Ratiometric Change Research Articles

Preparation of biosensor based on triarylmethane loaded cellulose acetate xerogel for the detection of urea

Urea released by kidney into blood and urine is a major reason for the gradual loss of kidney function. Therefore, it is of great importance to construct a real-time detection method for Urea. On the other side, a sponge-like microporous cellulose acetate (CA) xerogel has been introduced as a low-density biomaterial with various promising applications. In this study, a facile, portable, fast, and highly sensitive microporous CA biopolymer test dipstick, comprising triarylmethane (TAM) as a spectroscopic chromophore and urease (U) enzyme as a catalytic agent, is constructed for colorimetric detection of urea. Identification of urea occurs via proton transfer from the hydroxyl substituent of TAM to ammonia released in an aqueous environment from the hydrolysis of urea/urease reaction. Importantly, TAM probe was in-situ integrated within the generated sponge-like CA dipstick sensor assay (CA-U-TAM). This resulted in ratiometric changes of 131 nm red-shift in the absorption spectra, from 439 nm to 580 nm, as a function of the urea total content in the aqueous medium. Additionally, composition/morphology of the prepared CA-TAM dipstick was explored and revealed the presence of large surface area and high porous scaffolds with a pore size of ∼7.5 μm.

A ratiometric styryl bridging triphenylamine-indolinium based fluorescent dye for detection of cyanide with a large emission shift in human breast cancer cells and test strips

ABSTRACT A new type of styryl bridging triphenyl amine-indolium conjugated dye has been developed for the colorimetric and ratiometric detection of cyanide. The detection of cyanide is confirmed by means of the fast nucleophilic attack of cyanide by the indolium group of the probe that results a speedy sensing process for cyanide with clear color and fluorescence change of the ICT process. The ratiometric fluorescence changes illustrated a linear response in the range of 0-18 μM with a low LOD value (1.7×10-7 M-1). The as-reported sensor not only function as a colorimetric sensor for “in-the-field” measurement by virtue of a “dip-stick” approach but also interact with a human breast cancer cell (MDA-MB 231) which reveals the realistic value of this probe for tracking cyanide anions in biological systems.

Isophthalamide bearing 1-pyrenylethynyl group as a highly fluorescent hydrogen bond motif for anion receptors

Isophthalamide-based receptor 2 bearing 1-pyrenylethynyl group as a fluorophore was prepared for a ratiometric fluorescence sensor for anions. Receptor 2 showed small hypsochromic shift by UV–vis titrations and ratiometric fluorescence changes upon the addition of anions, in particular biologically important anions such as AcO−, H2PO4−, and Cl− with high association constants. The high quantum yield of receptor 2 (ΦF = 0.88) implies that 5-(1-pyrenyl)isophthaloyl amide spacer is a versatile component for various fluorescence receptors.

Dipyrromethane‐Based Receptor for Fluorometric Sensing of Hydrogenpyrophosphate

AbstractA new dipyrromethane‐based tetramide 1 has been designed and synthesized. It serves as potential chemosensor for fluorometric detection of hydrogenpyrophosphate (HP2O73−; HPPi) in organic and semi‐aqueous medium. In CH3CN, the tetramide 1 shows strong excimer formation upon complexation with HPPi and results in a ratiometric change in fluorescence. Other anions did not bring such change. In aqueous CH3CN, this is observed although the change is less pronounced. Hydrogen bonding of HPPi in the cleft pulls the pendant naphthalene to form the excimer. The complexation has been established by spectroscopic and theoretical studies. The tetramide 1 selectively senses HPPi in CH3CN with binding constant and detection limit of 3.2×103 M−1 and 2.08×10−5 M, respectively.

