Colorimetric bacteria sensing using a supramolecular enzyme-nanoparticle biosensor

Biosynthesis of Iron Oxide Nanoparticles by Marine Streptomyces sp. SMGL39 with Antibiofilm Activity: In Vitro and In Silico Study

One of the major global health threats in the present era is antibiotic resistance. Biosynthesized iron oxide nanoparticles (FeNPs) can combat microbial infections and can be synthesized without harmful chemicals. In the present investigation, 16S rRNA gene sequencing was used to discover Streptomyces sp. SMGL39, an actinomycete isolate utilized to reduce ferrous sulfate heptahydrate (FeSO4.7H2O) to biosynthesize FeNPs, which were then characterized using UV-Vis, XRD, FTIR, and TEM analyses. Furthermore, in our current study, the biosynthesized FeNPs were tested for antimicrobial and antibiofilm characteristics against different Gram-negative, Gram-positive, and fungal strains. Additionally, our work examines the biosynthesized FeNPs' molecular docking and binding affinity to key enzymes, which contributed to bacterial infection cooperation via quorum sensing (QS) processes. A bright yellow to dark brown color shift indicated the production of FeNPs, which have polydispersed forms with particle sizes ranging from 80 to 180 nm and UV absorbance ranging from 220 to 280 nm. Biosynthesized FeNPs from actinobacteria significantly reduced the microbial growth of Fusarium oxysporum and L. monocytogenes, while they showed weak antimicrobial activity against P. aeruginosa and no activity against E. coli, MRSA, or Aspergillus niger. On the other hand, biosynthesized FeNPs showed strong antibiofilm activity against P. aeruginosa while showing mild and weak activity against B. subtilis and E. coli, respectively. The collaboration of biosynthesized FeNPs and key enzymes for bacterial infection exhibits hydrophobic and/or hydrogen bonding, according to this research. These results show that actinobacteria-biosynthesized FeNPs prevent biofilm development in bacteria.

Progress and challenges in bacterial infection theranostics based on functional metal nanoparticles

The rapid proliferation and infection of bacteria, especially multidrug-resistant bacteria, have become a great threat to global public health. Focusing on the emergence of "super drug-resistant bacteria" caused by the abuse of antibiotics and the insufficient and delayed early diagnosis of bacterial diseases, it is of great research significance to develop new technologies and methods for early targeted detection and treatment of bacterial infection. The exceptional effects of metal nanoparticles based on their unique physical and chemical properties make such systems ideal for the detection and treatment of bacterial infection both in vitro and in vivo. Metal nanoparticles also have admirable clinical application prospects due to their broad antibacterial spectrum, various antibacterial mechanisms and excellent biocompatibility. Herein, we summarized the research progress concerning the mechanism of metal nanoparticles in terms of antibacterial activity together with the detection of bacterial. Representative achievements are selected to illustrate the proof-of-concept in vitro and in vivo applications. Based on these observations, we also give a brief discussion on the current problems and perspective outlook of metal nanoparticles in the diagnosis and treatment of bacterial infection.

Recent advances on nanomaterial-based glutathione sensors

Glutathione (GSH) is one of the most common thiol-containing molecules discovered in biological systems, and it plays an important role in many cellular functions, where changes in physiological glutathione levels contribute to the progress of a variety of diseases. Molecular imaging employing fluorescent probes is thought to be a sensitive technique for online fluorescence detection of GSH. Although various molecular probes for (intracellular) GSH sensing have been reported, some aspects remain unanswered, such as quantitative intracellular analysis, dynamic monitoring, and compatibility with biological environment. Some of these drawbacks can be overcome by sensors based on nanostructured materials, that have attracted considerable attention owing to their exceptional properties, including a large surface area, heightened electro-catalytic activity, and robust mechanical resilience, for which they have become integral components in the development of highly sensitive chemo- and biosensors. Additionally, engineered nanomaterials have demonstrated significant promise in enhancing the precision of disease diagnosis and refining treatment specificity. The aim of this review is to investigate recent advancements in fabricated nanomaterials tailored for detecting GSH. Specifically, it examines various material categories, encompassing carbon, polymeric, quantum dots (QDs), covalent organic frameworks (COFs), metal-organic frameworks (MOFs), metal-based, and silicon-based nanomaterials, applied in the fabrication of chemo- and biosensors. The fabrication of nano-biosensors, mechanisms, and methodologies employed for GSH detection utilizing these fabricated nanomaterials will also be elucidated. Remarkably, there is a noticeable absence of existing reviews specifically dedicated to the nanomaterials for GSH detection since they are not comprehensive in the case of nano-fabrication, mechanisms and methodologies of detection, as well as applications in various biological environments. This research gap presents an opportune moment to thoroughly assess the potential of nanomaterial-based approaches in advancing GSH detection methodologies.

Genetically engineered bacteriophages as novel nanomaterials: applications beyond antimicrobial agents

Bacteriophages, also known as phages, are viruses that replicate in bacteria and archaea. Phages were initially discovered as antimicrobial agents, and they have been used as therapeutic agents for bacterial infection in a process known as "phage therapy." Recently, phages have been investigated as functional nanomaterials in a variety of areas, as they can function not only as therapeutic agents but also as biosensors and tissue regenerative materials. Phages are nontoxic to humans, and they possess self-assembled nanostructures and functional properties. Additionally, phages can be easily genetically modified to display specific peptides or to screen for functional peptides via phage display. Here, we demonstrated the application of phage nanomaterials in the context of tissue engineering, sensing, and probing.

Development of Optical Differential Sensing Based on Nanomaterials for Biological Analysis

The discrimination and recognition of biological targets, such as proteins, cells, and bacteria, are of utmost importance in various fields of biological research and production. These include areas like biological medicine, clinical diagnosis, and microbiology analysis. In order to efficiently and cost-effectively identify a specific target from a wide range of possibilities, researchers have developed a technique called differential sensing. Unlike traditional "lock-and-key" sensors that rely on specific interactions between receptors and analytes, differential sensing makes use of cross-reactive receptors. These sensors offer less specificity but can cross-react with a wide range of analytes to produce a large amount of data. Many pattern recognition strategies have been developed and have shown promising results in identifying complex analytes. To create advanced sensor arrays for higher analysis efficiency and larger recognizing range, various nanomaterials have been utilized as sensing probes. These nanomaterials possess distinct molecular affinities, optical/electrical properties, and biological compatibility, and are conveniently functionalized. In this review, our focus is on recently reported optical sensor arrays that utilize nanomaterials to discriminate bioanalytes, including proteins, cells, and bacteria.

