Nucleobases functionalized quantum dots and gold nanoparticles bioconjugates as a fluorescence resonance energy transfer (FRET) system – Synthesis, characterization and potential applications

Luminescent Quantum Dots: Synthesis, Optical Properties, Bioimaging and Toxicity

Luminescent nanomaterials such as semiconductor nanocrystals (NCs) and quantum dots (QDs) attract much attention to optical detectors, LEDs, photovoltaics, displays, biosensing, and bioimaging. These materials include metal chalcogenide QDs and metal halide perovskite NCs. Since the introduction of cadmium chalcogenide QDs to biolabeling and bioimaging, various metal nanoparticles (NPs), atomically precise metal nanoclusters, carbon QDs, graphene QDs, silicon QDs, and other chalcogenide QDs have been infiltrating the nano-bio interface as imaging and therapeutic agents. Nanobioconjugates prepared from luminescent QDs form a new class of imaging probes for cellular and in vivo imaging with single-molecule, super-resolution, and 3D resolutions. Surface modified and bioconjugated core-only and core-shell QDs of metal chalcogenides (MX; M = Cd/Pb/Hg/Ag, and X = S/Se/Te,), binary metal chalcogenides (MInX₂; M = Cu/Ag, and X = S/Se/Te), indium compounds (InAs and InP), metal NPs (Ag, Au, and Pt), pure or mixed precision nanoclusters (Ag, Au, Pt), carbon nanomaterials (graphene QDs, graphene nanosheets, carbon NPs, and nanodiamond), silica NPs, silicon QDs, etc. have become prevalent in biosensing, bioimaging, and phototherapy. While heavy metal-based QDs are limited to in vitro bioanalysis or clinical testing due to their potential metal ion-induced toxicity, carbon (nanodiamond and graphene) and silicon QDs, gold and silica nanoparticles, and metal nanoclusters continue their in vivo voyage towards clinical imaging and therapeutic applications. This review summarizes the synthesis, chemical modifications, optical properties, and bioimaging applications of semiconductor QDs with particular references to metal chalcogenide QDs and bimetallic chalcogenide QDs. Also, this review highlights the toxicity and pharmacokinetics of QD bioconjugates.

Stable Enzymatic Nanoparticles from Nucleases, Proteases, Lipase and Antioxidant Proteins with Substrate-Binding and Catalytic Properties

Limited membrane permeability and biodegradation hamper the intracellular delivery of the free natural or recombinant enzymes necessary for compensatory therapy. Nanoparticles (NP) provide relative protein stability and unspecific endocytosis-mediated cellular uptake. Our objective was the fabrication of NP from 7 biomedicine-relevant enzymes, including DNase I, RNase A, trypsin, chymotrypsin, catalase, horseradish peroxidase (HRP) and lipase, the analysis of their conformation stability and enzymatic activity as well as possible toxicity for eukaryotic cells. The enzymes were dissolved in fluoroalcohol and mixed with 40% ethanol as an anti-solvent with subsequent alcohol evaporation at high temperature and low pressure. The shapes and sizes of NP were determined by scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic light scattering (DLS). Enzyme conformations in solutions and in NP were compared using circular dichroism (CD) spectroscopy. The activity of the enzymes was assayed with specific substrates. The cytotoxicity of the enzymatic NP (ENP) was studied by microscopic observations and by using an MTT test. Water-insoluble ENP of different shapes and sizes in a range 50-300 nm consisting of 7 enzymes remained stable for 1 year at +4 °C without any cross-linking. CD spectroscopy of the ENP permitted us to reveal changes in proportions of α-helixes, β-turns and random coils in comparison with fresh enzyme solutions in water. Despite the minor conformation changes of the proteins in the ENP, the enzymes retained their substrate-binding and catalytic properties. Among the studied bioactive ENP, only DNase NP were highly toxic for 3 cell lines with granulation in 1 day posttreatment, whereas other NP were less toxic (if any). Taken together, the enzymes in the stable ENP retained their catalytic activity and might be used for intracellular delivery.

