Superparamagnetic Nanostructures Coupled with an Entropy-Driven DNA Circuit for Elegant and Robust Photoelectrochemical Biosensing

Entropy driven-based catalytic biosensors for bioanalysis: From construction to application-A review

The rapid advancement of precision medicine and the continuous emergence of novel pathogens have presented new challenges for biosensors, necessitating higher requirements. Target amplification technology serves as the core component in biosensor construction. Enzyme-based amplification methods are often sensitive and selective but involve relatively complex operational steps, whereas enzyme-free amplification methods offer simplicity but frequently fail to meet both sensitivity and selectivity simultaneously. Existing research has confirmed that entropy-driven catalyst (EDC) biosensors not only fulfills the demands for sensitivity and selectivity concurrently but also offers ease of operation and flexibility in construction. In this review, we summarize the key advantages of EDC, explore how to construct DNA nanomachines based on these advantages to achieve intracellular detection and simultaneous detection of multiple targets, as well as point-of-care testing (POCT) to address practical issues in clinical diagnosis and treatment. We also anticipate potential challenges, propose corresponding solutions, and outline future development directions for EDC-based biosensors in practical clinical applications. We firmly believe that EDC sensors will emerge as a crucial branch within the realm of biosensor development.

All-In-One Entropy-Driven DNA Nanomachine for Tumor Cell-Selective Fluorescence/SERS Dual-Mode Imaging of MicroRNA

An entropy-driven catalysis (EDC) strategy is appealing for amplified bioimaging of microRNAs in living cells; yet, complex operation procedures, lacking of cell selectivity, and insufficient accuracy hamper its further applications. Here, we introduce an ingenious all-in-one entropy-driven DNA nanomachine (termed as AIO-EDN), which can be triggered by endogenous apurinic/apyrimidinic endonuclease 1 (APE1) to achieve tumor cell-selective dual-mode imaging of microRNA. Compared with the traditional EDC strategy, the integrated design of AIO-EDN achieves autocatalytic signal amplification without extra fuel strands. Moreover, the AIO-EDN leverages an endogenous APE1 overexpressed in cancer cells to activate the EDC reaction, which, however, exerts no target sensing activity in normal cells. Combining fluorescence- and surface-enhanced Raman scattering (FL/SERS) dual-mode imaging techniques, this DNA nanomachine exhibits significantly improved accuracy and tumor cell selectivity for microRNA imaging in living cells. This study provides a new paradigm to develop an integrated EDC-based platform and shows great potential in in-depth cancer diagnosis with high precision.

Nucleic acid-functionalized upconversion luminescence biosensor based on strand displacement-mediated signal amplification for the detection of trivalent chromium ions

BACKGROUND

Rapid industrial development has generated serious pollution, including the presence of toxic and harmful heavy metal ions. Among them, trivalent chromium ion (Cr3+) is a very important element that poses a threat to life and health in our industrial wastewater pollution. Thus, it is important to develop efficient fluorescence methods for Cr3+ detection. In this study, an upconversion luminescence biosensor for detecting Cr3+ was constructed based on a DNAzyme, strand displacement reaction (SDR), and DNA-functionalized upconversion nanoparticles (UCNPs).

RESULTS

The sulfonate-rich poly (sodium 4-styrene sulfonate) (PSS) was modified onto the surface of UCNPs, forming UCNPs@PSS. Then, NH2-Capture probe DNA (NH2-Cp) was further modified onto the UCNPs@PSS surface through sulfonylation, resulting in UCNPs@PSS@NH2-Cp. The DNAzyme activated by Cr3+ triggered the release of the primer probe (Pp), which initiated the SDR system cycle, thereby releasing a tetramethylrhodamine (TAMRA)-modified signal probe (TAMRA-Sp). Finally, UCNPs@PSS@NH2-Cp bound to TAMRA-Sp through complementary base pairing, causing UCNPs and TAMRA to approach each other. Because of the luminescence resonance energy transfer (LRET) mechanism, the upconversion luminescence (UCL) signal of the UCNPs was quenched by TAMRA, enabling the detection of Cr3+ by the change of I585/I545 ratio. This biosensor has good stability, selectivity, and sensitivity, with a linear range of 0.5-75 nM and a detection limit of 0.135 nM for Cr3+.

SIGNIFICANCE AND NOVELTY

Firstly, based on LRET between UCNPs and TAMRA, the quantitative analysis of Cr3+ is achieved through the changes of ratio fluorescence. Secondly, the specificity of the biosensor is improved by utilizing the specific recognition of DNA enzymes. Thirdly, the signal amplification technology of the SDR cycle greatly improves the sensitivity of biosensor. This biosensor will be useful for future environmental safety monitoring and biopsy of biological fluids.

