Anthryl-Doped Conjugated Polyelectrolytes as Aggregation-Based Sensors for Nonquenching Multicationic Analytes

Ophthalmic drug effects on the amyloidogenesis of a transforming growth factor β-induced protein (TGFBIp) peptide fragment

Drugs that can treat one disease may either be detrimental or beneficial toward another due to possible cross-interactions. Therefore, care in choosing a suitable drug for patients with multiple diseases is crucial in successful patient management. This study explores several currently available ophthalmic drugs used to treat common ocular diseases to understand how they can affect the amyloidogenesis of a transforming growth factor β-induced protein (TGFBIp) peptide fragment found in abundance in the corneal protein aggregation deposits of lattice corneal dystrophy (LCD) patients. Results from this study provided supporting evidence that some drugs intended to treat other diseases can enhance or inhibit fibrillar aggregation of TGFBIp peptide, which may have potential implication of affecting the disease progression of LCD by either worsening or ameliorating it. Comparisons of the different properties of ophthalmic compounds explored in this study may also provide some guidance for future design of drugs geared toward the treatment of LCD.

A simple and effective method for smartphone-based detection of polyamines in oral cancer

Oral cancer accounts for 50%-70% of all cancer-related deaths in India and ranks sixth among the most frequent cancers globally. Roughly 90% of oral malignancies are histologically arise from squamous cells and are therefore called oral squamous cell carcinoma. Organic polycations known as biogenic polyamines, for example, putrescine (Put), spermidine (Spd), and spermine (Spm), are vital for cell proliferation, including gene expression control, regulation of endonuclease-mediated fragmentation of DNA, and DNA damage inhibition. Higher Spm and Spd levels have been identified as cancer biomarkers for detecting tumour development in various cancers. The current study utilises tannic acid, a polyphenolic compound, as a reducing and capping agent to fabricate AuNPs via a one-step microwave-assisted synthesis. The fabricated TA@AuNPs were utilised as a nanoprobe for colourimetric sensing of polyamines in PBS. When TA@AuNPs are added to the polyamine, the amine groups in polyamines interact with the phenolic groups of TA@AuNPs via hydrogen bonding or electrostatic interactions. These interactions cause the aggregation of TA@AuNPs, resulting in a red shift of the Surface Plasmon Resonance band of TA@AuNPs from 530 nm to 560 nm. The nanoprobe was found to be highly specific for Spm at low concentrations. TA@AuNPs were able to detect Spm successfully in artificial saliva samples. On recording the RGB values of the sensing process using a smartphone app, it was found that as the nanoparticles aggregated due to the presence of Spm, the intensity of theR-value decreased, indicating the aggregation of TA@AuNPs due to interaction with the polyamine.

Fluorescence 'turn-off-on' assays for neomycin sulphate and K+ ions with orange-red fluorescent molybdenum nanoclusters

Fluorescent metal nanoclusters (MNCs) have found extensive application in recognizing molecular species. Here, orange-red fluorescent Arg-A. paniculata-MoNCs were synthesized using Andrographis paniculata leaf extract, arginine as a ligand, and MoCl5 as a metal precursor. The Arg-A. paniculata-MoNCs complex exhibited a quantum yield (QY) of 16.91% and excitation/emission wavelengths of 400/665 nm. The synthesized Arg-A. paniculata-MoNCs successfully acted as a probe for assaying neomycin sulphate (NS) via fluorescence turn-off and K+ ions via fluorescence turn-on mechanisms, respectively. Moreover, the developed probe was effectively used to develop a cellulose paper strip-based sensor for detection of NS and K+ ions. Arg-A. paniculata-MoNCs demonstrated great potential for sensing NS and K+ ions, with concentration ranges of 0.1-80 and 0.25-110 μM for NS and K+ ions, respectively. The as-synthesized Arg-A. paniculata-MoNCs efficiently detected NS and K+ ions in food and biofluid samples, respectively.

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.

