A covalent-organic framework-based platform for simultaneous smartphone detection and degradation of aflatoxin B1.

This study developed a smartphone-based biosensor that could simultaneously detect and degrade aflatoxin B1 (AFB1). A donor-acceptor covalent organic framework (COF) was bound onto the surface of stainless-steel mesh (SSM) via the in-situ synthesis, which was used to immobilize the aptamer (Apt) to specifically capture AFB1 and was also as a photocatalyst to degrade AFB1. Au@Ir nanospheres were synthesized, which exhibited better peroxidase catalytic activity (Km=5.36 × 10-6 M, Vmax=3.48 × 10-7 Ms-1, Kcat=1.00 × 107 s-1) than Ir@Au nanospheres, so Au@Ir nanospheres were linked with Apt2 to be utilized as the signal probe. The density functional theory calculation also described that Au@Ir nanospheres possessed the lower energy barriers to decompose H2O2 than Ir@Au nanospheres. Coupled with the "Color Picker" application in the smartphone, the established "sandwich-structure" colorimetric method exhibited a linear range of 0.5-200 µg L-1 and a detection limit of 0.045 µg L-1. The photocatalytic capacity of SSM/COF towards AFB1 was investigated and the degradation rate researched 81.14 % within 120 min under the xenon lamp irradiation, and the degradation products were validated by ESI-MS. It was applied for the detection of AFB1 in peanuts, corn, and wheat samples. Recoveries were ranging from 77.90 % to 112.5 %, and the matrix effect was 75.10-111.6 %. Therefore, the smartphone-based biosensor provided a simple, fast, and sensitive platform for the detection of AFB1, and meanwhile could realize the efficient degradation of AFB1.

A new colorimetric lactate biosensor based on CUPRAC reagent using binary enzyme (lactate-pyruvate oxidases)-immobilized silanized magnetite nanoparticles.

A novel optical lactate biosensor is presented that utilizes a colorimetric interaction between H2O2 liberated by a binary enzymatic reaction and bis(neocuproine)copper(II) complex ([Cu(Nc)2]2+) known as CUPRAC (cupric reducing antioxidant capacity) reagent. In the first step, lactate oxidase (LOx) and pyruvate oxidase (POx) were separately immobilized on silanized magnetite nanoparticles (SiO2@Fe3O4 NPs), and thus, 2 mol of H2O2 was released per 1 mol of the substrate due to a sequential enzymatic reaction of the mixture of LOx-SiO2@Fe3O4 and POx-SiO2@Fe3O4 NPs with lactate and pyruvate, respectively. In the second step, the absorbance at 450 nm of the yellow-orange [Cu(Nc)2]+ complex formed through the color reaction of enzymatically produced H2O2 with [Cu(Nc)2]2+ was recorded. The results indicate that the developed colorimetric binary enzymatic biosensor exhibits a broad linear range of response between 0.5 and 50.0 µM for lactate under optimal conditions with a detection limit of 0.17 µM. The fabricated biosensor did not respond to other saccharides, while the positive interferences of certain reducing compounds such as dopamine, ascorbic acid, and uric acid were minimized through their oxidative removal with a pre-oxidant (NaBiO3) before enzymatic and colorimetric reactions. The fabricated optical biosensor was applied to various samples such as artificial blood, artificial/real sweat, and cow milk. The high recovery values (close to 100%) achieved for lactate-spiked samples indicate an acceptable accuracy of this colorimetric biosensor in the determination of lactate in real samples. Due to the increase in H2O2 production with the bienzymatic lactate sensor, the proposed method displays double-fold sensitivity relative to monoenzymatic biosensors and involves a neat color reaction with cupric-neocuproine having a clear stoichiometry as opposed to the rather indefinite stoichiometry of analogous redox dye methods.

Enzymes encapsulated in organic-inorganic hybrid nanoflower with spatial localization for sensitive and colorimetric detection of formate.