Upgraded and Light-Up Biosensing Platform: Entropy-Driven Catalysis Circuit Manipulates the Configuration Transformation of Novel DNA Silver Nanoclusters on the Graphene Oxide Surface

To tackle the predicament of the traditional turn-off mechanism, exploring an activated turn-on system remains an intriguing and crucial objective in biosensing fields. Herein, a dark DNA Ag nanocluster (NC) with hairpin-structured DNA containing a six-base cytosine loop (6C loop) as a template is atypically synthesized. Intriguingly, the dark DNA Ag NCs can be lit to display strong red-emission nanoclusters. Building upon these exciting findings, an unprecedented and upgraded turn-on biosensing system [entropy-driven catalysis circuit (EDCC)-Ag NCs/graphene oxide (GO)] has been created, which employs an EDCC to precisely manipulate the conformational transition of DNA Ag NCs on the GO surface from adsorption to desorption. Benefiting from the effective quenching of GO and signal amplification capability of the EDCC, the newly developed EDCC-Ag NCs/GO biosensing system displays a high signal-to-background (S/B) ratio (26-fold) and sensitivity (limit of detection as low as 0.4 pM). Meanwhile, it has good specificity, excellent stability, and reliability in both buffer and biological samples. To the best of our knowledge, it is the first example that adopts an EDCC to precisely modulate the configuration transformation of DNA Ag NCs on the GO surface to obtain a biosensor with low background, strong fluorescence, high contrast, and sensitivity. This exciting finding may provide a new route to fabricate a novel turn-on biosensor based on hairpin-templated DNA Ag NCs in the optical imaging and bioanalytical fields.

Programmable Entropy-Driven Circuit-Cascaded Self-Feedback DNAzyme Network for Ultra-Sensitive Fluorescence and Photoelectrochemical Dual-Mode Biosensing

Inspired by natural DNA networks, programmable artificial DNA networks have become an attractive tool for developing high-performance biosensors. However, there is still a lot of room for expansion in terms of sensitivity, atom economy, and result self-validation for current microRNA sensors. In this protocol, miRNA-122 as a target model, an ultrasensitive fluorescence (FL) and photoelectrochemical (PEC) dual-mode biosensing platform is developed using a programmable entropy-driven circuit (EDC) cascaded self-feedback DNAzyme network. The well-designed EDC realizes full utilization of the DNA strands and improves the atomic economy of the signal amplification system. The unique and rational design of the double-CdSe quantum-dot-released EDC substrate and the cascaded self-feedback DNAzyme amplification network significantly avoids high background signals and enhances sensitivity and specificity. Also, the enzyme-free, programmable EDC cascaded DNAzyme network effectively avoids the risk of signal leakage and enhances the accuracy of the sensor. Moreover, the introduction of superparamagnetic Fe3O4@SiO2-cDNA accelerates the rapid extraction of E2-CdSe QDs and E3-CdSe QDs, which greatly improves the timeliness of sensor signal reading. In addition to the strengths of linear range (6 orders of magnitude) and stability, the biosensor design with dual signal reading makes the test results self-confirming.

Base-Stacking-Driven Catalytic Hairpin Assembly: A Nucleic Acid Amplification Reaction Using Electrode Interface as a "Booster" for SARS-CoV-2 Point-of-Care Testing

Electrochemical DNA (E-DNA) biosensors based on interface-mediated hybridization reactions are promising for point-of-care testing (POCT). However, the low efficiency of target recycle amplification and the steric hindrance at the electrode interface limit their sensing performance. Herein, we propose a base-stacking-driven catalytic hairpin assembly (BDCHA), a nucleic acid amplification reaction strategy, for POCT. The introduction of the base-stacking effect in this strategy increases the thermodynamic stability of the product, thereby effectively improving the recycling efficiency. Also, it enables the interface-mediated hybridization to maintain stability with even fewer bases in the reaction-binding domain, hence minimizing DNA secondary structure formation or intertwining at the electrode surface and ameliorating the steric hindrance limitation. The introduced base-stacking effect makes the electrode serve as a "booster" by integrating the advantages of homogeneous and heterogeneous reactions, giving BDCHA an increased reaction rate of about 20-fold, compared to the conventional catalytic hairpin assembly. As a proof of concept, our BDCHA was applied in constructing a portable E-DNA biosensor for the detection of a SARS-CoV-2 N gene sequence fragment. A simple 30 min one-pot incubation is required, and the results can be readily read on a smartphone, making it portable and user-friendly for POCT.

