Split aptamer mediated endonuclease amplification for small-molecule detection

Rapid nanomolar detection of Δ9-tetrahydrocannabinol in biofluids via electrochemical aptamer-based biosensor

BACKGROUND

The fabrication of sensors capable of achieving rapid, sensitive, and highly selective detection of target molecules in complex fluids is key to realizing their real-world applications. For example, there is an urgent need in drugged driving roadside screening scenarios to develop a method that can be used for rapid drug detection and that avoids interference from the matrix in the sample. How to minimize the interference of complex matrices in biofluids at the electrode interface is the key to improve the sensitivity of the sensor.

RESULTS

This work develops a facile and green method to prepare rough electrodes with a porous structure for constructing electrochemical aptamer-based (EAB) sensors for rapid, sensitive and accurate detection of Δ9-tetrahydrocannabinol (THC) in biofluids. The electroactive area of the rough electrode was 21 times of smooth electrode. And the antifouling performance of the rough electrode was much better than that of smooth electrode. Based on the unique advantages of the rough electrode, the developed EAB sensor achieves rapid nanomolar detection of THC in undiluted serum, undiluted urine and 50 % saliva with the detection limit of 5.0 nM, 10 nM and 10 nM, respectively. Moreover, our method possesses good reproducibility, accuracy and specificity.

SIGNIFICANCE

The porous structure can effectively reduce the non-specific adsorption and enhance the stability of the signal, while the larger active area can modify more aptamers, thus improving the sensitivity. The detection limits of the EAB sensor were lower than the cutoff concentration of THC in drugged driving and the measuring process was completed within 60 s after target addition, which makes the present sensors capable for real-world applications.

Improving aptamer performance: key factors and strategies

Aptamers are functional single-stranded oligonucleotide fragments isolated from randomized libraries by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), exhibiting excellent affinity and specificity toward targets. Compared with traditional antibody reagents, aptamers display many desirable properties, such as low variation and high flexibility, and they are suitable for artificial and large-scale synthesis. These advantages make aptamers have a broad application potential ranging from biosensors, bioimaging to therapeutics and other areas of application. However, the overall performance of aptamer pre-selected by SELEX screening is far from being satisfactory. To improve aptamer performance and applicability, various post-SELEX optimization methods have been developed in the last decade. In this review, we first discuss the key factors that influence the performance or properties of aptamers, and then we summarize the key strategies of post-SELEX optimization which have been successfully used to improve aptamer performance, such as truncation, extension, mutagenesis and modification, splitting, and multivalent integration. This review shall provide a comprehensive summary and discussion of post-SELEX optimization methods developed in recent years. Moreover, by discussing the mechanism of each approach, we highlight the importance of choosing the proper method to perform post-SELEX optimization.

A DNAzyme-mediated target-initiated rolling circle amplification strategy based on a microchip platform for the detection of apurinic/apyrimidinic endonuclease 1 at the single-cell level

A DNAzyme-mediated target-initiated rolling circle signal amplification strategy based on a microchip platform was developed for detecting apurinic/apyrimidine endonuclease 1 (APE1) at the single-cell level. This strategy was applied to assays of lysate samples from HL-7702, HeLa and MCF-7 cells, with a detection limit of lower than 1 HeLa cell.

Nucleic Acid Tests for Clinical Translation

Nucleic acids, including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are natural biopolymers composed of nucleotides that store, transmit, and express genetic information. Overexpressed or underexpressed as well as mutated nucleic acids have been implicated in many diseases. Therefore, nucleic acid tests (NATs) are extremely important. Inspired by intracellular DNA replication and RNA transcription, in vitro NATs have been extensively developed to improve the detection specificity, sensitivity, and simplicity. The principles of NATs can be in general classified into three categories: nucleic acid hybridization, thermal-cycle or isothermal amplification, and signal amplification. Driven by pressing needs in clinical diagnosis and prevention of infectious diseases, NATs have evolved to be a rapidly advancing field. During the past ten years, an explosive increase of research interest in both basic research and clinical translation has been witnessed. In this review, we aim to provide comprehensive coverage of the progress to analyze nucleic acids, use nucleic acids as recognition probes, construct detection devices based on nucleic acids, and utilize nucleic acids in clinical diagnosis and other important fields. We also discuss the new frontiers in the field and the challenges to be addressed.

