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To address the urgent demand for sensitive and stable detection applications, significant efforts have been made in the development of dual-signal readout assays for precise target detection and timely health risk control. Here, a new nanomaterial, Pt@PCN-224-HRP-initiator DNA (PP-HRP-iDNA), was exploited to construct a dual-signal readout biosensing platform. Zr-MOF (PCN-224) was loaded with as many Pt nanoparticles (NPs) and as much horseradish peroxidase (HRP) as possible to enhance the brightness of the colorimetric signal recognizable to the naked eye while also acting as a gatekeeper to protect the enzyme activity and ensuring the stability of the assay process. Moreover, the Pt NPs and HRP displayed a synergistic catalytic effect, which promoted the sensitivity of detection. Further, the formation of the Zr

An electrical resistance-based particle counter (ERPC) with simple operation and high resolution has proved to be a promising biosensing toolkit, whereas amplification-free ERPC biosensors are incapable of analyzing trace small molecules due to their relatively low sensitivity. In this work, click chemistry-mediated particle counting sensing of small-molecule hazards in food samples with high sensitivity was developed. In this strategy, unbound alkyne-functionalized polystyrene microspheres were collected by magnetic separation from the copper-ion-mediated click reaction between alkyne-functionalized polystyrene microspheres and azido-functionalized magnetic beads, which could be used as signal probes for the readout. This click chemistry-mediated ERPC biosensor converts the detection of targets to the quantification of copper ions or ascorbic acid by performing competitive immunoassay-based coordination chemistry and enzymatic reaction, respectively. The sensitivity of the ERPC biosensor has been improved by an order of magnitude due to the signal amplification effects of click chemistry, coordination adsorption, and enzyme catalysis. Furthermore, because of the efficient separation and enrichment of immunomagnetic beads and the robustness of click chemistry, the interference from food matrixes and immunoassay is effectively reduced, and thus, our strategy is exceedingly suitable for detecting trace targets in complex samples.

The frequent emergence of SARS-CoV-2 variants increased viral transmissibility and reduced protection afforded by vaccines. The rapid, multichannel, and intelligent screening of variants is critical to minimizing community transmissions. DNA molecular logic gates have attracted wide attention in recent years due to the powerful information processing capabilities and molecular data biocomputing functions. In this work, some molecular switches (MSs) were connected with each other to implement arbitrary binary functions by emulating the threshold switching of MOS transistors and the decision tree model. Using specific sequences of different SARS-CoV-2 variants as inputs, the MSs net was used to build several molecular biocomputing circuits, including NOT, AND, OR, INHIBIT, XOR, half adder, half subtractor, full adder, and full subtractor. Four fluorophores (FAM, Cy3, ROX, and Cy5) were employed in the logic systems to realize the multichannel monitoring of the logic operation results. The logic response is fast and can be finished with 10 min, which facilitates the rapid wide-population screening for SARS-CoV-2 variants. Importantly, the logic results can be directly observed by the naked eye under a portable UV lamp, thus providing a simple and intelligent method to enable high-frequency point-of-care diagnostics, particularly in low-resource communities.

Based on aptamer recognition and target-mediated competitive hybridization of hairpin probes, we developed a fluorescence sensor for kanamycin (KAN) detection. The aptamer and KAN binding will open hairpin H1 to release the trigger DNA fragment, which can initiate the competitive hybridization between hairpins H2 and H3. Then, exonuclease III (Exo III) can cleave H2 and H3 to produce numerous DNA3 and DNA4. Through the synergetic hybridization among DNA1, DNA2, DNA3, and DNA4, an active Mg

We successfully constructed several molecular logic gates using heavy metal ions as inputs based on catalytic hairpin assembly (CHA) and CRISPR-Cas12a. The corresponding DNAzymes were used to recognize heavy metal ions (Hg

Utilizing statistical models of binary images is a common and effective means to steganalyze binary images, and the design of the statistical model is essential to the performance of steganalysis. In this paper, we propose a new model based on a histogram of pixel structuring elements (SEs), which is a suitable representation of a binary image for the task of steganalysis. The texture property and the dependency among pixels are considered inside the SEs. The SEs with different patterns will be evaluated comprehensively according to a statistical criterion, and some of them will be selected to construct the feature set for training the steganalyzer. The distributions of these selected SEs, which contain many highly flippable pixels, will be emphasized by the criterion, and they can reflect the difference between cover images and stego-images. Finally, a series of experiments are conducted on two datasets, and the results show that the proposed scheme significantly outperforms state-of-the-art schemes.

