A specific DNA-nanoprobe for tracking the activities of human apurinic/apyrimidinic endonuclease 1 in living cells.

Human apurinic/apyrimidinic endonuclease/redox effector factor 1 (APE1) is an essential DNA repair protein. Herein, we demonstrate that avidin-oriented abasic site-containing DNA strands (AP-DNA) on the surface of silica coated magnetic nanoparticles (SiMNP) can selectively respond to APE1 while resist the digestion by other nucleases. Mechanism studies have revealed that avidin may serve as an organizer protein and recruit APE1 to the DNA substrates on the nanoparticles via strong and specific interactions. Taking advantage of this newly disclosed property, we for the first time successfully displayed the intracellular activities of APE1 in living cells by fluorescence imaging. The avidin organized AP-DNA-SiMNP assembly holds great potential for enzyme-mediated release of drugs inside tumor cells which often contain higher levels of APE1 than normal cells.

Single-Stranded DNA Assisted Cell Penetrating Peptide-DNA Conjugation Strategy for Intracellular Imaging of Nucleases.

Cell penetrating peptides (CPPs) are very useful tools for delivery of DNA molecules into living cells without damaging the cell membranes. However, covalent conjugation of DNAs to CPPs is technically difficult, and the reactions between DNA and target nucleases are also liable to be affected by the cationic CPP molecules. In this work, we demonstrate that the electrostatic interactions between CPPs and single-stranded DNA (ssDNA) were stronger than those between CPP and double-stranded DNA (dsDNA). Taking advantage of this property, we developed an ssDNA protected CPP-DNA fluorescent probe which allowed for noninvasive and efficient cellular uptake and rapid imaging of target nucleases in living cells. The probe is highly sensitive and selective. This work represents the first example of using CPP-DNA conjugate to deliver DNA fluorescent probes for in situ imaging of nucleases within cells. The developed approach also holds great potential for the cellular delivery of other nucleic acid molecules for diagnosis or therapeutics purposes.

A fuel-limited isothermal DNA machine for the sensitive detection of cellular deoxyribonucleoside triphosphates.

A fuel-limited isothermal DNA machine has been built for the sensitive fluorescence detection of cellular deoxyribonucleoside triphosphates (dNTPs) at the fmol level, which greatly reduces the required sample cell number. Upon the input of the limiting target dNTP, the machine runs automatically at 37 °C without the need for higher temperature.

Unimolecular Chemically Modified DNA Fluorescent Probe for One-Step Quantitative Measurement of the Activity of Human Apurinic/Apyrimidinic Endonuclease 1 in Biological Samples.

A novel DNA structure containing a 3' internal-loop modified abasic site has been constructed which enables effective differentiation between apurinic/apyrimidinic endonuclease (APE1) and nonspecific endonuclease (DNase I). When this unique substrate structure is employed, a double-loop frayed-end chimeric fluorescent probe is successfully developed for quantitative measurement of the activity of APE1 in biological samples without the need of additional cleanup or preconcentration steps. The method is simple and rapid and has a single-step with a linear working range between 0.1 and 5.0 U/mL and a lower limit of detection of 0.1 U/mL. It holds great potential in real-time monitoring of the variation of intracellular and extracellular APE1, which will be very useful for further understanding of the DNA repair pathways in different organisms.

[Research and realization of signal processing algorithms based on FPGA in digital ophthalmic ultrasonography imaging].

OBJECTIVE: To design and improve signal processing algorithms of ophthalmic ultrasonography based on FPGA. METHODS: Achieved three signal processing modules: full parallel distributed dynamic filter, digital quadrature demodulation, logarithmic compression, using Verilog HDL hardware language in Quartus II. RESULTS: Compared to the original system, the hardware cost is reduced, the whole image shows clearer and more information of the deep eyeball contained in the image, the depth of detection increases from 5 cm to 6 cm. CONCLUSION: The new algorithms meet the design requirements and achieve the system's optimization that they can effectively improve the image quality of existing equipment.

Construction of antibody-like nanoparticles for selective protein sequestration in living cells.

We demonstrate the successful construction of fluorescently labeled magnetic antibody-like nanoparticles (ANPs) via a facile one-step surface-initiated in situ molecular imprinting approach over silica coated magnetite (Fe3O4@SiO2) core-shell nanocomposites. The as-prepared ANPs had a highly compact structure with an overall size of 83 ± 5 nm in diameter and showed excellent aqueous dispersion stability. With the predetermined high specificity to the target protein and high biocompatibility, the ANPs enabled rapid, efficient, selective and optically trackable sequestration of target proteins within living cells. This work represents the first example of fully artificially engineered multifunctional ANPs for the intracellular protein-sequestration without disruption of the cells. The established approach may be further extended to generate ANPs for various proteins of interest and provide useful tools for related biological research and biomedical applications.

Simultaneous fluorescence imaging of the activities of DNases and 3' exonucleases in living cells with chimeric oligonucleotide probes.

Real-time fluorescence imaging of the activity of nucleases in living cells has been a difficult issue because of unintended degradation of the natural oligonucleotides by nontarget nucleases or interactions with other proteins. In this work, we demonstrate two types of highly selective, sensitive, and robust oligonucleotide probes for simultaneous imaging of the activities of two different nucleases in living cells. The probes consist of the desired substrate structure of the target nuclease and partially phosphorothioate modified backbone labeled with fluorophore and quencher for protection from undesired degradation by other nucleases and signal transduction. Upon reaction with the target nuclease, the initially fluorescence quenched probe was cleaved and the fluorophore was separated from the quencher, giving out strong fluorescence signals. Two nucleases, DNase I and Exonuclease III, were employed as model enzymes to demonstrate the concept. In vitro studies proved that the two probes could discriminate their respective target nucleases in serum with high resistance to other coexisting enzymes. The lower limits of detection for DNase I and Exonuclease III were observed to be 40 U/L and 2.0 U/L, respectively. By labeling the two probes with different fluorophores and quenchers, simultaneous visualization of the activities of DNases and 3' exonucleases was achieved in both HeLa cells and the suspension cells of Arabidopsis thaliana. The developed approaches may greatly facilitate the studies on the intracellular functions of the two nucleases and other related biological processes. The probe design concept may also be further adapted to the detection of many other nucleases.