Photonic Crystal Surface Mode Real-Time Imaging of RAD51 DNA Repair Protein Interaction with the ssDNA Substrate.

Photonic crystals (PCs) are promising tools for label-free sensing in drug discovery screening, diagnostics, and analysis of ligand-receptor interactions. Imaging of PC surface modes has emerged as a novel approach to the detection of multiple binding events at the sensor surface. PC surface modification and decoration with recognition units yield an interface providing the highly sensitive detection of cancer biomarkers, antibodies, and oligonucleotides. The RAD51 protein plays a central role in DNA repair via the homologous recombination pathway. This recombinase is essential for the genome stability and its overexpression is often correlated with aggressive cancer. RAD51 is therefore a potential target in the therapeutic strategy for cancer. Here, we report the designing of a PC-based array sensor for real-time monitoring of oligonucleotide-RAD51 recruitment by means of surface mode imaging and validation of the concept of this approach. Our data demonstrate that the designed biosensor ensures the highly sensitive multiplexed analysis of association-dissociation events and detection of the biomarker of DNA damage using a microfluidic PC array. The obtained results highlight the potential of the developed technique for testing the functionality of candidate drugs, discovering new molecular targets and drug entities. This paves the way to further adaption and bioanalytical use of the biosensor for high-content screening to identify new DNA repair inhibitor drugs targeting the RAD51 nucleoprotein filament or to discover new molecular targets.

Impact of Macrophages on the Interaction of Cetuximab-Functionalized Polyelectrolyte Capsules with EGFR-Expressing Cancer Cells.

Polyelectrolyte capsules (PCs) are a promising tool for anticancer drug delivery and tumor targeting. Surface functionalization of PCs with antibodies is widely used for providing their specific interactions with cancer cells. The efficiency of PC-based targeted delivery systems can be affected by the cellular heterogeneity of the tumor, particularly by the presence of tumor-associated macrophages. We used human epidermoid carcinoma cells and macrophages derived from human leukemia monocytic cells in either monoculture or coculture to analyze the targeting capacity and internalization efficiency of PCs with a mean size of 1.03 ± 0.11 µm. The PCs were functionalized with the monoclonal antibody cetuximab targeting the human epidermal growth factor receptor (EGFR). We have shown that surface functionalization of the PCs with cetuximab ensures a specific interaction with EGFR-expressing cancer cells and promotes capsule internalization. In monoculture, the macrophages derived from human leukemia monocytic cells have been found to internalize both nonfunctionalized PCs and cetuximab-functionalized PCs (Cet-PCs) more intensely compared to epidermoid carcinoma cells. The internalization of Cet-PCs by cancer cells is mediated by lipid rafts of the cell membrane, whereas the PC internalization by macrophages is only slightly influenced by lipid rafts. Experiments with a coculture of human epidermoid carcinoma cells and macrophages derived from human leukemia monocytic cells have shown that Cet-PCs preferentially interact with cancer cells, which are subsequently attacked by macrophages. These data can be used to further improve the strategy of PC functionalization for targeted delivery, with the cellular heterogeneity of the tumor microenvironment taken into consideration.

Biosensors Based on Inorganic Composite Fluorescent Hydrogels.

Fluorescent hydrogels are promising candidate materials for portable biosensors to be used in point-of-care diagnosis because (1) they have a greater capacity for binding organic molecules than immunochromatographic test systems, determined by the immobilization of affinity labels within the three-dimensional hydrogel structure; (2) fluorescent detection is more sensitive than the colorimetric detection of gold nanoparticles or stained latex microparticles; (3) the properties of the gel matrix can be finely tuned for better compatibility and detection of different analytes; and (4) hydrogel biosensors can be made to be reusable and suitable for studying dynamic processes in real time. Water-soluble fluorescent nanocrystals are widely used for in vitro and in vivo biological imaging due to their unique optical properties, and hydrogels based on these allow the preservation of these properties in bulk composite macrostructures. Here we review the techniques for obtaining analyte-sensitive fluorescent hydrogels based on nanocrystals, the main methods used for detecting the fluorescent signal changes, and the approaches to the formation of inorganic fluorescent hydrogels via sol-gel phase transition using surface ligands of the nanocrystals.

Nontoxic Fluorescent Nanoprobes for Multiplexed Detection and 3D Imaging of Tumor Markers in Breast Cancer.

