Dynamic Fusion of Nucleic Acid Functionalized Nano-/Micro-Cell-Like Containments: From Basic Concepts to Applications.

Membrane fusion processes play key roles in biological transformations, such as endocytosis/exocytosis, signal transduction, neurotransmission, or viral infections, and substantial research efforts have been directed to emulate these functions by artificial means. The recognition and dynamic reconfiguration properties of nucleic acids provide a versatile means to induce membrane fusion. Here we address recent advances in the functionalization of liposomes or membranes with structurally engineered lipidated nucleic acids guiding the fusion of cell-like containments, and the biophysical and chemical parameters controlling the fusion of the liposomes will be discussed. Intermembrane bridging by duplex or triplex nucleic acids and light-induced activation of membrane-associated nucleic acid constituents provide the means for spatiotemporal fusion of liposomes or nucleic acid modified liposome fusion with native cell membranes. The membrane fusion processes lead to exchange of loads in the fused containments and are a means to integrate functional assemblies. This is exemplified with the operation of biocatalytic cascades and dynamic DNA polymerization/nicking or transcription machineries in fused protocell systems. Membrane fusion processes of protocell assemblies are found to have important drug-delivery, therapeutic, sensing, and biocatalytic applications. The future challenges and perspectives of DNA-guided fused containments and membranes are addressed.

Photocleavable Ortho-Nitrobenzyl-Protected DNA Architectures and Their Applications.

This review article introduces mechanistic aspects and applications of photochemically deprotected ortho-nitrobenzyl (ONB)-functionalized nucleic acids and their impact on diverse research fields including DNA nanotechnology and materials chemistry, biological chemistry, and systems chemistry. Specific topics addressed include the synthesis of the ONB-modified nucleic acids, the mechanisms involved in the photochemical deprotection of the ONB units, and the photophysical and chemical means to tune the irradiation wavelength required for the photodeprotection process. Principles to activate ONB-caged nanostructures, ONB-protected DNAzymes and aptamer frameworks are introduced. Specifically, the use of ONB-protected nucleic acids for the phototriggered spatiotemporal amplified sensing and imaging of intracellular mRNAs at the single-cell level are addressed, and control over transcription machineries, protein translation and spatiotemporal silencing of gene expression by ONB-deprotected nucleic acids are demonstrated. In addition, photodeprotection of ONB-modified nucleic acids finds important applications in controlling material properties and functions. These are introduced by the phototriggered fusion of ONB nucleic acid functionalized liposomes as models for cell-cell fusion, the light-stimulated fusion of ONB nucleic acid functionalized drug-loaded liposomes with cells for therapeutic applications, and the photolithographic patterning of ONB nucleic acid-modified interfaces. Particularly, the photolithographic control of the stiffness of membrane-like interfaces for the guided patterned growth of cells is realized. Moreover, ONB-functionalized microcapsules act as light-responsive carriers for the controlled release of drugs, and ONB-modified DNA origami frameworks act as mechanical devices or stimuli-responsive containments for the operation of DNA machineries such as the CRISPR-Cas9 system. The future challenges and potential applications of photoprotected DNA structures are discussed.

Optical and Electrochemical Probes for Monitoring Cytochrome†c in Subcellular Compartments During Apoptosis.

Cytochrome c (Cyt. c) is a key initiator of the caspases that activate cell apoptosis. The spatiotemporal evaluation of the contents of Cyt. c in cellular compartments and the detection of Cyt. c delivery between cellular compartments upon apoptosis is important for probing cell viabilities. We introduce an optical probe and an electrochemical probe for the quantitative assessment of Cyt. c in cellular compartments at the single cell level. The optical or electrochemical probes are functionalized with photoresponsive o-nitrobenzylphosphate ester-caged Cyt. c aptamer constituents. These are uncaged by light stimuli at single cell compartments, allowing the spatiotemporal detection of Cyt. c through the formation of Cyt. c/aptamer complexes at non-apoptotic or apoptotic conditions. The probes are applied to distinguish the contents of Cyt. c in cellular compartments of epithelial MCF-10A breast cells and malignant MCF-7 and MDA-MB-231 breast cells under apoptotic/non-apoptotic conditions.

Photoactivated DNA Walker Based on DNA Nanoflares for Signal-Amplified MicroRNA Imaging in Single Living Cells.

