Synthesis, Properties and Bioimaging Applications of Silver-Based Quantum Dots

Advances on chalcogenide quantum dots-based sensors for environmental pollutants monitoring

Water contamination represents a significant ecological impact with global consequences, contributing to water scarcity worldwide. The presence of several pollutants, including heavy metals, pharmaceuticals, pesticides, and pathogens, in water resources underscores a pressing global concern, prompting the European Union (EU) to establish a Water Watch List to monitor the level of these substances. Nowadays, the standard methods used to detect and quantify these contaminants are mainly liquid or gas chromatography coupled with mass spectrometry (LC/GC-MS). While these methodologies offer precision and accuracy, they require expensive equipment and experienced technicians, and cannot be used on the field. In this context, chalcogenide quantum dots (QDs)-based sensors have emerged as promising, user-friendly, practical, and portable tools for environmental monitoring. QDs are semiconductor nanocrystals that possess excellent properties, and have demonstrated versatility across various sensor types, such as fluorescent, electrochemical, plasmonic, and colorimetric ones. This review summarizes recent advances (2019-2023) in the use of chalcogenide QDs for environmental sensing, highlighting the development of sensors capable of detect efficiently heavy metals, anions, pharmaceuticals, pesticides, endocrine disrupting compounds, organic dyes, toxic gases, nitroaromatics, and pathogens.

CdSe/ZnS quantum dots as a booster in the active layer of distributed ternary organic photovoltaics

Organic solar cells are a promising candidate for practical use because of their low material cost and simple production procedures. The challenge is selecting materials with the right properties and how they interrelate in the context of manufacturing the device. This paper presents studies on CdSe/ZnS nanodots as dopants in a polymer-fullerene matrix for application in organic solar cells. An assembly of poly(3-hexylthiophene-2,5-diyl) and 6,6-phenyl-C71-butyric acid methyl ester was used as the active reference layer. Absorption and luminescence spectra as well as the dispersion relations of refractive indices and extinction coefficient were investigated. The morphologies of the thin films were studied with atomic force microscopy. The chemical boundaries of the ternary layers were determined by Raman spectroscopy. Based on UPS studies, the energy diagram of the potential devices was determined. The resistivity of the layers was determined using impedance spectroscopy. Simulations (General-Purpose Photovoltaic Device Model) showed a performance improvement in the cells with quantum dots of 0.36-1.45% compared to those without quantum dots.

Nanomaterials for intelligent CRISPR-Cas tools: improving environment sustainability

Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) is a desirable gene modification tool covering a wide area in various sectors of medicine, agriculture, and microbial biotechnology. The role of this incredible genetic engineering technology has been extensively investigated; however, it remains formidable with cargo choices, nonspecific delivery, and insertional mutagenesis. Various nanomaterials including lipid, polymeric, and inorganic are being used to deliver the CRISPR-Cas system. Progress in nanomaterials could potentially address these challenges by accelerating precision targeting, cost-effectiveness, and one-step delivery. In this review, we highlighted the advances in nanotechnology and nanomaterials as smart delivery systems for CRISPR-Cas so as to ameliorate applications for environmental remediation including biomedical research and healthcare, strategies for mitigating antimicrobial resistance, and to be used as nanofertilizers for enhancing crop growth, and reducing the environmental impact of traditional fertilizers. The timely co-evolution of nanotechnology and CRISPR technologies has contributed to smart novel nanostructure hybrids for improving the onerous tasks of environmental remediation and biological sustainability.

