Magnetic bead-gold nanoparticle hybrids probe based on optically countable gold nanoparticles with dark-field microscope for T4 polynucleotide kinase activity assay

Construction of self-enhanced luminescence probes based on Ti3C2 reducibility for ultrasensitive PNK analysis

Au nano-clusters (Au NCs) were promising electrochemiluminescence (ECL) nano-materials. However, the small size of Au NCs presented a challenge in terms of their immobilization during the construction of an ECL biosensing platform. This limitation significantly hindered the wider application of Au NCs in the ECL field. In this work, we successfully used the reducibility of Ti3C2 to fabricate in situ a self-enhanced nano-probe Ti3C2-TiO2-Au NCs. The strategy of in situ generation not only improved the immobilization of Au NCs on the probe but also eliminated the requirement of adding reducing agents during preparation. In addition, in situ generated TiO2 could serve as a co-reaction accelerator, shortening the electron transfer distance between S2O82- and Au NCs, thereby improving the utilization of intermediates and enhancing the ECL response of Au NCs. The constructed ECL sensing platform could achieve sensitive detection of polynucleotide kinase (PNK). At the same time, the 5'-end phosphate group of DNA phosphorylation could chelate with a large amount of Ti on the surface of Ti3C2, thereby achieving the goal of specific detection of PNK. The sensor based on self-enhanced ECL probes had a broad dynamic range spanning for PNK detection from 10.0 to 1.0 × 107 μU mL-1, with a limit of detection of 1.6 μU mL-1. Moreover, the ECL sensor showed satisfactory detection performance in HeLa cell lysate and serum. This study not only provided insights for addressing the issue of ECL luminescence efficiency in Au NCs but also presented novel concepts for ECL self-enhancement strategies.

Construction of Magnetic Core-Large Mesoporous Satellite Immunosensor for Long-Lasting Chemiluminescence and Highly Sensitive Tumor Marker Determination

Chemiluminescence immunoassay exhibits high sensitivity and signal-to-noise ratio, thus attracting great attention in the early diagnosis and dynamic monitoring of diseases. However, the collection of conventional flash-type chemiluminescence signal (<5 s) relies heavily on automatic sampling and reading instrument. Herein, a novel core-satellite multifunctional chemiluminescence immunosensor is designed for the efficient enrichment and highly sensitive determination of cancer biomarker carcinoembryonic antigen (CEA) with enhanced and long-lasting output signal that can be conveniently recorded by a simple microplate plate reading instrument. Anti-CEA monoclonal antibody 2 (Ab2) modified Fe3 O4 @SiO2 microspheres (Fe3 O4 @SiO2 -Ab2, 370 nm in diameter) are synthesized as the core for selectively capturing and enriching target CEA in solution, and anti-human CEA monoclonal antibody 1 (Ab1) and horseradish peroxidase (HRP) co-immobilized dendritic large-mesoporous silica nanospheres (MSNs-HRP/Ab1, 80 nm in diameter, pore size: 17 nm) are synthesized as the satellite for efficient immunological recognition and signal amplification. The as-designed core-satellite magnetic chemiluminescence immunosensors exhibit a broad linear range of 0.01-20 ng mL-1 and a low detection limit of 3.0 pg mL-1 for the convenient, highly specific, and sensitive determination of CEA in human serum. Such core-satellite chemiluminescence immunosensors are expected to act as a powerful tool for in vitro detection of various biomarkers, overcome the defect of conventional chemiluminescence relying heavily on expensive and bulky automatic instruments and popularize chemiluminescence analysis to primary medical institutions and remote areas.

Versatile fluorescence detection of T4 PNK and mRNA based on unique DNA nanomachine amplification

The development of DNA nanomachines provides a new strategy for the detection of tumor markers. In this work, an intelligent three-dimensional (3D) DNA walking machine with polynucleotide kinase (PNK) activator was designed, which was coupled with unique nanomachine formed by DNA nanowire cascade amplification reaction for versatile fluorescence detection of T4 PNK activity and messenger RNA (mRNA). When PNK exists, the free DNA walker was formed by hydrolysis cleavage of exonuclease, then the fluorophore-labeled report probe on the Au nanoparticles (NPs) was sheared during cycling cleavage reaction, thus the fluorescence signal was recovered for detection of PNK. Moreover, the DNA nanowires were produced by rolling ring amplification, then target mRNA sequentially initiated interval hybridization of hairpin probes through DNA nanowire, thus realizing DNA cascade reaction (DCR) with high "on" signal of DNA nanomachine for mRNA assay. This developed novel fluorescence nanomachine reported a new assay method with promising application for versatile targets and showed great potential for molecular-target therapies, and clinic diagnostics.

