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The outbreak of citrus brown spot because of Alternaria is one of the most destructive citrus diseases. Additionally, Alternaria species produce highly toxic mycotoxins. Mass screening is a valid method to control the spread of Alternaria. Morphological analysis and polymerase chain reaction combined with gene-sequencing technique are the most commonly used techniques for detecting Alternaria. However, they are limited by either low convenience and accuracy or low instrument accessibility and high cost. To balance the convenience, accuracy, test availability, and low cost, we develop a CRISPR/Cas12a-based photothermal platform for the portable detection of Alternaria genes using a thermometer. Using this platform, the Alternaria genes from the synthetic sequences and cultured fungus of citrus, tomato, and apple can be detected using a thermometer with a detection limit of 1.5 pM. With the aid of the CRISPR/Cas12a system, citrus-associated Alternaria can be specifically differentiated from other citrus disease-associated microorganisms. When the photothermal platform is applied to analyze the citrus fruit samples collected in the field, good-consistency results are obtained with the gene-sequencing technology. The excellent performance of this portable method shows that it can be applied to screen for Alternaria in resource-poor settings.

Portable and sensitive detection of carbendazim (CBD) is highly desirable for food safety and environmental protection. Herein, a portable immunosensor for the sensitive detection of CBD is proposed based on alkaline phosphatase (ALP)-labeled and secondary antibody-modified gold nanoparticles (AuNPs). The quantification is based on ALP catalyzing the dephosphorylation of glucose-1-phosphate disodium salt to generate glucose, thus converting the concentration of CBD into glucose, thereby realizing the portable detection of CBD by personal glucose meter. Benefiting from signal amplification strategy that integrates the large specific surface area of AuNPs, the enzymatic reactions of terminal deoxynucleotidyl transferase and ALP, a low detection limit of 0.37 ng/mL for CBD is achieved. When this portable method is used to analyze citrus fruit, canned citrus, and cabbage, good-consistency results are obtained with the UPLC-MS/MS method. The good performance demonstrates the great potential of this portable method for CBD monitoring in resource-poor settings.

A convenient, fast, and colorful colorimetric platform with high resolution for acetylcholinesterase (AChE) activity and its inhibitors detection based on the regulation of oxidase-like nanozyme-me...

Enzyme-linked immunosorbent assay (ELISA) with high specificity and sensitivity is one of the most popular techniques for detecting carbendazim (CBD), a commonly used benzimidazole fungicide in agriculture. However, the traditional ELISA based on the horseradish peroxidase (HRP)-3,3′,5,5′-tetramethylbenzidine (TMB) system for CBD only displays the yellow color of TMB2+ from deep to light, making it difficult for the naked eye to judge whether CBD in fruits and vegetables exceeds the maximum residue limit. In this article, we intend to improve the traditional ELISA method to establish a multicolor signal output ELISA to achieve visual semiquantitative detection of CBD. This method is based on the optical properties of gold nanorods (AuNRs). After introducing AuNRs into TMB2+ solution, which was produced by the HRP-TMB system of traditional ELISA, AuNRs were quickly etched by TMB2+. Consequently, the longitudinal localized surface plasmon resonance peak of AuNRs shows a clear blue shift and a vivid color change. Different concentrations of CBD generate different amounts of TMB2+, which in turn leads to different etching degrees of AuNRs, and ultimately results in a rainbow-like color change. As a result, CBD from 0.08 to 100 ng mL−1 can be easily distinguished by the naked eye, which does not require any large instruments. Moreover, the colors displayed by 0.49 ng mL−1 (purple) and 0 ng mL−1 (pink) are significantly different from each other. It should be noted that 0.49 ng mL−1 is far below the most stringent maximum residue limit of CBD in the world. Additionally, the quantitative determination of CBD spiked in canned citrus, citrus fruits, chives, and cabbage samples showed satisfactory recoveries. The good performance of the AuNR-based ELISA makes it have a wide range of application prospects in food safety and international trade.

Herein, we report a colorful colorimetric method for semiquantitative visual identification of Staphylococcus aureus (S. aureus) based on dual enzyme-induced gold–silver (Au–Ag) alloy nanorods (NRs...

