Resonance Energy Transfer Signal Research Articles

Multiplexed genomic encoding of non-canonical amino acids for labeling large complexes.

Stunning advances in the structural biology of multicomponent biomolecular complexes (MBCs) have ushered in an era of intense, structure-guided mechanistic and functional studies of these complexes. Nonetheless, existing methods to site-specifically conjugate MBCs with biochemical and biophysical labels are notoriously impracticable and/or significantly perturb MBC assembly and function. To overcome these limitations, we have developed a general, multiplexed method in which we genomically encode non-canonical amino acids (ncAAs) into multiple, structure-informed, individual sites within a target MBC; select for ncAA-containing MBC variants that assemble and function like the wildtype MBC; and site-specifically conjugate biochemical or biophysical labels to these ncAAs. As a proof-of-principle, we have used this method to generate unique single-molecule fluorescence resonance energy transfer (smFRET) signals reporting on ribosome structural dynamics that have thus far remained inaccessible to smFRET studies of translation.

Development of Ratiometric Bioluminescent Sensors for in Vivo Detection of Bacterial Signaling.

Second messenger signaling networks allow cells to sense and adapt to changing environmental conditions. In bacteria, the nearly ubiquitous second messenger molecule cyclic di-GMP coordinates diverse processes such as motility, biofilm formation, and virulence. In bacterial pathogens, these signaling networks allow the bacteria to survive changing environmental conditions that are experienced during infection of a mammalian host. While studies have examined the effects of cyclic di-GMP levels on virulence in these pathogens, it has not been possible to visualize cyclic di-GMP levels in real time during the stages of host infection. Toward this goal, we generate the first ratiometric, chemiluminescent biosensor scaffold that selectively responds to c-di-GMP. By engineering the biosensor scaffold, a suite of Venus-YcgR-NLuc (VYN) biosensors is generated that provide extremely high sensitivity (KD < 300 pM) and large changes in the bioluminescence resonance energy transfer (BRET) signal (up to 109%). As a proof-of-concept that VYN biosensors can image cyclic di-GMP in tissues, we show that the VYN biosensors function in the context of a tissue phantom model, with only ∼103-104 biosensor-expressing E. coli cells required for the measurement. Furthermore, we utilize the biosensor in vitro to assess changes in cyclic di-GMP in V. cholerae grown with different inputs found in the host environment. The VYN sensors developed here can serve as robust in vitro diagnostic tools for high throughput screening, as well as genetically encodable tools for monitoring the dynamics of c-di-GMP in live cells, and lay the groundwork for live cell imaging of c-di-GMP dynamics in bacteria within tissues and other complex environments.

Adaption of an autonomously cascade DNA circuit for amplified detection and intracellular imaging of polynucleotide kinase with ultralow background

Polynucleotide kinase (PNK) plays a crucial role in phosphorylation-related DNA repair, while its real time tracking and monitoring is unexplored for limited sensitivity and robustness of current PNK sensing strategies in complex biological environment. Herein, we proposed a concatenated hybridization chain reaction (Con-HCR)-based PNK sensing platform for ultra-sensitive PNK assay and intracellular imaging. In the presence of PNK, the 5′-hydroxyl termini of hairpin Hp was phosphorylated for λ exonuclease (λ Exo)-mediated DNA cleavage reaction. This leads to the generation of initiator I for stimulating the subsequent Con-HCR-motivated assembly of branched dsDNA nanostructures with tremendously amplified Förster resonance energy transfer (FRET) signal. Owing to the multiple-responsive recognitions of PNK/exonuclease and the dual amplification of Con-HCR, the proposed method realized the sensitive and selective PNK assay as well as the screening of PNK inhibitors. This FRET-based signal transduction provides a straightforward and accurate procedure for analyzing PNK from complex cell lysate. Furthermore, the robust feature of the present system enabled their extensive application in monitoring the varied expression levels of intracellular PNK in living cells. In view of these remarkable characters, our Con-HCR-mediated PNK sensing strategy shows more potential applications in clinical diagnosis and new drug discovery researches.

Triplex-Functionalized DNA Tetrahedral Nanoprobe for Imaging of Intracellular pH and Tumor-Related Messenger RNA.