Formate is an important environmental pollutant, and meanwhile its concentration change is associated with a variety of diseases. Thus, rapid and sensitive detection of formate is critical for the biochemical analysis of complex samples and clinical diagnosis of multiple diseases. Herein, a colorimetric biosensor was constructed based on the cascade catalysis of formate oxidase (FOx) and horseradish peroxidase (HRP). These two enzymes were co-immobilized in Cu3(PO4)2-based hybrid nanoflower with spatial localization, in which FOx and HRP were located in the shell and core of nanoflower, respectively (FOx@HRP). In this system, FOx could catalyze the oxidation of formate to generate H2O2, which was then utilized by HRP to oxidize 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid to yield blue product. Ideal linear correlation could be obtained between the absorbance at 420 nm and formate concentration. Meanwhile, FOx@HRP exhibited excellent detection performance with low limit of detection (6 µM), wide linear detection range (10-900 µM), and favorable specificity, stability and reusability. Moreover, it could be applied in the detection of formate in environmental, food and biological samples with high accuracy. Collectively, FOx@HRP provides a useful strategy for the simple and sensitive detection of formate and is potentially to be used in biochemical analysis and clinical diagnosis.

Poly (ionic liquid) cross-linked hydrogel encapsulated with AuPt nanozymes for the smartphone-based colorimetric detection of zearalenone.

A poly (ionic liquid) enhanced poly(acrylamide-acrylic acid) (PIL-PAM/AA) hydrogel-based colorimetric sensor was designed to detect zearalenone (ZEN). Different AuxPty nanoparticles were synthesized via the on-pot method. Through the kinetic analysis and the theoretical calculation, Au0.4Pt0.6 possessed the relatively low energy barriers to adsorb and decompose H2O2 so that it exhibited relatively better catalytic activity (Km = 2.02 × 10-3, Vmax = 6.14 × 10-7). AuPt nanoparticles were encapsulated into PIL-PAM/AA hydrogel via the interaction between aptamer and cDNA. In the presence of ZEN, the embedded AuPt nanoparticles were released to complete the catalytic reaction. Coupled with the smartphone application, the established method provided the linear range of 1-250 ng mL-1, with a detection limit of 0.6979 ng mL-1 for ZEN. Meanwhile, it also possessed excellent selectivity and good anti-interference performance. In wheat and corn samples, spiked recoveries were ranging from 75% to 113.30%.

Sensitive colorimetric detection of Vibrio vulnificus based on target-induced shielding against the peroxidase-mimicking activity of CeO2@PtRu nanozyme.

Vibrio vulnificus infection caused by contaminated aquatic products and seawater can lead to severe disease and high mortality. The development of a rapid and sensitive detection method for Vibrio vulnificus is vital to effectively prevent infection in advance. In this study, CeO2@PtRu with high peroxidase activity was used to construct a colorimetric immunoassay for Vibrio vulnificus detection by conjugating polyclonal antibodies via the biotin-streptavidin system. The developed colorimetric biosensor for Vibrio vulnificus demonstrated rapid operability and good sensitivity with a detection range from 104 CFU/mL to 109 CFU/mL, and the limit of detection (LOD) is 193 CFU/mL. Moreover, the colorimetric biosensor showed excellent specificity and good recoveries from 98.70% to 102.10% with RSD < 7.45% for spiked real samples. This novel CeO2@PtRu-based colorimetric biosensor has great application potential for the sensitive detection of Vibrio vulnificus in seafood.

AI-assisted smartphone-based colorimetric biosensor for visualized, rapid and sensitive detection of pathogenic bacteria.

