Dual-functional nano-photosensitizers: Eosin-Y decorated gold nanorods for plasmon-enhanced fluorescence and singlet oxygen generation.

Photosensitizer (PS) with enhanced fluorescence is attractive for image-guided photodynamic therapy (PDT) due to its dual functional role in Singlet Oxygen Generation (SOG) and producing high fluorescence signals. Here, Eosin-Y (Ey) decorated polymer coated gold nanorods (GNRs) of different aspect ratios are synthesized and introduced as novel plasmon-enhanced nano-photosensitizers for this purpose. We show, upon excitation at 519 nm, simultaneous enhancement in fluorescence and SOG was achieved for the hybrid nanostructure. The best enhancement factors of 110 and 18 for metal-enhanced fluorescence and metal-enhanced SOG, respectively, are obtained with GNRs of length 133 nm and width 45 nm, where Ey is positioned at 12.6 nm from the metal core using layer-by-layer assembly of oppositely charged polymers. The observed plasmonic effect is critically analysed by comparing the near field damping rate along with decay length, far field scattering and nonradiative energy transfer of the nanohybrids.

Ag-Au-Cu Trimetallic Alloy Microflower: A Highly Sensitive SERS Substrate for Detection of Low Raman Scattering Cross-Section Thiols.

Trimetallic Ag-Au-Cu alloy microflowers (MFs) with various surface compositions were synthesized on a glass coverslip and used as efficient surface-enhanced Raman spectroscopy (SERS) substrates for highly sensitive label-free detection of smaller Raman scattering cross-section molecules, namely, L-cysteine and toxic thiophenols. MFs of different compositions were synthesized via appropriate mixing of metal-alkyl ammonium halide precursors followed by a single-step thermolysis at 350 °C. While the Ag percentage was kept constant at 90% for all the substrates, the composition of Au and Cu was varied between 1 and 9% sequentially. The synthesized MFs were thoroughly characterized by using field emission scanning electron microscopy (FE-SEM), wide-angle X-ray scattering, X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence techniques. FE-SEM studies revealed that the MFs were present throughout the substrate, and the average size varied from 20 to 40 µm. XPS studies showed that the top surface of the alloy substrates was rich in either Au or Cu atoms, while Ag remained underneath. The performance of the trimetallic MFs as SERS substrates was evaluated using Rhodamine 6G as a probe molecule, which showed that the MFs with Ag-Au-Cu compositions 90-7-3 and 90-3-7 were found to be the best and of equal SERS efficiency. The SERS enhancement factor (EF) of both these MFs was found to be the same, approximately 9 × 107, when calculated using 1,2,3-benzatriazole as the probe molecule. Between the two, the trimetallic substrate with a higher Au percentage (Ag-Au-Cu as 90-7-3) was used for the sensitive SERS-based detection of thiols to exploit the strong Au-S binding interaction. By virtue of the high EF of the substrate, the inherently low Raman scattering cross-sections of the probe molecules were greatly enhanced in SERS mode. The 'limit of quantification (LOQ)' values were found to be 1 nM for aliphatic L-Cysteine and 1-0.1 pM for aromatic thiols using the trimetallic SERS sensor.

Designing a nanothermometer using gel-to-liquid phase transition property of hybrid niosome.

The gel-to-liquid phase transition property of a hybrid niosome, which is made with a non-ionic surfactant, span 60 (S60), and triblock copolymer L64, is effectively utilized to design a nanothermometer for temperature sensing in the physiological range (20 °C to 50 °C). The fluorescence signal of a polarity-sensitive probe, Coumarin 153, loaded into the niosome, is used as an indicator for temperature sensing. Due to its excellent temperature sensitivity and resolution, the sensor is capable of sensing temperature inside FaDu cells.

Bimetallic Ag-Cu Alloy SERS Substrates as Label-Free Biomedical Sensors: Femtomolar Detection of Anticancer Drug Mitoxantrone with Multiplexing.

