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.

Colorimetric sensing for translational applications: from colorants to mechanisms

Colorimetric sensing offers instant reporting via visible signals. Versus labor-intensive and instrument-dependent detection methods, colorimetric sensors present advantages including short acquisition time, high throughput screening, low cost, portability, and a user-friendly approach. These advantages have driven substantial growth in colorimetric sensors, particularly in point-of-care (POC) diagnostics. Rapid progress in nanotechnology, materials science, microfluidics technology, biomarker discovery, digital technology, and signal pattern analysis has led to a variety of colorimetric reagents and detection mechanisms, which are fundamental to advance colorimetric sensing applications. This review first summarizes the basic components (e.g., color reagents, recognition interactions, and sampling procedures) in the design of a colorimetric sensing system. It then presents the rationale design and typical examples of POC devices, e.g., lateral flow devices, microfluidic paper-based analytical devices, and wearable sensing devices. Two highlighted colorimetric formats are discussed: combinational and activatable systems based on the sensor-array and lock-and-key mechanisms, respectively. Case discussions in colorimetric assays are organized by the analyte identities. Finally, the review presents challenges and perspectives for the design and development of colorimetric detection schemes as well as applications. The goal of this review is to provide a foundational resource for developing colorimetric systems and underscoring the colorants and mechanisms that facilitate the continuing evolution of POC sensors.

Surface-Engineered Nanomaterials for Optical Array Based Sensing

Array based sensing governed by optical methods provides fast and economic way for detection of wide variety of analytes where the ideality of detection processes depends on the sensor element's versatile mode of interaction with multiple analytes in an unbiased manner. This can be achieved by either the receptor unit having multiple recognition moiety, or their surface property should possess tuning ability upon fabrication called surface engineering. Nanomaterials have a high surface to volume ratio, making them viable candidates for molecule recognition through surface adsorption phenomena, which makes it ideal to meet the above requirements. Most crucially, by engineering a nanomaterial's surface, one may produce cross-reactive responses for a variety of analytes while focusing solely on a single nanomaterial. Depending on the nature of receptor elements, in the last decade the array-based sensing has been considering as multimodal detection platform which operates through various pathway including single channel, multichannel, binding and indicator displacement assay, sequential ON-OFF sensing, enzyme amplified and nanozyme based sensing etc. In this review we will deliver the working principle for Array-based sensing by using various nanomaterials like nanoparticles, nanosheets, nanodots and self-assembled nanomaterials and their surface functionality for suitable molecular recognition.

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.

Different sized gold nanoparticles for array-based sensing of pesticides and its application for strawberry pollution monitoring

The use of pesticides plays an essential role in improving crop quality and yield, however, it causes air, water, and soil pollution and the residue of these pesticides in agricultural products threatens the ecosystem and human life. Therefore, it is highly desirable to develop rapid, simple, and cost-effective methods for regular monitoring of pesticide residues in agricultural products especially strawberry that is consumed fresh and unpeeled. In this study, gold nanoparticles (AuNPs) of varying sizes have been exploited as sensing units to design a non-enzymatic colorimetric sensor array for the detection and discrimination of various pesticides including; bifenazate (BF), paraquat (PQ), diazinon (DZ), thiometon (TM), and carbendazim (CD) and chlorpyrifos (CP). Because of their strong size- and environmentally-dependent properties, AuNPs with different sizes produced distinguished plasmonic patterns in the presence of pesticides at a vast range of concentrations (25-800 ng mL-1). Plasmonic patterns of sensor units have been analyzed by various data visualization (bar plots and heat maps) and pattern recognition methods (linear discriminant analysis (LDA)). The multivariate calibrations showed linear responses ranging from 50 to 800 ng mL-1 for carbendazim, chlorpyrifos, paraquat, and bifenazate and 25-800 ng mL-1 for diazinon and thiometon. The limit of detection (LOD) was calculated to be 17.7, 22.8, 22.4, 9.7, 7.4, and 23.8 ng mL-1 for carbendazim, chlorpyrifos, paraquat, diazinon, thiometon, and bifenazate respectively. Finally, the applicability of the designed sensor was evaluated in real samples comprising tap water, well water, soil, and fruit, leave, drainage water, and culture substrate of strawberry.

