Liping Ding

An Ultrasensitive Fluorescent Sensing Nanofilm for Organic Amines Based on Cholesterol‐Modified Perylene Bisimide

A stable, ultrasensitive, and fully reversible fluorescent sensing film for organic amines has been fabricated by assembling cholesterol (Chol)-derived perylene bisimide on a glass plate surface. The compound exhibits excellent film formation properties and forms well-defined nanofibers, as evidenced by SEM and AFM measurements. It has been revealed that besides the molecular structure of the specially designed perylene derivative, the existence of nanofibers in the film is another key factor to endow the film with superior sensing ability for organic amines, including aniline. The detection limit of the amine is ca. 150.0 ppt in the vapor phase and at room temperature. Furthermore, the sensing process is free of interference from common organic solvents, nitroaromatics, and particularly phenols, which makes the film a potential candidate to be used in lung cancer diagnoses and related applications.

Micelle-Induced Versatile Sensing Behavior of Bispyrene-Based Fluorescent Molecular Sensor for Picric Acid and PYX Explosives

The effect of surfactant micelles on the photophysical properties of a cationic bispyrene fluorophore, Py-diIM-Py, was systemically examined. The results from series of measurements including UV-vis absorption, steady-state fluorescence emission, quantum yield, fluorescence lifetime, and time-resolved emission spectra reveal that the cationic fluorophore is only encapsulated by the anionic sodium dodecyl sulfate (SDS) surfactant micelles and not incorporated in the cationic dodecyltrimethylammonium bromide (DTAB) and neutral Triton X-100 (TX100) surfactant micelles. This different fluorophore location in the micellar solutions significantly influences its sensing behavior to various explosives. Fluorescence quenching studies reveal that the simple variation of micellar systems leads to significant changes in the sensitivity and selectivity of the fluorescent sensor to explosives. The sensor exhibits an on-off response to multiple explosives with the highest sensitivity to picric acid (PA) in the anionic SDS micelles. In the cationic DTAB micelles, it displays the highest on-off responses to PYX. Both the sensitivity and selectivity to PYX in the cationic micelles are enhanced compared with that to PA in the anionic micelles. However, the poor encapsulation in the neutral surfactant TX100 micelles leads to fluorescence instability of the fluorophore and fails to function as a sensor system. Time-resolved fluorescence decays in the presence of explosives reveal that the quenching mechanism of two micellar sensor systems to explosives is static in nature. The present work demonstrates that the electrostatic interaction between the cationic fluorophore and differently charged micelles plays a determinative role in adjusting its distribution in micellar solutions, which further influences the sensing behavior of the obtained micellar sensor systems.

Single-layer assembly of pyrene end-capped terthiophene and its sensing performances to nitroaromatic explosives

A terthiophene (3T) derivative of 5-(1-pyrenyl)-2,2′:5′,2′′-terthiophene (Py-3T) was synthesized and chemically immobilized onto a glass wafer surface via a flexible spacer by employing a single-layer chemistry technique. Unlike the film fabricated in the same way but with 3T as the fluorophore, the film fabricated in the present study possesses unprecedented photochemical stability at ambient conditions. Fluorescence studies revealed that the emission of the film as fabricated is significantly and selectively quenched by the presence of nitroaromatic compounds (NACs), a group of typical explosives, both in the vapor phase and in aqueous solution. Experimental and theoretical studies demonstrated that the quenching may be a result of electron transfer from the electron-rich Py-3T to the electron-deficient NACs. It was found that for vapor phase sensing, the response time and the quenching efficiency of the systems are dominantly determined by the vapor pressures of the NACs tested. The sensing performances of the film to NACs in aqueous phase were also investigated. In this case, however, the specific binding of the film to picric acid (PA), a typical NAC, makes the compound show a superior quenching efficiency than other NACs. Moreover, the response is fast and reaches equilibrium within 90 s. Furthermore, acids, bases, apple juice, perfume, and commonly found organic solventsetc. show little effect upon the sensing in aqueous phase. Both the vapor phase sensing and the aqueous solution sensing are reversible. Furthermore, the film is stable for at least 6 months provided it is properly preserved. The basic contribution of the present work is not only creating a new fluorescent film of superior sensing properties to NACs in the vapor phase, in particular to PA in the aqueous phase, but also providing a new photochemically stable fluorophore, which may combine the advantages of small molecular fluorophores and those of conjugated polymers/oligomers, for developing new fluorescent sensing films.