A linearized model of frequency measurement for the Free Induction Decay (FID) signal is proposed to increase the Proton Magnetometer (PM) precision. First, the nonlinear model of frequency measurement is set up according to the characteristic of the FID signal. Then, according to the error analysis of the MCFM method, the model is linearized on the condition of precision requirement. Furthermore, to reduce the nonlinear error caused by approximate treatment and the trigger time error caused by the random noise, the Least Squares (LS) method is adopted to estimate the slope of the linearized model, and the frequency to be measured is the inverse of the slope. Finally, a PM Prototype is made to verify the effectiveness of the proposed method. Experimental results show that the precision of frequency measurement is obviously increased if the proposed method is adopted for the noised sine signal. Moreover, the RMSD and the NPSD of magnetic-field measurement are about 0.13 nT and 80 pT/Hz1/2, respectively if the proposed method is adopted by PM, which is better than the comparison method.

Herein, we propose a sensitive fluorescent assay for organophosphorus pesticides (OPs) detection based on a novel strategy of activating the CRISPR-Cas12a system. Specifically, acetylcholinesterase (AChE) hydrolyzes acetylthiocholine into thiocholine (TCh). Subsequently, TCh induces the degradation of MnO

Herein, we report a colorful colorimetric method for semiquantitative visual identification of

A convenient, fast, and colorful colorimetric platform with high resolution for acetylcholinesterase (AChE) activity and its inhibitors detection based on the regulation of oxidase-like nanozyme-mediated etching of gold nanorods (AuNRs) has been proposed in this work. MnO

Photothermal reagent-mediated portable detection platforms using thermometers as signal readers have received extensive attention due to their simplicity, low cost, and practicality. However, exploitation photothermal reagent with excellent photothermal conversion effect, convenient to synthesize, preferably without any modification for biosensing application, is still challenging. Herein, a simple and rapid seed-mediated in situ synthesis strategy has been developed for the preparation of gold nanostars (AuNSs) with remarkable photothermal conversion effect. By simply changing the seed size and component concentrations involved in the in situ synthesis process, AuNSs have adjustable geometries, allowing the photothermal conversion to be tuned to a high level optimal for biosensing. Meanwhile, an accurate understanding of the photothermal conversion mechanism is obtained by studying the relationship between the morphology of AuNSs and the photothermal effect. Subsequently, using ascorbic acid (AA) as a model target, the preliminary application of AuNSs in constructing a portable photothermal detection platform has been demonstrated. This in situ preparation strategy of AuNSs not only exhibits remarkable photothermal conversion effect, but also avoids complicated and time-consuming synthesis and modification. Therefore, it has great potential to be extended to portable detection of other targets by simply converting the concentration of the target to that of AA.

Ionizing radiation (IR) therapy for malignant tumors can damage adjacent tissues, leading to severe wound complications. Plasma-derived exosome treatment has recently emerged as a safe and impactful cell-free therapy. Herein, we aimed to determine whether plasma-derived exosomes could improve the healing of post-radiation wound. Rat plasma-derived exosomes (RP-Exos) were locally injected on cutaneous wounds created on the backs of irradiated rats and boosted the healing process as well as the deposition and remodeling of the extracellular matrix with collagen formation. Subsequently, the effects of RP-Exos were further evaluated on irradiated fibroblasts in vitro. The results suggested that exosomes promoted fibroblast proliferation, migration, cell cycle progression, and cell survival. Moreover, transcriptome sequencing analysis and quantitative polymerase chain reaction validation were performed to identify potential mechanisms. RPExos enhanced the expression of cell proliferation and radioresistance-related genes, and yet downregulated ferroptosis pathway in irradiated fibroblasts. Inhibition of ferroptosis by RP-Exos was further confirmed through colorimetric assay, fluorescence probe and flow cytometry in ferroptosis-induced fibroblasts. Our results suggest that RP-Exos regulate cell proliferation and ferroptosis in irradiated fibroblasts, thereby boosting the healing of irradiated wound. These findings support plasma-derived exosomes as a potential therapeutic method for post-radiation wound complications.

