Homogeneous detection of unamplified genomic DNA sequences based on colorimetric scatter of gold nanoparticle probes

Rapid detection of Cyprinid herpesvirus-3 (CyHV-3) using a gold nanoparticle-based hybridization assay

Cyprinid herpesvirus-3 (CyHV-3) is a highly infectious pathogen that causes fatal disease in common and koi carp Cyprinus carpio L. CyHV-3 detection is usually based on virus propagation or amplification of the viral DNA using the PCR or LAMP techniques. However, due to the limited susceptibility of cells used for propagation, it is not always possible to successfully isolate CyHV-3 even from tissue samples that have high virus titres. All previously described detection methods including PCR-based assays are time consuming, laborious and require specialized equipment. To overcome these limitations, gold nanoparticles (AuNPs) have been explored for direct and sensitive detection of DNA. In this study, a label-free colorimetric nanodiagnostic method for direct detection of unamplified CyHV-3 DNA using gold nanoparticles is introduced. Under appropriate conditions, DNA probes hybridize with their complementary target sequences in the sample DNA, which results in aggregation of the gold nanoparticles and a concomitant colour change from red to blue, whereas test samples with non complementary DNA sequences remain red. In this study, gold nanoparticles were used to develop and evaluate a specific and sensitive hybridization assay for direct and rapid detection of the highly infectious pathogen termed Cyprinid herpesvirus-3.

Cell-SELEX-based aptamer-conjugated nanomaterials for cancer diagnosis and therapy

Nucleic acid aptamers, which are generated by a novel technique called SELEX (systematic evolution of ligands by exponential enrichment), have recently attracted significant attention in the field of early detection and treatment of cancer based on their numerous merits, such as high affinity, high specificity, small size, little immunogenicity, stable structures, and ease of chemical modification. Furthermore, aptamers can gain more flexibility as cancer cell targeting tools when conjugated to nanomaterials, including metallic nanoparticles, carbon nanomaterials, DNA nanodevices, and polymeric nanoparticles. We discuss the progress achieved in cancer diagnosis and therapy through the conjugation of cell-SELEX-based aptamers with different nanomaterials.

Detection of unamplified HCV RNA in serum using a novel two metallic nanoparticle platform

BACKGROUND

The unique properties of metallic nanoparticles have enabled their utilization in biosensing applications. A novel assay for the detection of hepatitis C virus (HCV) RNA in serum specimens has been developed using magnetic nanoparticles and unmodified cationic gold nanoparticles (AuNPs).

METHODS

HCV RNA was extracted using magnetic nanoparticles functionalized with an oligonucleotide specific to HCV RNA. Extracted RNA is reacted with oligonucleotide sequence specific for HCV RNA in presence of unmodified cationic AuNPs. In positive samples, AuNPs are aligned onto the phosphate backbone of the RNA and their aggregation changes the solution color from red to blue. In the absence of target, solution color remains red. The assay has been tested on 50 serum clinical samples (25 HCV positive and 25 controls).

RESULTS

The dual nanoparticles assay detected HCV RNA in serum and generated comparable results to real-time PCR. The assay had specificity and a sensitivity of 96% and 96.5%, respectively, and a detection limit of 15 IU/mL.

CONCLUSIONS

The developed colorimetric dual nanoparticles HCV RNA assay is simple and inexpensive and can be used for rapid detection of unamplified HCV RNA in serum. Similar sensing platforms can be developed to detect other nucleic acid targets.

