Synthesis and bioanalytical applications of nanostructures multiloaded with quantum dots

A nanoparticle-assisted signal-enhancement technique for lateral flow immunoassays

Lateral flow immunoassay (LFIA), an affordable and rapid paper-based detection technology, is employed extensively in clinical diagnosis, environmental monitoring, and food safety analysis. The COVID-19 pandemic underscored the validity and adoption of LFIA in performing large-scale clinical and public health testing. The unprecedented demand for prompt diagnostic responses and advances in nanotechnology have fueled the rise of next-generation LFIA technologies. The utilization of nanoparticles to amplify signals represents an innovative approach aimed at augmenting LFIA sensitivity. This review probes the nanoparticle-assisted amplification strategies in LFIA applications to secure low detection limits and expedited response rates. Emphasis is placed on comprehending the correlation between the physicochemical properties of nanoparticles and LFIA performance. Lastly, we shed light on the challenges and opportunities in this prolific field.

Layer-by-layer assembly of nanotheranostic particles for simultaneous delivery of docetaxel and doxorubicin to target osteosarcoma

Osteosarcoma (OS) is a rare form of primary bone cancer, impacting approximately 3.4 × 106 individuals worldwide each year, primarily afflicting children. Given the limitations of existing cancer therapies, the emergence of nanotheranostic platforms has generated considerable research interest in recent decades. These platforms seamlessly integrate therapeutic potential of drug compounds with the diagnostic capabilities of imaging probes within a single construct. This innovation has opened avenues for enhanced drug delivery to targeted sites while concurrently enabling real-time monitoring of the vehicle's trajectory. In this study, we developed a nanotheranostic system employing the layer-by-layer (LbL) technique on a core containing doxorubicin (DOXO) and in-house synthesized carbon quantum dots. By utilizing chitosan and chondroitin sulfate as polyelectrolytes, we constructed a multilayered coating to encapsulate DOXO and docetaxel, achieving a coordinated co-delivery of both drugs. The LbL-functionalized nanoparticles exhibited an approximate size of 150 nm, manifesting a predominantly uniform and spherical morphology, with an encapsulation efficiency of 48% for both drugs. The presence of seven layers in these systems facilitated controlled drug release over time, as evidenced by in vitro release tests. Finally, the impact of the LbL-functionalized nanoparticles was evaluated on U2OS and Saos-2 osteosarcoma cells. The synergistic effect of the two drugs was found to be crucial in inducing cell death, particularly in Saos-2 cells treated with nanoparticles at concentrations higher than 10 μg/ml. Transmission electron microscopy analysis confirmed the internalization of the nanoparticles into both cell types through endocytic mechanisms, revealing an underlying mechanism of necrosis-induced cell death.

Advances in quantum dots as diagnostic tools

Quantum dots (QDs) are crystalline inorganic semiconductor nanoparticles a few nanometers in size that possess unique optical electronic properties vs those of larger materials. For example, QDs usually exhibit a strong and long-lived photoluminescence emission, a feature dependent on size, shape and composition. These special optoelectronic properties make them a promising alternative to conventional luminescent dyes as optical labels in biomedical applications including biomarker quantification, biomolecule targeting and molecular imaging. A key parameter for use of QDs is to functionalize their surface with suitable (bio)molecules to provide stability in aqueous solutions and efficient and selective tagging biomolecules of interest. Researchers have successfully developed biocompatible QDs and have linked them to various biomolecule recognition elements, i.e., antibodies, proteins, DNA, etc. In this chapter, QD synthesis and characterization strategies are reviewed as well as the development of nanoplatforms for luminescent biosensing and imaging-guided targeting. Relevant biomedical applications are highlighted with a particular focus on recent progress in ultrasensitive detection of clinical biomarkers. Finally, key future research goals to functionalize QDs as diagnostic tools are explored.