A novel methylenemalononitrile-BODIPY-based fluorescent probe for highly selective detection of hydrogen peroxide in living cells

Hydrogen peroxide (H2O2) plays vital roles in oxidative stress and signal transduction in living organisms, and its abnormal levels could be linked to many diseases. Despite numerous efforts spent, it is still urgent and of high importance to develop better H2O2 probes with good selectivity, high sensitivity and low backgrounds. To this end, a novel boron dipyrromethene (BODIPY)-based fluorescent probe with an electron-withdrawing methylenemalononitrile at the meso position has been rationally designed, successfully synthesized and investigated for detection of H2O2 in aqueous solutions and living cells, which exhibited high selectivity and sensitivity, fluorescent “turn-on” phenomenon at 540 nm, and ratiometric changes from 506 to 540 nm. Upon exposure to H2O2, a strong fluorescent emission at 540 nm appeared and the corresponding quantum yields changed from 0.009 to 0.13. The detection limit towards H2O2 was calculated to be 31 nM by the linear fluorescence change at 540 nm in the H2O2-concentration ranging from 2 to 10 μM. This probe was applicable in a pH range from 6 to 10. Meanwhile, the sensing mechanism was also confirmed by the 1H NMR and mass spectrometry, suggesting that the above changes might be ascribed to the quick addition and oxidization of the double bond. Furthermore, confocal imaging results also showed great enhancement of intracellular fluorescence upon exposure to H2O2 and PMA in RAW264.7 cells, unambiguously confirming its great potentials as a fluorescent probe for highly sensitive detection of both exogenous and endogenous H2O2 in living cells.

A ratiometric solid AIE sensor for detection of acetone vapor

Acetone serves as a routine solvent and synthetic intermediate in chemical factories and laboratories. Monitoring the level of acetone vapor in working environment is of great necessity to employee health due to its strong volatility and toxicity, but there is still in lack of simple and easy-to-use portable sensors. In this study, we report a portable and intuitive indicator for real-time displaying acetone vapor concentration in air, based on the ratiometric fluorescence response of the designed organic molecule, PhB-SSB, to acetone. As an aggregation-induced emission (AIE) fluorophore, PhB-SSB underwent specific reaction with acetone through the salicylaldehyde Schiff base and phenylboronate groups to realize ratiometric fluorescence change from green to red after acetone vapor treatment. The reaction mechanism was proposed as acetone-induced breakage of the imine bond in PhB-SSB. We further fabricated PhB-SSB into a film fluorescent sensor for acetone vapor with good sensitivity and selectivity. Taking advantage of its intuitive fluorescent color contrast, acetone-specific response and small size, our sensor is practical in real-time alarming the acetone vapor hazard in the workplaces.

Golgi-targetable fluorescent probe for ratiometric imaging of CO in cells and zebrafish

Carbon monoxide (CO) plays a vital role in living organisms. The detection of CO at the subcellular level is of great significance to clarify its biological functions. Increasing evidence shows that CO is important in Golgi apparatus, but so far, no probe has been reported to detect CO in Golgi. In this paper, an effective fluorescence probe Gol-CO was reported for CO imaging in Golgi apparatus. Gol-CO uses a Golgi-targetable aminoquinoline derivative as the fluorophore and importantly, it shows significant ratiometric fluorescence signal changes at 520/425 nm in aqueous solutions with high selectivity and sensitivity (about 41 nM of detection limit) for CO. Imaging experiments showed that Gol-CO has excellent targeting ability to Golgi apparatus and excellent ratiometric fluorescence imaging ability for CO in cells and zebrafish. Gol-CO also succeeded in visualizing the level increase of CO in living cells under oxidative stress.

Enhanced Sulfite-Selective Sensing and Cell Imaging with Fluorescent Nanoreactors Containing a Ratiometric Lipid Peroxidation Sensor.