Nano metal-organic framework (NMOF)-based strategies for multiplexed microRNA detection in solution and living cancer cells

MiRNAs are an emerging type of biomarker for diagnostics and prognostics. A reliable sensing strategy that can monitor miRNA expression in living cancer cells would be critical in view of its extensive advantages for fundamental research related to miRNA-associated bioprocesses and biomedical applications. Conventional miRNA sensing methods include northern blot, microarrays and real-time quantitative PCR. However, none of them is able to monitor miRNA levels expressed in living cancer cells in a real-time fashion. Some fluorescennt biosensors developed recently from carbon nanomaterials, such as single-walled carbon nanotubes (SWNTs), graphene oxide (GO), and carbon nanoparticles, have been successfully used for assaying miRNA in vitro; however the preparation processes are often expensive, complicated and time-consuming, which have motivated the research on other substitute and novel materials. Herein we present a novel sensing strategy based on peptide nucleic acid (PNA) probes labeled with fluorophores and conjugated with an NMOF vehicle to monitor multiplexed miRNAs in living cancer cells. The NMOF works as a fluorescence quencher of the labelled PNA that is firmly bound with the metal center. In the presence of a target miRNA, PNA is hybridized and released from the NMOF leading to the recovery of fluorescence. This miRNA sensor not only enables the quantitative and highly specific detection of multiplexed miRNAs in living cancer cells, but it also allows the precise and in situ monitoring of the spatiotemporal changes of miRNA expression.

Plasmonic nanorod arrays of a two-segment dimer and a coaxial cable with 1 nm gap for large field confinement and enhancement

Seeking plasmonic nanostructures with large field confinement and enhancement is significant for photonic and electronic nanodevices with high sensitivity, reproducibility, and tunability. Here, we report the synthesis of plasmonic arrays composed of two-segment dimer nanorods and coaxial cable nanorods with ∼1 nm gap insulated by a self-assembled Raman molecule monolayer. The gap-induced plasmon coupling generates an intense field in the gap region of the dimer junction and the cable interlayer. As a result, the longitudinal plasmon resonance of nanorod arrays with high tunability is obviously enhanced. Most interestingly, the field enhancement of dimer nanorod arrays can be tuned by the length ratio L1/L2 of the two segments, and the maximal enhancement appears at L1/L2 = 1. In that case, the two-photon luminescence (TPL) of dimer nanorod arrays and the Raman intensity in the dimer junction is enhanced by 27 and 30 times, respectively, under resonant excitation. In the same way, the Raman intensity in the gap region is enhanced 16 times for the coaxial cable nanorod arrays. The plasmonic nanorod arrays synthesized by the facile method, having tunable plasmon properties and large field enhancement, indicate an attractive pathway to the photonic nanodevices.

Colorimetric detection of microcystin-LR based on disassembly of orient-aggregated gold nanoparticle dimers

Recently we demonstrated oriented formation of gold nanoparticle (AuNP) dimers for ultrasensitive sensing oligonucleotides (J. Am. Chem. Soc. 2013, 135, 12338). Herein, we investigate the reverse process of this sensing mechanism using target analytes to disassemble the orient-aggregated AuNP dimers. This enables us to expand the analytes from oligonucleotides to other molecules, e.g. highly sensitive and selective determination of microcystin-LR (MC-LR) is selected for a demonstration in this work. Aptamers specific to the target molecules are used as linkers to prepare the AuNP dimers. In the presence of the target molecule, the aptamer changes its structure to bind the target molecule. Thus the pre-formed AuNP dimers are disassembled. As a result, the solution color is changed from blue to red. This sensing design retains the advantages of the previously developed sensors based on target molecules guided formation of AuNP dimers, e.g. the overwhelming sensitivity and stability comparing with those non-oriented sensors based on the formation of large aggregates, with the additional advantages as follows: 1) the target molecules are expanded from oligonucleotides to arbitrary molecules that can specifically bind to aptamers; 2) the color change is completed within 5 min, while the previous sensor based on the formation of AuNP dimers cost ~1 hour to obtain stable responses.

Adsorption between TC-stabilized AuNPs and the phosphate group: application of the PTP1B activity assay

Based on the adsorption between tetracycline (TC) and phosphate groups, a general colorimetric method is explored in this work by using TC-stabilized gold nanoparticles (TC/AuNPs) and 4-aminophenyl phosphate-functionalized Fe₃O₄ magnetic nanoparticles (APP/MNPs).

