Simultaneous Detection of Intracellular Tumor mRNA with Bi-Color Imaging Based on a Gold Nanoparticle/Molecular Beacon

From Structure to Application: The Evolutionary Trajectory of Spherical Nucleic Acids

Since the proposal of the concept of spherical nucleic acids (SNAs) in 1996, numerous studies have focused on this topic and have achieved great advances. As a new delivery system for nucleic acids, SNAs have advantages over conventional deoxyribonucleic acid (DNA) nanostructures, including independence from transfection reagents, tolerance to nucleases, and lower immune reactions. The flexible structure of SNAs proves that various inorganic or organic materials can be used as the core, and different types of nucleic acids can be conjugated to realize diverse functions and achieve surprising and exciting outcomes. The special DNA nanostructures have been employed for immunomodulation, gene regulation, drug delivery, biosensing, and bioimaging. Despite the lack of rational design strategies, potential cytotoxicity, and structural defects of this technology, various successful examples demonstrate the bright and convincing future of SNAs in fields such as new materials, clinical practice, and pharmacy.

DNA-enabled fluorescent-based nanosensors monitoring tumor-related RNA toward advanced cancer diagnosis: A review

As a burgeoning non-invasive indicator for reproducible cancer diagnosis, tumor-related biomarkers have a wide range of applications in early cancer screening, efficacy monitoring, and prognosis predicting. Accurate and efficient biomarker determination, therefore, is of great importance to prevent cancer progression at an early stage, thus reducing the disease burden on the entire population, and facilitating advanced therapies for cancer. During the last few years, various DNA structure-based fluorescent probes have established a versatile platform for biological measurements, due to their inherent biocompatibility, excellent capacity to recognize nucleic and non-nucleic acid targets, obvious accessibility to synthesis as well as chemical modification, and the ease of interfacing with signal amplification protocols. After decades of research, DNA fluorescent probe technology for detecting tumor-related mRNAs has gradually grown to maturity, especially the advent of fluorescent nanoprobes has taken the process to a new level. Here, a systematic introduction to recent trends and advances focusing on various nanomaterials-related DNA fluorescent probes and the physicochemical properties of various involved nanomaterials (such as AuNP, GO, MnO2, SiO2, AuNR, etc.) are also presented in detail. Further, the strengths and weaknesses of existing probes were described and their progress in the detection of tumor-related mRNAs was illustrated. Also, the salient challenges were discussed later, with a few potential solutions.

Engineering nanosystems to overcome barriers to cancer diagnosis and treatment

Over the past two decades, multidisciplinary investigations into the development of nanoparticles for medical applications have continually increased. However, nanoparticles are still subject to biological barriers and biodistribution challenges, which limit their overall clinical potential. This has motivated the implementation of innovational modifications to a range of nanoparticle formulations designed for cancer imaging and/or cancer treatment to overcome specific barriers and shift the accumulation of payloads toward the diseased tissues. In recent years, novel technological and chemical approaches have been employed to modify or functionalize the surface of nanoparticles or manipulate the characteristics of nanoparticles. Combining these approaches with the identification of critical biomarkers provides new strategies for enhancing nanoparticle specificity for both cancer diagnostic and therapeutic applications. This review discusses the most recent advances in the design and engineering of nanoparticles as well as future directions for developing the next generation of nanomedicines.

Dynamic tracking of p21 mRNA in living cells by sticky-flares for the visual evaluation of the tumor treatment effect

Monitoring the expression level of the intracellular tumor suppressor gene p21 mRNA is essential to reveal the progress and prognosis of a tumor. Methods widely reported for the detection of p21 mRNA are the real-time polymerase chain reaction and Northern blot. However, these methods only detect mRNA in vitro and cannot realize the in situ monitoring of the p21 mRNA expression level in living cells. Additionally, the sensor for the real-time tracking and monitoring of the p21 mRNA location without the help of a transfection reagent in living cells is still limited. Herein, a novel sticky-flare was constructed for the dynamic monitoring of the temporal and spatial variations of p21 mRNA in living cells. The nanoprobe consists of AuNP, a recognition sequence modified with Cy5, and a thiol-modified DNA sequence. The thiol oligonucleotide strand could act partially complementary to the Cy5-modified oligonucleotide strand to form a double-stranded DNA linked to AuNP, resulting in the fluorescence quenching of Cy5 due to the energy transfer from Cy5 to the gold sphere. In the presence of p21 mRNA, the Cy5-modified recognition nucleic acid specifically bound to p21 mRNA to form a more stable double chain and escaped from the gold sphere, leading to the recovery of red fluorescence. Our method is better than other methods in its ability to quantify the spatial distribution and expression level of p21 mRNA in living cells and discriminate various tumor cell lines with different p21 mRNA expression levels by the naked eye. Particularly, the sticky-flare probe used in this assay could allow the visual evaluation of the tumor treatment effect and the determination of the tumor progression stage by enabling monitoring of the relative expression level of p21 mRNA in tumor cells after cisplatin treatment. The method reported here is accurate, reliable and needs no auxiliary tools (transfection reagent), and thereby provides a promising route for the prognostic evaluation and drug development of cancer treatment in the future.