Multiplex Detection of Biogenic Amines for Meat Freshness Monitoring Using Nanoplasmonic Colorimetric Sensor Array

Biogenic amines (BAs) were presented as significant markers for the evaluation of the spoilage of meat and meat products. In this work, a colorimetric sensor array was developed for the discrimination and detection of spermine (SP), spermidine (SD), histamine (HS), and tryptamine (TP) as important BAs in food assessment. For this aim, two important spherical plasmonic nanoparticles, namely gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs), were utilized as the sensing elements of the probes. The cross-reactive interaction of the target biogenic amines and the plasmonic nanoparticles caused the aggregation-induced UV-Vis spectra changes, which were accompanied by visual color variation in the solution. The collected responses were analyzed by principal component analysis-linear discrimination analysis (PCA-LDA) to classify the four BAs. This colorimetric sensor array can also discriminate between the individual BAs and their mixture accurately. Partial least squares regression (PLS-R) was also utilized for quantitative analysis of the BAs. The wide linear concentration ranges of 0.1-10.0 µM for the four BAs and desirable figures of merits (FOMs) showed the potential of the developed sensor for quantitative detection of the BAs. Finally, the practical ability of the developed probe was studied by the determination of the BAs in the meat samples, which successfully proved the potential of the colorimetric sensor array in a food sample.

Recent Advances in Colorimetric Tests for the Detection of Infectious Diseases and Antimicrobial Resistance

Diagnosis of infection-causing microorganisms with sensitive, rapid, selective and economical diagnostic tests is critical to start the right treatment. With these tests, the spread of infections can be prevented. In addition to that, the detection of antimicrobial resistance also makes a significant contribution to public health. In recent years, different types of diagnostic tests have been developed as alternatives to traditional diagnostic tests used in clinics. In particular, colorimetric tests, which minimize the need for an instrument, have advantages owing to their cost effectiveness, rapid response and naked-eye detection and practical use. In this review, we especially focused on pH indicators and nanomaterial-based colorimetric tests in detection of infection-causing microorganisms and antimicrobial resistance.

Colorimetric Sensing of Gram-Negative and Gram-Positive Bacteria Using 4-Mercaptophenylboronic Acid-Functionalized Gold Nanoparticles in the Presence of Polyethylene Glycol

Gold nanoparticles (GNPs) have been used as detection probes for rapid and sensitive detection of various analytes, including bacteria. Here, we demonstrate a simple strategy for bacterial detection using GNPs functionalized with 4-mercaptophenylboronic acid (4-MPBA). 4-MPBA can interact with peptidoglycan or lipopolysaccharides present in bacterial organelles. After the addition of a high concentration of sodium hydroxide (NaOH), the functionalization of the surface of 50 nm GNPs with 4-MPBA (4-MPBA@GNPs) in the presence of polyethylene glycol results in a color change because of the aggregation of 4-MPBA@GNPs. This color change is dependent on the amount of bacteria present in the tested samples. Escherichia coli (E. coli) K-12 and Staphylococcus aureus (S. aureus) are used as Gram-negative and Gram-positive bacterial models, respectively. The color change can be detected within an hour by the naked eye. A linear relationship is observed between bacterial concentrations and the absorbance intensity at 533 nm; R ² values of 0.9152 and 0.8185 are obtained for E. coli K-12 and S. aureus, respectively. The limit of detection of E. coli K-12 is ∼2.38 × 10² CFU mL^-1 and that of S. aureus is ∼4.77 × 10³ CFU mL^-1. This study provides a promising approach for the rapid detection of target Gram-negative and Gram-positive bacteria.

Mixed-Ligand gold nanoparticles based optical sensor array for the recognition and quantification of seven toxic metals

Sensor arrays use pattern recognition for the identification and quantification of analytes. In the presented work, a gold nanoparticle (GNP) based optical sensor array was employed to classify and quantify seven toxic metals (arsenic, barium, cadmium, cerium, chromium, lead, and mercury). The sensor array receptors were GNPs functionalized by mercaptoundecanoic acid, 2-mercaptoethanesulfonate, and a 1:1 mixture of the two ligands. The mixed-ligand particle responds to the same analytes as the mono-ligand particles but in a distinctive way. This behavior demonstrates the high potential of mixed-ligand particles in the fabrication of sensor array receptors. The responses of the GNPs to different concentrations of the seven metal ions were analyzed, and a unique "classification trajectory" was produced for every metal. Samples of different metal concentrations were then measured and identified using the "classification trajectories". Once sample composition has been identified, a PLSR model, produced from the concatenated sensor array spectra of four calibration samples for each nanoparticle, was used to determine the metal concentration.

Machine Learning-Assisted Sensor Array Based on Poly(amidoamine) (PAMAM) Dendrimers for Diagnosing Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder, and the early diagnosis of AD remains challenging. Here we have developed a fluorescent sensor array composed of three modified polyamidoamine dendrimers. Proteins of various properties were differentiated via this array with 100% accuracy, proving the rationality of the array's design. The mechanism of the fluorescence response was discussed. Furthermore, the robust three-element array enables parallel detection of multiple Aβ40/Aβ42 aggregates (0.5 μM) in diverse interferents, serum media, and cerebrospinal fluid (CSF) with high accuracy, through machine learning algorithms, demonstrating the tremendous potential of the sensor array in Alzheimer's disease diagnosis.

