Novel nanosensors for rapid analysis of telomerase activity

Magnetic Relaxation Switching Assay Using IFNα-2b-Conjugated Superparamagnetic Nanoparticles for Anti-Interferon Antibody Detection

Type I interferons, particularly IFNα-2b, play essential roles in eliciting adaptive and innate immune responses, being implicated in the pathogenesis of various diseases, including cancer, and autoimmune and infectious diseases. Therefore, the development of a highly sensitive platform for analysis of either IFNα-2b or anti-IFNα-2b antibodies is of high importance to improve the diagnosis of various pathologies associated with the IFNα-2b disbalance. For evaluation of the anti-IFNα-2b antibody level, we have synthesized superparamagnetic iron oxide nanoparticles (SPIONs) coupled with the recombinant human IFNα-2b protein (SPIONs@IFNα-2b). Employing a magnetic relaxation switching assay (MRSw)-based nanosensor, we detected picomolar concentrations (0.36 pg/mL) of anti-INFα-2b antibodies. The high sensitivity of the real-time antibodies' detection was ensured by the specificity of immune responses and the maintenance of resonance conditions for water spins by choosing a high-frequency filling of short radio-frequency pulses of the generator. The formation of a complex of the SPIONs@IFNα-2b nanoparticles with the anti-INFα-2b antibodies led to a cascade process of the formation of nanoparticle clusters, which was further enhanced by exposure to a strong (7.1 T) homogenous magnetic field. Obtained magnetic conjugates exhibited high negative MR contrast-enhancing properties (as shown by NMR studies) that were also preserved when particles were administered in vivo. Thus, we observed a 1.2-fold decrease of the T2 relaxation time in the liver following administration of magnetic conjugates as compared to the control. In conclusion, the developed MRSw assay based on SPIONs@IFNα-2b nanoparticles represents an alternative immunological probe for the estimation of anti-IFNα-2b antibodies that could be further employed in clinical studies.

Nanomaterial-Based Immunocapture Platforms for the Recognition, Isolation, and Detection of Circulating Tumor Cells

Circulating tumor cells (CTCs) are a type of cancer cells that circulate in the peripheral blood after breaking away from solid tumors and are essential for the establishment of distant metastasis. Up to 90% of cancer-related deaths are caused by metastatic cancer. As a new type of liquid biopsy, detecting and analyzing CTCs will provide insightful information for cancer diagnosis, especially the in-time disease status, which would avoid some flaws and limitations of invasive tissue biopsy. However, due to the extremely low levels of CTCs among a large number of hematologic cells, choosing immunocapture platforms for CTC detection and isolation will achieve good performance with high purity, selectivity, and viability. These properties are directly associated with precise downstream analysis of CTC profiling. Recently, inspired by the nanoscale interactions of cells in the tissue microenvironment, platforms based on nanomaterials have been widely explored to efficiently enrich and sensitively detect CTCs. In this review, various immunocapture platforms based on different nanomaterials for efficient isolation and sensitive detection of CTCs are outlined and discussed. First, the design principles of immunoaffinity nanomaterials are introduced in detail. Second, the immunocapture and release of platforms based on nanomaterials ranging from nanoparticles, nanostructured substrates, and immunoaffinity microfluidic chips are summarized. Third, recent advances in single-cell release and analysis of CTCs are introduced. Finally, some perspectives and challenges are provided in future trends of CTC studies.

Rapid detection of Salmonella in milk by a nuclear magnetic resonance biosensor based on the streptavidin-biotin system and O-carboxymethyl chitosan target gadolinium probe

Rapid and sensitive detection of foodborne pathogens is of great importance for food safety. Here, a set of nuclear magnetic resonance (NMR) biosensors based on a O-carboxymethyl chitosan target gadolinium (Gd) probe was developed to quickly detect Salmonella in milk by combining NMR technology and bioimmunotechnology with membrane filtration technology. First, O-carboxymethyl chitosan (O-CMC) was biotinylated to prepare biotinylated O-carboxymethyl chitosan (biotin-O-CMC) through amide reaction, and biotinylated magnetic complexes (biotin-O-CMC-Gd) were obtained by using O-CMC, which has strong chelating adsorption on Gd. The target probe was obtained by combining biotin-O-CMC-Gd with the biotinylated antibody (biotin-antibody) via streptavidin (SA) by introducing the SA-biotin system. Then, Salmonella was captured by the target probe through antigen-antibody interaction. Finally, NMR was used to measure the longitudinal relaxation time (T₁) of the filtrate collected by membrane filtration. This NMR biosensor with good specificity and high efficiency can detect Salmonella with the sensitivity of 1.8 × 10³ cfu/mL within 2 h; in addition, it can realize the detection of complex samples because of its strong anti-interference capability and may open up a new method for rapid detection of Salmonella, which has a great application potential.