Self-Organized SERS Substrates with Efficient Analyte Enrichment in the Hot Spots

One of the requirements of an efficient surface-enhanced Raman spectroscopy (SERS) substrate is a developed surface morphology with a high density of "hot spots", nm-scale spacings between plasmonic nanoparticles. Of particular interest are plasmonic architectures that could enable self-localization (enrichment) of the analyte in the hot spots. We report a straightforward method of fabrication of efficient SERS substrates that comply with these requirements. The basis of the substrate is a large-area film of tightly packed SiO2 spheres formed by their quick self-assembling upon drop casting from the solution. Thermally evaporated thin Ag layer is converted by quick thermal annealing into nanoparticles (NPs) self-assembled in the trenches between the silica spheres, i.e., in the places where the analyte molecules get localized upon deposition from solution and drying. Therefore, the obtained substrate morphology enables an efficient enrichment of the analyte in the hot spots formed by the densely arranged plasmonic NPs. The high efficiency of the developed SERS substrates is demonstrated by the detection of Rhodamine 6G down to 10-13 mol/L with an enhancement factor of ∼108, as well as the detection of low concentrations of various nonresonant analytes, both small dye molecules and large biomolecules. The developed approach to SERS substrates is very straightforward for implementation and can be further extended to using gold or other plasmonic NPs.

One-pot synthesis of Ag-In-Ga-S nanocrystals embedded in a Ga2O3 matrix and enhancement of band-edge emission by Na+ doping

I-III-VI-based semiconductor quantum dots (QDs) have been intensively explored because of their unique controllable optoelectronic properties. Here we report one-pot synthesis of Na-doped Ag-In-Ga-S (AIGS) QDs incorporated in a Ga2O3 matrix. The obtained QDs showed a sharp band-edge photoluminescence peak at 557 nm without a broad-defect site emission. The PL quantum yield (QY) of such QDs was 58%, being much higher than that of AIGS QDs without Na+ doping, 29%. The obtained Na-doped AIGS/Ga2O3 composite particles were used as an emitting layer of green QD light-emitted diodes. A sharp electroluminescence (EL) peak was observed at 563 nm, being similar to that in the PL spectrum of the QDs used. The external quantum efficiency of the device was 0.6%.

SERS-substrates based on ZnO nanoflowers prepared by green synthesis

ZnO nanoparticles (NPs) with a flower-like morphology, synthesized by an affordable colloidal route using an aqueous fungi extract of Ganoderma lucidum as a reducing agent and stabilizer, are investigated as SERS-substrate. Each "flower" has large effective surface that is preserved at packing particles into a dense film and thus exhibits an advantageous property for SERS and similar sensing applications. The mycoextract used in our low-cost and green synthesis as surface stabilizer allows subsequent deposition of metal NPs or layers. One type of SERS substrates studied here was ZnO NPs decorated in situ in the solution by Ag NPs, another type was prepared by thermally evaporating Ag layer on the ZnO NP film on a substrate. A huge difference in the enhancement of the same analyte in the solution and in the dried form is found and discussed. Detection down to 10-7 M of standard dye analytes such as rhodamine 6G and methylene blue was achieved without additional optimization of the SERS substrates. The observed SERS-activity demonstrate the potential of both the free-standing flower-like ZnO NPs and thereof made dense films also for other applications where large surface area accessible for the external agent is crucial, such as catalysis or sensing.

NIR-II Nanoprobes: A Review of Components-Based Approaches to Next-Generation Bioimaging Probes

Fluorescence and photoacoustic imaging techniques offer valuable insights into cell- and tissue-level processes. However, these optical imaging modalities are limited by scattering and absorption in tissue, resulting in the low-depth penetration of imaging. Contrast-enhanced imaging in the near-infrared window improves imaging penetration by taking advantage of reduced autofluorescence and scattering effects. Current contrast agents for fluorescence and photoacoustic imaging face several limitations from photostability and targeting specificity, highlighting the need for a novel imaging probe development. This review covers a broad range of near-infrared fluorescent and photoacoustic contrast agents, including organic dyes, polymers, and metallic nanostructures, focusing on their optical properties and applications in cellular and animal imaging. Similarly, we explore encapsulation and functionalization technologies toward building targeted, nanoscale imaging probes. Bioimaging applications such as angiography, tumor imaging, and the tracking of specific cell types are discussed. This review sheds light on recent advancements in fluorescent and photoacoustic nanoprobes in the near-infrared window. It serves as a valuable resource for researchers working in fields of biomedical imaging and nanotechnology, facilitating the development of innovative nanoprobes for improved diagnostic approaches in preclinical healthcare.

