Highly selective fluorometric determination of polyamines based on intramolecular excimer-forming derivatization with a pyrene-labeling reagent

Recent Advances in Fluorescent Methods for Polyamine Detection and the Polyamine Suppressing Strategy in Tumor Treatment

The biogenic aliphatic polyamines (spermine, spermidine, and putrescine) are responsible for numerous cell functions, including cell proliferation, the stabilization of nucleic acid conformations, cell division, homeostasis, gene expression, and protein synthesis in living organisms. The change of polyamine concentrations in the urine or blood is usually related to the presence of malignant tumors and is regarded as a biomarker for the early diagnosis of cancer. Therefore, the detection of polyamine levels in physiological fluids can provide valuable information in terms of cancer diagnosis and in monitoring therapeutic effects. In this review, we summarize the recent advances in fluorescent methods for polyamine detection (supramolecular fluorescent sensing systems, fluorescent probes based on the chromophore reaction, fluorescent small molecules, and fluorescent nanoparticles). In addition, tumor polyamine-suppressing strategies (such as polyamine conjugate, polyamine analogs, combinations that target multiple components, spermine-responsive supramolecular chemotherapy, a combination of polyamine consumption and photodynamic therapy, etc.) are highlighted. We hope that this review promotes the development of more efficient polyamine detection methods and provides a comprehensive understanding of polyamine-based tumor suppressor strategies.

Spiropyran based recognitions of amines: UV-Vis spectra and mechanisms

As one of the important photochromic molecules, spiropyran (SP) compounds are widely used as detectors and fluorescence probes in the environment and bio-imaging field. Although great achievements have been attained for various sophisticated spiropyrans in metal ion sensing, less success is achieved in sensing organic molecules due to the weak interaction between the spiropyran and the target of the organic molecule. In this study, a spiropyran derivative containing a hydroxyl group (SPOH) was employed for the recognition of four kinds of amines via ultraviolet-visible (UV-Vis) spectra. The aliphatic primary amines, aromatic primary amines, aliphatic secondary and tertiary amines, aromatic secondary and tertiary amines were successfully distinguished according to the shapes and trends of their UV-Vis absorption spectra. The chemical reaction between aliphatic, aromatic primary amines and SPOH as well as alkalinity are two vital interaction mechanisms for the recognition process which are testified by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR). Although SP is generally water-insoluble, it is easy to achieve soluble by fixing SPOH inside micelle or vesicle and thus the results in this study is meaningful for amine recognition utility in environments and biological systems.

A gas pressure and colorimetric signal dual-mode strategy for sensitive detection of spermine using ssDNA-coated Au@Pt nanoparticles as the probe

The naturally occurring spermine (Spm), as one of the many cationic polyamines, plays a key role in biological processes and is involved in a variety of diseases. The very similar structures among biogenic polyamines present a major challenge to achieve discriminative testing among them. In this contribution, using arbitrary ssDNA-coated Au@PtNPs as the probe, we demonstrated that a dual-mode strategy via a gas pressure and colorimetric signal readout can be used for the sensitive and specific detection of Spm, due to the target-responsive aggregation of the Au@PtNPs leading to the inhibition of the catalyzed gas-generation reaction and the colorimetric change of the Au@PtNP solution. The proposed pressure-based signaling strategy has a detection limit of 9.6 nM, and can be used not only in the laboratory but also in the point-of-care setting. Meanwhile, the colorimetric assay displays the advantage of being easily discerned with the naked eye. Compared with the traditional methods of chromatography and capillary electrophoresis combined with chemical derivatization, the strategy described here would provide a convenient new alternative for the specific detection of Spm in biological samples.

Elucidating sensing mechanisms of a pyrene excimer-based calix[4]arene for ratiometric detection of Hg(ii) and Ag(i) and chemosensor behaviour as INHIBITION or IMPLICATION logic gates

This article reports the synthesis and characterisation of two lower rim calix[4]arene derivatives with thiourea as spacer and pyrene or methylene-pyrene as fluorophore. Both derivatives exhibit a fluorimetric response towards Hg²⁺, Ag⁺ and Cu²⁺. Only methylene-pyrenyl derivative 2 allows for selective detection of Hg²⁺ and Ag⁺ by enhancement or decrease of excimer emission, respectively. The limits of detection of 2 are 8.11 nM (Hg²⁺) and 2.09 nM (Ag⁺). DFT and TD-DFT computational studies were carried out and used to identify possible binding modes that explain the observed response during fluorescence titrations. Calculations revealed the presence of different binding sites depending on the conformation of 2, which suggest a reasonable explanation for non-linear changes in fluorescence depending on the physical nature of the interaction between metal centre and conformer. INHIBITION and IMPLICATION logic gates have also been generated monitoring signal outputs at pyrene monomer (395 nm) and excimer (472 nm) emission, respectively. Thus 2 is a potential primary sensor towards Ag⁺ and Hg²⁺ able to configure two different logic gate operations.