Spermine and Spermidine Detection through Restricted Intramolecular Rotations in a Tetraphenylethylene Derivative

Biogenic polyamines, especially spermine and spermidine, are associated with cell growth and development. These amines can be found at high concentrations in the tumor cells, tissues, and urine of cancer patients. In contrast, spermidine levels drop with age, and a possible connection between low endogenous spermidine concentrations and age-related deterioration has been suggested. Thus, the quantification of these amines in body fluids like urine could be used in the diagnosis of different pathological situations. Here a new fluorescent molecular probe based on a tetraphenylethylene derivative is reported. This probe is able to selectively detect these amines through the enhancement of the fluorescence emission of the resulting complex. This fluorescence enhancement may be related to restricted intramolecular rotations of TPE phenyl rings induced by the analyte. Theoretical studies were carried out to shed light on the observed selectivity. Finally, the detection of these amines in urine was performed with limits of detection of 0.70 µM and 1.17 µM for spermine and spermidine, respectively.

Aggregation-Induced Emission-Active Poly(phenyleneethynylene)s for Fluorescence and Raman Dual-Modal Imaging and Drug-Resistant Bacteria Killing

Poly(phenyleneethynylene) (PPE) is a widely used functional conjugated polymer with applications ranging from organic optoelectronics and fluorescence sensors to optical imaging and theranostics. However, the fluorescence efficiency of PPE in aggregate states is generally not as good as their solution states, which greatly compromises their performance in fluorescence-related applications. Herein, a series of PPE derivatives with typical aggregation-induced emission (AIE) properties is designed and synthesized. In these PPEs, the diethylamino-substituted tetraphenylethene units function as the long-wavelength AIE source and the alkyl side chains serve as the functionalization site. The obtained AIE-active PPEs with large π-conjugation show strong aggregate-state fluorescence, interesting self-assembly behaviors, inherently enhanced alkyne vibrations in the Raman-silent region of cells, and efficient antibacterial activities. The PPE nanoparticles with good cellular uptake capability can clearly and sensitively visualize the tumor region and residual tumors via their fluorescence and Raman signals, respectively, to benefit the precise tumor resection surgery. After post-functionalization, the obtained PPE-based polyelectrolyte can preferentially image bacteria over mammalian cells and possesses efficient photodynamic killing capability against Gram-positive and drug-resistant bacteria. This work provides a feasible design strategy for developing functional conjugated polymers with multimodal imaging capability as well as photodynamic antimicrobial ability.

Anionic Polyelectrolyte-Induced Aggregation of Basic Orange 21: A Clue toward Metachromasia

The change in the color of chromophore upon being embedded in a biological tissue is known as metachromasia. Basic Orange 21 (BO21) is a cationic polymethine dye that has been implied as a supravital dye, which produces metachromasia in leukocytes. An improved differential counting of leukocytes has been achieved in the clinical setup based on characteristic metachromatic expressions of BO21 for different types of leukocytes. Although BO21 has been utilized as a chromatic indicator for leukocyte counting, there are limited number of investigations that focus on the factors that may be responsible for the spectral shift in absorption and emission spectra of BO21, which leads to its metachromatic behavior. In this work, we have investigated the effect of a synthetic anionic polyelectrolyte, polystyrene sulfonate (PSS), on the photophysical properties of BO21, using steady-state emission, ground-state absorption, and time-resolved emission measurements, to get an understanding of the factors that may be responsible for the spectral shift of BO21 in the cellular environment. PSS induces aggregation of BO21 molecules with large changes in its photophysical properties; this appears to be most likely the mechanism of spectral shift for BO21 reported in the cellular environment. The employment of external stimulus reveals BO21 aggregates to be significantly responsive toward external stimuli, for example, temperature and presence of salt in the medium, which further strengthens the proposal of aggregate formation. Further, we have also employed fluorescence upconversion spectroscopy with subpicosecond time resolution to estimate the excited-state lifetime of BO21.

Simple fluorescence optosensing probe for spermine based on ciprofloxacin-Tb3+ complexation

We developed a facile detection method of spermine based on the fluorescence (FL) quenching of the ciprofloxacin-Tb3+ complex, which shows astrong green emission. Ciprofloxacin (CP) makes efficient bondings to Tb3+ ion as a linker molecule through carboxylic and ketone groups to form a kind of lanthanide coordination polymer. The addition of spermine that competes with Tb3+ ions for the interaction with CP due to its positive charge brings about weakened coordination linkage of CP and Tb3+. The probe exhibited high sensitivity, selectivity, and good linearity in the range of 2-180 μM with a low limit of detection of 0.17 μM. Moreover, we applied this method on the paper strip test (PST), along with the integration of a smartphone and Arduino-based device. The practical reliability of the developed probe was evaluated on human serum samples with acceptable analytical results.

