Neural Network Enables High Accuracy for Hepatitis B Surface Antigen Detection with a Plasmonic Platform.

The detection of hepatitis B surface antigen (HBsAg) is critical in diagnosing hepatitis B virus (HBV) infection. However, existing clinical detection technologies inevitably cause certain inaccuracies, leading to delayed or unwarranted treatment. Here, we introduce a label-free plasmonic biosensing method based on the thickness-sensitive plasmonic coupling, combined with supervised deep learning (DL) using neural networks. The strategy of utilizing neural networks to process output data can reduce the limit of detection (LOD) of the sensor and significantly improve the accuracy (from 93.1%-97.4% to 99%-99.6%). Compared with widely used emerging clinical technologies, our platform achieves accurate decisions with higher sensitivity in a short assay time (∼30 min). The integration of DL models considerably simplifies the readout procedure, resulting in a substantial decrease in processing time. Our findings offer a promising avenue for developing high-precision molecular detection tools for point-of-care (POC) applications.

A Naked Eye and Fluorescence Turn-on Sensor for Smartphone Assisted Solid and Solution Phase Sensing of Highly Toxic Triphosgene.

A naked eye and fluorescence turn-on 1,8-naphtahlimide based chemosensor,1, possessing Schiff base linkage was utilized for the rapid detection of highly toxic triphosgene. The proposed sensor selectively detected triphosgene over various other competitive analytes including phosgene with the detection limit of 6.15 and 1.15 µM measured using UV-vis and fluorescence spectrophotometric techniques, respectively. Colorimetric changes observed in solution phase were processed by image analysis using smartphone leading to on-site and inexpensive determination of triphosgene. Further, solid phase sensing of triphosgene was carried out by 1 loaded PEG membranes and silica gel.

A Chromogenic Probe for Detection of Biologically Important Anions and its Implications for Designing Molecular Logic Gates.

Detection of fluoride (F-), acetate (AcO-), and cyanide (CN-) anions is vital from the biological and environmental aspects. In the present contributions, we have introduced a simple Salen-type chromogenic sensor, BEN, to detect these biologically important anions. Changes in UV-visible absorption spectra and color of BEN solution from very pale yellow to pink color are similar for each of these anions and found to be reversible only in the case of F- ions in attendance of HSO4- ions. The estimated limit of detection of BEN solution for detecting F-, AcO-, and CN- anions is found to be below the micromolar (µM) concentration level. Our fabricated handy paper test kit is suitable for qualitatively naked-eye detection of the anions. An immediate quantitative estimation of these important anions is possible using our BEN employing a smartphone, avoiding any costly experimental setup.

Naked-Eye Readable Microarray for Rapid Profiling of Antibodies against Multiple SARS-CoV-2 Variants.

Novel high-throughput protein detection technologies are critically needed for population-based large-scale SARS-CoV-2 antibody detection as well as for monitoring quality and duration of immunity against virus variants. Current protein microarray techniques rely heavily on labeled transduction methods that require sophisticated instruments and complex operations, limiting their clinical potential, particularly for point-of-care (POC) applications. Here, we developed a label-free and naked-eye readable microarray (NRM) based on a thickness-sensing plasmon ruler, enabling antibody profiling within 30 min. The NRM chips provide 100% accuracy for neutralizing antibody detection by efficiently screening antigen types and experimental conditions and allow for the profiling of antibodies against multiple SARS-CoV-2 variants in clinical samples. We further established a flexible "barcode" NRM assay with a simple tape-based operation, enabling an effective smartphone-based readout and analysis. These results demonstrate new strategies for high-throughput protein detection and highlight the potential of novel protein microarray techniques for realistic clinical applications.

A "Pincer" Type of Acridine-Triazole Fluorescent Dye for Iodine Detection by Both 'Naked-Eye' Colorimetric and Fluorometric Modes.