A new triplex-functionalized DNA tetrahedral nanoprobe is proposed herein for monitoring pH and messenger RNA (mRNA) in living cells. Different from traditional DNA tetrahedron-based nanoprobes, DNA triplex was employed to serve as important conformational conversion elements. Inspired by the low extracellular pH in tumor cells, the mRNA-targeted H1 and H2 were stably assembled on the extended short hairpin probes of DNA tetrahedron via Hoogsteen bonding to form DNA triplex. Due to the high intracellular pH and presence of target mRNA, hybridization chain reaction (HCR) was triggered between H1 and H2 which were released from the dissociation of DNA triplex, and the generated long double-stranded DNA activated a Föster resonance energy transfer (FRET) signal indicating target mRNA expression even at very low contents. By combining the distinguishing feature of DNA triplex structure (pH-responsive) and HCR (signal amplification), sensitive imaging of intracellular pH and tumor-related mRNA can be realized. As a further application, dynamic imaging of intracellular pH and mRNA during "mitochondria-dependent" pathway apoptosis was successfully achieved in human breast cancer cells, which indicated huge potential of our proposed nanoprobe in early diagnosis and treatment of diseases.

Alginate/Cucurbit[7]uril/Dequalinium-Based Supramolecular Carbohydrates: Modulation of FRET Signals by Temperature Control

Herein, we describe the synthesis of a bioactive, inexpensive, and easy-to-handle supramolecular carbohydrate polymer by grafting of cucurbit[7]uril macrocycle (CB7)-encapsulated dequalinium chloride hydrate (DCH) onto alginic acid carbohydrates (ALG) via amide linkage formation and show that light energy transfer based on energy migration can be controlled by altering polymer temperature without changing polymer composition. DCH (donor) and 2-anilinonaphthalene-6-sulfonic acid (acceptor) were used to generate Förster resonance energy transfer (FRET) signals. Stationary and time-resolved photoluminescence spectra of the modified carbohydrate platform revealed that FRET resulted in a color change from violet (∼387 nm) to blue (∼429 nm), which could be repeatedly switched on and off in response to temperature stimuli at 298–368 K. Temperature-dependent NMR measurements suggested that the responsiveness of DCH/CB7ALG to thermal stimuli was due to the threading of CB7 onto the DCH backbone in solution and upon grafting onto ALG polymers.

Nanolantern-Based DNA Probe and Signal Amplifier for Tumor-Related Biomarker Detection in Living Cells.

The introduction of nanotechnology can overcome some inherent drawbacks of traditional DNA probes, thus promoting their applications in living cells. Herein, a three-dimensional DNA nanostructure, a DNA nanolantern, was prepared via simple nucleotide hybridization of four short-stranded oligonucleotides and successfully applied to the construction of a novel DNA probe and signal amplifier. Compared to most reported DNA nanostructures, a DNA nanolantern shows the distinct advantages of low cost, easy design and preparation, more and arbitrary adjusted probe numbers, and high fluorescence resonance energy transfer (FRET) signal readout. Compared to traditional DNA probes, the constructed nanolantern-based one has improved cell internalization efficiency, enhanced biostability, accelerated reaction kinetics, excellent biocompatibility, and greatly reduced false-positive output and was demonstrated to work well for probing the expression level of tumor-related mRNA and microRNA in living cells. The DNA nanolantern can also be easily integrated with some reported signal amplification strategies, e.g., isothermal hybridization chain reaction (HCR), and the obtained signal amplifier combines the advantages of the DNA nanolantern and the HCR, enabling sensitive imaging detection of ultralow abundance targets in living cells. This work demonstrated that this simple DNA nanostructure can not only improve the performance of traditional DNA probes but can also be easily integrated with reported DNA-based strategy and technology, thus showing a broad application prospect.

A spatial-confinement hairpin cascade reaction-based DNA tetrahedral amplifier for mRNA imaging in live cells

The three-dimensional (3D) DNA nanostructure has been got much attention due to its excellent biocompatibility, enhanced structural stability, highly programmable and perfect cell-delivery performance. Here, a novel 3D DNA tetrahedron amplifier (DTA) has been developed for rapid and efficient mRNA imaging in living cells using target catalyzing spatial-confinement hairpin DNA assembly cascade reaction inside the DNA nanostructure. The DTA was constructed by assembling a DNA tetrahedron with four DNA strands at first, and then by assembling two metastable DNA hairpins H1 (Cy5) and H2 (Cy3) at specific locations of the DNA tetrahedron. In the presence of target mRNA, the catalyzed hairpin assembly (CHA) reaction on the DTA could be triggered and a H1-H2 duplexes nanostructure could be formed, which would obtain a significant fluorescence resonance energy transfer (FRET) signal, and release the target mRNA could trigger next H1-H2 duplexes formation. Due to the 3D DNA tetrahedral spatial-confinement effect, the circular reaction of DTA could achieve rapid and efficient amplification detection of target mRNA in living cells. Moreover, the DTA show excellent structural stability and non-cytotoxicity. This strategy presents a versatile method for the ultrasensitive detection of biomarkers in living system and gains a deeper development of the DNA nanostructures in biomedical functions.