Solid-Supported Amplification of Aggregation Emission: A Tetraphenylethylene-Cucurbit[6]uril@Hydroxyapatite-Based Supramolecular Sensing Assembly for the Detection of Spermine and Spermidine in Human Urine and Blood

The development of sensitive and selective tools for the detection and quantification of biomarkers is important in the diagnosis and treatment of clinical diseases. Spermine (SP) and spermidine (SPD) act as biomarkers for early-stage diagnosis of cancer in humans as their increased levels in urine are indicative of abnormal biological processes associated with this fatal disease. In this study, we introduced a strategy for solid-supported amplification of the effective aggregation-induced-emission (AIE) effect of a water-soluble tetraphenylethylene (TPE)-based probe in developing a supramolecular sensing platform for the rapid, sensitive, and selective detection of SP and SPD in water. The nonemissive TPE derivative (TPEHP) forms a less emissive conjugate with hydroxyl cucurbit[6]uril (CB[6]OH) in water, which undergoes several-fold enhancement of effective emission upon electrostatic interaction with the solid surface of hydroxyapatite nanoparticles (HAp NPs), dispersed in the aqueous media. The corresponding three-component supramolecular assembly disrupts by the intrusion of SP and SPD in the CB[6] portal because of the stronger binding ability with CB[6], resulting in a turn-off fluorescence sensor for SP and SPD with enhanced sensitivity. The assembly-disassembly-based sensing mechanism was thoroughly demonstrated by carrying out isothermal titration calorimetry (ITC), spectroscopic, and microscopic experiments. The sensing system showed low limits of detection (LODs) of 1.4 × 10^-8 and 3.6 × 10^-8 M for SP and SPD, respectively, which are well below the required range for the early diagnosis of cancer. Besides, a good linear relationship was obtained for both SP and SPD. Nominal interference from various metal ions, anions, common chemicals, amino acids, and other biogenic amines makes this sensing platform suitable for the real-time, low-level measurement of spermine (and spermidine) in human urinary and blood samples.

Smart materials for point-of-care testing: From sample extraction to analyte sensing and readout signal generator

The last decade has seen a surge of technical developments in the field on point-of-care testing (POCT). While these developments are extremely diverse, the common aim is to implement improved methods for quick, reliable and inexpensive diagnosis of patients within the clinical setting. While examples of successful introduction and use of POCT techniques are growing, further developments are still necessary to create POCT devices with better portability, usability and performance. Advances in smart materials emerge as potentially valuable know-hows to provide a competitive edge to the development of next generation POCT devices. This review describes the key advantages of adopting smart material-based technologies at different analytical stages of a POCT platform. Under these analytical stages which involves sample pre-treatment, analyte sensing and readout signal generator, several concepts and approaches from contemporary research work in using smart material-based technologies will be the major focus in this review. Lastly, challenges and potential outlook in implementing materials technologies from the application point of view for POCT will be discussed.

A Remarkable Fluorescence Quenching Based Amplification in ATP Detection through Signal Transduction in Self-Assembled Multivalent Aggregates

Signal transduction is essential for the survival of living organisms, because it allows them to respond to the changes in external environments. In artificial systems, signal transduction has been exploited for the highly sensitive detection of analytes. Herein, a remarkable signal transduction, upon ATP binding, in the multivalent fibrillar nanoaggregates of anthracene conjugated imidazolium receptors is reported. The aggregates of one particular amphiphilic receptor sensed ATP in high pm concentrations with one ATP molecule essentially quenching the emission of thousands of receptors. A cooperative merging of the multivalent binding and signal transduction led to this superquenching and translated to an outstanding enhancement of more than a millionfold in the sensitivity of ATP detection by the nanoaggregates; in comparison to the "molecular" imidazolium receptors. Furthermore, an exceptional selectivity to ATP over other nucleotides was demonstrated.