Surface-enhanced Raman spectroscopy (SERS) has been recognized as a promising label-free technology for clinical monitoring due to its high sensitivity and multiplexing ability, which should accelerate the screening of important drugs in the blood and plasma of cancer patients in a simpler, faster, and less-expensive manner. In this work, bimetallic Ag-Au and Ag-Cu alloy microflowers (MFs) with tunable surface compositions were fabricated on a glass cover slip by simple thermolysis of a metal alkyl ammonium halide precursor and used as SERS substrates for the sensitive detection of anticancer drug mitoxantrone (MTO). Two different laser excitation sources, 532 and 632.8 nm, were used to explore the possibility of surface-enhanced resonance Raman scattering. The Ag-Cu substrate showed superior detection capability over Ag-Au, whereby the sensor recorded a noteworthy "limit of detection" value of 1 fM for MTO. Theoretical electromagnetic field maps were simulated on appropriately chosen plasmonic systems to compare the electromagnetic field enhancements with the experimental SERS efficiencies of the substrates. Further, using a 10% Ag-Cu substrate, efficient multiplexing detection of MTO was demonstrated with another anticancer drug doxorubicin (DOX) in water and mouse blood plasma.

Development of low-cost copper nanoclusters for highly selective "turn-on" sensing of Hg2+ ions.

The development of low-cost earth abundant metal based fluorescent sensors for a rapid and selective nanomolar level detection of Hg2+ is essential due to the increasing world-wide concern of its detrimental effect on humans as well as the environment. Herein, we present a perylene tetracarboxylic acid functionalized copper nanoclusters (CuNCs) based "turn-on" fluorescence probe for highly selective detection of toxic Hg2+ ions. The fabricated CuNCs exhibited high photostability with emission maximum centered at 532 nm (λex = 480 nm). The fluorescence intensity of CuNCs was remarkably enhanced upon the addition of Hg2+ over other competing ions and neutral analytes. Notably, the 'turn-on' fluorescence response exhibits highly sensitive detection limit as low as 15.9 nM (S/N âˆ¼ 3). The time resolved fluorescence spectroscopy suggested the energy transfer between CuNCs and Hg2+ ions following either inhibited fluorescence resonance energy transfer (FRET) or surface modification of CuNCs during Hg2+ sensing. This study offers the systematic design and development of new fluorescent 'turn-on' nanoprobes for rapid and selective recognition of heavy metal ions.

Management of Post-Infectious Anosmia and Hyposmia: A Systematic Review.

BACKGROUND: Anosmia and hyposmia significantly affect patients' quality of life and have many etiologies, including trauma, inflammatory conditions including chronic rhinosinusitis, neoplasm, and viral infections, such as rhinovirus and SARS-CoV-2. OBJECTIVE: Our purpose was to establish whether a consensus exists regarding optimal management of olfactory dysfunction and to provide insight into the treatment of anosmia in the current climate of increased prevalence secondary to COVID-19. Thus, we aimed to systematically review the literature on the management of non-Chronic-rhinosinusitis- related anosmia/hyposmia. METHODS: PubMed, EMBASE, and Cochrane databases were searched for articles published since January 1990 using terms combined with Medical Subject Headings (MeSH). We included articles evaluating management of anosmia and hyposmia written in the English language, with original data, a minimum of 3 months of follow-up except for COVID-related studies, at least 2 patients, and well-defined and measurable outcomes. RESULTS: A total of 3013 unique titles were returned upon the initial search. Of these, 297 abstracts were examined, yielding 19 full texts meeting inclusion criteria (8 with level 1 evidence, 3 with level 2, 1 with level 3, and 7 with level 4). The studies included a total of 1522 subjects, with follow up ranging from 3 to 72 months, with an exception for COVID related studies. Endpoints were based on clinically significant improvements of olfactory functions as measured through validated smell tests. Treatments with the most robust data were intranasal corticosteroids and olfactory training. CONCLUSION: The literature on the treatment of anosmia and hyposmia includes randomized trials showing the efficacy of a few modalities. While further research is needed to expand therapeutic options for this debilitating condition, the current literature supports the use of olfactory training and topical corticosteroids.

Red-emitting carbon nanoparticles with unprecedented singlet oxygen generation efficiency for cancer theranostics.

Fluorescent Red-emitting carbon nanoparticles (RCNPs) are produced by an economical and green hydrothermal method using Eucalyptus leaves as a precursor. This is the first report of its kind demonstrating RCNPs in combined PDT-Chemo combination therapy, as RCNPs bind with mitoxantrone (MTO) electrostatically. The synthesized RCNPs before and after conjugation of MTO are characterised using DLS, SEM, TEM, UV-Vis, Fluorescence, FTIR, and 1H NMR Spectroscopy. FTIR and 1H NMR confirm the interaction between -NH proton of MTO with carboxylic acid oxygen of RCNPs. RCNPs are demonstrated as brightly fluorescent, type II photosensitizer (PS) with an extraordinary 1O2 quantum yield of 0.96, when triggered with a red laser at 660 nm. Moreover, the biocompatibility of RCNPs and RCNPs-MTO are examined and confirmed by performing a cytotoxicity assay on MCF-7 cell lines. Subsequently, to explore the internalization process of the RCNPs as a function of concentration, confocal imaging study is also carried out. The cell viability and the apoptosis assay indicates that RCNPs-MTO can achieve the PDT-Chemo synergistic cancer therapy. To the best of our knowledge, this is the first time that Eucalyptus leaves, a natural source of great abundance, is used as raw material and applied for combined PDT-chemotherapy.