Iodine, primarily in the form of iodide (I-), is the bioavailable form for the thyroid in the human body. Both deficiency and excess intake of iodide can lead to serious health issues, such as thyroid disease. Selecting iodide ions among anions has been a significant challenge for decades due to interference from other anions. In this study, we designed and synthesized a new pincer-type acridine-triazole fluorescent probe (probe 1) with an acridine ring as a spacer and a triazole as a linking arm attached to two naphthol groups. This probe can selectively recognize iodide ions in a mixed solvent of THF/H2O (v/v, 9/1), changing its color from colorless to light yellow, making it suitable for highly sensitive and selective colorimetric and fluorescent detection in water systems. We also synthesized another molecular tweezer-type acridine-triazole fluorescent probe (probe 2) that exhibits uniform detection characteristics for iodide ions in the acetonitrile system. Interestingly, compared to probe 2, probe 1 can be detected by the naked eye due to its circulation effect, providing a simple method for iodine detection. The detection limit of probe 1 is determined to be 10-8 mol·L-1 by spectrometric titration and isothermal titration calorimetry measurements. The binding stoichiometry between probe 1 and iodide ions is calculated to be 1:1 by these methods, and the binding constant is 2 × 105 mol·L-1.

Rapid Visible Detection of African Swine Fever Virus Using Hybridization Chain Reaction-Sensitized Magnetic Nanoclusters and Affinity Chromatography.

African swine fever virus (ASFV) is a severe and persistent threat to the global swine industry. As there are no vaccines against ASFV, there is an immense need to develop easy-to-use, cost-effective, and rapid point-of-care (POC) diagnostic platforms to detect and prevent ASFV outbreaks. Here, a novel POC diagnostic system based on affinity column chromatography for the optical detection of ASFV is presented. This system employs an on-particle hairpin chain reaction to sensitize magnetic nanoclusters with long DNA strands in a target-selective manner, which is subsequently fed into a column chromatography device to produce quantitatively readable and colorimetric signals. The detection approach does not require expensive analytical apparatus or immobile instrumentation. The system can detect five genes constituting the ASFV whole genome with a detection limit of ≈19.8 pm in swine serum within 30 min at laboratory room temperature. With an additional pre-amplification step using polymerase chain reaction (PCR), the assay is successfully applied to detect the presence of ASFV in 30 suspected swine samples with 100% sensitivity and specificity, similar to quantitative PCR. Thus, this simple, inexpensive, portable, robust, and customizable platform for the early detection of ASFV can facilitate the timely surveillance and implementation of control measures.

Multicomponent Reaction Based Tolyl-substituted and Pyrene-Pyridine Conjugated Isomeric Ratiometric Fluorescent Probes: A Comparative Investigation of Photophysical and Hg(II)-Sensing Behaviors.

Herein, the synthesis of pyrene conjugated 2,6-di-ortho-tolylpyridine and 2,6-di-para-tolylpyridine structural isomers were achieved efficiently through multicomponent Chichibabin pyridine synthesis reaction. The DFT, TD-DFT and experimental investigations were carried out to investigate the photophysical behaviors of the synthesized novel pyrene-pyridine based isomeric probes. Our studies revealed that, due to the continuous conjugation of the pyrene, pyridine and tolyl moieties, the dihedral angles of the trisubstituents on the central pyridine moiety significantly influences the photophysical properties of the synthesized novel pyrene based fluorescent probes. Further, we have comparatively investigated the sensing behaviors of the synthesized tolyl-substituted isomeric ratiometric fluorescent probes with metal ions, our studies reveals that both the ortho and para tolyl ratiometric fluorescent probes have distinct photoemissive properties in selectively sensing of Hg2+ ions. Our studies indicates that, the para-tolyl substituted isomer displays more red-shift in wavelength of emission band compared to its ortho isomer analogue during ratiometric fluorescent specific detection of Hg2+ ions.

Fluorescence Sensor for Water in Organic Solvent Using Graphene Oxide- Rhodamine B and Cucurbit[7]uril.

Detection of water in organic solvents gained much importance as these solvents have been used as a medium for conducting organic reactions and water was considered as an inhibitor, when it is present in the reaction medium. There are number of methods available to measure the water content in organic solvents, however, such methods are time consuming and expensive. Here, we developed a facile method for detecting water in organic solvents using an inexpensive fluorescent probe - Rhodamine B decorated Graphene oxide (RBGO). The fluorescent probe, RBGO can be conveniently prepared by mixing the rhodamine B (RB) with graphene oxide (GO) in water. However, the probe will function as a sensor for water in the organic solvents through the release of dye upon interaction with the water present in organic solvents. Surprisingly, combination of cucurbit[7]uril (CB[7]) and RBGO increased the sensitivity of this sensor dramatically for the detection of water. This is the first example of water sensor with best detection limit by the involvement of host molecules such as CB[7]. This sensor displayed the low limit of detection (LOD) for organic solvents (LOD: 0.0015% for DMSO, 0.0025% for DMF), through the two-way process such as decomplexation and encapsulation. We presume that the role of CB [7] can be implemented in other similar sensors to enhance the sensitivity.