Creation of High-Density and Low-Defect Molecular Films with a Flat-on Conformation by Interfacial Organization of Triphosphasumanene Trisulfides

This paper focuses on the formation of high-density, low-defect monolayers of triphosphasumanene trisulfides, which are newly synthesized electronic and geometric Janus-type molecules, in a flat-on conformation. Although the molecules stack easily because of the developed π-conjugated plane, their application as a metal coating in a flat-on conformation via an interfacial molecular film enables the work function to be tuned. Surface pressure-area isotherms of the triphosphasumanene trisulfides show a two-dimensional phase transition at the air/water interface. Atomic force microscopy observations of the transferred monolayer and in- and out-of-plane X-ray diffraction patterns of the corresponding multilayers reveal that this phase transition occurs from the flat-on to the end-on conformation. The X-ray diffraction patterns obtained in the two directions completely reversed before and after the phase transition, indicating that the molecular arrangement that is generated by layers of molecular films and resultant molecular stacking is similar. The flat-on conformation of the molecules was evident from the out-of-plane X-ray diffraction and polarized infrared spectroscopy results, which indicate that a large, low-defect monomolecular film is obtained using a toluene solution with a small diffusion coefficient. The spectroscopic results reveal triphosphasumanene trisulfide aggregation in the organized molecular film, suggesting high-density molecular packing.

Fluorescence spectral shape analysis for nucleotide identification

We report a conjugated polyelectrolyte fluorescence-based biosensor P-C-3 and a general methodology to evaluate spectral shape recognition to identify biomolecules using artificial intelligence. By using well-defined analytes, we demonstrate that the fluorescence spectral shape of P-C-3 is sensitive to minor structural changes and exhibits distinct signature patterns for different analytes. A method was also developed to select useful features to reduce computational complexity and prevent overfitting of the data. It was found that the normalized intensity of 3 to 5 selected wavelengths was sufficient for the fluorescence biosensor to classify 13 distinct nucleotides and distinguish as little as single base substitutions at distinct positions in the primary sequence of oligonucleotides rapidly with nearly 100% classification accuracy. Photophysical studies led to a model to explain the mechanism of these fluorescence spectral shape changes, which provides theoretical support for applying this method in complicated biological systems. Using the feature selection algorithm to measure the relative intensity of a few selected wavelengths significantly reduces measurement time, demonstrating the potential for fluorescence spectrum shape analysis in high-throughput and high-content screening.

Design, synthesis and study of a photochromic α,ω-diene: toward new classes of photoswitchable polymers

A 4,5-dithienylimidazolium salt outfitted with pendant styrenyl groups was synthesized and studied. The salt was found to undergo reversible electrocyclization upon UV irradiation; subsequent exposure to visible light reversed the reaction. Acyclic diene metathesis (ADMET) polymerization of the salt afforded a novel fluorescent polyelectrolyte.

Temporally Programmed Disassembly and Reassembly of C3Ms

Responsive materials, which can adapt and operate autonomously under dynamic conditions, are a stepping stone towards functional, life-like systems inspired by fueled self-assembly processes in nature. Complex coacervate core micelles (C3Ms) comprising oppositely charged macromolecules constitute a novel class of polymeric micelles ideally suited for use as responsive nanoscopic delivery vehicles of hydrophilic and hydrophobic cargo. To fully exploit their potential, it is important that the C3Ms form and fall apart in an autonomous fashion as orchestrated by dynamic cues in their environment. Herein a means to temporally program the self-regulated C3M coassembly pathway, using a modulated base-catalyzed feedback system, is presented. Incorporated in the C3Ms is a pH responsive polyfluorene-based conjugated polyelectrolyte (CPF) as a building block and trace amounts of a molecular sensor (doxorubicin HCl) as cargo, both of which report on micellar coassembly and disassembly via binding-induced fluorescence quenching. CPF additionally reports on the pH of its microenvironment as its pH-dependent conformational states are mirrored in the transitions of its vibronic bands. This experimental design enables one to monitor solution pH, C3M disassembly and reassembly, as well as cargo release and recapture noninvasively in a closed system with real time florescence experiments.