Specific and sensitive detection and imaging of cancer-related miRNA in living cells are desirable for cancer diagnosis and treatment. Because of the spatiotemporal variability of miRNA expression level during different cell cycles, signal amplification strategies that can be activated by external stimuli are required to image miRNAs on demand at desired times and selected locations. Herein, we develop a signal amplification strategy termed as the photoactivated DNA walker based on DNA nanoflares, which enables photocontrollable signal amplification imaging of cancer-related miRNA in single living cells. The developed method is achieved via combining photoactivated nucleic acid displacement reaction with the traditional exonuclease III (EXO III)-assisted DNA walker based on DNA nanoflares. This method is capable of on-demand activation of the DNA walker for dictated signal amplification imaging of cancer-related miRNA in single living cells. The developed method was demonstrated as a proof of concept to achieve photoactivated signal amplification imaging of miRNA-21 in single living HeLa cells via selective two-photon irradiation (λ = 740 nm) of single living HeLa cells by using confocal microscopy equipped with a femtosecond laser.

Photoactivated Biosensing Process for Dictated ATP Detection in Single Living Cells.

The subcellular distribution of adenosine 5'-triphosphate (ATP) and the concentration of ATP in living cells dynamically fluctuate with time during different cell cycles. The dictated activation of the biosensing process in living cells enables the spatiotemporal target detection in single living cells. Herein, a kind of o-nitrobenzylphosphate ester hairpin nucleic acid was introduced as a photoresponsive DNA probe for light-activated ATP detection in single living cells. Two methods to spatiotemporally activate the probe in single living cells were discussed. One method was the usage of the micrometer-sized optical fiber (about 5 µm) to guide the UV light (λ = 365 nm) to selectively activate the photoresponsive DNA probe in single living cells. The second method involved a two-photon laser confocal scanning microscope to selectively irradiate the photoresponsive DNA probes confined in single living cells via two-photon irradiation (λ = 740 nm). ATP aptamer integrated in the activated DNA probes selectively interacted with the target ATP, resulting in dictated signal generation. Furthermore, the photoactivated biosensing process enables dictated dual-model ATP detection in single living cells with "Signal-ON" fluorescence signal and "Signal-OFF" electrochemical signal outputs. The developed photoactivated biosensor for dictated ATP detection with high spatiotemporal resolution in single living cells at a desired time and desired place suggests the possibility to monitor biomarkers during different cell cycles.

Spatiotemporal patterning of photoresponsive DNA-based hydrogels to tune local cell responses.

Understanding the spatiotemporal effects of surface topographies and modulated stiffness and anisotropic stresses of hydrogels on cell growth remains a biophysical challenge. Here we introduce the photolithographic patterning or two-photon laser scanning confocal microscopy patterning of a series of o-nitrobenzylphosphate ester nucleic acid-based polyacrylamide hydrogel films generating periodically-spaced circular patterned domains surrounded by continuous hydrogel matrices. The patterning processes lead to guided modulated stiffness differences between the patterned domains and the surrounding hydrogel matrices, and to the selective functionalization of sub-regions of the films with nucleic acid anchoring tethers. HeLa cells are deposited on the circularly-shaped domains functionalized with the MUC-1 aptamers. Initiation of the hybridization chain reaction by nucleic acid tethers associated with the continuous hydrogel matrix results in stress-induced ordered orthogonal shape-changes on the patterned domains, leading to ordered shapes of cell aggregates bound to the patterns.

Cationic Nanomaterials for Autoimmune Diseases Therapy.

Cationic nanomaterials are defined as nanoscale structures smaller than 100 nm bearing positive charges. They have been investigated to apply to many aspects including clinical diagnosis, gene delivery, drug delivery, and tissue engineering for years. Recently, a novel concept has been made to use cationic nanomaterials as cell-free nucleic acid scavengers and inhibits the inflammatory responses in autoimmune diseases. Here, we highlighted different types of cationic materials which have the potential for autoimmune disease treatment and reviewed the strategy for autoimmune diseases therapy based on cationic nanoparticles. This review will also demonstrate the challenges and possible solutions that are encountered during the development of cationic materials-based therapeutics for autoimmune diseases.

Nucleic Acids Analysis.