Specific separation and sensitive detection of foodborne pathogens by phage-derived bacterial-binding protein-nano magnetic beads coupled with smartphone-assisted paper sensor

Foodborne pathogen infection poses a significant threat to public health and is considered as one of the most serious hazards in global food safety. Herein, a sensitive and efficient method for on-site monitoring of foodborne pathogens was developed by using a smartphone-assisted paper-sensor combined with phage-derived bacterial-binding proteins-nano magnetic beads (PBPs-MBs). PBPs including tail fiber protein (TFP:gp13), cell-wall binding domain (CBD) of endolysin and tailspike protein (TSP) coated on the surface of MBs were applied for rapid separation and enrichment of targeted bacteria (Escherichia coli O157:H7, Staphylococcus aureus and Salmonella typhimurium, respectively) from food samples in 20 min before detection on paper-based sensors. The paper-based sensor was loaded with the lytic agent (polymyxin B) to induce bacterial lysis and release specific endogenous enzymes. Subsequently, three distinct chromogenic substrates were hydrolyzed by their corresponding enzymes, resulting in characteristic color changes on the paper, respectively. In addition, a smartphone APP for red-green-blue (RGB) color analysis of paper was able to directly detect three foodborne pathogens. As a result, the limit of detection (LOD) values for three foodborne pathogens were found to be 2.44 × 102, 2.68 × 104 and 4.62 × 103 CFU/mL, respectively, which were much lower than other studies (106-108 CFU/mL) based on enzymes. Moreover, the feasibility of this approach was further assessed through the successful detection of targeted bacteria in real samples with satisfactory recovery rates. In conclusion, this smartphone-assisted biosensor offers promising application potential for point-of-care testing (POCT) of foodborne pathogens in resource-scarce areas.

Gold Nanoparticle-Based Colorimetric Biosensing for Foodborne Pathogen Detection

Ensuring safe high-quality food is an ongoing priority, yet consumers face heightened risk from foodborne pathogens due to extended supply chains and climate change in the food industry. Nanomaterial-based assays are popular and have recently been developed to ensure food safety and high quality. This review discusses strategies for utilizing gold nanoparticles in colorimetric biosensors. The visible-signal biosensor proves to be a potent sensing technique for directly measuring targets related to foodborne pathogens in the field of food analysis. Among visible-signal biosensors, the localized surface plasmon resonance (LSPR) biosensor has garnered increasing attention and experienced rapid development in recent years. This review succinctly introduces the origin of LSPR theory, providing detailed insights into its fundamental principles. Additionally, this review delves into the application of nanotechnology for the implementation of the LSPR biosensor, exploring methods for utilizing gold nanoparticles and elucidating the factors that influence the generation of visible signals. Several emerging technologies aimed at simple and rapid immunoassays for onsite applications have been introduced in the food industry. In the foreseeable future, field-friendly colorimetric biosensors could be adopted in food monitoring systems. The onsite and real-time detection of possible contaminants and biological substances in food and water is essential to ensure human health and safety.

Rhodamine B functionalized silver nanoparticles paper discs as turn-on fluorescence sensor, coupled with a smartphone for the detection of microbial contamination in drinking water

The precise detection of pathogenic microorganisms is crucial for the reduction of water-borne diseases. Herein, a filter-paper-based florescent chemosensor was fabricated for the detection of Escherichia coli and Staphylococcus aureus contamination exploiting protein-DNA interaction between the target and a specific probe. The sensing mechanism involved the self-assembly of Rhodamine B (RhB) on silver nanoparticles (AgNPs) surface that was labeled with a single-stranded DNA probe. This causes the fluorescence quenching of RhB by a distant-dependant process. The hybridization between pathogen-specific probe and bacterial surface protein causes the release of fluorescence of RhB, which was observed under UV light. For paper-based bio-surface preparation, the mixture comprising RhB-AgNP-ssDNA was drop-casted on filter paper discs. The conditions were optimized using isolated genomic DNA of the microbes. The method was applied for E.coli detection using an eae gene-based probe targeting intimin protein and S. aureus detection using tuf gene-based probe targeting EF-tuf protein on the microbe's surface. The chemosensor had a notable specificity and selectivity for E.coli, and S. aureus, with detection limits of 0.6 × 108 and 0.37 × 103 CFU/mL respectively. Moreover, the sensor was tested on real water samples, which presented excellent reproducibility of results (RSD ≤ 0.24%). Furthermore, the gradient change of fluorescence was captured by a smartphone, which allows direct detection of pathogens in a sensitive semi-quantitative way without the need for expensive instruments. The designed chemosensor can serve as a simple, inexpensive, and rapid method for the on-site detection of microbial contamination in drinking water.

Iron Oxide Nanoparticles: Green Synthesis and Their Antimicrobial Activity

The rise of antimicrobial resistance caused by inappropriate use of these agents in various settings has become a global health threat. Nanotechnology offers the potential for the synthesis of nanoparticles (NPs) with antimicrobial activity, such as iron oxide nanoparticles (IONPs). The use of IONPs is a promising way to overcome antimicrobial resistance or pathogenicity because of their ability to interact with several biological molecules and to inhibit microbial growth. In this review, we outline the pivotal findings over the past decade concerning methods for the green synthesis of IONPs using bacteria, fungi, plants, and organic waste. Subsequently, we delve into the primary challenges encountered in green synthesis utilizing diverse organisms and organic materials. Furthermore, we compile the most common methods employed for the characterization of these IONPs. To conclude, we highlight the applications of these IONPs as promising antibacterial, antifungal, antiparasitic, and antiviral agents.

Optical biosensors for environmental monitoring: Recent advances and future perspectives in bacterial detection

The environmental contamination due to bacterial proliferation vs their identification is the major deciding factor in the spread of diseases leading to pandemics. The advent of drug-resistant pathogenic contaminants in our environment has further added to the load of complications associated with their diagnosis and treatment. Obstructing the spread of such infections, prioritizes the expansion of sensor-based diagnostics, effectuating, a sturdy detection of disease-causing microbes, contaminating our surroundings in shortest possible time, with minimal expenditure. Among many sensors known, optical biosensors promote the recognition of pathogens befouling the environment through a comparatively intuitive, brisk, portable, multitudinous, and thrifty approach. This article reviews the recent progresses in optical biosensor-based systems for effective environmental monitoring. The technical and methodological perspectives of fundamental optical-sensing platforms are reviewed, combined with the pros and cons of every procedure. Eventually, the obstacles lying in the path of development of an effective optical biosensor device for bio-monitoring and its future perspectives are highlighted in the present work.