Controlling the Hierarchical Assembly of π-Conjugated Oligoelectrolytes

Here, a means of controlling the assembly pathways of p-conjugated oligoelectrolytes into supramolecular fibers and microtubes is presented, and it is shown how the addition of small end-caps to well-defined and pH-responsive conjugated oligomers can alter the balance between repulsive and attractive supramolecular forces and enables control of the morphology of the hierarchical assembly process. The assembly stages from nuclei to protofibers are evidenced and a hypothesis on the mechanism of microtubes formation using a combination of analytical methods is provided, revealing different degrees of order at different scales along the structural hierarchy.

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.

Emission Tuning with Size-Controllable Polymer Dots from a Single Conjugated Polymer

Two conjugated polymers (CPs) with various compositions of phenylene and benzoselenadiazoben (BSD) are synthesized to have a special emitting property; different fluorescence colors in solution and in the solid states, allowing the resulting conjugated polymer dots (Pdots) to emit different fluorescence colors upon their size variation. The photophysical property of such different-sized Pdots is investigated using fluorescence spectra and fluorescence lifetimes. A decrease in the fluorescence lifetime of Pdots is observed with an increase in the size of Pdots, caused by quantitative change in energy transfer from phenylene (energy donor) to the BSD unit (energy acceptor). The results provide that any CP can be used for the fabrication of Pdots with size-tunable emission, as long as the CP shows different emissions according to its phases. Such emission of Pdots can even be observed when in the solid solution in polymer matrix, which emits different fluorescence colors depending on the size of embedded Pdots in the polymer matrix.

Synthesis of fluorescent conjugated polymer nanoparticles and their immobilization on a substrate for white light emission

Fluorescent conjugated polymers (CPs) for blue, green, and red emission were polymerized via the Suzuki coupling reaction.

Distinct Interfacial Fluorescence in Oil-in-Water Emulsions via Exciton Migration of Conjugated Polymers

Commercial dyes are extensively utilized to stain specific phases for the visualization applications in emulsions and bioimaging. In general, dyes emit only one specific fluorescence signal and thus, in order to stain various phases and/or interfaces, one needs to incorporate multiple dyes and carefully consider their compatibility to avoid undesirable interactions with each other and with the components in the system. Herein, surfactant-type, perylene-endcapped fluorescent conjugated polymers that exhibit two different emissions are reported, which are cyan in water and red at oil-water interfaces. The interfacially distinct red emission results from enhanced exciton migration from the higher-bandgap polymer backbone to the lower-bandgap perylene endgroup. The confocal microscopy images exhibit the localized red emission exclusively from the circumference of oil droplets. This exciton migration and dual fluorescence of the polymers in different physical environments can provide a new concept of visualization methods in many amphiphilic colloidal systems and bioimaging.

Chemical Tongues and Noses Based upon Conjugated Polymers

We report the uses of conjugated polymers in multisensory applications and in chemical and optoelectronic tongues. We look at the potential of single polymers to discriminate multiple analytes and into small libraries of conjugated polymers that represent sensors. These small libraries combine several barely selective, promiscuous sensor elements and react with the analytes in a fairly non-selective fashion by change of color, emission wavelength, or emission intensity. In such optoelectronic noses and tongues, response of a single element is not specific or particularly useful at all, but the response pattern after the combination of several sensor elements is often specific for an analyte and allows discrimination and identification without any problem. These types of tongues and noses are well suited for quality control of foodstuff, beverages, and biological species such as proteins or cells. The discriminative process is often not well understood but it is powerful, particularly if the obtained data are analyzed by sophisticated statistical methods, i.e., linear discriminant analysis and/or principal component analysis. This added layer of analysis extracts the hidden information/patterns out of the data and allows visualization of the results.

Interfacial Pressure/Area Sensing: Dual-Fluorescence of Amphiphilic Conjugated Polymers at Water Interfaces

Exciton migration to emissive defects in π-conjugated polymers is a robust signal amplification strategy for optoelectronic sensors. Herein we report end-capped conjugated polymers that show two distinct emissions as a function of interpolymer distances at the air-water and hydrocarbon-water interfaces. Amphiphilic poly(phenylene ethynylene)s (PPEs) end-capped with perylene monoimides display two distinct emission colors (cyan from PPE and red from perylene), the relative intensity of which depends on the surface pressure applied on the Langmuir monolayers. This behavior produces a ratiometric interfacial pressure indicator. Relative quantum yields are maintained at the different surface pressures and hence display no sign of self-quenching of the excitons in an aggregated state. These polymers can be organized at the micelle-water interface in lytropic liquid crystals, thereby paving the way for potential applications of end-capped amphiphilic conjugated polymers in biosensors and bioimaging.

