Simple Probe Research Articles

A Simple Near-Infrared Fluorescent Probe for the Detection of Peroxynitrite.

Herein, we report the evaluation and synthesis of a reaction based fluorescent probe DCM‐Bpin for the detection of Peroxynitrite (ONOO−). DCM‐Bpin exhibits selective fluorescence off‐on response for ONOO− over other reactive oxygen species, including H2O2. Moreover, DCM‐Bpin is biocompatible and has been used to visualize exogenous ONOO− in HeLa cells.

Crown daisy leaf waste–derived carbon dots: A simple and green fluorescent probe for copper ion

In this paper, N‐doped carbon quantum dots (N‐CDs) were fabricated using crown daisy leaves, a kitchen waste, as carbon source. The synthesized N‐CDs possessed abundant surface functional groups, such as hydroxyl, carboxyl, and amino groups, and had good dispersibility in water. Because of the special fluorescence quenching property toward Cu2+, the synthesized N‐CDs can be exploited as an effective label‐free fluorescent probe for Cu2+ determination. The possible fluorescence sensing mechanism considered the selective coordination interaction between Cu2+ ion and the hydroxyl, carboxyl, and amino groups of the N‐CDs. The control experiments also showed that the N‐doped aromatic C–N heterocycle structure played a crucial role in selective sensing of Cu2+. The decrease in fluorescence efficiencies was linearly related with the Cu2+ concentrations in the range of 10.0nM to 120.0nM, with a response limit of 1.0nM. The prepared probe was also applied for Cu2+ determination in real river water.

An efficient NIR-to-NIR signal-based LRET system for homogeneous competitive immunoassay

Upconversion nanoparticles (UCNPs) are promising materials for biological applications based on luminescence resonance energy transfer (LRET). In contrast to classical RET donors such as quantum dots, gold nanoparticles, UCNPs can emit near-infrared (NIR) upon the NIR irradiation, which provides enhanced signal-to-noise due to strong penetration and low autofluorescence in the NIR region known as the diagnostic window. Here we report the first efficient NIR-to-NIR signal-based LRET system for the detection of progesterone, chosen as a proof-of-concept target, via homogeneous competitive immunoassay. To enhance the efficiency of LRET, we constructed inert-core/active-shell/inert-ultrathin shell UCNPs (NaYF4@NaYF4:Yb,Tm@NaYF4) as an LRET donor and a compact progesterone/horseradish peroxidase/IRdyeQC-1 (P-HRP-dyes) complex as an LRET acceptor. The designed donor and acceptor showed significantly improved LRET efficiencies (95% and 85% for donor and acceptor, respectively) compared with conventional donor and acceptor (70% and 50%, respectively). Using the developed NIR-to-NIR LRET system, progesterone was successfully detected with a background-free signal and low limit of detection (1.36 pg/ml in ten-fold diluted human serum). We believe that the efficient NIR-to-NIR signal-based LRET system developed here has potential as a simple probe for homogeneous competitive immunoassay, with the ability to rapidly detect biomarkers.

Label-free one-step fluorescent method for the detection of endonuclease activity based on thioflavin T/G-quadruplex.

Endonucleases, one of the basic tool enzymes of modern molecular biology and medical genetics, have also been clarified as the potential targets for antimicrobial and antiviral drugs screening. However, traditional assays to monitor endonuclease activity can be expensive, time-consuming, or laborious. In order to provide new detective platform, we proposed a novel label-free one-step fluorescent method for the detection of endonuclease activity based on cleavage-induced G-quadruplex formation. In this detection system, a simple DNA probe can spontaneously form a duplex structure with recognition sites of EcoRI and prevent the generation of the G-quadruplex. Once EcoRI is present, the recognition sites in the duplex DNA are cleavage, producing a free guanine-rich sequence to form G-quadruplex. When thioflavin T (ThT) is added, a strong fluorescence signal is given by ThT/G-quadruplex, and therefore the EcoRI activity can be detected. After systematic investigation and optimization, this method has gained a sensitive limit of detection at 0.75U/mL, and a wide detection range between 0.75U/mL and 120U/mL. Furthermore, the inhibitory effect of 5-fluorouracil on EcoRI activity was verified and IC50 was calculated. Taken together, these experimental results have proven that this turn-on fluorescent method has considerable analytical performances. As far as we are concerned, this method is the first reported EcoRI assay based on ThT/G-quadruplex, and only one kind of probe and one kind of dye are involved, providing one of the simplest detective strategies on EcoRI. More importantly, the convenience and cost make this one-step method quite attractive for application transformation. Therefore, we hope this method could be a hopeful option for EcoRI activity determination, and further to help monitoring the quality of tool enzymes and promote the development of high-through automatic drug screening system.

