A water-soluble conjugated polyelectrolyte for selective and sensitive detection of carcinogenic chromium(VI).

Environmental water pollution caused by hexavalent chromium (Cr(VI)) is a threat to living beings due to its carcinogenic nature. Herein, we report the synthesis of a highly fluorescent water-soluble conjugated polyelectrolyte PPMI and its application as a fluorescence sensor to monitor traces of carcinogenic Cr(VI) ions in water. PPMI was synthesized via the oxidative polymerization method followed by post-polymer functionalization. Fluorescent PPMI exhibited a photoluminescence quantum yield of 23.87 and displayed a rapid, very selective, and sensitive turn-off fluorescence signal in response to Cr(VI), with a significantly high quenching constant of 1.32 × 106 M-1. The mechanism of sensing was found to be static quenching. The limit of detection of this highly accessible analytical method was found to be in nanomolar ranges, i.e. 0.85 nM. Additionally, sensing on solid platforms such as economical paper strips was successfully achieved, which is very challenging and highly recommended for any reliable, portable, and economical analytical method.

Dual "Static and Dynamic" Fluorescence Quenching Mechanisms Based Detection of TNT via a Cationic Conjugated Polymer.

A rare combination of dual static and dynamic fluorescence quenching mechanisms is reported, while sensing the nitroexplosive trinitrotoluene (TNT) in water by a cationic conjugated copolymer PFPy. Since the fluorophore PFPy interacts with TNT in both ground state as well as the excited states, a greater extent of interaction is facilitated between PFPy and the TNT, as a result of which the magnitude of the signal is amplified remarkably. The existence of these collective sensing mechanisms provides additional advantages to the sensing process and enhances the sensing parameters, such as LoD and highly competitive sensing processes in natural water bodies irrespective of the pH and at ambient conditions. These outcomes involving dual sensing mechanistic pathways expand the scope of developing efficient sensing probes for toxic chemical analyte and biomarker detection, preventing environmental pollution and strengthening security at sensitive locations while assisting in early diagnosis of disease biomarkers.

AIE active polymers for biological applications.

The discovery of aggregation-induced emission (AIE) phenomenon, significantly altered the understanding of the scientific world about the luminophore aggregation. Polymers with AIE features have recently emerged as promising materials with wide range of applications in optoelectronics devices, chemosensors, bioimaging, cancer theranostics and drug delivery. By introducing the AIE active molecule into the polymer structure, novel materials encompassing the characteristics properties of both the functional materials such as excellent brightness, versatile structure modification, high biocompatibility, exceptional stability and facile processability are achieved. This chapter presents the advances in synthetic design as well as potential biological applications of AIE active polymers, beginning with a brief introduction to the AIE phenomenon. The versatile synthetic route, easier functionalization, and light up feature of the AIE active polymers offer direct visualization of the physiological processes within or outside the living organisms. This chapter also precisely describes the photodynamic therapy/photothermal therapy (PDT/PTT) with up-to-date advancement of AIE active polymer and their emerging applications in biomedical field. The AIE active Photosensitizers (PSs) are much more efficient in singlet oxygen (1O2) production than their small molecule AIE active PSs due to their enhanced inter system crossing (ISC) process and improved light-harvesting ability. Additionally, the present chapter aims to focus on all recent AIE active polymers for drug screening and drug delivery. The AIE active polymer often shows decent drug loading capacity, high stability and good biocompatibility comprising image guided drug monitoring features. Lastly, the concluding discussion reveals the future prospective of the AIE active polymers.

Stepwise elucidation of fluorescence based sensing mechanisms considering picric acid as a model analyte.

In most of the sensing systems, specific detection mechanisms are involved during the detection process for a certain analyte irrespective of probes. However, unlike that of various sensing analytes, the detection of the highly toxic and explosive picric acid (PA) analyte was found to involve significant types of distinct sensing mechanisms depending on the nature of probes. Moreover, in the past five years, apart from the plethora of fluorescent probes designed, a number of unique organic small molecules and polymers have been strategically developed at our laboratory for the detection of PA, wherein the involvement of several diverse mechanisms along with a few new mechanisms depending on the electronic and photophysical properties of the probes has been unveiled. This involvement of several distinct mechanisms for the detection of PA motivated us to compile a step-by-step guide for the elucidation of the fluorescence sensing mechanism by taking PA as a model analyte. This "tutorial review" summarizes all the common sensing mechanisms involved for the detection of PA hitherto and provides a step-by-step guide to design experiments for the elucidation of sensing mechanisms for any newly designed sensing system. In addition to the appropriate classification of mechanisms involved for the fluorescence sensing of PA using various fluorescent systems developed at our laboratory, this tutorial review also includes most other possible mechanistic approaches studied previously. The present tutorial also provides a very unique method of a flow chart, which could help readers to elucidate the likely sensing mechanism via stepwise experimental and theoretical studies. Apart from the elucidation of the sensing mechanism for PA, this review presents an easy and distinct approach for the identification of all the involved mechanisms that would be of primary concern in the detection process of any analyte and could accurately help researchers in the easy and quick elucidation of sensing mechanisms in any kind of fluorophore-analyte system.

An Unprecedented Blueshifted Naphthalimide AIEEgen for Ultrasensitive Detection of 4-Nitroaniline in Water via "Receptor-Free" IFE Mechanism.

