Ratiometric Fluorescent Detection of Phosphate in Aqueous Solution Based on Near Infrared Fluorescent Silver Nanoclusters/Metal–Organic Shell Composite

Simple construction of ratiometric fluorescent probe for the detection of dopamine and tyrosinase by the naked eye

A simple and effective method for constructing a ratiometric fluorescent probe for the detection of dopamine and tyrosinase was developed.

A reusable ratiometric electrochemical biosensor on the basis of the binding of methylene blue to DNA with alternating AT base sequence for sensitive detection of adenosine

We develop a reusable ratiometric electrochemical biosensor on the basis of the binding of methylene blue (MB) to DNA with alternating AT base sequence for sensitive detection of adenosine. We design a strand 1 with MB-modified thymine (T) base in the proximal 3' termini as the capture probe for its immobilization on the gold electrode and a 3' termini ferrocene (Fc)-modified aptamer for the recognition of adenosine. The hybridization of strand 1 with the aptamer leads to the formation of a double-stranded DNA (dsDNA) and consequently the away of MB from the electrode surface and the close of Fc to the electrode surface, generating a small value of I_MB/I_Fc (I_MB and I_Fc are the peak currents of MB and Fc, respectively). In the presence of adenosine, its binding with the aptamer induces the release of Fc from the electrode surface and the close of MB to the electrode surface, generating a large value of I_MB/I_Fc. As a result, adenosine may be accurately quantified by the measurement of ratiometric signal (I_MB/I_Fc). This ratiometric electrochemical biosensor can be simply fabricated and exhibits high sensitivity with a limit of detection of as low as 90.8pM and a large dynamic range from 0.1nM to 100μM. Moreover, this biosensor demonstrates good performance with excellent selectivity, regeneration capability, high reliability and good reproducibility, and may become a universal platform for the detection of various biomolecules which can be recognized by aptamers, holding great potential for further applications in biomedical research and clinical diagnosis.

One-Step Synthesis of Rox-DNA Functionalized CdZnTeS Quantum Dots for the Visual Detection of Hydrogen Peroxide and Blood Glucose

As the blood glucose concentration is an important clinical parameter of diabetes, the rapid and effective detection of blood glucose is very significant for monitoring and managing diabetes. Here, a facile method to prepare Rox-DNA functionalized CdZnTeS quantum dots (QDs) was developed. The Rox-DNA functionalized CdZnTeS QDs were prepared by a one-pot hydrothermal method through phosphorothioate DNA bound to QDs, which were employed as a ratiometric fluorescent probe for the rapid and sensitive detection of H₂O₂ and glucose. Compared with the traditional multistep construction of ratiometric fluorescent probes, this presented approach is simpler and more effective without chemical modification and complicated separation. The CdZnTeS QDs with green fluorescence is specifically sensitive to H₂O₂, while the red fluorescence of Rox is invariable. H₂O₂ is the product from the oxidation of glucose catalyzed by glucose oxidase (GOx). Therefore, a facile method to detect H₂O₂ and glucose with a detection limit of 0.075 μM for H₂O₂ and 0.042 μM for glucose was developed. In addition, this proposed probe has been employed for the detection of glucose in human serum with a satisfactory result. Moreover, this probe has been used for visual detection, and the health and diabetics can be distinguished by the naked eye. Meanwhile, this nanoprobe is also generalizable and can be extended to the detection of many other H₂O₂-mediated analytes.

High-Crystallinity Covalent Organic Framework with Dual Fluorescence Emissions and Its Ratiometric Sensing Application

High crystallinity of covalent organic frameworks (COFs) with dual fluorescence emissions has not been reported so far. Here, we show the rational design and preparation of high-crystallinity COF TzDa via the synergetic interaction of docking sites and hydrogen bonds: 4,4',4″-(1,3,5-Triazine-2,4,6-triyl)trianiline (Tz) with the docking site and 2,5-dihydroxyterephthalaldehyde (Da) with the OH group are employed to synthesize the imine-linked two-dimensional high-crystallinity layered structure TzDa. The prepared mesoporous TzDa (ca. 36 Å) exhibits high thermal and chemical stability. The intramolecular charge transfer (ICT) and excited-state intramolecular proton transfer (ESIPT) effects bring TzDa two main fluorescence emissions around 500 and 590 nm. Water molecules can interfere with the ICT and ESIPT effects, allowing the development of a ratiometric fluorescent sensor for water in organic solvents. The proposed sensor shows high sensitivity to trace water in conventional organic solvents. The high stability of TzDa allows its recyclable uses for trace water detection. This work not only offers a platform for the construction of high-crystallinity COFs, but also provides a rational design of COFs with dual fluorescence emissions for ratiometric sensing applications.

pH and Urea Estimation in Urine Samples using Single Fluorophore and Ratiometric Fluorescent Biosensors

Kidney diseases remain often undiagnosed due to inefficient screening methods available at patient's disposal. Early diagnosis and effective management of kidney problems can best be addressed by the development of biosensors for commonly occurring clinical biomarkers. Here we report the development of single fluorophore and dual fluorophore ratiometric biosensors based on alginate microspheres for pH and urea analysis in urine samples. A facile method of air driven atomization was used for developing these polymeric fluorophore and enzyme based biosensors. Ratiometric biosensors were developed using layer-by-layer coating of polyelectrolyte conjugated to reference fluorophores. Biosensing studies using these biosensors showed that samples in pathophysiological range can be measured having pH range of 4-8 and urea levels between 0-50 mM. Testing of urine samples using these biosensors showed that both pH and urea detection can be accurately performed without interference. Thus, we believe that FITC-Dextran and FITC-Dextran/RuBpy based pH and urea biosensors show a great potential to be translated as a point of care device for pH and urea biosensing in early detection and continuous monitoring of kidney diseases.

