Inhibited aptazyme-based catalytic molecular beacon for amplified detection of adenosine

Surfactant-mediated colorimetric assay assisted with in-situ rolling circle amplification on magnetic beads

Gold nanoparticles (AuNPs) with localized surface plasmon resonance effect have been widely used for colorimetric detection based on the interparticle plasmon coupling during AuNPs aggregation. However, it is still challenging to develop portable and quantitative methods with good sensitivity and excellent selectivity. In this study, a smartphone-based colorimetric assay is developed on the principle of surfactant-mediated AuNPs aggregation assisted with rolling circle amplification (RCA) on magnetic beads (MBs). The detection of adenosine is demonstrated as an example. The cetyl trimethyl ammonium bromide (CTAB) causes the negatively charged AuNPs to aggregate, which results in the color change from red to blue. When adenosine is in solution, the RCA process is triggered on the MBs because of specific adenosine-aptamer recognition, resulting in prolongation of single-stranded nucleic acid (ssDNA). The solution color remains red due to the electrostatic interaction between CTAB and ssDNA. Using this method, the limit of detection (LOD) for adenosine can be as low as 16 pM. Besides, it also works well in human serum. In addition, a portable device integrated with in-situ RGB analysis software is developed for the detection with a smartphone. This study offers a new strategy to improve the sensitivity and selectivity for the AuNPs-based colorimetric assay, taking advantages of specific aptamer recognition, in-situ RCA on MBs, magnetic separation, and smartphone-based portable device.

Unraveling the Kinetics of the 10-23 RNA-Cleaving DNAzyme

DNA-based enzymes, or DNAzymes, are single-stranded DNA sequences with the ability to catalyze various chemical reactions, including the cleavage of the bond between two RNA nucleotides. Lately, an increasing interest has been observed in these RNA-cleaving DNAzymes in the biosensing and therapeutic fields for signal generation and the modulation of gene expression, respectively. Additionally, multiple efforts have been made to study the effects of the reaction environment and the sequence of the catalytic core on the conversion of the substrate into product. However, most of these studies have only reported alterations of the general reaction course, but only a few have focused on how each individual reaction step is affected. In this work, we present for the first time a mathematical model that describes and predicts the reaction of the 10-23 RNA-cleaving DNAzyme. Furthermore, the model has been employed to study the effect of temperature, magnesium cations and shorter substrate-binding arms of the DNAzyme on the different kinetic rate constants, broadening the range of conditions in which the model can be exploited. In conclusion, this work depicts the prospects of such mathematical models to study and anticipate the course of a reaction given a particular environment.

RNA-Cleaving DNAzyme-Based Amplification Strategies for Biosensing and Therapy

Since their first discovery in 1994, DNAzymes have been extensively applied in biosensing and therapy that act as recognition elements and signal generators with the outstanding properties of good stability, simple synthesis, and high sensitivity. One subset, RNA-cleaving DNAzymes, is widely employed for diverse applications, including as reporters capable of transmitting detectable signals. In this review, the recent advances of RNA-cleaving DNAzyme-based amplification strategies in scaled-up biosensing are focused, the application in diagnosis and disease treatment are also discussed. Two major types of RNA-cleaving DNAzyme-based amplification strategies are highlighted, namely direct response amplification strategies and combinational response amplification strategies. The direct response amplification strategies refer to those based on novel designed single-stranded DNAzyme, and the combinational response amplification strategies mainly include two-part assembled DNAzyme, cascade reactions, CHA/HCR/RCA, DNA walker, CRISPR-Cas12a and aptamer. Finally, the current status of DNAzymes, the challenges, and the prospects of DNAzyme-based biosensors are presented.

Complexing deoxyribozymes with RNA aptamers for detection of the small molecule theophylline

Biointegrative information processing systems offer a great advantage to autonomous biodevices, as their capacity for biological computation provides the ability to sense the state of more complex environments and better integrate with downstream biological regulation systems. Deoxyribozymes (DNAzymes) and aptamers are of interest to such computational biosensing systems due to the enzymatic properties of DNAzymes and the ligand-inducible conformational structures of aptamers. Herein, we describe a novel method for providing ligand-responsive allosteric control to a DNAzyme using an RNA aptamer. We designed a NOT-logic-compliant E6 DNAzyme to be complementary to an RNA aptamer targeting theophylline, such that the aptamer competitively interacted with either theophylline or the DNAzyme, and disabled the DNAzyme only when theophylline concentration was below a given threshold. Out of our seven designed "complexing aptazymes," three demonstrated effective theophylline-responsive allosteric regulation (2.84 ± 3.75%, 4.97 ± 2.92%, and 8.91 ± 4.19% activity in the absence of theophylline; 46.29 ± 3.36%, 50.70 ± 10.15%, and 61.26 ± 6.18% activity in the presence of theophylline). Moreover, the same three complexing aptazymes also demonstrated the ability to semi-quantitatively determine the concentration of theophylline present in solution, successfully discriminating between therapeutically ineffective (<20 μM), safe (20-100 μM), and toxic (>100 μM) theophylline concentrations. Our method of using an RNA aptamer for ligand-responsive allosteric control of a DNAzyme expands the way aptamers can be configured for biosensing, and suggests a pathway for embedding DNAzymes to provide enhanced information processing and control of biological systems.

DNA-only bioassay for simultaneous detection of proteins and nucleic acids

Testing multiple biomarkers, as opposed to one, has become a preferred approach for diagnosing many heterogeneous diseases, such as cancer and infectious diseases. However, numerous technologies, including gold standard ELISA and PCR, can detect only one type of biomarker, either protein or nucleic acid (NA), respectively. In this work, we report for the first time simultaneous detection of proteins and NAs in the same solution, using solely functional NA (FNA) molecules. In particular, we combined the thrombin binding aptamer (TBA) and the 10-23 RNA-cleaving DNA enzyme (DNAzyme) in a single aptazyme molecule (Aptazyme1.15-3'), followed by extensive optimization of buffer composition, sequences and component ratios, to establish a competitive bioassay. Subsequently, to establish a multiplex bioassay, we designed a new aptazyme (Aptazyme2.20-5') by replacing the target recognition and substrate sequences within Aptazyme1.15-3'. This designing process included an in silico study, revealing the impact of the target recognition sequence on the aptazyme secondary structure and its catalytic activity. After proving the functionality of the new aptazyme in a singleplex bioassay, we demonstrated the capability of the two aptazymes to simultaneously detect thrombin and NA target, or two NA targets in a multiplex bioassay. High specificity in target detection was achieved with the limits of detection in the low nanomolar range, comparable to the singleplex bioassays. The presented results deepen the barely explored features of FNA for diagnosing multiple targets of different origins, adding an extra functionality to their catalogue.