A Label-Free Photoelectrochemical Biosensor Based on CRISPR/Cas12a System Responsive Deoxyribonucleic Acid Hydrogel and "Click" Chemistry

CRISPR/Cas12a-based transition state molecular switch for low-background detection of HPV-16 on a microfluidic platform

Human papillomavirus type 16 (HPV-16) is a high-risk oncogenic subtype of HPV, strongly associated with the pathogenesis of multiple cancers. Researchers have developed many detection methods for HPV-16, among which, the detection method based on microfluidic has the characteristics of high efficiency and high sensitivity. However, non-specific adsorption remains a critical challenge, often leading to elevated background signals. Here, we propose an On-Chip assay integrated by transition state molecular switch based on CRISPR-Cas12a (OCTMS-CRISPR) for stable, sensitive, and low-background fluorescence detection of HPV-16. This system leverages a highly integrated molecular switch and Cas12a to perform dual-screening, while the dissociation products of the molecular switch activate trans-cleavage activity. Our data suggest that OCTMS-CRISPR suppresses background signals on microfluidic chip while maintaining the specificity and sensitivity of trans-cleavage. For demonstration, we detected five HPV subtypes and base mismatches at varying positions and quantities. The LOD can reach 7.64 pM (average fluorescence intensity) and 9.91fM (pixel counting), showing great potential in the field of biosensing and DNA chips.

"Turn-on" aptamer-immune lateral flow assays for the detection of small molecule targets based on CHA-assisted and CRISPR/Cas12a mediated signal transduction and amplification

Lateral flow assays (LFAs) have emerged as crucial tools for on-site food safety detection due to their simple operation and intuitive detection results. Nevertheless, LFAs for small molecule targets such as pesticides often present a "Turn-off" signal output, which leads to their low sensitivity and the risk of false positives. In this study, a CRISPR/Cas12a system-mediated strategy was employed to convert aptamer signals into the signals of immune LFAs, achieving a "Turn-on" signal output for highly sensitive detection of small molecule targets. The binding of aptamers to targets released the trigger sequence to initiate the catalytic hairpin assembly (CHA) reaction, generating double-stranded DNA, which subsequently activated the CRISPR/Cas12a system to cleave the FAM-labeled Reporter. Eventually, the "Turn-on" visual output of the signal was realized through an anti-6-FAM immune LFAs. The experiment optimized the sample pool preparation, CHA reaction conditions, CRISPR/Cas12a activation parameters, and the assembly process of the LFAs. The limit of detection for procymidone was as low as 0.015 ng/mL, which was 52.67 times more sensitive than those of conventional aptamer-based LFAs without signal amplification strategies. This method exhibits high specificity for procymidone and a recovery rate ranging from 94.00% to 104.20% in vegetable samples, demonstrating excellent stability and practicability.

One-pot synthesized three-way junction based multiple strand displacement amplification for sensitive assay of H5N1 DNA

The rapid and sensitive detection of H5N1, a highly pathogenic avian influenza virus, is crucial for controlling its spread and minimizing its impact on public health. In this study, we developed a novel biosensor based on strand displacement amplification (SDA) coupled with CRISPR/Cas12a for highly sensitive detection of H5N1 DNA. The biosensor utilizes a combination of a three-way junction structure, composed of three hairpins (H1, H2, H3), to initiate amplification through SDA, resulting in the production of numerous activators. These activators then trigger CRISPR/Cas12a's collateral cleavage activity, which generates a detectable fluorescence signal. The biosensor demonstrated a linear detection range from 100 fM to 800 pM, with a detection limit as low as 72.87 fM. The optimized biosensor exhibited excellent sensitivity, high specificity, and a broad dynamic range, making it a promising tool for the early detection of H5N1 DNA in complex biological samples. Additionally, the use of CRISPR/Cas12a's trans-cleavage activity significantly improved signal amplification and specificity, allowing for more reliable detection compared to traditional methods. The results highlight the advantages of the integrated SDA and CRISPR/Cas12a approach, which addresses the limitations of conventional detection methods, such as low sensitivity, lengthy analysis times, and high costs. The biosensor's ability to perform well in complex sample matrices demonstrates its potential for point-of-care diagnostics, especially in resource-limited settings. Future applications of this technology could extend to the detection of other pathogens, offering a versatile and adaptable platform for disease surveillance and management.

Hybridization chain reaction and CRISPR/Cas12a-integrated biosensor for precise Ago2 detection

This study introduces an innovative electrochemiluminescence (ECL) biosensor for the highly sensitive and specific detection of Argonaute 2 (Ago2) activity. Ago2, a key enzyme in the RNA interference (RNAi) pathway, plays a crucial role in gene regulation, and its dysregulation is associated with diseases such as cancer and viral infections. The biosensor integrates hybridization chain reaction (HCR) amplification and the CRISPR/Cas12a system, leveraging a multi-stage signal amplification strategy. The detection mechanism begins with Ago2-mediated cleavage of a designed hairpin RNA (HP-RNA), releasing single-stranded RNA (ssRNA) that triggers HCR. This amplification step generates long DNA polymers, which serve as activators for the CRISPR/Cas12a system. Cas12a's collateral cleavage activity amplifies the signal further by cleaving a DNA reporter labeled with a ruthenium-based luminophore, enhancing the ECL output. This dual amplification strategy achieves exceptional sensitivity, with a detection limit of 0.126 aM. The biosensor demonstrates excellent specificity, distinguishing Ago2 from other Argonaute proteins, and maintains high reproducibility and stability, retaining 94 % of its signal after two weeks of storage. Real-world applicability was confirmed by accurately detecting Ago2 in spiked cell lysates, with recovery rates exceeding 100 %. The combination of HCR, CRISPR/Cas12a, and ECL establishes a robust platform for biomarker detection, offering superior sensitivity and adaptability for clinical diagnostics, disease monitoring, and therapeutic evaluation. This biosensor represents a significant advancement in the development of next-generation diagnostic tools.