Recent advances of fluorescent biosensors based on cyclic signal amplification technology in biomedical detection

The cyclic signal amplification technology has been widely applied for the ultrasensitive detection of many important biomolecules, such as nucleic acids, proteins, enzymes, adenosine triphosphate (ATP), metal ions, exosome, etc. Due to their low content in the complex biological samples, traditional detection methods are insufficient to satisfy the requirements for monitoring those biomolecules. Therefore, effective and sensitive biosensors based on cyclic signal amplification technology are of great significance for the quick and simple diagnosis and treatment of diseases. Fluorescent biosensor based on cyclic signal amplification technology has become a research hotspot due to its simple operation, low cost, short time, high sensitivity and high specificity. This paper introduces several cyclic amplification methods, such as rolling circle amplification (RCA), strand displacement reactions (SDR) and enzyme-assisted amplification (EAA), and summarizes the research progress of using this technology in the detection of different biomolecules in recent years, in order to provide help for the research of more efficient and sensitive detection methods.

Development of a long noncoding RNA BC032469-dependent gold nanoparticle molecular beacon for the detection of gastric cancer cells

Aim: Long noncoding RNA (lncRNA) BC032469-dependent gold nanoparticle molecular beacons (AuNP-MB) were constructed for the detection of gastric cancer cells. Materials & methods: The AuNP-MBs were prepared according to well-established procedures based on the Au-S interaction between the gold lattice and thiol functionalized oligonucleotides. More importantly, the stability and targeting ability of AuNP-MB were verified by a series of in vitro and in vivo experiments. Results: The lncRNA-dependent probes were successfully utilized for AuNP-MB-based intracellular imaging, with fluorescence effectively emitted in GC cells, but not in normal cells. Notably, such fluorescent emission was positively correlated with lncRNA BC032469 expression. Conclusion: The authors developed an effective fluorescent imaging probe for the recognition of gastric cancer cells.

Gold Nanoparticles; Potential Nanotheranostic Agent in Breast Cancer: A Comprehensive Review with Systematic Search Strategy

BACKGROUND

Breast cancer is a heterogeneous disease typically prevalent among women and is the second-largest cause of death worldwide. Early diagnosis is the key to minimize the cancer-induced complication, however, the conventional diagnostic strategies have been sluggish, complex, and, to some extent, non-specific. Therapeutic tools are not so convenient and side effects of current therapies offer the development of novel theranostic tool to combat this deadly disease.

OBJECTIVE

This article aims to summarize the advances in the diagnosis and treatment of breast cancer with gold nanoparticles (GNP or AuNP).

METHODS

A systematic search was conducted in the three popular electronic online databases including PubMed, Google Scholar, and Web of Science, regarding GNP as breast cancer theranostics.

RESULTS

Published literature demonstrated that GNPs tuned with photosensitive moieties, nanomaterials, drugs, peptides, nucleotide, peptides, antibodies, aptamer, and other biomolecules improve the conventional diagnostic and therapeutic strategies of breast cancer management with minimum cytotoxic effect. GNP derived diagnosis system assures reproducibility, reliability, and accuracy cost-effectively. Additionally, surface-modified GNP displayed theranostic potential even in the metastatic stage of breast cancer.

CONCLUSION

Divergent strategies have shown the theranostic potential of surface tuned GNPs against breast cancer even in the metastatic stage with minimum cytotoxic effects both in vitro and in vivo.

Ion-exchanged glass microrods as hybrid SERS/fluorescence substrates for molecular beacon-based DNA detection

Ion-exchange in molten nitrate salts containing metal ions (i.e. silver, copper, etc.) represents a well-established technique able to modify the chemical-physical properties of glass materials. It is widely used not only in the field of integrated optics (IO) but also, more recently, in plasmonics due to the possibility to induce the formation of metal nanoparticles in the glass matrix by an ad hoc thermal post-process. In this work, the application of this technology for the realisation of low-cost and stable surface-enhanced Raman scattering (SERS) active substrates, based on soda-lime glass microrods, is reported. The microrods, with a radius of a few tens of microns, were obtained by cutting the end of an ion-exchanged soda-lime fibre for a length less than 1 cm. As ion source, silver nitrate was selected due to the outstanding SERS properties of silver. The ion-exchange and thermal annealing post-process parameters were tuned to expose the embedded silver nanoparticles on the surface of the glass microrods, avoiding the use of any further chemical etching step. In order to test the combined SERS/fluorescence response of these substrates, labelled molecular beacons (MBs) were immobilised on their surface for deoxyribonucleic acid (DNA) detection. Our experiments confirm that target DNA is attached on the silver nanoparticles and its presence is revealed by both SERS and fluorescence measurements. These results pave the way towards the development of low-cost and stable hybrid fibres, in which SERS and fluorescence interrogation techniques are combined in the same optical device.

