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

Multifunctional N-fused fluorescent probes for detection of iron ions and nitro explosives

In this work, two novel probes 4a and 4b were synthesized through Suzuki-Miyaura coupling reaction, whose structures were further confirmed by 1H NMR, 13C NMR, high-resolution mass spectrometry (HRMS) and X-ray single crystal diffraction. The optical properties of the obtained molecules were investigated accordingly. Owing to different bridging fluorophores, there are certain differences in optical performance and detection ability between the two synthesized compounds. Especially, due to the subtle difference in orbitals energy and electron distribution displayed by the DFT calculations, 4a possesses the characteristics of dual-state emission (DSE) molecule, while 4b is an aggregation-induced emission (AIE) molecule. Interestingly, these two molecules can be developed into multifunctional detection probes, successfully applied for the fluorescence recognition of iron ions and common nitroaromatic compounds (NACs). At the same time, the probe molecules can also be applied to the detection of NACs in aqueous environment. What's more, they can also be loaded on test strips and thin-films for fluorescence identification of NACs, thus being expected to be developed into portable detection tools for NACs.

A Fluorescent Covalent Organic Cage for Ultrafast Detection of Picric Acid and HCl Vapor Sensing

Covalent organic cages (COCs) have recently gained massive attention owing to their solution processability and structural flexibility. Herein, we report an amine-linked fluorescent COC (COC2) synthesized by adopting dynamic covalent imine chemistry followed by imine bond reduction and characterized with different spectroscopic techniques. The COC2 was utilized for highly sensitive, selective, and ultrafast detection of picric acid at the nanomolar level. The fluorescence quenching efficiency of PA towards the COC2 is 98.6 %, with a detection limit of 2.7 nM. PA sensing with the COC2, coated on a TLC plate and paper strip, exhibited an outstanding fluorescence quenching property. Furthermore, the COC2 unveiled solid-state acidochromism upon exposure to HCl acid fumes and was transferred back to the original form on exposure to NH3 vapors.

Magnetism-Functionalized Lanthanide MOF-on-MOF with Plasmonic Differential Signal Amplification for Ultrasensitive Fluorescence Immunoassays

The successful application of fluorescence immunoassays for clinical diagnosis requires stable photoluminescent materials and highly efficient signal amplification strategies. In this work, the magnetism-functionalized lanthanide MOF-on-MOF (Fe3O4@SiO2@MOF-on-MOF) was synthesized through intermolecular (van der Waals) interaction-assisted growth and further homogeneous epitaxial growth, which significantly improved the fluorescence performances and uncovered the underlying mechanism. The quantum chemical theory calculation and experimental studies revealed that the introduced magnetic Fe3O4@SiO2 not only endowed magnetic separation capability but also promoted fluorescence performances, which increased the energy transfer of the intersystem crossing process and suppressed the luminescence of ligands and aggregation-induced quenching. Furthermore, the plasmonic Ag/Au nanocages were developed as highly efficient fluorescence quenchers to improve the sensitivity of the fluorescence immunoassay. On the basis of the proposed differential signal amplification (DSA) strategy, the immunoassay displayed superior detection ability, with a limit of detection of 0.13 pg·mL-1 for severe acute respiratory syndrome coronavirus 2 nucleocapsid protein. The designed magnetic lanthanide MOF-on-MOF and proposed DSA strategy give new insights into ultrasensitive fluorescence immunoassays.

Self-Similar Ligand for 2D Zr(IV)-Based Metal-Organic Frameworks: Fluorescent Sensing and Catalysis

Two-dimensional (2D) metal-organic framework sheets, in comparison to the 3D analogues, offer potential advantages for intercalation of guest components between the layers, exfoliation/dispersion into solutions, and processing into thin films. As a versatile platform for leveraging organic functions, the 2D Zr(IV)-carboxylate net here features a dendritic Sierpinski tritopic linker with conjugated alkyne branches and a photoactive triphenylamine core. The 2D solid can be easily dispersed in water and many other solvents, resulting in stable and fluorescent suspension for sensing nitro aromatic compounds and Fe3+ ions with high quenching efficiencies and ultralow limits of detection. Also, the neighboring alkyne units of the coordination solid undergo thermal cyclization (e.g., at 320 °C) to form cross-linked nanographene-like components to afford robust porosity, which substantially takes up PdCl2 (atomic ratio of Zr/Pd, 2.4:1) to afford a heterogeneous catalyst for Suzuki-Miyaura coupling reactions─direct in air and without the need for phosphine ligands.