Fluorescence Resonance Energy Transfer-Mediated Immunosensor Based on Design and Synthesis of the Substrate of Amp Cephalosporinase for Biosensing.

The traditional enzyme-linked immunosorbent assay (ELISA) has some disadvantages, such as insufficient sensitivity and low stability of the labeled enzyme, which limit its further applications. In this study, a more stable enzyme, Amp cephalosporinase (AmpC), was selected as the labeled enzyme, and its substrate was designed and synthesized. This substrate contained the cephalosporin ring core as the enzymatic recognition section and the structural motif of the 3-hydroxyflavone (3-HF) as the reporter molecule. AmpC can specifically catalyze the substrate and release 3-HF, which can enter the cavity of β-cyclodextrin (β-CD) on the surface of ZnS quantum dots and form a fluorescence resonance energy transfer (FRET) signal amplification system. An AmpC-catalyzed, FRET-mediated ultrasensitive immunosensor (ACF immunosensor) for procalcitonin (PCT) was developed by combining the signal amplification system of the polystyrene microspheres and effective immune-based magnetic separation. The ACF immunosensor has high sensitivity and specificity for the detection of PCT: its linear range is from 0.1 ng mL-1 to 70 ng mL-1, and the limit of detection can reach 0.03 ng mL-1. The spiking recoveries of PCT in human serum samples range from 98.3% to 107%, with relative standard deviations ranging from 2.14% to 12.0%. This approach was applied to detect PCT in real patient serum samples, and the results are consistent with those obtained with a commercial ELISA kit.

Molecular Switching of a Self-Assembled 3D DNA Nanomachine for Spatiotemporal pH Mapping in Living Cells.

DNA nanomachines have received great interest due to their potential to mimic various natural biomolecular machines. Intracellular pH sensing and imaging are of great significance to understand cellular behaviors and disease diagnostics. In this work, we report the novel molecular switching of a self-assembled 3D DNA triangular prism nanomachine (TPN) for pH sensing and imaging in living cells. The TPN was self-assembled in quantitative yields by hybridization with two DNA triangles and three I-strands (containing i-motif sequences). At acidic conditions, the TPN was compressed due to the I-strand that formed an intramolecular i-tetraplex, which was in between the fluorophores Cy3 and Cy5, resulting in a significant fluorescence resonance energy transfer (FRET) signal. At neutral or weakly alkaline conditions, the TPN adopted an extended state due to the random coil form of the I-strand, leading to spatial separation of the two fluorophores and the FRET being blocked. The TPN was fully reversible and could rapidly respond to the pH changes, entered into living cells automatically via an endocytic pathway, monitored spatiotemporal pH changes during endocytosis, maintained its structural integrity after escape from lysosomes, still had the ability for pH sensing, and also visualized pH fluctuations under varying stimuli in living cells. We foresee that this TPN can become a generic platform for a pH-related cell biology study and in disease diagnostics.

Netlike hybridization chain reaction assembly of DNA nanostructures enables exceptional signal amplification for sensing trace cytokines.

The monitoring and detection of molecular biomarkers play crucial roles in disease diagnosis and treatment. In this work, we proposed a target-responsive netlike hybridization chain reaction (nHCR) DNA nanostructure construction method, which can offer an exceptional signal enhancement, for highly sensitive fluorescence detection of cytokine, interferon-gamma (IFN-γ). The presence of the target cytokine can lead to the conformational change of the aptamer recognition hairpin probes and the liberation of the nHCR initiator strands, which further trigger the nHCR process between two dye-labeled and double hairpin-structured probes to form netlike DNA nanostructures. The formation of the DNA nanostructures brings the dyes into close proximity, resulting in significantly amplified fluorescence resonance energy transfer signals for sensitive and enzyme-free detection of IFN-γ. The present method has a detection limit of 1.2 pM and a dynamic linear range of 5 to 1000 pM for IFN-γ detection. Besides, with the high specificity of the aptamer probe and the significant signal amplification of the nHCR, such an IFN-γ detection strategy shows excellent selectivity and high sensitivity, which can be potentially applied to detect IFN-γ in human serums. With such a demonstration of the detection of IFN-γ, this proposed method can be extended for detecting different types of biomolecules.

