Ratiometric bioassay and visualization of dopamine β-hydroxylase in brain cells utilizing a nanohybrid fluorescence probe

A novel "Turn-on" fluorometric assays triggered reaction for β-glucosidase activity based on quercetin derived silicon nanoparticles and its potential use for cell imaging

β-Glucosidase (β-Gluco) is an enzyme that is crucial to numerous diseases, including cancer, and in sector of industries, it is used in the manufacturing of food. Measuring its enzymatic activity is critical for biomedical studies and other activities. Herein, we have developed a novel and precise fluorescent sensing method for measuring β-Gluco activity based on the production of yellow-green fluorescent quercetin-silicon nanoparticles (Q-SiNPs) produced from quercetin (QN) as a reducing agent and 3-[2-(2-aminoethyl amino) ethylamino] propyl-trimethoxy silane (AEEA) as a silane molecule. β-Gluco hydrolyzed quercetin-3-O-β-d-glucopyranoside (QO-β-DG) to produce QN, which was then used to produce Q-SiNPs. Reaction parameters, including temperature, time, buffer, pH, and probe concentration, were carefully tuned in this study. Subsequently, the fluorescence intensity was performed, showing good linearity (R2 = 0.989), a broad linear dynamic range between 0.5 and 12 U L-1, and a limit of detection (LOD) as low as 0.428 U L-1, which was proven by fluorescence measurements. Most importantly, various parameters were detected and characterized with or without β-Gluco. The designed probe was successively used to assess β-Gluco activity in human serum and moldy bread. However, the mathematical findings revealed recoveries for human serum ranging from 99.3 to 101.66% and for moldy bread from 100.11 to 102.5%. Additionally, Q-SiNPs were well suited to being incubated in vitro with L929 and SiHa living cells, and after using an Olympus microscope, imaging showed good fluorescence cell images, and their viability evinced minimal cytotoxicity of 77% for L929 and 88% for SiHa. The developed fluorescence biosensor showed promise for general use in diagnostic tests. Therefore, due to this outstanding sensing modality, we anticipate that this research can provide a novel schematic project for creating simple nanostructures with a suitable plan and a green synthetic option for enzyme activity and cell imaging.

BSA Capped gold Nanoclusters Modulated by Copper ion for Sensitive and Selective Detection of Histidine in Biological Fluid

This research proposed a sample and environmentally sustainable technique for the synthesis of bovine serum albumin capped gold nanoclusters (BSA-AuNCs) with outstanding fluorescence. The synthesized BSA-AuNCs were investigated using various ways before being combined with Cu2+ to produce a fluorescent switch probe (BSA-AuNCs-Cu2+) for histidine determination. After adding Cu2+, the fluorescence of the BSA-AuNCs was quenched, the fluorescence intensity was enhanced after adding histidine due to good coordination between Cu2+ and histidine. The significant chelation of histidine with Cu2+ demonstrated the viability of developing a selective "switch on" probe for histidine detecting over other amino acids. Unlike existing fluorescent nanomaterial-based approaches for detecting histidine, this study promises good selectivity, high efficiency, and the avoiding of chemical solvents. The designed BSA-AuNCs-Cu2+ fluorescent probe demonstrated an acceptable linear detection range of 0 to 240 µM under optimum circumstances, with a detection limit of 0.9 µM. The BSA-AuNCs-Cu2+ system was investigated in rat serum and human urine, with recoveries ranging from 97.2 to 108.2%, demonstrating its potential applicability for histidine detection with favorable results.

Catechin-inspired gold nanocluster nanoprobe for selective and ratiometric dopamine detection via forming azamonardine

The sensitive and selective perception of dopamine (DA, a typical neurotransmitter) is important to evaluate the biological environment. In this study, a catechin-functionalized gold nanocluster (C-Au NC) nanoprobe has been explored for the ratiometric DA sensing. The detection mechanism is based on the formation of azamonardine via selective DA-catechin chemical reaction and subsequent enhanced fluorescence emission. Using Au NC emission as the internal reference, ratiometric fluorescence variation is realized, which allows sensitive DA analysis with a limit of detection of 1.0 nM (S/N = 3) and linear response concentration range from 0 to 500 nM. The characteristic chemical reaction between catechin and DA affords favorable selectivity over other amino acids, metal ions and small molecules. In addition, the practical application of the proposed nanoprobe is validated by the accurate detection of DA content in urea and cell lysate samples.