Development of a label-free impedimetric aptasensor for the detection of Acinetobacter baumannii bacteria

Acinetobacter baumannii (A. baumannii) is responsible for various nosocomial infections, which is known as a clinically crucial opportunistic pathogen. Therefore, rapid detection of this pathogen is critical to prevent the spread of infection and appropriate treatment. Biological detection probes, such as aptamers and synthetic receptors can be used as diagnostic layers to detect bacteria. In this work, an electrochemical aptasensor was developed for the ultrasensitive detection of A. baumannii by electrochemical impedance spectroscopy (EIS). The aptamer was immobilized on the surface of a CSPE modified with the nanocomposite Fe3O4@SiO2@Glyoxal (Gly) for selective and label-free detection of A. baumannii. The charge transfers resistance (Rct) between redox couple [Fe(CN)63-/4-] and the surface of aptasensor in the Nyquist plot of EIS study was used as electroanalytical signal for detection and determination of A. baumannii. The obtained results showed that the constructed aptasensor could specifically detect A. baumannii in the concentration range from 1.0 × 103-1.0 × 108 Colony-forming unit (CFU)/mL and with a detection limit of 150 CFU/mL (S/N = 3). In addition to its sensitivity, the biosensor exhibits high selectivity over some other pathogens. Therefore, a simple, inexpensive, rapid, label-free, selective, and sensitive electrochemical aptasensor was developed to detect A. baumannii.

A Label-Free and Ultrasensitive Prussian Blue-Based Dipstick Sensor for Bacterial and Biofilm Detection

Water and food contamination has become the major contributor to infections and deaths. However, rapid and sensitive bacterial detection still remains an unmet demand that has attracted widespread attention. Often water and food samples are sent out for laboratory testing to detect the presence of contamination, which is time-consuming and laborious. Herein, we have developed a highly sensitive, tenable, affordable, and robust (STAR) paper-based colorimetric dipstick sensor based on the principle of Prussian blue (PB) synthesis as an indicator of bacterial contamination. In the presence of bacteria, it leads to the formation of PB, a dye that acts as a colorimetric indicator. The intensity of the PB is the direct measure of the degree of contamination. The fabrication of the STAR dipstick sensor involves a simple and cost-effective process. The STAR dipstick sensor is ultrasensitive and can detect up to 101 CFU/mL of bacteria within minutes of contact with the test sample. The STAR dipstick sensor is fabricated using biodegradable components, which is speculated to facilitate quick and environmentally friendly degradation after each use. The sensor has been validated for its properties and capabilities at different pH to detect both Gram-positive and Gram-negative bacterial strains in real-time samples. The stability and degradation were also monitored. Comprehensively, the proposed STAR dipstick sensor can serve as a point-of-care device to detect bacterial contamination in a swift and sensitive manner.

Nano-Biotechnology for Bacteria Identification and Potent Anti-bacterial Properties: A Review of Current State of the Art

Sepsis is a critical disease caused by the abrupt increase of bacteria in human blood, which subsequently causes a cytokine storm. Early identification of bacteria is critical to treating a patient with proper antibiotics to avoid sepsis. However, conventional culture-based identification takes a long time. Polymerase chain reaction (PCR) is not so successful because of the complexity and similarity in the genome sequence of some bacterial species, making it difficult to design primers and thus less suitable for rapid bacterial identification. To address these issues, several new technologies have been developed. Recent advances in nanotechnology have shown great potential for fast and accurate bacterial identification. The most promising strategy in nanotechnology involves the use of nanoparticles, which has led to the advancement of highly specific and sensitive biosensors capable of detecting and identifying bacteria even at low concentrations in very little time. The primary drawback of conventional antibiotics is the potential for antimicrobial resistance, which can lead to the development of superbacteria, making them difficult to treat. The incorporation of diverse nanomaterials and designs of nanomaterials has been utilized to kill bacteria efficiently. Nanomaterials with distinct physicochemical properties, such as optical and magnetic properties, including plasmonic and magnetic nanoparticles, have been extensively studied for their potential to efficiently kill bacteria. In this review, we are emphasizing the recent advances in nano-biotechnologies for bacterial identification and anti-bacterial properties. The basic principles of new technologies, as well as their future challenges, have been discussed.

Ag+-gated peroxidase activity of gold nanoparticles for sensitive detection of Escherichia coli

Escherichia coli (E. coli) is one of the most ubiquitous foodborne pathogens that can cause infections and threaten human health. Herein, a colorimetric method for sensitive detection of E. coli was established by using enzyme-nanozyme cascade reaction for signal amplification. Gold nanoparticles (AuNPs) are well-known nanozymes due to their high peroxidase-like activity. When the dense cetyltrimethylammonium bromide (CTAB) membrane on the surfaces of AuNPs kept the substrate away from AuNPs, the peroxidase activity of AuNPs was inhibited. However, the CTAB membrane could be disrupted by Ag⁺, resulting in enhanced peroxidase activity of AuNPs. When E. coli was present, the enzyme-nanozyme cascade reaction was initiated. The substrate p-aminophenyl β-D-galactopyranoside (PAPG) was hydrolyzed to the reductive p-aminophenol (PAP) by beta-galactosidase (β-gal) in E. coli, reducing Ag⁺ to Ag. Consequently, CTAB-AuNPs remained weak peroxidase activity and could not catalyze the H₂O₂-mediated oxidation of TMB. As the amount of E. coli increased, the absorbance of TMB decreased along with a color change from deep blue to pink. The absorbance intensity displayed a linear dependence on E. coli from 1.0 × 10² to 1.0 × 10⁹ CFU mL^-1. Therefore, the proposed method holds good prospects in foodborne pathogenic bacteria detection.

Target Enzyme-Triggered Click Chemistry and Hybridization Chain Reaction for Fluorescence Nonculture Homogeneous Analysis of E. coli in Bloodstream Infections

Escherichia coli is the major pathogen that causes bloodstream infections (BSI). It is critical to develop nonculture identification methods which can meet the urgent need of clinical diagnosis and treatment. In this study, we reported a homogeneous fluorescence E. coli analysis system using β-galactosidase (β-Gal) as the biomarker and double-stranded DNA-templated copper nanoparticles (dsDNA-Cu NPs) as the signal output. The product of the enzymatic hydrolysis reaction, p-aminophenol (PAP), could reduce Cu²⁺ to Cu⁺, triggering the alkyne-azido cycloaddition reaction (CuAAC). Subsequently, the hybrid chain reaction (HCR) was initiated, producing the dsDNA template used to generate Cu NPs in situ. The system achieved a wide linear range for β-Gal and E. coli 1-10⁴ mU/L and 10^-2-10 colony-forming unit (CFU)/mL, and a detection limit of 0.3 mU/L and 0.003 CFU/mL, respectively. 65 samples (45 blood and 20 urine) were collected to evaluate the clinical practicality. The results demonstrated remarkable area under the curve (AUC) values of 0.95 and 0.916 from uncultured urine and blood, respectively. It had 100% specificity and 83.3% sensitivity. The whole duration of the strategy was 3.5 h, which significantly reduced the turnaround time (TAT) and facilitated early BSI diagnosis to improve patients' prognosis. Our work had the potential to be an alternative to culture-based methods in clinics.