Multiplexed fluorescent immunohistochemical analysis of breast cancer (BC) markers and high-resolution 3D immunofluorescence imaging of the tumor and its microenvironment not only facilitate making the disease prognosis and selecting effective anticancer therapy (including photodynamic therapy), but also provides information on signaling and metabolic mechanisms of carcinogenesis and helps in the search for new therapeutic targets and drugs. The characteristics of imaging nanoprobe efficiency, such as sensitivity, target affinity, depth of tissue penetration, and photostability, are determined by the properties of their components, fluorophores and capture molecules, and by the method of their conjugation. Regarding individual nanoprobe components, fluorescent nanocrystals (NCs) are widely used for optical imaging in vitro and in vivo, and single-domain antibodies (sdAbs) are well established as highly specific capture molecules in diagnostic and therapeutic applications. Moreover, the technologies of obtaining functionally active sdAb-NC conjugates with the highest possible avidity, with all sdAb molecules bound to the NC in a strictly oriented manner, provide 3D-imaging nanoprobes with strong comparative advantages. This review is aimed at highlighting the importance of an integrated approach to BC diagnosis, including the detection of biomarkers of the tumor and its microenvironment, as well as the need for their quantitative profiling and imaging of their mutual location, using advanced approaches to 3D detection in thick tissue sections. The existing approaches to 3D imaging of tumors and their microenvironment using fluorescent NCs are described, and the main comparative advantages and disadvantages of nontoxic fluorescent sdAb-NC conjugates as nanoprobes for multiplexed detection and 3D imaging of BC markers are discussed.

Label-Free Multiplexed Microfluidic Analysis of Protein Interactions Based on Photonic Crystal Surface Mode Imaging.

High-throughput protein assays are crucial for modern diagnostics, drug discovery, proteomics, and other fields of biology and medicine. It allows simultaneous detection of hundreds of analytes and miniaturization of both fabrication and analytical procedures. Photonic crystal surface mode (PC SM) imaging is an effective alternative to surface plasmon resonance (SPR) imaging used in conventional gold-coated, label-free biosensors. PC SM imaging is advantageous as a quick, label-free, and reproducible technique for multiplexed analysis of biomolecular interactions. PC SM sensors are characterized by a longer signal propagation at the cost of a lower spatial resolution, which makes them more sensitive than classical SPR imaging sensors. We describe an approach for designing label-free protein biosensing assays employing PC SM imaging in the microfluidic mode. Label-free, real-time detection of PC SM imaging biosensors using two-dimensional imaging of binding events has been designed to study arrays of model proteins (antibodies, immunoglobulin G-binding proteins, serum proteins, and DNA repair proteins) at 96 points prepared by automated spotting. The data prove feasibility of simultaneous PC SM imaging of multiple protein interactions. The results pave the way to further develop PC SM imaging as an advanced label-free microfluidic assay for the multiplexed detection of protein interactions.

Statistical Analysis of Photoluminescence Decay Kinetics in Quantum Dot Ensembles: Effects of Inorganic Shell Composition and Environment.

Discerning the kinetics of photoluminescence (PL) decay of packed quantum dots (QDs) and QD-based hybrid materials is of crucial importance for achieving their promising potential. However, the interpretation of the decay kinetics of QD-based systems, which usually are not single-exponential, remains challenging. Here, we present a method for analyzing photoluminescence (PL) decay curves of fluorophores by studying their statistical moments. A certain combination of such moments, named as the n-th order moments' ratio, R n , is studied for several theoretical decay curves and experimental PL kinetics of CdSe quantum dots (QDs) acquired by time-correlated single photon counting (TCSPC). For the latter, three different case studies using the R n ratio analysis are presented, namely, (i) the effect of the inorganic shell composition and thickness of the core-shell QDs, (ii) QD systems with Förster resonance energy transfer (FRET) decay channels, and (iii) system of QDs near a layer of plasmonic nanoparticles. The proposed method is shown to be efficient for the detection of slight changes in the PL kinetics, being time-efficient and requiring low computing power for performing the analysis. It can also be a powerful tool to identify the most appropriate physically meaningful theoretical decay function, which best describes the systems under study.

Dependence of Quantum Dot Toxicity In Vitro on Their Size, Chemical Composition, and Surface Charge.

