John F Callan

University of Ulster, Aontroim, N Ireland, United Kingdom

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Publications (41)155.85 Total impact

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    ABSTRACT: A polymeric ratiometric fluorescent sensor for Zn(II) has been developed based on a Zn(II) responsive naphthalimide fluorophore (λEM 535 nm) and a Zn(II) insensitive rhodamine calibration fluorophore (λEM 579 nm) both coupled to a common poly(allyl amine) backbone. A concentration dependent increase in the ratiometric response (I535 nm/I579 nm) was observed in the 0–25 mM Zn(II) ion range for the sensor in aqueous buffer. The effect of dilution on the ratiometric intensity of the polymeric sensor was also studied and no change in ratiometric response was observed upon dilution to 50% of its original concentration. In contrast, when the polymeric sensor was incorporated within a Gantrez AN-139 hydrogel matrix, a linear ratiometric response was observed upon addition of increasing amounts of Zn(II) to the gel. Therefore, this approach offers the opportunity to determine Zn(II) concentration in environments where sensor concentration may vary dramatically.
    New Journal of Chemistry 06/2014; 38(7). · 2.97 Impact Factor
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    ABSTRACT: Decyl and oligo(ethylene glycol) chains were appended to the same poly(methacrylate) backbone to generate an amphiphilic polymer with a ratio between hydrophobic and hydrophilic segments of 2.5. At concentrations greater than 10 g mL-1 in neutral buffer, multiple copies of this particular macromolecule assemble into nanoparticles with hydrodynamic diameter of 15 nm. In the process of assembling, these nanoparticles can capture anthracene donors and borondipyrromethene acceptors within their hydrophobic interior and permit the transfer of excitation energy with an efficiency of 95%. Energy transfer is observed also if nanocarriers containing exclusively the donors are mixed with nanoparticles pre-loaded separately with the acceptors in aqueous media. The two sets of supramolecular assemblies exchange their guests with fast kinetics upon mixing to co-localize complementary chromophores within the same nanostructured container and enable energy transfer. After guest exchange, the nanoparticles can cross the membrane of cervical cancer cells and bring the co-entrapped donors and acceptors within the intracellular environment. Alternatively, intracellular energy transfer is also established after sequential cell incubation with nanoparticles containing the donors first and then with nanocarriers pre-loaded with the acceptors or vice versa. Under these conditions, the nanoparticles exchange their cargo only after internalization and allow energy transfer exclusively within the cell interior. Thus, the dynamic character of such supramolecular containers offers the opportunity to transport independently complementary species inside cells and permit their interaction only within the intracellular space.
    Journal of the American Chemical Society 05/2014; · 10.68 Impact Factor
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    ABSTRACT: A carbon quantum dot (CQD)-protoporphyrin (IX) sensitisier conjugate was designed to exploit the large two-photon absorption cross section of CQDs and enable the indirect excitation of the sensitiser with 800 nm irradiation via FRET.
    Chemical Communications 08/2013; · 6.38 Impact Factor
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    ABSTRACT: A novel vitamin B6 Schiff base analog () was synthesized by combining vitamin B6 cofactor pyridoxal with 2-aminophenol. Receptor displays a color change detectable by the naked-eye from yellow to red in the presence of fluoride and acetate due to the formation of hydrogen bonding host-guest complexes in 1 : 1 stoichiometry. Importantly, receptor showed fluoride-selective 'turn-on' fluorescent response with a detection limit (3σ) of 7.39 × 10(-8) M.
    The Analyst 05/2013; · 4.23 Impact Factor
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    ABSTRACT: Nanotechnology has the potential to have a revolutionary impact on targeted cancer diagnosis and therapy. A major challenge in cancer diagnosis is to be able to non-invasively detect tumors at an early stage for maximum therapeutic benefit. In the development of effective therapeutic approaches, targeting and localized delivery are the key challenges. However, because many anticancer drugs are designed to simply kill cancer cells, often in a semi-specific fashion, the distribution of anticancer drugs in healthy cells and tissues is especially undesirable due to the potential for severe side effects. This review will address the state of the art in nanotechnologies, and their ongoing applications focused on addressing the challenges posed by the early detection and targeted treatment of cancer. Some relevant patents have also been discussed.
    Recent Patents on Nanomedicine. 01/2013; 3(2).
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    ABSTRACT: Highly luminescent, water-soluble and biocompatible Carbon Quantum Dots (aqCQDs) were prepared by encapsulating the parent hydrophobic CQDs in an amphiphilic polymer. The resulting aqCQDs were non-toxic to living cells, and were found to cross the cell membrane and localise primarily in the cytosol.