A functional ratio fluorescence sensor platform based on the graphene/Mn-ZnS quantum dots loaded with molecularly imprinted polymer for selective and visual detection sinapic acid

A functional ratio fluorescence sensor based on the molecularly imprinted polymer (MIP) coated double quantum dots (QDs) being composited of Mn-ZnS QDs and silica-coated graphene quantum dots (GQDs@SiO₂) had been established for the sensitive, selective and visual detection of sinapic acid (SA). MIPs@Mn-ZnS/GQDs@SiO₂ was synthesized through a simple one-pot sol-gel reaction, and it exhibited two fluorescence emission peaks with yellow fluorescence of Mn-ZnS QDs at 580 nm and the blue fluorescence of GQDs at 445 nm. SA can selectively enhance the fluorescence of GQDs but quench the Mn-ZnS QDs fluorescence to the MIPs@Mn-ZnS/GQDs@SiO₂. The ratio of fluorescence enhancement to fluorescence reduction is linear with the concentration of SA from 9 to 81 nM with the detection limits of 0.8388 nM (S/N = 3). And the constructed fluorescent probe can also be used to visually detect SA according to the change of color. More importantly, molecular imprinting technique enables the sensors to selectively recognize the SA while other similar structure molecules hardly interfere with the SA determination in the measurement environment. Meanwhile, the fluorescence sensors have the advantages of fast response time and long duration of fluorescence intensity. These excellent performances made the proposed method to be applied for the determination of SA in Semen Sinapis and Descurainiae Semen.

Fluorescent AgInS/ZnS quantum dots microplate and lateral flow immunoassays for folic acid determination in juice samples

A noninstrumental rapid test for folic acid (FA) detection with visual results evaluation utilizing bright water-stable AgInS/ZnS (AIS/ZnS) quantum dots (QDs) is reported . AIS/ZnS QDs are hydrophilic photostable nanocrystals with size < 7 nm and emission in the visible range. They were synthesized directly in the water phase by a simple method compared to the synthesis of other QDs and conjugated with monoclonal antibodies specific for FA via ligand carboxyl groups. The conjugate was used for the development of instrumental qualitative and rapid quantitative FA detection methods. The competitive fluorescent microplate immunosorbent assay provided a limit of detection of 0.1 ng/mL FA and half maximal inhibitory concentration (IC₅₀) of 24 ng/mL FA. The analytical signal was measured at ʎ_ex = 410 nm and ʎ_em=590 nm. The proposed method showed no cross-reaction with other group B vitamins. For FA screening in juice samples, the lateral flow immunoassay was developed with a visual cutoff level of 3 μg/mL. In our perception, the developed methods are convenient for proving the perception of the AIS/ZnS QDs application as a luminescent label for immunoassay and are effective for FA detection. Graphical abstract.

Current Status and Future Prospects of Semiconductor Quantum Dots in Botany

The development of botanical applications of nanomaterials has produced a new generation of technologies that can profoundly impact botanical research. Semiconductor quantum dots (QDs) are an archetype nanomaterial and have received significant interest from diverse research communities, owing to their unique and optimizable optical properties. In this review, we describe the most recent progress on QD-based botanical research and discuss the uptake, translocation, and effects of QDs on plants and the potential applications of QDs in botany. A critical evaluation of the current limitations of QD technologies is discussed, along with the future prospects in QD-based botanical research.

Multiplex Lateral Flow Immunoassay: An Overview of Strategies towards High-throughput Point-of-Need Testing

Simultaneous measurement of different substances from a single sample is an emerging issue for achieving efficient and high-throughput detection in several fields of application. Although immunoanalytical techniques have well-established and prevailing advantages over alternative screening analytical platforms, one of the incoming challenges for immunoassay is exact multiplexing. Lateral flow immunoassay (LFIA) is a leading immunoanalytical technique for onsite analysis, thanks to its simplicity, rapidity, and cost-effectiveness. Moreover, LFIA architecture is adaptable to multiplexing, and is therefore a possible answer to the pressing demand of multiplexing point-of-need analysis. This review presents an overview of diverse approaches for multiplex LFIA, with a special focus on strategies based on new types of magnetic, fluorescent, and colored labels.