Machine Learning-Assisted Nanoenzyme/Bioenzyme Dual-Coupled Array for Rapid Detection of Amyloids

Array-based sensing methods offer significant advantages in the simultaneous detection of multiple amyloid biomarkers and thus have great potential for diagnosing early-stage Alzheimer's disease. Yet, detecting low concentrations of amyloids remains exceptionally challenging. Here, we have developed a fluorescent sensor array based on the dual coupling of a nanoenzyme (AuNPs) and bioenzyme (horseradish peroxidase) to detect amyloids. Various ss-DNAs were bound to the nanoenzyme for regulating enzymatic activity and recognizing amyloids. A simplified sensor array was generated from a screening model via machine learning algorithms and achieved signal amplification through a two-step enzymatic reaction. As a result, our sensing system could discriminate the aggregation species and aggregation kinetics at 200 nM with 100% accuracy. Moreover, AD model mice and healthy mice were distinguished with 100% accuracy through the sensor array, providing a powerful sensing platform for diagnosing AD.

Nano-biofertilizers as bio-emerging strategies for sustainable agriculture development: Potentiality and their limitations

Nanotechnology is a burgeoning revolutionary technology in the 21st century. Climate emergencies caused by natural or anthropogenic activities have tragically consequential repercussions on agricultural output worldwide. Modern cropping systems profoundly rely on synthetic fertilizers to deliver necessary nutrients, yet their prolonged and persistent administration is hazardous to the environment, soil fertility, and nutritional dynamics of the rhizospheric microbiome. By addressing the drawback of physico-chemically synthesized nano-dimensioned fertilizer, this review emphasizes on integrating nanoparticles and biofertilizers conjointly as nano-biofertilizers (NBF) which can safeguard global food security, in light of the population surge. Inoculation with nanoparticles and biofertilizers strengthens plant growth and stress tolerance. However, combined together (NBF), they have emerged as a more economically and environmentally sustainable, highly versatile, and long-lasting agriculture tool. Microbe-based green synthesis using the encapsulation of inorganic nanoparticles of Si, Zn, Cu, Fe, Ni, Ti, and Ag as well as organic materials, including chitosan, cellulose, and starch, to formulate NBFs can eliminate the constraints of conventional fertilizer contamination. The application of NBFs is in its infancy in agriculture, yet it has promising potential for transforming traditional farming techniques into smart agriculture, compared to any of the existing strategies. From this perspective, this review is an attempt to provide a comprehensive understanding of the formulations, fabrication, and characterization of NBFs while unraveling the underlying mechanisms of plant-NBF interactions along with their contribution to climate change-induced biotic and abiotic stress tolerance. We substantially summarize the latest advancements of field applications of NBFs for precision farming. Moreover, we critically revised their applications in agro-ecosystems according to the current literature, while also discussing the bottlenecks and future trends for developing potent NBFs.

Functionalized graphene-based electrochemical array sensors for the identification of distinct conformational states of Amyloid Beta in Alzheimer's disease

Aβ oligomers have been widely accepted as significant biomarkers for Alzheimer's disease (AD) detection, monitoring, and therapy since they are highly correlated with AD development. In this work, an electrochemical array-based sensing platform was successfully built using a group of functionalized graphene with different physicochemical features. Since the electro-insulated Aβ peptide species severely interfered with the electron transport on the electrode surface, the presence of Aβ led to a significant change in the electrochemical impedance signal. The resulting variety of the impedance was then classified and processed by linear discriminant analysis. The constructed sensing platform can discriminate different Aβ forms, the mixture of various Aβ forms, and different ratios of Aβ42 to Aβ40 with 100% accuracy by only the combination of dual probes. Furthermore, it also exhibited excellent performance for screening Aβ inhibitors and metal chelators. The strategy utilizes the infinitesimal general discrepancy instead of specific biomarker recognition, exhibiting the advantage of no requirement to know the exact information about the specific ligand and receptor in advance, which is promising to be widened for the other biosensing detection fields.

Isolation of Bacteria Aptamers with Non-SELEX for the Development of a Highly Sensitive Colorimetric Assay Based on Dual Signal Amplification

In this work, an aptamer against Escherichia coli is isolated via non-SELEX, which executes efficient selection by employing repetitive cycles of centrifugation-based partitioning, and the binding site of the aptamer on E. coli cell surfaces is inferred to be a membrane protein. Moreover, truncated sequence 2-17-2 with a higher affinity (K_d = 101.76 nM) is employed for highly sensitive colorimetric detection of bacteria based on the dual signal amplification strategy. When targets exist, the release of DNA 1 from the polymer activates a hybridization chain reaction (HCR) between DNA 1 and DNA 2, thereby inducing the aggregation of probe 1. Subsequently, DNA 3 dissociated from probe 1 as a linker DNA further assembles probe 2/3. In this system, two types of DNA@gold nanoparticles (AuNPs) coexist and successively aggregate AuNPs based on divergent triggering mechanisms. Under optimal conditions, the dual signal amplification strategy presents excellent sensitivity (10 CFU mL^-1) and specificity, as well as the realization of real sample analysis.

Metallic and Metal Oxides Nanoparticles for Sensing Food Pathogens—An Overview of Recent Findings and Future Prospects

Nowadays, special importance is given to quality control and food safety. Food quality currently creates significant problems for the industry and implicitly for consumers and society. The effects materialize in economic losses, alterations of the quality and organoleptic properties of the commercial products, and, last but not least, they constitute risk factors for the consumer’s health. In this context, the development of analytical systems for the rapid determination of the sanitary quality of food products by detecting possible pathogenic microorganisms (such as Escherichia coli or Salmonella due to the important digestive disorders that they can cause in many consumers) is of major importance. Using efficient and environmentally friendly detection systems for identification of various pathogens that modify food matrices and turn them into food waste faster will also improve agri-food quality throughout the food chain. This paper reviews the use of metal nanoparticles used to obtain bio nanosensors for the purpose mentioned above. Metallic nanoparticles (Au, Ag, etc.) and their oxides can be synthesized by several methods, such as chemical, physical, physico-chemical, and biological, each bringing advantages and disadvantages in their use for developing nanosensors. In the “green chemistry” approach, a particular importance is given to the metal nanoparticles obtained by phytosynthesis. This method can lead to the development of good quality nanoparticles, at the same time being able to use secondary metabolites from vegetal wastes, as such providing a circular economy character. Considering these aspects, the use of phytosynthesized nanoparticles in other biosensing applications is also presented as a glimpse of their potential, which should be further explored.