The pathogen of viral hemorrhagic fever (VHF), which is harmful to human health, is a hemorrhagic fever virus. Clinicians have long needed convenient and sensitive point-of-care rapid diagnostic tests (RDTs) for hemorrhagic fever viruses. Commonly used methods for pathogen detection rely on conventional culture-based tests, antibody-based assays and polymerase chain reaction (PCR)-based techniques. However, these methods are costly, laborious and time-consuming. Herein, we present a simple and sensitive biosensor for the rapid detection of hemorrhagic fever viruses. For this assay, we develop lateral flow biosensors (LFBs) based on magnetic beads and nicking enzyme-assisted isothermal strand-displacement amplification (SDA) for the detection of hemorrhagic fever viruses. The detection limit of this assay is 10 fM.

Nasopharyngeal carcinoma (NPC) is one of the most common malignant tumors in the world, and several studies have associated Epstein-Barr virus (EBV) with NPC occurrence and development. EBV-PCR (polymerase chain reaction), in situ hybridization and immunoassays are the most common methods for NPC identification. However, these approaches have drawbacks, which include tedious procedures and false results. Therefore, a rapid, accurate, and sensitive clinical diagnostic method for the prognosis of EBV-related diseases is needed. In this study, we developed a simple and sensitive approach for EBV detection based on the combination of CRISPR-Cas12a and a lateral flow biosensor (LFB). Cas12a exhibits collateral cleavage propensity of both target DNA and any single-stranded(ss) DNA in the vicinity (herein referred to as a reporter). The LFB test line contained an ssDNA probe complementary to the reporter. In the presence of the target, Cas12a trans-cleaved the ssDNA reporter, which resulted in the inability of cleaved sequences to bind the LFB test line. With a PCR pre-amplification of the target (45 min), the assay achieved a sensitivity of 7.1 × 10-14 M (∼42 000 copies per μl) both in plasmid and plasmid-spiked samples. The assay attained a high specificity in the presence of various bacteria and applicability in EBV Burkitt's lymphoma serum samples. This method could be applied for the detection of EBV and other infectious diseases.

Vibrio infectious diseases spreading every day through aquatic food may be a life-threatening problem for people with weak immune and growing menace to society. It was estimated that the cost of foodborne diseases was approximately $5–6 billion per year. Traditional methods for Vibrio spp. sensing showed high accuracy but very low detection limit. Immunoassays and nucleic acid-based assays could provide results within 24 h, while they are expensive, labor-cost and tedious. Hence, it was urgently needed for the development of cost-effective, rapid and reliable alternative methods for real-time biosensing of Vibrio spp. Several biosensors have been established for the screening of Vibrio spp. in seafood and water. In this review, we have updated the advances in biosensing assays for screening of Vibrio spp., such as electrochemical, optical and novel nano-scaled aptamers based biosensors. Meanwhile, attentions have been paid on the principal concepts, applications, and examples that have been achieved up to determine Vibrio spp.