Nucleic acids are natural biopolymers of nucleotides that store, encode, transmit and express genetic information, which play central roles in diverse cellular events and diseases in living things. The analysis of nucleic acids and nucleic acids-based analysis have been widely applied in biological studies, clinical diagnosis, environmental analysis, food safety and forensic analysis. During the past decades, the field of nucleic acids analysis has been rapidly advancing with many technological breakthroughs. In this review, we focus on the methods developed for analyzing nucleic acids, nucleic acids-based analysis, device for nucleic acids analysis, and applications of nucleic acids analysis. The representative strategies for the development of new nucleic acids analysis in this field are summarized, and key advantages and possible limitations are discussed. Finally, a brief perspective on existing challenges and further research development is provided.

Near-infrared light-activated membrane fusion for cancer cell therapeutic applications.

The spatiotemporal stimulation of liposome-liposome or liposome-membrane fusion processes attracts growing interest as a means to mimic cell-cell interactions in nature and for using these processes for biomedical applications. We report the use of o-nitrobenzyl phosphate functionalized-cholesterol tethered nucleic acid-modified liposomes as functional photoresponsive units for inducing, by NIR-irradiation, spatiotemporal liposome-liposome or liposome-membrane fusion processes. The liposomes are loaded with upconversion nanoparticles (UCNPs) and their NIR irradiation (λ = 980 nm) yields luminescence at λ = 365 nm, providing a localized light-source to deprotect the o-nitrobenzyl phosphate groups and resulting in the fragmentation of the nucleic acid structures. In one system, the NIR-triggered fusion of two liposomes, L1 and L2, is exemplified. Liposome L1 is loaded with UCNPs and Tb3+ ions, and the liposome boundary is functionalized with a cholesterol-tethered, o-nitrobenzyl phosphate caged hairpin nucleic acid structure. Liposome L2 is loaded with 2,6-pyridinedicarboxylic acid, DPA, and its boundary is modified with a cholesterol-tethered nucleic acid, complementary to a part of the caged hairpin, associated with L1. NIR-irradiation of the L1/L2 mixture resulted in the photocleavage of the hairpin structure, associated with L1, and the resulting fragmented nucleic acid associated with L1 hybridized with the nucleic acid linked to L2, leading to the fusion of the two liposomes. The fusion process was followed by dynamic light scattering, and by monitoring the fluorescence of the Tb3+-DPA complex generated upon the fusion of the liposomes and their exchange of contents (fusion efficiency 30%). In a second system, the fusion of the liposomes L1, loaded with UCNPs and doxorubicin (DOX), with HeLa cancer cells functionalized with nucleic acid tethers, complementary to the hairpin units associated with the boundary of L1, and linked to the MUC-1 receptor sites associated with the HeLa cells, through a MUC-1 aptamer unit is exemplified. The effect of DOX-loaded L1/HeLa cell fusion on the cytotoxicity towards HeLa cells is addressed. The NIR UCNP-stimulated cleavage of the o-nitrobenzyl phosphate caged hairpin units associated with L1 leads to the fragmentation of the hairpin units and the resulting nucleic acid tethers hybridize with the nucleic acid-modified HeLa cells, resulting in the liposome-HeLa cell fusion and the release of DOX into the HeLa cells. Selective spatiotemporal cytotoxicity towards HeLa cells is demonstrated (ca. 40% cell killing within two days). The study presents a comprehensive stepwise set of experiments directed towards the development of NIR-driven liposome-liposome or liposome-membrane fusion processes.

Photoresponsive Electrochemical DNA Biosensors Achieving Various Dynamic Ranges by Using Only-One Capture Probe.

The rational design of DNA capture probes for modulating the binding affinity to tune the dynamic range of electrochemical DNA (E-DNA) biosensors is valuable and effective. Most of current strategies, however, require designing several DNA capture probes to achieve the tunable dynamic range, which is cumbersome and costly. Herein, we develop the photoresponsive E-DNA biosensors with tunable dynamic ranges by using only one photocleavable capture probe (PC-CP). The photoresponsive PC-CP is a stem-loop DNA structure containing a photocleavable linker (PC-linker) in the loop. The PC-linker can be cleaved by UV irradiation to switch the structure of PC-CP, through which the binding affinity to the target could be tuned. In this way, the dynamic range, the sensitivity, and the specificity of photoresponsive E-DNA biosensors can be tuned. Furthermore, the developed photoresponsive E-DNA biosensors enable sensitive and selective detection of target DNA in complex samples with a tunable dynamic range, which offers the possibility of clinical applications.

