Fluorescence based turn-on strategy for determination of microRNA-155 using DNA-templated copper nanoclusters

The authors report on a new approach for the determination of the breast cancer biomarker microRNA-155 (miRNA-155). It is based on the measurement of the fluorescence shift of oligonucleotide-templated copper nanoclusters (DNA-CuNC). A probe DNA was designed that acts as a template for the preparation of CuNC which, under 400 nm excitation, exhibit strong fluorescence enhancement at 490 nm and a 90 nm Stokes shift after binding to target miRNA-155 and formation of a DNA-RNA heteroduplex. Under the optimal conditions, the fluorescence of the DNA-CuNC increases with increasing concentration of miRNA-155 in the range from 50 pM to 10 nM, with a 11 pM detection limit. The assay has excellent selectivity over noncomplementary RNA. The method was applied to the determination of miRNA-155 in the presence of human plasma and saliva.

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Graphical abstract Schematic of the detection strategy that relies on the fluorescence shift of DNA-CuNCs resulting from the specific binding of DNA-CuNCs with target miRNA-155. Fluorescence intensities are linearly proportional to the concentrations of target RNA from 50 pM to 10 nM.

     

Fluorometric determination of microRNA via FRET between silver nanoclusters and CdTe quantum dots

This paper describes a CdTe quantum dot-based fluorescence resonance energy transfer (FRET) based assay for the detection of the breast cancer biomarker microRNA. The method relies on energy transfer between DNA-templated silver nanoclusters (AgNCs) and CdTe QDs. Interaction between double strand oligonucleotide and QDs can be detected qualitatively through gel analysis and quantitatively by the signal amplification from AgNCs to QDs via FRET, best measured at an excitation wavelength of 350 nm and at emission wavelengths of 550 and 590 nm. Three microRNAs (microRNA-21, microRNA-155 and Let-7a) were quantified to verify the feasibility of the method, and a high sensitivity for microRNAs was achieved. Fluorescence intensity increases linearly with the log of the concentration of microRNA 155 in the 5.0 pM to 50 nM range, with a 1.2 pM detection limit.

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Graphical abstract Schematic presentation of a quantum dot-based (QD-based) fluorescence resonance energy transfer technique for the detection of microRNA (miRNA). The method relies on energy transfer between DNA-templated silver nanoclusters (AgNCs) and QDs.

     

Retention of lysozyme activity by physical immobilization in nanocellulose aerogels and antibacterial effects

Aerogels prepared from aqueous dispersions of anionic and cationic cellulose nanofibrils (CNFs) were investigated as solid supports for enzymes and silver nanoparticles and to elicit a sustained antibacterial effect. The imparted stabilization in dry conditions was studied with aerogels that were cast after mixing the enzymes with CNFs followed by dehydration (freeze-drying). The activity of lysozyme immobilized in the given CNF system was analyzed upon storage in liquid and air media. In contrast with aqueous solutions of free, unbound enzyme, which lost activity after the first day, the enzyme immobilized physically in unmodified and cationic CNF presented better stability (activity for a longer time). However, the enzyme activity was reduced in the case of anionic CNF, which was prepared by TEMPO-mediated oxidation (TO-CNF). Both humidity and temperature reduced the stability of the enzyme immobilized in the respective CNF aerogel. The antibacterial activity of CNF aerogels carrying lysozyme was also tested against gram-negative and gram-positive bacteria. The results were compared with those obtained from CNF systems loaded with silver nanoparticles (AgNP) after in situ synthesis via UV reduction. Storage in cold or dry conditions preserved the activity and antibacterial performance of enzyme-loaded CNF aerogels. As expected, the lysozyme-containing aerogels showed lower inhibition than the AgNP-containing aerogel. In this latter case, the antibacterial activity depended on the concentration and size of the nanoparticles. Compared to unmodified CNF and TO-CNF, the aerogels prepared with cationic CNF, loaded with either lysozyme or AgNPs, showed remarkably better antibacterial activity. Similar experiments were conducted with horseradish peroxidase, which confirmed, to different degrees, the observations derived from the lysozyme systems. Overall, the results indicate that non-toxic and biodegradable CNF is a suitable support for bio-active materials and is effective in protecting and retaining enzymatic and antibacterial activities.     

Synthesis,characterization and electrochemical performance of a new imidazoline derivative as an environmentally friendly corrosion and scale inhibitor

Research on Chemical Intermediates - A new imidazoline derivative, {[(benzimidazol-2-ylmethyl)imino]bis(methylene)} bis(phosphonicacid), named as BMIBMBPA, was synthesized as an environmentally...     

