SERS as a tool for determination of structurally related compounds: The case of sulfanilamide class antibiotics.

Analysis of real objects based on surface-enhanced Raman spectroscopy (SERS) often utilizes new SERS substrates and/or complex analysis procedures, and they are optimized for only the determination of a single analyte. Moreover, analysis simplicity and selectivity are often sacrificed for maximum (sometimes unnecessary) sensitivity. Consequently, this trend limits the versatility of SERS analysis and complicates its practical implementation. Thus, we have developed a universal, but simple SERS assay suitable for the determination of structurally related antibiotics (five representatives of the sulfanilamide class) in complex objects (human urine and saliva). The assay involves only mixing of acidified analyzed solution with co-activating agent (polydiallyldimethylammonium chloride - PDDA) and SERS substrate (standard colloidal silver nanoparticles). Acidification promotes the generation of SERS spectra with maximum similarity and intensity, which is explained by the favorable enhancement of the protonated sulfanilamide moiety (a structurally similar part of the studied antibiotics) as a result of its strong electrostatic interaction with the SERS-active surface. Meanwhile, the addition of PDDA improves analysis selectivity by reducing background signal from body fluids, enabling to simplify sample pretreatment (dilution for urine; mucin removal and dilution for saliva). Therefore, the assay allows for rapid (≤10 min), precise, and accurate class-specific determination of sulfanilamides within concentration ranges suitable for non-invasive therapeutic drug monitoring in urine (40-600 µM) and saliva (10-30 µM). We also believe that thorough investigation of structurally related analytes and accompanying effects (e.g., high spectral similarity) is a promising direction to improve the understanding of SERS in general and expand its capabilities as an analytical tool.

Multiple dyes applications for fluorescent convertible polymer capsules as macrophages tracking labels.

Tracing individual cell pathways among the whole population is crucial for understanding their behavior, cell communication, migration dynamics, and fate. Optical labeling is one approach for tracing individual cells, but it typically requires genetic modification to induce the generation of photoconvertible proteins. Nevertheless, this approach has limitations and is not applicable to certain cell types. For instance, genetic modification often leads to the death of macrophages. This study aims to develop an alternative method for labeling macrophages by utilizing photoconvertible micron-sized capsules capable of easy internalization and prolonged retention within cells. Thermal treatment in a polyvinyl alcohol gel medium is employed for the scalable synthesis of capsules with a wide range of fluorescent dyes, including rhodamine 6G, pyronin B, fluorescein, acridine yellow, acridine orange, thiazine red, and previously reported rhodamine B. The fluorescence brightness, photostability, and photoconversion ability of the capsules are evaluated using confocal laser scanning microscopy. Viability, uptake, mobility, and photoconversion studies are conducted on RAW 264.7 and bone marrow-derived macrophages, serving as model cell lines. The production yield of the capsules is increased due to the use of polyvinyl alcohol gel, eliminating the need for conventional filtration steps. Capsules entrapping rhodamine B and rhodamine 6G meet all requirements for intracellular use in individual cell tracking. Mass spectrometry analysis reveals a sequence of deethylation steps that result in blue shifts in the dye spectra upon irradiation. Cellular studies on macrophages demonstrate robust uptake of the capsules. The capsules exhibit minimal cytotoxicity and have a negligible impact on cell motility. The successful photoconversion of RhB-containing capsules within cells highlights their potential as alternatives to photoconvertible proteins for individual cell labeling, with promising applications in personalized medicine.

Effect of photoconversion conditions on the spectral and cytotoxic properties of photoconvertible fluorescent polymer markers.

Fluorescence labeling of cells is a versatile tool used to study cell behavior, which is of significant importance in biomedical sciences. Fluorescent photoconvertible markers based on polymer microcapsules have been recently considered as efficient and perspective ones for long-term tracking of individual cells. However, the dependence of photoconversion conditions on the polymeric capsule structure is still not sufficiently clear. Here, we have studied the structural and spectral properties of fluorescent photoconvertible polymeric microcapsules doped with Rhodamine B and irradiated using a pulsed laser in various regimes, and shown the dependence between the photoconversion degree and laser irradiation intensity. The effect of microcapsule composition on the photoconversion process was studied by monitoring structural changes in the initial and photoconverted microcapsules using X-ray diffraction analysis with synchrotron radiation source, and Fourier transform infrared, Raman and fluorescence spectroscopy. We demonstrated good biocompatibility of free-administered initial and photoconverted microcapsules through long-term monitoring of the RAW 264.7 monocyte/macrophage cells with unchanged viability. These data open new perspectives for using the developed markers as safe and precise cell labels with switchable fluorescent properties.