N-Deficient B-Doped g-C3N4/CdS Heterojunction-Based PEC-FL Biosensor Assisted by CRISPR-Cas12a System for Ultrasensitive Determination of microRNA

Near-infrared light (NIR)-driven photoelectrochemical (PEC) processes are mainly faced with the limitation of weak photocurrents. Here, N-deficient B-doped g-C3N4/CdS (NB-g-C3N4/CdS) is proposed to construct a NIR-driven PEC biosensor assisted by CRISPR-Cas12a system for the determination of microRNA-21 (miRNA-21). To promote the optical absorption as well as the separation of photogenerated electrons and holes of g-C3N4, NB-g-C3N4/CdS is constructed via engineering the electronic and band structure in terms of N defect, B doping, and heterojunction, achieving high PEC performance. To obtain the high luminescence efficiency for exciting NB-g-C3N4/CdS under NIR, the core-shell NaYF4:Yb3+, Tm3+@NaYF4 upconversion nanoparticles (UCNPs) with repaired defects are prepared. Furthermore, the rolling circle amplification (RCA)-assisted CRISPR-Cas12a system is integrated to fragment the DNA on UCNPs, achieving sensitive detection of miRNA-21. On the one hand, the uncleavaged signal probes on UCNPs combined with NB-g-C3N4/CdS through π-π stacking interaction, generating photocurrents under the irradiation of NIR. On the other hand, the cleavaged signal probes which cannot link with NB-g-C3N4/CdS exhibited the fluorescence (FL) signals. The proposed PEC-FL dual-mode biosensor provides a mutual authentication of testing results and demonstrates ultrasensitivity (the detection limit of 1.1 fM for PEC mode and 7.0 fM for FL mode) and excellent specificity, which is promising in the clinical analysis of miRNA.

CRISPR-Cas12a2-based rapid and sensitive detection system for target nucleic acid

Infectious diseases are extremely important public health issues, where the design of effective, rapid, and convenient detection platforms is critical. In this study, we coupled SuCas12a2, a novel Cas12 family RNA-targeting nuclease, with conventional PCR and recombinase polymerase amplification (RPA), respectively, to develop novel detection approaches, named PCR-SuCas12a2 and RPA-SuCas12a2. SuCas12a2 possesses collateral cleavage activity and cuts the additional single-stranded RNA (ssRNA) added to the reaction system once the ternary complex RNA-SuCas12a2-CRISPR RNA (crRNA) is formed. SuCas12a2 is specifically activated, where the cleaved fluorescent-labeled probes release fluorescent signals, with the strength of the fluorescent signal being proportional to the concentration of nucleic acids specifically bound to crRNA. Simultaneous transcription and SuCas12a2 detection can be performed in a single tube by introducing the T7 promoter sequence into the forward primer. Entamoeba histolytica (E. histolytica) and Mycoplasma pneumoniae (M. pneumoniae) were used as proof specimens to evaluate the performance of the platform. PCR-SuCas12a2 has excellent capabilities, including high specificity with no cross-reactivity from other species and ultra-sensitivity that achieves a detection of one copy per reaction for E. histolytica and M. pneumoniae. However, the sensitivity of the RPA-SuCas12a2 assay was 102 copies per reaction, which was inferior to PCR-SuCas12a2. Clinical samples were obtained from suspected infection patients of E. histolytica and M. pneumoniae, and used to evaluate the systems demonstrated 100 % specificity. The technique shows robust performance and suggests great potential for point-of-care testing of other pathogens to facilitate effective management and control of the spread of diseases.

Self-powered dual-photoelectrode photoelectrochemical aptasensor amplified by hemin/G-quadruplex-based DNAzyme

A self-powered dual-electrode aptasensor was developed for the detection of tumor marker carcinoembryonic antigen (CEA). The composite BiVO4/ZnIn2S4, which is capable of forming a Z-scheme heterojunction, was chosen as the photoanode, and the AuNP/CuBi2O4 complex was chosen as the photocathode in photoelectrochemical (PEC) detection. The experiments showed that the constructed self-powered dual-electrode system had a good photoelectric response to white light, and the photocurrent signal of the photocathode was significantly enhanced under the influence of the photoanode. The introduction of G-quadruplex/hemin DNAzyme through aptamer recognition resulted in the generation of insoluble species through catalytic reaction, which led to a significant decrease in the photocurrent, and achieved a highly sensitive detection of the target CEA with a detection limit of 0.021 pg/mL. At the same time, the developed photocathode detection exhibited good selectivity and could effectively avoid interference, making it suitable for real sample analysis. It is expected that this study can facilitate the application of PEC sensors in point-of-care (POC) diagnosis for life analysis.