The development of a new naphthalene appended naphthalimide derivative (NMI) with aggregation-induced enhanced emission (AIEE) property for the sensitive detection of 4-nitroaniline (4-NA) in aqueous media is presented here. The newly designed naphthalimide AIEEgen has an exceptional blue-shifted condensed state emission that is devoid of any receptor site, accomplished ultrasensitive detection of 4-NA, which is one of the broad-spectrum pesticides that belong to the class III toxic chemical, at parts per billion level (LOD/36 ppb, Ksv =4.1×104 m-1 ) in water with excellent selectivity even in the presence of potentially competing aliphatic and aromatic amines. The reported probe is the first of its kind, demonstrating major advantages of receptor-free inner filter effect (IFE) mechanism for the sensitive detection of 4-NA using an AIEEgenic probe. Excellent sensitivity for 4-NA is also achieved on paper-based test-strip for low-cost on-site detection.

"Receptor free" inner filter effect based universal sensors for nitroexplosive picric acid using two polyfluorene derivatives in the solution and solid states.

Two "receptor-free" blue fluorescent conjugated polymers (CPs) of fluorene namely 9,9-bis(6-bromohexyl)-2-phenyl-9H-fluorene (PF1) and 9,9-bis(6-bromohexyl)-9H-fluorene (PF2) were synthesized using Suzuki cross coupling polymerization and oxidative coupling polymerization methods in high yields and well characterized by gel permeable chromatography, NMR, UV-vis, fluorescence and time-resolved photoluminescence (TRPL) spectroscopy. Both CPs explicitly recognized nitroexplosive picric acid (PA) and displayed a fluorescence quenching response in solution and on a solid support via the Inner Filter Effect (IFE) mechanism. Both CPs were highly selective and sensitive towards PA with high quenching constant values (Ksv) of 5.1 × 104 M-1 and 5.0 × 104 M-1 and remarkably low limit of detection (LOD) values of 110 nM and 219 nM. Contact mode detection of PA was also accomplished using economical and transportable fluorescent paper test strip devices for on-site sensing, which detect a minimum of 22.9 femtograms of PA. The IFE mechanism for PA sensing (or for other analytes) is an interesting concept that can detect PA by just having blue fluorescence. Therefore, careful experiments for IFE correction were performed herein for PA detection to observe ∼77% suppression efficiency due to the IFE. These studies provide fundamentally important information on the IFE based mechanism for the detection of various analytes.

Inner Filter Effect and Resonance Energy Transfer Based Attogram Level Detection of Nitroexplosive Picric Acid Using Dual Emitting Cationic Conjugated Polyfluorene.

A novel conjugated cationic polyfluorene (polyelectrolyte) derivative, PFBT, was developed by means of simple and cost-effective oxidative coupling polymerization method. PFBT displayed dual state emission in dimethyl sulfoxide (DMSO) as well as in water, a characteristic phenomenon of polyfluorene homopolymers, and tested for nitroexplosive analytes detection to observe a remarkable fluorescence quenching response for picric acid (PA) in the both solvents. The polymer PFBT demonstrated substantial selectivity and ultrasensitivity toward nitroexplosive PA in both the solvents (DMSO and H2O) with exceptional quenching constant values of 2.69 × 104 and 2.18 × 105 M-1 and a ultralow limit of detection of 92.7 nM (21.23 ppb) and 0.19 nM (43.53 ppt) in respective solvents. Furthermore, economical portable test strip devices were prepared for easy and fast on-site PA sensing, which can detect up to 0.22 ag level of PA. PA sensing in vapor phase was also established, that could detect up to 42.6 ppb level of PA vapors. Interestingly, the mechanism of sensing in DMSO solvent was attributed to substantial inner filter effect and photoinduced electron transfer, while in H2O the sensing occurs via possible resonance energy transfer and photoinduced electron transfer, which is exceptional and not reported earlier for a single probe.

Fluorescence "Turn-On" Indicator Displacement Assay-Based Sensing of Nitroexplosive 2,4,6-Trinitrophenol in Aqueous Media via a Polyelectrolyte and Dye Complex.

A water-soluble nonfluorescent cationic conjugated polyelectrolyte poly(1,1'-((1,4-phenylenebis(oxy))bis(propane-3,1-diyl))bis(pyridin-1-ium)bromide) (PPPy) was specifically synthesized via an economical method of oxidative coupling polymerization in high yields. PPPy selectively recognized nitroexplosive picric acid (PA) by fluorescence "turn-on" in the presence of closely related nitroexplosive compounds, namely, 2,4,6-trinitrotoluene, 2,4-dinitrophenol, and 4-nitrophenol via fluorescence indicator displacement assay (IDA) technique in water at pH 7.0. The polymer PPPy was characterized by NMR spectroscopy, gel permeable chromatography, UV-vis spectroscopy. The polymer PPPy forms an electrostatic complex with uranine dye. This ensemble scheme was utilized to detect PA with a limit of detection value of 295 nM (solution state) and 0.22 ppm (vapor state) through IDA, a phenomenon that is very different from the widely reported Förster resonance energy transfer, photoinduced electron transfer, ground-state charge transfer and inner filter effect based probes used for nitroexplosive PA detection.

An anionic conjugated polymer as a multi-action sensor for the sensitive detection of Cu(2+) and PPi, real-time ALP assaying and cell imaging.

A Cu(2+) ensemble polyfluorene derivative, poly[5,5'-(((9H-fluorene-9,9-diyl)bis(hexane-6,1-diyl))bis(oxy))diisophthalate] sodium salt (PFT), displays unprecedented selectivity for PPi (LOD = 2.26 ppb) in aqueous solution as well as in random urine samples at physiological pH vis-a-vis monitoring ALP activity. Furthermore, intracellular imaging of Cu(2+) and PPi in mouse macrophage (J774A.1) and human breast cancer cells (MDA-MB231) was achieved to confirm the viability of PFT in biological systems.