The detection of SO2 and its derivatives is indispensable for monitoring atmospheric, water quality, and biological fluctuation of oxidative stress and metabolism of biothiols within native cellular contexts. In this article, the brush copolymer nanoreactors containing amine-terminated PDMS were used to encapsulate the fluorescent indicator C11-BDP, forming sulfite-sensitive nanoreactors (ssNRs). Surprisingly, the ssNRs were found to be highly selective to sulfite over a range of reactive oxygen/nitrogen/sulfur species and anions, which was not observed with freely dissolved indicators. The ssNRs showed a rapid response (t95 = 65 s), an excellent detection limit (0.7 μM), and a very high sensitivity (ca. 1000-fold ratiometric intensity change) to sulfite. For cellular studies, the ssNRs exhibited negligible toxicity and could be endocytosed into endosomes and lysosomes. Finally, the ssNRs allowed us to visualize the different responses of three different types of cells (pre-adipocytes, RAW264.7, and HeLa cells) to external stimuli in the culture media with sulfites and lipopolysaccharides.

A porphyrin platform for ratiometric fluorescence monitoring of Zn2+ ion

An innovative ratiometric-type fluorescent chemosensor (SP), which appending a 3-picolyl thiourea pendant to a porphyrin fluorophore, has been synthesized for Zn2+ monitoring in aqueous buffer and in biological samples. SP behaved a Zn2+-selective ratiometric change in emission over a broad pH range with a 1:1 stoichiometry. The peculiar and strong coordination ability between Zn2+ and nitrogen atoms facilitating SP to capture Zn2+ via an axial ligation. Spectrofluorimetric titration, NMR analysis, mass spectrometry, and structure derivation further confirmed the proposed pentacoordinated binding mode between SP and Zn2+. Advantages of the SP probe also include a low detection limit, a small dissociation constant, high selectivity and reversibility. Benefiting from the remarkable analytical performance, low cytotoxicity as well as excellent photostability, ratiometric imaging of exogenous Zn2+ fluctuation in live cells is realized with the as-prepared probe. Moreover, SP is able to visualize the endogenous Zn2+ distribution during the development of zebrafish larval. The present strategy may inspire and stimulate the molecular design of more cation probes involves other particular coordination modes.

A Ratiometric, Fast-Responsive, and Single-Wavelength Excited Fluorescent Probe for the Discrimination of Cys and Hcy

The ratiometric detection of cysteine (Cys) and homocysteine (Hcy) is very challenging because of their highly similar chemical structures and properties. By introducing the phenylethynyl group into a coumarin dye as the sensing group, the ratiometric fluorescent probe CP was developed to selectively and rapidly discriminate between Cys and Hcy. With a single-wavelength excitation, the presence of Cys or Hcy induced the probe to produce distinct ratiometric fluorescence changes: from red (λmaxem = 608 nm) to blue (λmaxem = 485 nm) toward Cys and from red to mixed red/blue toward Hcy. Moreover, the probe was capable of visualizing and discriminating between intracellular Cys and Hcy in HeLa cells and zebrafish by exhibiting different ratiometric fluorescence signals.

Development of carbon dot-thiochrome-based sensing system for ratiometric fluorescence detection of D-penicillamine.

A simple and rapid ratiometric fluorescent sensing system for D-penicillamine (D-PA) determination is developed based on yellow carbon dots (Y-CDs) combined with thiochrome (oxVB1) for the first time. The oxidization of thiamine (VB1) can be catalyzed by Alkaline-hydrolyzed artemisinin (a-ART) to form oxVB1, which leads to the occurrence of fluorescence emission peak at 466nm. Furthermore, the oxidation reaction between a-ART and VB1 could be inhibited by D-PA, and accompanied with the decrease of fluorescence at 466nm. However, the fluorescence peak of Y-CDs as an internal reference at 566nm was almost unchanged. The ratiometric signal changes contributed to a robust and sensitive D-PA sensing. Under the optimal condition, a good linear response for the D-PA detection was obtained in the ranges of 0.5-50μM with a detection limit of 0.33μM. In addition, Y-CDs and thiochrome-based sensing system was applied to D-PA determination in real samples and obtained acceptable results. We developed a new carbon dots/thiochrome fluorescent nanoprobe for ratiometric fluorescence sensing of D-penicillamine.