Bimetallic Ag-Cu Alloy Microflowers as SERS Substrates with Single-Molecule Detection Limit.

Bimetallic Ag-Cu alloy microflowers with tunable surface compositions were fabricated as surface-enhanced Raman spectroscopy (SERS) substrates with a limit of detection in the zeptomolar range for the analyte molecule rhodamine 6G (R6G). The substrates were prepared on a glass coverslip through a bottom-up strategy by simple thermolysis of metal-alkyl ammonium halide precursors. The reaction temperature and composition of the alloy were varied sequentially to find out the maximum SERS efficiency from the substrates. While UV-vis spectroscopy was employed to characterize the optical properties of the substrates, the bulk and surface compositions of the microflowers were determined using energy-dispersive X-ray fluorescence (ED-XRF) and X-ray photoelectron spectroscopy (XPS) techniques, respectively. Also, the structural and morphological characterizations of the substrates were performed by X-ray diffraction and scanning electron microscope (SEM), respectively. For alloys, the ED-XRF studies confirmed that the bulk compositions matched with the feed ratio, while the surface compositions were found to be rich in copper in the form of both elementary copper and copper oxide, as revealed by XPS studies. From the efficiency studies for different compositions prepared, it was found that 10% Ag-Cu alloy microflowers produced the maximum SERS intensity for resonant R6G molecules as probes. In fact, R6G evidences a 50-fold enhancement in SERS spectra with 10% alloy microflowers as against pure Ag microflowers. Using 1, 2, 3-benzotriazole as a nonresonant Raman probe, uniform enhancement factors on the order of ≈108 were achieved from different parts of the 10% Ag-Cu alloy microflower. The same substrate showed excellent Raman response for detecting R6G at very low concentrations such as 10 zM, leading to detection and analysis of SERS spectra from a single R6G molecule.

Diagnosis of Anosmia and Hyposmia: A Systematic Review.

BACKGROUND: Anosmia and hyposmia have many etiologies, including trauma, chronic sinusitis, neoplasms, and respiratory viral infections such as rhinovirus and SARS-CoV-2. We aimed to systematically review the literature on the diagnostic evaluation of anosmia/hyposmia. METHODS: PubMed, EMBASE, and Cochrane databases were searched for articles published since January 1990 using terms combined with Medical Subject Headings (MeSH). We included articles evaluating diagnostic modalities for anosmia, written in the English language, used original data, and had two or more patients. RESULTS: A total of 2065 unique titles were returned upon the initial search. Of these, 226 abstracts were examined, yielding 27 full-text articles meeting inclusion criteria (Level of evidence ranging from 1 to 4; most level 2). The studies included a total of 13,577 patients. The most utilized diagnostic tools were orthonasal smell tests (such as the Sniffin' Sticks and the UPSIT, along with validated abridged smell tests). Though various imaging modalities (including MRI and CT) were frequently mentioned in the workup of olfactory dysfunction, routine imaging was not used to primarily diagnose smell loss. CONCLUSION: The literature includes several studies on validity and reliability for various smell tests in diagnosing anosmia. Along with a thorough history and physical, validated orthonasal smell tests should be part of the workup of the patient with suspected olfactory dysfunction. The most widely studied modality was MRI, but criteria for the timing and sequence of imaging modalities was heterogenous.

The Effects of Age and Race on Calvarium, Tegmen, and Zygoma Thickness.