An electrochemical sensing strategy for the detection of the hepatitis B virus sequence with homogenous hybridization based on host–guest recognition

Schematic for electrochemically sensing DNA with hybridization in homogeneous solutionviahost–guest recognition based on MNPs/β-CD.

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.

Gold nanoparticles as a potential tool for diagnosis of fish diseases

Infectious diseases are a serious problem and a major contributor to severe economic losses in intensive fish culture. Therefore, rapid and sensitive detection of fish pathogens is extremely important. Although various assays for determination of fish pathogens have been developed, most of these diagnostic methods are time-consuming and laborious. To overcome these limitations, functional nanomaterials have been actively investigated to improve detection ability and rapidity of diagnostic assays. Gold nanoparticles (AuNPs) have been widely studied for their unique optical properties arising from their surface plasmon resonance, which is responsible for their large absorption and scattering properties. These unique properties are four to five orders of magnitude larger than those of conventional dyes and can be controlled by varying their sizes, shapes, and compositions. Moreover, AuNPs can be easily synthesized and functionalized with different biomolecules, including pathogen-specific oligonucleotides or antibodies. Recently, nanoparticle-based assays have been introduced as a tool for laboratory diagnosis. They have been used for the direct detection of unamplified nucleic acids in hybridization assays. Single- and double-stranded oligonucleotides can be adsorbed on AuNPs in colloidal solution under certain conditions. The result of the hybridization process can be visually detected within 1 min after addition of AuNPs, when the color of the reaction mixture changes from red to blue (positive reaction) or remains red (negative). The development of such nanoparticle-based strategies holds the potential to become powerful approaches for diagnosis of fish pathogens.

Gold nanoprobes for detecting DNA adducts

A colorimetric probe for the detection of a mutagenic DNA adduct within a sequence was created. The probe involves incorporation of a synthetic nucleoside that selectively pairs opposite a target DNA adduct into oligonucleotides conjugated to gold nanoparticles (AuNPs).

Synergetic approach for simple and rapid conjugation of gold nanoparticles with oligonucleotides

Attaching thiolated DNA on gold nanoparticles (AuNPs) has been extremely important in nanobiotechnology because DNA-AuNPs combine the programmability and molecular recognition properties of the biopolymers with the optical, thermal, and catalytic properties of the inorganic nanomaterials. However, current standard protocols to attach thiolated DNA on AuNPs involve time-consuming, tedious steps and do not perform well for large AuNPs, thereby greatly restricting applications of DNA-AuNPs. Here we demonstrate a rapid and facile strategy to attach thiolated DNA on AuNPs based on the excellent stabilization effect of mPEG-SH on AuNPs. AuNPs are first protected by mPEG-SH in the presence of Tween 20, which results in excellent stability of AuNPs in high ionic strength environments and extreme pHs. A high concentration of NaCl can be applied to the mixture of DNA and AuNP directly, allowing highly efficient DNA attachment to the AuNP surface by minimizing electrostatic repulsion. The entire DNA loading process can be completed in 1.5 h with only a few simple steps. DNA-loaded AuNPs are stable for more than 2 weeks at room temperature, and they can precisely hybridize with the complementary sequence, which was applied to prepare core-satellite nanostructures. Moreover, cytotoxicity assay confirmed that the DNA-AuNPs synthesized by this method exhibit lower cytotoxicity than those prepared by current standard methods. The proposed method provides a new way to stabilize AuNPs for rapid and facile loading thiolated DNA on AuNPs and will find wide applications in many areas requiring DNA-AuNPs, including diagnosis, therapy, and imaging.

Detection of Kaposi's sarcoma associated herpesvirus nucleic acids using a smartphone accessory

Kaposi's sarcoma (KS) is an infectious cancer occurring in immune-compromised patients, caused by Kaposi's sarcoma associated herpesvirus (KSHV). Our vision is to simplify the process of KS diagnosis through the creation of a smartphone based point-of-care system capable of yielding an actionable diagnostic readout starting from a raw biopsy sample. In this work we develop the sensing mechanism for the overall system, a smartphone accessory capable of detecting KSHV nucleic acids. The accessory reads out microfluidic chips filled with a colorimetric nanoparticle assay targeted at KSHV. We calculate that our final device can read out gold nanoparticle solutions with an accuracy of 0.05 OD, and we demonstrate that it can detect DNA sequences from KSHV down to 1 nM. We believe that through integration with our previously developed components, a smartphone based system like the one studied here can provide accurate detection information, as well as a simple platform for field based clinical diagnosis and research.