Gold-Nanoparticle Hybrid Nanostructures for Multimodal Cancer Therapy

With the urgent need for bio-nanomaterials to improve the currently available cancer treatments, gold nanoparticle (GNP) hybrid nanostructures are rapidly rising as promising multimodal candidates for cancer therapy. Gold nanoparticles (GNPs) have been hybridized with several nanocarriers, including liposomes and polymers, to achieve chemotherapy, photothermal therapy, radiotherapy, and imaging using a single composite. The GNP nanohybrids used for targeted chemotherapy can be designed to respond to external stimuli such as heat or internal stimuli such as intratumoral pH. Despite their promise for multimodal cancer therapy, there are currently no reviews summarizing the current status of GNP nanohybrid use for cancer theragnostics. Therefore, this review fulfills this gap in the literature by providing a critical analysis of the data available on the use of GNP nanohybrids for cancer treatment with a specific focus on synergistic approaches (i.e., triggered drug release, photothermal therapy, and radiotherapy). It also highlights some of the challenges that hinder the clinical translation of GNP hybrid nanostructures from bench to bedside. Future studies that could expedite the clinical progress of GNPs, as well as the future possibility of improving GNP nanohybrids for cancer theragnostics, are also summarized.

Photoluminescence Properties of CdSe/ZnS Quantum Dot Donor-Acceptor via Plasmon Coupling of Metal Nanostructures and Application on Photovoltaic Devices

Hybrid nanostructures composed of quantum dots (QDs) and metal nanoparticles (MNS) have gained immense research interest because of their unique optical properties. In optoelectronic applications, quenching and enhancement in QD photoluminescence (PL) are critical parameters. Herein, gold nanoparticles coating a silica layer decorated with quantum dots (AuNPs@SiO₂@QDs) are prepared with diverse SiO₂ thickness and QD diameter for investigating the exciton-plasmon interaction. This reveals the charge interaction between QDs and AuNPs@SiO₂ resulting from different impacts of the Föster energy-transfer process and plasmon resonance enhancement. The variation in both radiative and nonradiative energy-transfer processes in CdSe/ZnS QDs donor-acceptor pairs clarifies the impact of AuNPs@SiO₂. In addition, the hybrid structures are plainly incorporated with silicon solar cells, which activated the improvement in the power conversion efficiency (PCE). With the significant tunability of the PL intensity in the visible and near-infrared regions, this hybrid nanostructure provides potential strategies for developing efficient optoelectronics via facile methods.

Capability of novel fluorescence DNA-conjugated CdTe/ZnS quantum dots nanoprobe for COVID-19 sensing

Urgent identification of COVID-19 in infected patients is highly important nowadays. Förster or fluorescence resonance energy transfer (FRET) is a powerful and sensitive method for nanosensing applications, and quantum dots are essential materials in FRET-based nanosensors. The QDs are conjugated to DNA or RNA and used in many applications. Therefore, in the present study, novel fluorescence DNA-conjugated CdTe/ZnS quantum dots nanoprobe designed for detection of Covid-19 after extracting their RNA from saliva of hesitant people. For achieving this purpose, the water-soluble CdTe/ZnS QDs-DNA prepared via replacing the thioglycolic acid (TGA) on the surface of QDs with capture DNA (thiolated DNA) throw a ligand-exchange method. Subsequently, by adding the different concentrations of complementary (target DNA) in a mixture of quencher DNA (BHQ₂-labeled DNA) and the QDs-DNA conjugates at different conditions, sandwiched hybrids were formed. The results showed that the fluorescence intensity was decreased with increasing the concentration of target DNA (as a positive control). The linear equation and regression (Y = 40.302 X  + 1 and R² = 0.98) were obtained by using the Stern-Volmer relationship. The Limit of detection (LOD) was determined 0.000823 µM. The achieved results well confirm the outcomes of the RT-PCR method in real samples.