We have developed an equipment-free biosensor for visual pesticide residue (acetamiprid) detection with high sensitivity and selectivity. The target acetamiprid associates with an aptamer sequence and releases trigger DNA to initiate the cyclic signal amplification process. An ingeniously designed hairpin DNA probe was employed as the sensing element, which contains the same sequence as the trigger DNA in the stem part of the hairpin and a G-rich sequence in the loop part of the hairpin. An exonuclease III (Exo III)-mediated target recycling strategy was utilized to achieve quadratic amplification. This two-step cyclic signal amplification results in the generation of numerous G-quadruplex DNAzymes that can catalyze the H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate a colored signal readout, thus providing the amplified colorimetric detection of the target. This assay is ultrasensitive, enabling the visual detection of acetamiprid at concentrations as low as 10 pM without instrumentation. Our proposed sensing system also displays high selectivity and can be applied to determine acetamiprid residues in food samples. Moreover, the assay does not involve any chemical modification of DNA, which is simple and low-cost. This sensing platform provides a promising approach for on-site detection of target molecules in resource-constrained regions because of the easy and straightforward readout of results without the use of sophisticated apparatus.

An enzyme-free DNA circuit was designed for the amplified detection of Cd2+ based on hairpin probe-mediated toehold binding and branch migration. A Cd2+-specific aptamer was used to recognize Cd2+ and a G-quadruplex was used to report the detection signal. The assay is sensitive, with a detection limit of 5 pM.

Utilizing some special pixels patterns constructing the steganalytic features is popular in binary image steganalysis, which could be also used in halftone image. There is almost no specific image steganalysis for halftone image. In this paper, a halftone image steganalysis scheme is proposed and achieves a satisfactory performance, which is totally different from the previous works focussing on some special pixels patterns. Inspired by the fact that halftoning techniques based on the low-pass characteristic of human visual system model (HVS model), the grayscale image is considered reconstructing with a Gaussian filter. And the distortions caused by embedding secret messages will still exist. After that, some common grayscale image steganalysis can be used for extracting the steganalytic features. Furthermore, a series of experiments are conducted and the experimental results show that the proposed scheme is effective on halftone image steganalysis.

Herein, we propose a novel indoor structure extraction (ISE) method that can reconstruct an indoor planar structure with a feature structure map (FSM) and enable indoor robot navigation using a navigation structure map (NSM). To construct the FSM, we first propose a two-staged region growing algorithm to segment the planar feature and to obtain the original planar point cloud. Subsequently, we simplify the planar feature using quadtree segmentation based on cluster fusion. Finally, we perform simple triangulation in the interior and vertex-assignment triangulation in the boundary to accomplish feature reconstruction for the planar structure. The FSM is organized in the form of a mesh model. To construct the NSM, we first propose a novel ground extraction method based on indoor structure analysis under the Manhattan world assumption. It can accurately capture the ground plane in an indoor scene. Subsequently, we establish a passable area map (PAM) within different heights. Finally, a novel-form NSM is established using the original planar point cloud and the PAM. Experiments are performed using three public datasets and one self-collected dataset. The proposed plane segmentation approach is evaluated on two simulation datasets and achieves a recall of approximately 99%, which is 5% higher than that of the traditional plane segmentation method. Furthermore, the triangulation performance of our method compared with the traditional greedy projection triangulation show that our method performs better in terms of feature representation. The experimental results reveal that our ISE method is robust and effective for extracting indoor structures.

Conventional transverse relaxation time (T2)-mediated magnetic resonance sensors (MRS) that utilizing the target-induces state change of magnetic nanoparticles (MNPs) mainly suffer from low sensiti...

CRISPR/Cas systems have displayed remarkable potential in developing novel biosensing applications for nucleic acid detection owing to the collateral cleavage activity of Cas effector proteins (Cas12, Cas13, etc.). Despite tremendous progress in recent years, the existing CRISPR/Cas based biosensing platforms have several limitations, including reliance on proper amplification methods, expensive fluorescence detection equipment, or lateral flow biosensor (LFB). Herein, we report a simple, inexpensive, and ultrasensitive DNA probe based LFB with C RISPR/Cas and loop-mediated I sothermal A mplification (namely CIA). The concept behind this approach is a non-detectable test line on the LFB when the Cas effector protein collaterally cleaves the cognate target and an ssDNA reporter sequence. The CIA based LFB can detect as low as a single copy cloned Pseudomonas aeruginosa acyltransferase gene, 1 cfu/ml plasmid containing E. coli DH5α pure cultures, as well as clinical samples without DNA extraction/purification or advanced apparatuses. No cross-reactivity with other non-target bacteria was observed. The naked eye result readout was obtained in 15 min of LAMP amplification, 30 min of Cas12 reaction, and 5 min of LFB readout. This platform is robust and of low cost for on-site testing.