Semiconductor nanocrystals known as quantum dots (QDs) are of great interest for researchers and have potential use in various applications in biomedicine, such as in vitro diagnostics, molecular tracking, in vivo imaging, and drug delivery. Systematic analysis of potential hazardous effects of QDs is necessary to ensure their safe use. In this study, we obtained water-soluble core/shell QDs differing in size, surface charge, and chemical composition of the core. All the synthesized QDs were modified with polyethylene glycol derivatives to obtain outer organic shells protecting them from degradation. The physical and chemical parameters were fully characterized. In vitro cytotoxicity of the QDs was estimated in both normal and tumor cell lines. We demonstrated that QDs with the smallest size had the highest in vitro cytotoxicity. The most toxic QDs were characterized by a low negative surface charge, while positively charged QDs were less cytotoxic, and QDs with a greater negative charge were the least toxic. In contrast, the chemical composition of the QD core did not noticeably affect the cytotoxicity in vitro. This study provides a better understanding of the influence of the QD parameters on their cytotoxicity and can be used to improve the design of QDs.

Structure-function relationships in polymeric multilayer capsules designed for cancer drug delivery.

The targeted delivery of cancer drugs to tumor-specific molecular targets represents a major challenge in modern personalized cancer medicine. Engineering of micron and submicron polymeric multilayer capsules allows the obtaining of multifunctional theranostic systems serving as controllable stimulus-responsive tools with a high clinical potential to be used in cancer therapy and detection. The functionalities of such theranostic systems are determined by the design and structural properties of the capsules. This review (1) describes the current issues in designing cancer cell-targeting polymeric multilayer capsules, (2) analyzes the effects of the interactions of the capsules with the cellular and molecular constituents of biological fluids, and (3) presents the key structural parameters determining the effectiveness of capsule targeting. The influence of the morphological and physicochemical parameters and the origin of the structural components and surface ligands on the functional activity of polymeric multilayer capsules at the molecular, cellular, and whole-body levels are summarized. The basic structural and functional principles determining the future trends of theranostic capsule development are established and discussed.

Label-Free Detection of the Receptor-Binding Domain of the SARS-CoV-2 Spike Glycoprotein at Physiologically Relevant Concentrations Using Surface-Enhanced Raman Spectroscopy.

Surface-enhanced Raman scattering (SERS) spectroscopy is a surface- or cavity-enhanced variant of Raman scattering spectroscopy that allows the detection of analytes with a sensitivity down to single molecules. This method involves the use of SERS-active surfaces or cavities capable of concentrating incident radiation into small mode volumes containing the analyte. Here, we have engineered an ultranarrow metal-dielectric nano-cavity out of a film of the receptor-binding domain (RBD) of SARS-CoV-2 spike (S) glycoprotein and a silver surface, held together by interaction between reduced protein sulfhydryl groups and silver. The concentration of light in this nano-cavity allows the label-free recording of the characteristic Raman spectra of protein samples smaller than 1 pg. This is sufficient for the ultrasensitive detection of viral protein antigens at physiologically relevant levels. Moreover, the protein SERS signal can be increased by several orders of magnitude by coating the RBD film with a nanometer-thick silver shell, thereby raising the cavity Q-factor. This ensures a sub-femtogram sensitivity of the viral antigen detection. A simple theoretical model explaining the observed additional enhancement of the SERS signal from the silver-coated protein is proposed. Our study is the first to obtain the characteristic Raman and SERS spectra of the RBD of S glycoprotein, the key SARS-CoV-2 viral antigen, directly, without the use of Raman-reporter molecules. Thus, our approach allows label-free recording of the characteristic spectra of viral antigens at concentrations orders of magnitude lower than those required for detecting the whole virus in biological media. This makes it possible to develop a high-performance optical detection method and conformational analysis of the pathogen and its variants.

Anisotropic nanomaterials for asymmetric synthesis.

The production of enantiopure chemicals is an essential part of modern chemical industry. Hence, the emergence of asymmetric catalysis led to dramatic changes in the procedures of chemical synthesis, and now it provides the most advantageous and economically executable solution for large-scale production of chiral chemicals. In recent years, nanostructures have emerged as potential materials for asymmetric synthesis. Indeed, on the one hand, nanomaterials offer great opportunities as catalysts in asymmetric catalysis, due to their tunable absorption, chirality, and unique energy transfer properties; on the other hand, the advantages of the larger surface area, increased number of unsaturated coordination centres, and more accessible active sites open prospects for catalyst encapsulation, partial or complete, in a nanoscale cavity, pore, pocket, or channel leading to alteration of the chemical reactivity through spatial confinement. This review focuses on anisotropic nanomaterials and considers the state-of-the-art progress in asymmetric synthesis catalysed by 1D, 2D and 3D nanostructures. The discussion comprises three main sections according to the nanostructure dimensionality. We analyze recent advances in materials and structure development, discuss the functional role of the nanomaterials in asymmetric synthesis, chirality, confinement effects, and reported enantioselectivity. Finally, the new opportunities and challenges of anisotropic 1D, 2D, and 3D nanomaterials in asymmetric synthesis, as well as the future prospects and current trends of the design and applications of these materials are analyzed in the Conclusions and outlook section.