    Chemical Communications 08/2012; 48(75):9361-3. · 6.38 Impact Factor
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    ABSTRACT: Iron is one of the most important elements in metabolic processes, being indispensable for all living systems and therefore it is extensively distributed in environmental and biological materials. However, both its deficiency and excess from the normal permissible limit can induce serious disorders. Therefore, several analytical techniques have been adopted for the detection of iron. Among the various techniques used for its detection, the method based on fluorescent sensors has received considerable interest in recent years because of its ability to provide online monitoring of very low concentrations without any pre-treatment of the sample together with the advantages of spatial and temporal resolution. In this article, efforts have been made to review the various molecular and supramolecular fluorescent sensors that have been developed for the selective detection of iron(iii).
    Chemical Society Reviews 08/2012; 41(21):7195-227. · 24.89 Impact Factor
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    ABSTRACT: A Rose Bengal sonosensitiser has been covalently attached to a lipid microbubble and the resulting conjugate shown to produce higher levels of singlet oxygen, enhanced cytotoxicity in a cancer cell line and a greater reduction in tumour growth than the sonosensitiser alone.
    Chemical Communications 07/2012; 48(67):8332-4. · 6.38 Impact Factor
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    ABSTRACT: Photodynamic therapy (PDT) is emerging as a treatment modality for the management of neoplastic disease. Despite considerable clinical success, its application for the treatment of deep-seated lesions is constrained by the inability of visible light to penetrate deeply into tissues. An emerging alternative approach exploits the fact that many photosensitisers respond to ultrasound, eliciting cytotoxic effects on target cells and tissues; this has become known as sonodynamic therapy (SDT). The objectives of this study were 1) to determine whether the IR-absorbing dye, indocyanine green (ICG), can be employed as a sonosensitiser and 2) to determine whether ultrasound can be used to enhance ICG-mediated PDT. Exposing ICG-treated mouse fibrosarcoma cells to ultrasound at an energy density of 30 J cm(-2) decreased cell viability by 65 %. Prior exposure of ICG-treated cells to light (λ 830 nm) and subsequent treatment with ultrasound led to a 90 % decrease in cell viability. In combination treatments a synergistic effect was observed at lower doses of ultrasound. Microscopic examination of cell populations treated with light or ultrasound demonstrated the production of intracellular reactive oxygen species (ROS). Using a mouse tumour model, treatment with light, ultrasound, or a combination thereof led to respective decreases in tumour growth of 42, 67, and 98 % at day 27 post-treatment. These results could provide a means of circumventing light-penetration issues that currently challenge the widespread use of PDT in the treatment of cancer.
    ChemMedChem 06/2012; 7(8):1465-71. · 2.84 Impact Factor
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    ABSTRACT: In search of strategies to develop deeply penetrating agents for use in Photodynamic Therapy (PDT), we have devised a Quantum Dot-Rose Bengal conjugate that is effective at producing singlet oxygen upon two-photon irradiation. The CdSe/ZnS Quantum Dot, with its high two photon absorption cross section, serves as a two-photon absorbing antenna and transfers its excited state energy to the attached photosensitiser which engages with molecular oxygen to produce cytotoxic singlet oxygen. Thus, we were able to excite the photosensitiser indirectly, which has an absorption maximum of 565 nm, with two-photon irradiation at 800 nm. Given the tissue penetration depth of 800 nm light is at least four times greater than 565 nm light, this offers the opportunity to access much deeper-seated tumours than is currently possible with pharmaceutically approved photosensitisers. Furthermore, the attachment of the photosensitiser to the hydrophilic quantum dot improved the aqueous solubility of the photosensitiser by 48
    Journal of Materials Chemistry 03/2012; 22(13):6456-6462. · 5.97 Impact Factor
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    ABSTRACT: N-Phenyl-2-(2-hydroxynaphthalen-1-ylmethylene)hydrazinecarbothioamide has been investigated as a fluorescent sensor for the determination of Fe(III) in aqueous solutions. The probe was prepared by the facile Schiff base condensation of 2-hydroxy-1-napthaldehyde with N-phenylhydrazinecarbothioamide. The sensor displayed good selectivity for Fe(III) when tested against a range of biologically and environmentally important cations. A concentration dependent increase in the emission of two fluorescent bands at 425 and 495 nm was observed upon increasing Fe(III) addition resulting in a linear ratiometric response in the 17–37 μM range. The binding stoichiometry was confirmed as 1:1 (host/guest) with the binding constant (log β) calculated as 4.56.
