Dual-Signal Integrated Aptasensor for Microcystin-LR Detection via In Situ Generation of Silver Nanoclusters Induced by Circular DNA Strand Displacement Reactions

Ultrasensitive Homogeneous Electrochemiluminescence Biosensor for N-Nitrosodimethylamine Detection Based on Vertically-Ordered Mesoporous Silica Film-Modified Electrode and CRISPR/Cas12a-Driven HRCA with Triple Signal Amplification

Herein, we present an innovative electrochemiluminescence (ECL) biosensor for the ultrasensitive detection of N-nitrosodimethylamine (NDMA). The biosensor utilizes a triple signal amplification strategy, combining rolling circle amplification (RCA), CRISPR/Cas12a-driven hyperbranched rolling circle amplification (HRCA), and electrostatic repulsion with size exclusion effects from vertically ordered mesoporous silica film (VMSF)/indium tin oxide (ITO) on double-stranded DNA (dsDNA)-Ru(phen)32+ complexes. In this system, aptamers and circular DNA undergo RCA reactions, followed by the CRISPR/Cas12a-mediated HRCA process, producing abundant dsDNA. The electropositive ECL indicator, namely Ru(phen)32+, was subsequently adsorbed onto the electronegative dsDNA, forming dsDNA-Ru(phen)32+ complexes. These complexes are subjected to electrostatic repulsion and size exclusion by the VMSF-modified ITO electrode, resulting in a lower ECL intensity. Upon introducing NDMA, the aptamer preferentially binds to NDMA, thereby preventing the formation of long dsDNA. This process releases free Ru(phen)32+, which diffuses to the electrode surface through narrow mesoporous channels via electrostatic adsorption. Consequently, an enhanced and strong ECL signal is observed. The integration of VMSF enhances selectivity and sensitivity by excluding larger impurities and promoting the electrostatic repulsion of dsDNA-Ru(phen)32+ complexes near the electrode surface. Additionally, the CRISPR/Cas12a system eliminates the formation of primer dimers and reduces false positives through its unique cis- and trans-cleavage activities. The biosensor demonstrated excellent performance with a linear correlation between the ECL signal and NDMA concentration in the range spanning from 10 pg/mL to 10 μg/mL, achieving a low limit of detection of 5.33 pg/mL. This platform offers a reliable and robust solution for detecting NDMA in complex matrices, making it a promising tool for environmental monitoring, public health, and safety applications.

A dual mode biosensor based on self-enhanced polyfluorene nanomaterial for fluorescence and electrochemiluminescence detection of Tau protein

Dual mode detection can overcome the poor anti-interference ability of single-mode detection, and greatly improve the detection accuracy. Fluorescence/electrochemiluminescence (FL/ECL) dual mode detection combines the advantages of FL and ECL, and has a promising application in bioanalysis. Common FL/ECL dual mode detection used different signal probes. Multiple signal probes inevitably have complex operation and uncontrollable differences between the two modes. In this work, poly [9,9-dioctylfluorenyl-2,7-diyl]-End-capped with 2,5-diphenyl-1,2,4-oxadiazole (PFO) was functionalized by sodium dodecyl sulfate (SDS) and polyethylenimine (PEI), and the resulting PFO-SDS-PEI nanoparticles (PSP NPs) exhibited excellent FL and ECL performance at the same time, so were creatively developed as mono-luminophore-based signal probe for FL/ECL dual-mode detection. The functional reagent SDS can significantly improve the water dispersion of luminophores, and PEI can not only provide amino functional groups for assembling biomolecules, but also significantly enhance the FL and ECL signals of the luminophores. Self-enhanced PSP NPs coupled strand displacement reaction (SDR) mediated by exonuclease Ⅲ (Exo Ⅲ) to achieve FL/ECL dual-mode detection of Tau protein, a biomarker of Alzheimer's disease (AD). The linear ranges for FL and ECL detection were 0.001-500 pg/mL and 0.00001-1.0 pg/mL and the limit of detections were 549.16 ag/mL and 5.45 ag/mL, respectively, showing good application potential. Self-enhanced PSP NPs provided an ideal mono-luminophore-based signal probe for FL/ECL dual-mode detection, and built a new method for detecting AD biomarker.