A promising road with challenges: where are gold nanoparticles in translational research?

Nanoenabled technology holds great potential for health issues and biological research. Among the numerous inorganic nanoparticles that are available today, gold nanoparticles are fully developed as therapeutic and diagnostic agents both in vitro and in vivo due to their physicochemical properties. Owing to this, substantial work has been conducted in terms of developing biosensors for noninvasive and targeted tumor diagnosis and treatment. Some studies have even expanded into clinical trials. This article focuses on the fundamentals and synthesis of gold nanoparticles, as well as the latest, most promising applications in cancer research, such as molecular diagnostics, immunosensors, surface-enhanced Raman spectroscopy and bioimaging. Challenges to their further translational development are also discussed.

Spherical nucleic acids as a divergent platform for synthesizing RNA-nanoparticle conjugates through enzymatic ligation

Herein, we describe a rapid, divergent method for using spherical nucleic acids (SNAs) as a universal platform for attaching RNA to DNA-modified nanoparticles using enzyme-mediated techniques. This approach provides a sequence-specific method for the covalent attachment of one or more in vitro transcribed RNAs to a universal SNA scaffold, regardless of RNA sequence. The RNA-nanoparticle constructs are shown to effectively knock down two different gene targets using a single, dual-ligated nanoparticle construct.

Biosafe nanoscale pharmaceutical adjuvant materials

Thanks to developments in the field of nanotechnology over the past decades, more and more biosafe nanoscale materials have become available for use as pharmaceutical adjuvants in medical research. Nanomaterials possess unique properties which could be employed to develop drug carriers with longer circulation time, higher loading capacity, better stability in physiological conditions, controlled drug release, and targeted drug delivery. In this review article, we will review recent progress in the application of representative organic, inorganic and hybrid biosafe nanoscale materials in pharmaceutical research, especially focusing on nanomaterial-based novel drug delivery systems. In addition, we briefly discuss the advantages and notable functions that make these nanomaterials suitable for the design of new medicines; the biosafety of each material discussed in this article is also highlighted to provide a comprehensive understanding of their adjuvant attributes.

AuNPs for identification of molecular signatures of resistance

The increasing levels of drug resistance are one of biggest threats to overcome microbial infection. The ability to rapidly and accurately detect a given pathogen and its drug resistance profile is essential for the appropriate treatment of patients and for preventing further spread of drug-resistant strains. The predictive and informative value of these molecular markers needs to be translated into robust surveillance tools that correlate to the target and extent of resistance, monitor multiresistance and provide real time assessment at point-of-need. Rapid molecular assays for the detection of drug-resistance signatures in clinical specimens are based on the detection of specific nucleotide sequences and/or mutations within pre-selected biomarkers in the genome, indicative of the presence of the pathogen and/or associated with drug resistance. DNA and/or RNA based assays offer advantages over phenotypic assays, such as specificity and time from collection to result. Nanotechnology has provided new and robust tools for the detection of pathogens and more crucially to the fast and sensitive characterisation of molecular signatures of drug resistance. Amongst the plethora of nanotechnology based approaches, gold nanoparticles have prompt for the development of new strategies and platforms capable to provide valuable data at point-of-need with increased versatility but reduced costs. Gold nanoparticles, due to their unique spectral, optical and electrochemical properties, are one of the most widely used nanotechnology systems for molecular diagnostics. This review will focus on the use of gold nanoparticles for screening molecular signatures of drug resistance that have been reported thus far, and provide a critical evaluation of current and future developments of these technologies assisting pathogen identification and characterisation.