Phenolic -OH-Induced Fluorescence and Chemoselectivity in a Triptycene-Based trans-Azo Oligomer for Sensing Applications

A novel triptycene-based trans-azo fluorescent oligomer exhibiting phenolic groups has been designed. The presence of phenolic -OH in conjugation with the azo group rendered the oligomer fluorescence active by keto-enol tautomerism, which was evidenced by quenching the fluorescence intensity of TP1 in 1 M aq. NaOH. A green synthetic protocol was employed to synthesize this oligomer as a dark-brown solid, and it was characterized by using diverse analytical tools such as FTIR, 13C-CPMAS NMR, GPC, FESEM, EDS, TGA, and PXRD techniques. FESEM and PXRD confirmed its existence as amorphous nanoclusters. The oligomer displayed efficient chemosensing properties toward the detection of picric acid with the LOD value of 391 nM. The specific recognition of PA in the presence of other explosives and the results of real water sample analysis further indicated the high efficacy of the TP1 as a chemosensor.

A Conjugated Polymer-Based Portable Smartphone Platform for Sensitive and Point-Of-Care Detection of Monoamine Neurotransmitter

The precise and effective detection of neurotransmitters (NTs) is crucial for clinical investigation of neuronal processes, and timely monitoring of NT-related chronic diseases. However, sensitive detection of specific NT with unprecedented selectivity is highly challenging due to similarities in chemical and electronic structures of various interfering neurochemicals. Herein, an anionic conjugated polyelectrolyte Poly[(9,9-bis(4'-sulfonatobutyl)fluorene-co-alt-1,4-phenylene) sodium], PFPS was rationally designed and synthesized for amplified detection and point-of-care (PoC) determination of monoamine neurotransmitter, serotonin (5-Hydroxy tryptamine or 5-HT, also diagnostic biomarker of carcinoid tumor) in human blood plasma. The PFPS displayed a remarkable sensing response with an exceptionally high fluorescence quenching constant of 1.14×105 M-1 and an ultralow detection limit of 0.67 μM or 0.142 ppm, much below the clinical range. Furthermore, a smartphone-enabled portable platform was constructed for real-time onsite detection of 5-HT by quantification of visual fluorescence response of PFPS into RGB values using a color recognizer android application. The smartphone platform could be readily applied for convenient, non-invasive PoC testing of 5-HT levels in complex biological fluids accurately and is expected to revolutionize clinical diagnosis and personalized health care devices.

An investigation of the Excitation Wavelength-Dependent Dynamic Changes in the Mechanism of Detection of Picric Acid using Pyrene-Based Donor-Acceptor Systems

Picric acid (PA) is an important industrial feedstock and hence the release of industrial effluents without proper remediation results in its buildup in soil and water bodies. The adverse effects of PA accumulation in living beings necessitate the development of efficient methods for its detection and quantification. Herein, we describe pyrene-based fluorescent sensors for PA, where pyrene is appended with electron-withdrawing groups, malononitrile, and 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile (DCDHF). These molecules displayed the typical emission of pyrene monomers, as well as a broad red-shifted emission resulting from an intramolecular charge transfer (ICT) in the excited state. Both the emissions displayed a turn-off response to PA with high selectivity and sensitivity and the lowest limit of detection was estimated as 27 nM. To prove the feasibility of on-site detection, test paper strips were prepared, which could detect PA up to 4.58 picograms. Using a combination of experimental and theoretical studies the mechanism of the detection was identified as primary/secondary inner filter effect, oxidative photoinduced electron transfer, or a combination of both depending on the excitation wavelength. Interestingly, the contribution of each of these mechanisms to the total quenching process varied with a change in the excitation wavelength.

Three robust Cd(II) coordination polymers as bifunctional luminescent probes for efficient detection of pefloxacin and Cr2O72- in water

The accurate and rapid detection of antibiotics and heavy-metal-based toxic oxo-anions in water media employing coordination polymers (CPs) as luminescent probes has attracted a lot of attention. Three new Cd(II)-based ternary CPs derived from first-presented L ligands, including [Cd(DCTP)(L)(OH)]n (1), [Cd(TBTA)(L)(OH)]n (2), and [Cd(NPHT)(L)(H2O)]n (3) (L = 2-((1H-imidazol-1-yl)methyl)-5,6-dimethyl-1H-benzo[d]imidazole, H2DCTP = 2,5-dichloroterephthalic acid, H2TBTA = tetrabromoterephthalic acid and H2NPHT = 3-nitrophthalic acid), were successfully assembled and characterized. 1 and 2 show 2D hcb layers, which can be further extended into a 3D supramolecular framework via classic hydrogen bonding interactions. 3 features a 1D double chain that ultimately spreads into a 2D network through weak hydrogen bonding interactions. With the advantages of high stability and excellent luminescent properties, the three CPs display high sensitivity, selectivity, and good anti-interference for the sensing of pefloxacin (PEF) and Cr2O72- ions (LOD values toward PEF: 3.82 × 10-7 mol L-1 for 1, 4.06 × 10-7 mol L-1 for 2, and 1.36 × 10-8 mol L-1 for 3, and toward Cr2O72- ions: 5.97 × 10-7 mol L-1 for 1, 5.87 × 10-7 mol L-1 for 2, and 8.21 × 10-8 mol L-1 for 3). These CPs are the first examples of bifunctional luminescent sensors to detect PEF and Cr2O72- in aqueous solutions. The luminescence quenching mechanisms are explored in detail.