Application of smart-responsive hydrogels in nucleic acid and nucleic acid-based target sensing: A review

In recent years, nucleic acid-related sensing and detection have become essential in clinical diagnostics, treatment and genotyping, especially in connection with the Human Genome Project and the COVID-19 pandemic. Many traditional nucleic acid-related sensing strategies have been employed in analytical chemistry, including fluorescence, colorimetric and chemiluminescence methods. However, their key limitation is the lack of understanding of the interaction during analysis, particularly at the 3D matrix level close to biological tissue. To address this issue, smart-responsive hydrogels are increasingly used in biosensing due to their hydrophilic and biocompatible properties. By combining smart-responsive hydrogels with traditional nucleic acid-related sensing, biological microenvironments can be mimicked, and targets can be easily accessed and diffused, making them ideal for nucleic acid sensing. This review focuses on utilizing smart-responsive hydrogels for nucleic acid-related sensing and detection, including nucleic acid detection, other nucleic acid-based analyte detection and nucleic acid-related sensing platforms applying nucleic acid as sensing tools in hydrogels. Additionally, the analytical mechanisms of smart-responsive hydrogels with the combination of various detection platforms such as optical and electrochemical techniques are described. The limitations of using smart-responsive hydrogels in nucleic acid-related sensing and proposed possible solutions are also discussed. Lastly, the future challenge of smart-responsive hydrogels in nucleic acid-related sensing is explored. Smart-responsive hydrogels can be used as biomimetic materials to simulate the extracellular matrix, achieve biosensing, and exhibit great potential in nucleic acid-related sensing. They serve as a valuable complement to traditional detection and analytical methods.

An Entropy-Driven Multipedal DNA Walker Microsensor for In Situ Electrochemical Detection of ATP

Microelectrode- and nanoelectrode-based electrochemistry has become a powerful tool for the in situ monitoring of various biomolecules in vivo. However, two challenges limit the application of micro- and nanoelectrodes: the difficulty of highly sensitive detection of nonelectroactive molecules and the specific detection of target molecules in complex biological environments. Herein, we propose an electrochemical microsensor based on an entropy-driven multipedal DNA walker for the highly sensitive and selective detection of ATP. An ATP aptamer was immobilized on the microelectrode surface to form the DNA walker track for selective ATP recognition. Multiple walking "legs" were attached to quantum dots to create the multipedal DNA walker. ATP was selectively captured by the ATP aptamer, triggering the autonomous movement of the multipedal DNA walker on the microelectrode interface, which brought methylene blue (MB) closer to the microelectrode interface, realizing a cascade signal amplification. Additionally, ATP release induced by hypotonic conditions in BV2 cells was successfully monitored, indicating that increased cell volume enhances ATP release. This multipedal DNA walker microsensor offers a novel strategy for in situ, highly sensitive, and selective monitoring of nonelectroactive biomolecules in vivo, which is crucial for investigating the neurochemical processes involved in neurological diseases.

CRISPR/Cas12a-Sheared ZIF-Based Heterojunction to Allow Polarity-Switchable Photoelectrochemical and Nanozyme-Enabled Colorimetric Dual-Modal Biosensing

Modulating the migration of interfacial carriers in heterojunctions is critical for driving the signal response of high-performance optical biosensors. In this study, a polarity-switchable photoelectrochemical (PEC) and nanozyme-enabled colorimetric dual-modal biosensor is designed to modulate the interfacial carrier migration of the zeolitic imidazolate framework (ZIF)-based heterojunction by exploiting stem-loop DNA and the CRISPR/Cas12a system. Specifically, ZIF-hemin (ZIF-Hemin) is assembled at the CdSe/NH2-rGO interface via stem-loop DNA to form a ZIF-based heterojunction. Stem-loop DNA with a reinforcing rib effect enhances binding and accelerates the interfacial carrier migration of the heterojunction. In the presence of the target Cry1Ab, the CRISPR/Cas12a system is activated to shear the ZIF-based heterojunction, resulting in the disintegration of the heterojunction and the disappearance of interfacial carrier migration. At this point, ZIF-Hemin is released from the CdSe/NH2-rGO interface, with the photocurrent switching from the anode to the cathode. Meanwhile, due to its rich accessible active sites, the released ZIF-Hemin nanosheet shows high peroxidase-like catalytic activity and generates colorimetric signals. The dual-modal biosensor demonstrates excellent performance in selectivity and sensitivity, with low detection limits of 0.05 pg mL-1 (PEC) and 0.4 pg mL-1 (colorimetric). This work provides a general strategy to improve the performance of optical biosensors by modulating the migration of interfacial carriers in heterojunctions.