Enrichment of Skeletal Stem Cells from Human Bone Marrow Using Spherical Nucleic Acids

Human bone marrow (BM)-derived stromal cells contain a population of skeletal stem cells (SSCs), with the capacity to differentiate along the osteogenic, adipogenic, and chondrogenic lineages, enabling their application to clinical therapies. However, current methods to isolate and enrich SSCs from human tissues remain, at best, challenging in the absence of a specific SSC marker. Unfortunately, none of the current proposed markers alone can isolate a homogeneous cell population with the ability to form bone, cartilage, and adipose tissue in humans. Here, we have designed DNA-gold nanoparticles able to identify and sort SSCs displaying specific mRNA signatures. The current approach demonstrates the significant enrichment attained in the isolation of SSCs, with potential therein to enhance our understanding of bone cell biology and translational applications.

Different Approaches to Develop Nanosensors for Diagnosis of Diseases

The success of clinical treatments is highly dependent on early detection and much research has been conducted to develop fast, efficient, and precise methods for this reason. Conventional methods relying on nonspecific and targeting probes are being outpaced by so-called nanosensors. Over the last two decades a variety of activatable sensors have been engineered, with a great diversity concerning the operating principle. Therefore, this review delineates the achievements made in the development of nanosensors designed for diagnosis of diseases.

Nucleic-Acid Structures as Intracellular Probes for Live Cells

The chemical composition of cells at the molecular level determines their growth, differentiation, structure, and function. Probing this composition is powerful because it provides invaluable insight into chemical processes inside cells and in certain cases allows disease diagnosis based on molecular profiles. However, many techniques analyze fixed cells or lysates of bulk populations, in which information about dynamics and cellular heterogeneity is lost. Recently, nucleic-acid-based probes have emerged as a promising platform for the detection of a wide variety of intracellular analytes in live cells with single-cell resolution. Recent advances in this field are described and common strategies for probe design, types of targets that can be identified, current limitations, and future directions are discussed.

Monitoring VEGF mRNA and imaging in living cells in vitro using rGO-based dual fluorescent signal amplification platform

VEGF mRNA, as an important biomarker for disease diagnosis and therapeutics, has received extensive attention. However, how to monitor its mRNA levels rapidly and sensitively remains a challenge. Herein, a strategy was designed for facile and efficient detection of VEGF mRNA and imaging in living cells using a collaborative system of a fluorophore-labeled single-stranded probe (P), reduced graphene oxide (rGO) and double-specific nuclease (DSN). The combination of strong fluorophore-quenching ability of rGO with DSN assisted signal amplification contributes to the superior sensitivity of the assay for VEGF mRNA, which was reflected by the lower limit of mRNA detection of 100 fM obtained using dual signal amplification manner. Furthermore, the developed sensor was directly used for intracellular mRNA imaging in vitro without the assistance of transfection reagent. In summary, the simple, ultra-sensitive and cost-effective mRNA assay system, which provided a general analysis strategy for other mRNAs assay by replacing the sequence of the probe, is hopeful for applying on the clinical diagnosis and therapy.

RNA imaging by chemical probes

Sequence-specific detection of intracellular RNA is one of the most important approaches to understand life phenomena. However, it is difficult to detect RNA in living cells because of its variety and scarcity. In the last three decades, several chemical probes have been developed for RNA detection in living cells. These probes are composed of DNA or artificial nucleic acid and hybridize with the target RNA in a sequence-specific manner. This hybridization triggers a change of fluorescence or a chemical reaction. In this review, we classify the probes according to the associated fluorogenic mechanism, that is, interaction between fluorophore and quencher, environmental change of fluorophore, and template reaction with/without ligation. In addition, we introduce examples of RNA imaging in living cells.