Impact of Surface Area on Sensitivity in Autonomously Reporting Sensing Hydrogel Nanomaterials for the Detection of Bacterial Enzymes

The rapid and selective detection of bacterial contaminations and bacterial infections in a non-laboratory setting using advanced sensing materials holds the promise to enable robust point-of-care tests and rapid diagnostics for applications in the medical field as well as food safety. Among the various possible analytes, bacterial enzymes have been targeted successfully in various sensing formats. In this current work, we focus on the systematic investigation of the role of surface area on the sensitivity in micro- and nanostructured autonomously reporting sensing hydrogel materials for the detection of bacterial enzymes. The colorimetric sensing materials for the detection of β-glucuronidase (ß-GUS) from Escherichia coli (E. coli) were fabricated by template replication of crosslinked pullulan acetoacetate (PUAA) and by electrospinning chitosan/polyethylene oxide nanofibers (CS/PEO NFs), both equipped with the chromogenic substrate 5-bromo-4-chloro-3-indolyl-β-D-glucuronide. The investigation of the dependence of the initial reaction rates on surface area unveiled a linear relationship of rate and thereby time to observe a signal for a given concentration of bacterial enzyme. This knowledge was exploited in nanoscale sensing materials made of CS/PEO NFs with diameters of 295 ± 100 nm. Compared to bulk hydrogel slabs, the rate of hydrolysis was significantly enhanced in NFs when exposed to bacteria suspension cultures and thus ensuring a rapid detection of living E. coli that produces the enzyme β-GUS. The findings afford generalized design principles for the improvement of known and novel sensing materials towards rapid detection of bacteria by nanostructuring in medical and food related settings.

Fluorescent dyes with multiple quaternary ammonium centers for specific image discrimination and Gram-positive antibacterial activity

Three quaternary ammonium compounds (QACs), TPQA, T2PQA, and T3PQA, were synthesized and employed in antimicrobial tests against E. coli and S. aureus. It was confirmed that they exhibit selective bacteriostasis against S. aureus. The antibacterial activities of the compounds were evaluated via determining their minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) against S. aureus using the 2,3,5-triphenyltetrazolium chloride (TTC) coloration method. Notably, T2PQA exhibited far better properties than TPQA and T3PQA, with the activity found to be dependent on the structure of the QA and the exposed hydrophobic groups. All three compounds showed promising potential for killing Gram-positive bacteria, efficiently guided by fluorescence imaging.

Smartphone-based surface plasmon resonance sensing platform for rapid detection of bacteria

Bacterial infection poses severe threats to public health, and early rapid detection of the pathogen is critical for controlling bacterial infectious diseases. Current methods are commonly labor intensive, time consuming or dependent on lab-based equipment. In this study, we proposed a novel and practical method for bacterial detection based on smartphones using the surface plasmon resonance (SPR) phenomena of gold nanoparticles (AuNPs). The proposed smartphone-based SPR sensing method is achieved by utilizing color development that arises from the change in interparticle distance of AuNPs induced by bacterial lysate. The pictures of bacteria/AuNPs color development were captured, and their color signals were acquired through a commercial smartphone. The proposed method has a detection range between 2.44 × 10⁵ and 1.25 × 10⁸ cfu mL⁻¹ and a detection limit of 8.81 × 10⁴ cfu mL⁻¹. Furthermore, this method has acceptable recoveries (between 85.7% and 95.4%) when measuring spiked real waters. Combining smartphone-based signal reading with AuNP-dependent color development also offers the following advantages: easy-to-use, real-time detection, free of complex equipment and low cost. In view of these features, this sensing platform would have widespread applications in the fields of medical, food, and environmental sciences.

In this study, we propose a novel and practical method for bacterial detection based on smartphones using the surface plasmon resonance (SPR) phenomena of gold nanoparticles (AuNPs).

Rapid Detection and Antimicrobial Susceptibility Testing of Pathogens Using AgNPs-Invertase Complexes and the Personal Glucose Meter

Rapid detection of pathogens and assessment of antimicrobial susceptibility is of great importance for public health, especially in resource-limiting regions. Herein, we developed a rapid, portable, and universal detection method for bacteria using AgNPs-invertase complexes and the personal glucose meter (PGM). In the presence of bacteria, the invertase could be released from AgNPs-invertase complexes where its enzyme activity of invertase was inhibited. Then, the enzyme activity of invertase was restored and could convert sucrose into glucose measured by a commercially PGM. There was a good linear relationship between PGM signal and concentration of E. coli or S. aureus as the bacteria model with high sensitivity. And our proposed biosensor was proved to be a rapid and reliable method for antimicrobial susceptibility testing within 4 h with consistent results of Minimum Inhibitory Concentrations (MICs) testing, providing a portable and convenient method to treat infected patients with correct antibiotics and reduce the production of antibiotic-resistant bacteria, especially for resource-limiting settings.

Nanoceria-based lateral flow immunoassay for hydrogen peroxide-free colorimetric biosensing for C-reactive protein

During the recent several decades, lateral flow immunoassay (LFIA) constructed with gold nanoparticle (AuNP) has been widely utilized to conveniently detect target analyte. However, AuNP-based LFIA has limitations, such as limited detection sensitivity and quantification capability. Herein, to overcome these constraints, we have developed cerium oxide nanoparticle (nanoceria)-based LFIA for C-reactive protein (CRP) detection in human serum samples. It was fabricated with nanoceria, a notable nanozyme that shows an oxidase activity to quickly oxidize organic substrate, such as 3,3',5,5'-tetramethylbenzidine (TMB), to produce colored product without any oxidizing agent (e.g., hydrogen peroxide), which is advantageous for realizing point-of-care testing (POCT) applications. By employing human blood serum spiked with CRP, the nanoceria-based LFIA showed two blue-colored lines on the test and control region within 3 min via TMB oxidation, by the captured nanoceria through antigen-antibody interaction. The produced blue-colored lines were distinguished by naked eyes and quantitated with real images acquired by a conventional smartphone with the ImageJ software. With this strategy, target CRP was specifically determined down to 117 ng mL^-1 with high detection precisions yielding coefficient of variation of 9.8-11.3% and recovery of 90.7-103.2% using human blood serum samples. This investigation demonstrates the potential of oxidase-like nanoceria for developing LFIA, which is particularly useful in instrumentation-free POCT environments.