Entropy-driven DNA circuit with two-stage strand displacement for elegant and robust detection of miRNA let-7a

MicroRNAs (miRNAs) research in cancer diagnosis is expanding, on account of miRNAs were demonstrated to be key indicator of gene expression and hopeful candidates for biomarkers. In this study, a stable miRNA-let-7a fluorescent biosensor was successfully designed based on an exonuclease Ⅲ-assisted two-stage strand displacement reaction (SDR). First, an entropy-driven SDR containing a three-chain structure of the substrate is used in our designed biosensor, leading to reduce the reversibility of the target recycling process in each step. The target acts on the first stage to start the entropy-driven SDR, which generates the trigger used to stimulate the exonuclease Ⅲ-assisted SDR in the second stage. At the same time, we design a SDR one-step amplification strategy as a comparison. Expectly, this developed two-stage strand displacement system has a low detection limit of 25.0 pM as well as a broad detection range of 4 orders of magnitude, making it more sensitive than the SDR one-step sensor, whose detection limit is 0.8 nM. In addition, this sensor has high specificity across members of the miRNA family. Therefore, we can take advantage of this biosensor to promote miRNA research in cancer diagnosis sensing systems.

A cathodic photoelectrochemical biosensor based on CRISPR/Cas12a trans-cleavage mediated p-n heterojunction quenching mode for microRNA determination

In this study, a cathodic photoelectrochemical (PEC) bioanalysis for sensitive determination of microRNA (miRNA) has been constructed based on CRISPR/Cas12a trans-cleavage mediated [(C6)₂Ir(dcbpy)]⁺PF₆^- (C6 represents coumarin-6 and dcbpy represents 4,4'-dicarboxyl-2,2'-bipyridine)-sensitized NiO photocathode and p-n heterojunction quenching mode. The [(C6)₂Ir(dcbpy)]⁺PF₆^--sensitized NiO photocathode exhibits a stable and dramatically improved photocurrent signal due to highly effective photosensitization of [(C6)₂Ir(dcbpy)]⁺ PF₆^-. Then Bi₂S₃ quantum dots (Bi₂S₃ QDs) is captured on the photocathode, resulting in markedly quenching of the photocurrent. When target miRNA is specifically recognized by the hairpin DNA to stimulate the trans-cleavage activity of CRISPR/Cas12a, leading to the leave of the Bi₂S₃ QDs. The photocurrent is gradually recovered with the increasing target concentration. Thus, the quantitative signal response to target is achieved. Benefiting from excellent performance of NiO photocathode, intense quenching effect of p-n heterojunction and accurate recognition ability of CRISPR/Cas12a, the cathodic PEC biosensor shows a wider linear range over 0.1 fM-10 nM, with a low detection limit of 36 aM. Also, the biosensor exhibits satisfying stability and selectivity.

N/S-Co-doped carbon dot-based FRET ratiometric fluorescence aptasensing platform modulated with entropy-driven DNA amplifier for ochratoxin A detection

This study proposes a nitrogen and sulfur co-doped carbon dot (N/S-CD)-based FRET ratiometric fluorescence aptasensing strategy modulated with entropy-driven DNA amplifier for sensitive and accurate detection of ochratoxin A (OTA). In the strategy, a duplex DNA probe containing OTA aptamer and complementary DNA (cDNA) is designed as a recognition and transformation element. Upon sensing of target OTA, the cDNA was liberated, and triggered a three-chain DNA composite-based entropy-driven DNA circuit amplification, making CuO probes anchor on a magnetic bead (MB). The CuO-encoded MB complex probe is finally turned into abundant Cu²⁺, which oxidizes o-phenylenediamine (oPD) to generate 2,3-diaminophenazine (DAP) with yellow fluorescence and further triggers FRET between the blue fluorescent N/S-CDs and DAP. The changes in ratiometric fluorescence are related to the OTA concentration. Originating from the synergistic amplifications from the entropy-driven DNA circuits and Cu²⁺ amplification, the strategy dramatically enhanced detection performance. A limit of detection as low as 0.006 pg/mL of OTA was achieved. Significantly, the aptasensor can visually evaluate the OTA via on-site visual screening. Moreover, the high-confidence quantification of the OTA in real samples with results consistent with that of the LC-MS method indicated that the proposed strategy has practical application prospects for sensitive and accurate quantification in food safety.