Flexible electrospun nanofibrous film integrated with fluorescent carbon dots for smartphone-based detection and cellular imaging application

The dose of administered chemotherapy drugs is crucial to determine due to the potential for efficient or adverse outcomes for cancer patients. To date, no user-friendly and low-cost method of doxorubicin (DOX) detection using nontoxic and biodegradable materials has been reported. For this reason, in this work, we have developed for the first time a nanofiber-based sensing platform for sensitive and on-site DOX assay in just 10 min. This is obtained thanks to printable, porosity and embeddability features of electrospun nanofibrous films (ENFFs) combined with nitrogen and sulfur co-doped carbon dots (NS-CDs) as sensing probes. The assay was done by just pipetting analyte on the hydrophilic spots of the fabricated photoluminescence water-stable ENFFs where the color intensity was being darkened. DOX quenched NS-CDs fluorescence onto ENFFs through inner filter effect. The developed sensor was either coupled with smartphone technology to provide miniaturized, portable and easy-to-use device or an ordinary spectrofluorimeter for solid-state sensing applications (detection limit of 5.4 nM). Moreover, applicability of the designed sensor was evaluated in human serum with satisfactory recoveries. It is more interesting that the fabricated NS-CDs/ENF scaffolds have a high potential to detect the intracellular DOX to enhance cell proliferation leading to be considered as a multimodal tool in biomedical research and clinical diagnostics.

Mesoporous silica-loaded gold nanocluster with enhanced fluorescence and ratiometric fluorescent detection of thiram in foods

A core-shell QDs@mSiO2@y-AuNCs nanoprobe was prepared, and a new ratiometric fluorescent sensor for thiram detection was developed. The mechanism of thiram sensing was investigated using FTIR, surface-enhanced Raman, XPS spectra, etc. The sensing of thiram was mainly ascribed to the formation of Au-S bonds between thiram and Au atoms on y-AuNCs surface, resulting in the dissociation of 11-MUA ligand from the y-AuNCs surface and the charge transfer between thiram and y-AuNCs. In the ratiometric fluorescence detection of thiram based on QDs@mSiO2@y-AuNCs, a linear range of 0.5-60 ng/mL was obtained with a LOD of 0.19 ng/mL. Compared with the fluorescence detection based on y-AuNCs, the ratiometric fluorescence detection of thiram demonstrated 3-fold enhanced sensitivity. The improvement was ascribed to two aspects: the fluorescence emission of y-AuNCs was enhanced after they were loaded onto the QDs@mSiO2 nanoparticles; the ratiometric detection mode provided more precise sensing. The detection of thiram can be completed immediately after mixing the nanoprobe with thiram. Good recoveries of thiram in apple and pear samples were achieved. All the above results demonstrated the high potential of this method in practical applications.

Ratiometric fluorescent nanoprobe based on CdTe/SiO2/folic acid/silver nanoparticles core-shell-satellite assembly for determination of 6-mercaptopurine

A sensitive and robust fluorescent assay of 6-MP is described which relies on the facile assembly of a fluorescence nanoprobe by design of silica nanosphere encapsulated CdTe quantum dots (CdTe QDs) as scaffold, coupling with chemically tethered folic acid (FA)-protected silver nanoparticles (AgNPs) that function as responsive element. In this way a stable ternary core-shell-satellite nanostructure with dual-emission signals can be established. On binding to the target molecules, 6-MP, FA molecules initially occupied by AgNPs are liberated to give dose-dependent fluorescence emission, which can further form a self-calibration ratiometric fluorescence assay using CdTe QDs as an internal reference. The nanoprobe color vividly changes from red to blue, enabling the direct visual detection. The linear concentration range is 0.15~50 μM with the detection limit of 67 nM. By virtue of the favorable selectivity and robust assays, the nanoprobe was applied to 6-MP detection in urine samples, with recoveries from 97.3 to 106% and relative standard deviations (RSD) less than 5%. Graphical abstract.

Advances in biomedical and pharmaceutical applications of protein-stabilized gold nanoclusters

The interest in using gold nanoclusters (AuNCs) as imaging probes is growing, covering wide ranges of applications. The stabilization of AuNCs with protein ligands enhances their biomedical and pharmaceutical applications. This is due to the biocompatibility, water solubility and bioactivity of proteins. Different factors can control the optical properties of AuNCs such as protein size, amino acids content and conformational structure. Controlling the synthesis conditions can result in tuning the AuNCs excitation, emission, fluorescence intensity and physicochemical properties to fulfill different applications. NIR-emitting protein-stabilized AuNCs are promising as imaging agents for targeting and visualization of cancer in vitro and in vivo. They are promising to be included as an important part of multifunctional theranostic nanosystems, due to their potential dual functions as imaging and photosensitizing agent for photodynamic therapy. Additionally, the protein around AuNCs represents a rich environment of active functional groups that are susceptible for conjugation with various biomolecules. Protein-AuNCs can act as fluorescent probes for rapid and selective analysis of different analytes in solution, cells or biological fluids. In conclusion, the variability of protein-AuNC applications can advance research in different biomedical and pharmaceutical fields.