InP Quantum Dots: Probing the Active Domain of Tau Peptide Using Energy Transfer

Abstract

Aggregation of Tau, a natively unfolded protein, is responsible for tauopathies, a class of neurodegenerative disorders. An active peptide sequence containing 20 amino acids is selected from the Tau microtubule binding region, which includes the essential V306-K311 residue, to monitor the structural change that initiates aggregation at very low concentrations. The synthesis of a peptide sequence is accomplished by employing solid-phase protocols. The active domain of Tau possesses an amino functionality on lysine and free thiol on cysteine. The former end is selectively labeled to rhodamine 101 which is further bound to the InP/ZnS quantum dot surface through the thiol linkage. Efficient resonance energy transfer is observed in its unfolded conformation which is confirmed using various steady state fluorescence techniques. The average distance between the quantum dot core and the chromophore is probed by Förster resonance energy transfer (FRET) as 24.5 ± 0.8 Å. Heparin, a negatively charged glycosaminoglycan, is used for inducing aggregation of the active domain of the Tau peptide. Structural changes in the peptide monomer, on addition of heparin, could be monitored at nanomolar concentrations through the inhibition of energy transfer from quantum dots to rhodamine dye.

Förster Resonance Energy Transfer Regulated Multicolor Photopatterning from Single Quantum Dot Nanohybrid Films

“…A drastic quenching in the photoluminescence (PL) of [+] InP/ZnS QD was observed along with the concomitant formation of a new peak at ∼590 nm (corresponding to the emission of the [−] MC dye), through an isosbestic point (Figure b). This clearly indicates the process of resonance energy transfer from the [+] InP/ZnS QD to the [−] MC dye in the wet agarose film. ,,− Time-resolved PL studies showed a quenching in the lifetime of the [+] InP/ZnS QD from 60 to 15 ns, confirming the process of energy transfer in the QD:::dye agarose wet film (inset of Figure b, Figure S2, and Table S1). ,,− The efficiency and rate of energy transfer in the QD::: dye agarose wet film were estimated to be ∼75% and ∼4.7 × 10 7 s –1 , respectively (Figure S3, Table S2).…”

“…This clearly indicates the process of resonance energy transfer from the [+] InP/ZnS QD to the [−] MC dye in the wet agarose film. ,,− Time-resolved PL studies showed a quenching in the lifetime of the [+] InP/ZnS QD from 60 to 15 ns, confirming the process of energy transfer in the QD:::dye agarose wet film (inset of Figure b, Figure S2, and Table S1). ,,− The efficiency and rate of energy transfer in the QD::: dye agarose wet film were estimated to be ∼75% and ∼4.7 × 10 7 s –1 , respectively (Figure S3, Table S2). Two-photon 2D and 3D confocal images, upon selective excitation of the QD at 800 nm, once again confirm the process of FRET in the QD:::dye agarose wet film (Figure c and Figures S4–S6).…”

How Trap States Affect Charge Carrier Dynamics of CdSe and InP Quantum Dots: Visualization through Complexation with Viologen

“…For example, II–VI semiconductor QDs (e.g., cadmium chalcogenides) are more ionic because of the large difference in the electronegativity between the constituent elements, whereas III–V semiconductors such as InP are more covalent in nature. − The surface states in relatively ionic II–VI QDs remain very shallow, whereas the III–V QDs possess deep surface states because of their covalent character. , For similar sized QDs (∼32 Å), the depth of the trap states in InP is 6.3 kJmol –1 below the conduction band, which is 25 times larger than that of the shallow trap states in II–VI CdSe QDs (0.25 kJ mol –1 ) . The degree of covalency also has a dramatic influence on the exciton radius and thus quantum confinement: III–V QDs are characterized by much larger exciton radius than the more ionic II–VI QDs (e.g., 9.6 nm for InP and 4.6 nm for CdSe). , In contrast to the ionic II–VI QDs, the covalent nature of the InP QDs makes it structurally more robust and relatively nontoxic by preventing the leakage of ions. , By virtue of these properties, the InP QDs have been recently proposed as an environmentally friendly material for energy-transfer applications. − Despite these several favorable characteristics, the use of InP QDs for photovoltaic applications is more rare compared to II–VI QDs , essentially because of a lesser understanding of the trap states of the former one.…”

Multicolor Luminescent Patterning via Photoregulation of Electron and Energy Transfer Processes in Quantum Dots

“…A green emitting InP/ZnS QD was chosen as the donor component, based on the previous reports on their use as efficient donors in both photoinduced electron and energy transfer processes. − One of the major challenges in the present work was the selection of electron and energy acceptor components. The organic fluorophores have to meet the following four conditions to qualify as acceptors for the triad system. The two acceptors should selectively and independently participate in photoinduced electron and energy transfer processes with the InP/ZnS QD. The process of photoinduced electron transfer should dominate the energy transfer to generate a nonluminescent complex, which can act as the black background for further photopatterning. There should be minimal overlap between the absorption spectra of the two acceptors, so that the electron acceptor can be selectively photodegraded. There should be negligible photophysical interactions between the electron and energy acceptors. …”