Volume 95 Issue 16 | p. 5 | News of The Week
Issue Date: April 17, 2017 | Web Date: April 13, 2017

Photoluminescent lanthanide-based sensor distinguishes solvents

Metal-organic framework materials could provide rapid field analysis of environmental contamination
Department: Science & Technology
News Channels: Organic SCENE, Materials SCENE, Analytical SCENE,
Keywords: chemical sensing, analytical chemistry, metal-organic frameworks, materials
A triphenylphosphine metal-organic framework containing EuIII and TbIII in a 1:1 ratio emits different colors depending on its solvent exposure.
Credit: Chem
Photos of MOF material in dishes glowing red with dioxane, orange with dimethylformamide, green with H2O, and tan with D2O.
A triphenylphosphine metal-organic framework containing EuIII and TbIII in a 1:1 ratio emits different colors depending on its solvent exposure.
Credit: Chem

With the help of a little light, a metal-organic framework (MOF) containing photoluminescent lanthanides can uniquely identify and measure the concentrations of multiple solvents, a research team reports (Chem 2017, DOI: j.chempr.2017.02.010).

Applied to a dipstick, the material could enable rapid identification of environmental contaminants on-site rather than require responders to send samples to a lab. The approach could also solve the tricky analytical problem of determining how much H2O contaminates D2O, an issue for isotopic labeling in biomolecular experiments and calibration for spectroscopic methods such as nuclear magnetic resonance.

Led by University of Texas, Austin, chemistry professor Simon M. Humphrey, the team investigated a MOF composed of tris(p-carboxylato)triphenylphosphine and europium(III), gadolinium(III), and terbium(III). Each lanthanide has a unique emission spectrum: EuIII emits red, GdIII emits ultraviolet, and TbIII emits green light.

But when solvent molecules bind within the MOF, the molecules’ vibrational frequencies quench the lanthanide emissions in a way that’s unique to each solvent-lanthanide combination. The researchers exploited those properties to identify solvents by creating several MOFs with varying ratios of the lanthanides. They exposed each of four MOF varieties to a solvent, excited them at 365 nm, and compared the resulting emission intensity at three wavelengths. The approach allowed the scientists to identify a characteristic fingerprint for each solvent, thereby distinguishing among H2O, D2O, methanol, ethanol, toluene, benzene, and 12 other solvents.

“We were lucky that we stumbled across the right combination of lanthanides to do this,” Humphrey says. He and colleagues created dipstick-like sensors by using spray glue to deposit the MOFs onto glass slides and immersing them in solvents. The researchers could reuse the dipsticks multiple times by heating them to drive off the solvent.

Preliminary data suggest the MOFs also work to selectively detect halogens and heavy metals, Humphrey says.

Distinguishing between H2O and D2O is particularly difficult because the two molecules are so similar. “Using a lanthanide MOF as a sensor to detect a trace amount of H2O in D2O is really fantastic work that not only greatly deepens the research of luminescent lanthanide MOFs but also proposes a new application,” comments Peng Cheng, a chemistry professor at Nankai University.

CORRECTION: This story was updated on April 19, 2017, to correct the spelling of Peng Cheng’s family name.

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
hi (Thu Apr 13 19:02:54 EDT 2017)
The name of Peng Chen is incorrectly spelled.
Jyllian Kemsley (Tue Apr 18 13:12:35 EDT 2017)
@hi - Thank you for commenting! I've requested a correction.
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