OBJECTIVE: Temporal bone spontaneous cerebrospinal fluid (sCSF) leaks are characterized by defects in the tegmen along with calvarial thinning without associated thinning of the extracranial zygoma. The authors sought to determine the effect of age and race on calvarial, tegmen, and zygoma thickness. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary Referral Center. PATIENTS: A total of 446 patients with high-resolution head computer tomography (CT) imaging from 2003 to 2018.Intervention(s): Calvarial, tegmen, and zygoma thicknesses were measured using 3D slicer.Main Outcome Measure(s): Effects of age and race on calvarium, tegmen, zygoma thickness. RESULTS: Among all patients, increased age was associated with increased thickness of the calvarium [95% CI, 0.0002 to 0.007 mm/year, P < 0.05] and tegmen [95% CI, 0.00039 to 0.0075 mm/year, P = 0.03], but decreased thickness of the zygoma [95% CI, -0.013 to -0.005 mm/year, P < 0.001]. When compared to white patients, black patients had thicker mean [SD] calvaria (2.63 [0.61] versus 3.30 [0.79] mm; difference, 0.67 mm; [95% CI, 0.57 to 0.77]; Cohen d, 1.02), tegmen (0.73 [0.34] versus 0.92 [0.36] mm; difference 0.19 mm; [95% CI, 0.101 to 0.279]; Cohen d, 0.533) and zygoma (4.89 [0.81] versus 5.55 [0.91] mm; difference, 0.66 mm; [95% CI, 0.53 to 0.79]; Cohen d, 0.78). CONCLUSIONS: Racial differences exist in calvarial and zygoma thickness. Aging generally leads to increased calvarium and tegmen thickness, suggesting that early onset of obesity and comorbid conditions known to thin the skull base may predispose patients to developing sCSF leaks by reversing the effects of age.

A metal-enhanced fluorescence sensing platform for selective detection of picric acid in aqueous medium.

Apart from national security and military purposes, it is also of great importance to detect picric acid (PA) in aqueous solution for pollution control. Herein, we report a gold nanoparticle (AuNP)-based sensor for detection of PA in aqueous condition, based on metal-enhanced fluorescence (MEF) of poly(allylamine)hydrochloride (PAH). Notable enhancement in fluorescence intensity is observed when PAH is incubated with Au@SiO2 nanoparticles, where silica shell controls the distance between gold core and PAH. Almost ∼280 fold enhancement is recorded when PAH is incubated with ∼45 nm diameter Au nanoparticles. A significant reduction in excited state lifetime followed the enhancement in fluorescence intensity, identifying the mechanism to be primarily obtained from the intrinsic radiative decay rate enhancement of PAH. The MEF sensor shows excellent selectivity for detection of PA in water, among similar electron deficient compounds via fluorescence quenching. The detection limit of the sensor is calculated to be 79 nM, in the linear range. Detection of PA is demonstrated in simulated water samples, where matrix effects are taken into account to assess the efficacy of the sensor.

Green Synthesis of Full-Color Fluorescent Carbon Nanoparticles from Eucalyptus Twigs for Sensing the Synthetic Food Colorant and Bioimaging.

Full-color fluorescent carbon nanoparticles (CNPs) are produced by a facile and green hydrothermal method followed by the differential washing technique. Eucalyptus twigs are used as a precursor to synthesize multiemissive light blue, blue, green, and red CNPs. Brilliant Blue FCF (BB) is a widely used synthetic food colorant, which is toxic for the human body, when consumed beyond the permitted limit. Herein, we demonstrate light blue CNPs as a sensor for selective and sensitive detection of BB via a fluorescence quenching mechanism with a limit of detection of 200 nM. Temperature-dependent fluorescence and 1H NMR studies confirmed the mechanism as combined dynamic and static quenching. To demonstrate the practical efficacy of the sensor, BB is effectively detected and estimated in selected food samples procured from the market. Moreover, the biocompatibility of light blue and blue CNPs is examined and confirmed by performing a cytotoxicity assay on MDA-MB-231 cell lines. Subsequently, the cellular imaging study is also carried out to explore the internalization process of the CNPs as a function of concentration. To the best of our knowledge, this is the first time that Eucalyptus twigs, a natural source of high abundance, are used as raw materials and valorized for sensing artificial food color and bioimaging purposes.

Red-Emitting Carbon Dots as a Dual Sensor for In3+ and Pd2+ in Water.

We have demonstrated the synthesis, characterization, and application of nitrogen-doped red-emitting carbon dots (NRCDs) for dual sensing of indium (In3+) and palladium (Pd2+) in water. The detection of In3+ was associated with "turn-on" fluorescence response with a red shift, while in the presence of Pd2+, the fluorescence intensity of NRCDs was quenched to show a "turn-off" response. The interaction of NRCDs with the metal ions was investigated using 1H nuclear magnetic resonance and Fourier-transform infrared spectroscopy studies. The synthesized nanoprobes possessed good biocompatibility and photostability and were found to be suitable candidates for bioimaging due to their emission profiles in the near-infrared (NIR) window. Applicability of the as-prepared NRCDs was demonstrated in the NIR region when they were loaded in vesicle membranes with and without cations and subjected to confocal imaging successfully.