Mitochondria-targeting turn-on fluorescent probe for HClO detection and imaging in living cells.

Hypochlorous/hypochlorite (HClO/ClO-), one of the most important signal molecule, plays a crucial role in many cellular signaling pathways. It is reported that the HClO/ClO- level in mitochondria is important to maintain the normal mitochondrial function. Herein, we present two simple fluorescent probes BAC and mitochondria-targeting fluorescent probe TACB for the detection of ClO-. Probes BAC &TACB could be sensitively and selectivity detecting ClO- at the nanomolar levels with the detection limit of 1.64×10-9M and 9.86×10-8M, respectively. Additionally, probes BAC &TACB with the response unit of CO moiety could selectively detect ClO- over other various analytes such as anions, metal ions and OH, 1O2, H2O2. The response time of probe TACB for ClO- (<20s), implying that it could offer a real-time analytical assay of ClO-. Finally, probe BAC was used for monitoring the ClO- in HEK293T cells and probe TACB could be utilized to track the fluctuations of exogenous ClO- levels in the mitochondria of Hela cells.

Accessing scrambling using matrix product operators

Scrambling, a process in which quantum information spreads over a complex quantum system becoming inaccessible to simple probes, happens in generic chaotic quantum many-body systems, ranging from spin chains, to metals, even to black holes. Scrambling can be measured using out-of-time-ordered correlators (OTOCs), which are closely tied to the growth of Heisenberg operators. In this work, we present a general method to calculate OTOCs of local operators in local one-dimensional systems based on approximating Heisenberg operators as matrix-product operators (MPOs). Contrary to the common belief that such tensor network methods work only at early times, we show that the entire early growth region of the OTOC can be captured using an MPO approximation with modest bond dimension. We analytically establish the goodness of the approximation by showing that if an appropriate OTOC is close to its initial value, then the associated Heisenberg operator has low entanglement across a given cut. We use the method to study scrambling in a chaotic spin chain with $201$ sites. Based on this data and OTOC results for black holes, local random circuit models, and non-interacting systems, we conjecture a universal form for the dynamics of the OTOC near the wavefront. We show that this form collapses the chaotic spin chain data over more than fifteen orders of magnitude.

A simple H2S fluorescent probe with long wavelength emission: Application in water, wine, living cells and detection of H2S gas

As an important endogenous signal molecule, abnormal levels of H2S are closely related with many diseases. Although numerous H2S-specific fluorescent probes have been designed, most of them have some limitations including synthetic complexity, short emission wavelength, restricted applications. In this work, a simple H2S selective fluorescent probe (L) has been designed and synthesized by two-step reactions using 4-diethylaminosalicylaldehyde and 1,4-dimethylpyridinium iodide as raw materials. Probe L displays high selectivity and sensitivity to H2S in DMF/H2O (4/6, v/v, HEPES, 10 mM, pH = 7.4) with a long-wavelength emission, a large Stokes shift, and good anti-interference ability. The practical applicabilities of probe L to detect H2S were evaluated in actual water samples, wine samples, and living cells. Moreover, the L-doped polylactic acid (PLA) nanofibrous film prepared by electrospinning can be used to detect H2S gas.

Data compensation and fiber optic probe for dynamic displacement measurement system with sinusoidally phase modulated reference light

We investigate data compensation and all fiber probe for an interferometric measurement of high-frequency dynamic displacement. In this measurement, the reference light is modulated with a high-frequency sinusoidal signal and then the displacement is derived by using the time width of produced pulsed interference signal. Error compensation based on the frequency response function of the system is introduced to correctly measure the dynamic displacement containing relatively high frequency components. In the proof-of-concept experiment that uses an optical phase modulator to simulate mechanical vibration, a 20 MHz vibration of a triangle waveform is successfully measured with reduced distortion. Additionally, we demonstrate a simple fiber probe that employs an unjacketed section as a sensitive area and measures tens-of-nanometer scale displacement with a data point interval of 100 ns.