A facile and label-free electrochemical aptasensor for tumour-derived extracellular vesicle detection based on the target-induced proximity hybridization of split aptamers

Facile detection of tumour-derived extracellular vesicles (EVs) is crucial to cancer diagnosis. Herein, a facile and label-free electrochemical aptasensor was fabricated to detect tumour-derived EVs based on the target-induced proximity hybridization of split aptamers. In this assay, two designed oligonucleotide probes containing fragments of a protein tyrosine kinase-7 (PTK7) aptamer were used to recognize and capture EVs containing PTK7. In the presence of target EVs, the aptamer-target ternary complex could induce proximity hybridization and form a DNA duplex on the electrode. The DNA duplex could bind more electroactive Ru(NH3)63+ through electrostatic attraction, resulting in an increased cathodic current signal. By virtue of the excellent electrochemical signal reporter RuHex, the specificity of the aptamer and proximity ligation, a facile EV electrochemical aptasensor with a detection limit of 6.607 × 105 particles per mL was realized. Furthermore, this aptasensor showed good selectivity to distinguish different tumour-derived EVs and was applied to detect EVs in complex biological samples. The proposed electrochemical aptasensor can be further extended to the detection of other EVs, thus showing great potential in clinical diagnosis.

Aptamers used for biosensors and targeted therapy

Aptamers are single-stranded nucleic acid sequences that can bind to target molecules with high selectivity and affinity. Most aptamers are screened in vitro by a combinatorial biology technique called systematic evolution of ligands by exponential enrichment (SELEX). Since aptamers were discovered in the 1990s, they have attracted considerable attention and have been widely used in many fields owing to their unique advantages. In this review, we present an overview of the advancements made in aptamers used for biosensors and targeted therapy. For the former, we will discuss multiple aptamer-based biosensors with different principles detected by various signaling methods. For the latter, we will focus on aptamer-based targeted therapy using aptamers as both biotechnological tools for targeted drug delivery and as targeted therapeutic agents. Finally, challenges and new perspectives associated with these two regions were further discussed. We hope that this review will help researchers interested in aptamer-related biosensing and targeted therapy research.

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.

Nanomaterial-based aptamer sensors for analysis of illicit drugs and evaluation of drugs consumption for wastewater-based epidemiology

The abuse of illicit drugs usually associated with dramatic crimes may cause significant problems for the whole society. Wastewater-based epidemiology (WBE) has been demonstrated to be a novel and cost-effective way to evaluate the abuse of illicit drugs at the community level, and has been used as a routine method for monitoring and played a significant role for combating the crimes in some countries, e.g. China. The method can also provide temporal and spatial variation of drugs of abuse. The detection methods mainly remain on the conventional liquid chromatography coupled with mass spectrometry, which is extremely sensitive and selective, however needs advanced facility and well-trained personals, thus limit it in the lab. As an alternative, sensors have emerged to be a powerful analytical tool for a wide spectrum of analytes, in particular aptamer sensors (aptasensors) have attracted increasing attention and could act as an efficient tool in this field due to the excellent characteristics of selectivity, sensitivity, low cost, miniaturization, easy-to-use, and automation. In this review, we will briefly introduce the context, specific assessment process and applications of WBE and the recent progress of illicit drug aptasensors, in particular focusing on optical and electrochemical sensors. We then highlight several recent aptasensors for illicit drugs in new technology integration and discuss the feasibility of these aptasensor for WBE. We will summarize the challenges and propose our insights and opportunity on aptasensor for WBE to evaluate community-wide drug use trends and public health.

Directly profiling intact Staphylococcus aureus in water and foods via enzymatic cleavage aptasensor

Staphylococcus aureus (S. aureus) causes serious food-borne diseases, and tools able to directly profile intact S. aureus would greatly facilitate food safety and public health. Herein, we proposed a biosensing platform for culture-independent and separation-free profiling S. aureus, thus allow us to directly detect intact S. aureus in complex samples. The binding protection effect of aptamer-cell complex was introduced to construct the aptasensor, and it allowed to eliminate the optimization of aptamer probe sequences. The proposed aptasensor, terms enzymatic cleavage aptasensor could achieve a sensitive (a detection limit of 64 CFU/mL) and broad-concentration quantification (dynamic range 10²-10⁷ CFU/mL) of S. aureus. Furthermore, it could specifically identify intact S. aureus in complex samples, and the quantifying of S. aureus was achieved in tap water, milk and porker with high precision. Therefore, enzymatic cleavage aptasensor could be a good candidate for on-site biosensing platform of S. aureus, as well as other pathogens by replacing the aptamer sequences.