Recent Advances in Quantum Dot-Based Lateral Flow Immunoassays for the Rapid, Point-of-Care Diagnosis of COVID-19

The COVID-19 pandemic has spurred demand for efficient and rapid diagnostic tools that can be deployed at point of care to quickly identify infected individuals. Existing detection methods are time consuming and they lack sensitivity. Point-of-care testing (POCT) has emerged as a promising alternative due to its user-friendliness, rapidity, and high specificity and sensitivity. Such tests can be conveniently conducted at the patient's bedside. Immunodiagnostic methods that offer the rapid identification of positive cases are urgently required. Quantum dots (QDs), known for their multimodal properties, have shown potential in terms of combating or inhibiting the COVID-19 virus. When coupled with specific antibodies, QDs enable the highly sensitive detection of viral antigens in patient samples. Conventional lateral flow immunoassays (LFAs) have been widely used for diagnostic testing due to their simplicity, low cost, and portability. However, they often lack the sensitivity required to accurately detect low viral loads. Quantum dot (QD)-based lateral flow immunoassays have emerged as a promising alternative, offering significant advancements in sensitivity and specificity. Moreover, the lateral flow immunoassay (LFIA) method, which fulfils POCT standards, has gained popularity in diagnosing COVID-19. This review focuses on recent advancements in QD-based LFIA for rapid POCT COVID-19 diagnosis. Strategies to enhance sensitivity using QDs are explored, and the underlying principles of LFIA are elucidated. The benefits of using the QD-based LFIA as a POCT method are highlighted, and its published performance in COVID-19 diagnostics is examined. Overall, the integration of quantum dots with LFIA holds immense promise in terms of revolutionizing COVID-19 detection, treatment, and prevention, offering a convenient and effective approach to combat the pandemic.

Application of Nanoparticles in the Diagnosis of Gastrointestinal Diseases: A Complete Future Perspective

The diagnosis of gastrointestinal (GI) diseases currently relies primarily on invasive procedures like digestive endoscopy. However, these procedures can cause discomfort, respiratory issues, and bacterial infections in patients, both during and after the examination. In recent years, nanomedicine has emerged as a promising field, providing significant advancements in diagnostic techniques. Nanoprobes, in particular, offer distinct advantages, such as high specificity and sensitivity in detecting GI diseases. Integration of nanoprobes with advanced imaging techniques, such as nuclear magnetic resonance, optical fluorescence imaging, tomography, and optical correlation tomography, has significantly enhanced the detection capabilities for GI tumors and inflammatory bowel disease (IBD). This synergy enables early diagnosis and precise staging of GI disorders. Among the nanoparticles investigated for clinical applications, superparamagnetic iron oxide, quantum dots, single carbon nanotubes, and nanocages have emerged as extensively studied and utilized agents. This review aimed to provide insights into the potential applications of nanoparticles in modern imaging techniques, with a specific focus on their role in facilitating early and specific diagnosis of a range of GI disorders, including IBD and colorectal cancer (CRC). Additionally, we discussed the challenges associated with the implementation of nanotechnology-based GI diagnostics and explored future prospects for translation in this promising field.

ZnO and Ag NP-decorated ZnO nanoflowers: green synthesis using Ganoderma lucidum aqueous extract and characterization

Fungi produce and excrete various proteins, enzymes, polysaccharides, and secondary metabolites, which may be used as media for the "green" synthesis of metal and semiconductor nanoparticles (NPs). ZnO NPs with a flower-like morphology were synthesized by an affordable colloidal route, using an aqueous extract of Ganoderma lucidum as a reducing agent and stabilizer. Each individual "flower" has a large effective surface, which is preserved when the particles are close packed into a dense film, which is advantageous for numerous applications. The phonon Raman spectrum and X-ray diffraction (XRD) pattern prove the high crystallinity of the NPs, with the distinct pattern of a hexagonal (wurtzite) lattice, negligible residual stress, and a crystallite size of 12-14 nm determined from the XRD. The photoluminescence (PL) spectrum of the as-synthesized ZnO NPs contains a structured defect-related feature in the violet-blue range, while the green PL, common for nanostructures synthesized by "green" routes, is very weak. By applying dimethylsulfoxide as an additional passivating agent, the excitonic (UV) PL band was activated without enhancement of the defect-related features. Ag NP-decorated ZnO flowers were synthesized by subsequent silver reduction by pepper extract. The ZnO/Ag NPs exhibited efficient surface-enhanced Raman scattering (SERS) of a standard dye analyte, rhodamine 6G, ensuring the feasibility of other applications that require close contact of ZnO/Ag to other nanostructures or molecules to realize the energy of the charge transfer.