A single fluorescent self-assembled monolayer film sensor with discriminatory power

A fluorescent self-assembled monolayer film sensor with discriminatory power was specially designed and prepared by using pyrene as a reporting unit and a oligo(oxyethylene) unit as a hydrophilic spacer. The chemical attachment of pyrene moieties on the surface was verified by contact angle, XPS, UV-vis and fluorescence measurements. The fluorescence responses of the present film to nitroaromatic compounds (NACs) including picric acid, 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and nitrobenzene were measured. Significantly, the present film exhibits cross-reactive responses to different NACs, and the array of fluorescence variation at four specific wavelengths (peaks for pyrenes monomer emission and excimer emission) provides a distinct recognition pattern for each NAC. The results from principle component analysis reveal that the present film has discriminatory power to identify structurally similar NACs. Moreover, the present film exhibits a high sensitivity, selectivity and reversibility towards NACs, and provides great potential in instrumentation and miniaturization. The use of multiple signals of a single film sensor based on fluorophores different aggregation states (e.g., pyrenes monomer, distorted excimer, and perfect excimer in the present work) instead of an array of sensor elements provides a novel strategy for developing discriminatory materials and remarkably simplifies the process of identifying similar chemicals.

Detection and Identification of Cu2+ and Hg2+ Based on the Cross-reactive Fluorescence Responses of a Dansyl-Functionalized Film in Different Solvents

A dansyl-functionalized fluorescent film sensor was specially designed and prepared by assembling dansyl on a glass plate surface via a long flexible spacer containing oligo(oxyethylene) and amine units. The chemical attachment of dansyl moieties on the surface was verified by contact angle, XPS, and fluorescence measurements. Solvent effect examination revealed that the polarity-sensitivity was retained for the surface-confined dansyl moieties. Fluorescence quenching studies in water declared that the dansyl-functionalized SAM possesses a higher sensitivity towards Hg(2+) and Cu(2+) than the other tested divalent metal ions including Zn(2+), Cd(2+), Co(2+), and Pb(2+). Further measurements of the fluorescence responses of the film towards Cu(2+) and Hg(2+) in three solvents including water, acetonitrile, and THF evidenced that the present film exhibits cross-reactive responses to these two metal ions. The combined signals from the three solvents provide a recognition pattern for both metal ions at a certain concentration and realize the identification between Hg(2+) and Cu(2+). Moreover, using principle component analysis, this method can be extended to identify metal ions that are hard to detect by the film sensor in water such as Co(2+) and Ni(2+).

Ternary System Based on Fluorophore−Surfactant Assemblies—Cu2+ for Highly Sensitive and Selective Detection of Arginine in Aqueous Solution

A new cationic dansyl derivative-based (DIlSD) fluorescence probe was designed and synthesized. Its combination with anionic surfactant SDS assemblies shows enhanced fluorescence intensity and blue-shifted maximum wavelength. Its fluorescence can be slightly quenched by Cu(2+); however, the fluorescence quenching efficiency by Cu(2+) is highly increased upon titration of arginine (Arg). As a result, the ternary system containing the cationic fluorophore, anionic surfactant, and Cu(2+) functions as a highly sensitive and selective sensor to Arg. The optimized sensor system displays a detection limit of 170 nM, representing the highest sensitivity to Arg in total aqueous solution by a fluorescent sensor. Control experiments reveal that the imidazolium groups in the fluorophore, the anionic surfactant, and Cu(2+) all play important roles in the process of sensing Arg. The electrostatic interaction between the cationic fluorophore and anionic surfactants facilitates the binding of imidazolium rings with Cu(2+), the surfactant surface-anchored Cu(2+) is responsible for further binding of Arg, and the electrostatic interaction between anionic surfactants and positively charged amino acids accounts for the selective responses to Arg.

Synthesis, optical properties and explosive sensing performances of a series of novel π-conjugated aromatic end-capped oligothiophenes

Four novel terthiophene (3T) derivatives, have been synthesized by employing Grignard coupling reaction via end-capping of naphthyl (NA) or pyrenyl (Py) unit to the one or two ends of 3T. It has been shown that both increasing electron donating strength and extending conjugation are effective approaches to improve the photochemical stability of the oligothiophene. Fluorescence studies demonstrated that the emission of the 3T derivatives is sensitive to the presence of some important nitro-containing explosives in their ethanol solution, in particular, 2,4,6-trinitrophenol (PA) and 3,5-dinitro-2,6-bispicrylamino pyridine (PYX). As an example, the detection limits of 4 to PA and PYX were determined to be 6.21 × 10(-7)mol/L and 8.95 × 10(-7)mol/L, respectively. Based on the discovery, a colorimetric detection method has been developed. The sensitive and selective response of the modified 3T to the explosives have been tentatively attributed to the adsorptive affinity of the compounds to the explosives, and to the higher probability of the electron transfer from the electron-rich 3T derivatives to the electron-poor nitro-containing explosives. No doubt, present study broadens the family of fluorophores which may be employed for the development of fluorescent sensors.