Toward early cancer detection: Focus on biosensing systems and biosensors for an anti-apoptotic protein survivin and survivin mRNA

The development of biosensors for cancer biomarkers has recently been expanding rapidly, offering promising biomedical applications of these sensors as highly sensitive, selective, and inexpensive bioanalytical tools that can provide alternative methodology to that afforded by the advanced hyphenated-instrumental techniques. In this review, we focus particularly on the detection of a member of the inhibitor of apoptosis proteins (IAP) family, protein survivin (Sur), a ubiquitous re-organizer of the cell life cycle with the ability to inhibit the apoptosis and induce an enhanced proliferation leading to the unimpeded cancer growth and metastasis. Herein, we critically evaluate the progress in the development of novel biosensing systems and biosensors for the detection of two survivin (Sur) biomarkers: the Sur protein and its messenger RNA (Sur mRNA), including immunosensors, electrochemical piezo- and impedance-sensors, electrochemi-luminescence biosensors, genosensors based on oligonucleotide molecular beacons (MBs) with fluorescent or electrochemical transduction, as well as the microfluidic and related analytical platforms based on solution chemistry. The in-situ applications of survivin biomarkers' detection technologies to equip nanocarriers of the controlled drug delivery systems with MB-based fluorescence imaging capability, apoptosis control, and mitigation of the acquired drug resistance are also presented and critically evaluated. Finally, we turn the attention to the application of biosensors for the analysis of Sur biomarkers in exosomes and circulating tumor cells for a non-invasive liquid biopsy. The prospect of a widespread screening for early cancers, based on inexpensive point-of-care testing using biosensors and multiplex biosensor arrays, as a means of reducing the high cancer fatality rate, is discussed.

DNA-Coated Gold Nanoparticles for the Detection of mRNA in Live Hydra Vulgaris Animals

Advances in nanoparticle design have led to the development of nanoparticulate systems that can sense intracellular molecules, alter cellular processes, and release drugs to specific targets in vitro. In this work, we demonstrate that oligonucleotide-coated gold nanoparticles are suitable for the detection of mRNA in live Hydra vulgaris, a model organism, without affecting the animal's integrity. We specifically focus on the detection of Hymyc1 mRNA, which is responsible for the regulation of the balance between stem cell self-renewal and differentiation. Myc deregulation is found in more than half of human cancers, thus the ability to detect in vivo related mRNAs through innovative fluorescent systems is of outmost interest.

Gold nanoparticle based fluorescent oligonucleotide probes for imaging and therapy in living systems

Gold nanoparticles (AuNPs) with unique physical and chemical properties have become an integral part of research in nanoscience.

Poly-adenine-mediated spherical nucleic acids for strand displacement-based DNA/RNA detection

DNA-gold nanoparticles (AuNPs) conjugate is one of the most versatile bionanomaterials for biomedical and clinical diagnosis. However, to finely tune the hybridization ability and precisely control the orientation and conformation of surface-tethered oligonucleotides on AuNPs remains a hurdle. In this work, we developed a poly adenine-mediated spherical nucleic acid (polyA-mediated SNA) strategy by assembling di-block DNA probes on gold nanoparticles (AuNPs) to spatially control interdistance and hybridization ability of oligonucleotides on AuNPs. By modulating length of poly A bound on the SNA with different degrees of constructing, we presented significant improved biosensing performance including high hybridization efficiency, and expanded dynamic range of analytes with more sensitive detection limit. Furthermore, this polyA design could facilitate the programmable detection for DNA in serum environment and simultaneous multicolor detection of three different microRNAs associated with pancreatic carcinoma. The demonstration of the link between modulation of SNA assembly strategy and biodetection capability will increase the development of high performance diagnostic tools for translational biomedicine.

Simultaneous Imaging of Three Tumor-Related mRNAs in Living Cells with a DNA Tetrahedron-Based Multicolor Nanoprobe

We constructed a DNA tetrahedron based multicolor nanoprobe, which could simultaneously imaging of three tumor-related mRNAs in living cells through fluorescence restoration caused by competitive chain replacement reaction. The oligonucleotides used to construct the tetrahedron were extended by adding three 21-base recognition sequences modified with different fluorophores (FAM, Cy3, and Cy5) in the 5' end. Three 11-base complementary sequences modified with quencher (BHQ1 for FAM and BHQ2 for Cy3 and Cy5) were hybridized with the recognition sequences to quench the fluorescence. In the presence of the specific mRNA targets, the recognition sequences hybridized with the targets to form longer duplexes and the fluorescence was restored. Compared with previously reported nanoprobes based on DNA tetrahedron, the multicolor nanoprobe can effectively avoid false positive results.

Simultaneous detection of multiple targets involved in the PI3K/AKT pathway for investigating cellular migration and invasion with a multicolor fluorescent nanoprobe

A fluorescent nanoprobe was developed for assessing cellular migration and invasion by imaging miRNA-221, PTEN mRNA and MMP-9 involved in the PI3K/AKT pathway regulating cellular mobility and invasiveness.

