Researchers increasingly envision an important role for artificial biochemical circuits in biological engineering, much like electrical circuits in electrical engineering. Similar to electrical circuits, which control electromechanical devices, biochemical circuits could be utilized as a type of servomechanism to control nanodevices in vitro, monitor chemical reactions in situ, or regulate gene expressions in vivo.1 As a consequence of their relative robustness and potential applicability for controlling a wide range of in vitro chemistries, synthetic cell-free biochemical circuits promise to be useful in manipulating the functions of biological molecules. Here we describe the first logical circuit based on DNA-protein interactions with accurate threshold control, enabling autonomous, self-sustained and programmable manipulation of protein activity in vitro. Similar circuits made previously were based primarily on DNA hybridization and strand displacement reactions. This new design uses the diverse nucleic acid interactions with proteins. The circuit can precisely sense the local enzymatic environment, such as the concentration of thrombin, and when it is excessively high, a coagulation inhibitor is automatically released by a concentration-adjusted circuit module. To demonstrate the programmable and autonomous modulation, a molecular circuit with different threshold concentrations of thrombin was tested as a proof of principle. In the future, owing to tunable regulation, design modularity and target specificity, this prototype could lead to the development of novel DNA biochemical circuits to control the delivery of aptamer-based drugs in smart and personalized medicine, providing a more efficient and safer therapeutic strategy.

Digital microfluidics (DMF) is a powerful platform for a broad range of applications, especially immunoassays having multiple steps, due to the advantages of low reagent consumption and high automatization. Surface enhanced Raman scattering (SERS) has been proven as an attractive method for highly sensitive and multiplex detection, because of its remarkable signal amplification and excellent spatial resolution. Here we propose a SERS-based immunoassay with DMF for rapid, automated, and sensitive detection of disease biomarkers. SERS tags labeled with Raman reporter 4-mercaptobenzoic acid (4-MBA) were synthesized with a core@shell nanostructure and showed strong signals, good uniformity, and high stability. A sandwich immunoassay was designed, in which magnetic beads coated with antibodies were used as solid support to capture antigens from samples to form a beads-antibody-antigen immunocomplex. By labeling the immunocomplex with a detection antibody-functionalized SERS tag, antigen can be sensitively detected through the strong SERS signal. The automation capability of DMF can greatly simplify the assay procedure while reducing the risk of exposure to hazardous samples. Quantitative detection of avian influenza virus H5N1 in buffer and human serum was implemented to demonstrate the utility of the DMF-SERS method. The DMF-SERS method shows excellent sensitivity (LOD of 74 pg/mL) and selectivity for H5N1 detection with less assay time (<1 h) and lower reagent consumption (∼30 μL) compared to the standard ELISA method. Therefore, this DMF-SERS method holds great potentials for automated and sensitive detection of a variety of infectious diseases.

Equipment-free devices with quantitative readout are of great significance to point-of-care testing (POCT), which provides real-time readout to users and is especially important in low-resource settings. Among various equipment-free approaches, distance-based visual quantitative detection methods rely on reading the visual signal length for corresponding target concentrations, thus eliminating the need for sophisticated instruments. The distance-based methods are low-cost, user-friendly and can be integrated into portable analytical devices. Moreover, such methods enable quantitative detection of various targets by the naked eye. In this review, we first introduce the concept and history of distance-based visual quantitative detection methods. Then, we summarize the main methods for translation of molecular signals to distance-based readout and discuss different microfluidic platforms (glass, PDMS, paper and thread) in terms of applications in biomedical diagnostics, food safety monitoring, and environmental analysis. Finally, the potential and future perspectives are discussed.

Aflatoxin B1 (AFB1), as the secondary metabolite of molds, is the most predominant and toxic mycotoxin that seriously threatens the health of humans and animals. In this work, an AFB1-responsive hydrogel was synthesized for highly sensitive and portable detection of AFB1. The AFB1-responsive hydrogel was prepared using an AFB1 aptamer and its two short complementary DNA strands as cross-linkers. For visual detection of AFB1, the hydrogel is preloaded with gold nanoparticles (AuNPs). Upon introduction of AFB1, the AFB1 aptamer binds with AFB1, leading to the disruption of the hydrogel and release of the AuNPs with a distinct color change of the supernatant from colorless to red. In order to lower the detection limit and extend the method to quantitative analysis, a distance-readout volumetric bar chart chip (V-chip) was combined with an AFB1-responsive hydrogel preloaded with platinum nanoparticles (PtNPs). In the presence of AFB1, the hydrogel collapses and releases PtNPs which can catalyze the decomposition of H2O2 to generate O2. The increasing gas pressure moves a red ink bar in the V-chip and provides a quantitative relationship between the distance and the concentration of AFB1. The method was applied for detection of AFB1 in beer, with a detection limit of 1.77 nM (0.55 ppb) where an immunoaffinity column (IAC) of AFB1 was used to cleanup and pre-concentrate the sample, which satisfies the testing requirement of 2.0 ppb set by the European Union. The combination of an AFB1-responsive hydrogel with a distance-based readout V-chip offers a user-friendly POCT device, which has great potential for rapid, portable, selective, and quantitative detection of AFB1 in real samples to ensure food safety and avoid subsequent economic losses.

SUMMARYIn this paper, a new multi-wing chaotic attractor is constructed. Based on the proposed multi-wing system, the paper presents a novel method to generate hyperchaotic multi-wing attractors. By introducing a flux-controlled memristor into the proposed multi-wing system, hyperchaotic multi-wing attractor is observed in new memristive system. At the same time, the new memristive system has no equilibrium. The phase portraits and Lyapunov exponents are used to analyze the dynamic behaviors of the no-equilibrium memristive system. Moreover, we analyze the influence on multi-wing system when adding the memristor in different position. The electronic circuit is realized by using off-the-shelf components.

Single-cell whole-genome sequencing (WGS) is critical for characterizing dynamic intercellular changes in DNA. Current sample preparation technologies for single-cell WGS are complex, expensive, and suffer from high amplification bias and errors. Here, we describe Digital-WGS, a sample preparation platform that streamlines high-performance single-cell WGS with automatic processing based on digital microfluidics. Using the method, we provide high single-cell capture efficiency for any amount and types of cells by a wetted hydrodynamic structure. The digital control of droplets in a closed hydrophobic interface enables the complete removal of exogenous DNA, sufficient cell lysis, and lossless amplicon recovery, achieving the low coefficient of variation and high coverage at multiple scales. The single-cell genomic variations profiling performs the excellent detection of copy number variants with the smallest bin of 150 kb and single-nucleotide variants with allele dropout rate of 5.2%, holding great promise for broader applications of single-cell genomics.

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