Susan J. Quinn

Lanthanide Luminescent Displacement Assays : The Sensing of Phosphate Anions Using Eu(III)-Cyclen-Conjugated Gold Nanoparticles in Aqueous Solution

1.Eu, a cyclen based Eu(III)-thiol conjugate, was incorporated onto the surface of water-soluble gold nanoparticles to give AuNP-1.Eu. The self-assembly between AuNP-1.Eu and the antenna 2 resulted in the formation of the highly luminescent lanthanide system, AuNP-1.Eu-2, at pH 7.4. The sensing of flavin monophosphate 3 is demonstrated, whereby 3 displaced the antenna 2 in AuNP-1.Eu-2, resulting in the formation of AuNP-1.Eu-3 and quenching of the Eu(III) emission.

Ordered DNA Wrapping Switches on Luminescence in Single-Walled Nanotube Dispersions

An extensive study of the time dependence of DNA wrapping in single-walled nanotube (SWNT) dispersions has been carried out, revealing a number of unusual phenomena. SWNTs were dispersed in water with salmon testes DNA and monitored over a three-month period. Between 20 and 50 days after the sample was first prepared, the SWNT photoluminescence (PL) intensity was observed to increase by a factor of 50. This increase was accompanied by a considerable sharpening of the van Hove absorption peaks. High-resolution transmission electron microscopy (HRTEM) images showed the progressive formation of a coating of DNA on the walls of the nanotubes over the three-month period. HRTEM and circular dichroism spectroscopy studies showed that the improvement in both the NIR PL intensity and the van Hove absorption peaks coincided with the completion of a monolayer coating of DNA on the SWNT walls. HRTEM images clearly showed the DNA wrapping helically around the SWNTs in a surprisingly ordered fashion. We suggest that the initial quenching of NIR photoluminescence and broadening of absorption peaks is related to the presence of protonated surface oxides on the nanotubes. The presence of an ordered DNA coating on the nanotube walls mediates both deprotonation and removal of the surface oxides. An extensive DNA coating is required to substantially restore the photoluminescence, and thus, the luminescence switch-on and subsequent saturation indicate the completion of the DNA-wrapping process. The temperature dependence of the PL switch-on, and thus of the wrapping process, was investigated by measuring as functions of temperature both the time before PL switch-on and the time required for the PL intensity to saturate. This allowed the calculation of the activation energies for both the process preceding PL switch-on and the process limiting the rise of PL intensity, which were found to be 31 and 41 kJ mol (-1), respectively. The associated entropies of activation were -263 and -225 J mol (-1) K (-1), respectively. These negative activation entropies suggest that the rate-limiting step is characterized by a change in the system from a less-ordered to a more-ordered state, consistent with the formation of an ordered DNA coating.

Mixed f―d Coordination Complexes as Dual Visible- and Near-Infrared-Emitting Probes for Targeting DNA

A new family of mixed-lanthanide (Yb(III) and Nd(III)) transition-metal (f-d) cyclen-Ru(II)(phen)(3) (phen = 1,10-phenanthroline) complexes were synthesized as dual visible- and near-infrared (NIR)-emitting DNA probes/sensors. Significant changes were seen in both the Ru(II) visible and the Yb(III)-centered NIR emission, which was switched off upon binding to DNA at pH 7.4. In contrast, no changes were seen in the Nd(III) emission of the analogue f-d conjugate.

Cellular uptake mediated off/on responsive near-infrared fluorescent nanoparticles.

Fluorescence imaging, utilizing molecular fluorophores, often acts as a central tool for the investigation of fundamental biological processes and offers huge future potential for human imaging coupled to therapeutic procedures. An often encountered limitation with fluorescence imaging is the difficulty in discriminating nonspecific background fluorophore emission from a fluorophore localized at a specific region of interest. This limits imaging to individual time points at which background fluorescence has been minimized. It would be of significant advantage if the fluorescence output could be modulated from off to on in response to specific biological events as this would permit imaging of such events in real time without background interference. Here we report our approach to achieve this for the most fundamental of cellular processes, i.e. endocytosis. We describe a new near-infrared off to on fluorescence switchable nanoparticle construct that is capable of switching its fluorescence on following cellular uptake but remains switched off in extracellular environments. This permits continuous real-time imaging of the uptake process as extracellular particles are nonfluorescent. The principles behind the fluorescence off/on switch can be understood by encapsulation of particles in cellular organelles which effect a microenvironmental change establishing a fluorescence signal.

