Impact of a conformationally restricted receptor on the BF2 chelated azadipyrromethene fluorosensing platform

Conformational control of the receptor-fluorophore orientation of BF2 chelated azadipyrromethene sensors reveals two photophysically different modes of analyte triggered fluorescence switching both of which exhibit large off-on fluorescence intensity responses to the light input-output of the sensors in the visible red spectral region.     

Functionalized BF2 chelated azadipyrromethene dyes

Fluorescent molecules that emit in the near infrared are potentially useful as probes for biotechnology. A relatively under-explored design for probes of this type are the aza-BODIPY dyes; this study was performed to enhance our understanding of these materials and ways in which they may be used in dye cassette systems. Thus, the aza-BODIPY dyes 1a-g were prepared. An advanced intermediate toward an eighth compound in the series, 6h, was made but it could not be complexed with boron effectively to give 1h. Spectroscopic properties of these compounds were recorded, and correlations between substituent effects, UV absorbance, fluorescence emissions, and quantum yields were made. Compound 1a was coupled with a fluorescein-alkyne derivative to give the energy transfer cassettes 2 and 3. Both these compounds gave poor energy transfer and the possible reasons for this were discussed.     

A label-free and signal-on supersandwich fluorescent platform for Hg sensing

A label-free supersandwich fluorescent assay was demonstrated for the first time by taking Hg²⁺ as a detection candidate. The principle of the proposed supersandwich fluorescent platform is based on the formation of supersandwich structure by T-Hg²⁺-T coordination and the fluorescence enhancement of the intercalated Genefinder (GF) in double strand DNA (dsDNA). Such supersandwich fluorescent DNA sensor exhibits a linear range of 10–300 nM for the detection of Hg²⁺, with a detection limit of 2.5 nM on the basis of the 3σ/slope (σ represents the standard deviation of the blank samples), which is well below the permit of the U.S. Environmental Protection Agency (<10 nM). The detection can be fulfilled in less than 10 min. The proposed mix-and-detect fluorescent platform exhibits excellent sensitivity, selectivity, and convenient manipulation. The assay was successfully used to detect Hg²⁺ in the lake water samples, which suggested its potential in practical samples.     

Label-free fluorescent detection of thrombin using G-quadruplex-based DNAzyme as sensing platform

We report herein a label-free and sensitive fluorescent method for detection of thrombin using a G-quadruplex-based DNAzyme as the sensing platform. The thrombin-binding aptamer (TBA) is able to bind hemin to form the G-quadruplex-based DNAzyme, and thrombin can significantly enhance the activity of the G-quadruplex-based DNAzyme. The G-quadruplex-based DNAzyme is found to effectively catalyze the H(2)O(2)-mediated oxidation of thiamine, giving rise to fluorescence emission. This allows us to utilize the H(2)O(2)-thiamine fluorescent system for the quantitative analysis of thrombin. The assay shows a linear toward thrombin concentration in the range of 0.01-0.12 nM. The present limit of detection for thrombin is 1 pM, and the sensitivity for analyzing thrombin is improved by about 10,000-fold as compared with the reported colorimetric counterpart. The work also demonstrates that thiamine is an excellent substrate for the fluorescence assay using the G-quadruplex-based DNAzyme as the sensing platform.     

Conjugated polymers containing a 2,2'-biimidazole moiety--a novel fluorescent sensing platform

Two novel conjugated polymers containing a 2,2'-biimidazole moiety have been designed, synthesized, and demonstrated to be used as an effective fluorescent sensing platform for detection of Ag(+) and cysteine. This is the first example utilizing a fluorescent conjugated polymer-Ag(+) complex to selectively detect Cys with a nanomolar range detection limit.     

Nucleic acid detection using carbon nanoparticles as a fluorescent sensing platform

In this communication, we demonstrate for the first time the proof of concept that carbon nanoparticles (CNPs) can be used as an effective fluorescent sensing platform for nucleic acid detection with selectivity down to single-base mismatch. The dye-labeled single-stranded DNA (ssDNA) probe is adsorbed onto the surface of the CNP via π-π interaction, quenching the dye. In the target assay, a double-stranded DNA (dsDNA) hybrid forms, recovering dye fluorescence.     