Metal-Enhanced Fluorescence Study in Aqueous Medium by Coupling Gold Nanoparticles and Fluorophores Using a Bilayer Vesicle Platform.

Gold nanoparticles (AuNPs) display excellent plasmonic properties, which are expected to assist fluorescence enhancement for dyes, and the phenomenon is known as "metal-enhanced fluorescence" (MEF). In this study, we demonstrate AuNP-induced MEF for a modified bipyridine-based construct 4-(pyridine-2-yl)-3H-pyrrolo[2,3-c]quinoline (PPQ) when it binds with biologically important Zn2+. Importantly, this phenomenon is observed under aqueous conditions in a biocompatible bilayer vesicle platform. When PPQ binds with Zn2+ to form the complex in the presence of appropriate AuNPs, MEF is evident once compared with the fluorescence intensity in the absence of AuNPs. Among the three different sizes of AuNPs used, the enhancement is observed with an average diameter of 33 nm, whereas 18 and 160 nm do not show any enhancement. A possible mechanism is ascribed to the radiating plasmons of the AuNPs, which can couple with the emission frequencies of the fluorophore under a critical distance-dependent arrangement. We witness that the enhancement in fluorescence is accompanied with a reduction in lifetime components. It is proposed that the mechanism may be predominantly derived from the enhancement of an intrinsic radiative decay rate and partly from the localized electric field effect. Overall, this work shows a rational approach to design fluorophore-metal configurations with the desired emissive properties and a basis for a useful nanophotonic technology under biological conditions.

Functionalized Chitosan-Carbon Dots: A Fluorescent Probe for Detecting Trace Amount of Water in Organic Solvents.

A novel nanoprobe was designed and synthesized by functionalizing chitosan-carbon dots (CDs) with a modified bipyridine-based heterocyclic molecule, 4-(pyridine-2-yl)-3H-pyrrolo[2,3-c]quinoline (PPQ), to detect trace amount of water via fluorescence methods. The functionalized CDs (PPQ-CDs) were thoroughly characterized using dynamic light scattering, UV-vis, X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and NMR techniques. The modified fluorescence intensity of PPQ-CDs was found to be an excellent indicator for water in organic solvents. The PPQ-CDs showed very weak fluorescence intensity in organic solvents due to a possible photoinduced electron transfer (PET) process between PPQ pyrrole nitrogen and acceptor groups of CDs. However, sequential addition of trace amount of water led to continuous enhancement in the fluorescence intensity for the PPQ-CD nanocomposites. The mechanism was proposed to follow suppression of the PET process due to the formation of "free-ions" by the proton transfer from the CD carboxyl group to pyrrole nitrogen through water bridging. The limit of water detection was determined to be 0.023% (v/v) in DMSO.

Association of Intracranial Hypertension With Calvarial and Skull Base Thinning.

OBJECTIVE: Determine if patients with increased opening pressure (OP) on lumbar puncture (LP) have thinner calvaria and skull bases. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary referral center. PATIENTS: Patients (≥18 yr of age) who had a recorded OP on LP and high-resolution computed tomography imaging of the head. Patient age, sex, body mass index were calculated. Intracranial hypertension (IH) was defined with an OP≥25 cm-H2O and low intracranial pressure with an OP<15 cm-H2O. INTERVENTION: Measurement of calvarial, zygoma, and skull base thickness when blinded to OP with three-dimensional slicer and radiologic calipers. MAIN OUTCOME MEASURES: Association of calvarial, skull base, and zygoma thickness with OP and age. RESULTS: Fifty-eight patients were included with a mean (SD) age of 53.1 (16.2) years and average (SD) body mass index of 30.1 (9.1) kg/m. Patients with IH had thinner mean (SD) calvaria (3.01 [0.81] versus 2.70 [0.58] mm; p = 0.036) and skull bases (5.17 [1.22] versus 4.60 [1.42] mm; p = 0.043) when compared with patients without IH. The mean (SD) extracranial zygoma thickness was similar between the two groups (5.09 [0.76] versus 5.00 [0.73] mm; p = 0.56). General linear model regression demonstrated advancing age was associated with increasing calvarial thickness in patients without IH and calvarial thinning in patients with IH (p = 0.038). CONCLUSION: IH is independently associated with intracranial bone (calvaria and skull base) thinning and not extracranial (zygoma) thinning. Skull thinning occurs with IH and advancing age. These findings support a possible role of increased ICP in the pathophysiologic development of spontaneous cerebrospinal fluid leaks.