Boric-Acid-Functional Lanthanide Metal-Organic Frameworks for Selective Ratiometric Fluorescence Detection of Fluoride Ions

Here, we report that boric acid is used to tune the optical properties of lanthanide metal-organic frameworks (LMOFs) for dual-fluorescence emission and improves the selectivity of LMOFs for the determination of F^- ions. The LMOFs are prepared with 5-boronoisophthalic acid (5-bop) and Eu³⁺ ions as the precursors. Emission mechanism study indicates that 5-bop is excited with UV photons to produce its triplet state, which then excites Eu³⁺ ions for their red emission. This is the general story of the antenna effect, but electron-deficient boric acid decreases the energy transfer efficiency from the triplet state of 5-bop to Eu³⁺ ions, so dual emission from both 5-bop and Eu³⁺ ions is efficiently excited at the single excitation of 275 nm. Moreover, boric acid is used to identify fluoride specifically as a free accessible site. The ratiometric fluorescent detection of F^- ions is validated with the dual emission at single excitation. The LMOFs are very monodisperse, so the determination of aqueous F^- ions is easily achieved with high selectivity and a low detection limit (2 μM). For the first time, we reveal that rational selection of functional ligands can improve the sensing efficiency of LMOFs through tuning their optical property and enhancing the selectivity toward targets.

Europium-based infinite coordination polymer nanospheres as an effective fluorescence probe for phosphate sensing

Uniform europium-based infinite coordination polymer nanospheres have been successfully fabricated as an effective fluorescence probe for phosphate sensing.

Fluorescent metal quantum clusters: an updated overview of the synthesis, properties, and biological applications

A brief history of metal quantum clusters, their synthesis methods, physical properties, and an updated overview of their applications is provided.

MnO2-induced synthesis of fluorescent polydopamine nanoparticles for reduced glutathione sensing in human whole blood

Polydopamine (PDA) nanoparticles, as a kind of popular polymer material, have attracted a great deal of attention from various areas including materials science, biomedicine, energy, environmental science and so on owing to their striking physicochemical properties. Herein, we reported for the first time the synthesis of intrinsic fluorescent PDA nanoparticles using MnO2 as an oxidant. In the presence of MnO2, dopamine was quickly oxidized into its quinone derivative, and autopolymerized into fluorescent PDA nanoparticles. Using fluorescent PDA nanoparticles as a fluorescence signal indicator, we further established a cost-effective sensor for rapid, sensitive and selective sensing of reduced glutathione (GSH) based on the redox reaction between MnO2 and GSH, and the key role of MnO2 in the formation of fluorescent PDA nanoparticles. GSH has the capability of reducing MnO2 into Mn(2+), which inhibited the formation of the fluorescent PDA nanoparticles. Thus, the concentration of GSH was directly related to the decreased fluorescence signal intensity of the PDA nanoparticles. The sensor showed good sensing performance for GSH detection with high sensitivity and desirable selectivity over other potential interfering species. Additionally, the sensor exhibited excellent practical applications for GSH detection in human whole blood samples, which presents potential applications in biological detection and clinical diagnosis.

Detection of cell surface calreticulin as a potential cancer biomarker using near-infrared emitting gold nanoclusters

Calreticulin (CRT) is a cytoplasmic calcium-binding protein. The aim of this study was to investigate CRT presence in cancer with the use of fluorescent gold nanoclusters (AuNCs) and to explore AuNC synthesis using mercaptosuccinic acid (MSA) as a coating agent. MSA-coated AuNCs conferred well-dispersed, bio-stable, water-soluble nanoparticles with bioconjugation capacity and 800-850 nm fluorescence after broad-band excitation. Cell-viability assay revealed good AuNC tolerability. A native CRT amino-terminus corresponding peptide sequence was synthesised and used to generate rabbit site-specific antibodies. Target specificity was demonstrated with antibody blocking in colorectal and breast cancer cell models; human umbilical vein endothelial cells served as controls. We demonstrated a novel route of AuNC/MSA manufacture and CRT presence on colonic and breast cancerous cell surface. AuNCs served as fluorescent bio-probes specifically recognising surface-bound CRT. These results are promising in terms of AuNC application in cancer theranostics and CRT use as surface biomarker in human cancer.

Potentiometric sensing of aqueous phosphate by competition assays using ion-exchanger doped-polymeric membrane electrodes as transducers

Using Zn(2+)-BPMP or Cu(2+)-BPMP as a receptor and o-mercaptophenol as an indicator, potentiometric sensing of aqueous phosphate by competition assays was achieved. With attractive features of portability, low cost and resistance to interference from turbidity and color, this sensor was successfully used for phosphate detection in biological and water samples.