Nuclease-containing media for resettable operation of DNA logic gates

Erasable and Field Programmable DNA Circuits Based on Configurable Logic Blocks

DNA is commonly employed as a substrate for the building of artificial logic networks due to its excellent biocompatibility and programmability. Till now, DNA logic circuits are rapidly evolving to accomplish advanced operations. Nonetheless, nowadays, most DNA circuits remain to be disposable and lack of field programmability and thereby limits their practicability. Herein, inspired by the Configurable Logic Block (CLB), the CLB-based erasable field-programmable DNA circuit that uses clip strands as its operation-controlling signals is presented. It enables users to realize diverse functions with limited hardware. CLB-based basic logic gates (OR and AND) are first constructed and demonstrated their erasability and field programmability. Furthermore, by adding the appropriate operation-controlling strands, multiple rounds of programming are achieved among five different logic operations on a two-layer circuit. Subsequently, a circuit is successfully built to implement two fundamental binary calculators: half-adder and half-subtractor, proving that the design can imitate silicon-based binary circuits. Finally, a comprehensive CLB-based circuit is built that enables multiple rounds of switch among seven different logic operations including half-adding and half-subtracting. Overall, the CLB-based erasable field-programmable circuit immensely enhances their practicability. It is believed that design can be widely used in DNA logic networks due to its efficiency and convenience.

Multifunctional Clip Strand for the Regulation of DNA Strand Displacement and Construction of Complex DNA Nanodevices

Strand displacement reactions are important bricks for the construction of various DNA nanodevices, among which the toehold-mediated strand displacement reaction is the most prevalently adopted. However, only a limited number of tools could be used to finely regulate the toehold reaction, thus restricting DNA nanodevices from being more multifunctional and powerful. Herein, we developed a regulation tool, Clip, and achieved multiple regulatory functions, including subtle adjustment of the reaction rates, allosteric strand displacement, selective activation, and resetting of the reaction. Taking advantages of the multiple functions, we constructed Clip-toehold-based DNA walking machines. They showed behaviors of controllable walking, concatenation, and programmable pathways. Furthermore, we built Clip-toehold-based AND and OR logic gates and integrated those logic gates to construct multilayer circuits, which could be reset and reused to process different input signals. We believe that the proposed Clip tool has expanded the functionality of DNA strand displacement-based nanodevices to a much more complex and diverse level and anticipate that the tool will be widely adopted in DNA nanotechnology.

RNA-Cleaving DNA Thresholder Controlled by Concentrations of miRNA Cancer Marker

Oligonucleotide gene therapy (OGT) agents suppress specific mRNAs in cells and thus reduce the expression of targeted genes. The ability to unambiguously distinguish cancer from healthy cells can solve the low selectivity problem of OGT agents. Cancer RNA markers are expressed in both healthy and cancer cells with a higher expression level in cancer cells. We have designed a DNA-based construct, named DNA thresholder (DTh) that cleaves targeted RNA only at high concentrations of cancer marker RNA and demonstrates low cleavage activity at low marker concentrations. The RNA-cleaving activity can be adjusted within one order of magnitude of the cancer marker RNA concentration by simply redesigning DTh. Importantly, DTh recognizes cancer marker RNA, while cleaving targeted RNA; this offers a possibility to suppress vital genes exclusively in cancer cells, thus triggering their death. DTh is a prototype of computation-inspired molecular device for controlling gene expression and cancer treatment.

Binary (Split) Light-up Aptameric Sensors

This Minireview discusses the design and applications of binary (also known as split) light-up aptameric sensors (BLAS). BLAS consist of two RNA or DNA strands and a fluorogenic organic dye added as a buffer component. When associated, the two strands form a dye-binding site, followed by an increase in fluorescence of the aptamer-bound dye. The design is cost-efficient because it uses short oligonucleotides and does not require conjugation of organic dyes with nucleic acids. In some applications, BLAS design is preferable over monolithic sensors because of simpler assay optimization and improved selectivity. RNA-based BLAS can be expressed in cells and used for the intracellular monitoring of biological molecules. BLAS have been used as reporters of nucleic acid association events in RNA nanotechnology and nucleic-acid-based molecular computation. Other applications of BLAS include the detection of nucleic acids, proteins, and cancer cells, and potentially they can be tailored to report a broad range of biological analytes.

Repeated Reuse of Deoxyribozyme-Based Logic Gates

Deoxyribozymes (DNAzymes) have demonstrated a significant capacity for biocomputing and hold promise for information processing within advanced biological devices if several key capabilities are developed. One required capability is reuse-having DNAzyme logic gates be cyclically, and controllably, activated and deactivated. We designed an oligonucleotide-based system for DNAzyme reuse that could (1) remove previously bound inputs by addition of complementary oligonucleotides via toe-hold mediated binding and (2) diminish output signal through the addition of quencher-labeled oligonucleotides complementary to the fluorophore-bound substrate. Our system demonstrated, for the first time, the ability for DNAzymes to have their activity toggled, with activity returning to 90-125% of original activity. This toggling could be performed multiple times with control being exerted over when the toggling occurs, with three clear cycles observed before the variability in activity became too great. Our data also demonstrated that fluorescent output of the DNAzyme activity could be actively removed and regenerated. This reuse system can increase the efficiency of DNAzyme-based logic circuits by reducing the number of redundant oligonucleotides and is critical for future development of reusable biodevices controlled by logical operations.