Biofertilizers and nanofertilizers for sustainable agriculture: Phycoprospects and challenges

Increased food demands and ceasing nutrient deposits have resulted in a great shortfall between the food supply and demand and would be worse in the years to come. Higher inputs of synthetic fertilizers on lands have resulted in environmental pollution, persistent changes in the soil ecology, and physicochemical conditions. This has greatly decreased the natural soil fertility thereby hindering agricultural productivity, human health, and hygiene. Bio-based resilient nutrient sources as wastewater-derived algae are promising as a complete nutrient for agriculture and have the potential to be used in soilless cultivations. Innovations in nano-fortification and nano-sizing of minerals and algae have the potential to facilitate nutrients bioavailability and efficacy for a multifold increase in productivity. In this context, various options on minerals nanofertilizer application in agricultural food production besides efficient biofertilizer have been investigated. Algal biofertilizer with the nanoscale application has huge prospects for further agriculture productivities and fosters suitable development.

Rapid measurement of waterborne bacterial viability based on difunctional gold nanoprobe

Rapid measurement of waterborne bacterial viability is crucial for ensuring the safety of public health. Herein, we proposed a colorimetric assay for rapid measurement of waterborne bacterial viability based on a difunctional gold nanoprobe (dGNP). This versatile dGNP is composed of bacteria recognizing parts and signal indicating parts, and can generate color signals while recognizing bacterial suspensions of different viabilities. This dGNP-based colorimetric assay has a fast response and can be accomplished within 10 min. Moreover, the proposed colorimetric method is able to measure bacterial viability between 0% and 100%. The method can also measure the viability of other bacteria including Staphylococcus aureus, Shewanella oneidensis, and Escherichia coli O157H7. Furthermore, the proposed method has acceptable recovery (95.5–104.5%) in measuring bacteria-spiked real samples. This study offers a simple and effective method for the rapid measurement of bacterial viability and therefore should have application potential in medical diagnosis, food safety, and environmental monitoring.

A colorimetric method is proposed to measure waterborne bacterial viability by using a difunctional gold nanoprobe that can generate color signals while recognizing bacterial suspensions of different viabilities.

Spot tests: past and present

Microchemistry, i.e., the chemistry performed at the scale of a microgram or less, has its roots in the late eighteenth and early nineteenth centuries. In the first half of the twentieth century a wide range of spot tests have been developed. For didactic reasons, they are still part of the curriculum of chemistry students. However, they are even highly important for applied analyses in conservation of cultural heritage, food science, forensic science, clinical and pharmacological sciences, geochemistry, and environmental sciences. Modern pregnancy tests, virus tests, etc. are the most recent examples of sophisticated spot tests. The present ChemTexts contribution aims to provide an overview of the past and present of this analytical methodology.

Futuristic CRISPR-based biosensing in the cloud and internet of things era: an overview

Biosensors-based devices are transforming medical diagnosis of diseases and monitoring of patient signals. The development of smart and automated molecular diagnostic tools equipped with biomedical big data analysis, cloud computing and medical artificial intelligence can be an ideal approach for the detection and monitoring of diseases, precise therapy, and storage of data over the cloud for supportive decisions. This review focused on the use of machine learning approaches for the development of futuristic CRISPR-biosensors based on microchips and the use of Internet of Things for wireless transmission of signals over the cloud for support decision making. The present review also discussed the discovery of CRISPR, its usage as a gene editing tool, and the CRISPR-based biosensors with high sensitivity of Attomolar (10^-18 M), Femtomolar (10^-15 M) and Picomolar (10^-12 M) in comparison to conventional biosensors with sensitivity of nanomolar 10^-9 M and micromolar 10^-3 M. Additionally, the review also outlines limitations and open research issues in the current state of CRISPR-based biosensing applications.

Advances in aggregation induced emission (AIE) materials in biosensing and imaging of bacteria

With their ubiquitous nature, bacteria have had a significant impact on human health and evolution. Though as commensals residing in/on our bodies several bacterial communities support our health in many ways, bacteria remain one of the major causes of infectious diseases that plague the human world. Adding to this, emergence of antibiotic resistant strains limited the use of available antibiotics. The current available techniques to prevent and control such infections remain insufficient. This has been proven during one of greatest pandemic of our generation, COVID-19. It has been observed that bacterial coinfections were predominantly observed in COVID-19 patients, despite antibiotic treatment. Such higher rates of coinfections in critical patients even after antibiotic treatment is a matter of concern. Owing to many reasons across the world drug resistance in bacteria is posing a major problem i. According to Center for Disease control (CDC) antibiotic report threats (AR), 2019 more than 2.8 million antibiotic resistant cases were reported, and more than 35,000 were dead among them in USA alone. In both normal and pandemic conditions, failure of identifying infectious agent has played a major role. This strongly prompts the need to improve upon the existing techniques to not just effective identification of an unknown bacterium, but also to discriminate normal Vs drug resistant strains. New techniques based on Aggregation Induced Emission (AIE) are not only simple and rapid but also have high accuracy to visualize infection and differentiate many strains of bacteria based on biomolecular variations which has been discussed in this chapter.

Nanotechnology for Targeted Detection and Removal of Bacteria: Opportunities and Challenges

The emergence of nanotechnology has created unprecedented hopes for addressing several unmet industrial and clinical issues, including the growing threat so-termed "antibiotic resistance" in medicine. Over the last decade, nanotechnologies have demonstrated promising applications in the identification, discrimination, and removal of a wide range of pathogens. Here, recent insights into the field of bacterial nanotechnology are examined that can substantially improve the fundamental understanding of nanoparticle and bacteria interactions. A wide range of developed nanotechnology-based approaches for bacterial detection and removal together with biofilm eradication are summarized. The challenging effects of nanotechnologies on beneficial bacteria in the human body and environment and the mechanisms of bacterial resistance to nanotherapeutics are also reviewed.