Accurate and effective detection is essential to against bacterial infection and contamination. Novel biosensors, which detect bacterial bioproducts and convert them into measurable signals, are attracting attention. We developed an artificial intelligence (AI)-assisted smartphone-based colorimetric biosensor for the visualized, rapid, sensitive detection of pathogenic bacteria by measuring the bacteria secreted hyaluronidase (HAase). The biosensor consists of the chlorophenol red-ß-D-galactopyranoside (CPRG)-loaded hyaluronic acid (HA) hydrogel as the bioreactor and the ß-galactosidase (ß-gal)-loaded agar hydrogel as the signal generator. The HAase degrades the bioreactor and subsequently determines the release of CPRG, which could further react with ß-gal to generate signal colors. The self-developed YOLOv5 algorithm was utilized to analyze the signal colors acquired by smartphone. The biosensor can provide a report within 60 min with an ultra-low limit of detection (LoD) of 10 CFU/mL and differentiate between gram-positive (G+) and gram-negative (G-) bacteria. The proposed biosensor was successfully applied in various areas, especially the evaluation of infections in clinical samples with 100% sensitivity. We believe the designed biosensor has the potential to represent a new paradigm of "ASSURED" bacterial detection, applicable for broad biomedical uses.

Rapid and practical colorimetric biosensor for leishmaniasis diseases.

In this article, a colorimetric biosensor for detection of Leishmania major surface protease (Gp63) antibody (anti-gp63) was developed by using gold nanoparticle (AuNP) as a color reagent. The dispersion or aggregation of AuNPs leads to a distinct and sensitive change in UV-vis spectra and solution color. For this purpose, kinetoplastid membrane protein-11 (KMP-11) was labeled with AuNPs surface directly. After that, Gp63 antibody was added in the KMP-11@AuNP solution and a color change from red/pink to purple/violet was observed. As a result, anti-gp63 solution diluted at a ratio of 1:640 can be detected with the developed colorimetric leishmania biosensor. The relative standard deviation value for 1:320 diluted anti-gp63 was calculated as 1.29 %. Furthermore, the linear range of the developed colorimetric biosensor was determined as 1:80 to 1:640. Moreover, developed Leishmania biosensor was applied for detection of leishmania parasite crude antigen and rabbit serum which were used as positive and negative samples respectively. As a result, the recovery values for the measurements of aforementioned samples were calculated as 95.3 % ± 0.02, 103.1 % ± 0.02, 96.2 % ± 0.01 and 95.5 % ± 0.03 for dilutions of 1:200, 1:160, 1:320 and 1:640 anti-gp63 solutions respectively.

Smartphone-based device for rapid and single-step detection of piRNA-651 using anti-DNA:RNA hybrid antibody and enzymatic signal amplification.

P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs/piRs) are a class of small noncoding RNAs that play a crucial role in regulating various biological processes, including carcinogenesis. One specific piRNA, piR-651, has been reported to be overexpressed in both human blood serum and solid cancer tissues, that can be used a viable biomarker in cancer diagnosis. Early diagnosis of cancer can help reduce the burden of the disease and improve survival rates. In the present work, we report for the first time a smartphone-based colorimetric biosensor for highly sensitive and specific detection of piR-651 thanks to an enzymatic signal amplification, which yielded high colorimetric intensities. Indeed, a heteroduplex DNA:RNA was formed in the presence of piR-651 with the capture DNA probe immobilized on the magnetic beads for easy magnetic separation. Then, a HRP tethered to anti-DNA:RNA (S9.6) was used to reveal the DNA-RNA heteroduplex formed by catalyzing the oxidation of TMB substrate into colorimetric TMBox, which absorbs at 630 nm. The absorbance is positively proportional to the piR-651 concentrations. On the other hand, the colorimetric product of the assay can be photographed with a smartphone camera and analyzed using ImageJ software. Using a smartphone and under optimal conditions, the biosensor responded linearly to the logarithm of piRNA-651 from 8 fM to 100 pM with a detection limit of 2.3 fM and discriminates against other piRNAs. It was also successfully applied to the determination of piRNA-651 levels in spiked human serum.

Colorimetric detection of circulating tumor cells in breast cancer based on ladder-branch hybridization chain reaction and DFs/AuNCs nanozyme.