Liquid Chromatographic Determination of Biogenic Amines in Fish Based on Pyrene Sulfonyl Chloride Pre-Column Derivatization

Monitoring of biogenic amines in food is important for quality control, in terms of freshness evaluation and even more for food safety. A novel and cost-effective method was developed and validated for the determination of the main biogenic amines: histamine, putrescine, cadaverine, spermidine and spermine in fish tissues. The method includes extraction of amines with perchloric acid, pre-column derivatization with Pyrene Sulfonyl Chloride (PSCl), extraction of derivatives with toluene, back-dissolution in ACN after evaporation and determination by reversed phase high performance liquid chromatography with UV and intramolecular excimer fluorescence detection. The structure of the pyrene-derivatives was confirmed by liquid chromatography-mass spectrometry with electrospray ionization. The standard addition technique was applied for the quantitation due to significant matrix effect, while the use of 1,7-diaminoheptane as internal standard offered an additional confirmation tool for the identification of the analytes. Method repeatability expressed as %RSD ranged between 7.4-14% for the different amines and recovery ranged from 67% for histamine up to 114% for spermine. The limits of detection ranged between 0.1-1.4 mg kg^-1 and the limits of quantification between 0.3-4.2 mg kg^-1. The method was applied to canned fish samples and the concentrations of the individual biogenic amines were below the detection limit up to 40.1 mg kg^-1, while their sum was within the range 4.1-49.6 mg kg^-1.

Gender-Related Differences on Polyamine Metabolome in Liquid Biopsies by a Simple and Sensitive Two-Step Liquid-Liquid Extraction and LC-MS/MS

Polyamines are involved in the regulation of many cellular functions and are promising biomarkers of numerous physiological conditions. Since the concentrations of these compounds in biological fluids are low, sample extraction is one of the most critical steps of their analysis. Here, we developed a comprehensive, sensitive, robust, and high-throughput LC-MS/MS stable-isotope dilution method for the simultaneous determination of 19 metabolites related to polyamine metabolism, including polyamines, acetylated and diacetylated polyamines, precursors, and catabolites from liquid biopsies. The sample extraction was optimized to remove interfering compounds and to reduce matrix effects, thus being useful for large clinical studies. The method consists of two-step liquid-liquid extraction with a Folch extraction and ethyl acetate partitioning combined with dansyl chloride derivatization. The developed method was applied to a small gender-related trial concerning human serum and urine samples from 40 obese subjects. Sex differences were found for cadaverine, putrescine, 1,3-diaminopropane, γ-aminobutyric acid, N8-acetylspermidine, and N-acetylcadaverine in urine; N1-acetylspermine in serum; and spermine in both serum and urine. The results demonstrate that the developed method can be used to analyze biological samples for the study of polyamine metabolism and its association with human diseases.

Turn-on fluorescent sensor for the detection of lipopolysaccharides based on a novel bispyrenyl terephtalaldehyde-bis-guanylhydrazone

A “turn-on” bispyrenyl sensor for lipopolysaccharide detection with unique molecular conformations exhibits excimer emission with sensitivity down to nanomolar.

Analyte-directed formation of emissive excimers for the selective detection of polyamines

A convenient and selective method for the sensing of polyamines, which are important biomarkers for cancers, has been developed. The fluorescence light-up mechanism utilizes the analyte-induced formation of emissive excimers of a sulfonated probe. Detection is achieved in aqueous media and artificial urine samples, as indicated by an excellent fluorescence turn-on signal with a large spectral shift.

Two-step FRET mediated metal ion induced signalling responses in a probe appended with three fluorophores

A tri-fluorophore appended Tren receptor based probe exhibited chelation induced ratiometric fluorescence signalling through a two-step FRET process; enhancement of F_An→ F_Rhenergy transfer efficiency through an F_NBDintermediate was observed.