Novel Fluorometric Assay for Detection of Cysteine as a Reducing Agent and Template in Formation of Copper Nanoclusters

This study was designed to develop a highly selective and sensitive method towards fluorimetric sensing of cysteine (Cys) in water and human serum by using copper nanocluster. The Cys-CuNCs were characterized by scanning electron microscopy (SEM), FTIR, fluorescence and UV–Vis analysis. Spectroscopic evidences showed different intensities that were attributed to the different size of Cys-CuNCs. Enhancement in fluorescence intensity of copper nanoclusters with an increase in concentration of cysteine may enable them to be good candidates in detection systems. Selective recognition of cysteine in aqueous and serum samples was achieved during the formation of various copper nanoclusters (Cys-CuNCs) with different size. Under the optimized conditions, two linear range of the nanobiosensor for cysteine were between the 5 μM to 50 μM with detection limit of 2.4 μM and between 60 μM to 500 μM with detection limit of 55 μM. Fluorescence intensity increased with addition of cysteine concentration from 5 to 50 μM. The proposed low-cost nanobiosensor exhibited high reproducibility and good selectivity. It has been used also for the determination of cysteine in human serum samples with recoveries of 97–103 % and RSDs of 1.8–3.6 %     

Determination of heavy metal ions by an amperometric biosensor based on glucose oxidase immobilized onto single-walled carbon nanotubes/Nile blue nanocomposite

An enzymatic electrochemical biosensor was prepared based on glucose oxidase (GOD) immobilized on single-walled carbon nanotubes/Nile blue (Nb–SWCNTs) nanocomposite cross-linked with glutaraldehyde on graphite electrode. The function of glucose biosensor is based on the electrocatalytic reduction of H₂O₂ generated by the reaction of the enzyme with glucose molecules. The biosensor was characterized by Fourier transform infrared (FTIR) spectroscopy, emission scanning (FESEM), UV–Vis spectrometry, and voltammetric and amperometric methods. Parameters influencing the performance of the biosensor, namely pH and applied potential, were optimized. Inhibition was carried out for the detection of Hg²⁺ and Pb²⁺ species under optimized condition. Inhibition investigations showed that the type of inhibition for both the abov- mentioned heavy metal ions were reversible and competitive.     

Visual detection of cancer cells by colorimetric aptasensor based on aggregation of gold nanoparticles induced by DNA hybridization

A simple but highly sensitive colorimetric method was developed to detect cancer cells based on aptamer–cell interaction. Cancer cells were able to capture nucleolin aptamers (AS 1411) through affinity interaction between AS 1411 and nucleolin receptors that are over expressed in cancer cells, The specific binding of AS 1411 to the target cells triggered the removal of aptamers from the solution. Therefore no aptamer remained in the solution to hybridize with complementary ssDNA-AuNP probes as a result the solution color is red. In the absence of target cells or the presence of normal cells, ssDNA-AuNP probes and aptamers were coexisted in solution and the aptamers assembled DNA-AuNPs, produced a purple solution. UV–vis spectrometry demonstrated that this hybridization-based method exhibited selective colorimetric responses to the presence or absence of target cells, which is detectable with naked eye. The linear response for MCF-7 cells in a concentration range from 10 to 10⁵ cells was obtained with a detection limit of 10 cells. The proposed method could be extended to detect other cells and showed potential applications in cancer cell detection and early cancer diagnosis.     

Cell Membrane-Coated AuNPs as a New Biomimetic Platform for ROS Scavenger Provides Cytoprotection from Apoptosis Induced by Oxidative Stress

Biocompatible nanoparticles have attracted considerable attention as cellular antioxidant agents for the improvement of new therapeutics for several and diverse oxidative stress related disorders. Here, it is shown that the biocompatible cell membrane@gold nanoparticle displays catalase-mimic behavior by decomposing H₂O₂. This interesting behavior can be used for cell protection against induced oxidative injury by reactive oxygen species (ROS). So, after characterizing this novel biocompatible nanostructure, the protective effect of cell membrane@AuNPs pretreatment in front of a well-defined oxidative stress-inducing chemotherapy drug, doxorubicin (Dox) is assessed. Doxorubicin pretreatment significantly reduces the intracellular ROS production. Similarly, a reduction in the levels of DNA oxidative damage, as measured with the AO/EB staining, is also observed. Obtained results would support that this novel nanostructure can show how a pharmacological agent can be used against oxidative stress-mediated diseases.