Separation and colorimetric detection of Escherichia coli by phage tail fiber protein combined with nano-magnetic beads.

A colorimetric detection method for Escherichia coli (E. coli) in water was established based on a T7 phage tail fiber protein-magnetic separation. Firstly, the tail fiber protein (TFP) was expressed and purified to specifically recognize E. coli, which was verified by using fusion protein GFP-tagged TFP (GFP-TFP) and fluorescence microscopy. Then TFP conjugated with magnetic beads were applied to capture and separate E. coli. The TFP was covalently immobilized on the surface of magnetic beads and captured E. coli as verified by scanning electron microscopy (SEM). Finally, polymyxin B was used to lyse E. coli in solution and the released intracellular ß-galactosidase (ß-gal) could hydrolyze the colorimetric substrate chlorophenol red-ß-D-galactopyranoside (CPRG), causing color change from yellow to purple. The high capture efficiencies of E. coli ranged from 88.70% to 95.65% and E. coli could be detected at a concentration of 102 CFU/mL by naked eyes. The specificity of the chromogenic substrate was evaluated using five different pathogen strains as competitors and tests with four kinds of real water samples showed recoveries of 86.00% to 92.25%. The colorimetric changes determined by visual inspection can be developed as an efficient platform for point-of-care detection of E. coli in resource-limited regions.

Real-Time Embedded Eye Image Defocus Estimation for Iris Biometrics.

One of the main challenges faced by iris recognition systems is to be able to work with people in motion, where the sensor is at an increasing distance (more than 1 m) from the person. The ultimate goal is to make the system less and less intrusive and require less cooperation from the person. When this scenario is implemented using a single static sensor, it will be necessary for the sensor to have a wide field of view and for the system to process a large number of frames per second (fps). In such a scenario, many of the captured eye images will not have adequate quality (contrast or resolution). This paper describes the implementation in an MPSoC (multiprocessor system-on-chip) of an eye image detection system that integrates, in the programmable logic (PL) part, a functional block to evaluate the level of defocus blur of the captured images. In this way, the system will be able to discard images that do not have the required focus quality in the subsequent processing steps. The proposals were successfully designed using Vitis High Level Synthesis (VHLS) and integrated into an eye detection framework capable of processing over 57 fps working with a 16 Mpixel sensor. Using, for validation, an extended version of the CASIA-Iris-distance V4 database, the experimental evaluation shows that the proposed framework is able to successfully discard unfocused eye images. But what is more relevant is that, in a real implementation, this proposal allows discarding up to 97% of out-of-focus eye images, which will not have to be processed by the segmentation and normalised iris pattern extraction blocks.

Rhodamine-Anchored Polyacrylamide Hydrogel for Fluorescent Naked-Eye Sensing of Fe3.

A fluorescent and colorimetric poly (acrylamide)-based copolymer probe P(AAm-co-RBNCH) has been designed via free radical polymerization of a commercial acrylamide monomer with a rhodamine-functionalized monomer RBNCH. Metal ion selectivity of RBNCH was investigated by fluorescence and colorimetric spectrophotometry. Upon addition of Fe3+, a visual color change from colorless to red and a large fluorescence enhancement were observed for the ring-opening of the rhodamine spirolactam mechanism. The monomer gives a sensitive method for quantitatively detecting Fe3+ in the linear range of 100-200 µM, with a limit of detection as low as 27 nM and exhibiting high selectivity for Fe3+ over 12 other metal ions. The hydrogel sensor was characterized by FTIR, and the effects of RBNCH amount on gel content and swelling properties were explored. According to the recipe of 1.0 mol% RBNCH to the total monomers, the fabricated hydrogel sensor displayed a good swelling property and reversibility performance and has potential for application in the imaging of Fe3+ level in industrial wastewater.

A novel design of multiple ligands for ultrasensitive colorimetric chemosensor of glutathione in plasma sample.

