Constructing highly sensitive ratiometric nanothermometers based on indirectly thermally coupled levels

Intracellular Temperature Sensing with Remarkably High Relative Sensitivity Using Nile Red-Loaded Biocompatible Niosome

Accurate temperature sensing at the nanoscale within biological systems is crucial for understanding various cellular processes, such as gene expression, metabolism, and enzymatic reactions. Current temperature-sensing techniques either lack the temperature resolution and sensitivity necessary for intracellular applications or require invasive procedures that can disrupt cellular activities. In this study, we present Nile Red (NR)-loaded hybrid (span 60-L64) niosomes and Nile Red-loaded L64 niosomes as highly sensitive fluorescent nanothermometers. These niosomes are synthesized via the thin-layer evaporation method, forming thermoresponsive vesicles, and they demonstrate reversible phase transition behavior with temperature. When loaded with polarity-sensitive Nile Red, vesicles exhibit a strong temperature-dependent fluorescence response (change in intensity, emission maximum, and lifetime), suitable for noncontact temperature sensing in the biologically important temperature range of 25 to 50 °C. While NR-hybrid niosomes exhibit a high relative sensitivity of 19% °C-1 at 42 °C, NR-L64 niosomes achieved extraordinary relative sensitivity of 36% °C-1 at 40 °C. Using NR-L64 niosomes, the temperature resolution is found to be 0.0004 °C at 40 °C. The nanothermometers displayed excellent photostability, thermal reversibility, and resistance to variations in ion concentration and pH. Temperature-dependent confocal microscopy using FaDu cells confirmed the biocompatibility and effectiveness of the designed nanothermometers for precise intracellular temperature sensing. The results demonstrate the significant potential of Nile Red-loaded niosomes for temperature monitoring using live cell imaging in biological media.

Triple-Mode upconversion emission for dynamic multicolor luminescent anti-Counterfeiting

Lanthanide (Ln³⁺) luminescent materials play a crucial role in information security and data storage owing to their excellent and unique optical properties. The advances in dynamic colorful luminescent anti-counterfeiting nanomaterials enable the generation of a high-level information encryption. In this work, a superior thermal, optical wavelength and excitation power triple-mode stimuli-responsive emission color modulation is demonstrated in a lanthanide-doped nanostructured luminescent material. The plentiful emission colors are manipulated by modulating the composition of a fluoride core-shell nanostructure with different Ln³⁺ at different doping concentrations. The nanomaterials display remarkable excitation wavelength/power-dependent color change, along with temperature-dependent color variation in the range from 298 K to 437 K, with a good relative sensitivity S_r of 1.1387% K^-1 at 398 K. The universal optical modulation, combined with the excellent optical and structural stability of the luminescent nanoparticles, renders many advantages for the anti-counterfeiting application. This work explores a universal strategy for the manipulation of triple-mode stimuli-responsive dynamic luminescence and demonstrates its good potential for anti-counterfeiting application.

Ratiometric fluorescent semiconducting polymer dots for temperature sensing

Semiconducting polymer dots (Pdots) have received much attention due to their unique characteristics, including high water solubility, good light stability, excellent biocompatibility, and low cost. Herein, we report a ratiometric nanoprobe based on Pdots-Eu for temperature sensing in vitro. The Pdots-Eu thermometer was composed of a blue temperature-insensitive semiconducting polymer, poly(9-vinylcarbazole) (PVK), a red temperature-sensitive complex tris(dibenzoylmethane)mono(5-amino-1,10-phenanthroline)europium (III) (Eu complex), and an amphiphilic polymer polystyrene graft ethylene oxide functionalized with carboxyl groups (PS-PEG-COOH). The Pdots-Eu thermometer showed two peaks at 368 nm from PVK and 611 nm from the Eu complex. The red/blue fluorescence intensity ratio of Pdots-Eu decreased with an increase in temperature, which could be used for the ratiometric monitoring of temperature change. The results showed that the red/blue fluorescence intensity ratio demonstrated a good linear relationship to the change of temperature from 25 °C to 55 °C. Impressively, the ratiometric probe featured good accuracy and high sensitivity for temperature detection in vitro, which could be used for monitoring temperature change in cells.

Stimuli-responsive fluorescent nanogel: a nonconventional donor for ratiometric temperature and pH sensing

A reactive stimuli responsive fluorescent polyaminoamide nanogel (NANO-PAMAM) is synthesized via an aza-Michael polyaddition reaction in water and subsequently transformed to a ratiometric nanosensor via post-polymerization modification of the reactive NANO-PAMAM.