Visual and Ultrasensitive Detection of a Coronavirus Using a Gold Nanorod Probe under Dark Field

Porcine epidemic diarrhea virus (PEDV), a coronavirus that causes highly infectious intestinal diarrhea in piglets, has led to severe economic losses worldwide. Rapid diagnosis and timely supervision are significant in the prophylaxis of PEDV. Herein, we proposed a gold-nanorod (GNR) probe-assisted counting method using dark field microscopy (DFM). The antibody-functionalized silicon chips were prepared to capture PEDV to form sandwich structures with GNR probes for imaging under DFM. Results show that our DFM-based assay for PEDV has a sensitivity of 23.80 copies/μL for simulated real samples, which is very close to that of qPCR in this study. This method of GNR probes combined with DFM for quantitative detection of PEDV not only has strong specificity, good repeatability, and a low detection limit, but it also can be implemented for rapid on-site detection of the pathogens.

Sensitive Autocatalytic Hybridization Circuit for Reliable In Situ Intracellular Polynucleotide Kinase Imaging

Exploring the characteristic functions of polynucleotide kinase (PNK) could substantially promote the elucidation of PNK-related mechanistic pathways. Yet, the sensitive and reliable detection of intracellular PNK still presents a challenging goal. Herein, we propose a simple autocatalytic hybridization circuit (AHC) for in situ intracellular imaging of PNK with high reliability. The AHC amplifier consists of two mutually activated hybridization chain reaction (HCR) modules for magnified signal transduction. The PNK is transduced into initiator I by phosphorylation and cleavage of mediator H_p. Initiator I activates the initial HCR-1 module, leading to the formation of long dsDNA nanowires that carry numerous initiator T. Then, T-initiated feedback HCR-2 module generates branched products that contain plentiful initiator I, thus realizing an autocatalytic HCR amplification reaction. Simultaneously, the HCR-2 module is also assembled as a versatile signal transduction unit for generating the amplified readout. Based on the mutually sustained accumulation of two initiators for the reciprocal activation of two reaction modules, continuous signal amplification and assembly of high-molecular-weight copolymers endow the AHC system with high sensitivity and robustness for the PNK assay. Moreover, the PNK-sensing AHC system achieves reliable imaging of intracellular PNK, thus showing great potential to decipher the correlation between PNK and related diseases.

An Autocatalytic DNA Circuit Based on Hybridization Chain Assembly for Intracellular Imaging of Polynucleotide Kinase

Polynucleotide kinase (PNK) plays an essential role in various cellular events by regulating phosphorylation processes, and abnormal homeostasis of PNK could cause many human diseases. Herein, we proposed an autocatalytic hybridization system (AHS) through the elaborate integration of hybridization chain assembly (HCA) and catalytic DNA assembly (CDA) that enables a highly efficient positive feedback amplification. The PNK-targeting AHS biosensor is composed of three modules: a recognition module, an HCA amplification module, and a CDA autocatalytic module. In the presence of PNK, the recognition module could transform the PNK input into an exposed nucleic acid initiator (I). Then the initiator strand I could trigger the autonomous HCA process in the amplification module, and the resulted HCA products could reassemble the split CDA trigger strand T, subsequently inducing the CDA process in the autocatalytic module to form abundant DNA duplex products. Consequently, the embedded initiator strand I was liberated from the CDA duplex product to autonomously trigger the new rounds of HCA circuit. The rational integration and cooperative cross-activation between the HCA and CDA module could prominently accelerate the reaction and realize the exponential amplification efficiency by initiator regeneration. As a result, the self-sustainable AHS amplifier could implement the sensitive detection of PNK in vitro and in biological samples and further fulfill accurate monitoring of the intracellular PNK activity and the effective screening of PNK inhibitors. This work paves a way for exploiting highly efficient artificial DNA circuits to analyze low-abundance biomarkers, holding great potential in biochemical research and clinical diagnosis.