Nanoparticle-Doped Hybrid Polyelectrolyte Microcapsules with Controlled Photoluminescence for Potential Bioimaging Applications.

Fluorescent imaging is widely used in the diagnosis and tracking of the distribution, interaction, and transformation processes at molecular, cellular, and tissue levels. To be detectable, delivery systems should exhibit a strong and bright fluorescence. Quantum dots (QDs) are highly photostable fluorescent semiconductor nanocrystals with wide absorption spectra and narrow, size-tunable emission spectra, which make them suitable fluorescent nanolabels to be embedded into microparticles used as bioimaging and theranostic agents. The layer-by-layer deposition approach allows the entrapping of QDs, resulting in bright fluorescent microcapsules with tunable surface charge, size, rigidity, and functional properties. Here, we report on the engineering and validation of the structural and photoluminescent characteristics of nanoparticle-doped hybrid microcapsules assembled by the deposition of alternating oppositely charged polyelectrolytes, water-soluble PEGylated core/shell QDs with a cadmium selenide core and a zinc sulfide shell (CdSe/ZnS), and carboxylated magnetic nanoparticles (MNPs) onto calcium carbonate microtemplates. The results demonstrate the efficiency of the layer-by-layer approach to designing QD-, MNP-doped microcapsules with controlled photoluminescence properties, and pave the way for the further development of next-generation bioimaging agents based on hybrid materials for continuous fluorescence imaging.

Plasmon-exciton interaction strongly increases the efficiency of a quantum dot-based near-infrared photodetector operating in the two-photon absorption mode under normal conditions.

Semiconductor quantum dots (QDs) are known for their high two-photon absorption (TPA) capacity. This allows them to efficiently absorb infrared photons with energies lower than the bandgap energy. Moreover, TPA in QDs can be further enhanced by the interaction of excitons of the QDs with plasmons of a metal nanoparticle. We fabricated nonlinear plasmon-exciton photodetectors based on QDs and silver nanoplates (SNPs) to demonstrate the optoelectronic application of these effects. A thin layer of CdSe QDs was used as a source of charge carriers for a photoresistor-type photodetector. SNPs with near-infrared plasmon modes were introduced into the layer of QDs to increase the light absorption efficiency. Under near-infrared irradiation, the power of the dependence of the photocurrent on the excitation intensity was twice the power of the corresponding dependence under one-photon excitation with visible light. This proved that the new photodetector efficiently operated under two-photon excitation. Although the SNP light absorption was linear, energy was transferred from plasmons to excitons in the two-quantum mode, which led to a nonlinear dependence. Moreover, we found that the photocurrent from the designed photodetector containing the QD-SNP composite was an order of magnitude higher than that from a photodetector containing QDs alone. This can be explained by the plasmon-induced increase in the TPA efficiency.

Designing Functionalized Polyelectrolyte Microcapsules for Cancer Treatment.

The engineering of delivery systems for drugs and contrasting labels ensuring the simultaneous imaging and treatment of malignant tumors is an important hurdle in developing new tools for cancer therapy and diagnosis. Polyelectrolyte microcapsules (MCs), formed by nanosized interpolymer complexes, represent a promising platform for the designing of multipurpose agents, functionalized with various components, including high- and low-molecular-weight substances, metal nanoparticles, and organic fluorescent dyes. Here, we have developed size-homogenous MCs with different structures (core/shell and shell types) and microbeads containing doxorubicin (DOX) as a model anticancer drug, and fluorescent semiconductor nanocrystals (quantum dots, QDs) as fluorescent nanolabels. In this study, we suggest approaches to the encapsulation of DOX at different stages of the MC synthesis and describe the optimal conditions for the optical encoding of MCs with water-soluble QDs. The results of primary characterization of the designed microcarriers, including particle analysis, the efficacy of DOX and QDs encapsulation, and the drug release kinetics are reported. The polyelectrolyte MCs developed here ensure a modified (prolonged) release of DOX, under conditions close to normal and tumor tissues; they possess a bright fluorescence that paves the way to their exploitation for the delivery of antitumor drugs and fluorescence imaging.

Polariton-assisted manipulation of energy relaxation pathways: donor-acceptor role reversal in a tuneable microcavity.