Fluorescence sensing of amine vapours based on ZnS-supramolecular organogel hybrid films

A selective fluorescent ZnS-supramolecular organogel hybrid film was constructed for sensing volatile organic monoamines and diamines vapour by adopting supramolecular gel films as substrates.

Room temperature triethylamine sensing properties of polyaniline–WO3 nanocomposites with p–n heterojunctions

A smart sensor based on PANI–WO₃ nanocomposite loaded on PET thin film not only exhibits high sensitivity and selectivity to triethylamine at room temperature, but also has flexibility, simple fabrication and portable characters.

A novel self-assembled platform for the ratiometric fluorescence detection of spermine

A novel self-assembled platform where the micelles of a pyrene derivative act as the shell and squaraine (SQ) as the nucleus was constructed for the ratiometric near infrared (NIR) fluorescence detection of urinary spermine with high selectivity.

Near Room Temperature, Fast-Response, and Highly Sensitive Triethylamine Sensor Assembled with Au-Loaded ZnO/SnO₂ Core-Shell Nanorods on Flat Alumina Substrates

Chemiresistive gas sensors with low power consumption, fast response, and reliable fabrication process for a specific target gas have been now created for many applications. They require both sensitive nanomaterials and an efficient substrate chip for heating and electrical addressing. Herein, a near room working temperature and fast response triethylamine (TEA) gas sensor has been fabricated successfully by designing gold (Au)-loaded ZnO/SnO2 core-shell nanorods. ZnO nanorods grew directly on Al2O3 flat electrodes with a cost-effective hydrothermal process. By employing pulsed laser deposition (PLD) and DC-sputtering methods, the construction of Au nanoparticle-loaded ZnO/SnO2 core/shell nanorod heterostructure is highly controllable and reproducible. In comparison with pristine ZnO, SnO2, and Au-loaded ZnO, SnO2 sensors, Au-ZnO/SnO2 nanorod sensors exhibit a remarkably high and fast response to TEA gas at working temperatures as low as 40 °C. The enhanced sensing property of the Au-ZnO/SnO2 sensor is also discussed with the semiconductor depletion layer model introduced by Au-SnO2 Schottky contact and ZnO/SnO2 N-N heterojunction.

Switching selectivity between Pb2+ and Hg2+ ions through variation of substituents at xanthene end; ‘turn-on’ signalling responses by FRET modulation

Substitution at amino groups attached to the xanthene core modulates the stereo-electronic situation to switch selectivity; a FRET mediated signalling with a distinctive coupling of fluorophores.

New probe design strategy by cooperation of metal/DNA-ligation and supermolecule inclusion interaction: application to detection of mercury ions(II)

In this paper, the development is described of an efficient pyrene excimer signaling-based fluorescent sensor for the measurement of mercury ions in aqueous solutions based on thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination chemistry and the inclusion interaction of γ-cyclodextrin. Introduction of cyclodextrin can provide cooperation for the molecular level space proximity of the two labeled pyrene molecules, moreover the hydrophobic cavity of γ-cyclodextrin can also offer protection for the pyrene dimer's emission from the quenching effect of Hg(2+) and enhance the fluorescence intensity of the pyrene excimer. To demonstrate the feasibility of the design, a bis-pyrene-labeled thymine-rich DNA strand was used as the detection probe. In the presence of Hg(2+), stem-close-shaped DNA strands can be formed with the cooperation of γ-cyclodextrin and ideally predominantly emit the excimer fluorescence. The selectivity of the sensor for Hg(2+) against other biologically and environmentally related metal ions is outstanding due to the high specificity of T-Hg(2+)-T formation. In addition, the pyrene excimer has a long fluorescence lifetime, which can tolerate intense background fluorescence interference from complex biological components, making it potentially applicable in the analysis of complex biological samples.

Development of surface-engineered yeast cells displaying phytochelatin synthase and their application to cadmium biosensors by the combined use of pyrene-excimer fluorescence

