A dual-emitting quantum dot complex nanoprobe for ratiometric and visual detection of Hg²⁺ and Cu²⁺ ions

Abstract

Ratiometric and visual sensing of Hg2+ and Cu2+ ions by a dual emitting quantum dot complex – following the changes in luminescence color, intensity ratio, chromaticity and hue – is described herein.

Probing How Various Metal Ions Interact with the Surface of QDs: Implication of the Interaction Event on the Photophysics of QDs

“…QDs with suitable surface ligands are expected to be useful for various applications related to electron and energy transfer , sensing, − photocatalysis, and tagging. Among these, designing and development of sensors that have been miniaturized to the nanoscale level can be used for detecting specific target analytes under proper physiological conditions and is an important direction in sensor development research. − While several molecule-based sensor systems are developed to detect specific target analytes, − only very recently, systems based on QDs are exploited for such a purpose.…”

A Ratiometric and Visual Sensing of Phosphate by White Light Emitting Quantum Dot Complex

“…The Qdots displayed emission at 585 nm while WLE QDC showed dual emissions at 585 and 480 nm (Figure B). Notably, the orange emission of WLE QDC at 585 nm originated from electronic transition ( 4 T 1 - 6 A 1 ) of Mn 2+ dopants of Qdots, whereas, the greenish blue emission of WLE QDC at 480 nm originated from the electronic transition of the newly formed surface Zn­(QS) 2 complex. − ,− It is to be noted here that the synchronous contributions of orange emission of Qdots and greenish blue emission of surface Zn­(QS) 2 complex led to the generation of white light from the QDC upon excitation by 335 nm light. The results clearly indicated the formation of Zn­(QS) 2 complex on the surface of Qdots. , The WLE QDC exhibited color chromaticity of (0.33, 0.35) and hue mean value of 99.47, whereas (0.54, 0.44) color chromaticity and 20.66 hue mean value were observed for Qdots (Figure C,D).…”

“…Mn 2+ -doped ZnS Qdots were fabricated using a reported method. , Briefly, to an aqueous mixture of 5.0 mM of zinc acetate dihydrate and 1.0 mM manganese acetate tetrahydrate, 5.0 mM of sodium sulfide was added and the resulting mixture was refluxed for 4 h under constant stirring at 100 °C. The milky white colloidal mixture was centrifuged with a speed of 20 000 rpm for 15 min.…”

“…Ratiometric photoluminescence sensing provides an accurate, and reliable optical detection of disease diagnostics and environmental pollutants. − The reduction of the influence from the fluctuations related to environmental factors, self-calibration and precise quantification make ratiometric luminescent probe as an advanced option for on-site detection and practical utilization compared to single emitting luminescent probe. − Additionally, the ratiometric luminescent probe has the ability to ensure the detection of analyte via the visual color changes, which has not been reported for single emitting luminescent probes. − Thus, development of such probes especially for chemical interaction specific changes are of great value.…”

“…Among others, colloidal quantum dot (Qdot) based luminescent nanoprobes are easy to develop and work efficiently for ratiometric and visual detection of environmental pollutants and molecular disease marker. − For instance, single peak emission based nanocomposite of Mn 2+ -doped ZnS Qdot-Ce 3+ ions detect phosphate in the linear range of 8–320 μM with LOD of 2.71 μM, whereas graphene Qdot-Ce 3+ senses phosphate with LOD of 0.1 μM in the linear range of 0.5–190 μM. , However, as mentioned before, multiple emission based detection is superior to single emission based techniques. , In other words, ratiometric sensor with emissions at a minimum of two different wavelengths would be able to sense analyte (visually and spectroscopically) by selectively quenching or enhancing one emission. Such clear distinction may not be possible with change in emission characteristics based on probes having single wavelength emission. , Recent results suggest that single particle composites of Qdot and inorganic luminescence complex on its surfacedefined as quantum dot complex (QDC)provide new opportunities in visual and ratiometric sensing of neurotransmitter dopamine, reversibly assessing physiological pH in the range of 6.5–10.6 and sensing of heavy metals (like Hg 2+ and Cu 2+ ions). − Thus, it may be possible to use water-soluble and biofriendly QDCthat emits white lightfor ratiometric and visual detection of phosphate. Importantly, QDC has been a preferred important white light emitting (WLE) material for optoelectronic and ratiometric sensing applications, in comparison to other multicomponent based WLE materials due to their ease of aqueous based synthesis, biocompatibity, relatively low toxicity, cost-effectiveness, single component nature, and for possible specific chemical interaction with the analyte. − …”