Anthracene and tetraphenylsilane based conjugated porous polymer nanoparticles for sensitive detection of nitroaromatics in water

Conjugated porous polymers (CPPs) are a kind of promising sensing materials for the detection of nitroaromatic compounds, but their sensing applications in aqueous media are limited because of their poor dispersity or solubility in water. In this study, we prepared anthracene and tetraphenylsilane based CPPs named PSiAn by conventional Suzuki coupling and Suzuki-miniemulsion polymerization, respectively. The structure, morphology and porosity of the CPPs were characterized by Fourier Transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H NMR), transmission electron microscope (TEM) and N2 sorption isotherm, respectively. Both of the CPPs have porous structure which is beneficial for the adsorption and diffusion of the analytes within them. The particle size of PSiAn nanoparticles prepared by Suzuki-miniemulsion polymerization is 10-40 nm from the TEM image, which facilitates the dispersion in the aqueous phase. Combined with the porosity and nanoparticle morphology, PSiAn nanoparticles realized the efficient photoluminescence (PL) sensing of nitroaromatic explosives in aqueous phase. The limit of detection (LOD) and limit of quantitation (LOQ) of PSiAn nanoparticles for 2,4,6-trinitrophenol (TNP) detection in the pure aqueous phase are 0.33 μM and 1.11 μM, respectively. Meanwhile, the good selectivity and anti-interference in presence of other nitro-compounds were observed. Furthermore, the spike/recovery test for the TNP detection in real water samples by PL sensing based on PSiAn nanoparticles indicates the quantitative recovery of TNP from 100.74 % to 101.00 %. The electrochemical test, ultraviolet-visible absorption spectra, excitation and emission spectra, and time-resolved PL spectra were investigated to explore the PL sensing mechanism. As a result, it is found that the fluorescence inner filter effect might be the predominant quenching mechanism during the detection of nitrophenolic compounds such as TNP and 4-nitrophenol (4-NP).

Label-Free Detection of Unbound Bilirubin and Nitrophenol Explosives in Water by a Mechanosynthesized Dual Functional Zinc Complex: Recognition of Picric Acid in Various Common Organic Media

High levels of unconjugated bilirubin (UB) in serum lead to asymptomatic and neonatal jaundice and brain dysfunctions. Herein, we have reported the detection of UB at as low as 1 μM in an aqueous alkaline medium using a Zn(II) complex. The specificity of the complex has been validated by the HPLC in the concentration window 6-90 μM, which is rare. The sensory response of the probe at physiological pH against nitro explosives developed it as an instant-acting fluorosensor for picric acid (PA) and 2,4-dinitrophenol (2,4-DNP). Spectroscopic titration provided a binding constant of 4×105  M-1 with PA. The naked eye detection was found to be 15 μM. The solid-state photoluminescent nature of the complex enabled it for PA sensing in the solid phase. Interestingly, the probe remained fluorescent in various volatile and non-volatile organic solvents. As a result, it can also detect PA and 2,4-DNP in a wide range of common organic media. NMR studies revealed the coordination of PA, 2,4-DNP, and UB to the Zn(II) center of the probe, which is responsible for the observed quenching of the probe with the analytes.

A facile and sensitive hexahomotrioxacalix[3]arene-based fluorescent sensor for the detection of trace amounts of 2,4,6-trinitrophenol

Nitroaromatic compounds are common explosives and toxic pollutants, the selective and sensitive detection of which is of great importance. Herein, a facile and sensitive fluorescent sensor L was constructed for the sensing of TNP based on the hexahomotrioxacalix[3]arene skeleton. The fluorescence emission of L was drastically quenched in the presence of 2,4,6-trinitrophenol (TNP), while other tested NACs, metal ions, and anions induced negligible changes. Under the optimized conditions, the spectroscopic studies revealed that L exhibited extremely sensitive and selective TNP recognition, with a detection limit of 9.17 × 10-7 M and a quenching constant of 2.44 × 104 M-1. The sensitivity of sensor L for TNP was attributed to the formation of a ground-state charge-transfer complex and an inner filter effect, which also contributed to the special selectivity of the sensor among the various nitroaromatic analogues. Compared with previous reports, L can serve as a highly efficient sensor for the sensing of TNP and can be employed over a wide pH range of 2 to 12. Sensor L was effectively used to quantify TNP in real water and soil samples. Additionally, fluorescent test strips were also developed for visual and rapid detection of TNP in both the solution and vapour phases.