Isolated mechanical systems -- e.g., those floating in space, in free-fall, or on a frictionless surface -- are able to achieve net rotation by cyclically changing their shape, even if they have no net angular momentum. Similarly, swimmers immersed in "perfect fluids" are able to use cyclic shape changes to both translate and rotate even if the swimmer-fluid system has no net linear or angular momentum. Finally, systems fully constrained by direct nonholonomic constraints (e.g., passive wheels) can push against these constraints to move through the world. Previous work has demonstrated that the net displacement induced by these shape changes corresponds to the amount of *constraint curvature* that the gaits enclose. To properly assess or optimize the utility of a gait, however, we must also consider the time or resources required to execute it: A gait that produces a small displacement per cycle, but that can be executed in a short time, may produce a faster average velocity than a gait that produces a large displacement per cycle, but takes much longer to complete a cycle at the same average instantaneous effort. In this paper, we consider two effort-based cost functions for assessing the costs associated with executing these cycles. For each of these cost functions, we demonstrate that fixing the average instantaneous cost to a unit value allows us to transform the effort costs into time-to-execute costs for any given gait cycle. We then illustrate how the interaction between the constraint curvature and these costs leads to characteristic geometries for optimal cycles, in which the gait trajectories resemble elastic hoops distended from within by internal pressures., Comment: 20 Pages, submitted to IEEE Transactions on Robotics

The monitoring of the fungal genus Alternaria, which causes destructive brown spot disease in citruses worldwide and produces highly toxic mycotoxins, is extremely important to protect citrus and human health. In this work, we describe an ultrasensitive colorimetric method for the detection of genomic DNA of Alternaria from citrus fruit samples, using a system consisting of five groups of reporter probes. Each reporter probe is prepared by coupling recognition DNA and horseradish peroxidase (HRP) on the surface of gold nanoparticle (AuNP) through a convenient and low-cost freezing-assisted method. Meanwhile, the capture DNA is immobilized on magnetic bead (MB) via biotin-streptavidin reaction. Then, the capture DNA, target DNA, and five groups of AuNP-based reporter probes form a stable DNA-heptamer sandwich structure on the MB, and then HRP generates a blue signal for the subsequent colorimetric detection. It should be noted that AuNP with a large specific surface area drives abundant HRP anchoring, resulting in significant signal amplification. In addition, there are five groups of AuNP-based reporter probes, which further amplify the detection signal. As a result, the detection limit of the artificial target DNA is as low as 15.6 pM. Because the detection signal can be recorded visually without any special equipment, and its sensitivity is high, this method represents a suitable diagnostic tool for Alternaria genetic detection.

Colorimetry has been considered as a potential instrument-free platform for point-of-care genomic detection. However, it is limited by the poor sensitivity and low color resolution. Herein, we report a high-resolution colorimetric biosensor based on multiple hybridization chain reactions (HCRs) on gold nanoparticle (AuNP) and alkaline phosphatase (ALP)-mediated in situ growth of gold nanobipyramids (AuNBPs) for ultrasensitive detection of the Staphylococcus aureus (S. aureus) mecA gene. In our design, target DNA is hybridized with capture hairpin DNA on magnetic beads and then amplified by multiple HCRs on AuNP. Since biotin-labeled hairpin-structured nucleic acids are utilized to conduct HCRs, together with the large specific surface area of AuNP, the biotin- and streptavidin- based reaction results in a large amount of ALP on AuNP. With the aid of NADPH, ALP-mediated in situ growth of AuNBPs is observed, and a series of rainbow-like colors are associated with different target DNA concentrations. Through the multiple-amplification strategy produced by AuNP, HCRs, and enzymatic reactions, the target DNA as low as 2.71 pM can be detected with high specificity. Moreover, this method has been successfully applied to detect the mecA gene extracted from S. aureus. Therefore, the proposed method holds great potential in clinical diagnosis.