The telomere world and aging: Analytical challenges and future perspectives

Telomeres, the terminal nucleoprotein structures of eukaryotic chromosomes, play pleiotropic functions in cellular and organismal aging. Telomere length (TL) varies throughout life due to the influence of genetic factors and to a complex balancing between "shortening" and "elongation" signals. Telomerase, the only enzyme that can elongate a telomeric DNA chain, and telomeric repeat-containing RNA (TERRA), a long non-coding RNA involved in looping maintenance, play key roles in TL during life. Despite recent advances in the knowledge of TL, TERRA and telomerase activity (TA) biology and their measurement techniques, the experimental and theoretical issues involved raise a number of problems that should carefully be considered by researchers approaching the "telomere world". The increasing use of such parameters - hailed as promising clinically relevant biomarkers - has failed to be paralleled by the development of automated and standardized measurement technology. Consequently, associating given TL values to specific pathological conditions involves on the one hand technological issues and on the other clinical-biological issues related to the planning of clinically relevant association studies. Addressing these issues would help avoid major biases in association studies involving TL and a number of outcomes, especially those focusing on psychological and bio-behavioral variables. The main challenge in telomere research is the development of accurate and reliable measurement methods to achieve simple and sensitive TL, TERRA, and TA detection. The discovery of the localization of telomeres and TERRA in cellular and extracellular compartments had added an additional layer of complexity to the measurement of these age-related biomarkers. Since combined analysis of TL, TERRA and TA may well provide more exhaustive clinical information than a single parameter, we feel it is important for researchers in the various fields to become familiar with their most common measurement techniques and to be aware of the respective merits and drawbacks of these approaches.

State of diagnosing infectious pathogens using colloidal nanomaterials

Infectious diseases are a major global threat that accounts for one of the leading causes of global mortality and morbidity. Prompt diagnosis is a crucial first step in the management of infectious threats, which aims to quarantine infected patients to avoid contacts with healthy individuals and deliver effective treatments prior to further spread of diseases. This review article discusses current advances of diagnostic systems using colloidal nanomaterials (e.g., gold nanoparticles, quantum dots, magnetic nanoparticles) for identifying and differentiating infectious pathogens. The challenges involved in the clinical translation of these emerging nanotechnology based diagnostic devices will also be discussed.

Nanotechnology-Enhanced No-Wash Biosensors for in Vitro Diagnostics of Cancer

In vitro biosensors have been an integral component for early diagnosis of cancer in the clinic. Among them, no-wash biosensors, which only depend on the simple mixing of the signal generating probes and the sample solution without additional washing and separation steps, have been found to be particularly attractive. The outstanding advantages of facile, convenient, and rapid response of no-wash biosensors are especially suitable for point-of-care testing (POCT). One fast-growing field of no-wash biosensor design involves the usage of nanomaterials as signal amplification carriers or direct signal generating elements. The analytical capacity of no-wash biosensors with respect to sensitivity or limit of detection, specificity, stability, and multiplexing detection capacity is largely improved because of their large surface area, excellent optical, electrical, catalytic, and magnetic properties. This review provides a comprehensive overview of various nanomaterial-enhanced no-wash biosensing technologies and focuses on the analysis of the underlying mechanism of these technologies applied for the early detection of cancer biomarkers ranging from small molecules to proteins, and even whole cancerous cells. Representative examples are selected to demonstrate the proof-of-concept with promising applications for in vitro diagnostics of cancer. Finally, a brief discussion of common unresolved issues and a perspective outlook on the field are provided.

Recent Advances on Magnetic Relaxation Switching Assay-Based Nanosensors

Magnetic relaxation switching assay (MRSw)-based nanosensors respond to the changes of transverse relaxation time (T₂) of water molecules resulted from the analyte-induced aggregation and disaggregation of magnetic nanoparticles (MNPs). This strategy has been widely applied to the detections of various substrates from heavy metal ions to organic pollutants, proteins, nucleic acids, bacteria and viruses, and specific cells. Compared with other nanosensors, MRSw-based nanosensors not only are free from the background interferences, signal bleaching, and quenching but also overcome light scattering from samples without pretreatments. Therefore, MRSw-based nanosensors have been developed as real-time and on-site detection platforms for environmental protection, food safety, and risk assessment. This review summarizes the latest developments of the principles, the applicable magnetic nanoparticles, and the exploited environmental and biological applications of MRSw-based nanosensors.

Homogeneous Biosensing Based on Magnetic Particle Labels

The growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuation.

Telomerase activity and its association with psychological stress, mental disorders, lifestyle factors and interventions: A systematic review

OBJECTIVE

To summarise and discuss the association between telomerase activity and psychological stress, mental disorders and lifestyle factors.

