An ultra-sensitive fluorescent “Turn On” biosensor for glutathione and its application in living cells

Aggregation emission of AuNCs induced by chitosan self-assembled multilayers and sensitive sensing for water content in ethanol

AuNCs with chemical groups such as -NH₂ and -COOH were synthesized using glutathione as the stabilizer and reducing agent. The aggregation emission of AuNCs in solution-induced self-assembled multilayers (SAMs) were first studied. Scanning electron microscopy and quartz crystal microbalance were used to characterize the morphology and aggregation process of AuNCs. Further AuNC SAMs were used for the solid-liquid interface sensing of water content in ethanol, and the sensitivity is obviously improved as compared with that in the pure solution phase. This aggregation emission induced by SAMs would have a good application prospect in analysis.

A sensitive and rapid detection of glutathione based on a fluorescence-enhanced "turn-on" strategy

Glutathione (GSH) plays important roles in the human body including protecting cells from oxidative damages and maintaining cellular redox homeostasis. Thus, developing a fast and sensitive method for detecting GSH levels in living bodies is of great importance. Many methods have been developed and used for GSH detection, such as high-performance liquid chromatography, capillary electrophoresis, and fluorescence resonance energy-based methods. However, these methods often lack sensitivity as well as efficiency. Herein, a rapid and sensitive method for glutathione detection was developed based on a fluorescence-enhanced "turn-on" strategy. In this study, a unique and versatile bifunctional linker 3-[(2-aminoethyl) dithio]propionic acid (AEDP)-modified gold nanoparticle (Au@PLL-AEDP-FITC) probe was designed for the simple, highly sensitive intracellular GSH detection, combined with the FRET technique. In the presence of GSH, the disulfide bonds of AEDP on Au@PLL-AEDP-FITC were broken through competition with GSH, and FITC was separated from gold nanoparticles, making the fluorescence signal switch to the "turn on" state. A change in the fluorescence signal intensity has a great linear positive correlation with GSH concentration, in the linear range from 10 nM to 180 nM (R2 = 0.9948), and the limit of detection (LOD) of 3.07 nM, which was lower than other reported optical nanosensor-based methods. Au@PLL-AEDP-FITC also has great selectivity for GSH, making it promising for application in complex biological systems. The Au@PLL-AEDP-FITC probe was also successfully applied in intracellular GSH imaging in HeLa cells with confocal microscopy. In short, the Au@PLL-AEDP-FITC probe-based fluorescence-enhanced "turn-on" strategy is a sensitive, fast, and effective method for GSH detection as compared with other methods. It can be applied in complex biological systems such as cell systems, with promising biological-medical applications in the future.

Target-triggered and controlled release plasmon-enhanced fluorescent AIE probe for conformational monitoring of insulin fibrillation

In this work, we constructed a target-triggered and controlled-release plasmon-enhanced fluorescent AIE probe to realize the purpose of conformational monitoring of insulin fibrillation. We synthesized a novel water-soluble anthracene derivative, 4,4',4'',4'''-(anthracene-9,10-diylbis(ethene-2,1,1-triyl))tetrakis(N,N,N-trimethylbenzenaminium) iodide (BDVAI), with AIE properties, high biocompatibility and good self-assembly effect. Gold nanocages (AuNCs) were selected as the substrate for PEF, and the inner space of hollow AuNCs was filled with BDVAI. Thiol-modified DNA chains were bonded to the surface of AuNCs by Au-S bonds, and an insulin aptamer was combined with the sulfhydryl chain to seal the AuNCs. This PEF-AIE sensor produces different fluorescence signals when interacting with native insulin and fibrillar insulin; thus, monitoring conformational changes in insulin can be realized by detecting fluorescence intensity changes during insulin fibrillation. Based on this design, this system realized sensitive detection of fibrillar insulin with a detection limit of 23.6 pM. This AIE molecular-based PEF fluorescence enhancement system improves the optical properties of fluorescent substances, which is of great significance in improving the detection sensitivity of amyloid fibrils conformational changes and providing a reliable basis for further understanding the pathogenesis of amyloidosis.

Visual Assay of Glutathione in Vegetables and Fruits Using Quantum Dot Ratiometric Hybrid Probes

Future food safety monitoring with simple, fast, and visual methods has become increasingly important. Accordingly, this work was designed to construct a new-style dual-emission ratiometric fluorescent probe (CdSe@SiO₂@CdTe) for visual assay of glutathione (GSH) with a "turn on" strategy. After adding Hg²⁺, the red fluorescence of the outer CdTe quantum dots (QDs) was quenched through both electron transfer and ion-binding processes. Upon the addition of GSH, the red fluorescence occurred again owing to the strong affinity between GSH and Hg²⁺, whereas the inner green fluorescence of CdSe QDs was unchanged, leading to a clearly recognizable fluorescence color change (from green to orange-red). In the concentration range from 0.1 to 10 μM, the relative fluorescence intensity ratios ( I₆₁₉/ I₅₃₅) showed an excellent linear correlation with the concentration of GSH, and the detection limit was as low as 42 nM under optimal conditions. Meanwhile, the ratiometric hybrid probes were successfully applied for direct visual sensing GSH in real vegetable and fruit samples.

Highly sensitive fluorescent detection of glutathione and histidine based on the Cu(ii)-thiamine system

A novel fluorescence method for the simultaneous detection of glutathione and histidine based on their inhibitory effects on the oxidation of thiamine by Cu(ii) is proposed.