Catalytic Molecular Imaging of MicroRNA in Living Cells by DNA-Programmed Nanoparticle Disassembly

Highly Sensitive Naked-Eye Assay for Enterovirus 71 Detection Based on Catalytic Nanoparticle Aggregation and Immunomagnetic Amplification

Development of sensitive, convenient, and cost-effective virus detection product is of great significance to meet the growing demand of clinical diagnosis at the early stage of virus infection. Herein, a naked-eye readout of immunoassay by means of virion bridged catalase-mediated in situ reduction of gold ions and growth of nanoparticles, has been successfully proposed for rapid visual detection of Enterovirus 71 (EV71). Through tailoring the morphologies of the produced gold nanoparticles (GNPs) varying between dispersion and aggregation, a distinguishing color changing was ready for observation. This colorimetric detection assay, by further orchestrating the efficient magnetic enrichment and the high catalytic activity of enzyme, is managed to realize highly sensitive detection of EV71 virions with the limit of detection (LOD) down to 0.65 ng/mL. Our proposed method showed a much lower LOD value than the commercial ELISA for EV71 virion detection. Comparing to the current clinical gold standard polymerase chain reaction (PCR) method, our strategy provided the same diagnostic outcomes after testing real clinical samples. Besides, this strategy has no need of complicated sample pretreatment or expensive instruments. Our presented naked-eye immunoassay method holds a promising prospect for the early detection of virus-infectious disease especially in resource-constrained settings.

Hybrid Nanoparticle Pyramids for Intracellular Dual MicroRNAs Biosensing and Bioimaging

This study strategically fabricates multifunctional nanopyramids to allow the ultrasensitive quantification of dual microRNAs (miR-203^b and miR-21) in living cells and their responsive bioimaging in vivo. The nanopyramids, composed of Au-Cu₉ S₅ nanoparticles (NPs), upconversion NPs (UCNPs), and Ag₂ S NPs, emit two luminescent signals simultaneously with excitation at 808 nm, arising from the UCNPs at 541 nm in the visible region and from the Ag₂ S NPs at 1227 nm in the second window of near-infrared (NIR-II) region. The upconversion luminescence has a linear relationship with miR-203^b from 0.13 to 54.54 fmol per 10 µg_RNA and a limit of detection (LOD) of 0.09 fmol per 10 µg_RNA , whereas the Ag₂ S NP luminescence has a linear relationship with miR-21 from 0.37 to 43.56 fmol per 10 µg_RNA , with a LOD of 0.23 fmol per 10 µg_RNA . Significantly, this study demonstrates that the nanopyramids can be successfully used for miRs-responsive bioimaging in a tumor-bearing animal model. Furthermore, taking advantage of the photothermal capabilities of pyramids, the tumors can also be eliminated completely. These nanopyramids not only overcome the obstacles in the simultaneous detection of multiple miRs at the cellular level but also provide a cancer theranostic platform in vivo.

Building Electromagnetic Hot Spots in Living Cells via Target-Triggered Nanoparticle Dimerization

Electromagnetic hot spots of surface-enhanced Raman scattering have been extensively employed for bioanalysis in solution or on a substrate, but building hot spots in living systems for probing targets of interest has not been achieved yet because of the complex and dynamic physiological environment. Herein, we show that a target-programmed nanoparticle dimerization can be combined with the background-free Raman reporters (alkyne, C≡C; nitrile, C≡N) for multiplexed imaging of microRNAs (miRNAs) in living cells. The in situ formation of plasmonic dimers results in an intense hot spot, thus dramatically enhancing the Raman signals of the reporters residing in the hot spot. More significantly, the reporters exhibit single nonoverlapping peaks in the cellular Raman-silent region (1800-2800 cm^-1), thus eliminating spectral unmixing and background interference. A 3D Raman mapping technique was harnessed to monitor the spatial distribution of the dimers and thus the multiple miRNAs in cells. This approach could be extended to probe other biomarkers of interest for monitoring specific pathophysiological events at the live-cell level.