A Water Soluble 2-Phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazole Based Probe: Antimicrobial Activity and Colorimetric/Fluorescence pH Response

The growing demand of responsive tools for biological and biomedical applications pushes towards new low-cost probes easy to synthesize and versatile. Current optical probes are theranostic tools simultaneously responsive to biological parameters/analyte and therapeutically operating. Among the optical methods for pH monitoring, simple small organic molecules including multifunctional probes for simultaneous biological activity being highly desired by scientists and technicians. Here, we present a novel pH-responsive probe with a three-ring heteroaromatic pattern and a flexible cationic chain. The novel molecule shows real-time naked-eye colorimetric and fluorescence response in the slightly acidic pH range besides its excellent solubility both in the organic phase and in water. In addition, the small probe shows significant antibacterial activity, particularly against Escherichia coli. Single-crystal X-ray study and density functional theory (DFT) calculations rationalize the molecule spectroscopic response. Finally, molecular dynamics (MD) elucidate the interactions between the probe and a model cell membrane.

A Smartphone-Based Fluorescent Electronic Tongue for Tracing Dopaminergic Agents in Human Urine

The importance of tracing dopaminergic agents in the progression assessment of Parkinson's disease has boosted the demand for fast, sensitive, and real-time multi-analyte detection. Herein, visual and fingerprint fluorimetric patterns have been created by an optical sensor array to simultaneously detect and discriminate among levodopa, carbidopa, benserazide, and entacapone, as important dopaminergic agents. A dual emissive nanoprobe consisting of red quantum dots and blue carbon dots with an overall pink emission has been fabricated to provide unique emission patterns in the presence of the target analytes. The sensor elements in the array come from it's differential response in the absence and presence of cetyltrimethylammonium bromide under alkaline conditions. A smartphone camera was used to take photos from the solutions in the wells. Distinct changes in the spectral profiles along with vivid and concentration-dependent color variations led to visual discrimination of dopaminergic agents in a broad concentration range. The results of linear discriminant analysis revealed great discrimination accuracies. Different concentrations of the target analytes were excellently recognized in human urine. The high sensitivity of the array, which is a bonus to rapid, on-site, and visual discrimination of dopaminergic agents, holds great promise for routine analysis of real-world clinical samples.

Importance of Substrate-Particle Repulsion for Protein-Templated Assembly of Metal Nanoparticles

We study the protein-directed assembly of colloidal gold nanoparticles on de novo designed protein nanofiber templates. Using sequential assembly on glass substrates, we attach positively charged gold nanoparticles to protein nanofibers engineered to have a high density of negatively charged surface residues. Using a combination of electron and optical microscopy, we measure the density of particle attachment and characterize binding specificity. By varying nanoparticle size and pH of the solution, we explore the importance of charge-dependent particle-fiber and particle-substrate interactions. We find an inverse correlation between particle size and attachment density to protein nanofibers, attributed to the balance between size-dependent electrostatic particle-fiber attraction and particle-substrate repulsion. We show pH-dependent particle attachment density and binding specificity in relation to the protonation fraction of each assembly layer. Finally, we employ hyperspectral scattering microscopy to draw conclusions about particle density and interparticle spacings of optically observable particle assemblies.

Simultaneous detection and identification of thiometon, phosalone, and prothioconazole pesticides using a nanoplasmonic sensor array

In this work, a colorimetric sensor array has been designed for the identification and discrimination of thiometon (TM) and phosalone (PS) as organophosphate pesticides and prothioconazole (PC) as a triazole pesticide. For this purpose, two different plasmonic nanoparticles including unmodified gold nanoparticles (AuNPs) and unmodified silver nanoparticles (AgNPs) were used as sensing elements. The principle of the proposed strategy relied on the aggregation AuNPs and AgNPs through the cross-reactive interaction between the target pesticides and plasmonic nanoparticles. Therefore, these aggregation-induced UV-Vis spectra changes were utilized to discriminate the target pesticides with the help of linear discriminant analysis (LDA). Besides, we have employed the bar plots and the heat maps as visual non-statistical methods to differentiate the pesticides in a wide range of concentrations (i.e., 20-5000 ng mL^-1). Multivariate calibration plots from partial least squares (PLS)- regression indicated that the responses linearly depend on the pesticide concentrations in the range of 100-1000 ng mL^-1 with the limit of detections (LOD) of 66.8, 68.3, and 41.4 ng mL^-1, for TM, PS, and PC, respectively. Finally, the potential applicability of the proposed sensor array has been evaluated for the detection and identification of the pesticides in the mixtures, water samples, and cucumber fruit.