Colorimetric aptasensors have been intensively studied for the ochratoxin A (OTA) detection, but they mostly exhibit just one-color change, resulting in poor visual resolution and limited use for semi-quantitative analysis. Thus, we designed a high-resolution colorimetric assay on the basis of aptamer structural switching and enzyme-induced metallization of gold nanorods (AuNRs). DNA-alkaline phosphatase (ALP)-immobilized magnetic beads were prepared. The aptamer bounded to OTA to form G-quadruplexes, releasing ALP-labelled complementary DNA (cDNA-ALP). After magnetic separation, cDNA-ALP catalyzed the decomposition of ascorbic acid 2-phosphate to ascorbic acid that reduced Ag+, forming an Ag shell on the surface of AuNRs. This caused a blue-shift of the longitudinal local surface plasmon resonance peak of the AuNRs and a naked eye visible multicolor change. Under optimal conditions, the assay exhibited a 9.0 nM detection limit for OTA, with high specificity. This method is promising for the on-site visual semi-quantitative detection of mycotoxins in foods.

The detection of carbendazim (CBZ) is important for food safety and human health. However, most current analytical methods require large instruments and highly trained operators. In order to solve this problem, herein, an innovative portable and quantitative photothermal assay platform relying on a thermometer readout for the detection of CBZ has been developed. Gold nanoparticles (AuNPs), which exhibit a strong distance-dependent photothermal effect under specific laser irradiation, were utilized as indicators. The CBZ aptamer was introduced to protect AuNPs from salt-mediated aggregation. When CBZ is present, the binding event between CBZ and aptamer leads to the loss of the aptamer protective effect on AuNPs, and AuNP aggregation occurs. Under 650-nm laser irradiation, the increase in temperature associated with an AuNP-dependent photothermal effect is highly related to the CBZ concentration. Having the advantages of user-friendliness, low cost, quick response, and portability, this method has great potential for on-site applications.

A simple and efficient strategy based on the manganese dioxide (MnO2) nanosheet-mediated etching of gold nanorods (AuNRs) has been demonstrated, affording an effective and convenient way to develop a high-resolution multicolor colorimetric method for the visual detection of antioxidants. The UV−visible absorption spectroscopy and transmission electron microscopy results revealed that the MnO2 nanosheets etched the AuNRs quickly in weakly acidic solutions at room temperature, resulting in a significant blue shift in the AuNR longitudinal local surface plasmon resonance peak and vivid color changes. The feasibility of the etching process was theoretically evaluated by comparing the standard electron potentials of Au(I)/Au(0) and Mn(IV)/Mn(II). Changes in the chemical valencies of Au and Mn during the etching process were analyzed via X-ray photoelectron spectroscopy, which further confirmed that the etching process occurred. Key factors, including the concentrations of the MnO2 nanosheets, cetyltrimethylammonium bromide, and H+, and incubation time, were then investigated. The application of MnO2 nanosheet-mediated AuNR etching for antioxidant analysis was based on the antioxidant-induced decomposition of MnO2 nanosheets. With the merits of simplicity and user-friendliness, this method provides a promising platform for the visual detection of total antioxidant capacity in real beverages.

An innovative colorimetric method based on enzyme-induced gold nanoparticle aggregation was developed to detect the activity of alkaline phosphatase (ALP), and it was further applied to construct an aptasensor to monitor ochratoxin A (OTA) concentrations. In the presence of ALP, the substrate ascorbic acid 2-phosphate was hydrolyzed to generate ascorbic acid (AA). Subsequently, reduction of MnO2 nanosheets by AA produced manganese ions, which mediated gold nanoparticle aggregation. The color of the detection solution changed from brown-red to purple to blue as the ALP concentration increased, and a detection limit of 0.05 U·L-1 was achieved. Furthermore, this strategy was successfully utilized to devise a target-responsive aptasensor for colorimetric detection of an important mycotoxin, OTA, which causes food poisoning and has various toxic effects on humans. The proposed method offers high sensitivity with a detection limit as low as 5.0 nM together with high specificity. When applied to analyze red wine and grape juice samples, no complex sample pretreatment or bulky instruments were required. Overall, a colorimetric platform based on enzyme-induced gold nanoparticle aggregation was successfully established to improve the simplicity and sensitivity of ALP and OTA detection. This platform appears highly promising for mycotoxin-related food safety monitoring.