Development of a PCR-free electrochemical point of care test for clinical detection of methicillin resistant Staphylococcus aureus (MRSA)

An MRSA assay requiring neither labeling nor amplification of target DNA has been developed. Sequence specific binding of fragments of bacterial genomic DNA is detected at femtomolar concentrations using electrochemical impedance spectroscopy (EIS). This has been achieved using systematic optimisation of probe chemistry (PNA self-assembled monolayer film on gold electrode), electrode film structure (the size and nature of the chemical spacer) and DNA fragmentation, as these are found to play an important role in assay performance. These sensitivity improvements allow the elimination of the PCR step and DNA labeling and facilitate the development of a simple and rapid point of care test for MRSA. Assay performance is then evaluated and specific direct detection of the MRSA diagnostic mecA gene from genomic DNA, extracted directly from bacteria without further treatment is demonstrated for bacteria spiked into saline (10(6) cells per mL) on gold macrodisc electrodes and into human wound fluid (10(4) cells per mL) on screen printed gold electrodes. The latter detection level is particularly relevant to clinical requirements and point of care testing where the general threshold for considering a wound to be infected is 10(5) cells per mL. By eliminating the PCR step typically employed in nucleic acid assays, using screen printed electrodes and achieving sequence specific discrimination under ambient conditions, the test is extremely simple to design and engineer. In combination with a time to result of a few minutes this means the assay is well placed for use in point of care testing.

Nanomedicine in the Management of Microbial Infection - Overview and Perspectives

For more than 2 billion years, microbes have reigned on our planet, evolving or outlasting many obstacles they have encountered. In the 20th century, this trend took a dramatic turn with the introduction of antibiotics and vaccines. Nevertheless, since then, microbes have progressively eroded the effectiveness of previously successful antibiotics by developing resistance, and many infections have eluded conventional vaccine design approaches. Moreover, the emergence of resistant and more virulent strains of bacteria has outpaced the development of new antibiotics over the last few decades. These trends have had major economic and health impacts at all levels of the socioeconomic spectrum - we need breakthrough innovations that could effectively manage microbial infections and deliver solutions that stand the test of time. The application of nanotechnologies to medicine, or nanomedicine, which has already demonstrated its tremendous impact on the pharmaceutical and biotechnology industries, is rapidly becoming a major driving force behind ongoing changes in the antimicrobial field. Here we provide an overview on the current progress of nanomedicine in the management of microbial infection, including diagnosis, antimicrobial therapy, drug delivery, medical devices, and vaccines, as well as perspectives on the opportunities and challenges in antimicrobial nanomedicine.

Multicolor and erasable DNA photolithography

The immobilization of DNA molecules onto a solid support is a crucial step in biochip research and related applications. In this work, we report a DNA photolithography method based on photocleavage of 2-nitrobenzyl linker-modified DNA strands. These strands were subjected to ultraviolet light irradiation to generate multiple short DNA strands in a programmable manner. Coupling the toehold-mediated DNA strand-displacement reaction with DNA photolithography enabled the fabrication of a DNA chip surface with multifunctional DNA patterns having complex geometrical structures at the microscale level. The erasable DNA photolithography strategy was developed to allow different paintings on the same chip. Furthermore, the asymmetrical modification of colloidal particles was carried out by using this photolithography strategy. This strategy has broad applications in biosensors, nanodevices, and DNA-nanostructure fabrication.

Revisiting 30 years of biofunctionalization and surface chemistry of inorganic nanoparticles for nanomedicine

In the last 30 years we have assisted to a massive advance of nanomaterials in material science. Nanomaterials and structures, in addition to their small size, have properties that differ from those of larger bulk materials, making them ideal for a host of novel applications. The spread of nanotechnology in the last years has been due to the improvement of synthesis and characterization methods on the nanoscale, a field rich in new physical phenomena and synthetic opportunities. In fact, the development of functional nanoparticles has progressed exponentially over the past two decades. This work aims to extensively review 30 years of different strategies of surface modification and functionalization of noble metal (gold) nanoparticles, magnetic nanocrystals and semiconductor nanoparticles, such as quantum dots. The aim of this review is not only to provide in-depth insights into the different biofunctionalization and characterization methods, but also to give an overview of possibilities and limitations of the available nanoparticles.