Breast cancer is the most common malignant tumor in women, which accounts for 6.9% of all cancer-related deaths. Early diagnosis is crucial for making the best clinical decision and improving the prognosis of patients. Circulating tumor cells (CTCs) have been regarded as significant tumor biomarkers. Herein, we designed a colorimetric biosensor for breast cancer CTCs quantification based on ladder-branch hybridization chain reaction (HCR) and DNA flowers/gold nanoclusters (DFs/AuNCs) nanozyme. With the assistance of complementary DNA labeled on magnetic beads (MBs), the cleavage products of RNA-cleaving DNAzymes (RCDs) could be rapidly captured, subsequently triggering ladder-branch HCR. In addition, the DFs/AuNCs nanozyme was applied for colorimetric analysis, which further improved the sensitivity for the detection of target CTCs. Benefiting from specific RCDs, ladder-branch HCR and DFs/AuNCs, we achieved a superior detection limit of 3 cells/mL as well as a broad linear range of 10 cells/mL to 104 cells/mL. Conclusively, this colorimetric biosensor achieved sensitively and selectively detection of breast cancer CTCs without the participation of enzymes at room temperature, which might provide new insight into the early detection of breast cancer.

Ionic liquid-enhanced silica aerogels for the specific extraction and detection of aflatoxin B1 coupled with a smartphone-based colorimetric biosensor.

The polymer ionic liquid (1-allyl-3-butylimidazolium bromide) enhanced silica aerogel was modified onto the surface of stainless-steel mesh to immobilize aptamer-1 for the specific recognition of AFB1. The porous channels of silica aerogel could prevent the interference of macromolecules in food samples. Enzyme kinetic analysis showed that the MoS2/Au was an effective peroxidase mimic with a relatively low Michaelis constant (Km) value of 0.17 mM and a high catalytic rate of 3.87 × 10-8 mol (L·s)-1, which exhibited obvious superiority compared with horseradish peroxidase. The established "sandwich-structure" biosensor was coupled with the smartphone "Color Picker" application was used to detect AFB1 with a wide linear range (1-100 ng mL-1) and low detection limit (0.25 ng mL-1). The anti-interference ability of the established biosensor was evaluated by adding different concentrations of standards in corn, peanut, and wheat and matrix effects were 90.84-106.11 %. The results showed that this method demonstrated high specificity, sensitivity, rapidity and low interference in food samples.

Rapid and Ultrasensitive Colorimetric Biosensors for Onsite Detection of Escherichia coli O157:H7 in Fluids.

This study presents a breakthrough in the field of onsite bacterial detection, offering an innovative, rapid, and ultrasensitive colorimetric biosensor for the detection of Escherichia coli (E. coli) O157:H7, using chemically modified melamine foam (MF). Different from conventional platforms, such as 96-well plates and fiber-based membranes, the modified MF features a macroporous reticulated three-dimensional (3D) framework structure, allowing fast and free movement of large biomolecules and bacteria cells through the MF structure in every direction and ensuring good accessibility of entire active binding sites of the framework structure with the target bacteria, which significantly increased sensitive and volume-responsive detection of whole-cell bacteria. The biosensing platform requires less than 1.5 h to complete the quantitative detection with a sensitivity of 10 cfu/mL, discernible by the naked eye, and an enhanced sensitivity of 5 cfu/mL with the help of a smartphone. Following a short enrichment period of 1 h, the sensitivity was further amplified to 2 cfu/mL. The biosensor material is volume responsive, making the biosensing platform sensitivity increase as the volume of the sample increases, and is highly suitable for testing large-volume fluid samples. This novel material paves the way for the development of volume-flexible biosensing platforms for the record-fast, onsite, selective, and ultrasensitive detection of various pathogenic bacteria in real-world applications.

Smartphone-assisted colorimetric biosensor for the determination of organophosphorus pesticides on the peel of fruits.