Splitting aptamers and nucleic acid enzymes for the development of advanced biosensors

In analogy to split-protein systems, which rely on the appropriate fragmentation of protein domains, split aptamers made of two or more short nucleic acid strands have emerged as novel tools in biosensor set-ups. The concept relies on dissecting an aptamer into a series of two or more independent fragments, able to assemble in the presence of a specific target. The stability of the assembled structure can further be enhanced by functionalities that upon folding would lead to covalent end-joining of the fragments. To date, only a few aptamers have been split successfully, and application of split aptamers in biosensing approaches remains as promising as it is challenging. Further improving the stability of split aptamer target complexes and with that the sensitivity as well as efficient working modes are important tasks. Here we review functional nucleic acid assemblies that are derived from aptamers and ribozymes/DNAzymes. We focus on the thrombin, the adenosine/ATP and the cocaine split aptamers as the three most studied DNA split systems and on split DNAzyme assemblies. Furthermore, we extend the subject into split light up RNA aptamers used as mimics of the green fluorescent protein (GFP), and split ribozymes.

Graphene/aptamer probes for small molecule detection: from in vitro test to in situ imaging

Small molecules are key targets in molecular biology, environmental issues, medicine and food industry. However, small molecules are challenging to be detected due to the difficulty of their recognition, especially in complex samples, such as in situ in cells or animals. The emergence of graphene/aptamer probes offers an excellent opportunity for small molecule quantification owing to their appealing attributes such as high selectivity, sensitivity, and low cost, as well as the potential for probing small molecules in living cells or animals. This paper (with 130 refs.) will review the application of graphene/aptamer probes for small molecule detection. We present the recent progress in the design and development of graphene/aptamer probes enabling highly specific, sensitive and rapid detection of small molecules. Emphasis is placed on the success in their development and application for monitoring small molecules in living cells and in vivo systems. By discussing the key advances in this field, we wish to inspire more research work of the development of graphene/aptamer probes for both on-site or in situ detection of small molecules and its applications for investigating the functions of small molecules in cells in a dynamic way. Graphical abstract Graphene/aptamer probes can be used to construct different platforms for detecting small molecules with high specificity and sensitivity, both in vitro and in situ in living cells and animals.

A novel fluorescent assay for uracil DNA glycosylase activity built on the 3′–5′ exonuclease activity-based endonuclease IV cyclic signal amplification strategy

The unique 3′-5′ exonuclease activity of endonuclease IV to DNA strands has been demonstrated, which enables the development of a novel highly sensitive assay for UDG activity.

Biodegradable MnO2 nanosheet mediated hybridization chain reaction for imaging of human apurinic/apyrimidinic endonuclease 1 activity in living cells

A highly sensitive enzyme-free amplification assay for the detection of apurinic/apyrimidinic endonuclease 1 activity was developed. By incorporating biodegradable MnO₂ nanosheets, in situ light up intracellular APE 1 activity was achieved.

Innovative engineering and sensing strategies for aptamer-based small-molecule detection

Aptamers are nucleic acid-based affinity reagents that have gained widespread attention as biorecognition elements for the detection of targets such as ions, small molecules, and proteins. Over the past three decades, the field of aptamer-based sensing has grown considerably. However, the advancement of aptamer-based small-molecule detection has fallen short of the high demand for such sensors in applications such as diagnostics, environmental monitoring, and forensics. This is due to two challenges: the complexity of developing generalized sensing platforms and the poor sensitivities of assays targeting small molecules. This paper will review new approaches for the streamlined development of high-performance aptamer-based sensors for small-molecule detection. We here provide historical context, explore the current state-of-the art, and offer future directions-with emphasis placed on new aptamer engineering methods, the use of cooperative binding, and label-free approaches using fully-folded, high-affinity aptamers for small-molecule sensing.

A transcription aptasensor: amplified, label-free and culture-independent detection of foodborne pathogens via light-up RNA aptamers

We report a transcription aptasensor by using a light-up RNA aptamer. It allows for sensitive, label-free and culture-free detection of intact foodborne pathogens, and no separation, purification or enrichment processes are involved.