One-pot facile synthesis of enzyme-encapsulated Zn/Co-infinite coordination polymer nanospheres as a biocatalytic cascade platform for colorimetric monitoring of bacteria viability

A rapid method for colorimetric monitoring of bacterial viability is described. The colorimetric method was carried out based on glucose oxidase-encapsulated Zn/Co-infinite coordination polymer (Zn/Co-ICP@GOx), which was prepared in aqueous solution free of toxic organic solvents at room temperature. The Zn/Co-ICP@GOx was confirmed to be a robust sphere structure with an average diameter of 147.53 ± 20.40 nm. It integrated the catalytic activity of natural enzyme (GOx) and mimetic peroxidase (Co (П)) all in one, efficiently acting as a biocatalytic cascade platform for glucose catalytic reaction. Exhibiting good multi-enzyme catalytic activity, stability, and selectivity, Zn/Co-ICP@GOx can be used for colorimetric glucose detection. The linear range was 0.01-1.0 mmol/L, and the limit of detection (LOD) was 0.005 mmol/L. As the glucose metabolism is a common expression of bacteria, the remaining glucose can indirectly represent the bacterial viability. Hence, a Zn/Co-ICP@GOx-based colorimetric method was developed for monitoring of bacterial viability. The color was intuitively observed with the naked eye, and the bacterial viability was accurately quantified by measurement of the absorbance at 510 nm. The method was applied to determination of bacterial viability in water and milk samples with recoveries of 99.0-103% and RSD of 0.43-7.5%. The method was rapid (less than 40 min) and applicable to different bacterial species irrespective of Gram-positive and Gram-negative bacteria, providing a universal and promising strategy for real-time monitoring of bacterial viability.

Detection of bacteria using antimicrobial polymer derived via ring-opening metathesis (romp) pathway

There is growing interest in the detection of bacteria in consumables, for example, in the food and water sectors. In this study, the aim was to produce a polymer-based bacteria biosensor via ROMP (ring opening metathesis polymerization). In the first part of the study, block and random copolymers were synthesized, and their biocidal activities were tested on the glass surface. Interdigitated electrode arrays coated with the polymers possessing the highest activity were used to screen the affinity towards different bacterial strains by monitoring impedance variations in real-time. The polymer-coated electrode could detect gram-positive and gram-negative bacteria strains at a concentration of 107 cfu/mL. The results show that ROMP-based polymer offers bacterial detection and can be used in developing biosensor devices for efficiently detecting pathogenic bacteria.

Cationic Tricyclic AIEgens for Concomitant Bacterial Discrimination and Inhibition

New ionic compounds with aggregation-induced emission (AIE) feature has been widely studied. These AIE-based luminogens (AIEgens) not only effectively resolve aggregation-caused quenching (ACQ) problems that are encountered for most of conventional fluorescent dyes, but also exhibit promising applications in biological imaging, potentially for a wide variety of diseases. However, such an AIE system needs to be further developed. In this work, a series of novel cationic AIEgens that are comprised of tricyclic 2-aminopyridinium derivatives with seven-membered rings are designed and synthesized via a simple, multicomponent reaction. Notably, these AIEgens exhibit the ability to specifically stain gram-positive bacteria. Moreover, a specific AIEgen, BMTAP-7, possesses highly efficient bacteriostatic ability for Staphylococcus aureus (S. aureus) in both liquid medium and solid agar plates, which have a minimum inhibitory concentration (MIC) between 4 and 8 µg mL^-1 . Using live-cell imaging and a wash-free process, it is observed that hydrophilic AIEgens are localized to mitochondria, whereas lipophilic AIEgens display specific staining of lysosomes. These AIEgens with bacteriostatic activity hold great promise for distinguishing between bacterial types and inhibiting bacterial infections in situ.

Portable detection of Staphylococcus aureus using personal glucose meter based on hybridization chain reaction strategy

Staphylococcus aureus is one of the most important food-borne bacterial pathogens and causes numerous illnesses. In this work, we report a sensitive and highly selective magnetic-aptamer biosensor based on a personal glucose meter (PGM) platform for the detection of Staphylococcus aureus. The aptamer for Staphylococcus aureus was immobilized on the magnetic bead by hybridization with the capture probe P. In the presence of Staphylococcus aureus, the aptamer was dissociated from the magnetic bead. Then the capture probe was exposed and could be hybridized with a biotinylated probe to trigger the DNA hybridization chain reaction (HCR), thus achieving the signal amplification. The concentration of streptavidin-labeled invertase can be read by PGM, thus can lead to the portable quantitative detection of Staphylococcus aureus. After optimization of various conditions, 5 μM probe P, the MB-P reaction time for 36 h, the competition time for 60 min, 0.5 μM H1 & H2, 0.5 M sucrose and the sucrose invertase catalytic reaction time for 50 min was chosen to achieve the better sensor performance. Under the optimal conditions, the fabricated sensor offers high sensitivity with the limit of detection about 2 CFU/mL. This sensitive PGM based sensor could successfully evaluate the Staphylococcus aureus concentration in real food samples, and the results are consistent with those obtained by using plate counting methods. Moreover, the PGM sensor can greatly reduce the required time compared to the plate counting methods. The fabricated sensor supplies an ideal solution for rapid portable detection of bacterial pathogens and holds its potential use in the quality control for agriculture and food enterprises, entry-exit inspection and quality testing for food.

Array-Based Biosensors for Bacteria Detection: From the Perspective of Recognition

Array-based biosensors have shown as effective and powerful tools to distinguish intricate mixtures with infinitesimal differences among analytes such as nucleic acids, proteins, microorganisms, and other biomolecules. In array-based bacterial sensing, the recognition of bacteria is the initial step that can crucially influence the analytical performance of a biosensor array. Bacteria recognition as well as the signal readout and mathematical analysis are indispensable to ensure the discrimination ability of array-based biosensors. Strategies for bacteria recognition mainly include the specific interaction between biomolecules and the corresponding receptors on bacteria, the noncovalent interaction between materials and bacteria, and the specific targeting of bacterial metabolites. In this review, recent advances in array-based bacteria sensors are discussed from the perspective of bacteria recognition relying on the characteristics of different bacteria. Principles of bacteria recognition and signal readout for bacteria detection are highlighted as well as the discussion on future trends in array-based biosensors.

Enzyme embedded microfluidic paper-based analytic device (μPAD): a comprehensive review

Low-cost paper-based analytical devices are the latest generation of portable lab-on-chip designs that offers an innovative platform for the on/off-site analysis (biosensing) of target analytes, especially in rural and remote areas. Recently, microfluidic paper-based analytical devices (μPADs) have attained significant recognition owing to their exciting fundamental features such as: ease of fabrication, rapid operation, and precise interpretations. The incorporation of enzymes with paper-based analytical devices significantly improves analytical performance while exhibiting excellent chemical and storage stability. In addition to that, these devices are highly compact, portable, easy-to-use, and do not require any additional sophisticated equipment for the detection and quantification of target analytes. This review provides a holistic insight into design, fabrication, and enzyme immobilization strategies for the development of enzyme-μPADs, which enables them to be widely implemented for in-field analysis. It also highlights the recent application of enzyme-μPADs in the area of: biomedical, food safety, and environmental monitoring while exploring the mechanisms of detection involved. Further, in order to improve the accuracy of analysis, researchers have designed a smartphone-based scanning tool for multi-variant point-of-care devices, which is summarized in the latter part of the review. Finally, the future perspectives and outlook of major challenges associated with enzyme-μPADs are discussed with their possible solutions. The development of enzyme integrated μPADs will open a new avenue as an exceptional analytical tool to explore various applications.HIGHLIGHTSEnzyme embedded paper-based analytical devices are a revolution in the field of biosensing.The design, fabrication, and enzyme immobilization on μPADs have been comprehensively discussed.The application of enzyme-μPADs food safety, environmental monitoring, and clinical diagnostic have been reviewed.Smartphones can be used as an on-site, user-friendly, and compact next-gen scanning tool for biosensing.