Synthesis and spectroscopic studies of chiral CdSe quantum dots

Using microwave irradiation, water soluble, optically active, penicillamine (Pen) capped CdSe nanocrystals with broad spectral distribution (430–780 nm) of photoluminescence have been produced and studied by a range of instrumental techniques including absorption, circular dichroism and both steady state and time resolved photoluminescence spectroscopy. The photoluminescence of these nanocrystals is attributed to emission from surface defect states. The decay of the excited state in the nanosecond region, which can be analysed as a triple exponential, depends strongly on the emission wavelength selected, but only weakly on the excitation wavelength.

Lanthanide luminescent gold nanoparticles: pH-driven self-assembly formation between Eu(III)-cyclen conjugated AuNPs and sensitising β-diketonate antenna in water

The formation of a self-assembly between water soluble gold nanoparticles AuNP-1.Eu, functionalised with a heptadentate macrocyclic Eu(III) cyclen conjugate via an alkyl thiol spacer, and a naphthalene β-diketone antenna was investigated as a function of pH in water. In the study, the changes in the absorption spectra of the antenna and the gold surface plasmon resonance band, the fluorescence and the delayed Eu(III) emission of the self-assembly were all monitored. We demonstrate that the Eu(III) emission arising from the self-assembly formation on AuNP is significantly modulated as a function of pH, where within the physiological pH range, the emission is ‘switched on’ and that a direct connection can be made between theses changes and the quenching in the antenna as a function of pH.

Picosecond Transient Infrared Study of the Ultrafast Deactivation Processes of Electronically Excited B-DNA and Z-DNA Forms of [poly(dG-dC)]2†

Unravelling the ultrafast processes within DNA is a challenge that continues to exploit the boundaries of both spectroscopic and computational capabilities. However, such studies are essential for the understanding of the nature and dynamics of the UV-activated processes that precede DNA damage and lead to mutagenesis and ultimately cause a number of diseases. Considerable effort has focused on the photophysics and photochemistry of the individual base components which have very short electronically excited singlet state lifetimes (< 1 ps). In contrast, UV excitation of the polynucleotide systems produces additional species that have much longer lifetimes, 4] which is currently a main topic of scientific interest and debate. Questions remain as to whether the electronic excited states of these polymeric forms of DNA are localized on a single base or delocalized over a number of bases. Furthermore, the structural features of polymeric DNA raise a number of additional questions, such as their influence on the excited-state properties and relaxation dynamics of base-stacking interactions, hydrogen bonding, hydration, and conformation. The advantages of picosecond time-resolved infrared spectroscopy (ps-TRIR) are that it can yield structural details about transient species and also that it allows the ground-state depletion to be directly monitored. DNA is only weakly emissive and excited-state decay occurs predominantly through nonradiative channels, thus making ps-TRIR an ideal tool for DNA investigations. ps-TRIR also provides information about such dark processes, which are difficult to observe by the traditional transient absorption and not detectable by transient fluorescence techniques. For these reasons, ps-TRIR has recently been used to study the photodynamics and photoreactions of mononucleotides and polynucleotide DNA. By using ps-TRIR, we have identified a number of processes following direct excitation at 267 nm. For example, the cooling of the vibrationally hot ground state (2–4 ps) of mononucleotides was observed. Direct spectroscopic evidence of a longer-lived state (34 ps) in 5’-dCMP was assigned, partially on the basis of the IR band position, to the nNp* dark state. [5] The participation of this latter state in the relaxation dynamics was predicted by computational work and inferred from transient absorption work by Hare et al. We have also studied G-rich polynucleotides that are known to participate in tetrad stacking formation. In addition, the photoionization of the B form of [poly(dG-dC)]2 by direct excitation at 200 nm has been investigated, and resulted in a structural fingerprint to identify DNA damage. The relaxation processes and electron transfer from DNA to an intercalated metal complex excited at 400 nm has also been reported. Herein, we focus on the ultrafast dynamics of doublestranded poly(dG-dC). This is interesting for a number of reasons. Firstly, the steady-state absorption of the G and C bases in the polymeric form indicates the presence of electronic interactions between the bases, which in turn alter the excited state dynamics from that of the parent bases. It was recently shown that the excited states of the bases in [poly(dG-dC)]2 decay at rates faster than those observed for the individual nucleotides, with a particular role ascribed to charge-transfer states, a process that is predicted to be followed by rapid proton transfer between the G and C units. Secondly, if, as predicted, proton transfer acts to modulate the decay of locally excited (LE) states, then the characteristic IR signatures of the deprotonated guanine and protonated cytosine products should be detectable by psTRIR. Thirdly, [poly(dG-dC)]2 can adopt the unusual lefthanded Z-DNA structure. Thus a comparison of how the base stacking arrangements in the structurally distinct righthanded Band left-handed Z-DNA forms influences the photophysical processes of the G–C base pairs is possible. Finally, and in particular, the recent characterization of a nNp* dark state for 5’-dCMP, with a strong IR identifiable transient band at 1574 cm 1 poses questions as to the possible role of this state in C-containing polynucleotide chemistry. The transient IR spectra for B-form double-stranded [poly(dG-dC)]2 show strong bleaching and weaker transient features (Figure 1a). The ground-state IR spectra of the individual bases can be considered to have three regions: the carbonyl stretching region (1640–1700 cm ), where both C and G bases absorb, the G ring region (1550–1600 cm ) and [*] G. W. Doorley, D. A. McGovern, Prof. J. M. Kelly, Dr. S. J. Quinn School of Chemistry, Centre for Synthesis and Chemical Biology Trinity College Dublin, Dublin 2 (Ireland) E-mail: quinnsu@tcd.ie