Resonant interaction between excitonic transitions of molecules and localized electromagnetic field allows the formation of hybrid light-matter polaritonic states. This hybridization of the light and the matter states has been shown to significantly alter the intrinsic properties of molecular ensembles placed inside the optical cavity. Here, we have observed strong coupling of excitonic transition in a pair of closely located organic dye molecules demonstrating an efficient donor-to-acceptor resonance energy transfer with the mode of a tuneable open-access cavity. Analysing the dependence of the relaxation pathways between energy states in this system on the cavity detuning, we have demonstrated that predominant strong coupling of the cavity photon to the exciton transition in the donor dye molecule can lead not only to an increase in the donor-acceptor energy transfer, but also to an energy shift large enough to cause inversion between the energy states of the acceptor and the mainly donor lower polariton energy state. Furthermore, we have shown that the polariton-assisted donor-acceptor chromophores' role reversal or "carnival effect" not only changes the relative energy levels of the donor-acceptor pair, but also makes it possible to manipulate the energy flow in the systems with resonant dipole-dipole interaction and direct energy transfer from the acceptor to the mainly donor lower polariton state. Our experimental data are the first confirmation of the theoretically predicted possibility of polariton-assisted energy transfer reversal in FRET systems, thus paving the way to new avenues in FRET-imaging, remote-controlled chemistry, and all-optical switching.

Conjugates of Ultrasmall Quantum Dots and Acridine Derivatives as Prospective Nanoprobes for Intracellular Investigations.

Designing nanoprobes in which quantum dots (QDs) are used as photoluminescent labels is an especially promising line of research due to their possible medical applications ranging from disease diagnosis to drug delivery. In spite of the significant progress made in designing such nanoprobes, the properties of their individual components, i.e., photoluminescent QDs, vectorization moieties, and pharmacological agents, still require further optimization to enhance the efficiency of diagnostic or therapeutic procedures. Here, we have developed a method of engineering compact multifunctional nanoprobes based on functional components with optimized properties: bright photoluminescence of CdSe/ZnS (core/shell) QDs, a compact and effective antitumor agent (an acridine derivative), and direct conjugation of the components via electrostatic interaction, which provides a final hydrodynamic diameter of nanoprobes smaller than 15 nm. Due to the possibility of conjugating various biomolecules with hydroxyl and carboxyl moieties to QDs, the method represents a versatile approach to the biomarker-recognizing molecule imaging of the delivery of the active substance as part of compact nanoprobes.

Optimizing the PMMA Electron-Blocking Layer of Quantum Dot Light-Emitting Diodes.

Quantum dots (QDs) are promising candidates for producing bright, color-pure, cost-efficient, and long-lasting QD-based light-emitting diodes (QDLEDs). However, one of the significant problems in achieving high efficiency of QDLEDs is the imbalance between the rates of charge-carrier injection into the emissive QD layer and their transport through the device components. Here we investigated the effect of the parameters of the deposition of a poly (methyl methacrylate) (PMMA) electron-blocking layer (EBL), such as PMMA solution concentration, on the characteristics of EBL-enhanced QDLEDs. A series of devices was fabricated with the PMMA layer formed from acetone solutions with concentrations ranging from 0.05 to 1.2 mg/mL. The addition of the PMMA layer allowed for an increase of the maximum luminance of QDLED by a factor of four compared to the control device without EBL, that is, to 18,671 cd/m2, with the current efficiency increased by an order of magnitude and the turn-on voltage decreased by ~1 V. At the same time, we have demonstrated that each particular QDLED characteristic has a maximum at a specific PMMA layer thickness; therefore, variation of the EBL deposition conditions could serve as an additional parameter space when other QDLED optimization approaches are being developed or implied in future solid-state lighting and display devices.

Multiphoton Deep-Tissue Imaging of Micrometastases and Disseminated Cancer Cells Using Conjugates of Quantum Dots and Single-Domain Antibodies.