Optical/electrochemical methods for detecting mitochondrial energy metabolism

This review highlights the biological importance of mitochondrial energy metabolism and the applications of multiple optical/electrochemical approaches to determine energy metabolites. Mitochondria, the main sites of oxidative phosphorylation and adenosine triphosphate (ATP) biosynthesis, provide the majority of energy required by aerobic cells for maintaining their physiological activity. They also participate in cell growth, differentiation, information transmission, and apoptosis. Multiple mitochondrial diseases, caused by internal or external factors, including oxidative stress, intense fluctuations of the ionic concentration, abnormal oxidative phosphorylation, changes in electron transport chain complex enzymes and mutations in mitochondrial DNA, can occur during mitochondrial energy metabolism. Therefore, developing accurate, sensitive, and specific methods for the in vivo and in vitro detection of mitochondrial energy metabolites is of great importance. In this review, we summarise the mitochondrial structure, functions, and crucial energy metabolic signalling pathways. The mechanism and applications of different optical/electrochemical methods are thoroughly reviewed. Finally, future research directions and challenges are proposed.

A sensitive immunosensor based on FRET between gold nanoparticles and InP/ZnS quantum dots for arginine kinase detection

Arginine kinase (AK) is one of the most important allergens in shrimp products. Herein, a novel immunoassay for quantitation of AK was developed using the antibody modified gold nanoparticle (AuNP) and quantum dot (QD). When the first antibody modified AuNP (AuNP-Ab1) was bridged by AK with the secondary antibody modified QD (QD-Ab2), fluorescence resonance energy transfer (FRET) would occur between the AuNP and QD, which led to a decrease in fluorescent signals. The decrease in fluorescence intensity was found to correlate linearly with the log of AK concentration in the range of 1.0 × 10^-6-1.0 × 10^-3 mg/mL (R² = 0.9909) and the detection limit was 0.11 ng/mL. The immunoassay was further proved to have encouraging specificity, precision and accuracy. Compared with existing methods, this study provided a promising approach to develop a highly sensitive and selective detection method for AK in shrimp related food samples.

Quenched or alive quantum dots: The leading roles of ligand adsorption and photoinduced protonation

HYPOTHESIS

The fluorescence emission of water-soluble CdTe quantum dots (QDs) capped with mercaptocarboxylic acids (MCAs) is known to be pH-dependent. However, this behaviour is quite different from a study to another, so that literature suffers from a lack of coherence. Here we assume that the QD fluorescence efficiency is actually driven by the acid-base equilibrium of MCA thiol groups, and that light-excited QDs open a non-radiative relaxation path through photoinduced protonation.

EXPERIMENTS

We address this issue by examining colloidal CdTe QDs with (time-resolved) fluorescence spectroscopy under various conditions of acidity and light excitation.

FINDINGS

It appears that the emission of QDs is quenched below a critical pH value of 6.87, and that light excitation power strengthens this quenching. We thus demonstrate the existence of an additional photochemical process and developed a mathematical modeling accounting for all our experimental results. With only three parameters, it is possible to accurately predict the fluorescence decay of QDs over time, at any pH. Further, we also related the critical pH value of 6.87 to QD surface properties, explaining why observations may differ from a study to another and making the literature much more coherent.

Label-Free Detection of Staphylococcus aureus Based on Bacteria-Imprinted Polymer and Turn-on Fluorescence Probes

The effective identification and quantitative determination of Staphylococcus aureus is a major public health concern. Here, an innovative strategy that combines a bacteria-imprinted polydimethylsiloxane film for bacterial recognition and fluorescence resonance energy transfer platform for turn-on fluorescence sensing is demonstrated. The bacteria-imprinted polydimethylsiloxane film was facilely fabricated to generate corresponding specific sites on the polydimethylsiloxane surface via stamp imprinting using Staphylococcus aureus as template followed by modification with 1H,1H,2H,2H-perfluorooctyltriethoxysilane. The fluorescence resonance energy transfer platform was developed through electrostatic interaction between citrate-functional copper clusters and dopamine-stabilized gold nanoparticles. When the Staphylococcus aureus are present, the 1H,1H,2H,2H-perfluorooctyltriethoxysilane-modified bacteria-imprinted polydimethylsiloxane film can precisely capture the target; subsequently, the negatively charged bacteria compete with citrate-functional copper clusters and bind to dopamine-stabilized gold nanoparticles, leading to the fluorescence recovery of citrate-functional copper clusters. The entire detection process was achieved within 135 min, showing a wide linear calibration response from 10 to 1 × 10⁷ cfu mL^-1 with a low detection limit of 11.12 cfu mL^-1. Furthermore, the recoveries from spiked samples were from 97.7 to 101.90% with relative standard derivations lower than 10%. The established label-free assay of measuring Staphylococcus aureus is rapid, sensitive, specific, and efficient.