In this study, we developed a novel colorimetric chemosensor for selective and sensitive recognition of Glutathione (GSH) using a simple binary mixture of commercially accessible and inexpensive metal receptors with names, Bromo Pyrogallol Red (BPR) and Xylenol Orange (XO). This procedure is based on the synergistic coordination of BPR and XO with cerium ion (Ce3+) for the recognition of GSH over other available competitive amino acids (AAs) especially thiol species in aqueous media. Generally, cysteine (Cys) and homocysteine (hCys) can seriously interfere with the detection of GSH among common biological species because they possess similar chemical behavior. Using all the information from 1HNMR and FT-IR studies, the proposed interaction is presented in which GSH acts as a tri-dentate ligand with three N donor atoms in conjunction with BPR and XO as mono and bi-dentate ligands respectively. This approach opens a path for selective detection of other AAs by argumentatively selecting the ensemble of mixed organic ligands from commercially available reagents, thereby eliminating the need for developing synthetic receptors, sample preparation, organic solvent mixtures, and expensive equipment. Evaluating the feasibility of the existing method was led to the determination of GSH in human plasma samples.

Recent progress in visual methods for aflatoxin detection.

Aflatoxins (AFs) contamination in food and agricultural products poses a significant threat to human health. Sensitive and accurate detection of AFs provides a strong guarantee for ensuring food safety. Conventional chromatographic-based or mass spectrum methods, which rely on bulky instrument and skilled personnel, are not suitable for on-site surveillance. By contrast, visual detections which possess the merits of rapidity and sophisticated instrument-free present an excellent potential for the on-site detection of AFs. This review intends to summarize the latest development of visual methods for AFs detection, including paper-based tests, chromogenic reactions, and luminescent methods. Emerging technologies, like nanotechnology, DNAzymes, and aptamers combined with these visual methods are introduced. The basic principles, features, and application advantages of each type of visual methods are discussed. The biggest challenges and perspectives on their future trends are also addressed.

Visual naked-eye detection of SARS-CoV-2 RNA based on covalent organic framework capsules.

The ongoing outbreak of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has highlighted that new diagnosis technologies are crucial for controlling the spread of the disease. Especially in the resources-limit region, conveniently operated detection methods such as "naked-eye" detection are urgently required that no instrument is needed. Herein, we have designed a novel and facile strategy to fabricate covalent organic framework (COF) capsules, which can be utilized to establish a new colorimetric assay for naked-eye detection of SARS-CoV-2 RNA. Specifically, we employ the digestible ZIF-90 as the sacrificial template to prepare the hollow COF capsules for horseradish peroxidase (HRP) encapsulation. The fabricated COF capsules can provide an appropriate microenvironment for the enzyme molecules, which may improve the conformational freedom of enzymes, enhance the mass transfer, and endow the enzyme with high environmental resistance. With such design, the proposed assay exhibits outstanding analytical performance for the detection of SARS-CoV-2 RNA in the linear range from 5 pM to 50 nM with a detection limit of 0.28 pM which can go parallel to qTR-PCR analysis. Our method also possesses excellent selectivity and reproducibility. Moreover, this method can also be served to analyze the clinical samples, and can successfully differentiate COVID-19 patients from healthy people, suggesting the promising potential in clinical diagnosis.

Naked-Eye Detection of Morphine by Au@Ag Nanoparticles-Based Colorimetric Chemosensors.

In this study, we report a novel and facile colorimetric assay based on silver citrate-coated Au@Ag nanoparticles (Au@AgNPs) as a chemosensor for the naked-eye detection of morphine (MOR). The developed optical sensing approach relied on the aggregation of Au@Ag NPs upon exposure to morphine, which led to an evident color variation from light-yellow to brown. Au@Ag NPs have been prepared by two different protocols, using high- and low-power ultrasonic irradiation. The sonochemical method was essential for the sensing properties of the resulting nanoparticles. This facile sensing method has several advantages including excellent stability, selectivity, prompt detection, and cost-effectiveness.

Cholesteric Chiral Molecular Tweezer for Rapid Detection of F- in Food Samples.

Chiral cholesteric molecular tweezer 7d was synthesized and its influences on changes in the ultraviolet (UV) and fluorescence spectra of various anions were investigated. The results displayed that molecular tweezer 7d selectively recognized F- ions in dimethyl sulfoxide with a detection limit of 5.14 µmol/L, while other anions had little interference. On this basis, a method for the rapid detection of F- ions by host molecular tweezer 7d was established, and the naked-eye detection of F- was realized through the unique yellow color of the complex solution. According to the determination of F- ions in real food samples, it was proved that the established method had good application prospects in F- ion detection.