Near-Infrared Light Activated Nucleic Acid Cascade Recycling Amplification for Spatiotemporally Controllable Signal Amplified mRNA Imaging.

The expression level and subcellular distribution of mRNA dynamically changed during the different cell circles. Spatiotemporally controllable signal amplification methods capable of controlling the when and where of the amplification process could allow the sensitive mRNA imaging of selected living cells at dictated time-intervals of the cell life-cycle. However, the present methods for amplified mRNA imaging are hard to control the where and when of the signal amplification due to the lack of an effective strategy to precisely trigger and control the signal amplification process. Herein, we present a conceptual study termed as photocontrollable nucleic acid cascade recycling amplification which uses near-infrared (NIR) light to precisely control and trigger the whole process. This strategy is achieved by integrating photocontrollable nucleic acid displacement reaction with exonuclease III (EXO III) assisted nucleic acid cascade recycling amplification and combination with upconversion nanoparticles (UCNPs), thus resulting in a NIR light activatable signal amplification. As a proof of concept, we demonstrate this developed NIR light triggered signal amplification process in selected living cancer cells for spatiotemporally controllable signal amplified mRNA imaging.

Bioinspired Programmable Engineering of a Color-Change Biointerface based on Dual-Stimulation Regulation.

Some animals can change their skin colors in response to multiple stimuli by controlling the skin pigment cell or guanine crystals. An artificial color-change interface inspired by these natural properties has been developed; the interface responded to different types of stimuli, however, is still rare. Herein, we design a color-change biointerface that responds to the cooperative stimulation of light and DNA by changing the conformation of DNA structures to achieve programmable activation of the interface. We construct the biointerface by the combination of a fluorescent dye-labeled hairpin DNA with a photoresponsive molecule, which is cleaved by the first stimulation of UV light (stimulus 1, S1) to expose the toehold domain. Then, the biointerface gets color changed through the toehold-mediated DNA strand displacement reaction with the second stimulation of the invading DNA probe (stimulus 2, S2). Moreover, the transformation efficiency of the biointerface increased from 6.8 to 64% with an increase of S1 from 0 to 600 s in the presence of S2. Also, after the stimulation of S1, the effective transformation efficiency was also tuned from 5.3 to 72% by different amounts of S2 in the complex matrix, indicating the potential for a high response in real-world settings.

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.

Photoactivated Nanoflares for mRNA Detection in Single Living Cells.

Gold nanoparticles (AuNPs) have shown great promise as a universal platform for biosensing and are often functionalized with a densely packed DNA for intracellular detection. While DNA-AuNP conjugates, such as nanoflares, have been used for single and multiple mRNA molecules detection in living cells, the target recognition reaction is triggered once they enter into cells, making it impossible to control the initial reaction at the desired time. To solve this problem, we have designed photoactivated (PA) nanoflares for intracellular mRNA analysis with high spatiotemporal control. PA nanoflares consist of AuNP and photoresponsive DNA hairpin probes. Without UV irradiation, the DNA hairpin could be kept unawakened and show no reactivity to target the probe. Upon UV activation, the hairpin structures are destroyed and expose the sticky domains, which act as toeholds to mediate strand displacement reactions, making flares release from the gold surface and causing an increase of fluorescence. By tuning light irradiation, PA nanoflares for mRNA detection in living cells can be temporally controlled. With the benefit from two-photon laser illumination, PA nanoflares can detect mRNA in selective cells at a desired time point at the single-cell level. Compared to the traditional nanoflares, the novel PA nanoflares have increased the detection sensitivity and achieved intracellular biomarkers detection at the single-cell level with high spatiotemporal control.

Tunable superamphiphobic surfaces: a platform for naked-eye ATP detection.

A superamphiphobic surface composed of two different size ranges of TiO2 nanoparticles was simply fabricated through spraying the perfluorosilane coated TiO2 nanoparticles suspension dispersing in ethanol. The surface chemistry was finely regulated through gradient UV irradiation-induced organic compound degradation to fabricate surface with gradient solid surface energy or wettability. The fabricated surface shows good droplet sorting ability, which can successfully discriminate ethanol droplets with different concentrations. As a proof-of-concept, the biosensor application of this surface was demonstrated by using it for naked-eye ATP detection. Liquid droplets with different concentrations of ATP after ATP-dependent rolling circle amplification (RCA) can be effectively sorted by the surface. This developed biosensor methodology based on droplet sorting ability of the fabricated surface is energy-efficient and economical which is promising for biosensors, point-of-care testing, and biochemical assays. Graphical abstract ᅟ.