Bispyrene/Surfactant-Assembly-Based Fluorescent Sensor Array for Discriminating Lanthanide Ions in Aqueous Solution

Lanthanides are valuable nonrenewable resources and widely used in a variety of industries. Detection and identification of lanthanide ions are in high demand but challenging because of the similarity among lanthanide ions. In the present work, a fluorescent sensor array of three cationic bispyrene derivatives mixed with anionic surfactant assemblies was developed. The sensor array exhibits cross-reactive responses to lanthanide ions when tested in aqueous solution. The combination of fluorescence variations at both monomer and excimer emission of each of the bispyrene sensor elements provides a six-signal recognition pattern for lanthanide ions. Principle component analysis illustrates that the sensor array could at least identify 6 of the 14 similar lanthanide ions including La(3+), Pr(3+), Nd(3+), Eu(3+), Ho(3+), and Er(3+). UV-vis absorption measurements rule out the possibility of binding lanthanides with fluorophores. Fluorescence titration experiments in both cationic and neutral surfactant aqueous solutions reveal that the three fluorophores show slight fluorescence responses to the lanthanide ions, indicating that electrostatic attraction between lanthanide ions and anionic surfactant plays an important role in the sensing behavior of the sensor array. Control experiments with divalent metal ions find no cross-reactive responses, suggesting that the stronger electrostatic interaction with trivalent lanthanide ions is responsible for the multiple fluorescence responses.

Protein binding-induced surfactant aggregation variation: a new strategy of developing fluorescent aqueous sensor for proteins.

Novel strategies of developing fluorescent sensors for proteins are highly demanded. In this work, we particularly synthesized a cholesterol-derivatized pyrene probe. Its fluorescence emission is effectively tuned by the aggregation state of a cationic surfactant dodecyltrimethylammonium bromide (DTAB). The used probe/DTAB assemblies exhibit highly sensitive ratiometric responses to pepsin and ovalbumin egg (o-egg) with detection limits of 4.8 and 18.9 nM, respectively. The fluorescence changes indicate the protein-surfactant interaction leads to further aggregation of DTAB assemblies. The results from Tyndall effect and dynamic light scattering verify this assumption. The responses to pepsin and o-egg are due to their strong electrostatic or hydrophobic interaction with DTAB assemblies at pH 7.4. The present noncovalent supramolecular sensor represents a novel and simple strategy for sensing proteins, which is based on the encapsulated fluorophore probing the aggregation variation of the surfactant assemblies.

A surfactant-modulated fluorescent sensor with pattern recognition capability: sensing and discriminating multiple heavy metal ions in aqueous solution

Pattern recognition has been widely used to detect and identify multiple analytes. The strategies for realizing pattern recognition of a single sensor are in significant demand. In the present work, a particular bispyrene-based fluorophore containing a hydrophilic spacer, Py-TOA-Py, was synthesized, and it was observed that its mixture with anionic surfactant assemblies realizes multiple fluorescence responses to different metal ions. The combination of fluorescence variation at four emission wavelengths enables the fluorophore/surfactant sensor system to provide specific recognition patterns to different metal ions. Principle component analysis shows that the present single sensor system could discriminate 6 metal ions, namely Fe3+, Co2+, Ni2+, Cu2+, Pb2+, and Hg2+, 5 of which are heavy metal ions. Results from UV-vis measurements rule out the possibility of the bispyrene fluorophore binding with metal ions. Fluorescence titration of metal ions with two other bispyrene fluorophores reveals that the ones with similar hydrophilic spacer, Py-EOA-Py, exhibit similar multiple fluorescence responses, whereas, the ones with hydrophobic spacer, Py-DDA-Py, display no cross-reactive responses. Time-resolved emission spectra measurements reveal that the spacer polarity plays an important role in determining the location of bispyrene in surfactant assemblies, which further influences its cross-reactive responses to metal ions. The present work provides a new strategy for developing fluorescent sensors with pattern recognition abilities.