Receptor-free phenothiazine derivative as fluorescent probe for picric acid: Investigation of the inner filter effect channel

In this study, a highly fluorescent and receptor-free phenothiazine derivative (PDAB) was developed to detect picric acid. A combination of steady-state and time-resolved fluorescence studies was conducted to examine the excited state behavior of PDAB with picric acid in solution. The PDAB probe displayed a significant degree of selectivity and was highly sensitive to picric acid, with an extremely low detection limit of 9.82 nM. Time-resolved fluorescence quenching studies exhibit direct evidence of an inner filter effect-based sensing mechanism. Using the Parker equation, a thorough analysis was done to correct the inner filter effect on the sensing of picric acid. Overall, these studies provide critical information on the sensing mechanism for picric acid detection.

A photoluminescent and electrochemiluminescent probe based on an iridium(III) complex with a boronic acid-functionalised ancillary ligand for the selective detection of mercury(II) ions

Exposure to mercury(II) ions (Hg2+) can cause various diseases such as Minamata disease, acrodynia, Alzheimer's disease, and Hunter-Russell syndrome, and even organ damage. Therefore, real-time and accurate monitoring of Hg2+ in environmental samples is crucial. In this study, we report a photoluminescent (PL) and electrochemiluminescent (ECL) probe based on a cyclometalated Ir(III) complex for the selective detection of Hg2+. The introduction of a reaction site, o-aminomethylphenylboronic acid, on the ancillary ligands allowed a prompt transmetalation reaction to take place between Hg2+ and boronic acid. This reaction resulted in significant decreases of the PL and ECL signals due to the photo-induced electron transfer from the Ir(III) complex to the Hg2+ ions. The probe was applied to the selective detection of Hg2+, and the signal changes revealed a linear correlation with Hg2+ concentrations in the range of 0-10 μM (LOD = 0.72 μM for PL, 8.03 nM for ECL). The designed probe allowed the successful quantification of Hg2+ in tap water samples, which proves its potential for the selective detection of Hg2+ in environmental samples.

Biogenic synthesis of highly fluorescent carbon dots using Azadirachta indica leaves: An eco-friendly approach with enhanced photocatalytic degradation efficiency towards Malachite green

A simpler and efficient method has been developed for the green synthesis of highly fluorescent carbon dots (CDs) from Azadirachta Indica leaves. The surface morphology of developed CDs has shown the existence of spherical particles in the size range of 3-8 nm with superior biocompatibility and high quantum yield value i.e. 42.3%. The particles exhibited a highly fluorescent and crystalline nature along with a bandgap value of 4.02 eV. The prepared CDs served as a factorial design for the sensing and degradation of Malachite green among other dyes. The main perspective of the current finding is that the designed catalyst exhibits excellent sensing results towards Malachite green with a limit of detection i.e. 0.144 μM in the concentration range of 0-50 μM. Moreover, the UV triggered results of photocatalysis illustrated a good dye removal efficacy by developed CDs with an average of 90.73, 98.25, 52 and 6.13% degradation in Methylene blue (MB), Malachite green (MG), Rhodamine 6G (Rh 6G) and Methyl orange (MO) upon 70 min of irradiation with mercury lamp. Additionally, the proton NMR, FTIR and FESEM results of the recycled samples also confirm the complete degradation of MG dye with the application of N-CDs.

Reusable, Ultrasensitive, Patterned Conjugated Polyelectrolyte-Surfactant Complex Film with a Wide Detection Range for Copper Ion Detection

Conjugated polyelectrolytes (CPEs) are emerging as promising materials in the sensor field because they enable high-sensitivity detection of various substances in aqueous media. However, most CPE-based sensors have serious problems in real-world application because the sensor system is operated only when the CPE is dissolved in aqueous media. Here, the fabrication and performance of a water-swellable (WS) CPE-based sensor driven in the solid state are demonstrated. The WS CPE films are prepared by immersing a water-soluble CPE film in cationic surfactants of different alkyl chain lengths in a chloroform solution. The prepared film exhibits rapid, limited water swellability despite the absence of chemical crosslinking. The water swellability of the film enables the highly sensitive and selective detection of Cu²⁺ in water. The fluorescence quenching constant and the detection limit of the film are 7.24 × 10⁶ L mol^-1 and 4.38 nM (0.278 ppb), respectively. Moreover, the film is reusable via a facile treatment. Furthermore, various fluorescent patterns introduced by different surfactants are successfully fabricated by a simple stamping method. By integrating the patterns, Cu²⁺ detection in a wide concentration range (nM-mM) can be achieved.