Single-Molecule Studies on a FRET Biosensor: Lessons from a Comparison of Fluorescent Protein Equipped versus Dye-Labeled Species.

Bacterial periplasmic binding proteins (PBPs) undergo a pronounced ligand-induced conformational change which can be employed to monitor ligand concentrations. The most common strategy to take advantage of this conformational change for a biosensor design is to use a Förster resonance energy transfer (FRET) signal. This can be achieved by attaching either two fluorescent proteins (FPs) or two organic fluorescent dyes of different colors to the PBPs in order to obtain an optical readout signal which is closely related to the ligand concentration. In this study we compare a FP-equipped and a dye-labeled version of the glucose/galactose binding protein MglB at the single-molecule level. The comparison demonstrates that changes in the FRET signal upon glucose binding are more pronounced for the FP-equipped sensor construct as compared to the dye-labeled analog. Moreover, the FP-equipped sensor showed a strong increase of the FRET signal under crowding conditions whereas the dye-labeled sensor was not influenced by crowding. The choice of a labeling scheme should therefore be made depending on the application of a FRET-based sensor.

Direct Detection of Hemi-methylated DNA by SRA-fused Luciferase Based on Bioluminescence Resonance Energy Transfer

Hemi-methylated DNA is double stranded (ds)DNA where only one of the complementary strands is methylated. Hemi-methylated DNA levels on a tandem repeat NBL2 and Sat2 are increased in ovarian carcinomas. To quantify hemi-methylation levels, a bisulfite-based method is widely used, but this approach requires multiple steps. Therefore, a simple hemi-methylation assay is required for cancer diagnosis and to elucidate the functions of hemi-methylated DNA. In this study, we aimed to develop a homogeneous assay for the detection of the hemi-methylated DNA level using SET- and RING-associated (SRA) domain-fused luciferase (SRA-luciferase), which recognizes hemi-methylated DNA. In the assay, the hemi-methylation level was quantified by measuring the bioluminescence resonance energy transfer signal between the fusion protein and the DNA intercalating dye. The fusion protein specifically recognizes hemi-methylated DNA to excite the dye by luciferase luminescence. Our results demonstrated that the hemi-methylation level was easily quantified within 35 min with an R2 value of 0.99.

A Chemical Approach for Profiling Intracellular AKT Signaling Dynamics from Single Cells.

We present here a novel chemical method to continuously analyze intracellular AKT signaling activities at single-cell resolution, without genetic manipulations. A pair of cyclic peptide-based fluorescent probes were developed to recognize the phosphorylated Ser474 site and a distal epitope on AKT. A Förster resonance energy transfer signal is generated upon concurrent binding of the two probes onto the same AKT protein, which is contingent upon the Ser474 phosphorylation. Intracellular delivery of the probes enabled dynamic measurements of the AKT signaling activities. We further implemented this detection strategy on a microwell single-cell platform, and interrogated the AKT signaling dynamics in a human glioblastoma cell line. We resolved unique features of the single-cell signaling dynamics following different perturbations. Our study provided the first example of monitoring the temporal evolution of cellular signaling heterogeneities and unveiled biological information that was inaccessible to other methods.

Mn2+-activated calcium fluoride nanoprobes for time-resolved photoluminescence biosensing

Time-resolved (TR) photoluminescence (PL) technique has shown great promise in ultrasensitive biodetection and high-resolution bioimaging. Hitherto, almost all the TRPL bioprobes are based on the parity-forbidden f→f transition of lanthanide ions. Herein, we report TRPL biosensing by taking advantage of the d→d transition of transition metal (TM) Mn2+ ion. We demonstrate that the Forster resonance energy transfer (FRET) signal can be distinguished from that of radiative reabsorption process through measuring the PL lifetime of Mn2+, thus establishing a reliable method for Mn2+ in homogeneous TR-FRET biodetection. We also demonstrate the biotin receptor-targeted cancer cell imaging by utilizing biotinylated CaF2:Ce,Mn nanoprobes. Furthermore, we show in a proof-of-concept experiment the application of the long-lived PL of Mn2+ for TRPL bioimaging through the burst shot with a cell phone. These findings provide a general approach for exploiting the long-lived PL of TM ions for TRPL biosensing, thereby opening up a new avenue for the exploration of novel and versatile applications of TM ions.