A light-up fluorescence assay for tumor cell detection based on bifunctional split aptamers

Light-up aptamers have attracted growing attention due to their advantages of being label-free and having low fluorescence background. In this work, we developed a light-up fluorescence assay for label-free detection of tumor cells based on a bifunctional split aptamer (BFSA) that contained two DNA strands (BFSA-a and BFSA-b). BFSA-a and BFSA-b were constructed by combining aptamers ZY11 and ThT.2-2, which could specifically bind to the tumor cell SMMC-7721 and activate the fluorescence of thioflavin T (ThT). A Helper strand was introduced to hybridize with BFSA-b, and then BFSA-a and BFSA-b were separated if the target cell was absent. Only when the target cell is present can BFSA-a approach and hybridize with BFSA-b due to the 'induced-fit effect', which made the Helper strand dissociate. Then ThT bound to BFSA and the fluorescence of ThT was activated. The results indicated that this fluorescence assay had a good linear response to the target cells in the range of 250-20 000 cells in 100 μL binding buffer; the lowest cell number actually detected was 125 cells in 100 μL buffer. This assay also displayed excellent selectivity and was successfully applied to detect target cells in 20% human serum samples. The design of bifunctional split aptamers realized no-washing, label-free, low-cost, one-step detection of tumor cells, which could generate detectable fluorescence signals just by mixing nucleic acid aptamers and fluorescent reporter molecules with target cells. Such a design of aptamer probes also has the potential to construct stimuli-responsive controlled drug delivery systems.

Fluorometric determination of mercury(II) via a graphene oxide-based assay using exonuclease III-assisted signal amplification and thymidine-Hg(II)-thymidine interaction

A highly sensitive and selective fluorometric method is described for determination of mercury(II). It is based on (a) the use of graphene oxide (GO) acting as a quencher of the fluoresence of the carboxy-fluorescein (FAM), and (b) of Hg(II)-triggered cleavage of the newly formed nucleic acid sequences harbored blunt 3'-hydroxyl termini by exonuclease III (Exo III) that leads to signal amplification. Two DNA probes are used, viz. a capture probe (CP) and a help probe; HP) that is partially complementary. In the absence of Hg(II), the FAM-labeled hairpin (signal probe, SP) is adsorbed onto the surface of GO via π-stacking interactions. CP blocks the release of the HP for binding to SP. This results in quenching of the green fluorescence of the label. Upon addition of Hg(II), the linear structure of CP is converted to a hairpin structure due to the formation of thymidine-Hg(II)-thymidine duplexes. HP is released from the CP/HP hybrids, and this causes SP to be released from from GO and fluorescence to be recovered. The signal is strongly amplified by using Exo III-assisted targeting and recycling of HP. Hence, Hg(II) can be detected via the strong increase in fluorescence. The method has a linear response in the 0.1 to 30 nM Hg(II) concentration range and a 10 pM detection limit. It was applied to the determination of Hg(II) in three (spiked) Chinese medicines. Graphical abstract Schematic representation of fluorescence sensing strategy for Hg²⁺ by using graphene oxide as a quencher and exonuclease III-assisted signal amplification.

A colorimetric ATP assay based on the use of a magnesium(II)-dependent DNAzyme

A colorimetric assay for ATP is described that uses a strategy that combines the concept of split Mg(II)-dependent DNAzyme, split aptamer, and hybridization-induced aggregation of gold nanoparticles (AuNPs). Both ATP aptamer and Mg(II)-dependent DNAzyme are split into two fragments which are allocated to two well-designed DNA probes. The probes also possess mutually complementary stem sequences and spacer sequences. In the presence of ATP, the separated DNAzyme sequences in the two probes assemble via the synchronous recognition of ATP with two fragments of the aptamer. Then, the activated DNAzyme catalyzes multiple cycles of the cleavage of its substrate DNA sequence. The latter acts as a linker and induces the aggregation of two types of ssDNA-modified AuNP through the hybridization between the complementary sequences. Thus, the color of the AuNP solution remains red. However, in the absence of ATP, the detached aptamer cannot induce the assembly of DNAzyme to cleave the linker DNA. This results in the aggregation of AuNP and a concomitant color transition from red to purple. This ATP assay, performed at a wavelength of 530 nm, has a linear detection range that extends from 10 pM to 100 nM, with a detection limit of 5.3 pM. It was applied to the detection of ATP in human serum. Conceivably, the strategy has a wide scope in that it may be applied to the colorimetric detection of various other analytes through the split aptamer configuration. Graphical abstract Schematic presentation of colorimetric assay for adenosine triphosphate (ATP) based on the use of a split Mg(II)-dependent DNAzyme, a split aptamer, and by exploiting the hybridization-induced aggregation of gold nanoparticles that leads to a color change from red to purple.