Bacterial infections may lead to diverse acute or chronic diseases (e.g., inflammation, sepsis and cancer). New antibiotics against bacteria are rarely discovered in recent years, which necessitates the exploration of new antibacterial agents. Engineered nanomaterials (ENMs) have been extensively studied for antibacterial use because of their long lasting killing effects in wide spectra of bacteria. Graphene oxide (GO) is one of the most widely studied ENMs and exhibit strong bactericidal effects. The physicochemical properties of GO play important roles in bacterial killing by triggering a cascade of toxic events. Many studies have explored the signaling pathways of GO in bacteria. Although molecular initiating events (MIEs) of GO in bacteria dominate its killing efficiency as well as toxicity mechanisms, they have been rarely reviewed. In this report, we discussed the structure-activity relationships (SARs) involved in GO-induced bacterial killing and the MIEs including redox reaction with biomolecules, mechanical destruction of membranes and catalysis of extracellular metabolites. Furthermore, we summarized the clinical or commercial applications of GO-based antibacterial products and discussed their biosafety in mammal. Finally, we reviewed the remaining challenges in GO for antibacterial applications, which may offer new insights for the development of nano antibacterial studies.

An enzyme-free DNA circuit was designed for the amplified detection of Cd2+ based on hairpin probe-mediated toehold binding and branch migration. A Cd2+-specific aptamer was used to recognize Cd2+ and a G-quadruplex was used to report the detection signal. The assay is sensitive, with a detection limit of 5 pM.

The rapid determination of human osteopontin (OPN) protein, a potential cancer biomarker, holds substantial promise for point-of-care diagnostics and biomedical applications. To date, most reported platforms for OPN detection are apparatus-dependent, time-consuming, and expensive. Herein, we established a lateral flow biosensor (LFB) for OPN detection. A biotinylated aptamer was used for OPN pre-capture from samples, an antibody for OPN was immobilized on the test line for a second specific target identification, and streptavidin-modified gold nanoparticles were sprayed on the conjugation pad for color detection. This LFB achieved as low as 0.1 ng mL−1 OPN sensitivity with a good dynamic detection between 10 and 500 ng mL−1 within 5 min. Intriguingly, the LFB allowed a qualitative and semi-quantitative detection of OPN in serum at clinically cut-off levels as in cancer patients, and can discriminate OPN from interfering proteins with high specificity. Thus, it is a promising alterative approach for point-of-care OPN screening and detection.

A binary image steganalysis scheme based on the statistic model of local residual pattern (LRP) is proposed in this paper. LRP means the pattern of a local area of the residual map of the binary image, which is calculated with the XOR operation. The XOR operation is sensitive to the difference between adjacent pixels, which leads to the emphasis on edge property of the residual map. The neighbouring LRPs of the modified pixel will be affect, which makes the statistic model of LRPs change. Thus the trace of steganography can be detected according to the difference between the statistic models. Finally, the experiments we conducted show that our proposed scheme is effective on binary image steganalysis.

Utilizing G-quadruplex as the signal report probe, an ultrasensitive and label-free autocatalytic DNA circuit for Hg

In recent years, different traditional interferometers have been the necessary diagnostic of electronic density measurement on fusion devices. Until now, two main problems always influence the density measurement: the mechanical vibration and fringe jump in the calculation. The dispersion interferometer (DI) with a long-wavelength infrared wavelength is a good choice because mechanical vibrations can be canceled and the fringe jump can be inhibited. This paper describes the bench test of phase measurement using a wedge instead of plasma on the DI. The results show good agreement with the theoretical calculations. In the background measurement, this DI without a vibration isolation system has good performance, and the drift of the baseline is less than 2 × 1017 m-2 in 3 s and less than 5 × 1017 m-2 in 400 s. Plasma data will be obtained during the next campaign on EAST (Experimental and Advanced Superconducting Tokamak).