In situ growth of TiO2/Ti3C2 MXene Schottky heterojunction as a highly sensitive photoelectrochemical biosensor for DNA detection

In this work, a heterojunction composed of a TiO2 nanosheet and layered Ti3C2 was synthesized by directly growing TiO2 in Ti3C2 MXene. Compared with pure TiO2, TiO2/Ti3C2 composites had increased surface area, and a light absorption range that extended from ultraviolet to visible light, which greatly extended the life of photogenerated carriers. A photoelectrochemical biosensor for DNA detection was constructed based on the TiO2/Ti3C2 heterogeneous structure, which was comprehensively studied based on photocurrent responses. In the absence of the target, the CdSe QDs were close to the surface of the electrode, resulting in enhanced sensitization and increased photocurrent. In the presence of the target, the photocurrent decreases due to the formation of rigid double strands with the probe DNA, which caused the CdSe QDs to be far away from the electrode surface. The sensor had stability and sensitivity for DNA detection in the range of 10 nM-10 fM, and the lower detection limit was 6 fM. Its outstanding characteristics also provided ideas for detecting various other target DNA for early diagnosis of various diseases.

Fluorescent aptasensor for the ultrasensitive detection of antibiotic residue in food samples based on dumbbell DNA-mediated signal amplification

Sensitive and reliable detection of antibiotics is of great significance for environmental and food safety due to its high risk in trace concentrations. Herein, we developed a fluorescence sensing system for chloramphenicol (CAP) detection based on dumbbell DNA-mediated signal amplification. Two hairpin dimers (2H1 and 2H2) were employed as the building blocks to construct the sensing scaffolds. The CAP-aptamer binding in another hairpin H0 can liberate the trigger DNA, which then activates the cyclic assembly reaction between 2H1 and 2H2. The separation of FAM and BHQ in the formed product of cascaded DNA ladder yields a high fluorescence signal for CAP monitoring. Compared with the monomer hairpin assembly between H1 and H2, the dimer hairpin assembly between 2H1 and 2H2 exhibits enhanced signal amplification efficiency and reduced reaction time. The developed CAP sensor showed a wide linear range from 10 fM to 10 nM with a detection limit of 2 fM. Importantly, this sensing platform has been successfully applied to the determination of CAP in fish, milk, and water samples with satisfactory recovery and accuracy. With the advantages of high sensitivity, mix-and-read pattern, and robustness, our proposed CAP sensor can be used as a simple and routine tool for the detection of trace amounts of antibiotic residues.

A novel detection of MicroRNA based on homogeneous electrochemical sensor with enzyme-assisted signal amplification

Rapid and sensitive detection of microRNAs is of great importance in biological researches and cancer diagnosis. Herein, we proposed a novel homogeneous electrochemical sensor to detect microRNA-21 (miRNA-21) using functionalized magnetic nanoparticles combined with enzyme-assisted signal amplification. The biotinylated capture probe (CP) labeled magnetic nanoparticles can capture miRNA-21 and introduce streptavidin-conjugated hydroxyapatite (HAP) nanoparticles. In the presence of miRNA-21, hybridization between RNA and DNA results in the formation of RNA/DNA duplexes, and then duplex-specific nuclease (DSN) cleave the duplexes to digest the capture chain and release the miRNA-21 in a loop. Meanwhile, the HAP nanoparticles strip from the magnetic nanoparticles and electrochemical signal by the reaction of HAP with molybdate is changed. The current variation before and after incubation with miRNA-21 is linearly correlated with the miRNA-21 concentration between 1 aM and 1 pM with a low detection limit (LOD) of 0.27 aM. Remarkably, the expression of miRNA-21 in human serum and different cell lysate was successfully performed, which fully demonstrates the great practical potentials in biomedical diagnostics and clinical therapeutics.

