Azamacrocycle Activated Quantum Dot for Zinc Ion Detection

Abstract

A new fluorescent nanosensor family for Zn (2+) determination is reported based on azamacrocycle derivatization of CdSe/ZnS core/shell quantum dot nanoparticles. They are the first zinc ion sensors using QD nanoparticles in a host-guest and receptor-fluorophore system. Three azamacrocycles are demonstrated as receptors: TACN (1,4,7-triazacyclononane), cyclen (1,4,7,10-tetraazacyclododecane), and cyclam (1,4,8,11-tetraazacyclotetradecane). Azamacrocycles conjugated to QDs via an amide link interact directly with one of the photoinduced QD charge carriers, probably transferring the hole in the QD to the azamacrocycle, thereby disrupting the radiative recombination process. When zinc ion enters the aza-crown, the lone pair electrons of the nitrogen atom become involved in the coordination and the energy level is no longer available for the hole-transfer mechanism, switching on the QD emission and a dramatic increase of the fluorescence intensity results, allowing the detection of low concentrations of zinc ions. Using this operating principle, three zinc ion sensors based on CdSe-ZnS core-shell QD nanoparticles showed a very good linearity in the range 5-500 microM, with detection limits lower than 2.4 microM and RSDs approximately 3% ( n = 10). In addition, the versatility of the sensors was demonstrated, since different sizes (and colors) of QDs can be employed and will respond to zinc in a similar way. In a study of interferences, the zinc-sensitive QDs showed good selectivity in comparison with other physiologically important cations and other transition metals tested. The results from fetal calf serum and samples mimicking physiological conditions suggested very good applicability in the determination of zinc ion in physiological samples.

Single molecule quantum-confined Stark effect measurements of semiconductor nanoparticles at room temperature

“…As a result, QDs and NRs have been increasingly used as local probes of their nanoscale environment. Examples include sensing of chemical properties such as pH, 16 anion, 17 and ion detection 18 and physical properties such as light intensity, 19 temperature, 20 stress, 21 and surface charge. 22 The utilization of QDs and NRs for local electric field (F) sensing is one such additional interesting proposition.…”

Ion and pH Sensing with Colloidal Nanoparticles: Influence of Surface Charge on Sensing and Colloidal Properties

“…Specific binding of ions to chelators on the surface of quantum dots can directly quench their fluorescence upon generation of surface states. [10,23,24] Alternatively, ion binding can lead to a conformation change of the chelator. This can be detected via a quencher attached to the chelator which upon conformation change of the chelator is brought into proximity of the quantum dot surface and thus leads to reduction in fluorescence.…”

Effect of Surface Modification on Semiconductor Nanocrystal Fluorescence Lifetime

“…[12][13][14] Indeed, a new and increasingly growing field of research is the development of QD-based nanosensors. A large number of these sensing applications use fluorescence resonance energy transfer (FRET), [15][16][17] charge transfer [18][19][20] or other interactions occurring at the QD surface for the development of nanoprobes. Most of these proposed nanoprobes are based on changes in the emission intensity upon reaction or interaction with the target molecule.…”

“…For example, target affinity and sensitivity of nanosensors [32] can be enhanced by attaching several receptor molecules that react with the corresponding analyte. [18,19] The immobilisation of a large number of enzymes on the surface is also an advantage for the development of biosensors in which the product of an enzymatic reaction may disturb the luminescent properties of the QD. [33] Because the photoluminescence of QDs arises from the recombination of the exciton, all changes in charge or composition on the surface and environment of QDs could affect the efficiency of core electron-hole recombination, and consequently, the luminescence efficiency, fluorescence decays and dynamics.…”