A Simple and Rapid Phosphorescence Probe Based on Mn-Doped ZnS Quantum Dots for Chloramphenicol Detection

An innovative phosphorescence probe based on Mn-doped ZnS quantum dots (Mn:ZnS QDs) was developed for selective detection of chloramphenicol (CAP) via inner-filter effect (IFE). Mn:ZnS QDs were synthesized by water method and modified with L-Cysteine for better stability, and the average diameter of the nanometer particle was 3.8[Formula: see text]nm. With the excitation wavelength at 289[Formula: see text]nm, the strong phosphorescence of Mn:ZnS QDs can be emitted at 583[Formula: see text]nm. The excitation spectrum of Mn:ZnS QDs was substantially overlapped with the absorption spectrum of the target CAP. The excited light of Mn:ZnS QDs can be absorbed partially by CAP when they coexist, the phosphorescence intensity decreased with the increasing concentration of CAP, and it has a good linear relationship. Under optimal conditions, the linear relational concentration range achieved four orders of magnitude from 25 to [Formula: see text] ([Formula: see text]), with a detection limit (LOD; [Formula: see text]) down to 0.81[Formula: see text][Formula: see text]. The simple, rapid and low cost IFE phosphorescent probe exhibited satisfactory recoveries ranging from 88.9% to 98.5% for CAP analysis in spiked honey, which shows a potential for routine screening of CAP in ensuring the food safety.

Identification and classification of epithelial cells in nephron segments by actin cytoskeleton patterns.

The basic functional unit in a kidney is the nephron, which is a long and morphologically segmented tubule. The nephron begins with a cluster of capillaries called glomerulus through which the blood is filtered into the Bowman's space. The filtrate flows through the nephron segments. During this flow, electrolytes and solutes are reabsorbed by channels and transport systems into the capillaries wrapped around the nephron. Many questions related to renal function focus on identifying the sites of expression of these systems. In this study, we mapped whole kidney sections by confocal microscopic imaging of fluorescent phalloidin, which binds to actin filaments. In tile scans (composed of hundreds of images) of these sections, the cortex and the medullary regions (outer and inner stripes of the outer medulla, and inner medulla) could be easily identified by their cytoskeletal patterns. At a higher resolution, we identified distinct features of the actin cytoskeleton in the apical, basal, and lateral borders of the cells. These features could be used to identify segments of a nephron (the proximal tubule, thin and thick segments of Henle's loop, and distal tubule), the collecting duct system, the papillary ducts in the papilla, and the urothelium that covers the pelvis. To verify our findings, we used additional markers, including aquaporin isoforms, cytokeratin 8‐18, and WGA lectin. This study highlights the power of high‐resolution confocal microscopy for identifying specific cell types using the simple probe of F‐actin‐binding phalloidin.

Fluorescence Anisotropy Reduction of An Allosteric G-Rich Oligonucleotide for Specific Silver Ion and Cysteine Detection Based on the G-Ag+-G Base Pair.

Silver is a common heavy metal, and the detection of silver ion (Ag+) is of great importance because of its wide application and hazardous effect on the environment and human health. However, it is a great challenge to produce a large fluorescence anisotropy (FA) change for small molecules (e.g, Ag+). Herein, we describe a novel fluorescence anisotropy reduction approach for the sensitive and specific detection of Ag+. The feasibility of this method is demonstrated through screening a number of guanine-rich oligonucleotide probes. By selectively labeling the oligonucleotides with a single fluorophore tetramethylrhodamine (TMR), the reduction in FA response is associated with the conformation change from the unfolded to a hairpin-like folded structure by inducing formation of the intermolecular G-Ag+-G base pair, which diminishes the interaction between guanine and TMR by photoinduced electron transfer (PET). The change in FA allows the selective detection of Ag+ at a concentration as low as 0.5 nM with a dynamic range from 2.0 to 100 nM. The interference from the other 14 metal ions with a 100-fold even to a 1000-fold excess amount is negligible. This simple and cost-effective probe was further explored to determine cysteine (Cys) based on competing with a guanine-rich oligonucelotide for Ag+-binding.

Determination of ultra trace amounts of metronidazole by 3-phenyl-N-[4-(10,15,20-triphenyl-porphyrin-5-yl)-phenyl]- acrylamide as the fluorescence spectral probe in CTAB microemulsion.

In this work, 3-Phenyl-N-[4-(10,15,20-triphenyl-porphyrin-5-yl)-phenyl]- acrylamide (TPPCA) was synthesized for the determination of metronidazole (MTZ). It was found that the type of fluorescence quenching was static quenching determined by Stern-Volmer plot and UV absorption spectroscopy, and thermodynamic related parameters were also obtained. Furthermore, the corresponding measurement conditions: the acidity of the system, the type of surfactant, the concentration of TPPCA and the sequence of reagent addition were optimized. Under the optimal experimental conditions, the linear range of MTZ was determined to be 0.01-0.20 μg mL-1, and the limit of detection (LOD) was 0.004 μg mL-1. Importantly, this report provides a simple, fast, and sensitive probe for the determination of MTZ in pharmaceutical practice.

