Spectroscopic System for Direct Lanthanide Photoluminescence Spectroscopy with Nanomolar Detection Limits

Abstract

A new spectroscopic system for direct photoluminescence of lanthanide ions (Ln(III)) through electronic transitions within the 4f(n) manifold is described. The system is based on an injection seeded frequency tripled (lambda = 355 nm) Nd:YAG pump laser coupled with a master oscillator power oscillator (MOPO). The MOPO delivers an average pulse energy of approximately 60 mJ/pulse, is continuously tunable from 425 to 690 nm (Signal) and 735 to 1800 nm (Idler) with a linewidth of <0.2 cm(-1), and has a pulse duration of 10-12 ns. Aqueous solutions containing two polyaminocarboxylate complexes, ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA), and Ln(3+) aqua ion for several lanthanides including Eu(III), Tb(III), Dy(III), and Sm(III)) are used as steady-state and time-resolved photoluminescence standards. The versatility of the instrument is demonstrated by excitation scans over a broad visible range for aqueous solutions of complexes of Eu(III), Dy(III), Sm(III), and Tb(III). The Eu(III) excitation band ((7)F(o)-->(5)D(o)) is recorded over a range of complex concentrations that are 1000-fold less than reported previously, including Eu(EDTA) (1.00 nM), Eu(DTPA) (1.00 nM), and Eu(III) aqua ion (50.0 nM). Emission spectra are recorded in the visible range for Ln(III) complexes at pH 6.5 and 1.00 mM. Excited-state lifetimes for the standards were constant as a function of concentration from 10.0 nM to 1.00 mM for Eu(EDTA) and Eu(DTPA) and from 100 nM to 1.00 mM for Eu(III) aqua ion. Photoluminescence lifetimes in H(2)O and D(2)O are recorded and used to calculate the number of bound water molecules for all complexes.

Luminescence Resonance Energy Transfer in Heterodinuclear LnIII Complexes for Sensing Biologically Relevant Anions

“…[65] In addition, some deviation from previous experiments is expected, given that pH, ionic strength, Eu 2 complex concentration, and anion concentration are slightly different and this will influence the coordination environment of the Eu III center.…”

“…The error in the D 2 O luminescence lifetimes was assumed to be Յ10 %, as shown previously for luminescence lifetimes measured for many different samples on different days. [65] (2) Absorbance Spectra UV/Vis absorbance spectra were collected for Nd 2 (1), Nd 2 (2), Eu 2 (1), and Eu 2 (2) complexes in the absence of anions at 1.00 and 10.0 mm concentrations of complex. At the concentrations required for these measurements, the complexes with bound anions were not soluble.…”

“…[65] An alteration was made to the previously described MOPO system: the NIR 5107 Hamamatsu PMT was replaced with a R982 Hamamatsu PMT for emission measurements. The 7 F 0 Ǟ 5 D 0 transition of the Eu III cation was scanned between 578 and 581 nm, while the 5 D 0 Ǟ 7 F 2 emission band was monitored at about 617 nm by using a 628 Ϯ 27 nm bandpass filter (Semrock, Inc.).…”

Solution Chemistry of Europium(III) Aqua Ion at Micromolar Concentrations as Probed by Direct Excitation Luminescence Spectroscopy

“…In addition, most of these studies using photoluminescence spectroscopy do not control pH. Our interest in complexation of micromolar concentrations of lanthanide ions to biopolymers in aqueous conditions has led us to reexamine Eu III aqueous solution chemistry by using a new MOPO (master oscillator power oscillator)/laser system, for direct excitation lanthanide photoluminescence [11]. The instrument is tunable over a broad wavelength range and facilitates direct excitation luminescence studies on Eu III complexes at as low as nanomolar concentrations in aqueous solutions.…”

“…5 D 0 excitation peak at pH 6.5 is consistent with multiple species existing under these conditions. Dilute solutions of Eu 3þ ðaqÞ (< 1 mm) at pH 6.5 [11] [16] show an excitation peak at 579.10 nm that is redshifted from that of solutions containing micromolar or greater concentrations of Eu 3þ ðaqÞ (578.74 nm) (Fig. 2).…”