Functioning of a Fluorescein pH-Probe in Aqueous Media: Impact of Temperature and Viscosity

A ratiometric fluorescence sensor based on Eu3+ doped LDH@CMCh gel for visual detection and effective adsorption of tetracycline antibiotics

Herein, a ratiometric fluorescence sensor (Eu3+/LDH@CMCh gel) was firstly designed by self-assembling Eu3+ doped ZnAl layered double hydroxide (LDH) on carboxymethyl chitosan (CMCh) for simultaneously visual detection and effective adsorption of tetracycline antibiotics (TCs). Blue fluorescence at 420 nm of Zn2+-sensitized CMCh was quenched by TCs through the inner filter effect, while the red fluorescence at 617 nm generated by the antenna effect was enhanced obviously. Based on reverse variation of two fluorescence signals, sensitive detection of TCs was achieved with a lower LOD (0.041 μM). Besides, the Eu3+/LDH@CMCh gel exhibited outstanding adsorption performance for TCs due to the unique porous sponge-like structure. The maximum adsorption capacity of 564.3 mg g-1 was obtained, aligning well with both the pseudo-second-order and Freundlich model, indicating the chemical adsorption process. Various characterization means and density functional theory showed that the adsorption mechanisms mainly involved hydrogen bonding, electrostatic interaction, and cation-π interaction. Combined with the smartphone, the Eu3+/LDH@CMCh gel was successfully applied to realize the portable visual detection of TCs in food matrixes with satisfactory recoveries (83.6 %-118.6 %). Therefore, this work provides a new strategy for sensitive detection and efficient removal of TCs, revealing considerable practical application potential.

Thienothiophene-based quantum dots: calibration of photophysical properties via carbon dot and biomolecular interactions

Semiconductor-based quantum dots (QDs) are size-tunable, photostable and extremely effective fluorophores with strong bandgap luminescence, which make them attractive for biological and medical nano-applications. Herein, we present a thienothiophene (TT)-based highly conjugated fluorescent semiconductor containing triphenylamine (TPA) and tetraphenylethylene (TPE) units, TT-TPE-TPA, as a QD conjugate. As TT-TPE-TPA exhibits remarkable photophysical properties such as a maximum solid-state quantum yield of 47%, a maximum fluorescence solution quantum yield of 81%, a mega Stokes shift of 133 nm and a positive solvatochromism from blue to orange colors, its carbon-nitrogen (CN) and carbon-nitrogen-boron (CNB) dots were prepared. While the dots changed the emission characteristics of TT-TPE-TPA, depending on the enhanced conjugation and fluorescence properties of TT-TPE-TPA/CDs, tunable optical properties were achieved towards vital biomolecules such as urea, NH4Cl and sucrose. By systematically modulating the composition and concentration of TT-TPE-TPA, CDs, and biomolecules, the detailed mechanisms of energy transfer, fluorescence quenching, and radiation enhancement were revealed. This work opens the door to a new class of promising optical nanomaterials that could be controlled in TT-based QDs.

Stepwise isolation of diverse metabolic cell populations using sorting by interfacial tension (SIFT)

We present here a passive and label-free droplet microfluidic platform to sort cells stepwise by lactate and proton secretion from glycolysis. A technology developed in our lab, Sorting by Interfacial Tension (SIFT), sorts droplets containing single cells into two populations based on pH by using interfacial tension. Cellular glycolysis lowers the pH of droplets through proton secretion, enabling passive selection based on interfacial tension and hence single-cell glycolysis. The SIFT technique is expanded here by exploiting the dynamic droplet acidification from surfactant adsorption that leads to a concurrent increase in interfacial tension. This allows multiple microfabricated rails at different downstream positions to isolate cells with distinct glycolytic levels. The device is used to correlate sorted cells with three levels of glycolysis with a conventional surface marker for T-cell activation. As glycolysis is associated with both disease and cell state, this technology facilitates the sorting and analysis of crucial cell subpopulations for applications in oncology, immunology and immunotherapy.

Stepwise Isolation of Diverse Metabolic Cell Populations Using Sorting by Interfacial Tension (SIFT)

We present here a passive and label-free droplet microfluidic platform to sort cells stepwise by lactate and proton secretion from glycolysis. A technology developed in our lab, Sorting by Interfacial Tension (SIFT), sorts droplets containing single cells into two populations based on pH by using interfacial tension. Cellular glycolysis lowers the pH of droplets through proton secretion, enabling passive selection based on interfacial tension and hence single-cell glycolysis. The SIFT technique is expanded here by exploiting the dynamic droplet acidification from surfactant adsorption that leads to a concurrent increase in interfacial tension. This allows multiple microfabricated rails at different downstream positions to isolate cells with distinct glycolytic levels. The device is used to correlate sorted cells with three levels of glycolysis with a conventional surface marker for T-cell activation. As glycolysis is associated with both disease and cell state, this technology facilitates the sorting and analysis of crucial cell subpopulations for applications in oncology, immunology and immunotherapy.

A tuning fork-shaped bisbenzothiazole derivative as a pH-responsive digital fluorescent probe and its ex vivo evaluation

A new highly emissive pH-responsive near-IR active digital probe was designed and synthesized. The probe is based on a bisbenzothiazole motif with a highly vulnerable hydrogen unit attached in an intramolecular fashion. The probe produced a large Stokes shift which was observed to be highly pH dependent. The optical pH dependence can be used for sensing pH over a wide range.

The Application of Fluorescence Anisotropy for Viscosity Measurements of Small Volume Biological Analytes

Time-resolved fluorescence anisotropy has been extensively used to detect changes in bimolecular rotation associated with viscosity levels within cells and other solutions. Physiological alterations of the viscosity of biological fluids have been associated with numerous pathological causes. This current work serves as proof of concept for a method to measure viscosity changes in small analyte volumes representative of biological fluids. The fluorophores used in this study were fluorescein disodium salt and Enhanced Green Fluorescent Protein (EGFP). To assess the ability of the method to accurately detect viscosity values in small volume samples, we conducted measurements with 12 μL and 100 μL samples. No statistically significant changes in determined viscosities were recorded as a function of sample volume for either fluorescent probe. The anisotropy of both fluorescence probes was measured in low viscosity standards ranging from 1.02 to 1.31 cP, representative of physiological fluid values, and showed increasing rotational correlation times in response to increasing viscosity. We also showed that smaller fluid volumes can be diluted to accommodate available cuvette volume requirements without a loss in the accuracy of detecting discrete viscosity variations. Moreover, the ability of this technique to detect subtle viscosity changes in complex fluids similar to physiological ones was assessed by using fetal bovine serum (FBS) containing samples. The presence of FBS in the analytes did not alter the viscosity specific rotational correlation time of EGFP, indicating that this probe does not interact with the tested analyte components and is able to accurately reflect sample viscosity. We also showed that freeze-thaw cycles, reflective of the temperature-dependent processes that biological samples of interest could undergo from the time of collection to analyses, did not impact the viscosity measurements' accuracy. Overall, our data highlight the feasibility of using time-resolved fluorescence anisotropy for precise viscosity measurements in biological samples. This finding is relevant as it could potentially expand the use of this technique for in vitro diagnostic systems.