Fluorescent and colorimetric dual-mode aptasensor for thrombin detection based on target-induced conjunction of split aptamer fragments

Since the lack of detection diversity of the single-signal readout strategy, it is urgent to develop fast and multisignal assay strategies. A highly selective and sensitive assay method with colorimetric and fluorometric dual signals readouts is presented in this paper. It is based on the principle that the target induced conjunction of split aptamer fragments assembled on the surface of Au nanoparticles (AuNPs). In the presence of targets, the color of solution changed from wine red to blue and can be measured both visual inspection and spectrophotometry because of the aggregation of AuNPs. At the same time, the report probes which are original hybrid with the anchoring aptamer fragments on the AuNPs surface can be released and recovers the fluorescence. By use of this detection strategy, the limit of detection for thrombin (TMB), as a model of analyte, were 0.45 and 0.16nM, respectively. Furthermore, this protocol can discriminate TMB from other analogue with high selectivity and can be used to detect TMB in human serum samples. The results came from the two signals were well consistent with each other, which demonstrated that it has application potential for detection of TMB in complex matrix.

Integrated signal probe based aptasensor for dual-analyte detection

For the multi-analyte detection, although the sensitivity has commonly met the practical requirements, the reliability, reproducibility and stability need to be further improved. In this work, two different aptamer probes labeled with redox tags were used as signal probe1 (sP1) and signal probe2 (sP2), which were integrated into one unity DNA architecture to develop the integrated signal probe (ISP). Comparing with the conventional independent signal probes for the simultaneous multi-analyte detection, the proposed ISP was more reproducible and accurate. This can be due to that ISP in one DNA structure can ensure the completely same modification condition and an equal stoichiometric ratio between sP1 and sP2, and furthermore the cross interference between sP1 and sP2 can be successfully prevented by regulating the complementary position of sP1 and sP2. The ISP-based assay system would be a great progress for the dual-analyte detection. Combining with gold nanoparticles (AuNPs) signal amplification, the ISP/AuNPs-based aptasensor for the sensitive dual-analyte detection was explored. Based on DNA structural switching induced by targets binding to aptamer, the simultaneous dual-analyte detection was simply achieved by monitoring the electrochemical responses of methylene blue (MB) and ferrocene (Fc) This proposed detection system possesses such advantages as simplicity in design, easy operation, good reproducibility and accuracy, high sensitivity and selectivity, which indicates the excellent application of this aptasensor in the field of clinical diagnosis or other molecular sensors.

A cooperative-binding split aptamer assay for rapid, specific and ultra-sensitive fluorescence detection of cocaine in saliva

Sensors employing split aptamers that reassemble in the presence of a target can achieve excellent specificity, but the accompanying reduction of target affinity mitigates any overall gains in sensitivity. We for the first time have developed a split aptamer that achieves enhanced target-binding affinity through cooperative binding. We have generated a split cocaine-binding aptamer that incorporates two binding domains, such that target binding at one domain greatly increases the affinity of the second domain. We experimentally demonstrate that the resulting cooperative-binding split aptamer (CBSA) exhibits higher target binding affinity and is far more responsive in terms of target-induced aptamer assembly compared to the single-domain parent split aptamer (PSA) from which it was derived. We further confirm that the target-binding affinity of our CBSA can be affected by the cooperativity of its binding domains and the intrinsic affinity of its PSA. To the best of our knowledge, CBSA-5335 has the highest cocaine affinity of any split aptamer described to date. The CBSA-based assay also demonstrates excellent performance in target detection in complex samples. Using this CBSA, we achieved specific, ultra-sensitive, one-step fluorescence detection of cocaine within fifteen minutes at concentrations as low as 50 nM in 10% saliva without signal amplification. This limit of detection meets the standards recommended by the European Union's Driving under the Influence of Drugs, Alcohol and Medicines program. Our assay also demonstrates excellent reproducibility of results, confirming that this CBSA-platform represents a robust and sensitive means for cocaine detection in actual clinical samples.