METHOD

A systematic review was carried out to identify prospective or retrospective studies and interventions published up to June 2015 that reported associations between telomerase activity and psychological stress, mental disorders and lifestyle factors. Electronic data bases of PubMed, ProQuest, CINAHL and Google Scholar were searched.

RESULTS

Twenty six studies on humans measured telomerase activity in peripheral blood mononuclear cells (PBMCs) or leukocytes and examined its association with psychological stress, mental disorders and lifestyle factors. Of those studies, three reported significantly decreased telomerase activity in individuals under chronic psychological stress. Interestingly, one of the three studies found that acute laboratory psychological stress significantly increased telomerase activity. Nine studies reported mixed results on association between mental disorders and telomerase activity. Of the nine studies, five reported that major depressive disorder (MDD) was associated with significantly increased telomerase activity. In thirteen out of fourteen studies on lifestyle factors, it was reported that physical exercise, diet micronutrient supplementation, mindfulness meditation, Qigong practice or yoga mediation resulted in increase in telomerase activity. In addition, two studies on animal models showed that depression-like behaviour was associated with decreased hippocampus telomerase activity. Five animal studies showed that physical exercise increased telomerase activity by cell-type-specific and genotype-specific manners.

CONCLUSION

Although multi-facet results were reported on the association between telomerase activity and psychological stress, mental disorders and lifestyle factors, there were some consistent findings in humans such as (1) decreased telomerase activity in individuals under chronic stress, (2) increased telomerase activity in individuals with MDD, and (3) increased telomerase activity in individuals under lifestyle interventions. Animal studies showed that physical exercise increased telomerase activity in specific cell-types. However, the exact mechanisms for the changes in telomerase activity have not been elucidated. We propose conglomerate models connecting chronic psychological stress, depression, mediation and physical exercise to telomerase activation. Several areas for future research are suggested.

Synthesis and Testing of Modular Dual-Modality Nanoparticles for Magnetic Resonance and Multispectral Photoacoustic Imaging

Magnetic resonance (MR) and photoacoustic (PA) imaging are currently being investigated as complementing strategies for applications requiring sensitive detection of cells in vivo. While combined MR/PAI detection of cells requires biocompatible cell labeling probes, water-based synthesis of dual-modality MR/PAI probes presents significant technical challenges. Here we describe facile synthesis and characterization of hybrid modular dextran-stabilized gold/iron oxide (Au-IO) multimetallic nanoparticles (NP) enabling multimodal imaging of cells. The stable association between the IO and gold NP was achieved by priming the surface of dextran-coated IO with silver NP resulting from silver(I) reduction by aldehyde groups, which are naturally present within the dextran coating of IO at the level of 19-23 groups/particle. The Au-IO NP formed in the presence of silver-primed Au-IO were stabilized by using partially thiolated MPEG5-gPLL graft copolymer carrying residual amino groups. This stabilizer served as a carrier of near-infrared fluorophores (e.g., IRDye 800RS) for multispectral PA imaging. Dual modality imaging experiments performed in capillary phantoms of purified Au-IO-800RS NPs showed that these NPs were detectible using 3T MRI at a concentration of 25 μM iron. PA imaging achieved approximately 2.5-times higher detection sensitivity due to strong PA signal emissions at 530 and 770 nm, corresponding to gold plasmons and IRDye integrated into the coating of the hybrid NPs, respectively, with no "bleaching" of PA signal. MDA-MB-231 cells prelabeled with Au-IO-800RS retained plasma membrane integrity and were detectable by using both MR and dual-wavelength PA at 49 ± 3 cells/imaging voxel. We believe that modular assembly of multimetallic NPs shows promise for imaging analysis of engineered cells and tissues with high resolution and sensitivity.

T2MR and T2Candida: novel technology for the rapid diagnosis of candidemia and invasive candidiasis

Candidemia and other forms of invasive candidiasis pose a significant diagnostic challenge. In order to provide the best treatment, it is important to accurately detect the fungal infection and identify the species. Historically, diagnosis of Candida infections depended upon three classical laboratory approaches: microbiologic, immunologic, histopathologic; and now includes new methods such as radiographic techniques, molecular, proteomic and biochemical methods. The T2Candida Panel has introduced a new class of infectious disease diagnostics that can rapidly detect and identify the causative pathogen of sepsis directly from a patient blood sample in a culture-independent manner. This test enables detection of Candida directly from the patient sample, a significant advance for the rapid and accurate diagnosis of invasive candidiasis.