Nowadays, the widespread use of organophosphorus pesticides (OPs) in agricultural production leads to varying degrees of residues in crops, which pose a potential threat to human health. Conventional methods used in national standard for the detection of OPs in fruits and vegetables require expensive instruments or cumbersome sample pretreatment steps for the analysis. To address these challenges, in this work, we took advantage of the peroxidase-like activity of PtCu3 alloy nanocrystals (NCs) for a colorimetric and smartphone assisted sensitive detection of OPs. With the assist of a smartphone, the concentration of OPs on the peel of fruits could be obtained by comparing the B/RG value (the brightness value of blue divided by those of red and green) of a test strip with a calibration curve. This work not only provides a facile and cost-effective method to detect pesticides but also makes a positive contribution to food safety warning.

Reusable Colorimetric Biosensors on Sustainable Silk-Based Platforms.

In biosensor development, silk fibroin is advantageous for providing transparent, flexible, chemically/mechanically stable, biocompatible, and sustainable substrates, where the biorecognition element remains functional for long time periods. These properties are employed here in the production of point-of-care biosensors for resource-limited regions, which are able to display glucose levels without the need for external instrumentation. These biosensors are produced by photopatterning silk films doped with the enzymes glucose oxidase and peroxidase and photoelectrochromic molecules from the dithienylethene family acting as colorimetric mediators of the enzymatic reaction. The photopatterning results from the photoisomerization of dithienylethene molecules in the silk film from its initial uncolored opened form to its pink closed one. The photoisomerization is dose-dependent, and colored patterns with increasing color intensities are obtained by increasing either the irradiation time or the light intensity. In the presence of glucose, the enzymatic cascade reaction is activated, and peroxidase selectively returns closed dithienylethene molecules to their initial uncolored state. Color disappearance in the silk film is proportional to glucose concentration and used to distinguish between hypoglycemic (below 4 mM), normoglycemic (4-6 mM), and hyperglycemic levels (above 6 mM) by visual inspection. After the measurement, the biosensor can be regenerated by irradiation with UV light, enabling up to five measurement cycles. The coupling of peroxidase activity to other oxidoreductases opens the possibility to produce long-life reusable smart biosensors for other analytes such as lactate, cholesterol, or ethanol.

Bimetallic nanozyme-bioenzyme hybrid material-mediated ultrasensitive and automatic immunoassay for the detection of aflatoxin B1 in food.

Aflatoxin B1 (AFB1) is one of the most prevalent and dangerous biotoxin in crops and feedstuff, which poses a great threat to human health and also cause significant financial losses. Therefore, there is an urgent need to develop an effective method for AFB1 detection. In this work, we developed an automatic reaction equipment and nanozyme-enhanced immunosorbent assay (Auto-NEISA) for sensitive and accurate detection of AFB1 by combining the highly effective signal probes with a self-designed automated immunoreactive equipment. Wherein, polystyrene (PS) nanoparticles were used as signal carriers for loading a massive in situ-synthesized platinum and palladium bimetallic nanozyme, which could enrich horseradish peroxidase-labeled goat anti-mouse antibody (HRP-Ab2) on the nanozyme surface to form a bimetallic nanozyme-bioenzyme hybrid material for multiple signal amplification. The entire reaction could be automatically completed by the self-developed immunoreactive equipment. The Auto-NEISA method realized the sensitive detection of AFB1 with a wide linear detection range of 10-104 pg/mL, at a low limit of detection (LOD) of 5.52 pg/mL. The LOD was 65-fold lower than that of the enzyme-linked immunosorbent assay (ELISA). Additionally, Auto-NEISA was successfully applied to detect AFB1 in real food samples, demonstrating that it has considerable potential for detecting food contaminants with high accuracy and efficiency.

Aptamer-functionalized polydiacetylene biosensor for the detection of three foodborne pathogens.