Chemo/Photoacoustic Dual Therapy with mRNA-Triggered DOX Release and Photoinduced Shockwave Based on a DNA-Gold Nanoplatform

A multifunctional nanoparticle based on gold nanorod (GNR), utilizing mRNA triggered chemo-drug release and near-infrared photoacoustic effect, is developed for a combined chemo-photoacoustic therapy. The constructed nanoparticle (GNR-DNA/FA:DOX) comprises three functional components: (i) GNR as the drug delivery platform and photoacoustic effect enhancer; (ii) toehold-possessed DNA dressed on the GNR to load doxorubicin (DOX) to implement a tumor cell specific chemotherapy; and (iii) folate acid (FA) modified on GNR to guide the nanoparticle to target tumor cells. The results show that, upon an effective and specific delivery of the nanoparticles to the tumor cells with overexpressed folate receptors, the cytotoxic DOX loaded on the GNR-DNA nanoplatform can be released through DNA displacement reaction in melanoma-associated antigen gene mRNA expressed cells. With 808 nm pulse laser irradiation, the photoacoustic effect of the GNR leads to a direct physical damage to the cells. The combined treatment of the two modalities can effectively destroy tumor cells and eradicate the tumors with two distinctively different and supplementing mechanisms. With the nanoparticle, photoacoustic imaging is successfully performed in situ to monitor the drug distribution and tumor morphology for therapeutical guidance. With further in-depth investigation, the proposed nanoparticle may provide an effective and safe alternative cancer treatment modality.

LNA-enhanced DNA FIT-probes for multicolour RNA imaging

The simultaneous imaging of different RNA molecules in homogeneous solution is a challenge and requires optimisation to enable unambiguous staining of intracellular RNA targets. Our approach relies on single dye forced intercalation (FIT) probes, in which a visco-sensitive reporter of the thiazole orange (TO) family serves as a surrogate nucleobase and provides enhancements of fluorescence upon hybridisation. Previous FIT probes spanned the cyan and green emission range. Herein, we report for the first time chromophores for FIT probes that emit in the red range (above 600 nm). Such probes are valuable to overcome cellular auto-fluorescent background and enable multiplexed detection. In order to find suitable chromophores, we developed a submonomer approach that facilitated the rapid analysis of different TO family dyes in varied sequence positions. A carboxymethylated 4,4'-methine linked cyanine, which we named quinoline blue (QB), provided exceptional response characteristics at the 605 nm emission maximum. Exceeding previously reported base surrogates, the emission of the QB nucleotide intensified by up to 195-fold upon binding of complementary RNA. Owing to large extinction coefficients and quantum yields (up to ε = 129.000 L mol-1 cm-1 and Φ = 0.47, respectively) QB-FIT probes enable imaging of intracellular mRNA. A mixture of BO-, TO- and QB-containing FIT probes allowed the simultaneous detection of three different RNA targets in homogenous solution. TO- and QB-FIT probes were used to localize oskar mRNA and other polyadenylated mRNA molecules in developing oocytes from Drosphila melanogaster by means of wash-free fluorescent in situ hybridisation and super resolution microscopy (STED).

Intracellular FRET-based probes: a review

Probes that exploit Förster resonance energy transfer (FRET) in their feedback mechanism are touted for their sensitivity, robustness, and low background, and thanks to the exceptional distance dependence of the energy transfer process, they provide a means of probing lengthscales well below the resolution of light. These attributes make FRET-based probes superbly suited to an intracellular environment, and recent developments in biofunctionalization and expansion of imaging capabilities have put them at the forefront of intracellular studies. Here, we present an overview of the engineering and execution of a variety of recent intracellular FRET probes, highlighting the diversity of this class of materials and the breadth of application they have found in the intracellular environment.

Molecular beacon-loaded polymeric nanoparticles for non-invasive imaging of mRNA expression

Assessment of intracellular mRNA expression is invaluable for understanding cellular signaling activities, identifying disease stages, and monitoring the gene expression pattern of therapeutic cells during their culture, expansion and/or differentiation process. Previous methods suffer from the need to disrupt the biological samples to perform polymerase chain reaction analysis which can be laborious, fragmented and destructive. Herein, we develop a mRNA nanosensor based on the sustained release of mRNA-specific molecular beacons (probes that fluoresce upon hybridization) from the biodegradable poly(d,l-lactide-co-glycolide) nanoparticles. Post cellular internalization, the particles gradually degrade and release the encapsulated probes which are initially weakly fluorescent. When the released probes meet and hybridize with target mRNA, they restore pre-quenched fluorescence. By virtue of quantifying the fluorescence intensity, we can estimate the cellular mRNA expression. As a case study, β-actin mRNA expression in mesenchymal stem cells cultured on a 3D matrix was monitored and compared with those cultured on a 2D plate for one week. Critically, the observed expression profile shows a great correlation with the established quantitative polymerase chain reaction analysis.