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.

Rapid Fluorescence Quenching Detection of Escherichia coli Using Natural Silica-Based Nanoparticles

The development of fluorescent silica nanoparticles (SNP-RB) from natural amorphous silica and its performance as an Escherichia coli (E. coli) biosensor is described in this paper. SNP-RB was derived from silica recovered from geothermal installation precipitation and modified with the dye, Rhodamine B. The Fourier Infrared (FTIR) confirms the incorporation of Rhodamine B in the silica matrix. Transmission Electron Microscopy (TEM) micrographs show that the SNP-RB had an irregular structure with a particle diameter of about 20-30 nm. The maximum fluorescence spectrum of SNP-RB was recorded at 580 nm, which was further applied to observe the detection performance of the fluorescent nanoparticles towards E. coli. The sensing principle was based on the fluorescence-quenching mechanism of SNP-RB and this provided a wide linear E. coli concentration range of 10-10⁵ CFU/mL with a limit detection of 8 CFU/mL. A rapid response time was observed after only 15 min of incubation of SNP-RB with E. coli. The selectivity of the biosensor was demonstrated and showed that the SNP-RB only gave quenching response only to live E. coli bacteria. The use of SNP-RB as a sensing platform reduced the response time significantly compared to conventional 3-day bacterial assays, as well having excellent analytical performance in terms of sensitivity and selectivity.

Narrower Nanoribbon Biosensors Fabricated by Chemical Lift-off Lithography Show Higher Sensitivity

Wafer-scale nanoribbon field-effect transistor (FET) biosensors fabricated by straightforward top-down processes are demonstrated as sensing platforms with high sensitivity to a broad range of biological targets. Nanoribbons with 350 nm widths (700 nm pitch) were patterned by chemical lift-off lithography using high-throughput, low-cost commercial digital versatile disks (DVDs) as masters. Lift-off lithography was also used to pattern ribbons with 2 μm or 20 μm widths (4 or 40 μm pitches, respectively) using masters fabricated by photolithography. For all widths, highly aligned, quasi-one-dimensional (1D) ribbon arrays were produced over centimeter length scales by sputtering to deposit 20 nm thin-film In₂O₃ as the semiconductor. Compared to 20 μm wide microribbons, FET sensors with 350 nm wide nanoribbons showed higher sensitivity to pH over a broad range (pH 5 to 10). Nanoribbon FETs functionalized with a serotonin-specific aptamer demonstrated larger responses to equimolar serotonin in high ionic strength buffer than those of microribbon FETs. Field-effect transistors with 350 nm wide nanoribbons functionalized with single-stranded DNA showed greater sensitivity to detecting complementary DNA hybridization vs 20 μm microribbon FETs. In all, we illustrate facile fabrication and use of large-area, uniform In₂O₃ nanoribbon FETs for ion, small-molecule, and oligonucleotide detection where higher surface-to-volume ratios translate to better detection sensitivities.

Quantitative E. coli Enzyme Detection in Reporter Hydrogel-Coated Paper Using a Smartphone Camera

There is a growing demand for rapid and sensitive detection approaches for pathogenic bacteria that can be applied by non-specialists in non-laboratory field settings. Here, the detection of the typical E. coli enzyme β-glucuronidase using a chitosan-based sensing hydrogel-coated paper sensor and the detailed analysis of the reaction kinetics, as detected by a smartphone camera, is reported. The chromogenic reporter unit affords an intense blue color in a two-step reaction, which was analyzed using a modified Michaelis-Menten approach. This generalizable approach can be used to determine the limit of detection and comprises an invaluable tool to characterize the performance of lab-in-a-phone type approaches. For the particular system analyzed, the ratio of reaction rate and equilibrium constants of the enzyme-substrate complex are 0.3 and 0.9 pM-1h-1 for β-glucuronidase in phosphate buffered saline and lysogeny broth, respectively. The minimal degree of substrate conversion for detection of the indigo pigment formed during the reaction is 0.15, while the minimal time required for detection in this particular system is ~2 h at an enzyme concentration of 100 nM. Therefore, this approach is applicable for quantitative lab-in-a-phone based point of care detection systems that are based on enzymatic substrate conversion via bacterial enzymes.

Portable Device for Quick Detection of Viable Bacteria in Water

(1) Background: Access to clean water is a very important factor for human life. However, pathogenic microorganisms in drinking water often cause diseases, and convenient/inexpensive testing methods are urgently needed. (2) Methods: The reagent contains 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and phenazine methosulfate (PMS) and can react with succinate dehydrogenase within bacterial cell membranes to produce visible purple crystals. The colorimetric change of the reagent after reaction can be measured by a sensor (AS7262). (3) Results: Compared with traditional methods, our device is simple to operate and can provide rapid (i.e., 5 min) semi-quantitative results regarding the concentration of bacteria within a test sample. (4) Conclusions: This easy-to-use device, which employs MTT-PMS reagents, can be regarded as a potential and portable tool for rapid water quality determination.

Polymer Electrochromism Driven by Metabolic Activity Facilitates Rapid and Facile Bacterial Detection and Susceptibility Evaluation

The electrochromism of a water-soluble naturally oxidized electrochromic polymer, ox-PPE, is harnessed for rapid and facile bacterial detection, discrimination, and susceptibility testing. The ox-PPE solution shows distinct colorimetric and spectroscopic changes within 30 min when mixed with live bacteria. For the underlying mechanism, it is found that ox-PPE responds to the reducing species (e.g. cysteine and glutathione) released by metabolically active bacteria. This reduction reaction is ubiquitous among various bacterial strains, with a noticeable difference that enables discrimination of Gram-negative and Gram-positive bacterial strains. Combining ox-PPE with antibiotics, methicillin-susceptible and -resistant S. aureus can be differentiated within 2.5 h. Proof-of-concept demonstration of ox-PPE for antimicrobial susceptibility testing is carried out by incubating E. coli with various antibiotics. The obtained minimum inhibition concentrations are consistent with the conventional culture-based methods, but with the procedure time significantly shortened to 3 h.