Fluorescent/colorimetric dual-mode for detecting of MC-LR using bidirectional RCA coupled with CdTe QDs

A fluorescent/colorimetric dual-mode biosensor was designed using CdTe QDs and CRISPR/Cas for the efficient and ultrasensitive detection of microcystin-leucine-arginine (MC-LR). The biosensor mainly activates the trans-cleavage activity of Cas12a through nucleic acid amplification technology, such as bidirectional rolling circle amplification (B-RCA), to perform signal conversion, release Ag+ from the cleaving hairpin, quench QD fluorescence, and perform signal presentation. The biosensor can perform fluorometric and colorimetric detection, enabling rapid field assays. It exhibits enhanced selectivity, increased sensitivity, and greater accuracy. The optimal conditions yield a detection range from 0.05 to 500 nM, with a minimum detectable concentration of 2.137 pM, surpassing the performance of traditional methods. The biosensor can effectively detect MC-LR in actual environmental samples. Overall, this study provided a general detection approach for the application of nucleic acid detection technology to detect trace pollutants in the environment.

Logic Circuits for Intelligent Microcystin Monitoring Based on Aptamer Recognition and Toehold-Mediated Hairpin DNA Self-Assembly

A sensitive fluorescence biosensor was developed for microcystin-LR (MC-LR) detection using H1, H2, and H3 DNA probes as sensing elements. The aptamer in H1 can recognize the target. H2 was labeled with FAM and BHQ. The MC-LR and H1 binding will activate the H2 and H3 self-assemblies through toehold-mediated strand displacement. In the formed products (MC-LR/H1/nH2/nH3), FAM and BHQ will be separated and a high FAM fluorescence signal can be observed for the MC-LR assay. The biosensor is sensitive with a detection limit of 53 fM. We further constructed several logic circuits (AND-AND cascaded circuit, feedforward circuit, and resource allocation circuit) using MC-LR, MC-LA, and MC-YR as the three inputs. The numbers 0 and 1 are used to code the input and output signals. The AND-AND cascade circuit can produce a high output signal only in the (111) input combination. In the feedforward circuit, MC-LR and MC-LA can activate the logic circuit to produce high signals, and MC-YR will inhibit the self-assembly and execute the negative feedforward operation. Through the rational design of the DNA probe hybridizations on four different magnetic beads (MBs), the resource allocation circuit can achieve an intelligent allocation of input information. Our proposed fluorescence biosensor can not only provide a sensitive platform for microcystin detection but also serve as a smart and intelligent logic system for microcystin sensing.

CRISPR/Cas12a dual-mode biosensor for Staphylococcus aureus detection via enzyme-free isothermal amplification

Accurate and reliable detection of Staphylococcus aureus (S. aureus) is essential for preventing infections, particularly in healthcare and food safety contexts. This work presents a novel dual-mode biosensor that integrates the CRISPR/Cas12a system with an enzyme-free isothermal amplification method for detecting S. aureus. Hybridization chain reaction (HCR) and catalytic hairpin assembly (CHA) amplify the aptamer-triggered response, significantly enhancing sensitivity. CRISPR/Cas12a's nuclease activity is utilized in two modes: cis cleavage generates a fluorescence signal, while trans cleavage produces an electrochemical signal, enabling dual-mode detection. The biosensor demonstrates outstanding performance, with a limit of detection (LOD) as low as 5.7 CFU mL-1 in electrochemical mode and 133.7 CFU mL-1 in fluorescence mode, showcasing excellent accuracy, stability, and sensitivity. It has been successfully applied to detecting actual samples, confirming its practical applicability. This innovative approach offers a powerful tool for the swift and precise identification of S. aureus and paves the way for developing next-generation dual-mode biosensors for various analytes. Future research will aim to simplify the detection process further, making it more accessible for use in resource-limited settings.