Fluorescence and colorimetric dual-mode sensor for visual detection of malathion in cabbage based on carbon quantum dots and gold nanoparticles

A dual-mode fluorescence/colorimetric sensor based on carbon quantum dots (CQDs) and gold nanoparticles (GNPs) was developed for visual detection of malathion in cabbage. The CQDs-GNPs nanocomposite exhibited emission wavelength at 527 nm and absorption wavelength at 524 nm. The fluorescence intensity increased and absorption decreased with addition of malathion. Fluorescence and colorimetric calibration curves were established based on fluorescence intensity (R² = 0.9914) and absorbance (R² = 0.9608) in the range of 1 × 10^-9-1 × 10^-2 M, respectively. Furthermore, fluorescence and colorimetric standard arrays were prepared for visual detection of malathion according to the change of fluorescence brightness and color. Finally, the approximate concentrations of malathion in cabbage samples were estimated by the standard arrays and naked eyes. The calibration curves were used for accurate detection in cabbage samples with recoveries of 89.9%-103.4% (fluorescence) and 88.7%-107.6% (colorimetric). The established sensor for visual malathion detection in cabbage was accurate with strong application potential, especially for rapid screening.

Exciton Dynamics in Droplet Epitaxial Quantum Dots Grown on (311)A-Oriented Substrates

Droplet epitaxy allows the efficient fabrication of a plethora of 3D, III–V-based nanostructures on different crystalline orientations. Quantum dots grown on a (311)A-oriented surface are obtained with record surface density, with or without a wetting layer. These are appealing features for quantum dot lasing, thanks to the large density of quantum emitters and a truly 3D lateral confinement. However, the intimate photophysics of this class of nanostructures has not yet been investigated. Here, we address the main optical and electronic properties of s-shell excitons in individual quantum dots grown on (311)A substrates with photoluminescence spectroscopy experiments. We show the presence of neutral exciton and biexciton as well as positive and negative charged excitons. We investigate the origins of spectral broadening, identifying them in spectral diffusion at low temperature and phonon interaction at higher temperature, the presence of fine interactions between electron and hole spin, and a relevant heavy-hole/light-hole mixing. We interpret the level filling with a simple Poissonian model reproducing the power excitation dependence of the s-shell excitons. These results are relevant for the further improvement of this class of quantum emitters and their exploitation as single-photon sources for low-density samples as well as for efficient lasers for high-density samples.

Gold Nanoparticles and Nanorods in Nuclear Medicine: A Mini Review

In the last decade, many innovative nanodrugs have been developed, as well as many nanoradiocompounds that show amazing features in nuclear imaging and/or radiometabolic therapy. Their potential uses offer a wide range of possibilities. It can be possible to develop nondimensional systems of existing radiopharmaceuticals or build engineered systems that combine a nanoparticle with the radiopharmaceutical, a tracer, and a target molecule, and still develop selective nanodetection systems. This review focuses on recent advances regarding the use of gold nanoparticles and nanorods in nuclear medicine. The up-to-date advancements will be shown concerning preparations with special attention on the dimensions and functionalizations that are most used to attain an enhanced performance of gold engineered nanomaterials. Many ideas are offered regarding recent in vitro and in vivo studies. Finally, the recent clinical trials and applications are discussed.

