InP-Bovine Serum Albumin Conjugates as Energy Transfer Probes

Single- and two-photon-induced Förster resonance energy transfer in InP-mCherry bioconjugates

Indium phosphide (InP) quantum dots (QDs) have recently garnered considerable interest in the design of bioprobes due to their non-toxic nature and excellent optical properties. Several attempts for the conjunction of InP QDs with various entities such as organic dyes and dye-labeled proteins have been reported, while that with fluorescent proteins remains largely uncharted. This study reports the development of a Förster resonance energy transfer pair comprising glutathione-capped InP/GaP/ZnS QDs [InP(G)] and the fluorescent protein mCherry. Glutathione on InP(G) undergoes effective bioconjugation with mCherry consisting of a hexahistidine tag, and the nonradiative energy transfer is investigated using steady-state and time-resolved measurements. Selective one-photon excitation of InP(G) in the presence of mCherry shows a decay of the emission of the QDs and a concomitant growth of acceptor emission. Time-resolved investigations prove the nonradiative transfer of energy between InP(G) and mCherry. Furthermore, the scope of two-photon-induced energy transfer between InP(G) and mCherry is investigated by exciting the donor in the optical transparency range. The two-photon absorption is confirmed by the quadratic relationship between the emission intensity and the excitation power. In general, near-infrared excitation provides a path for effective light penetration into the tissues and reduces the photodamage of the sample. The two-photon-induced energy transfer in such assemblies could set the stage for a wide range of biological and optoelectronic applications in the foreseeable future.

Fluorescence Resonance Energy Transfer in a Supramolecular Assembly of Luminescent Silver Nanoclusters and a Cucurbit[8]uril-Based Host-Guest System

The understanding of interactions between organic chromophores and biocompatible luminescent noble metal nanoclusters (NCs) leading to an energy transfer process that has applications in light-harvesting materials is still in its nascent stage. This work describes a photoluminescent supramolecular assembly, made in two stages, employing an energy transfer process between silver (Ag) NCs as the donor and a host-guest system as the acceptor that can find potential applications in diverse fields. Initially, we explored the host-guest chemistry between a cationic guest ethidium bromide and cucurbit[8]uril host to modulate the fluorescence property of the acceptor. The host-guest interactions were characterized by using UV-vis absorption, steady-state and time-resolved spectroscopy, molecular docking, proton ¹H nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and isothermal calorimetry studies. Next, we prepared a series of blue-emitting AgNCs using different templates such as proteins and peptides. We have found that these AgNCs can be employed as a donor in the energy transfer process upon mixing with the above acceptor for emission color tuning. Our in-depth studies also revealed that surface ligands could play a key role in modulating the energy transfer efficiency. Overall, by employing a noncovalent strategy, we have tried to develop Förster resonance energy transfer (FRET) pairs using blue-emitting NCs and a host-guest complex that could find potential applications in constructing advanced sustainable light-harvesting, white light-emitting, and anti-counterfeiting materials.