An electrochemiluminescent imaging strategy based on CRISPR/Cas12a for ultrasensitive detection of nucleic acid

BACKGROUND

Persistent infection with human papillomavirus (HPV) significantly contributes to the development of cervical cancer. Thus, it is urgent to develop rapid and accurate methods for HPV detection. Herein, we present an ultrasensitive CRISPR/Cas12a-based electrochemiluminescent (ECL) imaging technique for the detection of HPV-18 DNA.

RESULT

The ECL DNA sensor array is constructed by applying black hole quencher (BHQ) and polymer dots (Pdots) co-labeled hairpin DNA (hpDNA) onto a gold-coated indium tin oxide slide (Au-ITO). The ECL imaging method involves an incubation process of target HPV-18 with a mixture of crRNA and Cas12a to activate Cas12a, followed by an incubation of the active Cas12a with the ECL sensor. This interaction causes the indiscriminate cleavage of BHQ from Pdots by digesting hpDNA on the sensor surface, leading to the restoration of the ECL signal of Pdots. The ECL brightness readout demonstrates superior performance of the ECL imaging technique, with a linear detection range of 10 fM-500 pM and a limit-of-detection (LOD) of 5.3 fM.

SIGNIFICANCE

The Cas12a-based ECL imaging approach offers high sensitivity and a broad detection range, making it highly promising for nucleic acid detection applications.

Novel Efficient Selenium-Based D-π-A NIR Polymer Dots Anodic Electrochemiluminescence Emitter and Its Application in Simultaneous Detection of Two Pneumonia Pathogens with CdS Quantum Dots

Community-acquired pneumonia (CAP) is a major cause of death in children under 5 years old globally. With Streptococcus pneumoniae (S. pneumoniae) and Mycoplasma pneumoniae (M. pneumoniae) being the main pathogens linked to CAP that requires hospitalization, there is an urgent need for a straightforward, cost-efficient, and highly accurate diagnostic method for immediate and early detection of CAP. In this work, benzo[1,2-c;4,5-c']bis([1,2,5]thiadiazole) (BBT) as π-bridge spacer with the donor unit of poly(9,9-dioctylfluorene) (PF) and the acceptor unit of dithienylbenzoselenadiazole (DBS) has been successfully copolymerized to unprecedentedly prepare novel D-π-A selenium-based polymer dots with efficient NIR electrochemiluminescence (named as Se-Pdots in this work). Se-Pdots exclusively generated excellent anodic ECL in the two-component coreaction system comprising TPrA and K2S2O8. Moreover, a potential-resolved ECL biosensor to simultaneously detect S. pneumoniae and M. pneumoniae has also been successfully constructed based on this novel Se-based NIR Pdots as an anodic emitter with CdS QDs as a cathodic emitter. Under optimal conditions, the biosensor has a wide linear range for S. pneumoniae (10-15 to 10-9 M) and M. pneumoniae (10-15 to 10-9 M), with low detection limits for S. pneumoniae (0.56 fM) and M. pneumoniae (0.96 fM). The proposed ECL biosensor provides a simple, sensitive, and reliable method for the simultaneous detection of CAP pathogens in clinical applications.

A sensitive immunosensor via Pd@Au0.85Pd0.15 in situ electrocatalysis generating H2O2 for quenching electrochemiluminescence of Ir(pbi)2(acac)@Ti3C2Tx MXene-PVA

The establishment of rapid target analysis methods for cytokeratin fragment antigen 21-1 (CYFRA 21-1) is urgently needed. [Ir(pbi)2(acac)] (pbi = 2-(4-bromophenyl)-1-hydrogen -benzimidazole, acac = acetylacetonate) as traditional electrochemiluminescence (ECL) luminophores has been confined due to its non-negligible dark toxicity and poor water solubility leading to poor biocompatibility and electrical conductivity as an organic molecule. Hence, to overcome this limitation, [Ir(pbi)2(acac)] can be effectively loaded on the polyvinyl alcohol hydrogel modified Ti3C2Tx MXene surface (Ir@Ti3C2Tx-PVA) as sensing platform which can emit high ECL signals. Then, a quenching strategy was proposed to fabricate an ECL sandwich immunosensor using H2O2 as quencher molecules which can generated by Pd@Au0.85Pd0.15. Especially, the generation of O2 to H2O2 can be achieved through a two-electron (2e-) reaction pathway by Pd@Au0.85Pd0.15, to overcome the restriction that the H2O2 was virtually impossible to label or immobilize on the non-enzyme nanomaterials. The proposed ECL assay achieves a response to CYFRA 21-1 within the range of 0.1 pg/mL-100 ng/mL, with a detection limit of 8.9 fg/mL (S/N = 3). This work provided a feasible tactic to seek superior-performance ECL luminophore and quencher consequently set up a novel means to makeup ultrasensitive ECL biosensor, which extended the utilization potential of Ir(pbi)2(acac) in ECL assays.