Synthesis and design of biologically inspired biocompatible iron oxide nanoparticles for biomedical applications

During the last couple of decades considerable research efforts have been directed towards the synthesis and coating of iron oxide nanoparticles (IONPs) for biomedical applications. To address the current limitations, recent studies have focused on the design of new generation nanoparticle systems whose internalization and targeting capabilities have been improved through surface modifications. This review covers the most recent challenges and advances in the development of IONPs with enhanced quality, and biocompatibility for various applications in biotechnology and medicine.

Recent progress on magnetic iron oxide nanoparticles: synthesis, surface functional strategies and biomedical applications

This review focuses on the recent development and various strategies in the preparation, microstructure, and magnetic properties of bare and surface functionalized iron oxide nanoparticles (IONPs); their corresponding biological application was also discussed. In order to implement the practical in vivo or in vitro applications, the IONPs must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of IONPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The new functionalized strategies, problems and major challenges, along with the current directions for the synthesis, surface functionalization and bioapplication of IONPs, are considered. Finally, some future trends and the prospects in these research areas are also discussed.

Strategies for interfacing inorganic nanocrystals with biological systems based on polymer-coating

A representative set of nanocrystals made of semiconductors, Au and iron oxide, surface-capped with polymer ligands presenting various metal-coordinating groups.

Environment-responsive nanophores for therapy and treatment monitoring via molecular MRI quenching

The effective delivery of therapeutics to disease sites significantly contributes to drug efficacy, toxicity and clearance. Here we demonstrate that clinically approved iron oxide nanoparticles (Ferumoxytol) can be utilized to carry one or multiple drugs. These so called ‘nanophores’ retain their cargo within their polymeric coating through weak electrostatic interactions and release it in slightly acidic conditions (pH 6.8 and below). The loading of drugs increases the nanophores’ transverse T2 and longitudinal T1 NMR proton relaxation times, which is proportional to amount of carried cargo. Chemotherapy with translational nanophores is more effective than the free drug in vitro and in vivo, without subjecting the drugs or the carrier nanoparticle to any chemical modification. Evaluation of cargo incorporation and payload levels in vitro and in vivo can be assessed via benchtop magnetic relaxometers, common NMR instruments or MRI scanners.

NMR–DMF: a modular nuclear magnetic resonance–digital microfluidics system for biological assays

We present a modular nuclear magnetic resonance–digital microfluidics (NMR–DMF) system as a portable diagnostic platform for miniaturized biological assays.

Visual detection of telomerase activity with a tunable dynamic range by using a gold nanoparticle probe-based hybridization protection strategy

We developed a novel telomere complementary (TC) oligonucleotide modified AuNP probe (TC-AuNPs) for colorimetric analysis of telomerase activity. The mechanism of this method is that the telomerase reaction products (TRP), which can hybridize with the TC-AuNPs, are able to protect the AuNPs from the aggregation induced by salt. It is demonstrated that the colorimetric method enabled the analysis of the telomerase activity in 1000 HeLa cells with the naked eye, and down to 100 HeLa cells with the aid of UV-Vis spectroscopy. This strategy is not only convenient and sensitive, but also has a tunable dynamic range. The platform is also applicable for the initial screening of a telomerase inhibitor to discover new anticancer drugs.

Nanobiosensors: Concepts and Variations

Biosensing has been one of the hottest topic attracting scientific minds since long back. It is so as biological entities are very complex and are directly associated with the existence of a healthy environment. The design of biosensors also has witnessed significant changes in the recent past. Biosensors for applications as diverse as food quality estimation, environmental monitoring, and diagnosis of clinical and metabolic complications have come to the fore. Nanotechnology has bestowed some highly exciting ingredients for the improvement of sensing phenomenon. The use of diverse nanomaterials ranging from nanoparticles, nanotubes, nanorods, and nanowires has enabled faster detection and its reproducibility in a much better way. The unique properties of nanomaterials such as high electrical conductivity, better shock bearing ability, and the sensitive responses such as piezoelectric and versatile color based detection mechanisms are only the results of congregation of nanomaterial properties. This paper highlights the different types of biosensors based on different types of nanomaterials and their developmental and implicational aspects.

A highly sensitive telomerase activity assay that eliminates false-negative results caused by PCR inhibitors

An assay for telomerase activity based on asymmetric polymerase chain reaction (A-PCR) on magnetic beads (MBs) and subsequent application of cycling probe technology (CPT) is described. In this assay, the telomerase reaction products are immobilized on MBs, which are then washed to remove PCR inhibitors that are commonly found in clinical samples. The guanine-rich sequences (5'-(TTAGGG)n-3') of the telomerase reaction products are then preferentially amplified by A-PCR, and the amplified products are subsequently detected via CPT, where a probe RNA with a fluorophore at the 5' end and a quencher at the 3' end is hydrolyzed by RNase H in the presence of the target DNA. The catalyst-mediated cleavage of the probe RNA enhances fluorescence from the 5' end of the probe. The assay allowed us to successfully detect HeLa cells selectively over normal human dermal fibroblast (NHDF) cells. Importantly, this selectivity produced identical results with regard to detection of HeLa cells in the absence and presence of excess NHDF cells; therefore, this assay can be used for practical clinical applications. The lower limit of detection for HeLa cells was 50 cells, which is lower than that achieved with a conventional telomeric repeat amplification protocol assay. Our assay also eliminated false-negative results caused by PCR inhibitors. Furthermore, we show that this assay is appropriate for screening among G-quadruplex ligands to find those that inhibit telomerase activity.

