Comet-like Heterodimers “Gold Nanoflower @Graphene Quantum Dots” Probe with FRET “Off” to DNA Circuit Signal “On” for Sensing and Imaging MicroRNA In Vitro and In Vivo

Proximity-Induced Bipedal DNA Walker for Accurately Visualizing microRNA in Living Cancer Cell

DNA walker, a type of dynamic DNA device that is capable of moving progressively along prescribed walking tracks, has emerged as an ideal and powerful tool for biosensing and bioimaging. However, most of the reported three-dimensional (3D) DNA walker were merely designed for the detection of a single target, and they were not capable of achieving universal applicability. Herein, we reported for the first time the development of a proximity-induced 3D bipedal DNA walker for imaging of low abundance biomolecules. As a proof of concept, miRNA-34a, a biomarker of breast cancer, is chosen as the model system to demonstrate this approach. In our design, the 3D bipedal DNA walker can be generated only by the specific recognition of two proximity probes for miRNA-34a. Meanwhile, it stochastically and autonomously traveled on 3D tracks (gold nanoparticles) via catalytic hairpin assembly (CHA), resulting in the amplified fluorescence signal. In comparison with some conventional DNA walkers that were utilized for living cell imaging, the 3D DNA walkers induced by proximity ligation assay can greatly improve and ensure the high selectivity of bioanalysis. By taking advantage of these unique features, the proximity-induced 3D bipedal DNA walker successfully realizes accurate and effective monitoring of target miRNA-34a expression levels in living cells, affording a universal, valuable, and promising platform for low-abundance cancer biomarker detection and accurate identification of cancer.

One-Pot Synthesis of CdTe/ZnS Quantum Dots and their Physico-Chemical Characterization

A known property of quantum dots (QDs) is their characteristic luminescence, which would make it possible to detect different types of cancers after being functionalized with some type of biological molecule. For this reason, in the present investigation a methodological analysis of the physicochemical characteristics of the CdTe/ZnS core/shell QDs was carried out, using techniques such as Optical Absorbance Spectroscopy (UV-Vis), Molecular Fluorescence, Fourier Transform Infrared Spectroscopy (FT-IR), Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Zeta Potential that allowed to verify the photoluminescent effectiveness of these semiconductor nanocrystals as an alternative to conventional techniques currently used for the detection of specific cancers smaller than 1 cm. The study consisted of theoretically determining the bandgap energy, the size of the nanocrystals and the molar absorptivity from the wavelength value for the maximum intensity of the excitonic peak. It was also possible to verify the maximum intensity for each sample and thus evaluate its photoluminescent response, as well as it was possible to determine the charge distribution, the hydrodynamic size and the surface composition of each quantum dot. The results obtained correspond to what has been reported in the literature, which makes them good candidates for the detection of cancer in precancerous stages.

Ratiometric fluorescence platform for the ultrasensitive detection of kanamycin based on split aptamer co-recognition triggers Mg2+-DNAzyme-driven DNA walker systems

In this work, a novel 3D-DNA walker signal amplification strategy was designed to construct a fluorescent aptasensor for the detection of kanamycin (KAN). The aptasensor utilizes split aptamers for the synergistic recognition of KAN. The presence of KAN induces the split aptamers recombination to form the Mg2+-DNAzyme structure, which is activated by Mg2+ to drive the 3D-DNA walker process for cascading signal amplification. Employing gold nanoflowers (AuNFs) as walking substrate material increases the local DNA concentration to enhance the walker efficiency. The prepared fluorescent aptasensor achieved efficient and sensitive detection of KAN with satisfactory results in the concentration range of 1 × 10-8 - 1 × 10-3 μg/kg and the detection limit of 5.63 fg/kg. Meanwhile, the designed fluorescent aptasensor exhibited favorable specificity, anti-interference, storage stability and reproducibility, and verified the feasibility of its application in milk samples. The present work provides an effective tool for the regulation of KAN contamination in animal-derived foods with promising prospects.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Dual-signal output fluorescent aptasensor based on DNA programmability and gold nanoflowers for multiple mycotoxins detection

