Ray C. Mulrooney

Anion sensing with luminescent quantum dots - A modular approach based on the photoinduced electron transfer (PET) mechanism

A CdSe–ZnS quantum dot (QD) has been surface functionalised with 1-(2-mercapto-ethyl)-3-phenyl-thiourea in the fluorophore–spacer–receptor format typical of Photoinduced Electron Transfer (PET) based organic dye sensors. The resulting QD conjugate was tested for selectivity toward the tetrabutylammonium salts of fluoride, chloride, bromide, hydrogen sulfate and acetate. Addition of fluoride, chloride and acetate ions resulted in an approximate 90% quenching of the original fluorescence intensity, while bromide and hydrogen sulfate had almost no effect. The observed quench was attributed to an increase in the reduction potential of the receptor upon anion binding resulting in an increase in PET from the excited QD to the receptor and a concomitant reduction in fluorescence intensity. The selectivity and sensitivity were comparable to an analagous organic dye based sensor where a similar receptor was bound to an anthracene fluorophore. Thus a modular approach is evident where a receptor used in an organic dye based sensor can be adapted and successfully used with QD’s.

Fluorescent Recognition of Potassium and Calcium Ions Using Functionalised CdSe / ZnS Quantum Dots

Schiff base receptor 1a has been synthesised and attached to the surface of preformed CdSe/ZnS Quantum Dots (QDs) to form QD-conjugate 2a. While 1a was determined to be selective for Mg2+, 2a demonstrated selectivity for both K+ and Ca2+ when tested against a range of physiologically and environmentally relevant cations by changes in the fluorescence spectra. Thus, the nanoparticle surface functions as a scaffold for the organisation of receptors enabling semi-selective binding. The fluorescence response was shown to be linear between 15–50 μM for K+ and 2–35 μM for Ca2+. It was also demonstrated that 2a could measure both K+ and / or Ca2+ in solutions containing both ions.

Determination of zinc in aqueous solution using CdSe/ZnS quantum dots functionalised with [carboxymethyl-(4-mercapto-phenyl)-amino]-acetate

CdSe/ZnS quantum dots functionalised with [Carboxymethyl-(4-mercapto-phenyl)-amino]-acetate displayed selectivity for Zn2+ 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.

A new class of fluorescent chemosensors based on the β-aminobisphosphonate receptor

The photophysical properties of a range of fluorescent sensors with β-aminobisphosphonate receptors have been studied. The compounds were designed according to the fluorophore–spacer–receptor format of photoinduced electron transfer-based sensors. The sensors displayed unusual fluorescence intensity–pH profiles that were attributed to a receptor–fluorophore H-bonding interaction that resulted in a quenching of fluorescence. The number of receptors and the nature of the fluorophore were both shown to have an effect on the pH profiles of the sensors. In addition, compound 1 was also shown to be selective for Cu2+ ions, in water at pH 7.4 with sensitivity in the micromolar range.