One-pot hydrothermal synthesis of fluorophore-modified cerium oxide nanoparticles.

Cerium oxide nanoparticles (CeO2 NPs), which have powerful antioxidant properties, are promising nanomaterials for the treatment of diseases associated with oxidative stress. The well-developed surface of CeO2 NPs makes them promising for use as a multifunctional system for various biomedical applications. This work demonstrates a simple approach that allows the direct formation of a molecular fluorophore on the surface of CeO2 NPs using a simple one-pot hydrothermal synthesis. Thus, we were able to synthesize CeO2 NPs of ultra-small size ∼2 nm with a narrow distribution, highly stable fluorescence, and a quantum yield of ∼62%. UV-visible transmission studies revealed that the resulting CeO2 NPs exhibited fast autogenerative catalytic reduction. In vitro results showed high biocompatibility of CeO2 NPs; their internalization occurs mainly in the region of cell nuclei. Thus, the resulting NPs have the necessary parameters and can be successfully used in biovisualization and therapy.

Correction: Luminescence and photoelectrochemical properties of size-selected aqueous copper-doped Ag-In-S quantum dots.

[This corrects the article DOI: 10.1039/C8RA00257F.].

Labeling and Tracking of Individual Human Mesenchymal Stromal Cells Using Photoconvertible Fluorescent Microcapsules.

The behavior and migration of human mesenchymal stromal cells (hMSCs) are focal points of research in the biomedical field. One of the major aspects is potential therapy using hMCS, but at present, the safety of their use is still controversial owing to limited data on changes that occur with hMSCs in the long term. Fluorescent photoconvertible proteins are intensively used today as "gold standard" to mark the individual cells and study single-cell interactions, migration processes, and the formation of pure lines. A crucial disadvantage of this method is the need for genetic modification of the primary culture, which casts doubt on the possibility of exploring the resulting clones in personalized medicine. Here we present a new approach for labeling and tracking hMSCs without genetic modification based on the application of cell-internalizable photoconvertible polyelectrolyte microcapsules (size: 2.6 ± 0.5 µm). These capsules were loaded with rhodamine B, and after thermal treatment, exhibited fluorescent photoconversion properties. Photoconvertible capsules demonstrated low cytotoxicity, did not affect the immunophenotype of the hMSCs, and maintained a high level of fluorescent signal for at least seven days. The developed approach was tested for cell tracking for four days and made it possible to trace the destiny of daughter cells without the need for additional labeling.

Fluorescent Alloyed CdZnSeS/ZnS Nanosensor for Doxorubicin Detection.

Doxorubicin (DOX) is widely used in chemotherapy as an anti-tumor drug. However, DOX is highly cardio-, neuro- and cytotoxic. For this reason, the continuous monitoring of DOX concentrations in biofluids and tissues is important. Most methods for the determination of DOX concentrations are complex and costly, and are designed to determine pure DOX. The purpose of this work is to demonstrate the capabilities of analytical nanosensors based on the quenching of the fluorescence of alloyed CdZnSeS/ZnS quantum dots (QDs) for operative DOX detection. To maximize the nanosensor quenching efficiency, the spectral features of QDs and DOX were carefully studied, and the complex nature of QD fluorescence quenching in the presence of DOX was shown. Using optimized conditions, turn-off fluorescence nanosensors for direct DOX determination in undiluted human plasma were developed. A DOX concentration of 0.5 µM in plasma was reflected in a decrease in the fluorescence intensity of QDs, stabilized with thioglycolic and 3-mercaptopropionic acids, for 5.8 and 4.4 %, respectively. The calculated Limit of Detection values were 0.08 and 0.03 µg/mL using QDs, stabilized with thioglycolic and 3-mercaptopropionic acids, respectively.

SERS Assays Based on Electrospun Nanofibers: Preparation and Analytical Applications.

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool and an up-to-date method of analytical chemistry due to its high sensitivity and fingerprint recognition capabilities. Nowadays SERS due to its label-free detection capabilities is being actively developed in medical fields, for example in the analysis of biologically important substances in different matrixes, for potential on-site detection of toxic substances, food safety, and so on. To get the SERS signal, it is necessary the presence of plasmonic nanostructures in the SERS substrates. Electrospun nanofibers have been an attractive alternative to SERS-platforms due to the diversity of advantages, including ease of preparation, structure flexibility, and others. In this review, we summarized the methods of plasmonic nanostructures incorporating substrate based on electrospun nanofibers. Also, the analytical application of SERS-active electrospun nanofibers with embedded nanostructures focused on biologically significant molecules is observed in detail. Finally, the future outlook in the application of these substrates in bioanalysis as the most promising area in analytical chemistry is presented.