Herein, a dual-signal output fluorescent aptamer sensor was constructed for the simultaneous detection of aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) using the specific recognition ability of aptamers and the programmability of DNA. A functional capture probe (cDNA) was designed with the black hole quenching motif BHQ1 labeled at the 5' end and biotin (bio) labeled at the 3' end. The fluorescent dye Cy3-labeled aflatoxin B1 aptamer (AFB₁-Apt) and the carboxyfluorescein FAM-labeled ochratoxin A aptamer (OTA-Apt) were used as two fluorescent probes. The cDNA is anchored to the quenching material gold nanoflowers (AuNFs) by the action of streptavidin (SA) and biotin. Its ends can be complementarily paired with two fluorescent probe bases to form a double-stranded structure. The fluorescence of Cy3 was quenched by AuNFs, and the fluorescence of FAM was quenched by BHQ1 through the fluorescence energy resonance transfer (FRET) effect, forming a fluorescence quenching system. Due to the high affinity of the target and the aptamer, the structure of the aptamer probe changes and detaches from the sensor when AFB₁ and OTA are present, resulting in enhanced fluorescence. Under optimal conditions, the linear range of AFB₁ was 0.1-100 ng/mL (R² = 0.996), the limit of detection (LOD) was as low as 0.014 ng/mL, and the limit of quantification (LOQ) was 0.046 ng/mL. The linear range of OTA was 0.1-100 ng/mL (R² = 0.995), the limit of detection (LOD) was as low as 0.027 ng/mL, and the limit of quantification (LOQ) was 0.089 ng/mL. The sensor had high accuracy in detecting both AFB₁ and OTA in real sample analysis. The results of the t test show that there is no significant difference between the results of this study and the high-performance liquid phase (HPLC) method, indicating that the prepared sensor can be used as a potential platform for multiple mycotoxins detection.

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.

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.

Graphene oxide-based fluorescent biosensors and their biomedical applications in diagnosis and drug discovery

Graphene oxide (GO), an oxidized derivative of graphene, has received much attention for developing novel fluorescent bioanalytic platforms due to its remarkable optical properties and biocompatibility. The reliable performance and robustness of GO-based biosensors have enabled various applications in the biomedical field including diagnosis and drug discovery. Here, recent advances in the development of GO-based fluorescent biosensors are overviewed, particularly nucleic acid detection and enzyme activity assay. In addition, practical applications in biomarker detection and high-throughput screening are also examined. Lastly, basic design principles and remaining challenges of these types of biosensors are discussed for further progress.

Synthesis of Highly Near-Infrared Fluorescent Graphene Quantum Dots Using Biomass-Derived Materials for In Vitro Cell Imaging and Metal Ion Detection

Graphene quantum dots (GQDs) are a subset of fluorescent nanomaterials that have gained recent interest due to their photoluminescence properties and low toxicity and biocompatibility features for bioanalysis and bioimaging. However, it is still a challenge to prepare highly near-infrared (NIR) fluorescent GQDs using a facile pathway. In this study, NIR GQDs were synthesized from the biomass-derived organic molecule cis-cyclobutane-1,2-dicarboxylic acid via one-step pyrolysis. The resulting GQDs were then characterized by various analytical methods such as UV-Vis absorption spectroscopy, fluorescence spectroscopy, dynamic light scattering, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Moreover, the photostability and stability over a wide pH range were also investigated, which indicated the excellent stability of the prepared GQDs. Most importantly, two peaks were found in the fluorescence emission spectra of the GQDs, one of which was located in the NIR region of about 860 nm. Finally, the GQDs were applied for cell imaging with human breast cancer cell line, MCF-7, and cytotoxicity analysis with mouse macrophage cell line, RAW 246.7. The results showed that the GQDs entered the cells through endocytosis on the fluorescence images and were not toxic to the cells up to a concentration of 200 μg/mL. Thus, the developed GQDs could be a potential effective fluorescent bioimaging agent. Finally, the GQDs depicted fluorescence quenching when treated with mercury metal ions, indicating that the GQDs could be used for mercury detection in biological samples as well.

Applications of Graphene Quantum Dots in Biomedical Sensors

Due to the proliferative cancer rates, cardiovascular diseases, neurodegenerative disorders, autoimmune diseases and a plethora of infections across the globe, it is essential to introduce strategies that can rapidly and specifically detect the ultralow concentrations of relevant biomarkers, pathogens, toxins and pharmaceuticals in biological matrices. Considering these pathophysiologies, various research works have become necessary to fabricate biosensors for their early diagnosis and treatment, using nanomaterials like quantum dots (QDs). These nanomaterials effectively ameliorate the sensor performance with respect to their reproducibility, selectivity as well as sensitivity. In particular, graphene quantum dots (GQDs), which are ideally graphene fragments of nanometer size, constitute discrete features such as acting as attractive fluorophores and excellent electro-catalysts owing to their photo-stability, water-solubility, biocompatibility, non-toxicity and lucrativeness that make them favorable candidates for a wide range of novel biomedical applications. Herein, we reviewed about 300 biomedical studies reported over the last five years which entail the state of art as well as some pioneering ideas with respect to the prominent role of GQDs, especially in the development of optical, electrochemical and photoelectrochemical biosensors. Additionally, we outline the ideal properties of GQDs, their eclectic methods of synthesis, and the general principle behind several biosensing techniques.