Signal amplification strategies in photoelectrochemical sensing of carcinoembryonic antigen

Early detection of cancer markers is critical for cancer diagnosis and cancer therapy since these markers may indicate cancer risk, incidence, and disease prognosis. Carcinoembryonic antigen (CEA) is a type of non-specific and broad-spectrum cancer biomarker commonly utilized for early cancer diagnosis. Moreover, it serves as an essential tool to assess the efficacy of cancer treatment and monitor tumor recurrence as well as metastasis, thus garnering significant attention for precise and sensitive CEA detection. In recent years, photoelectrochemical (PEC) techniques have emerged as prominent methods in CEA detection due to the advantages of PEC, such as simple equipment requirements, cost-effectiveness, high sensitivity, low interference from background signals, and easy of instrument miniaturization. Different signal amplification methods have been reported in PEC sensors for CEA analysis. Based on these, this article reviews PEC sensors based on various signal amplification strategies for detection of CEA during the last five years. The advantages and drawbacks of these sensors were discussed, as well as future challenges.

Spatial-resolved and self-calibrated 3D-printed photoelectrochemical biosensor engineered by multifunctional CeO2/CdS heterostructure for immunoassay

A spatial-resolved and self-calibrated photoelectrochemical (PEC) biosensor has been fabricated by a multifunctional CeO2/CdS heterostructure, achieving portable and sensitive detection of carcinoembryonic antigen (CEA) using a homemade 3D printing device. The CeO2/CdS heterostructure with matched band structure is prepared to construct the dual-photoelectrodes to improve the PEC response of CeO2. In particular, as the photoactive nanomaterial, the CeO2 also plays the role of peroxidase mimetic nanozymes. Therefore, the catalytic performance of CeO2 with different morphologies (e.g., nano-cubes, nano-rods and nano-octahedra) have been studied, and CeO2 nano-cubes (c-CeO2) achieve the optimal catalytic activity. Upon introducing CEA, the sandwich-type immunocomplex is formed in the microplate using GOx-AuNPs-labeled second antibody as detection antibody. As a result, H2O2 can be produced from the catalytic oxidization of glucose substrate by GOx, which is further catalyzed by CeO2 to form •OH, thus in situ etching CdS and decreasing the photocurrents. The self-calibration is achieved by the dual-channel photoelectrodes on the homemade 3D printing device to obtain the photocurrents ratio, thus effectively normalizing the fluctuations of external factors to enhance the accuracy. This integrated biosensor with a detection limit as low as 0.057 ng mL-1 provides a promising way for ultrasensitive immunoassay in clinic application in complex environments.

Cu2O-Mediated Heterojunction Conversion from Dual Type II to Dual Z-Scheme: Its Application in Photoelectric-Colorimetric Dual-Mode Detection of Fat Mass and Obesity-Associated (FTO) Protein

Although the construction of heterojunction has been used in photoelectrochemical (PEC) biosensors, their potential for tunable optical properties has not been deeply explored. Based on the fact that a type-II heterojunction and Z-scheme heterojunction have the same energy band structure, effective alteration of the electron transfer pathway has been achieved by introducing unique photoactive materials into the system and exploiting the interactions between the photomaterials. Based on this, we reported a novel polarity-switchable dual-mode sensor for fat mass and obesity-associated (FTO) protein analysis. Specifically, the MgIn2S4/Bi2MoO6/Bi2S3 dual type-II heterojunction was used as the sensing interface in concert with the rolling circle amplification, CRISPR/Cas12, and terminal DNA transfer enzyme multiamplification strategies, and finally, Cu2O was captured at the sensing interface. Due to the matched energy band, the introduction of Cu2O effectively changed the electron transfer pathway and realized the conversion from a dual type-II heterojunction to a dual Z-scheme heterojunction. It caused the switch of the photocurrent from the anode to the cathode. The developed PEC method showed high sensitivity and selectivity for FTO protein detection in the range of 0.0005-500 μg/L. In addition, based on the peroxidase-like activity of Cu2O to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2, the electrode system also achieved the colorimetric detection of FTO protein using the naked eye with the change of the color of the detection solution from colorless to blue. The detection range was from 0.05 to 500 μg/L. This work developed a photoelectrochemical-colorimetric biosensing platform with consciously designed semiconductor structures, revealing the potential of semiconductor-structured transformations in future sensing fields.

CRISPR-Driven Biosensors: A New Frontier in Rapid and Accurate Disease Detection

This comprehensive review delves into the advancements and challenges in biosensing, with a strong emphasis on the transformative potential of CRISPR technology for early and rapid detection of infectious diseases. It underscores the versatility of CRISPR/Cas systems, highlighting their ability to detect both nucleic acids and non-nucleic acid targets, and their seamless integration with isothermal amplification techniques. The review provides a thorough examination of the latest developments in CRISPR-based biosensors, detailing the unique properties of CRISPR systems, such as their high specificity and programmability, which make them particularly effective for detecting disease-associated nucleic acids. While the review focuses on nucleic acid detection due to its critical role in diagnosing infectious diseases, it also explores the broader applications of CRISPR technology in detecting non-nucleic acid targets, thereby acknowledging the technology's broader potential. Additionally, the review identifies existing challenges, such as the need for improved signal amplification and real-world applicability, and offers future perspectives aimed at overcoming these hurdles. The ultimate goal is to advance the development of highly sensitive and specific CRISPR-based biosensors that can be used widely for improving human health, particularly in point-of-care settings and resource-limited environments.