A highly sensitive fluorescence biosensing system was designed for the detection of trace amounts of arsenic(III) (As3+) based on target-triggered successive signal amplification strategy. The specific recognition between the target As3+ and the aptamer sequence results in the release of the blocking DNA to trigger the subsequent signal amplification steps. Exonuclease III (Exo III)-mediated DNA recycling digest process is introduced into the sensing system to generate numerous Mg2+-dependent DNAzymes. After magnetic separation, the active DNAzyme with multiple turnovers could catalyze the continuous cleavage of the fluorophore-quencher-functionalized substrate strands, thus yielding a significantly amplified fluorescence signal for target detection. Due to the synergetic signal amplification of Exo III and DNAzyme, the fluorescent biosensor exhibits ultrasensitivity for As3+ monitoring, with a detection limit of 2 pM. Our established biosensor also displays excellent selectivity toward the target As3+ an...

To investigate the rapid and accurate method for the detection of dengue virus (DENV) by using nicking enzyme assisted strand-displacement amplification (SDA) combined with gold nanoparticles-based lateral flow strip.Total RNA of the virus was extracted by using magnetic beads method and transcribed to cDNA for SDA detection system. Nicking enzyme-assisted method was used for detecting DENV, and agarose gel electrophoresis was used for analyzing the sensitivity of SDA amplification products. A gold nanoparticles-based lateral flow strip was developed based on the principle of nucleic acid base complementary pairing to design the test line and control line. The gold particles were prepared by using sodium citrate reduction method for gold nanoparticles-based lateral flow strip construction.The sensitivity of the SDA method was 10 fmol/L, and the sensitivity of gold nanoparticles-based lateral flow strip based on SDA method was also 10 fmol/L. In a linear range from 10 fmol/L to 10A gold nanoparticles-based lateral flow strip based on SDA method for DENV detection has been established, which is convenient, fast, and the result is visible to naked eyes.

In this paper, a novel optimal design method for ground source heat pump (GSHP) system based on hydraulic characteristics of buried pipe network (BPN) is proposed. The influence of BPN hydraulic characteristics and soil thermal balance on the operation efficiency of GSHP system are considered. This paper studies the GSHP system of a building in Changsha in the Central and South China Hilly Region. First, referring to the soil thermal property test, a simple simulation model is built using TRNSYS. Furthermore, the influence extent of various factors on soil thermal balance are studied by orthogonal experimental design method (OED). Then, the BPN model of this system is established and TRNSYS is employed to establish the GSHP system model of the building. A comprehensive coefficient of performance of the whole year transportation system ( COP all ) is presented as the evaluation index to optimize the borehole depth ( B d ), borehole spacing ( B s ), buried pipe length ( B l ) and buried pipe form. These results indicate that, the resistance of vertical buried pipe accounts for 80% of the total resistance in a BPN partition. Reducing the B l from machine room to BPN by 80% in the whole BPN, and the total resistance decreases by 31.8%. It is found that there is a power function relationship between the average temperature rises of soil (ΔT) and the BPN resistance (H). Considering comprehensively, B d of this project should be designed within 60 m-100 m and B s should be designed 4.0 m-5.0 m. When the B l is certain, the COP all reaches its maximum when the B s is 3 m. For any B s between the two buried pipe forms, the B l corresponding to the maximum COP all is almost the same. They are 25.2 km for single U- tube and 67.2 km for double U- tube respectively. When the B l is the same, 24 km is the critical length of two buried pipe forms. Our work can provide theoretical basis and guidance for the optimization design of GSHP in similar areas.