Understanding the DNA binding of novel non-symmetrical guanidinium/2-aminoimidazolinium derivatives

Biophysical studies have been carried out on a family of asymmetric guanidinium-based diaromatic derivatives to assess their potential as DNA minor groove binding agents. To experimentally assess the binding of these compounds to DNA, solution phase biophysical studies have been performed. Thus, surface plasmon resonance, UV-visible spectroscopy and circular and linear dichroism have been utilized to evaluate binding constants, stoichiometry and mode of binding. In addition, the thermodynamics of the binding process have been determined by using isothermal titration calorimetry. These results show significant DNA binding affinity that correlates with the expected 1 : 1 binding ratio usually observed for minor groove binders. Moreover, a simple computational approach has been devised to assess the potential as DNA binders of this family of compounds.

Incandescent porous carbon microspheres to light up cells: solution phenomena and cellular uptake

Carbon based materials are attractive for biological applications because of their excellent biocompatibility profile. Porous carbons with high specific surface area are particularly interesting because it is possible in principle to leverage their properties to deliver high drug payloads. In this work, porous carbon microspheres with high specific surface area were prepared and studied in solution and in cells. Raman optical tweezer trapping of microspheres, excited at 532 nm, results in graphitization and incandescence in solvents that display poor heat conduction. Fluorescence confocal microscopy imaging was used to demonstrate the uptake of fluorescently labelled microspheres by cells and the ability to leverage their optical absorptivity in order to cause carbon graphitization and cell death.

A comparative picosecond transient infrared study of 1-methylcytosine and 5'-dCMP that sheds further light on the excited states of cytosine derivatives.

The role of N1-substitution in controlling the deactivation processes in photoexcited cytosine derivatives has been explored using picosecond time-resolved IR spectroscopy. The simplest N1-substituted derivative, 1-methylcytosine, exhibits relaxation dynamics similar to the cytosine nucleobase and distinct from the biologically relevant nucleotide and nucleoside analogues, which have longer-lived excited-state intermediates. It is suggested that this is the case because the sugar group either facilitates access to the long-lived (1)n(O)π* state or retards its crossover to the ground state.