Micro-viscosity of liquid oil confined in colloidal fat crystal networks

Utilization of photo-luminescent technique toward viscosity detection in the liquid food system with triphenylamine-michaelitic acid molecular sensor

A noninvasive and effective viscosity inspection method is expected to ease the burden of continued increased health problems caused by liquid food safety. In this study, we proposed the viscosity of the liquid food micro-environment as a marker and further developed a versatile optical sensor, DPTMDD, for monitoring liquid food micro-environmental viscosity alterations. This sensor was strategically constructed by the triphenylamine-thiophene derivate and michaelitic acid, rotatable conjugate structure was utilized as the recognition site. The molecular sensor was synthesized in a one-step facile way, and DPTMDD displayed a longer emission wavelength (592 nm), low detection limit (1.419 cP), and larger Stokes shift (193.7 nm in glycerol and 177.8 nm in water) with narrower energy band, endowing the sensor with the capacity of achieving high signal-to-noise ratio imaging. Meanwhile, DPTMDD exhibits high adaptability, selectivity, sensitivity, and good photo-stability in various liquid foods, bright fluorescent signal (37.5-fold) of DPTMDD is specifically activated in the high viscosity media. Thickening efficiencies can be identified as well. More importantly, the viscosity fluctuations during the metamorphic stages of liquid foods are also screened through in situ monitoring. We expected that this unique strategy will reinvigorate the continued perfection of liquid food safety investigation systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05699-y.

Visual detection of viscosity through activatable molecular rotor with aggregation-induced emission

Food safety has become one of the urgent affairs in the global public health studies, and irregular viscosity is closely associated with the food spoilage extent. In this study, one kind of activatable molecular rotor (TPA-PBZ) based on triphenylamine derivates has been synthesized via the Schiff base condensation reaction. This rotor is comprised by donor-accepter conjugated structure, with aggregation induced-emission feature and a large Stokes shift of 160 nm in water. The rotation of aromatic rings in TPA-PBZ is restricted in high-viscosity microenvironment, with the gradually increasing fluorescence emission signal at 568 nm. Significantly, this rotor TPA-PBZ has successfully been applied not only in the determination of thickening effects of food gum, but also in the detection of viscosity enhancement during the liquid food spoilage process. This molecular rotor can be utilized as an intelligent monitor platform for food quality and safety inspection in viscosity-related conditions.

Comparation of micro-viscosity of liquid oil in different colloidal fat crystal networks using molecular rotors

Micro-viscosity is an important parameter to describe the microenvironment of the fat crystal network. In this study, we evaluated the micro-viscosity of the liquid oil confined in mixtures of palm kernel stearin (PKS)/soybean oil (SO) and fully hydrogenated rapeseed oil (FHRSO)/SO using molecular rotors. The micro-viscosity was shown to increase with solid fat content (SFC), as well as with high proportion of triglycerides that crystallized and formed stronger linked networks. In addition, the thickness of nanocrystals decreased with the increase of solid fat and denser fat crystal network appeared with larger box-counting fractal dimension. Mathematic fit analysis further indicated that molecular confinement of the oil was strongly dependent on the microstructure with high-space filling colloidal fat crystal networks. Larger box-counting fractal dimension led to higher micro-viscosity. However, the critical box-counting fractal dimension was found to be 1.86 irrespective of the nature of the network.

A Method for High-Throughput Measurements of Viscosity in Sub-micrometer-Sized Membrane Systems

To unravel the underlying principles of membrane adaptation in small systems like bacterial cells, robust approaches to characterize membrane fluidity are needed. Currently available relevant methods require advanced instrumentation and are not suitable for high-throughput settings needed to elucidate the biochemical pathways involved in adaptation. We developed a fast, robust, and financially accessible quantitative method to measure the microviscosity of lipid membranes in bulk suspension using a commercially available plate reader. Our approach, which is suitable for high-throughput screening, is based on the simultaneous measurements of absorbance and fluorescence emission of a viscosity-sensitive fluorescent dye, 9-(2,2-dicyanovinyl)julolidine (DCVJ), incorporated into a lipid membrane. We validated our method using artificial membranes with various lipid compositions over a range of temperatures and observed values that were in good agreement with previously published results. Using our approach, we were able to detect a lipid phase transition in the ruminant pathogen Mycoplasma mycoides.

Enhancement of the lasing efficiency of vitamin B2 in a highly polar organic solvent via DNA-lipid complex

We experimentally demonstrated a green liquid laser at the wavelength of 570 nm, utilizing the optical gain of vitamin B₂ in a highly polar organic solvent, and proposed an efficient method to enhance its lasing efficiency by adding DNA-lipid complex (DNA-CTMA) in the solution. Optical properties of vitamin B₂ in the hexafluoro-2-propanol solvents were investigated by adding various amounts of DNA-CTMA in terms of the UV-visible absorbance, the visible emission, and the fluorescence lifetime. A Fabry-Perot cavity was built to obtain the laser oscillation at 570 nm using a pulsed pump source at the wavelength of 450 nm, 5 ns pulse duration, and 10 Hz repetition rate. By adding DNA-CTMA, both the output power and slope efficiency were enhanced along with a significant reduction of the lasing threshold pump power. The proposed scheme could open new potential for highly efficient biolasers.

Development of a viscosity sensitive fluorescent probe for real-time monitoring of mitochondria viscosity

Through rational design, two new mitochondria-targeted fluorescent viscosity probes were developed, which exhibited favorable properties such as large turn on fluorescence signal, good selectivity, low cytotoxicity, and high colocation coefficient (>0.90).

FRET-Based Nanobiosensors for Imaging Intracellular Ca²⁺ and H⁺ Microdomains

Semiconductor nanocrystals (NCs) or quantum dots (QDs) are luminous point emitters increasingly being used to tag and track biomolecules in biological/biomedical imaging. However, their intracellular use as highlighters of single-molecule localization and nanobiosensors reporting ion microdomains changes has remained a major challenge. Here, we report the design, generation and validation of FRET-based nanobiosensors for detection of intracellular Ca²⁺ and H⁺ transients. Our sensors combine a commercially available CANdot^®565QD as an energy donor with, as an acceptor, our custom-synthesized red-emitting Ca²⁺ or H⁺ probes. These ‘Rubies’ are based on an extended rhodamine as a fluorophore and a phenol or BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid) for H⁺ or Ca²⁺ sensing, respectively, and additionally bear a linker arm for conjugation. QDs were stably functionalized using the same SH/maleimide crosslink chemistry for all desired reactants. Mixing ion sensor and cell-penetrating peptides (that facilitate cytoplasmic delivery) at the desired stoichiometric ratio produced controlled multi-conjugated assemblies. Multiple acceptors on the same central donor allow up-concentrating the ion sensor on the QD surface to concentrations higher than those that could be achieved in free solution, increasing FRET efficiency and improving the signal. We validate these nanosensors for the detection of intracellular Ca²⁺ and pH transients using live-cell fluorescence imaging.