Quantum Dots as Efficient Energy Acceptors in a Time‐Resolved Fluoroimmunoassay

Abstract

Dedicated to Professor Herbert Dreeskamp on the occasion of his 76th birthdayThe last decade has witnessed the emergence of semiconductor nanoparticles as very attractive building blocks for nanotechnology. Spherically or ellipsoidally shaped nanoparticles, also called quantum dots (qdots), display sizedependent optical properties with extremely large absorption cross sections.[1] When appropriately protected from the surrounding media by a covering shell, they display narrow and symmetric emission bands with quantum yields approaching unity in some cases.[2] The inorganic cores of qdots are also more robust than organic dyes or luminescent proteins toward photobleaching. [3,4] Recent accounts have reported on the possibility of derivatizing qdot surfaces, [5] thereby offering a broad scope of opportunities for chemical and biological interactions.[6] These combined features make qdots excellent tools in analytical techniques associated with fluorescence spectroscopy, reaching sensitivity limits going down to the single particle.[4] Qdots display extremely high extinction coefficients over a wide range of wavelengths as a result of the absorption of photons with energies higher than the band gap of the semiconductor material. The resulting excitons (electron-hole pairs) recombine to generate photons with narrow emission bands. These properties make qdots excellent energy donors in fluorescence (or Förster) resonance energy transfer (FRET) experiments, [7] a technique that is ideally suited for events occurring at the nanometer scale, such as numerous biological processes. For instance, a homogeneous maltose sensor has been described in which the maltose concentration can be monitored by the recovery of qdot luminescence concomitant to the displacement of a quencher dye. [8] Importantly, if qdots are to be used as energy acceptors, significant direct excitation may be undesirable as it limits the extent of resonance transfer and results in spurious fluorescence emission. The use of qdots as energy acceptors has proven possible in a few solid-state devices based on semiconductor quantum wells, [9] with smaller-sized qdots, [10] and with a blue-emitting polymer [11] as the energy donor, but very rarely in discrete molecular systems in solution. [12,13] Mattoussi and co-workers explained low energy-transfer efficiency from organic or inorganic donors to the qdot acceptors by the fact that the rate of FRET is much slower than the fast radiative decay rates of the donors. [12] In the present work, we report that CdSe/ZnS core shell qdots are excellent energy acceptors in a time-resolved fluoroimmunoassay system in which a terbium chelate with long-lived luminescence lifetime is the energy donor and the strong biotin-streptavidin interaction is used for the recognition process.The TbL chelate consisted of a terbium cation embedded in a ligand made of two 6-carboxybipyridyl arms organized on a glutamate framework (Figure 1). The terminal carboxylate function of the glutamic residue was activated with the sodium salt of ...

Applications of Nanoparticles in Biology

“…Biotin functionalized quantum dots (QDs) were also used for specific protein binding in a time-resolved fluoroimmunoassay. [29] Another way to specifically bind proteins is through the use of transition metal complexes that can bind with surface-exposed histidines of proteins. [30] Xu et al…”

A mechanism to signal receptor–substrate interactions with luminescent quantum dots

“…In fact, clever assays for the recognition of various analytes are starting to be designed on the basis of energy transfer processes (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). Instead, mechanisms based on electron transfer still remain to be explored (35,36).…”

Relationship Between the Ligand Structure and the Luminescent Properties of Water‐Soluble Lanthanide Complexes Containing Bis(bipyridine) Anionic Arms

“…Melting points were measured by using a Büchi Melting Point 535 apparatus and are uncorrected. 1 H and 13 C NMR spectra were recorded on Bruker AC 200, Avance 300 and Avance 400 spectrometers working at 200, 300 or 400 MHz, respectively. 31 P (162 MHz) spectra were obtained by using the Bruker Avance 400 spectrometer, implemented with internal calibration mode.…”

“…In prior work in the field, we disclosed [11] that the Eu and Tb complexes formed with the octadentate ligand L are very good probes for luminescence microscopy [12] and time-resolved fluoroimmunoassays. [13] Based on a glutamate skeleton functionalised on the amino function by two 6-carboxy-bipyridine arms, this ligand formed complexes with the generic formula [Ln(L)A C H T U N G T R E N N U N G (H 2 O)] upon coordination with lanthanide cations in water. The resulting Eu and Tb complexes are highly luminescent with long-lived luminescence lifetimes (t) despite the presence of a single water molecule in the first coordination sphere of the cations.…”