Biomolecule-Based Optical Metamaterials: Design and Applications

Metamaterials are broadly defined as artificial, electromagnetically homogeneous structures that exhibit unusual physical properties that are not present in nature. They possess extraordinary capabilities to bend electromagnetic waves. Their size, shape and composition can be engineered to modify their characteristics, such as iridescence, color shift, absorbance at different wavelengths, etc., and harness them as biosensors. Metamaterial construction from biological sources such as carbohydrates, proteins and nucleic acids represents a low-cost alternative, rendering high quantities and yields. In addition, the malleability of these biomaterials makes it possible to fabricate an endless number of structured materials such as composited nanoparticles, biofilms, nanofibers, quantum dots, and many others, with very specific, invaluable and tremendously useful optical characteristics. The intrinsic characteristics observed in biomaterials make them suitable for biomedical applications. This review addresses the optical characteristics of metamaterials obtained from the major macromolecules found in nature: carbohydrates, proteins and DNA, highlighting their biosensor field use, and pointing out their physical properties and production paths.

Effect of the surface coverage of an alkyl carboxylic acid monolayer on waterborne and cellular uptake behaviors for silicon quantum dots

This article reports the development of highly waterborne silicon quantum dots (Si QDs) terminated with a reactive group for grafting of biomolecules. Hydrogen-terminated QDs were prepared by thermal disproportionation of amorphous hydrogen silsesquioxane derived from triethoxysilane followed by hydrofluoric etching. Next, the hydrogenated Si surfaces were exposed to 10-undecenoic acid at different temperatures in Ar atmosphere, yielding the termination of the QDs with a carboxyl group. The thermal hydrosilylation of 10-undecenoic acid yielded the termination of the QDs with a carboxyl group. An increase in molecular coverage of an undecanoic acid (UA) monolayer resulted in both the enhanced increase of zeta-potential in a negative direction for a greater water-dispersity and the increase of absolute quantum yield (QY) of photoluminescence (PL). PLQY improved for ~ 1% to 26% with increasing UA coverage. We assessed the molecular interaction between the UA-SiQDs and HeLa cells by means of cellular uptake experiments using the QDs with different UA coverages. Results showed that the QDs with the highest dispersity in water were not internalized in the cells under confocal fluorescence microscopic observation. In contrast, the QDs with lower coverage of UA monolayer were internalized by endocytosis when incubated with HeLa cells. This contrasting observation opens the possibility of successfully preparing carboxy-capped SiQDs that do not allow cellular uptake but are targeted to specific cells by appropriate conjugation with biomolecules.

New Advances in Lateral Flow Immunoassay (LFI) Technology for Food Safety Detection

With the continuous development of China’s economy and society, people and the government have higher and higher requirements for food safety. Testing for food dopants and toxins can prevent the occurrence of various adverse health phenomena in the world’s population. By deploying new and powerful sensors that enable rapid sensing processes, the food industry can help detect trace adulteration and toxic substances. At present, as a common food safety detection method, lateral flow immunochromatography (LFI) is widely used in food safety testing, environmental testing and clinical medical treatment because of its advantages of simplicity, speed, specificity and low cost, and plays a pivotal role in ensuring food safety. This paper mainly focuses on the application of lateral flow immunochromatography and new technologies combined with test strips in food safety detection, such as aptamers, surface-enhanced Raman spectroscopy, quantum dots, electrochemical test strip detection technology, biosensor test strip detection, etc. In addition, sensing principles such as fluorescence resonance energy transfer can also more effective. Different methods have different characteristics. The following is a review of the application of these technologies in food safety detection.