CRISPR/Cas12a cleavage triggered nanoflower for fluorescence-free and target amplification-free biosensing of ctDNA in the terahertz frequencies

The detection of tumor biomarkers in liquid biopsies requires high sensitivity and low-cost biosensing strategies. However, few traditional techniques can satisfy the requirements of target amplification-free and fluorescence-free at the same time. In this study, we have proposed a novel strategy for ctDNA detection with the combination of terahertz spectroscopy and the CRISPR/Cas12 system. The CRISPR/Cas12a system is activated by the target ctDNA, resulting in a series of reactions leading to the formation of an Au-Fe complex. This complex is easily extracted with magnets and when dropped onto the terahertz metamaterial sensor, it can enhance the frequency shift, providing sensitive and selective sensing of the target ctDNA. Results show that the proposed terahertz biosensor exhibits a relatively low detection limit of 0.8 fM and a good selectivity over interference species. This detection limit is improved by three orders of magnitude compared with traditional biosensing methods using terahertz waves. Furthermore, a ctDNA concentration of 100 fM has been successfully detected in bovine serum (corresponding to 50 fM in the final reaction system) without amplification.

Primer exchange reaction assisted CRISPR/Cas9 cleavage for detection of dual microRNAs with electrochemistry method

An electrochemical sensor assisted by primer exchange reaction (PER) and CRISPR/Cas9 system (PER-CRISPR/Cas9-E) was established for the sensitive detection of dual microRNAs (miRNAs). Two PER hairpin (HP) were designed to produce a lot of extended PER products, which could hybridize with two kinds of hairpin probes modified on the electrode and initiate the cleavage of two CRISPR/Cas9 systems guided by single guide RNAs (sgRNAs) with different recognition sequences. The decrease of the two electrochemical redox signals indicated the presence of dual-target miRNAs. With the robustness and high specificity of PER amplification and CRISPR/Cas9 cleavage system, simultaneous detection of two targets was achieved and the detection limits for miRNA-21 and miRNA-155 were 0.43 fM and 0.12 fM, respectively. The developed biosensor has the advantages of low cost, easy operation, and in-situ detection, providing a promising platform for point-of-care detection of multiple miRNAs.

Development of a label-free photoelectrochemical immunosensor for novel astrovirus detection

Since 2017, an infectious goose gout disease characterized by urate precipitation in viscera, mainly caused by novel goose astrovirus (GoAstV) infection, has emerged in the main goose-producing region of China. The current challenge in managing goose gout disease is largely due to the absence of a rapid and efficient detection method for the GoAstV pathogen. Notably, the potential application of immunosensors in detecting GoAstV has not yet been explored. Herein, a label-free PEC immunosensor was fabricated by using purchased TiO2 as the photoactive material and antibody against GoAstV P2 proteins as the specific recognition element. First, we successfully expressed the capsid spike domain P2 protein of ORF2 from GoAstV CHSH01 by using the pET prokaryotic expression system. Meanwhile, the polyclonal antibody against GoAstV capsid P2 protein was produced by purified protein. To our knowledge, this is the first establishment and preliminary application of the label-free photoelectrochemical immunosensor method in the detection of AstV. The PEC immunosensor had a linear range of 1.83 fg mL-1 to 3.02 ng mL-1, and the limit of detection (LOD) was as low as 0.61 fg mL-1. This immunosensor exhibited high sensitivity, great specificity, and good stability in detecting GoAstV P2 proteins. To evaluate the practical application of the immunosensor in real-world sample detection, allantoic fluid from goose embryos was collected as test samples. The results indicated that of the eight positive samples, one false negative result was detected, while both negative samples were accurately detected, suggesting that the constructed PEC immunosensor had good applicability and practical application value, providing a platform for the qualitative detection of GoAstV.

Multifunctional Supramolecular Hydrogel Modulated Heterojunction Interface Carrier Transport Engineering Facilitates Sensitive Photoelectrochemical Immunosensing

Highly responsive interface of semiconductor nanophotoelectrochemical materials provides a broad development prospect for the identification of low-abundance cancer marker molecules. This work innovatively proposes an efficient blank WO3/SnIn4S8 heterojunction interface formed by self-assembly on the working electrode for interface regulation and photoregulation. Different from the traditional biomolecular layered interface, a hydrogel layer containing manganese dioxide with a wide light absorption range is formed at the interface after an accurate response to external immune recognition. The formation of the hydrogel layer hinders the effective contact between the heterojunction interface and the electrolyte solution, and manganese dioxide in the hydrogel layer forms a strong competition between the light source and the substrate photoelectric material. The process effectively improves the carrier recombination efficiency at the interface, reduces the interface reaction kinetics and photoelectric conversion efficiency, and thus provides strong support for target identification. Taking advantage of the process, the resulting biosensors are being explored for sensitive detection of human epidermal growth factor receptor 2, with a limit of detection as low as 0.037 pg/mL. Also, this study contributes to the advancement of photoelectrochemical biosensing technology and opens up new avenues for the development of sensitive and accurate analytical tools in the field of bioanalysis.