Construction of Multiply Guaranteed DNA Sensors for Biological Sensing and Bioimaging Applications

Nucleic acids exhibit exceptional functionalities for both molecular recognition and catalysis, along with the capability of predictable assembly through strand displacement reactions. The inherent programmability and addressability of DNA probes enable their precise, on-demand assembly and accurate execution of hybridization, significantly enhancing target detection capabilities. Decades of research in DNA nanotechnology have led to advances in the structural design of functional DNA probes, resulting in increasingly sensitive and robust DNA sensors. Moreover, increasing attention has been devoted to enhancing the accuracy and sensitivity of DNA-based biosensors by integrating multiple sensing procedures. In this review, we summarize various strategies aimed at enhancing the accuracy of DNA sensors. These strategies involve multiple guarantee procedures, utilizing dual signal output mechanisms, and implementing sequential regulation methods. Our goal is to provide new insights into the development of more accurate DNA sensors, ultimately facilitating their widespread application in clinical diagnostics and assessment.

Nanoconfined Silver Nanoclusters Combined with X-Shaped DNA Recognizer-Triggered Cascade Amplification for Electrochemiluminescence Detection of APE1

Apurinic/apyrimidinic endonuclease 1 (APE1), as a vital base excision repair enzyme, is essential for maintaining genomic integrity and stability, and its abnormal expression is closely associated with malignant tumors. Herein, we constructed an electrochemiluminescence (ECL) biosensor for detecting APE1 activity by combining nanoconfined ECL silver nanoclusters (Ag NCs) with X-shaped DNA recognizer-triggered cascade amplification. Specifically, the Ag NCs were prepared and confined in the glutaraldehyde-cross-linked chitosan hydrogel network using the one-pot method, resulting in a strong ECL response and exceptional stability in comparison with discrete Ag NCs. Furthermore, the self-assembled X-shaped DNA recognizers were designed for APE1 detection, which not only improved reaction kinetics due to the ordered arrangement of recognition sites but also achieved high sensitivity by utilizing the recognizer-triggered cascade amplification of strand displacement amplification (SDA) and DNAzyme catalysis. As expected, this biosensor achieved sensitive ECL detection of APE1 in the range of 1.0 × 10-3 U·μL-1 to 1.0 × 10-10 U·μL-1 with the detection limit of 2.21 × 10-11 U·μL-1, rendering it a desirable approach for biomarker detection.

Confinement-enhanced electrochemiluminescence by Ru(dcbpy)32+-functionalized γ-CD-MOF@COF-LZU1 porous hybrid material as micro-reactor for CYFRA 21-1 detection

The improvement of electrochemiluminescence (ECL) performance relies on the electron transfer efficiency between luminophore and coreactant. An ultrasensitive ECL micro-reactor with confinement-enhanced performance was prepared by using the covalent organic framework-LZU1-functionalized metal-organic framework (MOF@COF-LZU1) as a platform to assemble enormous N,N-dibutyl-2-hydroxyethylamine (DBAE) and tris(4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) [Ru(dcbpy)32+] into its pore channels. Compared to individual substances of γ-CD-MOF and COF-LZU1, the synergistic effects can conduce to the enhancement of the intensity, durability and sensitivity of the micro-reactor. Besides, COF-LZU1 can provide a mild environment to accommodate a certain amount of DBAE by concentrating them from the aqueous solution into its hydrophobic cavities and boost the oxidation efficiency of DBAE to generate more DBAE●+ and profited the survival of DBAE●, leading to an improved reaction efficiency with the Ru(dcbpy)32+ intermediate. Thanks to the confinement-enhanced strategy, engineered as high-functioning luminescent materials, Ru@γ-CD-MOF@COF-LZU1 micro-reactors decorated with Au NPs can facilitate electron transfer and capture primary antibodies (Ab1). Moreover, Au-Pd-Pt noble metal aerogels (NMAs) functionalized MoS2 NFs (Au-Pd-Pt NMAs@MoS2 NFs) were chosen as base material due to its large specific surface areas, high porosity, and excellent electrical conductivity. Based on above merits, the sensor demonstrated a sensitive response to CYFRA 21-1 detection in a linear concentration gradient from 10 fg/mL to 50 ng/mL with a detection limit of 0.0055 pg/mL (S/N = 3). The COF-LZU1 decorated ECL micro-reactors were constructed based on the signal amplification strategies to realize accurate CYFRA 21-1 detection.