One-step shell polymerization of inorganic nanoparticles and their applications in SERS/nonlinear optical imaging, drug delivery, and catalysis

Surface functionalized nanoparticles have found their applications in several fields including biophotonics, nanobiomedicine, biosensing, drug delivery, and catalysis. Quite often, the nanoparticle surfaces must be post-coated with organic or inorganic layers during the synthesis before use. This work reports a generally one-pot synthesis method for the preparation of various inorganic-organic core-shell nanostructures (Au@polymer, Ag@polymer, Cu@polymer, Fe3O4@polymer, and TiO2@polymer), which led to new optical, magnetic, and catalytic applications. This green synthesis involved reacting inorganic precursors and poly(styrene-alt-maleic acid). The polystyrene blocks separated from the external aqueous environment acting as a hydrophobic depot for aromatic drugs and thus illustrated the integration of functional nanoobjects for drug delivery. Among these nanocomposites, the Au@polymer nanoparticles with good biocompatibility exhibited shell-dependent signal enhancement in the surface plasmon resonance shift, nonlinear fluorescence, and surface-enhanced Raman scattering properties. These unique optical properties were used for dual-modality imaging on the delivery of the aromatic photosensitizer for photodynamic therapy to HeLa cells.

Quantitative imaging of single mRNA splice variants in living cells

Alternative messenger RNA (mRNA) splicing is a fundamental process of gene regulation, and errors in RNA splicing are known to be associated with a variety of different diseases. However, there is currently a lack of quantitative technologies for monitoring mRNA splice variants in cells. Here, we show that a combination of plasmonic dimer probes and hyperspectral imaging can be used to detect and quantify mRNA splice variants in living cells. The probes are made from gold nanoparticles functionalized with oligonucleotides and can hybridize to specific mRNA sequences, forming nanoparticle dimers that exhibit distinct spectral shifts due to plasmonic coupling. With this approach, we show that the spatial and temporal distribution of three selected splice variants of the breast cancer susceptibility gene, BRCA1, can be monitored at single-copy resolution by measuring the hybridization dynamics of the nanoplasmonic dimers. Our study provides insights into RNA and its transport in living cells, which could improve our understanding of cellular protein complexes, pharmacogenomics, genetic diagnosis and gene therapies.

Operation of a wet near-field scanning optical microscope in stable zones by minimizing the resonance change of tuning forks

A resonant shift and a decrease of resonance quality of a tuning fork attached to a conventional fiber optic probe in the vicinity of liquid is monitored systematically while varying the protrusion length and immersion depth of the probe. Stable zones where the resonance modification as a function of immersion depth is minimized are observed. A wet near-field scanning optical microscope (wet-NSOM) is operated for a sample within water by using such a stable zone.

Clinical applications of nucleic acid aptamers in cancer

Nucleic acid aptamers are small single-stranded DNA or RNA oligonucleotide segments, which bind to their targets with high affinity and specificity via unique three-dimensional structures. Aptamers are generated by an iterative in vitro selection process, termed as systematic evolution of ligands by exponential enrichment. Owing to their specificity, non-immunogenicity, non-toxicity, easily modified chemical structure and wide range of targets, aptamers appear to be ideal candidates for various clinical applications (diagnosis or treatment), such as cell detection, target diagnosis, molecular imaging and drug delivery. Several aptamers have entered the clinical pipeline for applications in diseases such as macular degeneration, coronary artery bypass graft surgery and various types of cancer. The aim of this review was to summarize and highlight the clinical applications of aptamers in cancer diagnosis and treatment.

Ultrafast colorimetric detection of nucleic acids based on the inhibition of the oxidase activity of cerium oxide nanoparticles

A colorimetric method to detect nucleic acids involving target DNA induced shielding of the oxidase activity of CeO₂ NPs is developed.