Stimuli-responsive incremental DNA machine auto-catalyzed CRISPR-Cas12a feedback amplification permits ultrasensitive molecular diagnosis of esophageal cancer-related microRNA

Development of new diagnostic methods is essential for disease diagnosis and treatment. In this work, we present a stimuli-responsive incremental DNA machine auto-catalyzed CRISPR-Cas12a (SRI-DNA machine/CRISPR-Cas12a) feedback amplification for ultrasensitive molecular detection of miRNA-21, which is an important biomarker related closely to the initiation and development of cancers, such as esophageal cancer. Strategically, the powerful SRI-DNA machine and efficient trans-cleavage activity of the CRISPR-Cas12a system are ingeniously integrated via a rationally designed probe termed as stem-elongated functional hairpin probe (SEF-HP). The SRI-DNA machine begins with the target miRNA, the trigger of the reaction, binding complementarily to the SEF-HP, followed by autonomously performed mechanical strand replication, cleavage, and displacement circuit at multiple sites. This conversion process led to the amplified generation of numerous DNA activators that are complementary with CRISPR RNA (CrRNA). Once formed the DNA activator/CrRNA heteroduplex, the trans-cleavage activity of the CRISPR-Cas12a was activated to nonspecific cleavage of single-stranded areas of a reporter probe for fluorescence emission. Under optimal conditions, the target miRNA can be detected with a wide linear range and an excellent specificity. As a proof-of-concept, this SRI-DNA machine/CRISPR-Cas12a feedback amplification system is adaptable and scalable to higher-order artificial amplification circuits for biomarkers detection, highlighting its promising potential in early diagnosis and disease treatment.

Rapid detection of melamine by DNA Walker mediated SERS sensing technique based on signal amplification function

A new method is proposed for detecting typical melamine dopants in food using surface-enhanced Raman scattering (SERS) biosensing technology. Melamine specific aptamer was used as the identification probe, and gold magnets (AuNPs@MNPs) and small gold nanoparticles (AuNPs@MBA) were used as the basis for Raman detection. The Raman signal of the detection system can directly detect melamine quantitatively. Under optimized conditions, the detection of melamine was carried out in the low concentration range of 0.001-500 mg/kg, the enhancement factor (EF) was 2.3 × 107, and the detection limit was 0.001 mg/kg. The method is sensitive and rapid, and can be used for the rapid detection of melamine in the field environment.

Thermo-sensitive PLGA-PEG-PLGA hydrogel for sustained release of EGF to inhibit cervical cancer recurrence

Overexpression of epidermal growth factor receptor (EGFR) in cancer is a key cause of recurrence of cervical cancer (CC). Although the EGF-EGFR pathway has been studied for decades, preventing tumor growth and recurrence caused by peripheral EGF remains a great challenge. In this work, a strategy is proposed to reduce the stimulation of high concentration EGF on tumor growth by using a thermo-sensitive hydrogel. The hydrogel is a triblock copolymer composed of polyethylene glycol (PEG) and poly (lactide glycolide) (PLGA). Based on the excellent temperature sensitivity, carrier capacity, swelling property and biocompatibility, the hydrogel can absorb the liquid around the tumor by injection and release EGF continuously at low concentration. The inhibitory effect of hydrogel on tumor growth is fully confirmed by an implanted tumor mouse model with human cervical cancer cell lines (HeLa) using triple-immunodeficient NCG mice. Compared with free EGF, the EGF-loaded hydrogel can hardly induce surface plasmon resonance (SPR) response, which proves that hydrogel can effectively weaken cytoskeleton rearrangement and inhibit cell migration by continuously releasing low concentration EGF. In addition, the EGF-loaded hydrogel can reduce cell proliferation by delaying the progress of cell cycle progression. Taken together, the hydrogel can effectively protect tumor microenvironment from the stimulation of high concentration EGF, delay cancer cellular processes and tumor growth, and thus providing an approach for inhibiting tumor recurrence of CC.

MicroRNA Sensors Based on CRISPR/Cas12a Technologies: Evolution From Indirect to Direct Detection

MicroRNA (miRNA) has emerged as a promising biomarker for disease diagnosis and a potential therapeutic targets for drug development. The detection of miRNA can serve as a noninvasive tool in diseases diagnosis and predicting diseases prognosis. CRISPR/Cas12a system has great potential in nucleic acid detection due to its high sensitivity and specificity, which has been developed to be a versatile tool for nucleic acid-based detection of targets in various fields. However, conversion from RNA to DNA with or without amplification operation is necessary for miRNA detection based on CRISPR/Cas12a system, because dsDNA containing PAM sequence or ssDNA is traditionally considered as the activator of Cas12a. Until recently, direct detection of miRNA by CRISPR/Cas12a system has been reported. In this review, we provide an overview of the evolution of biosensors based on CRISPR/Cas12a for miRNA detection from indirect to direct, which would be beneficial to the development of CRISPR/Cas12a-based sensors with better performance for direct detection of miRNA.