Two-Photon Lithographic Patterning of DNA-Coated Single-Microparticle Surfaces.

The spatially defined functionalization of microparticles with asymmetric shape-controlled nucleic acid patterns is a major challenge in materials science. The asymmetric patterning of microparticles is important to allow the controlled fabrication of crystalline lattices or controlled aggregates of microparticles. We present the combination of two-photon lithography and photocleavable o-nitrobenzylphosphate ester nucleic acid coating-modified microparticles as a versatile means to asymmetrically pattern single microparticle surfaces. The two-photon patterning of microparticles with predesigned nucleic acid structures of different sizes (700 nm to 2.8 µm) and shapes (circles, rings, triangles, and squares) are demonstrated. In addition, complex patterned domains consisting of two different asymmetric nucleic acid domains are fabricated by the controlled Z-positioning of the microparticles in respect to the two-photon irradiation sources. In addition, the two-photon lithographic patterning of the photocleavable DNA coating allows the generation of functional nucleic acid domains for the photostimulated activation of the catalytic hybridization assembly (CHA) of branched nucleic acid structures on single microparticles.

Photoactivated Specific mRNA Detection in Single Living Cells by Coupling "Signal-on" Fluorescence and "Signal-off" Electrochemical Signals.

The spatiotemporal detection of a target mRNA in a single living cell is a major challenge in nanoscience and nanomedicine. We introduce a versatile method to detect mRNA at a single living cell level that uses photocleavable hairpin probes as functional units for the optical (fluorescent) and electrochemical (voltammetric) detection of MnSOD mRNA in single MCF-7 cancer cells. The fluorescent probe is composed of an ortho-nitrophenylphosphate ester functionalized hairpin that includes the FAM fluorophore in a caged configuration quenched by Dabcyl. The fluorescent probe is further modified with the AS1411 aptamer to facilitate the targeting and internalization of the probe into the MCF-7 cells. Under UV irradiation, the hairpin is cleaved, leading to the intracellular mRNA toehold-stimulated displacement of the FAM-functionalized strand resulting in a switched-on fluorescence signal upon the detection of the mRNA in a single cell. In addition, a nanoelectrode functionalized with a methylene blue (MB) redox-active photocleavable hairpin is inserted into the cytoplasm of a single MCF-7 cell. Photocleavage of the hairpin leads to the mRNA-mediated toehold displacement of the redox-active strand associated with the probe, leading to the depletion of the voltammetric response of the probe. The parallel optical and electrochemical detection of the mRNA at a single cell level is demonstrated.

DNA photonic nanowires with tunable FRET signals on the basis of toehold-mediated DNA strand displacement reactions.

A DNA photonic nanowire with tunable FRET signals was fabricated on the basis of cascaded toehold-mediated DNA strand displacement reactions. Different DNA inputs were added to trigger the reaction network, and the corresponding FRET signals were obtained. Compared to the direct hybridization, this design is sensitive for 2 nM targets within 20 min and also causes color changes of the solution with blue-light excitation. It could also be applied in live cells to monitor MicroRNA with a simple modification which might become a low-cost method for further application in the future.

Reversible Modulation of DNA-Based Hydrogel Shapes by Internal Stress Interactions.

We present the assembly of asymmetric two-layer hybrid DNA-based hydrogels revealing stimuli-triggered reversibly modulated shape transitions. Asymmetric, linear hydrogels that include layer-selective switchable stimuli-responsive elements that control the hydrogel stiffness are designed. Trigger-induced stress in one of the layers results in the bending of the linear hybrid structure, thereby minimizing the elastic free energy of the systems. The removal of the stress by a counter-trigger restores the original linear bilayer hydrogel. The stiffness of the DNA hydrogel layers is controlled by thermal, pH (i-motif), K+ ion/crown ether (G-quadruplexes), chemical (pH-doped polyaniline), or biocatalytic (glucose oxidase/urease) triggers. A theoretical model relating the experimental bending radius of curvatures of the hydrogels with the Young's moduli and geometrical parameters of the hydrogels is provided. Promising applications of shape-regulated stimuli-responsive asymmetric hydrogels include their use as valves, actuators, sensors, and drug delivery devices.