Cross-border pathogens such as the African swine fever virus (ASFV) still pose a socio-economic threat. Cheaper, faster, and accurate diagnostics are imperative for healthcare and food safety applications. Currently, the discovery of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) has paved the way for the diagnostics based on Cas13 and Cas12/14 that exhibit collateral cleavage of target and single-stranded DNA (ssDNA) reporter. The reporter is fluorescently labeled to report the presence of a target. These methods are powerful, however, fluorescence-based approaches require expensive apparatuses, complicate results readout, and exhibit high-fluorescence background. Here, we present a new CRISPR&ndash, Cas-based approach that combines polymerase chain reaction (PCR) amplification, Cas12a, and a probe-based lateral flow biosensor (LFB) for the simultaneous detection of seven types of ASFV. In the presence of ASFVs, the LFB responded to reporter trans-cleavage by naked eyes and achieved a sensitivity of 2.5 &times, 10&minus, 15 M within 2 h, and unambiguously identified ASFV from swine blood. This system uses less time for PCR pre-amplification and requires cheaper devices, thus, it can be applied to virus monitoring and food samples detection.

The umbilical cord contains different populations of stem/progenitor cells such as mesenchymal, hematopoietic, trophoblastic and endothelial cells. However, the isolation methods currently in use are different, and the resulted cells are liable to cross contamination. Thus it is increasingly difficult to compare and contrast the study outcomes, which hinders progress in the field of stem cell applications. In an attempt to address this issue, we have used a magnetism assisted self-assembly method for cell capturing and releasing in combination with antibodies to mesenchymal stem cell antigens, CD105, CD73 and CD90, to identify and localize stem cells within the placenta umbilical cord. This approach is capable of detecting a minimum of 10 000 mesenchymal stem cells, and has also shown excellent specificity to distinguish other types of cells.

Abnormal growth of uterine cervix cells may eventually lead to cervical cancer, which is mainly associated with the two most prevalent types of Human Papilloma Virus (HPV), namely HPV16 and HPV18. Cervical cancer can be prevented or treated owing to its slow progression. Therefore, its early, fast, and sensitive diagnosis is crucial. Herein, we developed an ultrasensitive approach for HPV16 and HPV18 detection based on a combination of loop-mediated isothermal amplification (LAMP), CRISPR-Cas12a trans-cleavage propensity and lateral flow biosensor (LFB), collectively termed CIALFB (CRISPR/Cas- I sothermal A mplification based LFB ). CIALFB is characterized by Cas12a-mediated trans-cleavage of the reporter ssDNA upon target recognition, which results in undetectable LFB test line signal. This method was highly sensitive to detect 3.1 attomoles (∼1.8 copies) of the target, and reliably specific to detect both virus types from clinical samples with various HPV strains. Our system possesses the potential to detect other infectious diseases without tedious DNA extraction and handling, and expensive apparatuses.

The advancement in developing sensitive, rapid, and specific sensing tools is crucial in diagnostics and biotechnological applications. Although various isothermal amplification approaches exist for the detection and identification of nucleic acids, post-amplicon analysis is still based on traditional methods such as gel electrophoresis, colorimetry, turbidity, which could be non-specific and inconvenient. Thus, this review will first elaborate various isothermal amplification techniques (principle, merits, and demerits) and their potentials when combined with lateral flow approach for point-of-care nucleic acid diagnostics. Different methods for monitoring carryover contamination resulting from amplification product contamination will be discussed. Then, we will present recent advances in diagnostics with both target pre-amplification and CRISPR-Cas systems, which exhibit collateral cleavage of target nucleic acid and a reporter single strand nucleic acid within the vicinity. When the reporter is fluorophore-labeled, it provides a detectable signal by fluorescence or lateral flow biosensors. Lastly, we will discuss how CRISPR-Cas system based diagnostics could be more effective, affordable and portable for on-site detection.