Optical imaging of individual plasmonic nanoparticles in biological samples

Imaging of plasmonic nanoparticles (PNP) with optical microscopy has aroused considerable attention in recent years. The unique localized surface plasmon resonance (LSPR) from metal nanoparticles facilitates the transduction of a chemical or physical stimulus into optical signals in a highly efficient way. It is therefore possible to perform chemical or biological assays at the single object level with the help of standard optical microscopes. Because the source of background noise from different samples is different, distinct imaging modalities have been developed to discern the signals of interest in complex surroundings. With these convenient yet powerful techniques, great improvements in chemical and biological assays have been demonstrated, and many interesting phenomena and dynamic processes have also been elucidated. Further development and application of optical imaging methods for plasmonic probes should lead to many exciting results in chemistry and biology in the future.

Ultrasensitive telomerase activity detection by telomeric elongation controlled surface enhanced Raman scattering

Telomerase is now considered to be a valuable biomarker and therapeutic target in the diagnosis and treatment of cancerous diseases, which brings an urgent need in the development of fast and efficient telomerase detection strategies. Here, a new surface enhanced Raman scattering (SERS) based protocol using telomeric elongation controlled SERS (TEC-SERS) effect for the ultrasensitive telomerase detection is presented. The TEC-SERS protocol not only provides an unprecedented high sensitivity but also avoids laborious PCR procedures. The detection limit is ≈2-3 orders of magnitude lower than those of previously reported methods. This highly sensitive and straightforward TEC-SERS protocol can be developed as a routine telomerase detection method, which would greatly facilitate the telomerase based ultra-early diagnosis of malignant tumors and the fast screening of anti-cancer drugs.

Point-of-care nucleic acid detection using nanotechnology

Recent developments in nanotechnology have led to significant advancements in point-of-care (POC) nucleic acid detection. The ability to sense DNA and RNA in a portable format leads to important applications for a range of settings, from on-site detection in the field to bedside diagnostics, in both developing and developed countries. We review recent innovations in three key process components for nucleic acid detection: sample preparation, target amplification, and read-out modalities. We discuss how the advancements realized by nanotechnology are making POC nucleic acid detection increasingly applicable for decentralized and accessible testing, in particular for the developing world.

A brief account of nanoparticle contrast agents for photoacoustic imaging

Photoacoustic imaging (PAI) is a hybrid, nonionizing modality offering excellent spatial resolution, deep penetration, and high soft tissue contrast. In PAI, signal is generated based on the absorption of laser-generated optical energy by endogenous tissues or exogenous contrast agents leading to acoustic emissions detected by an ultrasound transducer. Research in this area over the years has shown that PAI has the ability to provide both physiological and molecular imaging, which can be viewed alone or used in a hybrid modality fashion to extend the anatomic and hemodynamic sensitivities of clinical ultrasound. PAI may be performed using inherent contrast afforded by light absorbing molecules such as hemoglobin, myoglobin, and melanin or exogenous small molecule contrast agent such as near infrared dyes and porphyrins. However, this review summarizes the potential of exogenous nanoparticle-based agents for PAI applications including contrast based on gold particles, carbon nanotubes, and encapsulated copper compounds.

Atomic force microscopy reveals two phases in single stranded DNA self-assembled monolayers

We have investigated the structure of single-stranded (ss) DNA self-assembled monolayers (SAMs) on gold by combining peak force tapping, Kelvin probe and phase contrast atomic force microscopy (AFM) techniques. The adhesion, surface potential and phase shift signals show heterogeneities in the DNA film structure at two levels: microscale and nanoscale; which cannot be clearly discerned in the topography. Firstly, there is multilayer aggregation covering less than 5% of the surface. The DNA multilayers seem to be ordered phases and their existence suggests that DNA end-to-end interaction can play a role in the self-assembly process. Secondly, we find the formation of two phases in the DNA monolayer, which differ both in surface energy and surface potential. We relate the two domains to differences in the packing density and in the ssDNA conformation. The discovered heterogeneities in ssDNA SAMs provide a new scenario in our vision of these relevant films that have direct consequences on their biological, chemical and physical properties.