CRISPR/Cas systems combined with DNA nanostructures for biomedical applications

DNA nanostructures are easy to design and construct, have good biocompatibility, and show great potential in biosensing and drug delivery. Numerous distinctive and versatile DNA nanostructures have been developed and explored for biomedical applications. In addition to DNA nanostructures that are completely assembled from DNA, composite DNA nanostructures obtained by combining DNA with other organic or inorganic materials are also widely used in related research. The CRISPR/Cas system has attracted great attention as a powerful gene editing technology and is also widely used in biomedical diagnosis. Many researchers are committed to exploring new possibilities by combining DNA nanostructures with CRISPR/Cas systems. These explorations provide support for the development of new detection methods and cargo delivery pathways, provide inspiration for improving relevant gene editing platforms, and further expand the application scope of DNA nanostructures and CRISPR/Cas systems. This paper mainly reviews the design principles and biomedical applications of CRISPR/Cas combined with DNA nanostructures based on the types of DNA nanostructures. Finally, the application status, challenges and development prospects of CRISPR/Cas combined with DNA nanostructures in detection and delivery are summarized. It is expected that this review will enable researchers to better understand the current state of the field and provide insights into the application of CRISPR/Cas systems and the development of DNA nanostructures.

MscI restriction enzyme cooperating recombinase-aided isothermal amplification for the ultrasensitive and rapid detection of low-abundance EGFR mutations on microfluidic chip

The detection of low-abundance mutation genes of the epidermal growth factor receptor (EGFR) exon 21 (EGFR L858R) plays a crucial role in the diagnosis of non-small cell lung cancer (NSCLC), as it enables early cancer detection and facilitates the development of treatment strategies. A detection platform was developed by combining the MscI restriction enzyme with the recombinase-aided isothermal amplification (RAA) technique (MRE-RAA). During the RAA process, "TGG^CCA" site of the wild-type genes was cleaved by the MscI restriction enzyme, while only the low-abundance mutation genes underwent amplification. Notably, when the RAA product was combined with CRISPR-Cas system, the sensitivity of detecting the EGFR L858R mutation increased by up to 1000-fold for addition of the MscI restriction enzyme. This achievement marked the first instance of attaining an analytical sensitivity of 0.001%. Furthermore, a disk-shaped microfluidic chip was developed to automate pretreatment while concurrently analyzing four blood samples. The microfluidic features of the chip include DNA extraction, MRE-RAA, and CRISPR-based detection. The fluorescence signal is employed for detection in the microfluidic chip, which is visible to the naked eye upon exposure to blue light irradiation. Furthermore, this platform has the capability to facilitate early diagnosis for various types of cancer by enabling high-sensitivity detection of low-abundance mutation genes.

Mini crRNA-mediated CRISPR/Cas12a system (MCM-CRISPR/Cas12a) and its application in RNA detection

Some non-coding RNAs are abnormally expressed during the occurrence and development of diseases, so it is necessary to develop analytical methods that can specifically and sensitively detect them. In typical CRISPR/Cas12a system, a complete crRNA that can recognize single-stranded or double-stranded DNA is necessary to activate its trans-cleavage activity, which limits its direct application in RNA detection. Here, we prospectively find that slicing the facilitated crRNA in the typical CRISPR/Cas12a system at a fitted site did not affect its trans-cleavage activity, and a mini crRNA-mediated CRISPR/Cas12a system (MCM-CRISPR/Cas12a) was proposed based on this. This system can detect non-coding RNA to pM-level (10 pM for miRNA-21). To expand the application of this system, we combined it with HCR and CHA to establish a detection platform for non-coding RNA. The results show that the proposed method can specifically detect RNA to fM-level (2.5 fM for miRNA-21, 8.98 fM for miR-128-3p, and 81.6 fM for lncRNA PACER). The spiked recovery rates of miRNA-21, miR-128-3p, and lncRNA PACER in normal human serum were in range from 104.7 to 109.4 %, indicating the proposed method owns good applicability. In general, this MCM-CRISPR/Cas12a system further breaks the limitations of the typical CRISPR/Cas12a system that cannot be directly used for non-coding RNA detection. Besides, its combination with HCR and CHA achieves highly sensitive detection of non-coding RNA.

"One-to-many" signal-output strategy-based CRISPR/Cas12a system for sensitive label-free fluorescence detection of HBV-DNA

Although CRISPR/Cas12a systems significantly enhance the analytical accuracy and flexibility of fluorescent biosensors, their sensitivity is limited by traditional "one-to-one" mediation types and ineffective signal-output turnover routes. Herein, we demonstrate a "one-to-many" signal-output strategy-based CRISPR/Cas12a systems resembling a "seaweed" to enhance the sensitivity. Based on dendrimer DNA from high-dimensional hybridization chain (HCR) of three hairpin-free DNA building blocks, the 3D magnetic DNA machine was created. The HBV-DNA initiates the rolling circle amplification (RCA) reaction and produces DNA nanowires to activate the CRISPR/Cas12a system. The trans-cleavage of the "seaweed root" by CRISPR/Cas12a system left dendrimer DNA in solution, thus, adding SYBR Green I (SG I) to the high-density DNA duplexes, achieving multiple-turnover label-free fluorescence signal output demonstrated and a low LOD (1.502 pM). However, in the absence of target, the blocked RCA failed to activate the CRISPR/Cas12a system, resulting in complete separation from substrate and negligible fluorescence signals. Moreover, the mandatory RCA-based pre-amplification of the DNA activator could efficiently trigger the multiple-turnover trans-cleavage activity of Cas12a. it can cleave one single-stranded linker of "seaweed-like" DNA machine, thereby releasing massive DNA duplex-enriched dendrimer DNA with a "one-to-many" signal-output turnover. By coupling the periodically extended Cas12a activator generated by RCA with hyperbranched DNA duplex by high-dimensional HCR, compact 3D extension structures were formed, achieving high-density fluorescence distribution in focal volume, avoiding signal dilution and ensuring high enhancement. Additionally, spiked recoveries in physiological media exceeded 95%, demonstrating the potential application of such platforms in clinical diagnosis.