Visualization of the activation of the histamine H3 receptor (H3R) using novel fluorescence resonance energy transfer biosensors and their potential application to the study of H3R pharmacology.

Activation of the histamine-3 receptor (H3R) is involved in memory processes and cognitive action, while blocking H3R activation can slow the progression of neurological disorders, such as Alzheimer's disease, schizophrenia and narcolepsy. To date, however, no direct way to examine the activation of H3R has been utilized. Here, we describe a novel biosensor that can visualize the activation of H3R through an intramolecular fluorescence resonance energy transfer (FRET) signal. To achieve this, we constructed an intramolecular H3R FRET sensor with cyan fluorescent protein (CFP) attached at the C terminus and yellow fluorescent protein (YFP) inserted into the third intracellular loop. The sensor was found to internalize normally on agonist treatment. We measured FRET signals between the donor CFP and the acceptor YFP in living cells in real time, the results of which indicated that H3R agonist treatment (imetit or histamine) increases the FRET signal in a time- and concentration-dependent manner with Kon and Koff values consistent with published data and which maybe correlated with decreasing cAMP levels and the promotion of ERK1/2 phosphorylation. The FRET signal was inhibited by H3R antagonists, and the introduction of mutations at F419A, F423A, L426A and L427A, once again, the promotion of ERK1/2 phosphorylation, was diminished. Thus, we have built a H3R biosensor which can visualize the activation of receptor through real-time structure changes and which can obtain pharmacological kinetic data at the same time. The FRET signals may allow the sensor to become a useful tool for screening compounds and optimizing useful ligands.

Trauma and hemorrhagic shock activate molecular association of 5-lipoxygenase and 5-lipoxygenase–Activating protein in lung tissue

BackgroundPost-traumatic lung injury following trauma and hemorrhagic shock (T/HS) is associated with significant morbidity. Leukotriene-induced inflammation has been implicated in the development of post-traumatic lung injury through a mechanism that is only partially understood. Postshock mesenteric lymph returning to the systemic circulation is rich in arachidonic acid, the substrate of 5-lipoxygenase (ALOX5). ALOX5 is the rate-limiting enzyme in leukotriene synthesis and, following T/HS, contributes to the development of lung dysfunction. ALOX5 colocalizes with its cofactor, 5-lipoxygenase–activating protein (ALOX5AP), which is thought to potentiate ALOX5 synthetic activity. We hypothesized that T/HS results in the molecular association and nuclear colocalization of ALOX5 and ALOX5AP, which ultimately increases leukotriene production and potentiates lung injury. Materials and methodsTo examine these molecular interactions, a rat T/HS model was used. Post-T/HS tissue was evaluated for lung injury through both histologic analysis of lung sections and biochemical analysis of bronchoalveolar lavage fluid. Lung tissue was immunostained for ALOX5 and ALOX5AP with association and colocalization evaluated by fluorescence resonance energy transfer. In addition, rats undergoing T/HS were treated with MK-886, a known ALOX5AP inhibitor. ResultsALOX5 levels increase and ALOX5/ALOX5AP association occurred after T/HS, as evidenced by increases in total tissue fluorescence and fluorescence resonance energy transfer signal intensity, respectively. These findings coincided with increased leukotriene production and with the histological changes characteristic of lung injury. ALOX5/ALOX5AP complex formation, leukotriene production, and lung injury were decreased after inhibition of ALOX5AP with MK-886. ConclusionsThese results suggest that the association of ALOX5/ALOX5AP contributes to leukotriene-induced inflammation and predisposes the T/HS animal to lung injury.

Novel Labeling Strategy for Automated Detection of Single Virus Fusion and Assessment of HIV-1 Protease Activity in Single Virions

A common approach to visualizing single-virus fusion utilizes a fluorescently labeled Gag that, upon processing by HIV-1 viral protease, yields fluid-phase fluorescent proteins trapped within the virus particle. Upon loss of viral membrane integrity this content marker rapidly diffuses out of the particle, and, in combination with a viral core fiducial, such as a fluorescently tagged Vpr, can be used to reliably report single-particle fusion. But, this labeling approach is limited by an uncontrolled incorporation of the two markers, resulting in an excess of single-labeled particles and lack of correlation between intensities of the content and core markers. Here, we introduce a novel bi-functional mCherry-2xCL-YFP-Vpr label that encodes both the content (fluid-phase mCherry) and fiducial (core-associated YFP-Vpr) markers on a single construct separated by a 2xCL linker that contains a tandem of cleavage sites targeted by the viral protease. We show that the bi-functional label is efficiently incorporated and processed in single-virus particles and can be used to reliably report single-virus fusion in imaging assays. Further, by taking advantage of the nearly perfect colocalization and correlated intensities of content and fiducial markers in single-particles we are able to automate fusion event detection in both fixed and live cells, significantly increasing assay throughput. Finally, we show that the loss of Forster Resonance Energy Transfer (FRET) signal between YFP and mCherry is a good predictor of viral protease activity, and that the maturation status of single virions can be inferred by both FRET efficiency and YFP/mCherry signal ratio. Together, these results demonstrate that the new labeling strategy offers a number of advantages compared to the previous approaches, including reading out single-virus maturation status and increasing reliability and throughput of single-virus fusion imaging assays.