CdTe QDs-sensitized TiO2 nanocomposite for magnetic-assisted photoelectrochemical immunoassay of SARS-CoV-2 nucleocapsid protein

A sensitive, reliable, and cost-effective detection for SARS-CoV-2 was urgently needed due to the rapid spread of COVID-19. Here, a "signal-on" magnetic-assisted PEC immunosensor was constructed for the quantitative detection of SARS-CoV-2 nucleocapsid (N) protein based on Z-scheme heterojunction. Fe₃O₄@SiO₂@Au was used to connect the capture antibody to act as a capture probe (Fe₃O₄@SiO₂@Au/Ab₁). It can extract target analytes selectively in complex samples and multiple electrode rinsing and assembly steps were avoided effectively. CdTe QDs sensitized TiO₂ coated on the surface of SiO₂ spheres to form Z-scheme heterojunction (SiO₂@TiO₂@CdTe QDs), which broadened the optical absorption range and inhibited the quick recombination of photogenerated electron/hole of the composite. With fascinating photoelectric conversion performance, SiO₂@TiO₂@CdTe QDs were utilized as a signal label, thus further realizing signal amplification. The migration mechanism of photogenerated electrons was further deduced by active material quenching experiment and electron spin resonance (ESR) measurement. The elaborated immunosensor can detect SARS-CoV-2 N protein in the linear range of 0.005-50 ng mL^-1 with a low detection limit of 1.8 pg mL^-1 (S/N = 3). The immunosensor displays extraordinary sensitivity, strong anti-interference, and high reproducibility in detecting SARS-CoV-2 N protein, which envisages its potential application in the clinical diagnosis of COVID-19.

Entropy-Driven Three-Dimensional DNA Nanofireworks for Simultaneous Real-Time Imaging of Telomerase and MicroRNA in Living Cells

Real-time monitoring of different types of intracellular tumor-related biomarkers is of key importance for the identification of tumor cells. However, it is hampered by the low abundance of biomarkers, inefficient free diffusion of reactants, and complex cytoplasmic milieu. Herein, we present a stable and general method for in situ imaging of microRNA-21 and telomerase utilizing simple highly integrated dual tetrahedral DNA nanostructures (TDNs) that can naturally enter cells, which could initiate to form the three-dimensional (3D) higher-order DNA superstructures (DNA nanofireworks, DNFs) through a reliable target-triggered entropy-driven strand displacement reaction in living cells for remarkable signal amplification. Importantly, the excellent biostability, biocompatibility, and sensitivity of this approach benefited from (i) the precise multidirectional arrangement of probes with a pure DNA structure and (ii) the local target concentration enhanced by the spatially confined microdomain inside the DNFs. This strategy provides a pivotal molecular toolbox for broad applications such as biomedical imaging and early precise cancer diagnosis.

Multiply Guaranteed and Successively Amplified Activation of a Catalytic DNA Machine for Highly Efficient Intracellular Imaging of MicroRNA

DNA amplification machines show great promise for intracellular imaging, yet are always constrained by off-site machinery activation or signal leakage, originating from the inherent thermodynamically driven hybridization between machinery substrates. Herein, an entropy-driven catalytic DNA amplification machine is integrated with the on-site amplified substrate exposure procedure to realize the high-contrast in vivo imaging of microRNA (miRNA). The key machinery substrate (fuel strands) is initially split into substrate subunits that are respectively grafted into an auxiliary DNA polymerization amplification accessory for eliminating the undesired signal leakage. Meanwhile, in target cells, the auxiliary polymerization accessory can be motivated by cell-specific mRNA for successively restoring their intact machine-propelling functions for guaranteeing the on-site amplified imaging of miRNA with high specificity. This intelligent on-site multiply guaranteed machinery can improve the specificity of catalytic DNA machines for discriminating different cell types and, thus, can provide a remarkable prospect in biomedical diagnosis.

A waste-free entropy-driven DNA nanomachine for smartly designed photoelectrochemical biosensing of MicroRNA-155

DNA nanotechnology has been booming in many fields such as biosensors, logic gates, and material science. Typically, as a kind of powerful isothermal and enzyme-free DNA amplifier in biosensors, entropy-driven DNA nanomachines are superior to hairpin-based ones in speed, specificity, stability, and simplicity. However, the atomic economy of non-covalent molecular reactions in these machines is not high, and DNAs waste is typically generated during operation. Herein, in order to further save costs and improve the performance, we report a novel design for a smart photoelectrochemical (PEC) biosensor of microRNA-155 by engineering waste-free entropy-driven DNA amplifiers conjugated to superparamagnetic Fe₃O₄@SiO₂ particles. This elegant design efficiently avoids leaving redundant DNA strands and waste complex in the amplification system, and all the displaced DNA strands can be regenerated into double-stranded structures, making the reaction irreversible. Thanks to superparamagnetic Fe₃O₄@SiO₂ particles, this strategy is achieved by effectively enriching, extracting, and cleaning target analogs to prevent co-existing species from remaining on the modified electrode surface, enabling a highly specific and sensitive PEC biosensor. This innovative study will be a new perspective on microRNAs detection in complex biological systems, paving the way for the design of waste-free DNA molecular machines and promoting the development of DNA nanotechnology.

