Remarkable Enhancement Of Emission Intensity Research Articles

Colorimetric and fluorimetric detection of fluoride ion using thiazole derived receptor

Thiazole based receptor 3, was designed and synthesized by condensation reactionof5–chlorosalicylaldehyde with 4-(4-phenylthiazol-2-yl)semicarbazide for colorimetric and fluorimetric detection of fluoride ion. Receptor 3 was characterized by 1H NMR, 13C NMR, and HRMS, and shows absorption in 280–400 nm region with emission at 442 nm in tetrahydrofuran (THF). Addition of fluoride ion to the THF solution of receptor 3 results in color change from colorless to yellow with significant change in UV–Visible absorption. The receptor–anion interaction occurs via hydrogen bonding followed by deprotonation which results in large bathochromic shift in absorption spectra and naked-eye color change. The colorimetric changes show selective response for fluoride ions over other anions. Fluorescence studies exhibit remarkable enhancement in emission intensity upon addition of fluoride ion with a limit of detection (LOD) of 8.6 nM. The 1H NMR titration studies exhibit deprotonation of the –OH proton of the salicylaldimine moiety resulting significant colorimetric and fluorimetric changes.

Fabricating D-A type AIE luminogen into film sensor for turn-on detection of methanol vapour

Advances in sensor technique benefit considerably from the donor–acceptor (DA) type aggregation-induced emission (AIE) systems, owing to their sensitive ICT emission together with emission controllability at solid state. In this report, we present a tailor-made D–A type AIE luminogen, DBABN, and study its AIE and ICT natures. Our systematic investigation has observed remarkable enhancement in emission intensity together with hypsochromic shift in emission wavelength in response to methanol vapor, and further confirmed its high selectivity. As supported by DFT calculations, including electrostatic potential map and molecular orbital amplitude plots, hydrogen-bonding between DBABN and methanol molecule would be formed and further stabilized by electrostatic attraction, which weakens the ICT but simultaneously reinforces the AIE. Therefore the mechanism for the stimuli-responsive emission is illustrated. Utilizing such property, a film sensor for methanol was developed, with a detection limit down to 9.65 ppm. Furthermore, the signal can be easily visualized.

Validation of specific cation partitioning to molecular surfaces using fluorescent carbon quantum dots

Specific salt effects are significantly involved in the aqueous colloidal solutions of proteins, nucleic acids, surfactants and nanomaterials. The mechanism of such effects has been systematically investigated here with a simple nanomaterial-based model system. Water-soluble fluorescent carbon quantum dots were synthesized for this purpose. This research work highlights the unique advantage offered by fluorescent carbon quantum dots to be utilized as a sensing probe for the detection of selective ion interactions based on their fluorescence turn-on response. Synthesized carbon quantum dots exhibited surface potential dependent strong fluorescence emission. It was further found that the functional group chemistry on the carbon quantum dot surface plays a crucial role in the ion partitioning. A remarkable enhancement of emission intensity observed in the presence of metal cations can be attributed to their relative tendency to form ion-pairs with the nanomaterial surface functionalities. Carbon quantum dots with deprotonated carboxylic groups on their surface showed a stronger affinity for strongly hydrated cations as compared to weakly hydrated cations. Uncharged yet polar nanomaterial surface, however, showed no selectivity towards different ions.

Dopamine integrated B, N, S doped CQD nanoprobe for rapid and selective detection of fluoride ion

A simple fluorescence turn on sensor for the detection of fluoride ion in totally aqueous medium has been developed by integrating boronic acid functionalized carbon quantum dot (BNSCQD) and dopamine. The intense emission of BNSCQD is quenched due to photoelectron transfer (PET) from BNSCQD to dopamine. A remarkable enhancement of emission intensity in presence of F− is achieved due to high reactivity of F− towards boron centre of the BNSCQD-dopamine complex and hence restricting PET between BNSCQD and dopamine. The LOD of our sensor is 0.7 pM. The sensor is not cytotoxic and could be utilised to trace fluoride level changes in human serum as well as in living cells.