Heterogeneous dimer peptide-conjugated polylysine dendrimer-Fe3O4 composite as a novel nanoscale molecular probe for early diagnosis and therapy in hepatocellular carcinoma

A novel nanoscale molecular probe is formulated in order to reduce toxicity and side effects of antitumor drug doxorubicin (DOX) in normal tissues and to enhance the detection sensitivity during early imaging diagnosis. The mechanism involves a specific targeting of Arg-Gly-Asp peptide (RGD)-GX1 heterogeneous dimer peptide-conjugated dendrigraft poly-l-lysine (DGL)-magnetic nanoparticle (MNP) composite by α_vβ₃-integrin/vasculature endothelium receptor-mediated synergetic effect. The physicochemical properties of the nanoprobe were characterized by using transmission electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, dynamic light scattering (DLS), and vibrating sample magnetometer. The average diameter of the resulting MNP-DGL-RGD-GX1-DOX nanoparticles (NPs) was ~150-160 nm by DLS under simulate physiological medium. In the present experimental system, the loading amount of DOX on NPs accounted for 414.4 mg/g for MNP-DGL-RGD-GX1-DOX. The results of cytotoxicity, flow cytometry, and cellular uptake consistently indicated that the MNP-DGL-RGD-GX1-DOX NPs were inclined to target HepG2 cells in selected three kinds of cells. In vitro exploration of molecular mechanism revealed that cell apoptosis was associated with the overexpression of Fas protein and the significant activation of caspase-3. In vivo magnetic resonance imaging and biodistribution study showed that the MNP-DGL-RGD-GX1-DOX formulation had high affinity to the tumor tissue, leading to more aggregation of NPs in the tumor. In vivo antitumor efficacy research verified that MNP-DGL-RGD-GX1-DOX NPs possessed significant antitumor activity and the tumor inhibitory rate reached 78.5%. These results suggested that NPs could be promising in application to early diagnosis and therapy in hepatocellular carcinoma as a specific nanoprobe.

QD-Biopolymer-TSPP Assembly as Efficient BiFRET Sensor for Ratiometric and Visual Detection of Zinc Ion

In this work, we report a new type of quantum dot (QD)-based fluorescence resonance energy transfer (FRET) assembly and its utility for sensing Zn²⁺ in different media. The assembly on the QD scaffold is via first coating of poly(dA) homopolymer/double-stranded DNA, followed by loading of meso-tetra(4-sulfonatophenyl)porphine dihydrochloride (TSPP), both of which are electrostatic, offering the advantages of cost-efficiency and simplicity. More importantly, the biopolymer coating minimizes the interfacial thickness to be ≤2 nm for QD-TSPP FRET, which results in improvements of up to 60-fold for single FRET efficiency and nearly 4-fold for total FRET efficiency of the QD-biopolymer-TSPP assemblies in comparison with silica-coating-based QD-TSPP assemblies. On the basis of Zn²⁺-chelation-induced spectral modulation, dual-emission QD-poly(dA)-TSPP assemblies are developed as a ratiometric Zn²⁺ sensor with increased sensitivity and specificity. The sensor either in solution or on a paper substrate displays continuous color changes from yellow to bright green toward Zn²⁺, exhibiting excellent visualization capability. By utilizing the competitive displacement of Zn²⁺, the sensor is also demonstrated to have good reversibility. Furthermore, the sensor is successfully used to visualize exogenous Zn²⁺ in living cells. Together the QD-biopolymer-TSPP assembly provides an inexpensive, sensitive, and reliable sensing platform not only for on-site analytical applications but also for high-resolution cellular imaging.

Photo-clickable microRNA for in situ fluorescence labeling and imaging of microRNA in living cells

A photo-clickable microRNA was constructed for in situ fluorescence labeling and imaging of microRNA in living cells with spatiotemporal resolution.

Enzyme-free, signal-amplified nucleic acid circuits for biosensing and bioimaging analysis

Enzyme-free, signal-amplified nucleic acid circuits utilize programmed assembly reactions between nucleic acid substrates to transduce a chemical input into an amplified detection signal.