More and more convolution neural network (CNN) models are used for image steganalysis, which show superior performances than traditional steganalytic methods. However, no researches on halftone image steganalysis by CNN have yet been carried. In this paper, a novel residual CNN model with stego-signal diffusion for halftone image steganalysis is proposed and achieves state-of-the-art detection accuracy. Considering inverse halftoning can reconstruct the gray-scale image from the halftone image, inverse halftoning is used to preprocess the halftone image, which can diffuse the stego-signal to neighboring pixels. As a result, the difference between the cover and stego image is magnified on the texture. Then, the residual block is utilized to construct the CNN model, since it could preserve the stego-signal better than plain network, and the magnified difference allows the network to better identify cover and stego images. A series of experiments are conducted on a large-scale dataset. The detection accuracy is improved by the magnified difference, and our proposed model outperforms the previous methods.

Utilizing G-quadruplex as the signal report probe, an ultrasensitive and label-free autocatalytic DNA circuit for Hg2+ detection on the basis of exonuclease III (Exo III)-assisted cascade signal amplification has been proposed. In the absence of Hg2+, the hairpin A and the DNA1 cannot hybridize due to the thymine-thymine (T-T) mismatches. Therefore, hairpin probes with the 3′-protruding terminus can be resistant to Exo III digestion, preventing the G-rich sequence to be released. In the presence of Hg2+, the combination of the DNA1 with the 3′ end-extruding hairpin A via T-Hg2+-T coordination chemistry triggers the digestion reaction of Exo III, leading to the release of the DNA1 and the sequence with domains c, d, and e. Both of the DNA1 and the sequence with domains c, d, and e can combine with other hairpin probes and activate another round of the cleavage reaction. The produced G-rich sequence can form G-quadruplex structure by binding with N-Methyl mesoporphyrin IX (NMM). The biosensor exhibits excellent selectivity and high sensitivity for Hg2+. The linear range of this biosensor is from 10 fM to 100 nM, and the linear equation can be expressed as: F610 = 1.3 × 105 Lg C + 7.40 × 104 (R2 = 0.998), in which F610 is the fluorescence intensity at 610 nm, C represents the Hg2+ concentrations, and Lg is the logarithm of 10. The detection limit is 10 fM. The biosensor is robust and can be applied to the detection of Hg2+ in water samples. By substituting the target-recognition elements, this sensing system can also be used for the detection of other metal ions.

As an ubiquitous heavy metal pollutant, cadmium ion (Cd2+) is detrimental to food and human health even at low concentrations. Conventional methods require costly instruments and cannot meet the requirements of on-site analysis. Here we report the use of a personal glucose meter (PGM) as the point-of-use (POU) device for portable and quantitative detection of Cd2+. The specific recognition between the aptamer and Cd2+ trigger the recycling signal amplification process by exonuclease III (Exo III). After successive hybridization and cleavage reactions, numerous single-stranded DNA were liberated on the surface of the magnetic bead. An invertase-conjugated DNA that is complementary to the single-stranded DNA is introduced into the sensing system. After magnetic separation, the invertase conjugates hydrolyze sucrose into glucose, thus establishing direct conversion of Cd2+ concentration to glucose amount, which can be directly quantified by a PGM. Thanks to the synergistic signal amplification of Exo III and invertase, the POU device greatly improves the sensitivity for Cd2+ analysis, with a detection limit of 5 p.M. With the advantages of portability, cost-effectiveness, wide availability, and ease of use, the PGM-based detector has the potential to be used by the public as a routine tool for reliable and quantitative detection of Cd2+.

A wash-free and label-free colorimetric biosensor for the amplified detection of aflatoxin B1 (AFB1) has been constructed by the integration of an ingenious hairpin DNA probe with exonuclease III (Exo III)-assisted signal amplification. The presence of the AFB1 activates the continuous cleavage reactions by Exo III toward a hairpin probe, resulting in the autonomous accumulation of numerous free G-quadruplex sequences, which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to produce a colorimetric response. The naked-eye biosensor is ultrasensitive, enabling the visual detection of trace amounts of AFB1 as low as 1 pM without instrumentation. The sensor is robust and can work even when challenged with complex sample matrices such as peanut samples. With the advantages of simple operation, wash-free and label-free format, visible and intuitive output, and low cost, the naked-eye based colorimetric biosensor is expected to have potential applications for in-field detection of AFB1.