    Tetrahedron Letters 02/2012; 53(6):670–673. · 2.40 Impact Factor
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    ABSTRACT: In search of strategies to photoactivate the luminescence of semiconductor quantum dots, we devised a synthetic approach to attach photocleavable 2-nitrobenzyl groups to CdSe-ZnS core-shell quantum dots coated with hydrophilic polymeric ligands. The emission intensity of the resulting nanostructured constructs increases by more than 60% with the photolysis of the 2-nitrobenzyl appendages. Indeed, the photoinduced separation of the organic chromophores from the inorganic nanoparticles suppresses an electron-transfer pathway from the latter to the former and is mostly responsible for the luminescence enhancement. However, the thiol groups anchoring the polymeric envelope to the ZnS shell also contribute to the photoinduced emission increase. Presumably, their photooxidation eliminates defects on the nanoparticle surface and promotes the radiative deactivation of the excited quantum dots. This effect is fully reversible but its magnitude is only a fraction of the change caused by the photocleavage of the 2-nitrobenzyl groups. In addition, these particular quantum dots can cross the membrane of model cells and their luminescence increases by ~80% after the intracellular photocleavage of the 2-nitrobenzyl quenchers. Thus, photoswitchable luminescent constructs with biocompatible character can be assembled combining the established photochemistry of the 2-nitrobenzyl photocage with the outstanding photophysical properties of semiconductor quantum dots and the hydrophilic character of appropriate polymeric ligands.
    Journal of the American Chemical Society 01/2012; 134(4):2276-83. · 10.68 Impact Factor
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    ABSTRACT: A simple fluorescent sensor 1 has been developed for the recognition of Fe(III) in semi-aqueous solution at pH 7.0. The sensor, containing two Schiff base type receptors directly connected to naphthalene fluorophores, shows a concentration dependent decrease in emission intensity upon Fe(III) addition. The sensor was selective for Fe(III) over other metal ions and can measure Fe(III) ion concentration between 0.05 and 0.12 mM. The binding stoichiometry was established as 1:1 (host: guest) with a binding constant (Logβ) of 4.01. Furthermore, the addition of Fe(III) to a solution of 1 caused a colour change from light yellow to colourless meaning 1 is also capable of detecting Fe(III) by the naked eye.
    Journal of Fluorescence 11/2011; 22(3):795-8. · 1.79 Impact Factor
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    ABSTRACT: A combination of light and ultrasound activation of two conventional photosensitising drugs, methylene blue and rose bengal, was shown to generate higher levels of reactive oxygen species (ROS) and lower LD50 values than either light or ultrasound activation alone.
    Bioorganic & medicinal chemistry letters 08/2011; 21(19):5750-2. · 2.65 Impact Factor
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    ABSTRACT: CdSe/ZnS quantum dots functionalised with [Carboxymethyl-(4-mercapto-phenyl)-amino]-acetate displayed selectivity for Zn 2+ion when tested against a range of other commonly available metal ions in buffered aqueous solution (pH 7.0 ± 0.1). The probe displayed an enhancement in its fluorescence intensity upon addition of Zn2+attributed to a cancellation of a photoinduced electron transfer process from the bound receptor to the excited quantum dot that otherwise led to non-radiative decay. Good linearity was established for Zn2+in the 0.2 to 5.0 mM range.
    International Journal of Biomedical Nanoscience and Nanotechnology. 05/2011; 2(1):3-11.
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    ABSTRACT: We designed and synthesized an amphiphilic copolymer with pendant hydrophobic decyl and hydrophilic poly(ethylene glycol) chains along a common poly(methacrylate) backbone. This macromolecular construct captures hydrophobic boron dipyrromethene fluorophores and hydrophobic spiropyran photochromes and transfers mixtures of both components in aqueous environments. Within the resulting hydrophilic supramolecular assemblies, the spiropyran components retain their photochemical properties and switch reversibly to the corresponding merocyanine isomers upon ultraviolet illumination. Their photoinduced transformations activate intermolecular electron and energy transfer pathways, which culminate in the quenching of the boron dipyrromethene fluorescence. As a result, the emission intensity of these supramolecular constructs can be modulated in aqueous environments under optical control. Furthermore, the macromolecular envelope around the fluorescent and photochromic components can cross the membrane of Chinese hamster ovarian cells and transport its cargo unaffected into the cytosol. Indeed, the fluorescence of these supramolecular constructs can be modulated also intracellularly by operating the photochromic component with optical inputs. In addition, cytotoxicity tests demonstrate that these supramolecular assemblies and the illumination conditions required for their operation have essentially no influence on cell viability. Thus, supramolecular events can be invoked to construct fluorescent and photoswitchable systems from separate components, while imposing aqueous solubility and biocompatibility on the resulting assemblies. In principle, this simple protocol can evolve into a general strategy to deliver and operate intracellularly functional molecular components under optical control.