Early detection of malignant tumors, micrometastases, and disseminated tumor cells is one of the effective way of fighting cancer. Among the many existing imaging methods like computed tomography (CT), ultrasound (US), magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT), optical imaging with fluorescent probes is one of the most promising alternatives because it is fast, inexpensive, safe, sensitive, and specific. However, traditional fluorescent probes, based on organic fluorescent dyes, suffer from the low signal-to-noise ratio. Furthermore, conventional organic fluorescent dyes are unsuitable for deep tissue imaging because of the strong visible light absorption by biological tissues. The use of fluorescent semiconductor nanocrystals, or quantum dots (QDs), may overcome this limitation due to their large multiphoton cross section, which ensures efficient imaging of thick tissue sections inaccessible with conventional fluorescent probes. Moreover, the lower photobleaching and higher brightness of fluorescence signals from QDs ensures a much better discrimination of positive signals from the background. The use of fluorescent nanoprobes based on QDs conjugated to uniformly oriented high-affinity single-domain antibodies (sdAbs) may significantly increase the sensitivity and specificity due to better recognition of analytes and deeper penetration into tissues due to small size of such nanoprobes.Here, we describe a protocol for the fabrication of nanoprobes based on sdAbs and QDs, preparation of experimental xenograft mouse models for quality control, and multiphoton imaging of deep-tissue solid tumors, micrometastases, and disseminated tumor cells.

Strong increase in the effective two-photon absorption cross-section of excitons in quantum dots due to the nonlinear interaction with localized plasmons in gold nanorods.

Excitons in semiconductor quantum dots (QDs) feature high values of the two-photon absorption cross-sections (TPACSs), enabling applications of two-photon-excited photoluminescence (TPE PL) of QDs in biosensing and nonlinear optoelectronics. However, efficient TPE PL of QDs requires high-intensity laser fields, which limits these applications. There are two possible ways to increase the TPE PL of QDs: by increasing their photoluminescence quantum yield (PLQY) or by further increasing the TPACS. Plasmonic nanoparticles (PNPs) may act as open nanocavities for increasing the PLQY via the Purcell effect, but this enhancement is strictly limited by the maximum possible PLQY value of 100%. Here we directly investigated the effect of PNPs on the effective TPACS of excitons in QDs. We have found that effective TPACS of excitons in a QD-PMMA thin film can be increased by a factor of up to 12 near the linearly excited gold nanorods (GNRs). Using gold nanospheres (GNSs), in which plasmons cannot be excited in the infrared range, as a control system, we have shown that, although both GNSs and GNRs increase the recombination rate of excitons, the TPACS is increased only in the case of GNRs. We believe that the observed effect of TPACS enhancement is a result of the nonlinear interaction of the plasmons in GNRs with excitons in QDs, which we have supported by numerical simulations. The results show the way to the rational design of the spectral features of plasmon-exciton hybrids for using them in biosensing and nonlinear optoelectronics.

Quantum Dot-Polyfluorene Composites for White-Light-Emitting Quantum Dot-Based LEDs.

Colloidal quantum dots (QDs) are a promising luminescent material for the development of next generation hybrid light-emitting diodes (QDLEDs). In particular, QDs are of great interest in terms of the development of solid-state light sources with an emission spectrum that mimics daylight. In this study, we used CdSe(core)/ZnS/CdS/ZnS(shell) QDs with organic ligands mimicking polyfluorene and its modified derivatives to obtain QD-polymer composites emitting white light. We found that the emission of the composites obtained by spin-coating, being strongly dependent on the chemical structure of the polymer matrix and the QD-to-polymer mass ratio, can be accurately controlled and adjusted to bring its emission spectrum close to the spectrum of daylight (CIE coordinates: 1931 0.307; 0.376). Moreover, the light emission of these composites has been found to be temporally stable, which is due to the minimal structural instability and volume-uniform charge and energy transfer properties. Thus, the use of the synthesized polyfluorene-based organic ligands with controllable chemical structures adaptable to the structure of the polymer matrix can significantly increase the stability of white light emission from QD composites, which can be considered promising electroluminescent materials for fabrication of white QDLEDs.

Enhanced spontaneous emission from two-photon-pumped quantum dots in a porous silicon microcavity.

Photoluminescence (PL)-based sensing techniques have been significantly developed in practice due to their key advantages in terms of sensitivity and versatility of the approach. Recently, various nanostructured and hybrid materials have been used to improve the PL quantum yield and the spectral resolution. The near-infrared (NIR) fluorescence excitation has attracted much attention because it offers deep tissue penetration and it avoids the autofluorescence of the biological samples. In our study, we have shown both spectral and temporal PL modifications under two-photon excitation of quantum dots (QDs) placed in one-dimensional porous silicon photonic crystal (PhC) microcavities. We have demonstrated an up-to-4.3-fold Purcell enhancement of the radiative relaxation rate under two-photon excitation. The data show that the use of porous silicon PhC microcavities operating in the weak coupling regime permits the enhancement of the PL quantum yield of QDs under two-photon excitation, thus extending the limits of their biosensing applications in the NIR region of the optical spectrum.