Red/Green Tunable-Emission Carbon Nanodots for Smart Visual Precision pH Sensing

The development of novel carbon nanodots (CDs) with excellent optical properties and promising applications is an attractive but a challenging area. Herein, we demonstrate that the fluorescence properties of CDs can be optimized by simple modification of the molecular structure of the carbon source. Significantly, the final optimized CDs 1 exhibit a rare extremely acidic (pH 1-3) sensitivity. A distinguishable red/brown/green fluorescence color change is achieved for visual readout by simply tuning the pH to 1, 2, or 3. The distinguishable color change combined with ratiometric fluorescence changes greatly improves the naked-eye visual resolution up to 0.2 pH units, which is higher than that of commercial precision pH test strips. Furthermore, a smartphone was employed in a portable, low-cost, rapid, and precise pH measurement method, which satisfied the requirement of point-of-care testing. Inspired by the reversible color change of red/brown/green tri-fluorescence on tuning the pH to 1, 2, or 3, a simple yet efficient molecular logic circuit has been designed. Given the unique pH-dependent photoluminescence properties, these CDs have been further applied in the anti-counterfeiting and information encryption field, making the burn after readingencryption technology a reality.

Graphene quantum dot-decorated luminescent porous silicon dressing for theranostics of diabetic wounds

Diabetic wound healing is highly desirable but remains a great challenge owing to the continuous damage of excess reactive oxygen species (ROS) and degradation of therapeutic peptide drugs by over-expressed matrix metalloproteinase (MMP). Herein, we developed a stimuli-responsive smart dressing for theranostics of diabetic wounds using graphene quantum dots-decorated luminescent porous silicon (GQDs@PSi), which was further loaded with peptide and embedded in chitosan (CS) film. The confinement of GQDs in nanochannels of PSi endowed GQDs@PSi with efficient fluorescence resonance energy transfer (FRET) effect, leading to initial red fluorescence of PSi with complete quench of GQD's blue fluorescence. Furthermore, the decoration of GQDs on PSi surface significantly enhanced the loading capacity for peptide drugs including epidermal growth factor (EGF) and insulin (Ins) which can promote diabetic wounds healing. The peptides coloaded in GQDs@PSi exhibited sustained release behavior and could be protected in presence of MMP owing to size exclusion of PSi's nanochannels. As H2O2-triggered oxidation of PSi lead to weakened FRET effect and degradation of PSi, GQDs@PSi demonstrated H2O2-responsive ratiometric fluorescence change (from red PSi to blue GQDs) and drug release behavior. In combination with CS's degradation in the acidic and oxidation microenvironment, the smart dressing also showed stimuli-responsive drug release toward slightly acid and highly oxidative conditions in diabetic wounds. In vitro and in vivo results demonstrated the smart dressing enhanced the proliferation and migration of cells as well as significantly healed diabetic wounds. Real-time indicating of the exacerbation or healing of diabetic wounds was also realized using the rate of fluorescent discoloration of the dressing. Statement of significanceIn this work, a dual luminescent nanomaterial was created by hosting graphene quantum dots (GQDs) in the nanochannel of porous silicon (PSi), which was further applied for theranostics of diabetic wound. The synergistic effect of the host-guest nanohybrid is significant. The GQDs can significantly improve the capacity for peptide drug loading and form a stimuli-response visual ratiometric sensor with luminescent PSi, which can also protect and sustain release of peptide drugs for effective diabetic wounds treatment. After embedded in a chitosan film, the smart dressing displayed H2O2-responsive visual ratiometric fluorescence change and drug release behavior. In vitro and in vivo results demonstrated the smart dressing enhanced the proliferation and migration of cells as well as significantly healed diabetic wounds.