Thioflavin T behaves as an efficient fluorescent ligand for label-free ATP aptasensor

Here, we for the first time demonstrated thioflavin T (ThT) as an efficient fluorescent ligand for 27-mer ATP-binding aptamer (ABA27), providing a novel signal readout mode for label-free selective ATP detection. ABA27 can promote the fluorescence emission of ThT with an unprecedentedly high efficiency, attributed to the specific structure of ABA27 rather than the G-tracts. Polyacrylamide gel electrophoresis, fluorescence spectroscopy, and fluorometric titration reveal that ThT interacts with ABA27 with a lower binding affinity (Kd ~89 μM) than ATP, which allows ATP to easily compete with ThT for the DNA binder. In the presence of ThT, adding ATP induces ABA27 to undergo a structural change, thereby not favoring the binding to ThT, verified by circular dichroism and UV-Vis absorption spectroscopy. As a result, the fluorescence intensity of ThT decreases dramatically, enabling the sensitive detection of ATP with high selectivity over other analogs. Such a sensing strategy may make ThT able to serve as a facile signal reporter for DNA nanomechanical devices fueled with ATP. Graphical Abstract The principle of the displacement of ThT by ATP.

Ultrasensitive detection of mucin 1 biomarker by immuno-loop-mediated isothermal amplification

Mucin 1 (MUC-1), a glycoprotein over-expressed on most malignant epithelial cell surfaces, such as colorectal, lung, prostate, pancreatic, ovarian, and bladder carcinomas, has been confirmed as a useful biomarker for the diagnosis of early cancers. Therefore, it is very important for early cancer diagnoses to develop the sensitive and specific detection approach of MUC-1. In this paper, we report a novel technique of aptamer-based Immuno-Loop-Mediated Isothermal Amplification (Im-LAMP) for the quantitative detection of MUC-1 by MUC-1 aptamer with high affinity for MUC-1. The cycle time is linearly dependent on the logarithm (log) of the concentration of mucin 1 ranging from 1.0 pM to 1.0 aM. We call this technique Im-LAMP, which is a novel method for the detection of low-abundance proteins with high sensitivity (a low detection limit of 120 MUC-1 molecules by calculation)and specificity. Finally, this approach is also successfully applied in the analysis of human blood serum samples. It also lays the foundation for the early diagnosis of different types of low-abundance cancer biomarkers.

Ratiometric detection and imaging of endogenous hypochlorite in live cells and in vivo achieved by using an aggregation induced emission (AIE)-based nanoprobe

An AIE-based fluorescent nanoprobe (MTPE-M) has been developed and used for ratiometric detection of hypochlorite with high selectivity and sensitivity. More importantly, its application in live cells and zebrafish for ratiometric imaging of endogenous ClO(-) has also been achieved.

Endonuclease IV cleaves apurinic/apyrimidinic sites in single-stranded DNA and its application for biosensing

The cleaving capability of endonuclease IV to apurinic/apyrimidinic sites in single-stranded DNA has been demonstrated. It was further applied to construct a novel dual signal amplified sensing system for highly sensitive enzyme and protein detection.

Novel autonomous protein-encoded aptamer nanomachines and isothermal exponential amplification for ultrasensitive fluorescence polarization sensing of small molecules

We develop a new type of autonomous protein-encoded aptamer nanomachine for amplified fluorescence polarization (FP) sensing of small molecules in homogeneous solutions.

A Luminescent Cocaine Detection Platform Using a Split G-Quadruplex-Selective Iridium(III) Complex and a Three-Way DNA Junction Architecture

In this study, a series of 10 in-house cyclometalated iridium(III) complexes bearing different auxiliary ligands were tested for their selectivity toward split G-quadruplex in order to construct a label-free switch-on cocaine detection platform employing a three-way junction architecture and a G-quadruplex motif as a signal output unit. Through two rounds of screening, we discovered that the iridium(III) complex 7 exhibited excellent selectivity toward the intermolecular G-quadruplex motif. A detection limit as low as 30 nM for cocaine can be achieved by this sensing approach with a linear relationship between luminescence intensity and cocaine concentration established from 30 to 300 nM. Furthermore, this sensing approach could detect cocaine in diluted oral fluid. We hope that our simple, signal-on, label-free oligonucleotide-based sensing method for cocaine using a three-way DNA junction architecture could act as a useful platform in bioanalytical research.

A programmable Y-shaped junction scaffold-mediated modular and cascade amplification strategy for the one-step, isothermal and ultrasensitive detection of target DNA

A programmable Y-shaped junction probe-mediated modular and cascade amplification strategy was proposed for the one-pot, isothermal and ultrasensitive detection of target DNA.