Can nanotechnology improve cancer diagnosis through miRNA detection?

miRNAs are key regulators of gene expression, and alterations in their expression levels correlate with the onset and progression of cancer. Although miRNAs have been proposed as biomarkers for cancer diagnosis, their application in routine clinical praxis is yet to come. Current quantification strategies have limitation, and there is a great interest in developing innovative ones. Since a few years, nanotechnology-based approaches for miRNA quantification are emerging at fast pace but there is urgent need to go beyond the proof-of-concept stage. Nanotechnology will have a strong impact on cancer diagnosis through miRNA detection only if it is demonstrated that the newly developed approaches are indeed working on ‘real-world’ samples under standardized conditions.

Label-free detection of microRNA based on coupling multiple isothermal amplification techniques

MicroRNA (miRNA) was a promising class of cancer biomarkers. Here we developed a label-free method for sensitive measurement of let-7d miRNA based on multiple amplification techniques. The primer will bind to the duplex strand DNA that was formed by stem-loop template and target let-7d to initiate strand displacement amplification (SDA) in tandem. The released single strand DNA will be a primer to bind the circular template to initiate rolling circle amplification (RCA). The products based on multiple amplifications will be detected by a standard fluorimeter with N-methyl mesoporphyrin IX (NMM) as the fluorescent indicator. The proposed method exhibited excellent selectivity and high sensitivity with a detection limit of as low as 1.5 × 10⁻¹³ M. Moreover, this methodology was used for the determination of biomolecules in real serum samples with satisfying results.

A label-free colorimetric aptasensor for simple, sensitive and selective detection of Pt (II) based on platinum (II)-oligonucleotide coordination induced gold nanoparticles aggregation

Herein, a gold nanoparticles (AuNPs) based label-free colorimetric aptasensor for simple, sensitive and selective detection of Pt (II) was constructed for the first time. Four bases (G-G mismatch) mismatched streptavidin aptamer (MSAA) was used to protect AuNPs from salt-induced aggregation and recognize Pt (II) specifically. Only in the presence of Pt (II), coordination occurs between G-G bases and Pt (II), leading to the activation of streptavidin aptamer. Streptavidin coated magnetic beads (MBs) were used as separation agent to separate Pt (II)-coordinated MSAA. The residual less amount of MSAA could not efficiently protect AuNPs anymore and aggregation of AuNPs will produce a colorimetric product. With the addition of Pt (II), a pale purple-to-blue color variation could be observed by the naked eye. A detection limit of 150nM and a linear range from 0.6μM to 12.5μM for Pt (II) could be achieved without any amplification.

A pH-responsive DNA nanomachine-controlled catalytic assembly of gold nanoparticles

The toehold-mediated DNA-strand-displacement reaction has unique programmable properties for driving the catalytic assembly of gold nanoparticles (AuNPs). Herein, we introduced a pH-responsive triplex structure into the DNA-strand-displacement-based catalytic assembly system of DNA-AuNPs to add an additional controlling factor, namely the pH. In this catalytic system, the aggregation rate of AuNPs could be regulated by both internal factors (concentrations of substrate, target, etc.) and an external control (pH gradient). This strategy can be used to construct pH-induced DNA logic gates and sophisticated DNA networks as well as to image instantaneous pH changes in living cells.

Current techniques for visualizing RNA in cells

Labeling RNA is of utmost interest, particularly in living cells, and thus RNA imaging is an emerging field. There are numerous methods relying on different concepts ranging from hybridization-based probes, over RNA-binding proteins to chemo-enzymatic modification of RNA. These methods have different benefits and limitations. This review aims to outline the current state-of-the-art techniques and point out their benefits and limitations.

Cellular processing and destinies of artificial DNA nanostructures

This review gives a panoramic view of the many DNA nanotechnology applications in cells, mechanistic understanding of how and where their interactions occur and their subsequent outcomes.

Highly sensitive and selective miRNA detection based on a closed ring probe and multiple signal amplification

A highly sensitive and selective miRNA detection approach based on a small circular probe and dual signal amplification has been reported.