A bis-pyrene chalcone based fluorescent material for ratiometric sensing of hydrazine: An acid/base molecular switch and solid-state emitter

In this work, we have designed and synthesized a new fluorescent molecular probe, DPY comprising of pyrene-diacetylpyridine conjugate, which was found to be sensitive to hydrazine as well as protonation. DPY is characterised by a strong emission both in solution (λem = 530 nm) as well as in solid state (λem = 610 nm), attributed to intramolecular charge-transfer. The probe responds to hydrazine with a ratiometric fluorescence emission change from yellow to blue, due to chalcone cyclisation reaction of α, β-unsaturated carbonyl group resulting in the pyrazoline compound, DPY-Hy, imparting a strong greenish-blue emission in solution. Further, the strong fluorescence emission of DPY in powder and thin film was quenched upon exposure to TFA, and revived upon exposure to TEA. For developing on-site detection protocol, when DPY was drop-casted on nonfluorescent silica plate a vivid naked-eye colour change from orange-red to dark blue was realized. Interestingly, in the aggregated state, DPY exhibited a broad range emission from green to orange in a mixed solvent system of THF:H2O. A plausible explanation of the photophysical events is substantiated with theoretical calculations.

Tricolor emission carbon dots for label-free ratiometric fluorescent and colorimetric recognition of Al3+ and pyrophosphate ion and cellular imaging

Ratiometric determination endows fluorescence (FL) sensors improving accuracy and sensitivity by measuring intensity ratio of well-resolved emission peaks. Herein, tricolor-emission carbon dots (T-CDs) have been developed for ratiometric recognition of Al3+ and pyrophosphate ion (PPi). T-CDs were fabricated from hematoxylin and Tris by one-pot hydrothermal treatment. As-prepared T-CDs engender amusing triple emission bands, including bright yellow and orange FL, but weak blue FL. Upon introducing Al3+, yellow and orange FL is distinctly quenched while blue one is enhanced. On subsequent addition of PPi, T-CDs’ FL can be partially recovered. The ratiometric fluorescent changes of T-CDs have been utilized to detect Al3+ and PPi in aqueous solution with linear ranges of 5–15 μM and 0.75–10 μM, respectively, as well as limits of detection of 0.8 nM and 2.2 nM, respectively. More importantly, laser scanning confocal microscope imaging of HeLa cells demonstrates that T-CDs could be applied to visually monitor Al3+ and PPi fluctuations in living cells, illustrating that proposed T-CDs have tremendous potential in biological systems.

Single-Molecule White-Light-Emitting Starburst Donor-Acceptor Triphenylamine Derivatives and Their Application as Ratiometric Luminescent Molecular Thermometers.

White-light emission (WLE) from a single molecule is a highly desirable alternative to a complex mixture of complementary colour emitters, which suffers from poor stability and reproducibility for potential use in organic electronic devices and lighting applications. We report single-molecule WLE both in solution and thin films by judiciously controlled π-electron delocalisation between the triarylamine subchromophoric units. Triphenylamine (TPA) forms the central core, and the phenyl rings are substituted with the electron-deficient acceptor 3-ethylrhodanine (Rh) and electron-rich donors triphenylamine or carbazole. The enforced biphenyl configuration of the TPA core and the other donors renders the π-conjugation across the entire chromophore poor, thus the individual subchromophoric units retain their individual emission characteristics, which cover all three primary colour emissions, that is, red, green and blue (RGB). TPA-Rh units exhibit broad fluorescence in the green-red region originating from the local excited (LE) state and intramolecular charge transfer state (ICT), strongly influenced by the solvent, water, and temperature. Different fluorescence parameters, including spectral maxima, ratiometric changes in ICT emission at the expense of blue emission from terminal donor units, and changes in lifetime, have a linear relationship with temperature between 180-330 K, thus the molecules can function as a multiparameter luminescent molecular thermometer. A temperature coefficient of 0.19 K-1 in ratiometric fluorescence changes along with a spectral shift of 0.3 nm K-1 and their workability over the wide temperature makes these molecules promising materials for potential applications. At lower temperatures, individual subchromophoric properties subside because of the reduced dihedral angle of biphenyl, and fluorescence from the whole molecule becomes dominant.