A Facile Approach to the Hydrothermal Synthesis of Silica Nanoparticle/Carbon Nanostructure Luminescent Composites.

Luminescent carbon nanostructures (CNSs) have been intensively researched, but there is still no consensus on a fundamental understanding of their structure and properties that limits their potential applications. In this study, we developed a facile approach to the synthesis of luminescent composite SiO2 nanoparticles/CNSs by the targeted formation of a molecular fluorophore, as the significant luminescent component of CNSs, on the surface of a silica matrix during a one-stage hydrothermal synthesis. Silica nanoparticles were synthesized by reverse microemulsion and used as a matrix for luminescent composites. The as-prepared silica nanoparticles had a functional surface, a spherical shape, and a narrow size distribution of about 29 nm. One-stage hydrothermal treatment of citric acid and modified silica nanoparticles made it possible to directly form the luminescent composite. The optical properties of composites could be easily controlled by changing the hydrothermal reaction time and temperature. Thus, we successfully synthesized luminescent composites with an emission maximum of 450 nm, a quantum yield (QY) of 65 ± 4%, and an average size of ~26 nm. The synthesis of fluorophore doped composite, in contrast to CNSs, makes it possible to control the shape, size, and surface functionality of particles and allows for avoiding difficult and time-consuming fractionation steps.

Bioanalytical Applications of Graphene Quantum Dots for Circulating Cell-Free Nucleic Acids: A Review.

Graphene quantum dots (GQDs) are carbonaceous nanodots that are natural crystalline semiconductors and range from 1 to 20 nm. The broad range of applications for GQDs is based on their unique physical and chemical properties. Compared to inorganic quantum dots, GQDs possess numerous advantages, including formidable biocompatibility, low intrinsic toxicity, excellent dispensability, hydrophilicity, and surface grating, thus making them promising materials for nanophotonic applications. Owing to their unique photonic compliant properties, such as superb solubility, robust chemical inertness, large specific surface area, superabundant surface conjugation sites, superior photostability, resistance to photobleaching, and nonblinking, GQDs have emerged as a novel class of probes for the detection of biomolecules and study of their molecular interactions. Here, we present a brief overview of GQDs, their advantages over quantum dots (QDs), various synthesis procedures, and different surface conjugation chemistries for detecting cell-free circulating nucleic acids (CNAs). With the prominent rise of liquid biopsy-based approaches for real-time detection of CNAs, GQDs-based strategies might be a step toward early diagnosis, prognosis, treatment monitoring, and outcome prediction of various non-communicable diseases, including cancers.

Luminescent Composite Carbon/SiO2 Structures: Synthesis and Applications.

Luminescent carbon nanostructures (CNSs) have attracted great interest from the scientific community due to their photoluminescent properties, structural features, low toxicity, and a great variety of possible applications. Unfortunately, a few problems hinder their further development. These include the difficulties of separating a mixture of nanostructures after synthesis and the dependence of their properties on the environment and the aggregate state. The application of a silica matrix to obtain luminescent composite particles minimizes these problems and improves optical properties, reduces photoluminescence quenching, and leads to wider applications. We describe two methods for the formation of silica composites containing CNSs: inclusion of CNSs into silica particles and their grafting onto the silica surface. Moreover, we present approaches to the synthesis of multifunctional particles. They combine the unique properties of silica and fluorescent CNSs, as well as magnetic, photosensitizing, and luminescent properties via the combination of functional nanoparticles such as iron oxide nanoparticles, titanium dioxide nanoparticles, quantum dots (QDs), and gold nanoclusters (AuNCs). Lastly, we discuss the advantages and challenges of these structures and their applications. The novelty of this review involves the detailed description of the approaches for the silica application as a matrix for the CNSs. This will support researchers in solving fundamental and applied problems of this type of carbon-based nanoobjects.

Investigation of Technological and Load Intensity Parameters of the Finishing Process of Materials on Equipment with Tools Translational Kinematics.