Recent Advances of Plasmonic Gold Nanoparticles in Optical Sensing and Therapy

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Gold nanoparticles with special surface plasmon resonance have been widely used in sensing and therapy because of their easy preparation, unique optical properties, excellent biocompatibility, etc. The applications of gold nanoparticles in chemo/biosensing, imaging, and therapy reported in 2016-2019, are summarized in this review. Regarding the gold nanoparticle-based sensing or imaging, sensing mechanisms and strategies are provided to illustrate the concepts for designing sensitive and selective detection platforms. Gold nanoparticlemediated therapy is introduced by surface plasmon resonance-based therapy and delivery-based therapy. Beyond the sole therapeutic system, platforms through synergistic therapy are also discussed. In the end, discussion of the challenges and future trends of gold nanoparticle-based sensing and therapy systems is described.

Recent advances on nanomaterials-based fluorimetric approaches for microRNAs detection

MicroRNAs are types of small single-stranded endogenous highly conserved non-coding RNAs, which play main regulatory functions in a wide range of cellular and physiological events, such as proliferation, differentiation, neoplastic transformation, and cell regeneration. Recent findings have proved a close association between microRNAs expression and the development of many diseases, indicating the importance of microRNAs as clinical biomarkers and targets for drug discovery. However, due to a number of prominent characteristics like small size, high sequence similarity and low abundance, sensitive and selective identification of microRNAs has rather been a hardship through routine traditional assays, including quantitative polymerase chain reaction, microarrays, and northern blotting analysis. More recently, the soaring progression in nanotechnology and fluorimetric methodologies in combination with nanomaterials have promised microRNAs detection with high sensitivity, efficiency and selectivity, excellent reproducibility and lower cost. Therefore, this review will represent an overview of latest advances in microRNAs detection through nanomaterials-based fluorescent methods, like gold nanoparticles, silver and copper nanoclusters, graphene oxide, and magnetic silicon nanoparticles.

Application of Förster Resonance Energy Transfer (FRET) technique to elucidate intracellular and In Vivo biofate of nanomedicines

Extensive studies on nanomedicines have been conducted for drug delivery and disease diagnosis (especially for cancer therapy). However, the intracellular and in vivo biofate of nanomedicines, which is significantly associated with their clinical therapeutic effect, is poorly understood at present. This is because of the technical challenges to quantify the disassembly and behaviour of nanomedicines. As a fluorescence- and distance-based approach, the Förster Resonance Energy Transfer (FRET) technique is very successful to study the interaction of nanomedicines with biological systems. In this review, principles on how to select a FRET pair and construct FRET-based nanomedicines have been described first, followed by their application to study structural integrity, biodistribution, disassembly kinetics, and elimination of nanomedicines at intracellular and in vivo levels, especially with drug nanocarriers including polymeric micelles, polymeric nanoparticles, and lipid-based nanoparticles. FRET is a powerful tool to reveal changes and interaction of nanoparticles after delivery, which will be very useful to guide future developments of nanomedicine.

Cancer Cell Membrane Camouflaged Nanoprobe for Catalytic Ratiometric Photoacoustic Imaging of MicroRNA in Living Mice

Herein, a cancer cell (MCF-7 cell) membrane-encapsulated dendritic mesoporous silica nanoparticle simultaneously functionalized with DNA-photoacoustic (DNA-PA) probes and glutathione (GSH)-responsive DNA fuel strands for PA imaging of tumor-related miRNA in living mice with signal amplification ability is developed. It is demonstrated that one target miRNA can trigger disassembly of multiple PA fluorophore probes from the quencher with the aid of GSH-responsive DNA fuel strands via the entropy-driven process, resulting remarkable amplified change of PA signal ratio. Using oncogenic miRNA-21 as a model, a linear relationship between miRNA-21 concentrations and PA ratio in a dynamic range from 10 × 10^-12 m to 100 × 10^-9 m and a limit of detection down to 11.69 × 10^-12 m are established. The accurate PA signal observation related to miRNA-21s in the tumor area in living mice is demonstrated, and the PA signal ratio increases significantly via the injection of miRNA-21. It is anticipated that the catalytic ratiometric PA imaging system can be applied to an array of molecular detection in living system by rational detection probe design.