A water-soluble colorimetric and fluorescent probe for rapidly sensing of ClO− in organisms

A simple colorimetric and fluorescent probe bearing coumarin and p-toluenesulfonyl hydrazide moieties was developed, which was capable of displaying excellent selectivity for hypochlorite. The distinct absorption spectral shift (49 nm) was induced by ClO−-triggered oxidative hydrolysis of CN double bonds in aqueous solution, which was accompanied by the optical variation from yellow to colorless. Besides, this probe solution underwent a dramatic intensification (162-fold) of the fluorescence signaling at 444 nm via the addition of ClO− (3 equiv.) within a short time. More importantly, the results achieved by fluorescence spectra revealed an excellent linear relation of probe 1 for ClO− with excellent sensitivity (9.1 nM). Further, the good recoveries and cellular experiments verified the prospective functions of this probe in real water environment and SW 480 cells.

An ESIPT characteristic “turn-on” fluorescence sensor for Hg2+ with large Stokes shift and sequential “turn-off” detection of S2– as well as the application in living cells

An excited state intramolecular proton transfer (ESIPT) characteristic “turn-on” fluorescence sensor for Hg2+ with large Stokes shift was fabricated and then it had ability to sequentially detect S2– by the “turn-off” fluorescent signal in aqueous media. On account of it, a simple fluorescence probe ol-PIP based on the phenanthro[9,10-d]imidazole moiety bearing two phenol fragments was synthesized. Probe ol-PIP showed gradually the fluorescence enhancement with the increasing of water fraction due to the aggregation affect. Sequentially, the moderate fluorescence emission of ol-PIP in aqueous media was continuously and selectively illumined by the successive addition of Hg2+ with about 180 nm Stokes shift. Furthermore, the persistent “turn-on” fluorescence intensity could be quenched to the original state of ol-PIP in presence of S2–. This on–off sensing process was sustained for five times with the alternative addition of Hg2+ and S2–. The limits of detection for Hg2+ and S2– were 6.45 × 10–7 and 3.46 × 10–7 M, respectively. In addition, ol-PIP was successfully applied in Hg2+ detection in real water samples; simultaneously, ol-PIP with low cytotoxicity was also successfully used as a bioimaging reagent to detect Hg2+ and S2– in living cells.

A facile AIE fluorescent probe for broad range of pH detection.

Detection of pH has received more and more attention in various fields. Currently, a hot research topic is focused on how to use a facile fluorescent dye to achieve a wide range and accurate pH detection. Herein, we reported a simple fluorescence probe for pH detection with wide range and accuracy based on the Aggregation-Induced Emission (AIE) characteristics. The probe 2-oxo-N'-(2-(quinolin-8-yloxy)acetyl)-2H-chromene-3-carbo- hydrazide (CHBQ) as comprised of coumarin and quinoline as the electron donor and acceptor, N, N'-diformylhydrazine bond as the linking group, respectively. The probe displays good AIE characteristics under water content up to 99% in mixed medium. Furthermore, it can identify acid and base as fast as 30 s by color change of the solution under UV365 nm lamp. The detection of the probe for pH was hardly interfered with other ions. What's more, the probe CHBQ can be designed to be a broad range test paper of pH detection, which has a great practical value.

A Simple Long-wavelength Fluorescent Probe for Simultaneous Discrimination of Cysteine/Homocysteine and Glutathione/Hydrogen Sulfide with Two Separated Fluorescence Emission Channels by Single Wavelength Excitation.

Small molecular biothiols, such as cysteine (Cys), homocysteine (Hcy), reduced glutathione (GSH), and hydrogen sulfide (H2S), play crucial parts in regulating the redox balance of life activities, regulating normal physiological activities and preventing various diseases. Quantitative analysis of these important small molecular substances is very important for revealing their diverse physiological and pathological effects. Although many fluorescent probes have been reported to detect biothiols in cells, it is still not sufficiently advanced to detect biothiols with separated fluorescence emission peak by same wavelength excitation. In our work, we designed a simple conjugate of Nile red and NBD (7-nitro-1,2,3-benzoxadiazole) as long-wavelength fluorescent probe NR-NBD for the simultaneous discrimination of these biothiols at single wavelength excitation. Probe NR-NBD could efficiently discriminate Cys/Hcy, GSH and H2S by two separated fluorescence emission channels and absorption spectra. Importantly, probe NR-NBD has excellent specificity and sensitivity towards the monitoring of endogenous/exogenous Cys/Hcy and GSH/H2S in living cells and zebrafish.