A dual channel fluorescent probe with pH-based specificity to lysosomes for multicolor imaging and localization

We herein innovatively constructed the pure pH-dual channel probe DNOXA by the reaction of oxalyl chloride with 4-dimethylaminobenzaldehyde. DNOXA has two response sites for acidity, which are corresponding to pH-dual channel responses. When adding acid to pH 5.0, the protonation in the response site I enhanced the push-pull effect, and the absorption maxima of the optical spectra bathochromically shifted from 463 to 652 nm. When sequentially adding acid to pH 1.6, the response site II is awakened to work. The enhanced push-pull system was interrupted, and the absorption maxima hypochromatically shifted from 652 to 506 nm. In this process, the ratiometric change in the probe can be observed by naked-eye. Furthermore, quantum-chemical study well explained and supported the difference of their maxima absorption. Based on the excellent response of DNOXA to pH in vitro, DNOXA had commendable specific imaging and localization ability for lysosomes, undergoing dual channel images of protonation at the acidic microenvironment.

A near-infrared fluorescent probe for highly specific and ultrasensitive detection of hypochlorite ions in living cells.

Hypochlorite (ClO-) is an important reactive oxygen species (ROS) in organisms. In this work, a fluorescent probe DBTM based on triphenylamine was synthesized successfully and characterized by spectral methods. The designed probe can rapidly respond to ClO- in just 1 min, followed by the apparent color change from red to yellow. The colorimetric and ratiometric absorbance change of DBTM was attributed to the strong oxidation of ClO-, which broke the connected double bonds and destroyed the conjugate system. The probe DBTM showed an excellent selectivity towards ClO- in comparison with other ROS probes. Besides, the DBTM probe exhibited a highly sensitive response to ClO-, with the detection limits calculated to be 3.3nM. The probe can be applied in the form of cotton swabs and test strips that could detect ClO- easily, suggesting its potential use as imaging agents for realistic ClO- detection. In particular, DBTM exhibited very low background fluorescence in living cells and was able to detect the minor variation of endogenous hypochlorite in L929 cells. Based on these advantages, the probe DBTM could be a good candidate for detecting ClO- in biological systems.

Ratiometric Fluorescent Lateral Flow Immunoassay for Point‐of‐Care Testing of Acute Myocardial Infarction

AbstractWe report the development of a highly sensitive ratiometric fluorescent lateral flow immunoassay (RFLFIA) strip for rapid and accurate detection of acute myocardial infarction biomarker, namely heart‐type fatty acid binding protein (H‐FABP). The RFLFIA strip works in terms of ratiometric change of fluorescence signal, arising from blending of fluorescence emitted by two composite nanostructures conjugated to capture and probe antibodies and inner filter effect of gold nanoparticles. In conjunction with using custom smartphone‐based analytical device and tonality analysis, quantitative detection of H‐FABP was achieved with a low limit of detection at 0.21 ng mL−1. The RFLFIA strip can generate a visually distinguishable green‐to‐red color change around the threshold concentration of H‐FABP (6.2 ng mL−1), thus allowing the semi‐quantitative diagnosis by the naked eye.

Ratiometric Fluorescent Lateral Flow Immunoassay for Point-of-Care Testing of Acute Myocardial Infarction.

We report the development of a highly sensitive ratiometric fluorescent lateral flow immunoassay (RFLFIA) strip for rapid and accurate detection of acute myocardial infarction biomarker, namely heart-type fatty acid binding protein (H-FABP). The RFLFIA strip works in terms of ratiometric change of fluorescence signal, arising from blending of fluorescence emitted by two composite nanostructures conjugated to capture and probe antibodies and inner filter effect of gold nanoparticles. In conjunction with using custom smartphone-based analytical device and tonality analysis, quantitative detection of H-FABP was achieved with a low limit of detection at 0.21 ng mL-1 . The RFLFIA strip can generate a visually distinguishable green-to-red color change around the threshold concentration of H-FABP (6.2 ng mL-1 ), thus allowing the semi-quantitative diagnosis by the naked eye.