Ultrasensitive miRNA Detection Based on Magnetic Upconversion Nanoparticle Enhancement and CRISPR/Cas13a-Driven Signal Amplification

MicroRNAs (miRNAs), a class of small molecules with important regulatory functions, have been widely used in the field of biosensing as biomarkers for the early diagnosis of various diseases. Therefore, it is crucial to develop an miRNA detection platform with high sensitivity and specificity. Here, we have designed a CRISPR/Cas13-based enzymatic cyclic amplification system and regarded the magnetic upconversion nanoparticles (MUCNPs) as a biosensor of outputting the detection signal for the highly sensitive and high-fidelity detection of miRNAs. MUCNPs were composed of UCNPs (fluorescence donors) and Fe3O4@AuNPs (fluorescence acceptors) through double-stranded DNA hybrid coupling. The target miRNA acted as an activator, which could activate the trans-cleavage activity of Cas13a to the well-designed Trigger containing two uracil ribonucleotides (rU) in its loop and trigger a strand displacement reaction to generate a large amount of single-stranded DNA, resulting in the release of the UCNPs from MUCNPs. Benefiting from the high fidelity and high selectivity of CRISPR/Cas13a, the great effect of triggered enzymatic cycle amplification, and the high-intensity luminescent signal of MUCNPs, this method possessed miRNA detection capability with high sensitivity and specificity even in the complex environment with 10% fetal bovine serum (FBS) and a serum sample. Meanwhile, the detection limit could be as low as 83.2 fM. In addition, this method effectively reduced the effect of photobleaching and maintained high stability, which was expected to achieve efficient and sensitive miRNA detection.

A dual-model immobilization-free photoelectrochemical/visual colorimetric bioanalysis based on microemulsion self-assemblies mediated multifunctional signal amplification strategy

Herein, a novel silver ion-loaded gold microemulsion assemblies (Au/Ag+ MAs) mediated multifunctional signal amplification strategy was proposed to construct a sensitive immobilization-free photoelectrochemical (PEC)/colorimetric biosensor for carcinoembryonic antigen (CEA) detection. Through the sandwiched reaction among CEA, the CEA aptamer (DNA1) loaded on the Au nanoparticles (NPs) functionalized iron oxide (Fe3O4) nanospheres and another CEA aptamer (DNA2) immobilized on Au/Ag+ MAs, a complex is formed and acquired by magnetic separation. Then, Au/Ag+ MAs of the complex are disassembled into Au NPs and Ag+ ions driven by an acetone response, and the obtained demulsification solution is transferred to the cadmium sulfide/cadmium telluride (CdS/CdTe) photoactive composites modified electrode. Based on the multiple inhibition functions (blocking effect of oleylamine; energy transfer effect of Au NPs; and electron snatching effect of Ag+), the photocurrent of the electrode decreases obviously, resulting in the ultrasensitive detection of CEA (a detection limit of 16 fg mL-1). Interestingly, the ion-exchange reactions between CdS/CdTe composites and Ag+ ions generate silver sulfide/silver telluride (Ag2S/Ag2Te) composites, and a color change of composites can be distinguished directly, leading to a quick visual detection of CEA. Compared with the traditional single-modal assay for CEA, such dual-modal PEC/colorimetric assay is a more accurate and reliable due to different mechanisms and independent signal conversion. This work will offer a new perspective for the applications of various self-assemblies in PEC bioanalysis.

Chemiluminescence Sensor for miRNA-21 Detection Based on CRISPR-Cas12a and Cation Exchange Reaction

Herein, a chemiluminescence (CL) biosensor based on CRISPR-Cas12a and cation exchange reaction was constructed to detect the biomarker microRNA-21 (miRNA-21). The rolling circle amplification (RCA) reaction was introduced to convert each target RNA strand into a long single-stranded DNA with repeated sequences, which acted as triggers to initiate the transcleavage activity of CRISPR-Cas12a. The activated Cas12a could cleave the biotinylated linker DNA of CuS nanoparticles (NPs) to inhibit the binding of CuS NPs to streptavidin immobilized on the surface of the microplate, which strongly reduced the generation of Cu²⁺ from a cation exchange between CuS NPs and AgNO₃, and thus efficiently suppressed the CL of Cu²⁺-luminol-H₂O₂ system, giving a "signal off" biosensor. With the multiple amplification, the detection limit of the developed sensor for miRNA-21 reached 16 aM. In addition, this biosensor is not only suitable for a professional chemiluminescence instrument but also for a smartphone used as a detection tool for the purpose of portable and low-cost assay. This method could be used to specifically detect quite a low level of miRNA-21 in human serum samples and various cancer cells, indicating its potential in ultrasensitive molecular diagnostics.