The regularities of the formation of the resulting raster tool trajectories based on Lissajous figures for the lapping process of planes are established. This makes it possible to maximize the cutting ability of the tool, which contributes to its more uniform wear and increased productivity and processing quality. Optimal parameters of productivity and roughness of the treated surface during lapping of zirconium ceramics are achieved through the use of ASM paste 28/20 µm. Based on Preston's hypothesis, an exponential dependence of the change in the contact area during the lapping of planes of different initial shape of the macrorelief is obtained. The obtained theoretical and practical results of the study of the process of flat lapping with constant and variable clamping force of the treated surface to the surface of the tool. The influence of the force factor on the formation of the surface in the process of abrasive lapping has been established. Studies have been carried out and the main technological recommendations of precision surface treatment of workpieces based on hard, brittle ceramic material and bronze samples on equipment with a raster trajectory of the tool movement are presented. The optimal pressure value when processing ceramics should be considered 203-270 kPa (2.1-2.8 kg/cm2).

Surface-enhanced Raman scattering biosensors for detection of oncomiRs in breast cancer.

Surface-enhanced Raman scattering (SERS) has emerged as one of the most promising platforms for various biosensing applications. These sensing systems encompass the advantages of specificity, ultra-high sensitivity, stability, low cost, repeatability, and easy-to-use methods. Moreover, their ability to offer a molecular fingerprint and identify the target analyte at low levels make SERS a promising technique for detecting circulating cancer biomarkers with greater sensitivity and reliability. Among the various circulating biomolecules, oncomiRs are emerging as prominent biomarkers for the early screening of breast cancers (BCs). In this review, we provide a comprehensive understanding of different SERS-based biosensors and their application to identify BC-specific oncomiRs. We also discuss different SERS-based sensing strategies, nano-analytical frameworks, and challenges to be addressed for effective clinical translation.

Luminescent alloyed quantum dots for turn-off enzyme-based assay.

A new bioanalytical labeling system based on alloyed quantum dots' (QDs) photoluminescence quenching caused by an enzymatic reaction has been developed and tested for the first time. The catalytic role of the enzyme provides high sensitivity and the possibility of varying detecting time to improve assay sensitivity. Alloyed luminescent QDs were chosen in view of their small size (5-7 nm) and the high sensitivity of their optical properties to physicochemical interactions. Here, we described the synthesis of alloyed luminescent QDs and demonstrated the possibility of using them as a luminescent turn-off substrate for enzymatic assay. Synthesized alloyed QDs were found to be a sensitive turn-off substrate for glucose oxidase in homogeneous and heterogeneous assay models. CdZnSeS and CdZnSeS/ZnS QDs covered with dihydrolipoic acid and 2-mercaptoethanol were tested. A glucose oxidase limit of detection of 6.6 nM for the heterogenous high-throughput model assay was reached.

Influence of particle architecture on the photoluminescence properties of silica-coated CdSe core/shell quantum dots.

Light-emitting nanoparticles like semiconductor nanocrystals (termed quantum dots, QDs) are promising candidates for biosensing and bioimaging applications based on their bright and stable photoluminescent properties. As high-quality QDs are often synthesized in organic solvents, strategies needed to be developed to render them water-dispersible without affecting their optical properties and prevent changes in postmodification steps like the biofunctionalization with antibodies or DNA. Despite a large number of studies on suitable surface modification procedures, the preparation of water-soluble QDs for nanobiotechnology applications still presents a challenge. To highlight the advantages of surface silanization, we systematically explored the influence of the core/multishell architecture of CdSe/CdS/ZnS QDs and the silanization conditions on the optical properties of the resulting silanized QDs. Our results show that the optical properties of silica-coated CdSe/CdS/ZnS QDs are best preserved in the presence of a thick CdS (6 monolayers (ML)) intermediate shell, providing a high photoluminescence quantum yield (PL QY), and a relatively thick ZnS (4.5 ML) external shell, effectively shielding the QDs from the chemical changes during silica coating. In addition to the QD core/shell architecture, other critical parameters of the silica-coating process, that can have an influence on the optical properties of the QD, include the choice of the surfactant and its concentration used for silica coating. The highest PL QY of about 46% was obtained by a microemulsion silica-coating procedure with the surfactant Brij L4, making these water-dispersible QDs to well-suited optical reporters in future applications like fluorescence immunoassays, biomedicine, and bioimaging.

A photonic dual nano-hybrid assay for detection of cell-free circulating mitochondrial DNA.