Phosphorothioated and phosphate-terminal dumbbell (PP-TD) probe-based rapid detection of polynucleotide kinase activity

A primer-free, sensitive assay has been developed to detect polynucleotide kinase (PNK) activity. This proposed method provides a promising platform for PNK activity monitoring and inhibition screening for drug discovery and clinical treatment.

Aptamer-based biosensing through the mapping of encoding upconversion nanoparticles for sensitive CEA detection

An aptamer-based assay through the mapping and enumeration of encoding UCNPs for digital detection of CEA is reported.

An algorithm-assisted automated identification and enumeration system for sensitive hydrogen sulfide sensing under dark field microscopy

A sensitive H2S sensing strategy has been developed based on the automated identification and enumeration algorithm.

Plasmonic biosensor for the highly sensitive detection of microRNA-21 via the chemical etching of gold nanorods under a dark-field microscope

MicroRNAs involved in tumor-related tissues at abnormal expression level present tremendous potential in the early diagnosis of cancers. However, their intrinsic shortcomings, for instance, low abundance and high sequence homology, make it challengeable to quantify them with high sensitivity and selectivity. Herein, a highly sensitive platform with great specificity was developed for microRNA-21 based on the produced-I₂ triggered chemical etching of gold nanorods to a smaller size, resulting in a significant blue shift and a great intensity decrease in the localized surface plasmon resonance (LSPR) scattering. The synergism of strand displacement and enzymatic reaction enabled the proposed strategy with a high sensitivity and selectivity toward microRNA-21 in a dynamic range from 0.1 to 10,000 pM and a low limit of detection of 71.22 fM (3σ/k) by dark-field microscope. Additionally, the remarkable discrimination of single nucleotide difference suggested the superior selectivity towards microRNA-21, which presented a satisfactory recovery in human serum samples. The proposed plasmon platform could also serve as a universal and sensitive detection of cancer biomarkers, presenting the amusing application prospects in the early diagnosis of various cancers by adapting the corresponding nucleic acid sequences.

Artificial Intelligence-Aided Multiple Tumor Detection Method Based on Immunohistochemistry-Enhanced Dark-Field Imaging

The immunohistochemical method serves as one of the most practical tools in clinical cancer detection and thus has great application value to overcome the existing limits of the conventional method and further improve the detecting efficiency and sensitivity. This study employed 3,3'-diaminobenzidine (DAB), a conventional color indicator for immunohistochemistry, as a novel high-sensitive scattering reagent to provide a multidimensional image signal varying with the overexpression rate of tumor markers. Based on the scattering properties of DAB aggregates, an efficient and robust artificial intelligence-aided immunohistochemical method based on dark-field imaging has been established, with improvement in both the imaging quality and interpretation efficiency in comparison with the conventional manual-operated immunohistochemical method. Referencing the diagnosis from three independent pathologists, this method succeeded in detecting HER2 overexpressed breast tumors with a sensitivity of 95.2% and a specificity of 100.0%; meanwhile, it was found to be applicable for non-small-cell lung tumors and malignant lymphoma as well. As demonstrated, this study provided an effective and reliable means for making diagnostic suggestions, which exhibited great potential in multiple tumor pathological detection at low cost.

Single nanoparticle identification coupled with auto-identify algorithm for rapid and accurate detection of L-histidine

In this work, an auto-identify sensor was constructed for rapid and high-precision detection of L-histidine. The proposed strategy is based on the auto-identify algorithm and the aggregation of alkynyl and azide functionalized gold nanoparticles induced by the Cu⁺ catalyzed azides and alkynes cycloaddition (CuAAC) reaction. Specially, the color of scattering light spots for the aggregated gold nanoparticle (AuNPs) caused by CuAAC reaction was quite different from that of the monomers. However, L-histidine can bind to Cu²⁺ and inhibits the production of Cu⁺, hence preventing the aggregation of AuNPs. Therefore, there is a distinct change of color as the addition of L-histidine under dark-field microscopy. Then, L-histidine can be quantitatively detected by combining the color change with the Meanshift algorithm accurately and automatically. Such proposed method has been successfully applied for the detection of L-histidine in serum sample with satisfying result.