Enzyme-free nucleic acid dual-amplification strategy combined with mimic enzyme catalytic precipitation reaction for the photoelectrochemical detection of microRNA-21

A novel photoelectrochemical (PEC) biosensor based on an enzyme-free nucleic acid dual-amplification strategy combined with a mimic enzyme to catalyze the deposition of a quencher is reported for the ultrasensitive detection of miRNA-21. A limited amount of target miRNA-21 can trigger the formation of long DNA duplexes on the electrode, owing to the synergistic effect of the enzyme-free nucleic acid dual-amplification strategy of entropy-driven strand displacement reaction (ESDR) amplification and hybridization chain reaction (HCR) amplification. The embedded manganese porphyrin (MnPP) in the long DNA duplexes acts as a horseradish peroxidase (HRP)-mimicking enzyme to catalyze the transformation of benzo-4-chlorohexadienone on the electrode surface, resulting in a significant reduction in photocurrent intensity. As a photosensitive material, BiOCl-BiOI is used as a tag to provide strong initial PEC signals. Based on the cascade integration of the enzyme-free nucleic acid dual-amplification strategy and the mimic enzyme-catalyzed precipitation reaction, the current PEC biosensor exhibits outstanding performance for miRNA-21 detection with an ultralow detection limit (33 aM) and a wide quantification range (from 100 aM to 1 nM). This work provides a new avenue toward the ultrasensitive detection of miRNAs, and is expected to be used for clinical and biochemical samples. A unique PEC biosensor with the BiOCl-BiOI composite, as the photosensitive material, has been developed for ultrasensitive miRNA-21 determination based on the combination of an enzyme-free nucleic acid dual-amplification strategy and mimic enzyme catalytic precipitation reaction.

Novel Aggregation-Enhanced PEC Photosensitizer Based on Electrostatic Linkage of Ionic Liquid with Protoporphyrin IX for Ultrasensitive Detection of Molt-4 Cells

Nowadays, aggregation quenching of most organic photosensitizers in aqueous media seriously restricts analytical and biomedical applications of photoelectrochemical (PEC) sensors. In this work, an aggregation-enhanced PEC photosensitizer was prepared by electrostatically bonding protoporphyrin IX (PPIX) with an ionic liquid of 1-butyl-3-methylimidazole tetrafluoroborate ([BMIm][BF₄]), termed as PPIX-[BMIm] for clarity. The resultant PPIX-[BMIm] showed weak photocurrent in pure dimethyl sulfoxide (DMSO, good solvent), while the PEC signals displayed a 44.1-fold enhancement in a water (poor solvent)/DMSO binary solvent with a water fraction (f_w) of 90%. Such PEC-enhanced mechanism was critically studied by electrochemistry and density functional theory (DFT) calculation in some detail. Afterward, a label-free PEC cytosensor was built for ultrasensitive bioassay of acute lymphoblastic leukemia (molt-4) cells by electrodepositing Au nanoparticles (Au NPs) on the PPIX-[BMIm] aggregates and sequential assembly of protein tyrosine kinase (PTK) aptamer DNA (aptDNA). The resultant cytosensor showed a wide linear range (300 to 3 × 10⁵ cells mL^-1) with a limit of detection (LOD) as low as 63 cells mL^-1. The aggregation-enhanced PEC performance offers a valuable and practical pathway for synthesis of advanced organic photosensitizer to explore its PEC applications in early diagnosis of tumors.

Comparison of chemiluminescent heterogeneous and homogeneous–heterogeneous assays coupled with isothermal circular strand-displacement polymerization reaction amplification for the quantification of miRNA-141

A heterogeneous and homogeneous–heterogeneous chemiluminescent microplate assay was developed for the determination of miRNA-141 levels in human cells.

Spatially-extended 3D magnetic DNA nanodevice-based split-type photoelectrochemical strategy for sensitive and reliable miRNA detection in cancer cells

To improve the accuracy of PEC sensing. We developed a split-type “turn-off” PEC biosensor based on spatially-extended 3D magnetic DNA nanodevices with high-order DNA amplifiers for sensitive and reliable detection of miRNAs in cancer cells.