Rapid, simple and sensitive screening of foodborne pathogens is of great significance to ensure food safety. In this study, an aptamer-functionalized polydiacetylene (Apta-PDA) biosensor was developed for the detection of E. coli O157:H7, S. typhimurium or V. parahaemolyticus. First, aptamers responding to the target bacteria were modified on the surface of magnetic beads by covalent binding to form MBs-oligonucleotide conjugates for bacterial enrichment. Then, an Apta-PDA biosensor was obtained by connecting the aptamers to the PDA nanovesicles using the carbodiimide method. Molecular recognition occurred in the presence of the target bacteria, whereby the aptamer folded into a sequence-defined unique structure, resulting in an MBs-Apta/bacteria/Apta-PDA sandwich structure. Due to the optical properties of PDA, the blue-red transition of the detection system could be observed by the naked eye and quantified by the colorimetric response percentage (CR%). Under optimized conditions, the detection limits of E. coli O157:H7, S. typhimurium and V. parahaemolyticus were 39, 60 and 60 CFU/ml, respectively, with a selectivity of 100% and a reaction time of 30 min. Compared with the gold standard method, the accuracy of the three target bacteria detection reached 98%, 97.5% and 97%, respectively, and the sensitivity and specificity were both greater than 90%. The entire detection process was rapid and easy to execute without any special equipment, making this technology particularly suitable for resource-poor laboratories or regions.

High-Throughput Bioassay for Detection of Latent Fungi in Postharvest Produce.

Enormous fresh agricultural produce is wasted annually due to rots caused by pathogenic microorganisms. Most pathogenic fungi attack the harvested produce by penetrating the fruit at the field and remaining quiescent or latent until the fruit ripens or senescence. In this work, a recently developed simple, cost-effective, and high-throughput 96-well plate-based assay was applied to determine the presence of pathogenic fungi in their latent stage. The surface strands immobilized on the 96-well plate, only with the presence of the complementary RNA marker (enoyl-CoA hydratase (ECH)) of the latent fungal-pathogen Colletotrichum gloeosporioides will create a complex with the target and reporter (labeled with the horseradish peroxidase (HRP) enzyme) strands for positive signal generation. The developed assay demonstrated 3.1-fold higher specificity for the latent marker (ECH) of C. gloeosporioides compared to latent markers of other pathogenic fungi. A 2 nM detection limit of target strands was demonstrated, showing a high plate sensitivity, and was further validated with biological samples extracted from latent infection in tomato fruit. The developed assay provides a new economical tool for detecting the presence of latent RNA markers of pathogenic fungi in agricultural produce, ultimately improving postharvest decision-making and reducing postharvest losses.

Development of an Innovative Colorimetric DNA Biosensor Based on Sugar Measurement.

The development of biosensors for target detection plays a crucial role in advancing various fields of bioscience. This work presents the development of a genosensor that exploits the colorimetric phenol-sulfuric acid sugar reaction for the detection of DNA, and RNA as specific targets, and DNA intercalator molecules. The biosensor combines simplicity and reliability to create a novel bioassay for accurate and rapid analysis. A 96-well microplate based on a polystyrene polymer was used as the platform for an unmodified capture DNA immobilization via a silanization process and with (3-Aminopropyl) triethoxysilane (APTES). After that, a hybridization step was carried out to catch the target molecule, followed by adding phenol and sulfuric acid to quantify the amount of DNA or RNA sugar backbone. This reaction generated a yellow-orange color on the wells measured at 490 nm, which was proportional to the target concentration. Under the optimum conditions, a calibration curve was obtained for each target. The developed biosensor demonstrated high sensitivity, good selectivity, and linear response over a wide concentration range for DNA and RNA targets. Additionally, the biosensor was successfully employed for the detection of DNA intercalator agents that inhibited the hybridization of DNA complementary to the immobilized capture DNA. The developed biosensor offers a potential tool for sensitive and selective detection in various applications, including virus diagnosis, genetic analysis, pathogenic bacteria monitoring, and drug discovery.

A deep learning-enabled smartphone platform for rapid and sensitive colorimetric detection of dimethoate pesticide.