A robust thorium-organic framework as a bifunctional platform for iodine adsorption and Cr(VI) sensitization

Simple synthetic modulation based on thorium nitrate and tris((4-carboxyl)phenylduryl)amine (H₃TCBPA) gives rise to a new thorium-based metal-organic framework, Th-TCBPA, which features excellent hydrolytic and thermal stabilities. Incorporating electron-rich TCBPA^3- linkers not only endows Th-TCBPA with high adsorption capacity toward radioiodine vapor, but also makes it a luminescence sensor for the highly sensitive and selective detection of Cr(VI) anions.

A short review article on conjugated polymers

This article provides a brief review of conjugated polymers and the various typical polymerization reactions exploited by the community to synthesise different conjugated polyelectrolytes with varied conjugated backbone systems. We further discuss with detailed emphasises the mechanism involved such as photo-induced electron transfer, resonance energy transfer, and intra-molecular charge transfer in the detection or sensing of various analytes. Owing to their excellent photo-physical properties, facile synthesis, ease of functionalization, good biocompatibility, optical stability, high quantum yield, and strong fluorescence emission. Conjugated polymers have been explored for wide applications such as chemical and biological sensors, drug delivery and drug screening, cancer therapeutics and imaging. As such we believe it will be a timely review article for the community.

Non-aqueous onion like nano-carbons from waste diesel-soot used as FRET-based sensor for sensing of nitro-phenols

Herein, a simple-functionalization method is described to prepare the oleylamine functionalized non-aqueous version of onion-like nanocarbons (ONC-OA), where ONC was isolated from the waste pollutant soot exhausted from the diesel engine. The surface group analysis of ONC-OA has been investigated via Nuclear Magnetic Resonance and X-ray Photoelectron Spectroscopy. ONC-OA shows blue fluorescence with a quantum yield of ∼6% in tetrahydrofuran (THF). The fluorescence-based sensing applications of ONC-OA has been investigated for selective sensing of toxic aromatic nitro-phenols compounds (para-nitro, dinitro, and trinitro phenols) from the tested many nitro organic compounds. Based on the limit of detection values, ONC-OA shows much better results for tri-nitro phenol compared to di and mono nitrophenol. To understand the quenching mechanism, a time-resolved photoluminescence analysis of the sensor with and without the addition of quenchers is performed. The effective lowering in fluorescence lifetime of the sensor after the addition of quenchers concludes that the quenching observed is majorly due to the Förster Resonance Energy Transfer (FRET) mechanism. The real-life application of ONC-OA was analyzed by external spiking of N-PhOHs in soil samples.

A Pyrene-Rhodamine FRET couple as a chemosensor for selective detection of picric acid

Selective detection of nitroaromatic compounds such as Picric acid (PA), those being explosive materials and hazardous pollutants of environmental and biological concern is highly desirable. With the operational advantages of the chemosensing approach, a pyrene-rhodamine-B couple (1) was explored in this investigation as a ratiometric molecular probe for selective and sensitive detection of picric acid. The bi-fluorophoric probe displayed absorption and fluorescence enhancements along with colourless to reddish-brown colour transition as signaling responses in the selective presence of PA among all the nitro aromatic analyte investigated. The signaling module relies on PA- mediated modulation of various operational photo-physical processes such as (a) inhibition of photo-induced electron transfer (PET) operative from amino-donor to excited pyrene (b) a conformational translation through spiro-ring opening of rhodamine-B segment, and (c) initiation of Fluorescence Resonance Energy Transfer (FRET) between excited pyrene donor and ring-opened rhodamine acceptor. The ratio of fluorescence from both fluorophores (pyrene and Rhodamine) as output channel displayed sensitive signaling performance (LOD = 13.8 nM) in the detection of PA. The investigation that inferred to the PA-induced selectivity in signalling, higher binding affinity (log K_a≈11), a faster response time, and reversibility in signalling with a counter analyte and an operational pH range established the probe's efficacy as a chemosensor for PA detection.

Designing an intriguingly fluorescent N, B-doped carbon dots based fluorescent probe for selective detection of NO2- ions

Low-cost nitrogen and boron-doped carbon nanodots (CPAP-CDs) with a high quantum yield (64.07%) were synthesized through a facile hydrothermal treatment. The obtained CPAP-CDs exhibited wide absorption, strong fluorescence, and pH-dependent behavior. The high fluorescence of CPAP-CDs was quenching in the presence of the nitrite ion in a concentration-dependent manner. The detection limit was as low as 6.6 nM with a wide linear detection range of 2 μM - 1 mM. Diazotization between the NO₂^- ion and CPAP-CDs resulted in the aggregation of CPAP-CDs and aggregation-induced emission quenching. The as-designed method was tested further with different water samples, such as tap, drinking, and seawater.