Antibody immobilization strategy for the development of a capacitive immunosensor detecting zearalenone

A highly sensitive flow-injection capacitive immunosensor was developed for detection of the mycotoxin zearalenone (ZEN). Different strategies for immobilization of an anti-ZEN antibody on the surface of a gold electrode, i.e. polytyramine or self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (3-MPA) and lipoic acid (LA), were used and their performances were compared. The LA- and 3-MPA-based systems showed broad linear ranges for ZEN determination, i.e. from 0.010 nM to 10 nM and from 0.020 nM to 10 nM, respectively. Under optimal conditions, the LA-based immunosensor was capable of performing up till 13 regeneration-interaction cycles (with use of glycine HCl, pH 2.4) with a limit of detection (LOD) of 0.0060 nM, equivalent to 1.9 pg mL^-1. It also demonstrated a good inter-assay precision (RSD < 10%). However, the tyramine-based capacitive immunosensor showed a bad repeatability (only 4 regeneration-interaction cycles were possible) and inter-assay precision (RSD > 15%) which did not allow sensitive and precise measurements. The LA-based method was compared with a direct ELISA. These results demonstrated that the label-free developed capacitive immunosensor had a better sensitivity and shorter analysis time in comparison with the direct microwell-plate format.

Positively Charged Hyperbranched Polymers with Tunable Fluorescence and Cell Imaging Application

Fluorescence-tunable materials are becoming increasingly attractive because of their potential applications in optics, electronics, and biomedical technology. Herein, a multicolor molecular pixel system is realized using a simple copolymerization method. Bleeding of two complementary colors from blue and yellow fluorescence segments reproduced serious multicolor fluorescence materials. Interestingly, the emission colors of the polymers can be fine-tuned in the solid state, solution phase, and in hydrogel state. More importantly, the positive fluorescent polymers exhibited cell-membrane permeable ability and were found to accumulate on the cell nucleus, exhibiting remarkable selectivity to give bright fluorescence. The DNA/RNA selectivity experiments in vitro and in vivo verified that [tris(4-(pyridin-4-yl)phenyl)amine]-[1,8-dibromooctane] has prominent selectivity to DNA over RNA inside cells.

Movement of new direction from conjugated polymer to semiconductor composite polymer nanofiber

In the past few years, there was a tremendous growth in conjugated polymer nanofibers via design of novel conjugated polymers with inorganic materials. Synthetic routes to these conjugated polymers involve new, mild polymerization techniques, which enable the formation of well-defined polymer architectures. This review provides interest in the development of novel (semi) conducting polymers, which combine both organic and inorganic blocks in one framework. Due to their ability to act as chemosensors or to detect various chemical species in environmental and biological systems, fluorescent conjugated polymers have gained great interest. Nanofibers of metal oxides and sulfides are particularly interesting in both their way of applications and fundamental research. These conjugated nanofibers operated for many applications in organic electronics, optoelectronics, and sensors. Synthesis of electrospun fibers by electrospinning technique discussed in this review is a simple method that forms conjugated polymer nanofibers. This review provides the basics of the technique and its recent advances in the formation of highly conducting and high-mobility polymer fibers towards their adoption in electronic application.

Progress in utilisation of graphene for electrochemical biosensors

This review discusses recent graphene (GR) electrochemical biosensor for accurate detection of biomolecules, including glucose, hydrogen peroxide, dopamine, ascorbic acid, uric acid, nicotinamide adenine dinucleotide, DNA, metals and immunosensor through effective immobilization of enzymes, including glucose oxidase, horseradish peroxidase, and haemoglobin. GR-based biosensors exhibited remarkable performance with high sensitivities, wide linear detection ranges, low detection limits, and long-term stabilities. Future challenges for the field include miniaturising biosensors and simplifying mass production are discussed.

