Quantum dot to quantum dot Förster resonance energy transfer: engineering materials for visual color change sensing

Resonant energy transfer between rare earth atomic layers in nanolaminate films

Förster resonant energy transfer between atoms separated at a distance of a few nanometers has strong relevance to different properties of matter. In this work, the resonant energy transfer rate is derived from the electric potential in a system with one dipole interacting with a separated 2D plane of dipoles. It shows an R-² (R: distance between dipole and 2D plane of dipoles) dependency on the distance of dipole layers, which is different from previous theoretical evaluations with an R-⁴ dependency. The electroluminescence (EL) properties are studied in different rare earth (Re: Tm, Tb, Ho, Yb, Er) distributed single atomic layer doped Al₂O₃ nanolaminates prepared by atomic layer deposition, in which the distance between single atomic layers of Re³⁺ is modulated at the atomic scale. Our theoretical results are consistent with the changes of EL intensity and decay time with the distance between the single atomic rare earth doping layers. This result is crucial for increasing the accuracy in biosensing and design of photonic materials.

The quantum dot vs. organic dye conundrum for ratiometric FRET-based biosensors: which one would you chose?

Förster resonance energy transfer (FRET) is a widely used and ideal transduction modality for fluorescent based biosensors as it offers high signal to noise with a visibly detectable signal. While intense efforts are ongoing to improve the limit of detection and dynamic range of biosensors based on biomolecule optimization, the selection of and relative location of the dye remains understudied. Herein, we describe a combined experimental and computational study to systematically compare the nature of the dye, i.e., organic fluorophore (Cy5 or Texas Red) vs. inorganic nanoparticle (QD), and the position of the FRET donor or acceptor on the biomolecular components. Using a recently discovered transcription factor (TF)-deoxyribonucleic acid (DNA) biosensor for progesterone, we examine four different biosensor configurations and report the quantum yield, lifetime, FRET efficiency, IC50, and limit of detection. Fitting the computational models to the empirical data identifies key molecular parameters driving sensor performance in each biosensor configuration. Finally, we provide a set of design parameters to enable one to select the fluorophore system for future intermolecular biosensors using FRET-based conformational regulation in in vitro assays and new diagnostic devices.

Molecularly imprinted electrochemiluminescence sensor based on ZIF-8 doped with CdSe quantum dots for the detection of trace estriol

A composite of the metal-organic framework compound ZIF-8 doped with CdSe quantum dots (QDs) with sensitive and stable luminescence was synthesized, and a molecularly imprinted electrochemiluminescence (ECL) sensor was constructed on the basis of this composite. The ZIF-8@CdSe molecularly imprinted ECL sensor combines the high sensitivity of ECL and the high selectivity of molecular imprinting to realize the sensitive and specific detection of estriol. CdSe QDs and gold nanoparticles were encapsulated within ZIF-8 to obtain the ZIF-8@CdSe QDs/GNP (ZIF@CdSe/GNP) composite. Subsequently, the GNPs were further loaded on the surface of this composite to obtain the GNP/ZIF@CdSe/GNP composite. L-cysteine was used to immobilize the GNP/ZIF@CdSe/GNP composite on the surface of a gold electrode to obtain the GNP/ZIF@CdSe/GNP-modified gold electrode. A molecularly imprinted polymer (MIP) film was prepared on the surface of the modified electrode via electropolymerization with o-phenylenediamine as the functional monomer and estriol as the template molecule. After elution, estriol could be specifically recognized by the cavities. The re-adsoption of estriol by the MIP can prevent the coreactant from reaching the electrode surface through the cavities, thereby weakening ECL. A good linear relationship existed between the ∆ECL and lg C of estriol concentrations of 1 × 10^-14 - 1 × 10^-9 mol·L^-1 . The detection limit was as low as 8.9 × 10^-16 mol·L^-1 . The sensor was applied in the determination of estriol in serum samples with a recovery of 97.0 % - 102 %.