Fabrication and application of 2,4,6-trinitrophenol sensors based on fluorescent functional materials

2,4,6-Trinitrophenol (TNP) has been widely used for a long time. The adverse effects of TNP on ecological environment and human health have promoted researchers to develop various methods for detecting TNP. Among multifarious technologies utilized for the TNP detection, fluorescence strategy based on different functional materials has become an effective and efficient method attributed to its merits such as preferable sensitivity and selectivity, rapid response speed, simple operation, and lower cost, which is also the focus of review. This review summarizes the development status of fluorescence sensors for TNP in a detailed and systematic way, especially focusing on the research progress since 2015. The sensing properties of fluorescent materials for TNP are the core of this review, including nanomaterials, organic small molecules, emerging supramolecular systems, aggregation induced emission materials and others. Moreover, the development direction and prospect of fluorescence sensing method in the field of TNP detection are introduced and discussed at the end of review.

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.

Fluorene-Based Fluorometric and Colorimetric Conjugated Polymers for Sensitive Detection of 2,4,6-Trinitrophenol Explosive in Aqueous Medium

Nitroaromatic explosives are a class of compounds that are responsible for various health hazards and terrorist outrages. Among these, sensitive detection of 2,4,6-trinitrophenol (TNP) explosive has always been highly desirable considering public health and national security. In this regard, three fluorene-based conjugated polymers (CP 1, CP 2, and CP 3) were synthesized through the Suzuki-Miyaura coupling reaction and were found to be highly sensitive for fluorescence detection of TNP with detection limits of 3.2, 5.7, and 6.1 pM, respectively. Excellent selectivity of CPs toward TNP was attributed to their unique π-π interactions based on fluorescence studies and density functional theory (DFT) calculations. The high sensitivity of CPs to TNP was attributed to the static quenching mechanism based on the photoinduced electron transfer process and was evaluated by fluorescence, UV-visible absorption, dynamic light scattering, Job's plots, the Benesi-Hildebrand plots, and DFT calculations. CPs were also used for colorimetric and real-water sample analysis for the detection of TNP explosive. Meanwhile, sensor-coated test strips were fabricated for on-site detection of TNP, which makes them convenient solid-supported sensors.

Recent developments on carbon dots-based green analytical methods: New opportunities in fluorescence assay of pesticides, drugs and biomolecules

Fluorescent carbon dots (CDs) grabs huge attention in analytical and bioanalytical applications due to their high selectivity towards target analyte, specificity, photostability, and quantum yield. Cost-effective and biocompatible properties of...

Functionalized graphene oxide in situ initiated ring-opening polymerization for highly sensitive sensing of cytokeratin-19 fragment

Improving the sensitivity of detection is crucial to monitor biomarker, assess toxicity, and track therapeutic agent. Herein, a sensitivity-improved immunosensor is reported for the first time via functionalized graphene oxide (GO) and a "grafting-to" ring-opening polymerization (ROP) dual signal amplification strategy. Through the ROP reaction using 2-[(4-ferrocenylbutoxy)methyl] oxirane (FcEpo) as the monomer, lots of electroactive tags are linked in situ from multiple initiation sites on the GO surface modified with ethanol amine (GO-ETA), thereby achieving high sensitivity even in the case of trace amounts of tumor markers. The utmost important factor for achieving this high sensitivity is to select functionalized GO as the initiator that contains a large number of repeated hydroxyl functional groups so as to trigger additional ROP reaction. Under the optimal conditions, the high sensitivity and applicability is demonstrated by the use of GO-ETA-mediated ROP-based immunosensor to detect non-small cell lung cancer (NSCLC)-specific biomarker down to 72.58 ag/mL (equivalent to ~6 molecules in a 5 μL sample). Furthermore, the satisfactory results for the determination of biomarkers in clinical serum samples highlighted that this immunosensor holds a huge potential in practical clinical application. This work described an electrochemical immunosensor for ultrasensitive detection of CYFRA 21-1 via the functionalized graphene oxide (GO) and a "grafting-to" ring-opening polymerization (ROP) dual signal amplification strategy, which hold the merits of high sensitivity, applicability, selectivity, efficiency, easy operation and environmental friendliness.

A composite nanosensing array with two response channels for trinitrobenzoic acid optical test

In this paper, the authors reported a composite platform for the optical sensing of 2,4,6-trinitrobenzoic acid (TBA). This composite sensing platform consisted of luminescent rare earth MOF and a rhodamine-derived sensing probe. Its composite structure was confirmed by means of XRD, IR, TGA and photophysical measurement. It was found that there were two emission components in this sensing platform, which were rhodamine emission component and Eu(III) emission component, respectively. The rhodamine emission was enhanced with increasing TBA concentration, while the Eu(III) emission component was quenched by increasing TBA concentration, showing self-calibrated sensing signals for ratiometric fluorescent sensing. In addition, rhodamine absorption in visible region was increased with increasing TBA concentration, showing colorimetric sensing. The above mentioned two sensing channels both showed high selectivity and linear response towards TBA with LOD of 2.4 μM. By comparing emission lifetime under various TBA concentrations, the sensing mechanism was convinced as the combination of rhodamine emission turn on effect initiated by TBA -released protons and Eu(III) emission turn off effect caused by an ET (energy transfer) procedure from EuBTC to TBA. This sensing platform showed naked eye sensing and two sensing channels with linear response and high selectivity.