A highly selective dual-channel Cu2+ and Al3+ chemodosimeter in aqueous systems: Sensing in living cells and microfluidic flows

The design and development of fluorescent chemosensors have recently been the focus of considerable attention for the sensitive and specific detection of environmentally and biologically relevant metal ions in aqueous solutions and in living cells. Herein, we report photophysical results for a 1H-pyrrole-2-carboxaldehyde-substituted rhodamine 6G derivative (RCS) that possesses specific binding affinity toward Al3+ and Cu2+ at micromolar concentration levels. In an N,N-dimethylformamide (DMF) and water (v/v=2/8) medium, the RCS chemosensor exhibits a substantially enhanced absorbance intensity at 532nm and a color change from colorless to pink for Cu2+; it also exhibits significant “off–on” fluorescence at 557nm, accompanied by a color change from colorless to fluorescent-yellow upon binding to Al3+. The RCS sensor exhibits extremely high fluorescence enhancement upon complexation with Al3+, and it can be used as a “naked eye” sensor. Through fluorescence titration at 557nm, we confirmed that RCS exhibits a fluorescence response with a remarkable enhancement in emission intensity resulting from the complexation between RCS and Al3+, whereas no emission appeared in the case of competitive metal ions (Cu2+, Al3+, Li+, Na+, K+, Cs+, Mg2+, Ca2+, Fe2+, Co2+, Ag+, Zn2+, Cd2+, Hg2+ and Pb2+) in a DMF and water (v/v=2/8) solution. The reversible ring-opening mechanism of the rhodamine spirolactam induced by Al3+/Cu2+ binding and the 1:1 stoichiometric structure between RCS and Al3+ were adequately supported by Job-plot evaluation, optical titration and FT-IR analysis. The lowest detection limit for Al3+ is 3.20×106M−1 in a DMF and water (v/v=2/8) solution. Al3+-induced chelation-enhanced fluorescence (CHEF) is associated with spirolactam ring opening of the rhodamine unit. Finally, RCS was successfully applied for the bio-imaging of Al3+ in living HeLa cells and for fluorescence imaging of a microfluidic system.

A turn-on fluorescent solid-sensor for Hg(II) detection.

A rhodamine organosilane derivative (Rh-UTES) has been obtained by one-pot synthesis. The chemical structure of Rh-UTES was confirmed by nuclear magnetic resonance (NMR) and infrared (FTIR) techniques. To obtain an inorganic-organic hybrid sensor, Rh-UTES was covalently immobilized on a porous silicon microcavity (PSiMc) via triethoxysilane groups. The attachment of the organic derivative into PSiMc was confirmed by FTIR, specular reflectance, and scanning electron microscopy (SEM). The optical performance of Rh-UTES receptor for Hg2+ detection was investigated by fluorescent spectroscopy and microscopy. Upon the addition of increasing amounts of Hg2+ ions, a remarkable enhancement in emission intensity was produced in both systems. In the solid phase, an increase of integrated fluorescent emission of 0.12- and 0.15-fold after Hg2+ receptor coordination was observed. The light harvesting capability of PSiMc devices allowed obtaining an enhanced fluorescent emission after Rh-UTES immobilization (277-fold). The fluorescence microscopy of hybrid PSiMc sensor provided an optical qualitative test for Hg2+ detection.

222 nm single‐peaked deep‐UV LED with thin AlGaN quantum well layers

AbstractWe fabricated 222 nm AlGaN multi‐quantum well (MQW) deep‐ultraviolet (DUV) light emitting diode (LED) on high quality AlN buffers grown by ammonia (NH3) pulse‐flow multilayer growth method on sapphire substrate. We obtained remarkable enhancement of emission intensity of 220 nm‐band DUV LED by introducing thin (<1.6 nm) quantum well. We realized a single peaked operation of a 222 nm DUV AlGaN MQW LED under pulsed current injection, which is the shortest wavelength of AlGaN LED on sapphire substrate. The maximum output power and external quantum efficiency of 222 nm AlGaN MQW LED were 14 μW and 0.003%, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)