Fluorescence turn-on sensing of L-cysteine based on FRET between Au-Ag nanoclusters and Au nanorods

The applications of metallic nanoclusters and nanoparticles in biological sensing have attracted special attention owing to their optical interaction based on fluorescence and surface plasmon resonance (SPR). In this work, we designed a fluorescent nanoprobe for the determination of L-cysteine (L-Cys) based on fluorescence resonance energy transfer (FRET) from gold‑silver bimetallic nanoclusters (Au-Ag NCs) to gold nanorods (AuNRs). Firstly, the negatively charged Au-Ag NCs protected by bovine serum albumin (BSA) are directly adsorbed on the surface of the positively charged AuNRs through electrostatic interaction, and the FRET effect leads to distinct fluorescence quenching of Au-Ag NCs at 615nm. The SPR wavelength of AuNRs is dependent on the aspect ratio, so the SPR of AuNRs could be tuned to have a better spectral overlap with fluorescence of Au-Ag NCs, which enhances the fluorescence quenching effect. Because the SH group of L-Cys has an affinity with gold, the addition of L-Cys can result in the release of Au-Ag NCs from the surface of AuNRs via forming AuS bonds. Thus, the introduction of L-Cys could effectively restore the fluorescence emission of the AuNRs/Au-Ag NCs system because of the restraint of FRET effect. Under the optimized conditions, the fluorescence recovery of AuNRs/Au-Ag NCs probe exhibits a linear response to L-Cys concentration ranging from 5 to 100μM, and the corresponding theoretical detection limit (LOD) is 1.73μM. Meanwhile, this method displays excellent sensitivity and selectivity for L-Cys over other amino acids, and it has been successfully applied to detect L-Cys in real samples.

Engineered Gold-Based Nanomaterials: Morphologies and Functionalities in Biomedical Applications. A Mini Review

In the last decade, several engineered gold-based nanomaterials, such as spheres, rods, stars, cubes, hollow particles, and nanocapsules have been widely explored in biomedical fields, in particular in therapy and diagnostics. As well as different shapes and dimensions, these materials may, on their surfaces, have specific functionalizations to improve their capability as sensors or in drug loading and controlled release, and/or particular cell receptors ligands, in order to get a definite targeting. In this review, the up-to-date progress will be illustrated regarding morphologies, sizes and functionalizations, mostly used to obtain an improved performance of nanomaterials in biomedicine. Many suggestions are presented to organize and compare the numerous and heterogeneous experimental data, such as the most important chemical-physical parameters, which guide and control the interaction between the gold surface and biological environment. The purpose of all this is to offer the readers an overview of the most noteworthy progress and challenges in this research field.

Development and evaluation of fluorescent gold nanoparticles

OBJECTIVE

It is difficult to identify the gold nanoparticles (AuNPs) intracellularly due to their non-fluorescent nature. Although gold can quench the fluorescence of any fluorophore, hence it is also difficult to combine gold with a fluorophore such as a semiconductor quantum dots (QDs). The aim of this study was to prepare a single fluorescent stable AuNPs combined with QDs (QDs-Au-NPs) which can be easily detected intracellularly.

METHODS

QDs-Au-NPs were prepared via a simple one-step process through controlling the spacing between them using polyethylene glycol (PEG) as space linker in the form of PEGylated QDs. Furthermore, the applicability of this system was evaluated after coating the particles with somatostatin citrate, SST, to active target somatostatin receptors (SSTRs), and identification of the internalized particles via confocal laser scanning spectroscopy.

RESULTS

The results showed that the produced Au shell has a thickness of 2.0 ± 0.2 nm and QDs-Au-NPs showed the same fluorescence intensity compared to the unmodified QDs. Additionally, a stable monodisperse QDs-Au-NPs coated with SST were prepared after coating with 11-Mercaptoundecanoic acid. Moreover, cellular uptake study in Human Caucasian breast adenocarcinoma cell lines showed that QDs-Au-SST-NPs could be detected easily using the confocal microscope. In addition, they showed a significant (p ≤ .05) internalization per cell compared to untreated QDs-Au-NPs as detected by flow cytometry.

CONCLUSION

It could be concluded that the produced QDs-Au-NPs has a strong fluorescence property like QDs which enable them to be easily detected after cells internalization.