Rationally designed molecular beacons for bioanalytical and biomedical applications

Nucleic acids hold promise as biomolecules for future applications in biomedicine and biotechnology. Their well-defined structures and compositions afford unique chemical properties and biological functions. Moreover, the specificity of hydrogen-bonded Watson-Crick interactions allows the construction of nucleic acid sequences with multiple functions. In particular, the development of nucleic acid probes as essential molecular engineering tools will make a significant contribution to advancements in biosensing, bioimaging and therapy. The molecular beacon (MB), first conceptualized by Tyagi and Kramer in 1996, is an excellent example of a double-stranded nucleic acid (dsDNA) probe. Although inactive in the absence of a target, dsDNA probes can report the presence of a specific target through hybridization or a specific recognition-triggered change in conformation. MB probes are typically fluorescently labeled oligonucleotides that range from 25 to 35 nucleotides (nt) in length, and their structure can be divided into three components: stem, loop and reporter. The intrinsic merit of MBs depends on predictable design, reproducibility of synthesis, simplicity of modification, and built-in signal transduction. Using resonance energy transfer (RET) for signal transduction, MBs are further endowed with increased sensitivity, rapid response and universality, making them ideal for chemical sensing, environmental monitoring and biological imaging, in contrast to other nucleic acid probes. Furthermore, integrating MBs with targeting ligands or molecular drugs can substantially support their in vivo applications in theranositics. In this review, we survey advances in bioanalytical and biomedical applications of rationally designed MBs, as they have evolved through the collaborative efforts of many researchers. We first discuss improvements to the three components of MBs: stem, loop and reporter. The current applications of MBs in biosensing, bioimaging and therapy will then be described. In particular, we emphasize recent progress in constructing MB-based biosensors in homogeneous solution or on solid surfaces. We expect that such rationally designed and functionalized MBs will open up new and exciting avenues for biological and medical research and applications.

Optical fiber nanotips coated with molecular beacons for DNA detection

Optical fiber sensors, thanks to their compactness, fast response and real-time measurements, have a large impact in the fields of life science research, drug discovery and medical diagnostics. In recent years, advances in nanotechnology have resulted in the development of nanotools, capable of entering the single cell, resulting in new nanobiosensors useful for the detection of biomolecules inside living cells. In this paper, we provide an application of a nanotip coupled with molecular beacons (MBs) for the detection of DNA. The MBs were characterized by hybridization studies with a complementary target to prove their functionality both free in solution and immobilized onto a solid support. The solid support chosen as substrate for the immobilization of the MBs was a 30 nm tapered tip of an optical fiber, fabricated by chemical etching. With this set-up promising results were obtained and a limit of detection (LOD) of 0.57 nM was reached, opening up the possibility of using the proposed nanotip to detect mRNAs inside the cytoplasm of living cells.

Simultaneous Visualization of Multiple mRNAs and Matrix Metalloproteinases in Living Cells Using a Fluorescence Nanoprobe

Simultaneous monitoring of multiple tumour markers is of great significance for improving the accuracy of early cancer detection. In this study, a fluorescence nanoprobe has been prepared that can simultaneously monitor and visualize multiple mRNAs and matrix metalloproteinases (MMPs) in living cells. Confocal fluorescence imaging results indicate that the nanoprobe could effectively distinguish between cancer cells and normal cells even if one tumour maker of normal cells was overexpressed. Furthermore, it can detect changes in the expression levels of mRNAs and MMPs in living cells. The current approach could provide new tools for early cancer detection and monitoring the changes in expression levels of biomarkers during tumour progression.

Dual fluorophore doped silica nanoparticles for cellular localization studies in multiple stained cells

Fluorescently labeled nanoparticles (NPs) are used in a wide range of biomedical and nanotoxicological studies to elucidate their interactions with cellular components and their intracellular localization. As commonly used fluorescence microscopes are usually limited in their performance to a few channels which detect the emitted fluorescence light in the red, green and blue color range, the simultaneous colocalization of accumulated fluorescent NPs with cellular markers is often difficult and remains a challenge due to spectral overlay of NP fluorescence and fluorescence of stained cellular components. To overcome this problem we have synthesized three different photostable dual-labeled fluorescent core/shell silica NPs with high fluorescence intensity and well-defined shape, size and surface chemistry. The synthesis route of dual fluorophore doped silica (DFDS) NPs was based on a water-in-oil microemulsion method and includes the separate incorporation of two fluorophores in the core or shell. The suitability of DFDS for colocalization studies was assessed and successfully demonstrated with human osteoblast cells. Parallel visualization of DFDS NPs with two separate microscope channels allowed cellular NP uptake and discrimination from fluorescently stained cellular components, even in triple stained cells that show fluorescence for the cytoskeleton protein actin (green), the nucleus (blue) and collagen (red). Our results demonstrate the feasibility and straightforwardness of the approach for colocalization studies at a single-cell level to discern clearly the accumulation of NPs from triple-stained cellular components. Such NPs with multiple fluorescence characteristics have a great potential to replace single fluorescent NPs for in vitro studies, when multiple staining of cellular components is required.

