Concentration-Independent pH Detection with a Luminescent Dimetallic Eu(III)-Based Probe

Abstract

A pH-responsive, luminescent, dimetallic Eu(III)-containing complex has been synthesized and exhibits a unique mechanism of response. The luminescence-decay rate of the complex is slow, due to a lack of water molecules coordinated to the Eu(III) ions. However, the luminescence-decay rate decreases with increasing pH over a biologically relevant range of 4 to 8. Physical characterization and computational analysis suggest that the pH response is due to protonation of a bridging alkoxide at lower pH values. Modulation of the luminescence-decay rate is independent from the concentration of Eu(III), which we expect to be useful in the non-invasive imaging of in vivo pH.

Exceptional Oxygen Sensing Properties of New Blue Light‐Excitable Highly Luminescent Europium(III) and Gadolinium(III) Complexes

“…[22] These complexes are widely applied as labels in various luminescence assays both as free dyes bearing a functional group for conjugation and in the form of dye-doped nanoparticles, [22,23] but application in optical sensors and analyte-sensitive probes is comparably rare. [24][25][26][27] For example, luminescent Eu(III) complexes were applied as optical temperature probes, [27][28][29][30][31] pH indicators, [32][33][34][35][36] fluoroionophores for bicarbonate, [37,38] citrate [39] and lactate [40] and as hydrogen peroxide [41] and nitrogen monooxide probes. [42] Several Eu(III) complexes were applied as luminescent oxygen indicators.…”

Enabling the Triplet of Tetraphenylethene to Sensitize the Excited State of Europium(III) for Protein Detection and Time‐Resolved Luminescence Imaging

“…The complex exhibited an absorption peak at 300 nm ( ε max = 9420 m −1 cm −1 ) and a main emission peak at about 460 nm, which originated from the TPE unit 19, 20. In addition, a very weak emission peak located at approximately 615 nm was considered to be the 5 D 0 → 7 F 2 transition of Eu(III),1, 3 which was due to the energy transfer from the TPE triplet to the metal center (Figure 1A). When the concentration of TPEEu was increased to 100 × 10 −6 m in the solution, the luminescence assigned to the Eu(III) was still very weak (Figure 1A).…”

“…This change of lifetime can be explained by nonradiative deactivation processes upon interaction with OH oscillators from the solvent molecules 1. When TPEEu exists as a free monomer in solution, the water molecules coordinate with Eu(III) and quench its excited state, leading to a faster luminescence‐decay rate ( Scheme 2 ).…”

“…Luminescence probes are widely used for biological assays and imaging in biochemical research and disease diagnosis 1. Because time‐resolved luminescence techniques operate within the time domain and are directed toward the detection of events that occur at much longer timescales (phosphorescence),2 various probes with long emission lifetimes (e.g., phosphorescence and delayed fluorescence) have been reported.…”

“…By correlating this sensitization process with target recognition, researchers have designed numerous luminescent Ln(III)‐complex‐based molecular probes for analytical and biological applications 9, 10, 11, 12, 13, 14, 15. Unfortunately, except for a few probes that exhibit significant luminescence enhancement from an initial low level upon binding10 or reacting11 with targets, many of the Ln(III) complex‐based probes exhibit self‐luminescence, which may result in high background signals 1, 3, 12, 13, 14, 15. In cell cultures, this problem may be avoided by washing the samples to remove unbound probes 15.…”