The development of simple, portable, inexpensive, and rapid analytical methods for detecting and monitoring toxic heavy metals are important for the safety and security of humans and their environment. Herein, we describe the application of phytochelatin (PC) synthase, which plays a critical role in heavy metal responses in higher plants and green algae, in a novel fluorescent sensing platform for cadmium (Cd). We first created surface-engineered yeast cells on which the PC synthase from Arabidopsis (AtPCS1) was displayed with retention of enzymatic activity. The general concept for the sensor is based on the Cd level-dependent synthesis of PC2 from glutathiones by AtPCS1-displaying yeast cells, followed by simple discriminative detection of PC2 via sensing of excimer fluorescence of thiol-labeling pyrene probes. The intensity of excimer fluorescence increased in the presence of Cd up to 1.0 μM in an approximately dose-dependent manner. This novel biosensor achieved a detection limit of as low as 0.2 μM (22.5 μg/L) for Cd. Although its use may be limited by the fact that Cu and Pb can induce cross-reaction, the proposed simple biosensor holds promise as a method useful for cost-effective screening of Cd contamination in environmental and food samples. The AtPCS1-displaying yeast cells also might be attractive tools for dissection of the catalytic mechanisms of PCS.

Highly selective colorimetric detection of spermine in biosamples on basis of the non-crosslinking aggregation of ssDNA-capped gold nanoparticles

The selective adsorption of single-stranded oligonucleotides (ssDNA) on gold nanoparticles (AuNPs) is well known for stabilizing the AuNPs against aggregation even at high salt concentrations. Our investigation shows that the non-crosslinking aggregation of arbitrary ssDNA-capped AuNPs occurs due to their interaction with the cationic polyamine, spermine (Spm), even without any addition of NaCl. The non-crosslinking aggregation mechanism is that the Spm, served as multivalent counterions, plays the dual roles of charge shielding and ion bridging among the ssDNA-capped AuNPs, which jointly result in the aggregation of the ssDNA-capped AuNPs. Therefore, a sensitive and highly selective colorimetric method for the detection of Spm was developed. To the best of our knowledge, it is the first successful case as to the efforts towards the development of optical assays for cationic polyamine, showing neither natural UV absorption nor fluorescence. Compared with the traditional methods of chromatography and capillary electrophoresis, the approach described here would provide a convenient alternative and new train of thought for the specific detection of Spm in both biological fluid and fermented products.

Nucleic acid fluorescent probes for biological sensing

Nucleic acid fluorescent probes are playing increasingly important roles in biological sensing in recent years. In addition to the conventional functions of single-stranded DNA/RNA to hybridize with their complementary strands, affinity nucleic acids (aptamers) with specific target binding properties have also been developed, which has greatly broadened the application of nucleic acid fluorescent probes to the detection of a large variety of analytes, including small molecules, proteins, ions, and even whole cells. Another chemical property of nucleic acids is to act as substrates for various nucleic acid enzymes. This property can be utilized not only to detect those enzymes and screen their inhibitors, but also employed to develop effective signal amplification systems, which implies extensive applications. This review mainly covers the biosensing methods based on the above three types of nucleic acid fluorescent probes. The most widely used intensity-based biosensing assays are covered first, including nucleic acid probe-based signal amplification methods. Then fluorescence lifetime, fluorescence anisotropy, and fluorescence correlation spectroscopy assays are introduced, respectively. As a rapidly developing field, fluorescence imaging approaches are also briefly summarized.

Highly sensitive and selective derivatization-LC method for biomolecules based on fluorescence interactions and fluorous separations

A fluorescence derivatization LC method is a powerful tool for the analysis with high sensitivity and selectivity of biological compounds. In this review, we introduce new types of fluorescence derivatization LC analysis methods. These are (1) detection-selective derivatization methods based on fluorescence interactions generated from fluorescently labeled analytes: excimer fluorescence derivatization and fluorescence resonance energy transfer (FRET) derivatization; (2) separation-selective derivatization methods using the fluorous separation technique: fluorous derivatization, F-trap fluorescence derivatization, and fluorous scavenging derivatization (FSD).

Triethylenetetramine pharmacology and its clinical applications

Triethylenetetramine (TETA), a Cu(II)-selective chelator, is commonly used for the treatment of Wilson's disease. Recently, it has been shown that TETA can be used in the treatment of cancer because it possesses telomerase inhibiting and anti-angiogenesis properties. Although TETA has been used in the treatment of Wilson's disease for decades, a comprehensive review on TETA pharmacology does not exist. TETA is poorly absorbed with a bioavailability of 8 to 30%. It is widely distributed in tissues with relatively high concentrations measured in liver, heart, and kidney. It is mainly metabolized via acetylation, and two major acetylated metabolites exist in human serum and urine. It is mainly excreted in urine as the unchanged parent drug and two acetylated metabolites. It has a relatively short half-life (2 to 4 hours) in humans. The most recent discoveries in TETA pharmacology show that the major pharmacokinetic parameters are not associated with the acetylation phenotype of N-acetyltransferase 2, the traditionally regarded drug acetylation enzyme, and the TETA-metabolizing enzyme is actually spermidine/spermine acetyltransferase. This review also covers the current preclinical and clinical application of TETA. A much needed overview and up-to-date information on TETA pharmacology is provided for clinicians or cancer researchers who intend to embark on cancer clinical trials using TETA or its close structural analogs.