    Journal of the American Chemical Society 02/2011; 133(4):871-9. · 10.68 Impact Factor
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    ABSTRACT: Schiff base sensor 1, containing naphthalene and naphthalimide fluorophores with separate and distinct emission wavelengths, showed good selectivity for Cu(II) over other tested physiological and environmentally important cations through changes in its fluorescence spectra in THF/H2O (9:1) HEPES buffered solution. By taking the ratiometric change of the emissions at 435 nm (naphthalene–Schiff base) and 510 nm (naphthalimide) good linearity was observed in the 0–10 μM range. The enhancement of the 435 nm emission upon binding Cu2+ was attributed to a prevention of the rapid CN isomerisation that otherwise leads to non-radiative decay, while the quenching of the naphthalimide emission was attributed to electron transfer between the excited naphthalimide fluorophore and the redox active Cu2+.
    Tetrahedron Letters 06/2010; 51(26):3385–3387. · 2.40 Impact Factor
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    ABSTRACT: We synthesized macromolecular ligands for CdSe-ZnS core-shell quantum dots incorporating multiple thiol groups, poly(ethylene glycol) chains, and either carboxylic acids or primary amines along a common poly(methacrylate) backbone. The thiol groups encourage the adsorption of these macromolecular constructs on the ZnS shell of the nanoparticles, and the poly(ethylene glycol) chains impose hydrophilic character on the resulting assemblies. Indeed, the coated quantum dots are readily soluble in water and are stable under these conditions for months over a broad pH range (4.0-12.0) and even in the presence of large salt concentrations. In addition, these nanoparticles have relatively small hydrodynamic diameters (17-30 nm) and good quantum yields (0.3-0.4). Furthermore, the pendant carboxylic acids or primary amines of the macromolecular ligands can be exploited to modify the quantum dots after the adsorption of the polymers on their surface. For example, boron dipyrromethene dyes can be connected to the hydrophilic quantum dots on the basis of amide bond formation to encourage the transfer of energy from the luminescent CdSe core to the organic dyes. Our hydrophilic nanoparticles can also cross the membrane of Chinese hamster ovarian cells and accumulate in the cytosol with limited nuclear localization. Moreover, the internalized quantum dots are not cytotoxic and have essentially no influence on cell viability. Thus, our strategy for the preparation of biocompatible quantum dots can evolve into the development of valuable luminescent probes with nanoscaled dimensions and optimal photophysical properties for a diversity of biomedical applications.
    Langmuir 05/2010; 26(13):11503-11. · 4.38 Impact Factor
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    ABSTRACT: CdSe/ZnS quantum dots (QD) have been surface functionalised with mercaptoaniline and N-(o-methoxyphenyl)aza-15-crown-5 receptors, the former serving as a receptor for protons with the latter serving as a receptor for sodium ions. In conditions of low protons and sodium ions the QD fluorescence was quenched by a photoinduced electron transfer (PET) process from the receptors to the excited QD. The simultaneous addition of both protons and sodium ions, however, restored the QD emission while the independent addition of either ion had no effect. Thus, the conditions of a two input AND molecular logic gate were satified with protons and sodium ions as inputs and 560 nm QD fluorescence as output.
    Sensors and Actuators B: Chemical. 01/2010;
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    ABSTRACT: Polymer 1, a poly(olefin) with pendant Schiff base units is prepared by reacting poly(allylamine) and 2-hydroxynapthaldehyde in methanol. The optical properties of 1 are investigated in THF:H2O (9:1) solvent system buffered at pH 7.0±0.1 using HEPES. When tested against a range of physiological and environmentally relevant cations 1 displays selectivity for Ag+ from changes in the UV–vis spectra with linearity established in the range of 10–60μM. The addition of Ag+ to a solution of 1 also causes a colour change from colourless to dark yellow meaning Ag+ is also detectable by the naked eye. In contrast, selectivity is observed for Mn2+ from changes in the emission spectra again with good linearity observed in the range of 0–50nM. This is the first reported polymeric sensor capable of detecting both Ag+ and Mn2+ using two different detection modes.
    Tetrahedron Letters 07/2009; · 2.40 Impact Factor

Publication Stats

425 Citations
155.85 Total Impact Points


  • 2010–2014
    • University of Ulster
      • • School of Biomedical Sciences
      • • School of Pharmacy and Pharmaceutical Science
      Aontroim, N Ireland, United Kingdom
  • 2009–2012
    • University of Miami
      • Department of Chemistry
      Coral Gables, FL, United States
  • 2011
    • Universidad de Cádiz
      • Departamento de Química Analítica
      Cadiz, Andalusia, Spain
  • 2008–2009
    • The Robert Gordon University
      • School of Pharmacy and Life Sciences
      Aberdeen, SCT, United Kingdom
  • 2004–2008
    • Queen's University Belfast
      • School of Chemistry and Chemical Engineering
      Béal Feirste, N Ireland, United Kingdom
    • Queen's University
      Kingston, Ontario, Canada