A simple but efficient fluorescent sensor for ratiometric sensing of Cd2+ and bio-imaging studies

A very simple schiff base fluorescent probe (NIS) was facilely prepared via a one-step, one-pot condensation reaction between 2, 3-naphthalenediamine and imidazole-2-carboxaldehyde. Among common biologically relevant metal ions, NIS can selectively recognize Cd2+ via ratiometric fluorescence signal. The chelation of NIS with the Cd2+ ions resulted in a fluorescence enhancement together with a blue shift (˜74 nm) in the emission maxima, presumably due to the combined effects of ICT (internal charge transfer) and CHEF (chelation-enhanced fluorescence). The binding stoichiometry of NIS to Cd2+ is 1:1 and the fluorescence intensity ratio (F398/F472) changes allow a ratiometric detection of Cd2+ with the detection limit of 3.87 × 10−7 M. Under fluorescence confocal microscope and via two emission channels, the probe is capable to detect Cd2+ ions in Human liver cancer cells (SMMC-7721), zebrafish and live tissues of Arabidopsis thaliana, demonstrating its applicability for detecting Cd2+ ions in different biological context with low toxicity.

A Novel ESIPT Phthalimide-Based Fluorescent Probe for Quantitative Detection of H2O2.

Hydrogen peroxide (H2O2) is a majority reactive oxygen species (ROS) and acts as an essential role in pathological and physiological processes. Therefore, the development of quantitative detection of methods for H2O2 is necessary. Here, we constructed of a novel simple fluorescence probe for detection of H2O2 based on the excited-state intramolecular proton transfer process. The probe utilized a phthalimide derivative as the fluorophore and selected phenylboronic acid as the recognition site for H2O2. In response to H2O2, the probe exhibited 63-fold fluorescence intensity enhancement, a low detection limit (8.4 × 10–8 M), and large Stokes shift (111 nm). In addition, the probe displayed high selectivity for H2O2 over other ROS. Moreover, the probe was successfully employed for imaging of H2O2 in living cells.

Simple Defocused Fiber Optic Volume Probe for Subsurface Raman Spectroscopy in Turbid Media.

We investigated the ability to perform deep subsurface Raman spectroscopy in turbid media using a simple fiber optic volume probe. Being able to collect Raman signals from regions deep within a biological sample provides the ability to noninvasively study underlying living tissue and tissue engineered constructs with high chemical specificity. Spatially offset Raman spectroscopy has shown great potential for obtaining subsurface Raman signals in biological samples. The applicability of the method for invivo studies depends on the system complexity and small size probes are often desirable. Most real-time studies on human patients utilizing Raman spectroscopy have been performed with easy-to-handle miniaturized probes. Here we show both experimentally and theoretically that the sampling depth from a simple volume probe can be controlled by changing the probe to sample distance effectively suppressing Raman and fluorescence contributions from shallow sample layers while favoring the collection of signals from deeper layers. Relative spectral intensities as function of probe to sample distance were investigated for layered phantoms of poly(methyl methacrylate) and trans-stilbene and compared with theory. The volume probe was then utilized for the collection of spectra from phantoms mimicking invivo transcutaneous measurement configurations of bone and engineered scaffold as well as from an ex vivo sample of bone and soft tissue. Together the results show that Raman fiber optic volume probes can be utilized for subsurface Raman spectroscopy in turbid media, providing a simple alternative to spatially offset Raman systems for, e.g., noninvasive monitoring and studying mineralized tissue and implanted scaffolds invivo.

Bioluminescence Detection of Superoxide Anion Using Aequorin.

Although the superoxide anion (O2-·) is generated during normal cellular respiration and has fundamental roles in a wide range of cellular processes, such as cell proliferation, migration, apoptosis, and homeostasis, its dysregulation is associated with a variety of diseases. Regarding these prominent roles in biological systems, the development of accurate methods for quantification of superoxide anion has attracted tremendous research attention. Here, we evaluated aequorin, a calcium-dependent photoprotein, as a potential bioluminescent reporter protein of superoxide anion. The mechanism is based on the measurement of aequorin bioluminescence, where the lower the concentration of coelenterazine under the oxidation of superoxide anion, the lower the amount aequorin regeneration, leading to a decrease in bioluminescence. The bioluminescence intensity of aequorin was proportional to the concentration of superoxide anion in the range from 4 to 40 000 pM with a detection limit (S/N = 3) of 1.2 pM, which was 5000-fold lower than those of the chemiluminescence methods. The proposed method exhibited high sensitivity and has been successfully applied to the determination of superoxide anion in the plant cell samples. The results could suggest a photoprotein-based bioluminescence system as a highly sensitive, specific, and simple bioluminescent probe for in vitro detection of superoxide anion.