A novel deep learning-enabled smartphone platform is developed to assist a colorimetric aptamer biosensor for fast and highly sensitive detection of dimethoate. The colorimetric determination of dimethoate is based on the specific binding of dimethoate and aptamer, which leads to the aggregation of AuNPs in high-concentration NaCl solution, resulting in an obvious color change from red to blue. This color change provides sufficient data for self-learning enabled by a convolutional neural network (CNN) model, which is established to predict dimethoate concentration based on images acquired from a smartphone. To enhance user-friendliness for non-experts, the CNN model is then embedded into a smartphone app, enabling offline detection of dimethoate pesticide in real environments within just 15 min using a pre-configured colorimetric probe. The developed platform exhibits superior performance, achieving a regression coefficient of 0.9992 in the concentration range of 0-10 µM. Moreover, the app's performance is found to be consistent with the ELISA kit. These remarkable findings demonstrate the potential of combining colorimetric biosensors with smartphone-based deep learning methods for the development of portable and affordable tools for pesticide detection.

Goldilocks Energy Minimum: Peptide-Based Reversible Aggregation and Biosensing.

Colorimetric biosensors based on gold nanoparticle (AuNP) aggregation are often challenged by matrix interference in biofluids, poor specificity, and limited utility with clinical samples. Here, we propose a peptide-driven nanoscale disassembly approach, where AuNP aggregates induced by electrostatic attractions are dissociated in response to proteolytic cleavage. Initially, citrate-coated AuNPs were assembled via a short cationic peptide (RRK) and characterized by experiments and simulations. The dissociation peptides were then used to reversibly dissociate the AuNP aggregates as a function of target protease detection, i.e., main protease (Mpro), a biomarker for severe acute respiratory syndrome coronavirus 2. The dissociation propensity depends on peptide length, hydrophilicity, charge, and ligand architecture. Finally, our dissociation strategy provides a rapid and distinct optical signal through Mpro cleavage with a detection limit of 12.3 nM in saliva. Our dissociation peptide effectively dissociates plasmonic assemblies in diverse matrices including 100% human saliva, urine, plasma, and seawater, as well as other types of plasmonic nanoparticles such as silver. Our peptide-enabled dissociation platform provides a simple, matrix-insensitive, and versatile method for protease sensing.

Multiple electromagnet synergistic control enabled fast and automatic biosensing of Salmonella in a sealed microfluidic chip.

Point-of-care testing of pathogens is vital for prevention of food poisoning. Herein, a colorimetric biosensor was elaborately developed to rapidly and automatically detect Salmonella in a sealed microfluidic chip with one central chamber for housing immunomagnetic nanoparticles (IMNPs), bacterial sample and immune manganese dioxide nanoclusters (IMONCs), four functional chambers for housing absorbent pad, deionized water and H2O2-TMB substrate, and four symmetric peripheral chambers for achieving fluidic control. Four electromagnets were placed under peripheral chambers and synergistically controlled to manipulate their respective iron cylinders at the top of these chambers for deforming these chambers, resulting in precise fluidic control with designated flowrate, volume, direction and time. First, the electromagnets were automatically controlled to mix IMNPs, target bacteria and IMONCs, resulting in the formation of IMNP-bacteria-IMONC conjugates. Then, these conjugates were magnetically separated by a central electromagnet and the supernatant was directionally transferred to the absorbent pad. After these conjugates were washed by deionized water, the H2O2-TMB substrate was directionally transferred to resuspend the conjugates and catalyzed by the IMONCs with peroxidase-mimic activity. Finally, the catalysate was directionally transferred back to its initial chamber, and its color was analyzed by the smartphone APP to determinate bacterial concentration. This biosensor could detect Salmonella quantitatively and automatically in 30 min with a low detection limit of 101 CFU/mL. More importantly, the whole bacterial detection procedure from bacterial separation to result analysis was achieved on a sealed microfluidic chip through multiple electromagnet synergistic control, and this biosensor has great potential for point-of-care testing of pathogens without cross contaminations.