Luminescent semiconductor quantum dots (QDs) are one of the more popular nanomaterials currently utilized within biological applications. However, what is not widely appreciated is their growing role as versatile energy transfer (ET) donors and acceptors within a similar biological context. The progress made on integrating QDs and ET in biological configurations and applications is reviewed in detail here. The goal is to provide the reader with (1) an appreciation for what QDs are capable of in this context, (2) how this field has grown over a relatively short time span, and, in particular, (3) how QDs are steadily revolutionizing the development of new biosensors along with a myriad of other photonically active nanomaterial-based bioconjugates. An initial discussion of QD materials along with key concepts surrounding their preparation and bioconjugation is provided given the defining role these aspects play in the QDs ability to succeed in subsequent ET applications. The discussion is then divided around...

Energy Transfer with Semiconductor Quantum Dot Bioconjugates: A Versatile Platform for Biosensing, Energy Harvesting, and Other Developing Applications.

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Polymeric Nanoparticles for Drug Delivery.

Adding value to the intrinsic properties of quantum dots (QDs), a strategy to conjugate dyes on the surface of QDs offers new opportunities, since the coupling between QD and dyes can be designed to allow Forster resonance energy transfer (FRET) and/or electron transfer (eT). These processes are accompanied by the change of QD and/or dye fluorescence and subsequent photochemical reactions (e.g., generation of 1 O2 ). Based on the change of fluorescence signals by the interaction with biomolecules, QD-dye conjugates are exploited as biosensors for the detection of pH, O2 , nicotinamide adenine dinucleotide (phosphate), ions, proteases, glutathione, and microRNA. QD-dye conjugates also can be modulated by the irradiation of external light; this concept is demonstrated for fluorescence super-resolution imaging as photoactivatable or photoswitchable probes. When QDs are conjugated with photosensitizing dyes, the QD-dye conjugates can generate 1 O2 in a repetitive manner for better cancer treatment, and can also be available for approaches using two-photon excitation or bioluminescence resonance energy transfer mechanisms for deep tissue imaging. Here, the recent advances in QD-dye conjugates, where FRET or eT produces fluorescence readouts or photochemical reactions, are reviewed. Various QD-dye conjugate systems and their biosensing/imaging and photodynamic therapeutics are summarized.

/pdf/quantum-dot-dye-conjugates-for-biosensing-imaging-and-3lo1i2oz0w.pdf

Quantum Dot-Dye Conjugates for Biosensing, Imaging, and Therapy.

Microcapsules obtained by layer-by-layer assembly provide a good platform for biological analysis owing to their component diversity, multiple binding sites, and controllable wall thickness. Herein, different assembly species were obtained from two-photon dyes and traditional photosensitizers, and further assembled into microcapsules. Fluorescence resonance energy transfer (FRET) was shown to occur between the two-photon dyes and photosensitizers. Confocal laser scanning microscopy (CLSM) with one- and two-photon lasers, fluorescence lifetime imaging microscopy (FLIM), and time-resolved fluorescence spectroscopy were used to analyze the FRET effects in the microcapsules. The FRET efficiency could easily be controlled through changing the assembly sequence. Furthermore, the capsules are phototoxic upon one- or two-photon excitation. These materials are thus expected to be applicable in two-photon-activated photodynamic therapy for deep-tissue treatment.

Multilayer Microcapsules for FRET Analysis and Two-Photon-Activated Photodynamic Therapy.

Today, at the frontier of biomedical research, the need has been clearly established for integrating disease detection and therapeutic function in one single theranostic system. Light-emitting nanoparticles are being intensively investigated to fulfil this demand, by continuously developing nanoparticle systems simultaneously emitting in both the UV/visible (light-triggered release and activation of drugs) and the near-infrared (imaging and tracking) spectral regions. In this work, rare-earth (RE) doped nanoparticles (RENPs) were synthesized via a thermal decomposition process and spectroscopically investigated as potential candidates as all-in-one optical imaging, diagnostic and therapeutic agents. These core/shell/shell nanoparticles (NaGdF4:Er3+,Ho3+,Yb3+/NaGdF4:Nd3+,Yb3+/NaGdF4) are optically excited by heating-free 806 nm light that, aside from minimizing the local thermal load, also allows to obtain a deeper sub-tissue penetration with respect to the still widely used 980 nm light. Moreover, these water-dispersed nanoplatforms offer interesting assets as triggers/probes for biomedical applications, by virtue of a plethora of emission bands (spanning the 380–1600 nm range). Our results pave the way to use these RENPs for UV/visible-triggered photodynamic therapy/drug release, while simultaneously tracking the nanoparticle biodistribution and monitoring their therapeutic action through the near-infrared signal that overlaps with biological transparency windows.

Covering the optical spectrum through collective rare-earth doping of NaGdF4 nanoparticles: 806 and 980 nm excitation routes

A Forster resonance energy transfer (FRET) system of semiconductor quantum dots and porphyrins represents a new promising photosensitizing tool for the photodynamic therapy of cancer. In this work, we demonstrate the ability of a non-covalent complex formed between commercial lipid-coated CdSe/ZnS quantum dots (QD) bearing different terminal groups (carboxyl, amine or non-functionalized) and a second-generation photosensitizer, chlorin e6 (Ce6) to enter living HeLa cells with maintained integrity and perform FRET from two-photon excited QD to bound Ce6 molecules. Spectroscopic changes, the highly efficient FRET, observed upon Ce6 binding to QD, and remarkable stability of the QD–Ce6 complex in different media suggest that Ce6 penetrates inside the lipid coating close to the inorganic core of QD. Two-photon fluorescence lifetime imaging microscopy (FLIM) on living HeLa cells revealed that QD–Ce6 complexes localize within the plasma membrane and intracellular compartments and preserve high FRET efficiency (∼50%). The latter was confirmed by recovery of QD emission lifetime after photobleaching of Ce6. The intracellular distribution pattern and FRET efficiency of QD–Ce6 complexes did not depend on the charge of QD terminal groups. Given the non-covalent nature of the complex, its exceptional stability in cellulo can be explained by a combination of hydrophobic interactions and coordination of carboxyl groups of Ce6 with the ZnS shell of QD. These findings suggest a simple route to the preparation of QD-photosensitizer complexes featuring efficient FRET and high stability in cellulo without using time-consuming conjugation protocols.

/pdf/a-non-covalent-complex-of-quantum-dots-and-chlorin-e6-1rhcm5g19j.pdf

A non-covalent complex of quantum dots and chlorin e6: efficient energy transfer and remarkable stability in living cells revealed by FLIM

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A non-covalent complex of quantum dots and chlorin e6: efficient energy transfer and remarkable stability in living cells revealed by FLIM