Upconversion Nanomaterials in Bioimaging and Biosensor Applications and Their Biological Response

In recent decades, upconversion nanomaterials (UCNMs) have attracted considerable research interest because of their unique optical properties, such as large anti-Stokes shifts, sharp emissions, non-photobleaching, and long lifetime. These unique properties make them ideal candidates for unified applications in biomedical fields, including drug delivery, bioimaging, biosensing, and photodynamic therapy for specific cancers. This review describes the general mechanisms of upconversion, synthesis methods, and potential applications in biology and their biological responses. Additionally, the biological toxicity of UCNMs is explained and summarized with the associated intracellular association mechanisms. Finally, the prospects and future challenges of UCNMs at the clinical level in biological applications are described, along with a summary of opportunity for biological as well as clinical applications of UCNMs.

High Fructose Concentration Increases the Fluorescence Stability of DNA-Templated Copper Nanoclusters by Several Thousand Times

DNA-templated copper nanoclusters (CuNCs) have limited applications because of their low fluorescence stability (several tens of minutes). In this study, we prepared CuNCs with improved temporal fluorescence stability by introducing fructose into the CuNC synthesis process and optimizing the reaction conditions. The inclusion of fructose increased the operating lifetime of CuNCs by approximately 5200-fold from 30 min to 108 days and improved their stability against heat, acids, and bases compared to CuNCs synthesized under original conditions. In addition, the fluorescence signal of CuNCs was maintained for a significantly longer time when stored at refrigeration (4 °C) and freezing (-20 °C) temperatures. Importantly, this method did not require the addition of substances other than fructose or any additional physicochemical treatment to maintain the fluorescence of DNA-templated CuNCs for more than several tens of days. As such, this study could serve as a basis to improve the stability of CuNCs for various applications.

Quantum Dot-Antibody Conjugates for Immunofluorescence Studies of Biomolecules and Subcellular Structures

Quantum dots, or nanoscale semiconductors, are one of the most important materials for various research and development purposes. Due to their advantageous photoluminescence and electronic properties, namely, their unique photostability, high brightness, narrow emission spectra from visible to near-infrared wavelengths, convey them significant advantages over widely used fluorochromes, including organic dyes, fluorescent probes. Quantum dots are a unique instrument for a wide range of immunoassays with antibodies. The paper provides an overview of the developed and already applied methods of quantum dot surface modification, quantum dots conjugation to different antibodies (non-covalent, direct covalent linkage or with the use of special adapter molecules), as well as practical examples of recent quantum dot-antibody applications in the immunofluorescence microscopy for cell and cell structure imaging, fluorescent assays for biomolecules detection and in diagnostics of various diseases. The review presents advantages of quantum dot-antibody conjugation technology over the existing methods of immunofluorescence studies and a forward look into its potential prospects in biological and biomedical research.

Spectroscopic Study of Phytosynthesized Ag Nanoparticles and Their Activity as SERS Substrate

The affordable and scalable synthesis of noble metal nanoparticles that are biocompatible without additional functionalization steps has been a growing field of research, stimulated by numerous prospective applications of these NPs. In the case of phytosynthesized or biogenic noble metal NPs, the mechanism of NP stabilization by biomolecules contained in each particular plant extract or living organism determines the possible applications of these NPs. In this work, we investigated Ag NPs synthesized in water with plant extracts of common toothwort (Lathraea squamaria) and two species of pepper (Capsicum annuum and Capsicum chinense). From FTIR and XPS, we drew conclusions about the composition of the functional groups and molecules that stabilize NPs in each extract, such as polysaccharide compounds (pectins, cellulose, glycosides and phenolic acids). Distinct characteristic IR features of amide I and amide II proteins were observed, which are common in plant extracts, while features of amide III were not distinctly observed in our extracts. A Raman spectroscopy study revealed weak own-SERS activity of the biomolecules of the extract and high efficiency of the NPs in the enhancement of “external” analytes, such as dyes and antibodies. This is the first report of the efficient SERS application of phytosynthesized Ag NPs.