Fabrication and characterization of a folic acid-bound 5-fluorouracil loaded quantum dot system for hepatocellular carcinoma targeted therapy

In the present study, we covalently coupled folic acid (FA) and 5-fluorouracil acetic acid (FUA) on the surface of quantum dots (QDs) to produce a tumor targeting drug delivery system, FA-QDs-FUA.

Ultra-sensitive detection of ibuprofen (IBP) by electrochemical aptasensor using the dendrimer-quantum dot (Den-QD) bioconjugate as an immobilization platform with special features

This study describes a high-performance electrochemical aptasensor which is employed to detect Ibuprofen (IBP) as a painkiller drug by using a novel platform as an integrated sensing interface. In order to make the aptasensor, the Den-QD bioconjugate was immobilized on the surface of a GC electrode and followed the Apt was incubated on this surface. The incubation of the IBP on the aptasensor surface and the formation of the Apt/IBP complex, led to a hindered electron transfer reaction on the sensing surface, which decreased the peak current of the redox probe. Under the optimum condition, the assay had two dynamic ranges with a detection limit down to 333fM. The developed aptasensor reliably detects IBP in a real sample. Our results demonstrated that the proposed strategy has many advantages and the Den-QD bioconjugate may become a promising nanocomposite for the electrochemical sensing applications.

A Dual-Color Quantum Dots Encoded Frit-Based Immunoassay for Visual Detection of Aflatoxin M1 and Pirlimycin Residues in Milk

Mycotoxins and antibacterial agents are the main chemical hazards that lead to several health problems. Nowadays, multiplex immunoassay is a primary goal throughout the world. Here, aflatoxin M₁ and pirlimycin were selected as models, and a novel dual colorimetric encoded frit-based immunoassay was developed for simultaneously screening of aflatoxin M₁ and pirlimycin residues in milk. This multiplex frit-based immunoassay combined two monoclonal antibodies to extend the spectrum of analytes and to enable detection of two classes of analytes in a single test. The cutoff values were 0.02 μg/kg for aflatoxin M₁ and 0.5 μg/kg for pirlimycin, which satisfied the requirement to measure the maximum residue levels. The novel colorimetric frit-based immunoassay has the advantage of high throughput, short analysis time, reduced overall cost per assay, and can be used as a rapid screening technique for simultaneously detecting aflatoxin M₁ and pirlimycin residues in milk.

Metal-based quantum dots: synthesis, surface modification, transport and fate in aquatic environments and toxicity to microorganisms

The intense interest in metal-based QDs is diluted by the fact that they cause risks to aquatic environments.

Synthesis, modification, bioconjugation of silica coated fluorescent quantum dots and their application for mycotoxin detection

To create bright and stable fluorescent biolabels for immunoassay detection of mycotoxin deoxynivalenol in food and feed, CdSe/CdS/ZnS core-shell quantum dots (QDs) were encapsulated in silica nanoparticles through a water-in-oil reverse microemulsion process. The optical properties and stability of the obtained silica coated QDs (QD@SiO2), modified with amino, carboxyl and epoxy groups and stabilized with polyethylene glycol fragments, were characterized in order to assess their bioapplicability. The developed co-condensation techniques allowed maintaining 80% of the initial fluorescent properties and yielded stable fluorescent labels that could be easily activated and bioconjugated. Further, the modified QD@SiO2 were efficiently conjugated with antibodies and applied as a novel label in a microtiter plate based immunoassay and a quantitative column-based rapid immunotest for deoxynivalenol detection with IC50 of 473 and 20 ng/ml, respectively.

Sensitive electrochemical immunoassay with signal enhancement based on nanogold-encapsulated poly(amidoamine) dendrimer-stimulated hydrogen evolution reaction

A new electrochemical immunosensor with signal enhancement was designed for sensitive detection of disease-related protein (human carbohydrate antigen 19-9, CA 19-9 used in this case).