Ultrasensitive Photoelectrochemical Biosensor Based on Novel Z-Scheme Heterojunctions of Zn-Defective CdS/ZnS for MicroRNA Assay

The sensitive and accurate detection of microRNA (miRNA) has meaningful values for clinical diagnosis application as an early stage of tumor markers. Herein, a novel photoelectrochemical (PEC) biosensor was developed for the ultrasensitive and highly selective detection of microRNA-122 (miRNA-122) based on a direct Z-scheme heterojunction of Zn vacancy-mediated CdS/ZnS (CSZS-V_Zn). Impressively, the prepared Z-scheme heterojunction nanocomposite with defect level properties could make the photogenerated charges stay at the Zn vacancy defect levels and combine photogenerated holes in the valence bands of CdS, thus significantly achieving a better charge carrier separation efficiency and broadening the absorption of visible light and demonstrating 5-8 times enhancement of PEC response compared to single-component materials. Simultaneously, an exonuclease III (Exo-III)-assisted signal amplification strategy and a strand displacement reaction were combined to improve the conversion efficiency of the target and further increase the detection sensitivity. More importantly, the elaborated biosensor showed ultrasensitive and highly specific detection of the target miRNA-122 over a wide linear range from 10 aM to 100 pM with a low detection limit of 3.3 aM and exhibited enormous potential in the fields of bioanalysis and clinical diagnosis.

Engineering an Au nanostar-based liquid phase interfacial ratiometric SERS platform with programmable entropy-driven DNA circuits to detect protein biomarkers in clinical samples

Developing sensing platforms that simultaneously integrate high sensitivity and accuracy has been a promising but challenging task for the detection of protein biomarkers in clinical samples. Herein, we engineered an Au nanostar-based liquid phase interfacial ratiometric SERS platform with programmable entropy-driven DNA circuits to detect the protein biomarker Mucin 1 (MUC1) in clinical samples.

Rapid and highly sensitive hairpin structure-mediated colorimetric detection of miRNA

Herein, we report a novel hairpin structure-mediated diagnostic method for the simple and rapid colorimetric detection of miRNA through the sensing of pyrophosphate. When the hairpin structure of the template DNA (h-Probe) was hybridized with the primer, the DNA primer extension mediated by nPfu special enzyme was blocked. However, this h-Probe was extended using nPfu special enzyme, upon the structural change of the template DNA, from a hairpin to a linear structure, in the presence of the target miRNA. The miRNA-hybridized template DNA sequence was cleaved by a duplex-specific nuclease (DSN), which cleaved the DNA from the RNA-DNA hybrid, thereby allowing the target miRNA to be recycled. Primer extension using nPfu special enzyme produced pyrophosphate when nucleotide triphosphate was incorporated into the DNA; this pyrophosphate was sensed in terms of a color change, from pink to colorless, when using pp Probe, a probe developed previously by our group. This novel system for the colorimetric detection of target miRNA operated with high sensitivity (LOD = 132 aM) and selectivity, with the whole detection process requiring only 30 min. Furthermore, this system could also detect miRNA fluorimetrically with similar sensitivity (LOD = 105 aM), highlighting the dual-sensing properties of pp Probe. This unique, extremely simple, and rapid system for the detection of miRNA through a highly sensitive color change would presumably be useful in applications requiring point-of-care detection.

Programmable DNA Circuits for Flexible and Robust Exciton-Plasmon Interaction-Based Photoelectrochemical Biosensing

DNA circuits as one of the dynamic nanostructures can be rationally designed and show amazing geometrical complexity and nanoscale accuracy, which are becoming increasingly attractive for DNA entropy-driven amplifier design. Herein, a novel and elegant exciton-plasmon interaction (EPI)-based photoelectrochemical (PEC) biosensor was developed with the assistance of a programmable entropy-driven DNA amplifier and superparamagnetic nanostructures. Low-abundance miRNA-let-7a as a model can efficiently initiate the operation of the entropy-driven DNA amplifier, and the released output DNAs can open the partially hybridized double-stranded DNA anchored on Fe₃O₄@SiO₂ particles. The liberated Au nanoparticles (NPs)-cDNA can completely hybridize with CdSe/ZnS quantum dots (QDs)-cDNA-1 and result in proportionally decreased photocurrent of CdSe/ZnS QDs-cDNA-1. This unique entropy-driven amplification strategy is beneficial for reducing the reversibility of each step reaction, enables the base sequence invariant and the reaction efficiency improvement, and exhibits high thermal stability and specificity as well as flexible design. These features grant the PEC biosensor with ultrasensitivity and high selectivity. Also, instead of solid-liquid interface assembly for conventional EPI-based PEC biosensors, herein, DNA hybridization in the solution phase enables the improved hybridization efficiency and sensitivity. In addition, superparamagnetic Fe₃O₄@SiO₂ particles further ensure the enhancement of the selectivity and reliability of the as-designed PEC biosensor. Particularly, this single-step electrode modification procedure evidently improves the electrode fabrication efficiency, reproducibility, and stability.