Targeted nanoparticles in imaging: paving the way for personalized medicine in the battle against cancer

The way we view cancer has advanced greatly in the past few decades from simplistic approaches to finely honed systems. This transition has been made possible because of advancements on two fronts: the first is the rapidly expanding knowledge base of the mechanisms and characteristics of cancer; the second is innovation in imaging agent design. Rapid advancements in imaging and therapeutic agents are being made through the evolution from one-dimensional molecules to multi-functional nanoparticles. Powerful new agents that have high specificity and minimal toxicity are being developed for in vivo imaging. Here we detail the unique characteristics of cancer that allow differentiation from normal tissue and how they are exploited in nanoparticle imaging development. Firstly, genetic alterations, either endogenous or induced through gene therapy, are one such class of characteristics. Proteomic differences such as overexpressed surface receptors is another targetable feature used for enhanced nanoparticle retention. Increased need for nutrients and specific growth signals to sustain proliferation and angiogenesis are further examples of how cancer can be targeted. Lastly, migration and invasion through a unique microenvironment are two additional traits that are exploitable, due to differences in metalloproteinase concentrations and other factors. These differences are guiding current nanoparticle design to better target, image and treat cancer.

Applications and potential toxicity of magnetic iron oxide nanoparticles

Owing to their unique physical and chemical properties, magnetic iron oxide nanoparticles have become a powerful platform in many diverse aspects of biomedicine, including magnetic resonance imaging, drug and gene delivery, biological sensing, and hyperthermia. However, the biomedical applications of magnetic iron oxide nanoparticles arouse serious concerns about their pharmacokinetics, metabolism, and toxicity. In this review, the updated research on the biomedical applications and potential toxicity of magnetic iron oxide nanoparticles is summarized. Much more effort is required to develop magnetic iron oxide nanoparticles with improved biocompatible surface engineering to achieve minimal toxicity, for various applications in biomedicine.

Micro- and nanoscale technologies for tissue engineering and drug discovery applications

Micro- and nanoscale technologies are emerging as powerful enabling tools for tissue engineering and drug discovery. In tissue engineering, micro- and nanotechnologies can be used to fabricate biomimetic scaffolds with increased complexity and vascularization. Furthermore, these technologies can be used to control the cellular microenvironment (i.e., cell-cell, cell-matrix and cell-soluble factor interactions) in a reproducible manner and with high temporal and spatial resolution. In drug discovery, miniaturized platforms based on micro- and nanotechnology can be used to precisely control the fluid flow, enable high-throughput screening, and minimize sample or reagent volumes. In addition, these systems enhance reproducibility and significantly reduce reaction times. This paper reviews the recent developments in the field of micro- and nanoscale technology and gives examples of their tissue engineering and drug discovery applications.

Functionalized magnetic nanoparticles as vehicles for the delivery of the antitumor drug gemcitabine to tumor cells. Physicochemical in vitro evaluation

Gemcitabine is a chemotherapy drug used in different carcinomas, although because it displays a short biological half-life, its plasmatic levels can quickly drop below the effective threshold. Nanoparticle-based drug delivery systems can provide an alternative approach for regulating the bioavailability of this and most other anticancer drugs. In this work we describe a new model of composite nanoparticles consisting of a core of magnetite nanoparticles, coated with successive layers of high molecular weight poly(acrylic acid) and chitosan, and a final layer of folic acid. The possibility of using these self-assembled nanostructures for gemcitabine vehiculization is explored. First, the surface charge of the composite particles is studied by means of electrophoretic mobility measurements as a function of pH for poly(acrylic acid) (carbopol) of different molecular weights. The adsorption of folic acid, aimed at increasing the chances of the particles to pass the cell membrane, is followed up by optical absorbance measurements, which were also employed for drug adsorption determinations. As a main result, it is shown that gemcitabine adsorbs onto the surface of chitosan/carbopol-coated magnetite nanoparticles. In vitro experiments show that the functionalized magnetic nanoparticles are able to deliver the drug to the nuclei of liver, colon and breast tumor cells.