Naked-eye detection strategies coupled with isothermal nucleic acid amplification techniques for the detection of human pathogens.

Nucleic acid amplification-based techniques have gained acceptance by the scientific, and general, community as reference methodologies for many different applications. Since the development of the gold standard of these techniques, polymerase chain reaction (PCR), back in the 1980s many improvements have been made, and alternative techniques emerged reporting improvements over PCR. Among these, isothermal amplification approaches resulted of particular interest as could overcome the need of specialized equipment to accurately control temperature changes, but it was after year 2000 that these techniques have flourished in a huge number of novel alternatives with many different degrees of complexities and requirements. An added value is their possibility to be combined with many different naked-eye detection strategies, simplifying the resources needed, allowing to reduce cost, and serving as the basis for novel developments of lab-on-chip systems, and miniaturized devices, for point-of-care testing. In this review, we will go over different types of naked-eye detection strategies, combined with isothermal amplification. This will provide the readers up-to-date information for them to select the most appropriate strategies depending on the particular needs and resources for their experimental setup.

Visual Detection of Adenosine Triphosphate by Taylor Rising: A Simple Point-of-Care Testing Method Based on Rolling Circle Amplification.

Rapid and sensitive point-of-care testing (POCT) is an extremely critical mission in practical applications, especially for rigorous military medicine, home health care, and in the third world. Here, we report a visual POCT method for adenosine triphosphate (ATP) detection based on Taylor rising in the corner of quadratic geometries between two rod surfaces. We discuss the principle of Taylor rising, demonstrating that it is significantly influenced by contact angle, surface tension, and density of the sample, which are controlled by ATP-dependent rolling circle amplification (RCA). In the presence of ATP, RCA reaction effectively suppresses Taylor-rising behavior, due to the increased contact angle, density, and decreased surface tension. Without addition of ATP, untriggered RCA reaction is favorable for Taylor rising, resulting in a significant height. With this proposed method, visual sensitive detection of ATP without the aid of other instruments is realized with only a 5 µL droplet, which has good selectivity and a low detection limit (17 nM). Importantly, this visual method provides a promising POCT tool for user-friendly molecular diagnostics.

Introducing hierarchical hollow MnO2 microspheres as nanozymes for colorimetric determination of captopril.

A simple sensor was developed for the colorimetric determination of captopril (CPT). Herein, hierarchical hollow MnO2 microspheres (HH-MnO2) were applied as nanozymes with peroxidase-mimetic activity. Free cation radicals with a strong absorption signal (λmax at 653 nm) were generated via a redox reaction between 3, 3', 5, 5'-tetramethylbenzidine (TMB) and HH-MnO2. Captopril could successfully prevent the generation of blue-colored free cation radicals. The influence of CPT concentration on the absorption of the generated radicals was monitored by UV-Vis spectroscopy. The corresponding linear concentration range was from 1.0 to 30.0 µg mL-1 (4.6-138.1 µmol L-1), and the detection limit was found to be 0.26 µg mL-1 (1.2 µmol L-1). As a practical usage, the developed sensor was effectively utilized to measure the content of CPT in pharmaceutical formulations.

An AIE-Active Ultrathin Polymeric Self-Assembled Monolayer Sensor for Trace Volatile Explosive Detection.

This work has prepared polymeric self-assembled monolayer (SAM) sensors for the detection of trace volatile nitroaromatic compound (NAC) explosives by fluorescence quenching. A typical aggregation-induced emission (AIE) luminogen 1,1,2,2-tetraphenylethene (TPE) polymerizes into PTPE to increase the fluorescence intensity in the SAMs, and the phosphoric acid acts as the anchor group to form stable covalent bonds with the Al2 O3 substrate. This design takes advantage of the high sensitivity and good stability of SAMs, and high fluorescence intensity, and "wire effect" of the conjugated polymers. The polymeric SAM sensors are prepared on the Al2 O3 silicon wafer and testing paper. Both of them show good response speed, reversibility, selectivity, and sensitivity. The detection limits down to 0.07, 0.35, and 4.11 ppm for TNT, DNB, and NB, respectively, are achieved on the inorganic testing paper. Furthermore, due to the higher fluorescence intensity by interlacing and overlapping of fibers, the detection of the paper can be distinguished by naked eyes even with a low-power handheld UV lamp, which provides an experimental basis for the development of cheap and easy trace NAC explosive sensors.