Starch-Based Carbon Dots for Nitrite and Sulfite Detection

Nitrite and sulfite play important roles in human health and environmental science, so it is desired to develop a facile and efficient method to evaluate NO2 - and SO3 2- concentrations. In this article, the use of green alternatives with the potential of multi-functionality has been synthesized to detect nitrite and sulfite based on fluorescent probe. The carbon dots (CDs) with starch as only raw materials show fluorescence turn "on-off-on" response towards NO2 - and SO3 2- with the limits of detection of 0.425 and 0.243 μМ, respectively. Once nitrite was present in the solution, the fluorescence of CDs was quenched rapidly due to the charge transfer. When sulfite was introduced, the quenching fluorescence of CDs was effectively recovered because of the redox reaction between NO2 - and SO3 2-, and thus providing a new way for NO2 - and SO3 2- detection. Owing to their excellent analytical characteristics and low cytotoxicity, the "on-off-on" sensor was successfully employed for intracellular bioimaging of NO2 - and SO3 2-.

Highly Efficient Phosphorescent Blue-Emitting [3+2+1] Coordinated Iridium (III) Complex for OLED Application

Cyclometalated iridium (III) complexes are indispensable in the field of phosphorescent organic light-emitting diodes (PhOLEDs), while the improvement of blue iridium (III) complexes is as yet limited and challenging. More diversified blue emitters are needed to break through the bottleneck of the industry. Hence, a novel [3+2+1] coordinated iridium (III) complex (noted as Ir-dfpMepy-CN) bearing tridentate bis-N-heterocyclic carbene (NHC) chelate (2,6-bisimidazolylidene benzene), bidentate chelates 2-(2,4-difluorophenyl)-4-methylpyridine (dfpMepy), and monodentate ligand (-CN) has been designed and synthesized. The tridentate bis-NHC ligand enhances molecular stability by forming strong bonds with the center iridium atom. The electron-withdrawing groups in the bidentate ligand (dfpMepy) and monodentate ligand (-CN) ameliorate the stability of the HOMO levels. Ir-dfpMepy-CN shows photoluminescence peaks of 440 and 466 nm with a high quantum efficiency of 84 ± 5%. Additionally, the HATCN (10 nm)/TAPC (40 nm)/TcTa (10 nm)/10 wt% Ir-dfpMepy-CN in DPEPO (10 nm)/TmPyPB (40 nm)/Liq (2.5 nm)/Al (100 nm) OLED device employing the complex shows a CIE coordinate of (0.16, 0.17), reaching a deeper blue emission. The high quantum efficiency is attributed to rapid singlet to triplet charge transfer transition of 0.9–1.2 ps. The successful synthesis of Ir-dfpMepy-CN has opened a new window to develop advanced blue emitters and dopant alternatives for future efficient blue PhOLEDs.

Intrinsic Photoluminescence of Solid-State Gold Nanoclusters: Towards Fluorescence Lifetime Imaging of Tissue-Like Phantoms Under Two-Photon Near-Infrared Excitation

Gold nanoclusters (AuNCs) have attracted extensive attention as light-emissive materials with unique advantages such as high photostability, large Stoke shifts and low toxicity. However, a better understanding of their solid-state photoluminescence properties is still needed. Herein, we investigated for the first time the intrinsic photoluminescence properties of lyophilized bovine serum albumin stabilized AuNCs (BSA-AuNCs) via fluorescence lifetime imaging microscopy (FLIM) studies performed under both one and two photon excitations (OPE and TPE) on individual microflakes, combined with fluorescence spectroscopic investigations. Both in solution and solid-state, the synthesized BSA-AuNCs exhibit photoluminescence in the first biological window with an absolute quantum yield of 6% and high photostability under continuous irradiation. Moreover, under both OPE and TPE conditions, solid BSA-AuNCs samples exhibited a low degree of photobleaching, while FLIM assays prove the homogeneous distribution of the photoluminescence signal inside the microflakes. Finally, we demonstrate the ability of BSA-AuNCs to perform as reliable bright and photostable contrast agents for the visualization of cancer tissue mimicking agarose-phantoms using FLIM approach under non-invasive TPE. Therefore, our results emphasize the great potential of the as synthesized BSA-AuNCs for ex vivo and in vivo non-invasive NIR imaging applications.

Physical Origin of Dual-Emission of Au-Ag Bimetallic Nanoclusters

On the origin of photoluminescence of noble metal NCs, there are always hot debates: metal-centered quantum-size confinement effect VS ligand-centered surface state mechanism. Herein, we provided solid evidence that structural water molecules (SWs) confined in the nanocavity formed by surface-protective-ligand packing on the metal NCs are the real luminescent emitters of Au-Ag bimetal NCs. The Ag cation mediated Au-Ag bimetal NCs exhibit the unique pH-dependent dual-emission characteristic with larger Stokes shift up to 200 nm, which could be used as potential ratiometric nanosensors for pH detection. Our results provide a completely new insight on the understanding of the origin of photoluminescence of metal NCs, which elucidates the abnormal PL emission phenomena, including solvent effect, pH-dependent behavior, surface ligand effect, multiple emitter centers, and large-Stoke's shift.