Aggregation-Induced Enhanced Emission (AIEE)-Active Conjugated Mesoporous Oligomers (CMOs) with Improved Quantum Yield and Low-Cost Detection of a Trace Amount of Nitroaromatic Explosives

The article reports a straightforward strategy for the design and synthesis of highly luminescent conjugated mesoporous oligomers (CMOs) with an "aggregation-induced enhanced emission" (AIEE) feature through Wittig polymerization of a molecular rotor. Typical molecular rotors such as triphenylamine (TPA) and tetraphenylethene (TPE) as B2-, and A4- and A3-type nodes have been used to construct AIEE-active CMOs, namely, CMO1 and CMO2. The quick dissipation of the excited photons is successfully controlled by the restriction of rotation of the phenyl units through the formation of a mesoporous network scaffold in a solid/thin film, which provides high quantum yields for the interlocked CMO system. Both the CMOs are sensitive and selective to the various nitroaromatic explosives, whereas CMO1 is more sensitive (K_sv = 2.6 × 10⁶ M^-1) toward picric acid. The increased quenching constant for CMO1 is due to its increased quantum yield and high energy-transfer efficiency. The mechanism for sensing has been studied in detail. The larger pore size and pore density in the mesoporous network of CMO1 are found to be responsible for the greater extent of energy transfer from CMO1 to picric acid. Furthermore, CMO1 has been employed for low-cost filter-paper-based detection of a trace amount of nitroaromatic explosive materials.

A Sensor Array for the Nanomolar Detection of Azo Dyes in Water

Azo dyes are ubiquitous pollutants that contaminate water supplies and threaten human, biota, and ecosystem health. Their detection and discrimination are a considerable challenge owing to the numerous structural, chemical, and optical similarities between dyes, complexity of the wastewater in which they are found, and low environmental concentrations. Here, we demonstrate that the inner filter effect (IFE), in combination with conjugated polymer array-based sensing, offers a rapid approach for the quantitative profiling of these pollutants. The array was constructed using three anionic conjugated polyelectrolytes whose varying spectroscopic properties led to distinct IFE patterns in the presence of various dyes. These unique fluorescence response patterns were identified and processed using linear discriminant analysis (LDA), enabling the individual identification of 12 closely related azo dyes. To demonstrate the potential for utility in the environment, the array was used to differentiate between these dyes at nanomolar concentrations in water.

Conjugated Copolymers through Electrospinning Synthetic Strategies and Their Versatile Applications in Sensing Environmental Toxicants, pH, Temperature, and Humidity

Conjugated copolymers (CCPs) are a class of polymers with excellent optical luminescent and electrical conducting properties because of their extensive π conjugation. CCPs have several advantages such as facile synthesis, structural tailorability, processability, and ease of device fabrication by compatible solvents. Electrospinning (ES) is a versatile technique that produces continuous high throughput nanofibers or microfibers and its appropriate synchronization with CCPs can aid in harvesting an ideal sensory nanofiber. The ES-based nanofibrous membrane enables sensors to accomplish ultrahigh sensitivity and response time with the aid of a greater surface-to-volume ratio. This review covers the crucial aspects of designing highly responsive optical sensors that includes synthetic strategies, sensor fabrication, mechanistic aspects, sensing modes, and recent sensing trends in monitoring environmental toxicants, pH, temperature, and humidity. In particular, considerable attention is being paid on classifying the ES-based optical sensor fabrication to overcome remaining challenges such as sensitivity, selectivity, dye leaching, instability, and reversibility.

A Facilely Synthesized Dual-State Emission Platform for Picric Acid Detection and Latent Fingerprint Visualization

To achieve a highly efficient, dual-state emission platform for picric acid (PA) detection and latent fingerprint (LFP) visualization, flexible alkyl chains have been facilely attached to the commercial organic dye 3,4,9,10-perylenetetracarboxylic dianhydride to provide the target perylenetetracarboxylate molecules PTCA-C4, PTCA-C6, and PTCA-C12. Interestingly, all these molecules exhibited impressive fluorescence characteristics with high photoluminescence quantum yields (PLQYs) of around 93.0 % in dilute solution. Also, emissive features were observed in the solid state because close molecular packing is prevented by the alkyl chains, especially for PTCA-C6, which has a high PLQY value of 49.0 %. Benefiting from its impressive fluorescence performance in both solution and as aggregates, PTCA-C6 was used as a dual-state emission platform for PA detection and also LFP visualization. For example, double-responsive fluorescence quenching in solution was observed in PA detection studies, resulting in high quenching constants (K_SV ) and also low limit-of-detection values. Furthermore, the fingerprint powder based on PTCA-C6 also presented an impressive performance on various substrates in terms of fluorescence intensity and resolution, clearly providing the specific fine details of latent fingerprints. These results demonstrate that the facilely synthesized PTCA-C6 with efficient dual-state emission exhibits great potential in the real-world applications of PA detection and LFP visualization.