MoSe2/CdSe Heterojunction Destruction by Cation Exchange for Photoelectrochemical Immunoassays with a Controlled-Release Strategy

Herein, a split-type immunoassay strategy instigated by cation exchange (CE) and changing the capacity of an electron donor in an electrolyte solution is optimized, namely, for differentiating the biological-specific binding assay and photoelectrochemical (PEC) analysis. MoSe₂/CdSe, a Z-scheme heterojunction with efficient visible light absorption and a low recombination of carriers, is used as a photoelectrode substrate. Silver ions (Ag⁺) as the initiator of CE are generated by the acidolysis of evenly loaded silver nanoparticles on mesoporous silica nanospheres (MSNs). The theoretical calculation and experimental results confirm that Ag⁺ replaces Cd²⁺ in CdSe and retains the crystal structure of MoSe₂. However, this behavior destroys the perfectly matched heterojunction structure and introduces defects, which led to the reduction of the photocurrent response. In addition, ascorbate oxidase in combination with MSNs can be used as a consumptive agent of the electron donor, which further improves the sensitivity and reliability of the sensor. As a proof of principle, neuron-specific enolase was applied to elucidate the potential application of the PEC immunoassay in clinical diagnosis, and the obtained linear range of the sensor was from 0.0001 to 100 ng/mL with a detection limit of 28 fg/mL (S/N = 3).

A novel self-enhanced carbon nitride platform coupled with highly effective dual-recycle strand displacement amplifying strategy for sensitive photoelectrochemical assay

In this work, a novel self-enhanced photoelectric active material, Na⁺, K⁺-codoped carbon nitride (NaKCN), was synthesized for constructing sensitive photoelectrochemical (PEC) biosensor to detect target miRNA-182-5p. Ingeniously, the NaKCN displayed glucose oxidase (GOx)-mimicking photocatalytic property, which catalyzed glucose to in situ generate high levels of H₂O₂ as its own electron donor for enhancing photocurrent. Moreover, the Na⁺, K⁺ co-doping could reduce energy gap of carbon nitride material, effectively improving the optical absorptivity and photocatalytic efficiency. Additionally, a novel highly effective dual-recycle TSD amplifying strategy was constructed to convert a small amount of target into plentiful two types of output DNAs labeling with sensitizer MB to enhance photocurrent of NaKCN. As a result, this PEC biosensor achieved a high sensitivity with low detection limit of 3.3 fM, which provided a new avenue for improving sensitivity of bioanalysis and diagnosis of diseases.

A dual-model "on-super off" photoelectrochemical/ratiometric electrochemical biosensor for ultrasensitive and accurate detection of microRNA-224

A dual-model "on-super off" photoelectrochemical (PEC)/ratiometric electrochemical (EC) biosensor based on signal enhancing and quenching combining three-dimensional (3D) DNA walker strategy was designed for the ultrasensitive and accurate detection of microRNA-224 (miRNA-224). The "signal on" PEC state was achieved by methylene blue labeled hairpin DNA (MB-DNA) for sensitizing CdS QDs. Then numerous transformational ferrocene labeled DNAs (Fc-DNAs) converted by target-induced 3D DNA walker amplification with the help of Ag nanocubes (NCs) label DNA (Ag-DNA) were introduced to open hairpin MB-DNA. Such configuration change would relocate the sensitizer MB and the quencher Fc, whereas energy transfer placed between Ag NCs and CdS QDs, thereby significantly quenching the PEC signal to obtain "super off" state. Meanwhile, these changes resulted in a decreased oxidation peak current of MB (I_MB) and an increased that of Fc (I_Fc). MiRNA-224 was also detected on basis of the dual-signaling EC ratiometric method for complementary PEC detection. Benefiting from different mechanisms and relatively independent signal transduction, this approach not only avoided interference from difficult assembly but also outstandingly increased sensitivity by distance-controllable signal enhancing and quenching strategies. As a result, the detection ranges of 0.1-1000 fM with a low detection limit of 0.019 fM for PEC, and 0.52 to 500 fM with a low detection limit of 0.061 fM for EC, were obtained for miRNA-224, which opens a new avenue for designing numerous elegant biosensors with potential utility in bioanalysis and early disease diagnosis.