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.

Unraveling the aggregation effect on amorphous phase AIE luminogens: a computational study

To achieve the efficient and precise regulation of aggregation-induced emission (AIE), unraveling the aggregation effects on amorphous AIE luminogens is of vital importance. Using a theoretical protocol combining molecular dynamics simulations and quantum mechanics/molecular mechanics calculations, we explored the relationship between molecular packing, optical spectra and fluorescence quantum efficiency of amorphous AIE luminogens hexaphenylsilole (HPS). We confirmed that the redshifted emission of amorphous aggregates as compared to crystalline HPS is caused by the lower packing density of amorphous HPS aggregates and the reduced restrictions on their intramolecular low-frequency vibrational motions. Strikingly, our calculations revealed the size independent fluorescence quantum efficiency of nanosized HPS aggregates and predicted the linear relationship between the fluorescence intensity and aggregate size. This is because the nanosized aggregates are dominated by embedded HPS molecules which exhibit similar fluorescence quantum efficiency at different aggregate sizes. In addition, our results provided a direct explanation for the crystallization-enhanced emission phenomenon of propeller-shaped AIE luminogens in experiments. Our theoretical protocol is general and applicable to other AIE luminogens, thus laying solid foundation for the rational design of advanced AIE materials.

A fiber optic, ultraviolet light-emitting diode-based, two wavelength fluorometer for monitoring reactive adsorption

Construction and use of an ultraviolet light-emitting diode-based fluorometer for measuring photoluminescence (PL) from powder samples with a fiber optic probe is described. Fluorescence at two wavelengths is detected by miniature photomultiplier tubes, each equipped with a different band pass filter, whose outputs are analyzed by a microprocessor. Photoluminescent metal oxides and hydroxides, and other semiconducting nanoparticles, often undergo changes in their emission spectra upon exposure to reactive gases, and the ratio of the PL intensities at two wavelengths is diagnostic of adsorption. Use of this instrument for reactive gas sensing and gas filtration applications is illustrated by measuring changes in the PL ratio for zirconium hydroxide and zinc oxide particles upon exposure to air containing low concentrations of sulfur dioxide.

Influence of counterions on the conformation of conjugated polyelectrolytes: the case of poly(thiophen-3-ylacetic acid)

Binding of large hydrophobic counterions to poly(thiophen-3-ylacetate) provokes the conformational change of this conjugated polyelectrolyte.

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.

Spermine detection via metal-mediated ethynylarene 'turn-on' fluorescence signaling

A dicarboxylated ethynylarene was shown to behave as a fluorescent chemosensor for millimolar concentrations of polyamines when mixed with Cd(II), Pb(II) or Zn(II) ions at micromolar concentrations. A bathochromic shift and intensification of fluorescence emission was observed with increasing amounts of metal ion in the presence of aqueous polyamines buffered at pH = 7.6. Such perturbations manifested as 'turn-on' signals from a ratiometric comparison of emission intensities at 390 nm versus 340 nm. Using Pb(II) as the metal mediator, spermine was selectively detected as a 40-fold signal enhancement relative to spermidine, putrescine, cadaverine and several other non-biogenic diamines. Evaluation of additional triamine and tetraamine analytes showed the influence that amine group quantity and spacing had on signal generation. By increasing the ratio of Pb(II) relative to ethynylarene, the detection limit for spermine was successfully lowered to a 25 micromolar level. Noncovalent association between ethynylarene, metal ion and polyamine are believed to promote the observed spectroscopic changes. This study exploits the subtle impact that polyamine structural identity has on transition metal chelation to define a new approach towards polyamine chemosensor development.

Selective detection of Al3+and citric acid with a fluorescent amphiphile

The assembly and disassembly of a fluorescent amphiphile by Al³⁺and citrate, respectively, can be used to sense these analytes by fluorescence spectroscopy.