validates the high accuracy of the TTI prototype. [ABSTRACT FROM AUTHOR]

Insufficient sensitivity caused by low radiative intensity of employed fluorescent material is the main obstacle toward early accurate diagnosis of fatal diseases when applying fluorescence analysis. Herein, we have developed a dual amplification procedure to overcome this issue. We first synthesize high-quality CdSe@ZnS@SiO 2 core/shell quantum dots (QDs) with type-I band alignment to confine the carrier wave functions, thus ensuring high quantum yield (∼ 80%). The fluorescence intensity of those QDs is further amplified by localized surface plasmon resonance effect enabled by gold nanoparticles. We finally construct CdSe@ZnS@SiO 2 and Au@SiO 2 immune sandwich biosensor platform, and take C-reaction protein (CRP) as a test case. It is shown that this biosensor platform exhibits a wide detecting range between 0.5 and 100 ng/mL, and detecting limit of 0.076 ng/mL. We further apply this detecting scheme in serum and actual clinical, competing performance compared with the prevailing standard measurements in hospital has been obtained. Both experiment and the finite element analysis (FEA) approach calculation results indicate that a highly enhanced electric field between Au@SiO 2 and CdSe@ZnS@SiO 2 enhances the radiative recombination rates of the QDs@SiO 2 and decreases the fluorescence lifetime of that. The fluorescence intensity amplification scheme proposed herein is of great significance for the real-time and high-sensitivity early detection of biomarkers in the biomedicine. • Designing novel route of biological sensing via high-quality QDs-Gold system. • Highly enhanced electric field between Au@SiO 2 and QDs exists by Experiment and theoretical results. • By LSPR effect, the platform exhibits high sensitivity and wide detection range. [ABSTRACT FROM AUTHOR]

Nonalcoholic fatty liver disease (NAFLD) has emerged as a prevalent chronic liver condition worldwide. The dysregulated metabolism of lipid droplets (LDs) in cells is physiologically and pathologically linked to NAFLD. The development of fluorescent probes for imaging LD metabolism holds promise for noninvasive diagnosis and understanding of NAFLD. However, the development of such probes is challenging, and their in vivo diagnostic potential remains largely unexplored. Here, we present the synthesis of ZP-1 , a bright fluorophore serving as a specific probe for LDs. ZP-1 possesses a donor-acceptor electronic structure with intramolecular charge transfer characteristics and shows polarity-dependent emission. In highly polar solvents, such as water, ZP-1 exhibits minimal fluorescence, while in low-polarity solvents, it displays strong fluorescence. This property enables high-specificity LD detection with excellent imaging contrast. Attributed to its high photostability and pH stability, ZP-1 effectively visualizes LD metabolism in live cells via real-time imaging, encompassing processes such as growth, migration, fusion, and fission. Moreover, we demonstrate in vivo diagnosis of NAFLD in a mouse model, providing rich information regarding LD morphology, numbers, volumes, and tissue structures. This work introduces ZP-1 as a valuable tool for NAFLD diagnosis and research, facilitating noninvasive assessment and improved understanding of the disease. • An ICT-type fluorophore, ZP-1 , has been synthesized. • ZP-1 shows polarity-dependent emission. • ZP-1 targets lipid droplets (LDs) in live cells. • ZP-1 can monitor LD metabolism. • ZP-1 is capable of diagnosing NAFLD in vivo. [ABSTRACT FROM AUTHOR]