Circulating cell free mitochondrial DNA (ccf-mtDNA) has emerged as a potential marker for diagnosis and prognosis of different chronic and age associated non-communicable diseases. Therefore, owing to its biomarker potential, we herein assessed a novel nano-photonic dual hybrid assay system for rapid and specific detection of ccf-mtDNA. The assay comprised of two systems, i.e. a capture and screen facet containing aminopyrene tethered carbon quantum dots for effective screening of circulating cell free nucleic acids (ccf-NAs) and a quantum dot conjugated probe for precise detection of ccf-mtDNA in the screened ccf-NAs. Our observations suggested that the developed dual-assay system possesses high feasibility and selectivity in screening of ccf-NAs and estimation of ccfmtDNA in a given sample. It also offers high versatility of measurement in different analytical platforms, indicating the translational potential of the method for possible disease risk assessment in control and field settings.

Nets of biotin-derived gold nanoparticles as a label for the C-reactive protein immunoassay.

This study presents a promising approach for the one-pot generation of the biotin-derived gold nanoparticles (GNPs@biotin). We report a direct method for the reduction of tetrachloroauric acid with biotin and generation of the labels due to nets formed via biotin-streptavidin interactions. The synthesized GNPs@biotin have a characteristic plasmon maximum, excellent colloidal stability, and streptavidin coupling efficiency. The size of the GNPs@biotin:streptavidin nets and the efficiency of interaction with specific antibodies can be easily customized by the component concentrations and time of their interaction. Moreover, the proposed labels require no additional reagents or manipulations for the synthesis, separation, or purification. The developed labels were applied for the detection of the model antigen of C-reactive protein (CRP) as a major inflammation biomarker. The assembling labels demonstrated a competitive advantage limit of CRP detection (LOD) of 1.2 ng/mL and a limit of quantification (LOQ) of 3.9 ng/mL in human plasma comparable to classical immunoassays. Moreover, the proposed approach is universal and can be potentially applied for the quantitative determination of other biomarkers in a variety of immunoassays in a combination with specific biotinylated antibodies.

Gold based nano-photonic approach for point-of-care detection of circulating long non-coding RNAs.

Development of a rapid, sensitive and easy to use point of care assay for detection of circulating long non-coding RNAs (lncRNAs) is of great importance. These biomolecules possess the ability to regulate vital cellular processes and act as biomarkers for various human non-communicable diseases. The present work aimed to develop a simplified and reliable cytometric fluorescence-based approach for precise recognition of circulating lncRNAs in a given sample using biotinylated uracil-modified oligonucleotide tethered AlexaFluor488-labeled streptavidin gold colloidal (BiO-StrAG) nano-conjugates. The fluorophores in close proximity to the gold nanoparticles result in quenching of fluorescence; however, specific recognition of target lncRNAs increases this distance which causes plasmonic enhancement of fluorescence. As per the flow cytometry and fluorometry investigations, the developed methodology provides a precise and sensitive approach for detection of the target lncRNAs (up to 5 nM in any given sample). With advantages of high selectivity and feasibility, our strategy offers great potential of being developed as a promising tool for interrogating aberrant regulation of lncRNAs functions, especially indicated in various diseased states.

Fluorescent Convertible Capsule Coding Systems for Individual Cell Labeling and Tracking.

In modern biomedical science and developmental biology, there is significant interest in optical tagging to study individual cell behavior and migration in large cellular populations. However, there is currently no tagging system that can be used for labeling individual cells on demand in situ with subsequent discrimination in between and long-term tracking of individual cells. In this article, we demonstrate such a system based on photoconversion of the fluorescent dye rhodamine B co-confined with carbon nanodots in the volume of micron-sized polyelectrolyte capsules. We show that this new fluorescent convertible capsule coding system is robust and is actively uptaken by cell lines while demonstrating low toxicity. Using a variety of cellular lines, we demonstrate how this tagging system can be used for code-like marking and long-term tracking of multiple individual cells in large cellular populations.

Point-of-care diagnostics approaches for detection of lung cancer-associated circulating miRNAs.

Circulating cell-free miRNAs (ccf-miRs) have gained significant interest as biomarkers for lung cancer (LC) diagnosis. However, the clinical application of ccf-miRs is mainly limited by time, cost, and expertise-related problems of existing detection strategies. Recently, the development of different point-of-care (POC) approaches offers useful on-site platforms, because these technologies have important features such as portability, rapid turnaround time, minimal sample requirement, and cost-effectiveness. In this review, we discuss different POC approaches for detecting ccf-miRs and highlight the utility of incorporating nanomaterials for enhanced biorecognition and signal transduction, further improving their diagnostic applicability in LC settings.