Molecular body imaging: MR imaging, CT, and US. Part II. Applications

Molecular imaging is expected to have a major impact on the early diagnosis of diseases and disease monitoring in the next decade. Traditionally, nuclear imaging techniques have been the mainstay of molecular imaging in the clinical arena. However, with continued development of molecularly targeted contrast agents for nonnuclear imaging techniques such as magnetic resonance (MR), computed tomography (CT), and ultrasonography (US), the spectrum of clinical molecular imaging applications is expanding. In the second part of this review series, an overview of applications of molecular MR imaging-, CT-, and US-based imaging strategies that show promise for clinical translation is presented, and key challenges that need to be addressed to successfully translate these promising techniques in the future are discussed. © RSNA, 2012.

Molecular body imaging: MR imaging, CT, and US. part I. principles

Molecular imaging, generally defined as noninvasive imaging of cellular and subcellular events, has gained tremendous depth and breadth as a research and clinical discipline in recent years. The coalescence of major advances in engineering, molecular biology, chemistry, immunology, and genetics has fueled multi- and interdisciplinary innovations with the goal of driving clinical noninvasive imaging strategies that will ultimately allow disease identification, risk stratification, and monitoring of therapy effects with unparalleled sensitivity and specificity. Techniques that allow imaging of molecular and cellular events facilitate and go hand in hand with the development of molecular therapies, offering promise for successfully combining imaging with therapy. While traditionally nuclear medicine imaging techniques, in particular positron emission tomography (PET), PET combined with computed tomography (CT), and single photon emission computed tomography, have been the molecular imaging methods most familiar to clinicians, great advances have recently been made in developing imaging techniques that utilize magnetic resonance (MR), optical, CT, and ultrasonographic (US) imaging. In the first part of this review series, we present an overview of the principles of MR imaging-, CT-, and US-based molecular imaging strategies.

Label-free highly sensitive detection of telomerase activity in cancer cell by chemiluminescence imaging

We have developed a new methodology for label-free highly sensitive telomerase activity assay using chemiluminescence imaging. This method can detect the telomerase activity from as little as 10 cultured cancer cells without PCR. Furthermore, telomerase inhibition is shown, demonstrating the potential for screening of telomerase inhibitors as anticancer drug agents.

Fluorescence detection of DNA, adenosine-5'-triphosphate (ATP), and telomerase activity by zinc(II)-protoporphyrin IX/G-quadruplex labels

The zinc(II)-protoporphyrin IX (ZnPPIX) fluorophore binds to G-quadruplexes, and this results in the enhanced fluorescence of the fluorophore. This property enabled the development of DNA sensors, aptasensors, and a sensor following telomerase activity. The DNA sensor is based on the design of a hairpin structure that includes a "caged" inactive G-quadruplex sequence. Upon opening the hairpin by the analyte DNA, the resulting fluorescence of the ZnPPIX/G-quadruplex provides the readout signal for the sensing event (detection limit 5 nM). Addition of Exonuclease III to the system allows the recycling of the analyte and its amplified analysis (detection limit, 200 pM). The association of the ZnPPIX to G-quadruplex aptamer-substrate complexes allowed the detection of adenosine-5'-triphosphate (ATP, detection limit 10 μM). Finally, the association of ZnPPIX to the G-quadruplex repeat units of telomers allowed the detection of telomerase activity originating from 380 ± 20 cancer 293T cell extract.

Assays for human telomerase activity: progress and prospects

Human telomerase is a ribonucleoprotein complex that functions as a telomere terminal transferase by adding multiple TTAGGG hexamer repeats using its integral RNA as the template. There is a very strong association between telomerase activity and malignancy in nearly all types of cancer, suggesting that telomerase could be used not only as a diagnostic and prognostic marker but also as a therapeutic target for managing cancer. The significant progress in biomedical telomerase research has necessitated the development of new bioanalytical methods for the rapid, sensitive, and reliable detection of telomerase activity in a particular cell or clinical tissue and body fluids. In this review, we highlight some of the latest methods for identifying telomerase activity and inhibition and discuss some of the challenges for designing innovative telomerase assays. We also summarise the current technologies and speculate on future directions for telomerase testing.

Rapid and sensitive detection of an intracellular pathogen in human peripheral leukocytes with hybridizing magnetic relaxation nanosensors