Selective Sensing of Iron by Pyrrolo[2,3-c]Quinolines.

This paper reports development of an iron sensor, 2-(3H-pyrrolo[2,3-c]quinolin-4-yl)aniline (APQ). The fluorophore facilitates micromolar detection of Fe3+/Fe2+ in the presence of various cations, including well-known interfering cations Co2+and Cu2+ by the process of fluorescence quenching. Graphical Abstract.

Synthesis, Detailed Characterization, and Dual Drug Delivery Application of BSA Loaded Aquasomes.

Aquasomes (AQ) are self-assembled nanostructures, made up of a spherical hydroxyapatite core and a carbohydrate layer on top, for delivering bioactive molecules like proteins, peptides, etc., which are adsorbed on the carbohydrate layer. This is the first report of its kind demonstrating AQ as an efficient dual drug delivery system, capable of releasing bioactive molecule and a hydrophobic drug together. The synthesized AQ before and after adsorption of the bioactive molecule are characterized using dynamic light scattering, scanning electron microscopy, X-ray diffraction, small-angle X-ray scattering, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and Raman spectroscopy. BSA (bovine serum albumin) protein is used as the model bioactive molecule for the in vitro dual release studies along with representative hydrophobic drugs Coumarin 153 (C153), Warfarin (WAR), and Ibuprofen (IBU). The release behaviors of the hydrophobic drugs are explained by studying their binding interactions with BSA. The binding interactions of the drugs with BSA are analyzed by carrying out fluorescence quenching experiment of BSA, site marking competition experiment, anisotropy, and ET (30) studies. Further, in vitro biocompatibility studies are performed for dually loaded AQ by using hemolysis assay. The hemolysis assay do not show any lysing of the red blood cells, suggesting the formulations to be clinically capable for administration.

Z_{3} Parafermionic Zero Modes without Andreev Backscattering from the 2/3 Fractional Quantum Hall State.

Parafermionic zero modes are a novel set of excitations displaying non-Abelian statistics somewhat richer than that of Majorana modes. These modes are predicted to occur when nearby fractional quantum Hall edge states are gapped by an interposed superconductor. Despite substantial experimental progress, we argue that the necessary crossed Andreev reflection in this arrangement is a challenging milestone to reach. We propose a superconducting quantum dot array structure on a fractional quantum Hall edge that can lead to parafermionic zero modes from coherent superconducting forward scattering on a quantum Hall edge. Such coherent forward scattering has already been demonstrated in recent experiments. We show that for a spin-singlet superconductor interacting with loops of spin unpolarized 2/3 fractional quantum edge, even an array size of order 10 should allow one to systematically tune into a parafermionic degeneracy.

Zinc(II) Ion Sensing in Aqueous Micellar Solution Using Modified Bipyridine-Based "Turn-On" Fluorescent Probes and its Application in Bioimaging.

The bipyridine-based constructs 4-(pyridine-2-yl)-3H-pyrrolo[2,3-c]quinoline (PPQ) and [6-(3H-pyrrolo[2,3-c]quinolin-4-yl)pyridin-2-yl]methanol (PPQ-OH) and their assemblies with surfactants are evaluated as turn-on fluorescent sensors for Zn2+ ions in aqueous solution. This study strives to overcome the problem of low water solubility of the hydrophobic PPQ and PPQ-OH by using micelles. Whereas the ligands show selective sensing behavior for Zn2+ over important biological cations including Na+ , K+ , Ca2+ , Mg2+ in anionic sodium dodecyl sulfate and non-ionic Tween 80 micelles, no Zn2+ sensing is observed in cationic cetyltrimethylammonium bromide micelles. Unlike in DMF, Cd2+ interference is observed in aqueous conditions, which can be avoided either by performing the study at pH≥9 or by carrying out a time-resolved fluorescence study. Analysis of the Job plot data, the fluorescence lifetimes, and experiments on varying micellar shape and pH, confirms that the coordination volume of the resulting octahedral metal complex and formation of a five-membered chelate ring are critical factors for Cd2+ interference. The described sensing systems are capable of detecting Zn2+ ions at the micromolar level. Additionally, it is shown that PPQ and PPQ-OH can be used to detect Zn2+ in HeLa cells under physiological conditions in bioimaging studies.