Design of oligoaziridine-PEG coatings for efficient nanogold cellular biotagging

Biocompatible oligoaziridine-PEG coated gold nanoparticles overcome self-quenching while targeting the cell nucleus. The course of gold biotags within the cell's environment was tracked through confocal laser microscopy.

Recent advances in gold nanoparticle-based bioengineering applications

The recently developed gold nanoparticle-based bioengineering technologies for biosensors,in vitroandin vivobioimaging, drug delivery systems for improved therapeutics and tissue engineering are discussed.

Bioinspired nanocomplex for spatiotemporal imaging of sequential mRNA expression in differentiating neural stem cells

Messenger RNA plays a pivotal role in regulating cellular activities. The expression dynamics of specific mRNA contains substantial information on the intracellular milieu. Unlike the imaging of stationary mRNAs, real-time intracellular imaging of the dynamics of mRNA expression is of great value for investigating mRNA biology and exploring specific cellular cascades. In addition to advanced imaging methods, timely extracellular stimulation is another key factor in regulating the mRNA expression repertoire. The integration of effective stimulation and imaging into a single robust system would significantly improve stimulation efficiency and imaging accuracy, producing fewer unwanted artifacts. In this study, we developed a multifunctional nanocomplex to enable self-activating and spatiotemporal imaging of the dynamics of mRNA sequential expression during the neural stem cell differentiation process. This nanocomplex showed improved enzymatic stability, fast recognition kinetics, and high specificity. With a mechanism regulated by endogenous cell machinery, this nanocomplex realized the successive stimulating motif release and the dynamic imaging of chronological mRNA expression during neural stem cell differentiation without the use of transgenetic manipulation. The dynamic imaging montage of mRNA expression ultimately facilitated genetic heterogeneity analysis. In vivo lateral ventricle injection of this nanocomplex enabled endogenous neural stem cell activation and labeling at their specific differentiation stages. This nanocomplex is highly amenable as an alternative tool to explore the dynamics of intricate mRNA activities in various physiological and pathological conditions.

Single-point mutation detection in RNA extracts using gold nanoparticles modified with hydrophobic molecular beacon-like structures

Gold nanoparticles functionalized with oligonucleotides that bear a cholesterol group are used as gene sensors. The hydrophobic molecule is buried inside the nanostructure but when the complementary RNA sequence is present the structure unfolds exposing the cholesterol group to the water molecules. This rearrangement leads to the aggregation of the nanostructures.

A novel aptamer-based competition strategy for ultrasensitive electrochemical detection of leukemia cells

A robust, nanobiotechnology-based electrochemical cytosensing platform for the detection of acute leukemia cells was developed with high sensitivity, selectivity, acceptable rapidity and excellent extensibility. It utilized the competitive binding of cell-specific aptamers to acute leukemia cells and subsequent voltammetric quantification of the metal signature. Greatly enhanced sensitivity was achieved with dual signal amplification by using Fe3O4 magnetic nanoparticles (MNPs) as carriers to load a large amount of gold nanoparticles (AuNPs) and AuNP-catalyzed silver deposition. The proposed competitive cytosensor showed high sensitivity with a detection limit down to 10 cells. This simple and low-cost electrochemical cytosensing approach offers great promise to extend its application to early detection of human leukemia and possibly to other cancer cells.

New Gold Nanostructures for Sensor Applications: A Review

Gold based structures such as nanoparticles (NPs) and nanowires (NWs) have widely been used as building blocks for sensing devices in chemistry and biochemistry fields because of their unusual optical, electrical and mechanical properties. This article gives a detailed review of the new properties and fabrication methods for gold nanostructures, especially gold nanowires (GNWs), and recent developments for their use in optical and electrochemical sensing tools, such as surface enhanced Raman spectroscopy (SERS).

Stimuli-responsive cross-linked micelles for on-demand drug delivery against cancers

Stimuli-responsive cross-linked micelles (SCMs) represent an ideal nanocarrier system for drug delivery against cancers. SCMs exhibit superior structural stability compared to their non-cross-linked counterpart. Therefore, these nanocarriers are able to minimize the premature drug release during blood circulation. The introduction of environmentally sensitive cross-linkers or assembly units makes SCMs responsive to single or multiple stimuli present in tumor local microenvironment or exogenously applied stimuli. In these instances, the payload drug is released almost exclusively in cancerous tissue or cancer cells upon accumulation via enhanced permeability and retention effect or receptor mediated endocytosis. In this review, we highlight recent advances in the development of SCMs for cancer therapy. We also introduce the latest biophysical techniques, such as electron paramagnetic resonance (EPR) spectroscopy and fluorescence resonance energy transfer (FRET), for the characterization of the interactions between SCMs and blood proteins.