Bacterial infections are still a major global healthcare problem. The quick and sensitive detection of pathogens responsible for these infections would facilitate correct diagnosis of the disease and expedite treatment. Of major importance are intracellular slow-growing pathogens that reside within peripheral leukocytes, evading recognition by the immune system and detection by traditional culture methods. Herein, we report the use of hybridizing magnetic nanosensors (hMRS) for the detection of an intracellular pathogen, Mycobacterium avium spp. paratuberculosis (MAP). The hMRS are designed to bind to a unique genomic sequence found in the MAP genome, causing significant changes in the sample’s magnetic resonance signal. Clinically relevant samples, including tissue and blood, were screened with hMRS and results were compared with traditional PCR analysis. Within less than an hour, the hMRS identified MAP-positive samples in a library of laboratory cultures, clinical isolates, blood and homogenized tissues. Comparison of the hMRS with culture methods in terms of prediction of disease state revealed that the hMRS outperformed established culture methods, while being significantly faster (1 hour vs 12 weeks). Additionally, using a single instrument and one nanoparticle preparation we were able to detect the intracellular bacterial target in clinical samples at the genomic and epitope levels. Overall, since the nanoparticles are robust in diverse environmental settings and substantially more affordable than PCR enzymes, the potential clinical and field-based use of hMRS in the multiplexed identification of microbial pathogens and other disease-related biomarkers via a single, deployable instrument in clinical and complex environmental samples is foreseen.

Visualizing human telomerase activity with primer-modified Au nanoparticles

Telomerase is over-expressed in over 85% of all known human tumors. This renders the enzyme a valuable biomarker for cancer diagnosis and an important therapeutic target. The most widely used telomeric repeat amplification protocol (TRAP) assay has been questioned for telomerase detection. It is reported that human telomerase activity can be visualized by using primer-modified Au nanoparticles. The working principle is based on the elongated primers conjugated to the gold nanoparticle (AuNP) surface, which can fold into a G-quadruplex to protect the AuNPs from the aggregation. The developed simple and sensitive colorimetric assay can measure telomerase activity down to 1 HeLa cell µL(-1). More importantly, this assay can be easily extended to high-throughput and automatic format. The AuNP-TS method is PCR-free and therefore avoids the amplification-related errors and becomes more reliable to evaluate telomerase activity. This assay has also been used for initial screening of telomerase inhibitors as anticancer drug agents.

Magnetic Nanoparticles and microNMR for Diagnostic Applications

Sensitive and quantitative measurements of clinically relevant protein biomarkers, pathogens and cells in biological samples would be invaluable for disease diagnosis, monitoring of malignancy, and for evaluating therapy efficacy. Biosensing strategies using magnetic nanoparticles (MNPs) have recently received considerable attention, since they offer unique advantages over traditional detection methods. Specifically, because biological samples have negligible magnetic background, MNPs can be used to obtain highly sensitive measurements in minimally processed samples. This review focuses on the use of MNPs for in vitro detection of cellular biomarkers based on nuclear magnetic resonance (NMR) effects. This detection platform, termed diagnostic magnetic resonance (DMR), exploits MNPs as proximity sensors to modulate the spin-spin relaxation time of water molecules surrounding the molecularly-targeted nanoparticles. With new developments such as more effective MNP biosensors, advanced conjugational strategies, and highly sensitive miniaturized NMR systems, the DMR detection capabilities have been considerably improved. These developments have also enabled parallel and rapid measurements from small sample volumes and on a wide range of targets, including whole cells, proteins, DNA/mRNA, metabolites, drugs, viruses and bacteria. The DMR platform thus makes a robust and easy-to-use sensor system with broad applications in biomedicine, as well as clinical utility in point-of-care settings.

Dextran-coated iron oxide nanoparticles: a versatile platform for targeted molecular imaging, molecular diagnostics, and therapy

Advances in our understanding of the genetic basis of disease susceptibility coupled with prominent successes for molecular targeted therapies have resulted in an emerging strategy of personalized medicine. This approach envisions risk stratification and therapeutic selection based on an individual's genetic makeup and physiologic state (the latter assessed through cellular or molecular phenotypes). Molecularly targeted nanoparticles can play a key role in this vision through noninvasive assessments of molecular processes and specific cell populations in vivo, sensitive molecular diagnostics, and targeted delivery of therapeutics. A superparamagnetic iron oxide nanoparticle with a cross-linked dextran coating, or CLIO, is a powerful and illustrative nanoparticle platform for these applications. These structures and their derivatives support diagnostic imaging by magnetic resonance (MRI), optical, and positron emission tomography (PET) modalities and constitute a versatile platform for conjugation to targeting ligands. A variety of conjugation methods exist to couple the dextran surface to different functional groups; in addition, a robust bioorthogonal [4 + 2] cycloaddition reaction between 1,2,4,5-tetrazene (Tz) and trans-cyclooctene (TCO) can conjugate nanoparticles to targeting ligands or label pretargeted cells. The ready availability of conjugation methods has given rise to the synthesis of libraries of small molecule modified nanoparticles, which can then be screened for nanoparticles with specificity for a specific cell type. Since most nanoparticles display their targeting ligands in a multivalent manner, a detailed understanding of the kinetics and affinity of a nanoparticle's interaction with its target (as determined by surface plasmon resonance) can yield functionally important insights into nanoparticle design. In this Account, we review applications of the CLIO platform in several areas relevant to the mission of personalized medicine. We demonstrate rapid and highly sensitive molecular profiling of cancer markers ex vivo, as part of detailed, individualized molecular phenotyping. The CLIO platform also facilitates targeted magnetic resonance and combined modality imaging (such as MR/PET/fluorescence/CT) to enable multiplexed measurement of molecular phenotypes in vivo for early diagnosis and disease classification. Finally, the targeted delivery of a photodynamic therapy agent as part of a theranostic nanoparticle successfully increased local cell toxicity and minimized systemic side effects.