Near-infrared sensing properties of dimethlyamino-substituted BF2-azadipyrromethenes

[reaction: see text] The synthesis and sensing characteristics of a new class of organic colorimetric and fluorometric chemosensor which operates in the 850-650 nm spectral region is outlined. Judicious placing of amine substituents on the BF2-chelated tetraarylazadipyrromethene chromophore generates a triple absorption and emission responsive sensor. Dramatic pH responsive absorption and fluorescence changes can be observed across a broad acidity range, from pH 5 to 6 M HCl, in conjunction with a visible colorimetric change from red to purple to blue.     

Magnetic porous carbon nanocomposites derived from metal-organic frameworks as a sensing platform for DNA fluorescent detection

Metal-organic frameworks (MOFs) have emerged as very fascinating functional materials due to their tunable nature and diverse applications. In this work, we prepared a magnetic porous carbon (MPC) nanocomposite by employing iron-containing MOFs (MIL-88A) as precursors through a one-pot thermolysis method. It was found that the MPC can absorb selectively single-stranded DNA (ssDNA) probe to form MPC/ssDNA complex and subsequently quench the labelled fluorescent dye of the ssDNA probe, which is resulted from the synergetic effect of magnetic nanoparticles and carbon matrix. Upon the addition of complementary target DNA, however, the absorbed ssDNA probe could be released from MPC surface by forming double-stranded DNA with target DNA, and accompanied by the recovery of the fluorescence of ssDNA probe. Based on these findings, a sensing platform with low background signal for DNA fluorescent detection was developed. The proposed sensing platform exhibits high sensitivity with detection limit of 1 nM and excellent selectivity to specific target DNA, even single-base mismatched nucleotide can be distinguished. We envision that the presented study would provide a new perspective on the potential applications of MOF-derived nanocomposites in biomedical fields.     

Nucleic acid detection using single-walled carbon nanohorns as a fluorescent sensing platform

In this communication, we demonstrate for the first time the proof of concept that single-walled carbon nanohorns can be used as an effective fluorescent sensing platform for nucleic acid detection with a high selectivity down to single-base mismatch.     

CdS quantum dots as a fluorescent sensing platform for nucleic acid detection

We demonstrate that CdS quantum dots (QDs) can be applied to fluorescence-enhanced detection of nucleic acids in a two-step protocol. In step one, a fluorescently labeled single-stranded DNA probe is adsorbed on the QDs to quench its luminescence. In step two, the hybridization of the probe with its target ssDNA produces a double-stranded DNA which detaches from the QD. This, in turn, leads to the recovery of the fluorescence of the label. The lower detection limit of the assay is as low as 1?nM. The scheme (that was applied to detect a target DNA related to the HIV) is simple and can differentiate between perfectly complementary targets and mismatches.

Selective fluorescent PET sensing of fluoride (F) using naphthalimide-thiourea and -urea conjugates

The thiourea and urea functionalised 4-amino-1,8-naphthalimide sensors 1-3, based on the fluorophore-spacer-receptor principle, were synthesised in high yield in three steps. The sensors were shown to signal selectively the detection of fluoride in the fluorescence emission spectrum in DMSO. On all occasions the emission was quenched due to enhanced photoinduced electron transfer quenching (PET) from the receptor to the excited state of the fluorophore upon recognition of F⁻, particularly for the thiourea sensors 1 and 2. In comparison, the changes in the absorption spectra were minor for all three, even after the addition of 80-100 equiv of F⁻. The sensing of acetate or dihydrogenphosphate gave rise to only ∼5-20% quenching.     

Application of 3,4,9,10-perylenetetracarboxylic diimide microfibers as a fluorescent sensing platform for biomolecular detection

In this paper, we report on the use of 3,4,9,10-perylenetetracarboxylic diimide microfibers (PDIMs) as an effective fluorescent sensing platform for DNA detection for the first time. This sensing system exhibits a detection limit as low as 15 nmol L⁻¹ and has a high selectivity down to single-base mismatch. The general concept used in this approach is based on adsorption of fluorescently labeled single-stranded DNA (ssDNA) probe by PDIM due to the strong π–π stacking between unpaired DNA bases and PDIM. As a result, the fluorophore is brought into close proximity of PDIM, leading to substantial fluorescence quenching. In the presence of the target, the specific hybridization of the probe with its complementary DNA sequence generates a double stranded DNA (dsDNA) which detaches from PDIM, leading to fluorescence recovery. Its generality of this sensing platform for protein detection is also demonstrated.     