Azine based AIEgens with multi-stimuli response towards picric acid

Selective detection of picric acid using AIEgens via fluorescence enhancement and quenching in the monomer and aggregated from respectively.

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

The precise study of fluorescence-based sensing mechanisms and a step-by-step design experiment for the elucidation of the mechanism of sensing for newly designed sensing systems can be ascertained using the presented tutorial review.

Fluorometric determination of the activity of alkaline phosphatase based on a system composed of WS2 quantum dots and MnO2 nanosheets

A fluorometric method is described for the detection of alkaline phosphatase (ALP) activity. It is based on the use of the product of hydrolysis of the drug amifostine (a thiophosphoester) by ALP. It is known that MnO₂ nanosheets quench the blue fluorescence of tungsten disulfide quantum dots (WS₂ QDs) which have excitation/emission wavelengths of 320/448 nm. However, in the presence of ALP and amifostine, the product of hydrolysis [2-(3-aminopropylamino)ethanethiol] triggers the decomposition of the MnO₂ nanosheets. This results in the recovery of fluorescence. Based on this finding, an assay for ALP activity was developed that works in the 0.09-1.6 U L^-1 range, with a 40 mU L^-1 detection limit. The relative standard deviation is 1.87% for five repeated measurements of 0.8 U L^-1 ALP. The method was applied to the analysis of ALP in real samples and gave satifactory results. Graphical abstractSchematic representation of a fluorometric method for determination of the activity of alkaline phosphatase (ALP). The fluorescence of a system composed of WS₂ quantum dots and MnO₂ nanosheets is quenched. Hydrolysis of the cytoprotective adjuvant amifostine (a phosphothioester) by ALP leads to a thiol that causes the decomposition of the MnO2 nanosheets. As a result, the blue fluorescence of the system becomes increasingly restored.

Efficient detection of a biomarker for infant jaundice by a europium(iii)-organic framework luminescence sensor

Efficient detection of excess bilirubin in human serum and urine is highly important for the early diagnosis of infant jaundice. A highly stable Eu(iii)-based microporous framework with bent {Eu(COO)} chains interconnected by pairs of T-shaped 4,4'-(4,4'-bipyridine-2,6-diyl)dibenzoate (bpydb2-) linkers, {[Eu(H2O)(HCOO)(bpydb)]·solvent} n (1), was solvothermally synthesized and used as a chemical sensor for bilirubin response under clinically-applicable visible-light excitation. Due to the significant synergetic effect of the inner filter effect and photoinduced electron transfer, 1 can effectively probe trace amounts of bilirubin in aqueous solution through fluorescence decay with a strong quenching constant of 6.40 × 104 M-1 and low detection limit of 1.75 μM. More importantly, a portable test paper made from 1 was further developed to achieve qualitative, naked-eye visualized differentiation for the biomarker in clinical applications. These interesting findings highlight the importance of the π-conjugated antenna ligand for clinically applicable Ln-MOF sensors.

A sensor array for the discrimination of polycyclic aromatic hydrocarbons using conjugated polymers and the inner filter effect

The inner filter effect and multivariate array sensing using conjugated polymers are combined for the detection and challenging discrimination of closely related polycyclic aromatic hydrocarbons.

Natural and anthropogenic activities result in the production of polycyclic aromatic hydrocarbons (PAHs), persistent pollutants that negatively impact the environment and human health. Rapid and reliable methods for the detection and discrimination of these compounds remains a technological challenge owing to their relatively featureless properties, structural similarities, and existence as complex mixtures. Here, we demonstrate that the inner filter effect (IFE), in combination with conjugated polymer (CP) array-based sensing, offers a straightforward approach for the quantitative and qualitative profiling of PAHs. The sensor array was constructed from six fluorescent fluorene-based copolymers, which incorporate side chains with peripheral 2-phenylbenzimidazole substituents that provide spectral overlap with PAHs and give rise to a pronounced IFE. Subtle structural differences in copolymer structure result in distinct spectral signatures, which provide a unique “chemical fingerprint” for each PAH. The discriminatory power of the array was evaluated using linear discriminant analysis (LDA) and principal component analysis (PCA) in order to discriminate between 16 PAH compounds identified as priority pollutants by the US Environmental Protection Agency (EPA). This array is the first multivariate system reliant on the modulation of the spectral signatures of CPs through the IFE for the detection and discrimination of closely related polynuclear aromatic species.