Applications of gold nanoparticles in the detection and identification of infectious diseases and biothreats

The situation of infectious diseases and biothreats all over the world remains serious. The effective identification of such diseases plays a very important role. In recent years, gold nanoparticles have been widely used in biosensor design to improve the performance for the detection of infectious diseases and biothreats. Here, recent advances of gold-nanoparticle-based biosensors in this field are summarized.

Gold-nanoparticle-based colorimetric discrimination of cancer-related point mutations with picomolar sensitivity

Point mutations in the Kirsten rat sarcoma viral oncogene homologue (KRAS) gene are being increasingly recognized as important diagnostic and prognostic markers in cancer. In this work, we describe a rapid and low-cost method for the naked-eye detection of cancer-related point mutations in KRAS based on gold nanoparticles. This simple colorimetric assay is sensitive (limit of detection in the low picomolar range), instrument-free, and employs nonstringent room temperature conditions due to a combination of DNA-conjugated gold nanoparticles, a probe design which exploits cooperative hybridization for increased binding affinity, and signal enhancement on the surface of magnetic beads. Additionally, the scheme is suitable for point-of-care applications, as it combines naked-eye detection, small sample volumes, and isothermal (PCR-free) amplification.

Colorimetric visualization of glucose at the submicromole level in serum by a homogenous silver nanoprism-glucose oxidase system

In this study, we design a homogeneous system consisting of Ag nanoprisms and glucose oxidase (GOx) for simple, sensitive, and low-cost colorimetric sensing of glucose in serum. The unmodified Ag nanoprisms and GOx are first mixed with each other. Glucose is then added in the homogeneous mixture. Finally, the nanoplates are etched from triangle to round by H2O2 produced by the enzymatic oxidation, which leads to a more than 120 nm blue shift of the surface plasmon resonance (SPR) absorption band of the Ag nanoplates. This large wavelength shift can be used not only for visual detection (from blue to mauve) of glucose by naked eyes but for reliable and convenient glucose quantification in the range from 2.0 × 10(-7) to 1.0 × 10(-4) M. The detection limit is as low as 2.0 × 10(-7) M, because the used Ag nanoprisms possess (1) highly reactive edges/tips and (2) strongly tip sharpness and aspect ratio dependent SPR absorption. Owing to ultrahigh sensitivity, only 10-20 μL of serum is enough for a one-time determination. The proposed glucose sensor has great potential in the applications of point-of-care diagnostics, especially for third-world countries where high-tech diagnostics aids are inaccessible to the bulk of the population.

Aptamer-conjugated gold nanoparticles for bioanalysis

Aptamers are single-stranded oligonucleotides synthesized through an in vitro selection and amplification process that involves systematic evolution of ligands by exponential enrichment. Based on their high binding affinity and specificity towards other molecules, aptamers generated during the final rounds of selection can be utilized in applications ranging from biosensing to diagnostics and therapeutics. Meanwhile, advances in nanotechnology have led to new and improved materials for biomedical applications. Specifically, nanoparticles can readily interact with both intra- and extra-cellular biomolecules to yield improved signal amplification and target recognition. By combining both technologies, aptamer-conjugated nanoparticles, especially gold nanoparticles (Apt–AuNPs), offer great promise for applications in bioanalysis and biomedicine, including early diagnosis and drug delivery. This review summarizes recent methodologies that have increased the application of Apt–AuNPs in biomedicine, and discusses the potential of Apt–AuNPs in bioanalysis.

Improving the understanding of oligonucleotide-nanoparticle conjugates using DNA-binding fluorophores

A novel fluorescent-based method for characterisation of oligonucleotide-nanoparticle conjugates (ONPCs) is reported. We exploit the ability of the double-stranded DNA-binding dye, SYBR Green I, to develop a powerful analytical tool to investigate the melting properties and hybridisation behavior of ONPCs as well as their corresponding DNA-mediated assemblies.