A Co-Reactive Immunosensor Based on Ti3C2Tx MXene@TiO2-MoS2 Hybrids Promoting luminol@Au@Ni-Co NCs Electrochemiluminescence for CYFRA 21-1 Detection

The construction of assays is capable of accurately detecting cytokeratin-19 (CYFRA 21-1), which is critical for the rapid diagnosis of nonsmall cell lung cancer. In this work, a novel electrochemiluminescence (ECL) immunosensor based on the co-reaction promotion of luminol@Au@Ni-Co nanocages (NCs) as ECL probe by Ti3C2Tx MXene@TiO2-MoS2 hybrids as co-reaction accelerator was proposed to detect CYFRA 21-1. Ni-Co NCs, as a derivative of Prussian blue analogs, can be loaded with large quantities of Au NPs, luminol, and CYFRA 21-1 secondary antibodies due to their high specific surface area. To further improve the sensitivity of the developed ECL immunosensor, Ti3C2Tx MXene@TiO2-MoS2 hybrids were prepared by in situ growth of TiO2 nanosheets on highly conductive Ti3C2Tx MXene, and MoS2 was homogeneously grown on Ti3C2Tx MXene@TiO2 surfaces by the hydrothermal method. Ti3C2Tx MXene@TiO2-MoS2 hybrids possess excellent catalytic performance on the electro-redox of H2O2 generating more O2·- and obtaining optimal ECL intensity of the luminol/H2O2 system. Under the appropriate experimental conditions, the quantitative detection range of CYFRA 21-1 was from 0.1 pg mL-1 to 100 ng mL-1, and the limit of detection (LOD) was 0.046 pg mL-1. The present sensor has a lower LOD with a wider linear range, which provides a new analytical assay for the early diagnosis of small-cell-type lung cancer labels.

An electrochemiluminescence microsensor based on DNA-silver nanoclusters amplification for detecting cellular adenosine triphosphate

Adenosine triphosphate (ATP), as the primary energy source, plays vital roles in many cellular events. Developing an efficient assay is crucial to rapidly evaluate the level of cellular ATP. A portable and integrated electrochemiluminescence (ECL) microsensor array based on a closed bipolar electrode (BPE) was presented. In the BPE unit, the ECL chemicals and oxidation/reduction were separated from the sensing chamber. The ATP aptamer was assembled with single-stranded DNA (ssDNA) in the sensing chamber. ATP capture made the aptamer disassemble from the ssDNA and facilitated DNA-templated silver nanocluster (Ag NC) generation by the target-rolling circle amplification (RCA) reaction. The guanine-rich padlock sequence produced tandem periodic cytosine-rich sequences by the RCA, inducing Ag NC generation in the cytosine-rich region of the produced DNA strands through Ag+ reduction. The in situ Ag NC generation enhanced the circuit conductivity of the BPE and promoted the ECL reaction of [Ru(bpy)2dppz]2+/tripropylamine in the anodic reservoir. On this ECL microsensor, a good linear relationship of ATP was achieved ranging from 30 to 1000 nM. The ATP content in HepG2 cells was selectively and sensitively determined without complex pretreatment. The ATP amount of 25 cells could be successfully detected when a sub-microliter sample was loaded.