A pyrenyl-appended triazole-based calix[4]arene as a fluorescent sensor for Cd2+ and Zn2+

The synthesis and evaluation of a novel calix[4]arene-based fluorescent chemosensor 8 for the detection of Cd(2+) and Zn(2+) is described. The fluorescent spectra changes observed upon addition of various metal ions show that 8 is highly selective for Cd(2+) and Zn(2+) over other metal ions. Addition of Cd(2+) and Zn(2+) to the solution of 8 results in ratiometric measurement.

Rapid, sensitive and simultaneous determination of fluorescence-labeled polyamines in human hair by high-pressure liquid chromatography coupled with electrospray-ionization time-of-flight mass spectrometry

The rapid, sensitive and simultaneous determination of six polyamines, i.e., ornithine (ORN), 1,3-diaminopropane (DAP), putrescine (PUT), cadaverine (CAD), spermidine (SPD) and spermine (SPM), in human hairs was performed by ultra-performance liquid chromatography (UPLC) with fluorescence (FL) detection and electrospray-ionization time-of-flight mass spectrometry (ESI-TOF-MS). The primary (-NH(2)) and secondary (-NH) amines in the polyamine structures were first labeled with 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F) at 60 degrees C for 30 min in the mixture of 0.1M borax (pH 9.3) and acetonitrile (CH(3)CN). The resulting derivatives were perfectly separated using an ACQUITY UPLC BEH C(18) column (1.7 microm, 100 mm x 2.1mm i.d.) by a gradient elution with a mixture of water-acetonitrile containing 0.1% formic acid (HCOOH). The separated polyamine derivatives were sensitively detected with both FL and TOF-MS. The detection limits in FL and TOF-MS were 11-86 and 2-5 fmol, respectively. However, the determination of several polyamines by FL detection was interfered with by endogenous substances in the hair. Therefore, the simultaneous determination in hair was carried out by the combination of UPLC separation and the ESI-TOF-MS detection. The structures of the polyamines were identified from the protonated-molecular ions [M+H](+) obtained from the TOF-MS measurement. A good linearity was achieved from the calibration curves, that was obtained by plotting the peak area ratios of the analytes relative to the internal standard (IS), i.e., 1,6-diaminohexane (DAH), against the injected amounts of each polyamine (0.05-50 pmol, r(2)>0.999). The proposed method was applied to the determination in the hairs of healthy volunteers. The mean concentrations of ORN, DAP, PUT, CAD, SPD and SPM in 1mg of human hairs (n=20) were 1.46, 0.18, 1.18, 0.11, 1.97 and 0.98 pmol, respectively. Because the proposed method provides a good mass accuracy and the trace detection of the polyamines in hair, this analytical technique seems to be applicable for the determination of various biological compounds in hair.

Pyrene excimer signaling molecular beacons for probing nucleic acids

Molecular beacon DNA probes, containing 1-4 pyrene monomers on the 5' end and the quencher DABCYL on the 3' end, were engineered and employed for real-time probing of DNA sequences. In the absence of a target sequence, the multiple-pyrene labeled molecular beacons (MBs) assumed a stem-closed conformation resulting in quenching of the pyrene excimer fluorescence. In the presence of target, the beacons switched to a stem-open conformation, which separated the pyrene label from the quencher molecule and generated an excimer emission signal proportional to the target concentration. Steady-state fluorescence assays resulted in a subnanomolar limit of detection in buffer, whereas time-resolved signaling enabled low-nanomolar target detection in cell-growth media. It was found that the excimer emission intensity could be scaled by increasing the number of pyrene monomers conjugated to the 5' terminal. Each additional pyrene monomer resulted in substantial increases in the excimer emission intensities, quantum yields, and excited-state lifetimes of the hybridized MBs. The long fluorescence lifetime ( approximately 40 ns), large Stokes shift (130 nm), and tunable intensity of the excimer make this multiple-pyrene moiety a useful alternative to traditional fluorophore labeling in nucleic acid probes.