Quantum dots based sensitive nanosensors for detection of antibiotics in natural products: A review

Residual antibiotics in food products originated from administration of the antibiotics to animals may be accumulated through food metabolism in the human body and endanger safety and health. Thus, developing a prompt and accurate way for detection of antibiotics is a crucial issue. The zero-dimensional fluorescent probes including metals based, carbon and graphene quantum dots (QDs), are highly sensitive materials to use for the detection of a wide range of antibiotics in natural products. These QDs demonstrate unique optical properties like tunable photoluminescence (PL) and excitation-wavelength dependent emission. This study investigates the trends related to carbon and metal based QDs preparation and modification, and their diverse detection application. We discuss the performance of QDs based sensors application in various detection systems such as photoluminescence, photoelectrochemical, chemiluminescence, electrochemiluminescence, colorimetric, as well as describing their working principles in several samples. The detecting mechanism of a QDs-based sensor is dependent on its properties and specific interactions with particular antibiotics. This review also tries to describe environmental application and future perspective of QDs for antibiotics detection.

Two-photon absorption enhancement for organic acceptor molecules with QD antennas

The photophysics of an inorganic/organic hybrid system was studied by time-resolved optical spectroscopy, focusing on the goal of increasing the two-photon efficiency of photoresponsive systems. The hybrid system consists of CdS/ZnS core/shell quantum dots (QDs) as energy donor and coumarin derivatives as energy acceptor molecules. The spectral overlap of QD emission and coumarin 343 absorption promotes a Förster resonance energy tranfer (FRET) mechanism leading to a FRET efficiency up to nearly 90%. Additionally, time-correlated single photon counting showed a faster fluorescence decay while acceptor molecules were attached to the QD surface. Femtosecond transient absorption measurements demonstrated an ultrafast FRET reaction. Importantly, FRET was observed also after two-photon excitation of the QDs indicating that the chosen QDs can act as two-photon antennas.

The Peptide Functionalized Inorganic Nanoparticles for Cancer-Related Bioanalytical and Biomedical Applications

In order to improve their bioapplications, inorganic nanoparticles (NPs) are usually functionalized with specific biomolecules. Peptides with short amino acid sequences have attracted great attention in the NP functionalization since they are easy to be synthesized on a large scale by the automatic synthesizer and can integrate various functionalities including specific biorecognition and therapeutic function into one sequence. Conjugation of peptides with NPs can generate novel theranostic/drug delivery nanosystems with active tumor targeting ability and efficient nanosensing platforms for sensitive detection of various analytes, such as heavy metallic ions and biomarkers. Massive studies demonstrate that applications of the peptide-NP bioconjugates can help to achieve the precise diagnosis and therapy of diseases. In particular, the peptide-NP bioconjugates show tremendous potential for development of effective anti-tumor nanomedicines. This review provides an overview of the effects of properties of peptide functionalized NPs on precise diagnostics and therapy of cancers through summarizing the recent publications on the applications of peptide-NP bioconjugates for biomarkers (antigens and enzymes) and carcinogens (e.g., heavy metallic ions) detection, drug delivery, and imaging-guided therapy. The current challenges and future prospects of the subject are also discussed.

Engineering Brightness Matched Indium Phosphide Quantum Dots

The size-dependent optoelectronic properties of semiconductor nanocrystals quantum dots (QDs) are hugely beneficial for color tunability but induce an inherent relative PL brightness mismatch in QDs emitting different colors, as larger emitters absorb more incident photons than smaller particles. Here, we examine the effect of core composition, shell composition, and shell thickness on optical properties including high energy absorption, quantum yield (QY), and the relative brightness of InP/ZnS and InP/ZnSe core/shell and InP/ZnSe/ZnS core/shell/shell QDs at different excitation wavelengths. Our analysis reveals that the presence of an intermediate ZnSe shell changes the wavelength of enhanced absorption onset and leads to highly excitation wavelength dependent QYs. Switching from commercial CdSe/ZnS to InP/ZnS reduces the brightness-mismatch between green and red emitters from 33- to 5-fold. Incorporating a 4-monolayer thick optically absorbing ZnSe shell into the QD heterostructure and heating the QDs in a solution of zinc oleate and trioctylphosphine produces InP/ZnSe/ZnS QDs that are ~10-fold brighter than their InP/ZnS counterparts. In contrast to CdSe/CdS/ZnS core/shell/shell QDs, which only photoluminesce at red wavelengths with thicker CdS shells due to their Quasi-Type II bandstructure, Type I InP/ZnSe/ZnS QDs are uniquely suited to creating a rainbow of visible-emitting, brightness matched emitters. By tailoring the thickness of the intermediate ZnSe shell, heavy metal-free, brightness-matched green and red emitters are produced. This study highlights the ability to overcome the inherent brightness mismatch seen in QDs through concerted materials design of heterostructured core/shell InP-based QDs.