Recent Progress in Fluorescence Signal Design for DNA-Based Logic Circuits

DNA-based logic circuits, encoding algorithms in DNA and processing information, are pushing the frontiers of molecular computers forward, owing to DNA's advantages of stability, accessibility, manipulability, and especially inherent biological significance and potential medical application. In recent years, numerous logic functions, from arithmetic to nonarithmetic, have been realized based on DNA. However, DNA can barely provide a detectable signal by itself, so that the DNA-based circuits depend on extrinsic signal actuators. The signal strategy of carrying out a response is becoming one of the design focuses in DNA-based logic circuit construction. Although work on sequence and structure design for DNA-based circuits has been well reviewed, the strategy on signal production lacks comprehensive summary. In this review, we focused on the latest designs of fluorescent output for DNA-based logic circuits. Several basic strategies are summarized and a few designs for developing multi-output systems are provided. Finally, some current difficulties and possible opportunities were also discussed.

Enzyme-Regulated DNA-Based Logic Device

Herein, we report a carbazole (Cz) ligand that displays distinct turn-on fluorescence signals upon interaction with human telomeric G-quadruplex ( h-TELO) and nuclease enzymes. Interestingly, Cz selectively binds and stabilizes the mixed hybrid topology of h-TELO G-quadruplex that withstands digestion by exonucleases and nuclease S1. The distinct fluorescence signatures of Cz-stabilized h-TELO with nucleases are used to design conceptually novel DNA devices for selectively detecting the enzymatic activity of DNase I as well as performing logic operations. An INHIBIT logic gate is constructed using h-TELO and DNase I as the inputs while the inputs of h-TELO and nuclease S1 form a YES logic gate. Furthermore, a two-input two-output reusable logic device with "multireset" function is developed by using h-TELO and DNase I as inputs. On the basis of this platform, combinatorial logic systems (INHIBIT-INHIBIT and NOR-OR) have been successfully installed using different combinations of nucleases as inputs. Moreover, this new strategy of using a synthetic dual emissive probe and enzyme/DNA inputs for constructing reusable logic device may find important applications in biological computing and information processing.

A universal split spinach aptamer (USSA) for nucleic acid analysis and DNA computation

We demonstrate how a single universal spinach aptamer (USSA) probe can be used to detect multiple (potentially any) nucleic acid sequences. USSA can be used for cost-efficient and highly selective analysis of even folded DNA and RNA analytes, as well as for the readout of outputs of DNA logic circuits.

Self-Assembling Molecular Logic Gates Based on DNA Crossover Tiles

DNA-based computational hardware has attracted ever-growing attention due to its potential to be useful in the analysis of complex mixtures of biological markers. Here we report the design of self-assembling logic gates that recognize DNA inputs and assemble into crossover tiles when the output signal is high; the crossover structures disassemble to form separate DNA stands when the output is low. The output signal can be conveniently detected by fluorescence using a molecular beacon probe as a reporter. AND, NOT, and OR logic gates were designed. We demonstrate that the gates can connect to each other to produce other logic functions.

A Nanostructured SERS Switch Based on Molecular Beacon-Controlled Assembly of Gold Nanoparticles

In this paper, highly purified and stable gold nanoparticle (AuNP) dimers connected at the two ends of DNA linkage were prepared by a versatile method. A nanostructured, surface-enhanced Raman scattering (SERS) switching sensor system was fabricated based on the controlled organization of gold nanoparticles (AuNPs) by a DNA nanomachine through the controlled formation/deformation of SERS “hotspots”. This strategy not only opens opportunities in the precise engineering of gap distances in gold-gold nanostructures in a highly controllable and reproducible fashion, but also provides a unique ability to research the origin of SERS and sequence-specific DNA detection.

Target-triggered cascade recycling amplification for label-free detection of microRNA and molecular logic operations

A cascade recycling amplification (CRA) that implements cascade logic circuits with feedback amplification function is developed for label-free chemiluminescence detection of microRNA-122 with an ultrahigh sensitivity of 0.82 fM and excellent specificity, which is applied to construct a series of molecular-scale two-input logic gates by using microRNAs as inputs and CRA products as outputs.

Design of enzyme-interfaced DNA logic operations (AND, OR and INHIBIT) with an assaying application for single-base mismatch

We devised AND, OR and INHIBIT logic gates.