Rare-earth ions coordination enhanced ratiometric fluorescent sensing platform for quantitative visual analysis of antibiotic residues in real samples

Levofloxacin (LVFX) as a representative drug of quinolone antibiotics is widely used in clinical, and its residues enriched in water bodies and sideline products seriously damage human health. It is imperative to develop a real-time/on-site sensing method for monitoring residual antibiotics. Here, we report a portable sensing platform by utilizing a composite fluorescent nanoprobe constructed by the cerium ions (Ce³⁺) coordination functionalized CdTe quantum dots (QDs) for the visual and quantitative detection of LVFX residues. This fluorescent probe provides a distinct color variation from red to green, which shows a good linear relationship to LVFX residues concentrations in the range of 0-6.0 µmol/L with a sensitive limit of detection (LOD) of 16.3 nmol/L. The smartphone platform with Color Analyzer App installed, which could accomplish quantified detection of LVFX in water, milk, and raw pork with a LOD of 27.9 nmol/L. The facile sensing method we proposed realizes rapid visualization of antibiotics residual in the environment and provides a practical application pathway in food safety and human health.     

Ultraselective fluorescent sensing of Hg2+ through metal coordination-induced molecular aggregation

A new type of fluorescent sensor has been developed from a perylene based molecule, N,N'-dideoxythymidine-3,4,9,10-perylene-tetracarboxylic diimide (TT-PTCDI); the strong, highly selective binding between the thymine ligand (T) and Hg2+ ion enables efficient sensing of mercury ions based on a fluorescence quenching mechanism, which is primarily caused by metal-coordination induced molecular aggregation.     

A novel fluorescent aptasensor for thrombin detection: using poly(m-phenylenediamine) rods as an effective sensing platform

In this communication, we develop a novel fluorescent aptasensor for thrombin detection with the use of poly(m-phenylenediamine) (PMPD) rods as an effective sensing platform. This aptasensor exhibits extraordinarily high sensitivity with a detection limit as low as 100 pM and excellent selectivity.     

Functionalized fluorescent gold nanodots: synthesis and application for Pb2+ sensing

We developed a novel strategy to prepare functionalized fluorescent gold nanodots (AuNDs) based on a ligand exchange reaction and demonstrated that glutathione modified AuNDs can be utilized for highly sensitive and selective Pb(2+) sensing in aqueous solution.     

2, 2′-Dihydroxyazobenzene-based fluorescent system for the colorimetric ‘turn-on’ sensing of cyanide

2, 2′-Dihydroxyazobenzene (DHAB) demonstrated high sensitivity and low selectivity toward three anions: CN⁻, CO₃²⁻, and HCO₃⁻. In the presence of Cu(II), complex DHAB-Cu(II) could give rise to enhanced fluorescence intensity by about 45-fold at 590 nm and visible red-to-reddish orange color change upon the addition of cyanide by utilizing an indirect method, while no changes were observed in the presence of other anions, including F⁻, Cl⁻, Br⁻, I⁻, H₂PO₄⁻, CH₃COO⁻, NO₃⁻, CO₃²⁻ and HCO₃⁻, and SO₄²⁻, making the DHAB-Cu(II) complex a selective and sensitive cyanide chemosensor.     

Highly sensitive and selective detection of silver(I) ion using nano-C60 as an effective fluorescent sensing platform

In this Communication, we report water-soluble nano-C(60) in the first use as an effective fluorescent sensing platform for the highly sensitive and selective detection of Ag(+). The general concept used in this approach is based on a fluorescently labeled single-stranded DNA (ssDNA) probe that adsorbs on nano-C(60), leading to substantial dye fluorescence quenching; however, in the presence of Ag(+), C-Ag(+)-C coordination induces the probe to fold into a hairpin structure, which does not adsorb on nano-C(60) and thus retains the dye fluorescence. This sensing system exhibits a detection limit as low as 1 nM and has a high selectivity against other metal ions. Finally and most importantly, we demonstrate its performance in real sample analysis.     

Both visual and ratiometric fluorescent sensor for Zn2+ based on spirobenzopyran platform

A ratiometric fluorescent Zn²⁺ chemosensor, SPQH, based on spirobenzopyran platform, was synthesized. In aqueous HEPES 7.4 buffer solution, upon chelation with Zn(II), SPQH demonstrates high selectivity and subnanomolar sensitivity for zinc ion with 36-fold enhancement in the NIR fluorescence output.