An Exonuclease I-Aided Turn-Off Fluorescent Strategy for Alkaline Phosphatase Assay Based on Terminal Protection and Copper Nanoparticles

As an important DNA 3'-phosphatase, alkaline phosphatase can repair damaged DNA caused by replication and recombination. It is essential to measure the level of alkaline phosphatase to indicate some potential diseases, such as cancer, related to alkaline phosphatase. Here, we designed a simple and fast method to detect alkaline phosphatase quantitively. When alkaline phosphatase is present, the resulting poly T-DNA with a 3'-hydroxyl end was cleaved by exonuclease I, prohibiting the formation of fluorescent copper nanoparticles. However, the fluorescent copper nanoparticles can be monitored with the absence of alkaline phosphatase. Hence, we can detect alkaline phosphatase with this turn-off strategy. The proposed method is able to quantify the concentration of alkaline phosphatase with the LOD of 0.0098 U/L. Furthermore, we utilized this method to measure the effects of inhibitor Na₃VO₄ on alkaline phosphatase. In addition, it was successfully applied to quantify the level of alkaline phosphatase in human serum. The proposed strategy is sensitive, selective, cost effective, and timesaving, having a great potential to detect alkaline phosphatase quantitatively in clinical diagnosis.

Development of a multi-channel magnetic bead micro-probe assay for high-throughput detection of zearalenone in edible and medicinal Coix seed

A multi-channel magnetic bead micro-probes assay (MBPA) based on indirect competitive principle was developed for high-throughput detection of zearalenone (ZEA) in edible and medicinal Coix seed. This strategy introduced magnetic beads as the carriers, the specific primary antibodies as the capture probes for targets and the secondary antibodies functionalized goat anti-mouse immunoglobulin G labeled fluorescein isothiocyanate as the fluorescence signal probes. Through the competitive reaction of ZEA in Coix seed samples and that covalently coupled on the surface of MBs with their specific antibodies, as well as fast magnetic separation and sensitive fluorescence detection, the developed MBPA strategy allowed low limit of detection (2.03 ng/mL) with broad dynamic range (2.03-440.67 ng/mL), as well as excellent accuracy with the average recovery rate of 96.39% and relative standard deviation (RSD) of 5.48% for ZEA. 36 samples could realize simultaneous analysis in one operation within less than 20 min only needing 50 μL of solution and 30 s of sampling, avoiding large consumption of time and organic solvents. Multiple centrifugation and cleanup steps were omitted because of magnetic separation, avoiding the loss of targets. Diverse capture and fluorescent probes can be randomly bound onto the surface of MBs, making the MBPA strategy a promising tool for on-site high-throughput monitoring of various trace hazard factors in food safety, and environmental monitoring.

Electrochemical DNA Sensors Based on MoS2-AuNPs for Polynucleotide Kinase Activity and Inhibition Assay

The determination of T4 polynucleotide kinase (PNK) activity and the screening of PNK inhibitors are critical to disease diagnosis and drug discovery. Numerous electrochemical strategies have been developed for the sensitive measurement of PNK activity and inhibition. However, they often suffer from additional labels and multiple steps of the detection process for the electrochemical readout. Herein, we have demonstrated an electrochemical DNA (E-DNA) sensor for the one-step detection of PNK with "signal-on" readout with no need for additional labels. In our design, the highly switchable double-stranded DNA (dsDNA) probes are immobilized on the gold nanoparticle-decorated molybdenum disulfide nanomaterial (MoS₂-AuNPs), which possesses large surface area and high conductivity for elevating the signal gain in the PNK detection. This signal-on E-DNA sensor integrated with MoS₂-AuNPs exhibits a much higher sensitivity than that without MoS₂-AuNPs, showing a detection limit of 2.18 × 10^-4 U/mL. Furthermore, this assay shows high selectivity, with the ability to discriminate PNK from other enzymes and proteins, and can be utilized to screen inhibitors. The proposed sensor is easy to operate with one-step readout and robust for PNK detection in the biological matrix and shows great potential for point-of-care in clinical diagnostics and drug screening.