Nanoscale optical probes for cellular imaging

Nanomaterials with unique optical properties have shown great promise as probes for cellular imaging. Based on these properties, a wide range of plasmonic, fluorescent and Raman probes have been designed and prepared. Nanomaterials of different sizes and shapes have also been functionalized with various types of biomolecules, such as antibodies, DNA or RNA, which are actively exploited to realize targeted imaging. In this review, we will summarize recent advances in using functional nanomaterials for imaging, primarily cellular imaging. These nanomaterials are categorized based on their conducting properties, i.e. conductors, semiconductors and insulators.

A reusable sensor for the label-free detection of specific oligonucleotides by surface plasmon fluorescence spectroscopy

The development of a reusable molecular beacon (MB)-based sensor for the label-free detection of specific oligonucleotides using surface plasmon fluorescence spectroscopy (SPFS) as the readout method is described. The MBs are chemisorbed at planar gold surfaces serving as fluorescence quenching units. Target oligonucleotides of 24 bases can be detected within a few minutes at high single-mismatch discrimination rates.

Multiplexed detection and imaging of intracellular mRNAs using a four-color nanoprobe

Simultaneous detection and imaging of multiple intracellular biomarkers hold great promise for early cancer detection. Here, we introduce a four-color nanoprobe that can simultaneously detect and image four types of mRNAs in living cells. The nanoprobe composed of gold nanoparticles functionalized with a dense shell of molecular beacons, which can identify multiple intracellular mRNA transcripts. It shows rapid response, high specificity, nuclease stability, and good biocompatibility. Intracellular experiments indicate that the nanoprobe could effectively distinguish cancer cells from their normal cells, even some mRNAs are overexpressed in normal cells. Moreover, it can identify the changes of the expression levels of mRNA in living cells. The current strategy could provide more-accurate information for early cancer detection and availably avoid false positive results.

Engineering of switchable aptamer micelle flares for molecular imaging in living cells

Simultaneous monitoring of the expression, distribution, and dynamics of biological molecules in living cells is one of the most challenging tasks in the analytical sciences. The key to effective and successful intracellular imaging is the development of delivery platforms with high efficiency and ultrasensitive molecular probes for specific targets of interest. To achieve these goals, many nanomaterials are widely used as carriers to introduce nucleic acid probes into living cells for real-time imaging of biomolecules. However, limitations on their use include issues of cytotoxicity and delivery efficiency. Herein, we propose a switchable aptamer micelle flare (SAMF), formed by self-assembly of an aptamer switch probe-diacyllipid chimera, to monitor ATP molecules inside living cells. Similarity of hydrophobic composition between diacyllipids in the micelle flares and phospholipid bilayers in the dynamic membranes of living cells allows SAMFs to be uptaken by living cells more efficiently than aptamer switch probes without external auxiliary. Switchable aptamers were found to bind target ATP molecules with high selectivity and specificity, resulting in restoration of the fluorescence signal from "OFF" to "ON" state, thus indicating the presence of the analyte. These switchable aptamer micelle flares, which exhibit cell permeability and nanoscale controllability, show exceptional promise for molecular imaging in bioanalysis, disease diagnosis, and drug delivery.

Oligonucleotide optical switches for intracellular sensing

Fluorescence imaging coupled with nanotechnology is making possible the development of powerful tools in the biological field for applications such as cellular imaging and intracellular messenger RNA monitoring and detection. The delivery of fluorescent probes into cells and tissues is currently receiving growing interest because such molecules, often coupled to nanodimensional materials, can conveniently allow the preparation of small tools to spy on cellular mechanisms with high specificity and sensitivity. The purpose of this review is to provide an exhaustive overview of current research in oligonucleotide optical switches for intracellular sensing with a focus on the engineering methods adopted for these oligonucleotides and the more recent and fascinating techniques for their internalization into living cells. Oligonucleotide optical switches can be defined as specifically designed short nucleic acid molecules capable of turning on or modifying their light emission on molecular interaction with well-defined molecular targets. Molecular beacons, aptamer beacons, hybrid molecular probes, and simpler linear oligonucleotide switches are the most promising optical nanosensors proposed in recent years. The intracellular targets which have been considered for sensing are a plethora of messenger-RNA-expressing cellular proteins and enzymes, or, directly, proteins or small molecules in the case of sensing through aptamer-based switches. Engineering methods, including modification of the oligonucleotide itself with locked nucleic acids, peptide nucleic acids, or L-DNA nucleotides, have been proposed to enhance the stability of nucleases and to prevent false-negative and high background optical signals. Conventional delivery techniques are treated here together with more innovative methods based on the coupling of the switches with nano-objects.