Will nanotechnology influence targeted cancer therapy?

The rapid development of techniques that enable synthesis (and manipulation) of matter on the nanometer scale and the development of new nanomaterials will play a large role in disease diagnosis and treatment, specifically in targeted cancer therapy. Targeted nanocarriers are an intriguing means to selectively deliver high concentrations of cytotoxic agents or imaging labels directly to the cancer site. Often, solubility issues and an unfavorable biodistribution can result in a suboptimal response of novel agents even though they are very potent. New nanoparticulate formulations allow simultaneous imaging and therapy ("theranostics"), which can provide a realistic means for the clinical implementation of such otherwise suboptimal formulations. In this review, we did not attempt to provide a complete overview of the rapidly enlarging field of nanotechnology in cancer; rather, we presented properties specific to nanoparticles and examples of their uses, which show their importance for targeted cancer therapy.

Targeting human telomerase for cancer therapeutics

The enzyme telomerase is involved in the replication of telomeres, specialized structures that cap and protect the ends of chromosomes. Its activity is required for maintenance of telomeres and for unlimited lifespan, a hallmark of cancer cells. Telomerase is overexpressed in the vast majority of human cancer cells and therefore represents an attractive target for therapy. Several approaches have been developed to inhibit this enzyme through the targeting of its RNA or catalytic components as well as its DNA substrate, the single-stranded 3'-telomeric overhang. Telomerase inhibitors are chemically diverse and include modified oligonucleotides as well as small diffusable molecules, both natural and synthetic. This review presents an update of recent investigations pertaining to these agents and discusses their biological properties in the context of the initial paradigm that the exposure of cancer cells to these agents should lead to progressive telomere shortening followed by a delayed growth arrest response.

Miniature magnetic resonance system for point-of-care diagnostics

We have developed a next generation, miniaturized platform to diagnose disease at the point-of-care using diagnostic magnetic resonance (DMR-3). Utilizing a rapidly growing library of functionalized magnetic nanoparticles, DMR has previously been demonstrated as a versatile tool to quantitatively and rapidly detect disease biomarkers in unprocessed biological samples. A major hurdle for bringing DMR to the point-of-care has been its sensitivity to temperature variation. As an alternative to costly and bulky mechanisms to control temperature, we have implemented an automated feedback system to track and compensate for the temperature drift, which enables reliable and robust DMR measurements in realistic clinical environments (4-50 °C). Furthermore, the new system interfaces with a mobile device to facilitate system control and data sharing over wireless networks. With such features, the DMR-3 platform can function as a self-contained laboratory even in resource-limited, remote settings. The clinical potential of the new system is demonstrated by detecting trace amounts of proteins and as few as 10 bacteria (Staphylococcus aureus) in a short time frame (<30 min).

Molecular detection of biomarkers and cells using magnetic nanoparticles and diagnostic magnetic resonance

The rapid and sensitive detection of molecular targets such as proteins, cells, and pathogens in biological specimens is a major focus of ongoing medical research, as it could promote early disease diagnoses and the development of tailored therapeutic strategies. Magnetic nanoparticles (MNP) are attractive candidates for molecular biosensing applications because most biological samples exhibit negligible magnetic susceptibility, and thus the background against which measurements are made is extremely low. Numerous magnetic detection methods exist, but sensing based on magnetic resonance effects has successfully been developed into a general detection platform termed diagnostic magnetic resonance (DMR). DMR technology encompasses numerous assay configurations and sensing principles, and to date magnetic nanoparticle biosensors have been designed to detect a wide range of targets including DNA/mRNA, proteins, enzymes, drugs, pathogens, and tumor cells with exquisite sensitivity. The core principle behind DMR is the use of MNP as proximity sensors that modulate the transverse relaxation time of neighboring water molecules. This signal can be quantified using MR imagers or NMR relaxometers, including miniaturized NMR detector chips that are capable of performing highly sensitive measurements on microliter sample volumes and in a multiplexed format. The speed, sensitivity, and simplicity of the DMR principle, coupled with further advances in NMR biosensor technology should provide a high-throughput, low-cost, and portable platform for large-scale parallel sensing in clinical and point-of-care settings.