A novel gold-nanocluster-based fluorescent sensor for detection of sodium 2-mercaptoethanesulfonate

In Situ Labeling of the Aqueous Compartment of Extracellular Vesicles with Luminescent Gold Nanoclusters

Extracellular vesicles (EVs) are well-known membrane-limited particles secreted by both healthy and cancerous cells. They are considered as biomarkers for early cancer diagnosis and are involved in many pathologies and physiological pathways. They could serve as diagnostic tools in liquid biopsies, as therapeutics in regenerative medicine, or as drug delivery vehicles. Our aim is here to encapsulate luminescent nanoprobes in the aqueous compartment of human EVs extracted from reproductive fluids. The analysis and labeling of the EVs content with easily detectable luminescent nanoparticles could enable a powerful tool for early diagnosis of specific diseases and also for the design of new therapeutics. In this view, gold nanoclusters (AuNCs) appear as an attractive alternative as nontoxic fluorophore probes because of their luminescence properties, large window of fluorescence lifetimes (1 ns-1 μs), ultrasmall size (<2 nm), good biocompatibility, and specific ability as X-ray photosensitizers. Here, we investigated an attractive method that uses fusogenic liposomes to deliver gold nanoclusters into EVs. This approach guarantees the preservation of the EVs membrane without any breakage, thus maintaining compartmental integrity. Different lipid compositions of liposomes preloaded with AuNCs were selected to interact electrostatically with human EVs and compared in terms of fusion efficiency. The mixture of liposomes and EVs results in membrane mixing as demonstrated by FRET experiments and fusion revealed by flux cytometry and cryo-TEM. The resulting fused EVs exhibit typical fluorescence of the AuNCs together with an increased size in agreement with fusion. Moreover, the fusion events in mixtures of EVs and AuNCs preloaded liposomes were analyzed by using cryo-electron microscopy. Finally, the ratio of released AuNCs during the fusion between the fusogenic liposomes and the EVs was estimated to be less than 20 mol % by Au titration using ICP spectroscopy.

Fabrication of impedimetric sensor based on metallic nanoparticle for the determination of mesna anticancer drug

Electrochemical impedance spectroscopy (EIS) is a highly effective technique for studying the surface of electrodes in great detail. EIS-based electrochemical sensors have been widely reported, which measure the charge transfer resistance (Rct) of redox probes on electrode surfaces to monitor the binding of target molecules. One of the protective drugs against hemorrhagic cystitis caused by oxazaphosphorine chemotherapy drugs such as ifosfamide, cyclophosphamide and trophosphamide is Mesna (sodium salt of 2-mercaptoethanesulfonate). The increase in the use of Mesna due to the high consumption of anti-cancer drugs, the determination of this drug in biological samples is of particular importance. So far, no electrochemical method has been reported to measure Mesna. In this research, a novel impedimetric sensor based on a glassy carbon electrode (GCE) modified with oxidized multiwalled carbon nanotubes (MWCNTs)/gold nanoparticle (AuNPs) (denoted as Au NPs/MWCNTs/GCE) for impedimetric determination of Mesna anticancer drug was developed. The modified electrode materials were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), and EIS. The electrochemical behavior of Mesna at the surface of Au NPs/MWCNTs/GCE was studied by an impedimetric method. The detection mechanism of Mesna using the proposed impedimetric sensor relied on the increase in the Rct value of [Fe (CN)6]3-/4- as an electrochemical probe in the presence of Mesna compared to the absence of Mesna as the analyte. Under the optimum condition, which covered two linear dynamic ranges from 0.06 nmol L-1 to 1.0 nmol L-1 and 1.0 nmol L-1 to 130.0 µmol L-1, respectively. The detection limit was 0.02 nmol L-1. Finally, the performance of the proposed sensor was investigated for Mesna electrochemical detection in biological samples.

A Portable Sensing Platform Using an Upconversion-Based Nanosensor for Visual Quantitative Monitoring of Mesna

Mesna is an important regional antidote for protecting the urinary system of chemotherapy patients, which requires monitoring its level in real time to ensure the curative effect. The fluorescence method is a powerful tool in real-time detection with the advantages of fast response and visualization. However, the background interference limits its application in biological sensing. Here, we developed a portable sensing platform using an upconversion-based nanosensor for visual quantitative monitoring of mesna in real-time/on-site conditions. The nanosensor was constructed by upconversion nanoparticles (UCNPs) and ethyl violet (EV), in which the UCNPs emitted red and green light, while EV quenched the green light due to the inner filter effect (IFE). The reaction of mesna with EV caused its fading and broke the IFE process, leading to the recovery of green light. By the fluorescence and colorimetric chromaticity variations, the nanosensor achieved a dual-readout detection for mesna with low limits of detection (LODs) of 26 and 48 nM, respectively. Furthermore, a highly compatible sensing platform was fabricated for facile determination of mesna with an LOD of 56 nM, realizing visual quantitative monitoring of the mesna level to ensure the curative effect and providing a new strategy for point-of-care testing of drugs in clinical settings.

Gold nanoclusters: An ultrasmall platform for multifaceted applications

Gold nanoclusters (Au NCs) with a core size below 2 nm form an exciting class of functional nano-materials with characteristic physical and chemical properties. The properties of Au NCs are more prominent and extremely different from their bulk counterparts. The synthesis of Au NCs is generally assisted by template or ligand, which impart excellent cluster stability and high quantum yield. The tunable and sensitive physicochemical properties of Au NCs open horizons for their advanced applications in various interdisciplinary fields. In this review, we briefly summarize the solution phase synthesis and origin of the characteristic properties of Au NCs. A vast review of recent research work introducing biosensors based on Au NCs has been presented along with their specifications and detection limits. This review also highlights recent progress in the use of Au NCs as bio-imaging probe, enzyme mimic, temperature sensing probe and catalysts. A speculation on present challenges and certain future prospects have also been provided to enlighten the path for advancement of multifaceted applications of Au NCs.