Allosteric interactions between GABAB1 subunits control orthosteric binding sites occupancy within GABAB oligomers

The GABAB receptor was the first G protein-coupled receptor identified as an obligate heterodimer. It is composed of two subunits, GABAB1 containing the agonist binding site and GABAB2 responsible for G protein activation. The GABAB receptor was found to associate into larger complexes through GABAB1-GABAB1 interactions, both in transfected cells and in brain membranes. Here we assessed the possible allosteric interactions between GABAB heterodimers by analyzing the effect of mutations located at the putative interface between the extracellular binding domains. These mutations decrease, but do not suppress, the Förster resonance energy transfer (FRET) signal measured between GABAB1 subunits. Further analysis of one of these mutations revealed an increase in G protein-coupling efficacy and in the maximal antagonist binding by approximately two-fold. Hypothesizing that a tetramer is an elementary unit within oligomers, additional FRET data using fluorescent ligands and tagged subunits suggest that adjacent binding sites within the GABAB oligomers are not simultaneously occupied. Our data show a strong negative effect between GABAB1 binding sites within GABAB oligomers. Accordingly, GABAB receptor assembly appears to limit receptor signaling to G proteins, a property that may offer novel regulatory mechanism for this important neuronal receptor.This article is part of the “Special Issue Dedicated to Norman G. Bowery”.

Dimeric Drug Polymeric Micelles with Acid-Active Tumor Targeting and FRET-Traceable Drug Release.

Trans-activating transcriptional activator (TAT), a cell-penetrating peptide, is extensively used for facilitating cellular uptake and nuclear targeting of drug delivery systems. However, the positively charged TAT peptide strongly interacts with serum components and undergoes substantial phagocytosis by the reticuloendothelial system, causing a short blood circulation in vivo. In this work, an acid-active tumor targeting nanoplatform DA-TAT-PECL is developed to inhibit the nonspecific interactions of TAT in the bloodstream. 2,3-dimethylmaleic anhydride (DA) is used to convert the TAT's amines to carboxylic acid; the resulting DA-TAT is conjugated to poly(ethylene glycol)-poly(ε-caprolactone) (PEG-PCL, PECL) to get DA-TAT-PECL. After self-assembly into polymeric micelles, they are capable of circulating in the physiological condition for a long time and promoting cell penetration upon accumulation at the tumor site and deshielding the DA group. Moreover, camptothecin (CPT) is used as the anticancer drug and modified into a dimer (CPT)2 -ss-Mal, in which two CPT molecules are connected by a reduction-labile maleimide thioether bond. The Förster resonance energy transfer signal between CPT and maleimide thioether bond is monitored to visualize the drug release process, and effective targeted delivery of antitumor drugs is demonstrated. This pH/reduction dual-responsive micelle system provides a new platform for high fidelity cancer therapy.

γPNA FRET Pair Miniprobes for Quantitative Fluorescent In Situ Hybridization to Telomeric DNA in Cells and Tissue.

Measurement of telomere length by fluorescent in situ hybridization is widely used for biomedical and epidemiological research, but there has been relatively little development of the technology in the 20 years since it was first reported. This report describes the use of dual gammaPNA (γPNA) probes that hybridize at alternating sites along a telomere and give rise to Förster resonance energy transfer (FRET) signals. Bright staining of telomeres is observed in nuclei, chromosome spreads and tissue samples. The use of FRET detection also allows for elimination of wash steps, normally required to remove unhybridized probes that would contribute to background signals. We found that these wash steps can diminish the signal intensity through the removal of bound, as well as unbound probes, so eliminating these steps not only accelerates the process but also enhances the quality of staining. Thus, γPNA FRET pairs allow for brighter and faster staining of telomeres in a wide range of research and clinical formats.