Chemical sensing with Au and Ag nanoparticles

Noble metal nanoparticles (NPs) are ideal scaffolds for the fabrication of sensing devices because of their high surface-to-volume ratio combined with their unique optical and electrical properties which are extremely sensitive to changes in the environment. Such characteristics guarantee high sensitivity in sensing processes. Metal NPs can be decorated with ad hoc molecular building blocks which can act as receptors of specific analytes. By pursuing this strategy, and by taking full advantage of the specificity of supramolecular recognition events, highly selective sensing devices can be fabricated. Besides, noble metal NPs can also be a pivotal element for the fabrication of chemical nose/tongue sensors to target complex mixtures of analytes. This review highlights the most enlightening strategies developed during the last decade, towards the fabrication of chemical sensors with either optical or electrical readout combining high sensitivity and selectivity, along with fast response and full reversibility, with special attention to approaches that enable efficient environmental and health monitoring.

Array-Based Discriminative Optical Biosensors for Identifying Multiple Proteins in Aqueous Solution and Biofluids

Identification of proteins is an important issue both in medical research and in clinical practice as a large number of proteins are closely related to various diseases. Optical sensor arrays with recognition ability have been flourished to apply for distinguishing multiple chemically or structurally similar analytes and analyzing unknown or mixed samples. This review gives an overview of the recent development of array-based discriminative optical biosensors for recognizing proteins and their applications in real samples. Based on the number of sensor elements and the complexity of constructing array-based discriminative systems, these biosensors can be divided into three categories, which include multi-element-based sensor arrays, environment-sensitive sensor arrays and multi-wavelength-based single sensing systems. For each strategy, the construction of sensing platform and detection mechanism are particularly introduced. Meanwhile, the differences and connections between different strategies were discussed. An understanding of these aspects may help to facilitate the development of novel discriminative biosensors and expand their application prospects.

Nano-enabled sensing approaches for pathogenic bacterial detection

Infectious diseases caused by pathogenic bacteria, especially antibiotic-resistant bacteria, are one of the biggest threats to global health. To date, bacterial contamination is detected using conventional culturing techniques, which are highly dependent on expert users, limited by the processing time and on-site availability. Hence, real-time and continuous monitoring of pathogen levels is required to obtain valuable information that could assist health agencies in guiding prevention and containment of pathogen-related outbreaks. Nanotechnology-based smart sensors are opening new avenues for early and rapid detection of such pathogens at the patient's point-of-care. Nanomaterials can play an essential role in bacterial sensing owing to their unique optical, magnetic, and electrical properties. Carbon nanoparticles, metallic nanoparticles, metal oxide nanoparticles, and various types of nanocomposites are examples of smart nanomaterials that have drawn intense attention in the field of microbial detection. These approaches, together with the advent of modern technologies and coupled with machine learning and wireless communication, represent the future trend in the diagnosis of infectious diseases. This review provides an overview of the recent advancements in the successful harnessing of different nanoparticles for bacterial detection. In the beginning, we have introduced the fundamental concepts and mechanisms behind the design and strategies of the nanoparticles-based diagnostic platform. Representative research efforts are highlighted for in vitro and in vivo detection of bacteria. A comprehensive discussion is then presented to cover the most commonly adopted techniques for bacterial identification, including some seminal studies to detect bacteria at the single-cell level. Finally, we discuss the current challenges and a prospective outlook on the field, together with the recommended solutions.

Colorimetric Differentiation of Multiple Oxidizing Anions Based on Two Core-Shell Au@Ag Nanoparticles with Different Morphologies as Array Recognition Elements

The efficient discrimination of oxidizing anions is of considerable importance in environmental monitoring. Here, for the first time, we have developed a simple and fast colorimetric sensor array for detection and identification of oxidizing anions, which takes advantage of the etching of the Ag shell of two core-shell Au@Ag nanoparticles (Au@Ag nanospheres (Au@Ag NPs) and Au@Ag nanocubes (Au@Ag NCs)) by oxidizing anions. The differential etching ability of various oxidizing anions to the Ag shell of the two Au@Ag nanoparticles resulted in different absorbance and color change of the nanoparticles. Thus, employing Au@Ag NPs and Au@Ag NCs as the array's receptors and the indicators, six oxidizing anions (i.e., BrO₃^-, Cr₂O₇^2-, ClO₄^-, IO₃^-, IO₄^-, and MnO₄^-) down to 10 nM could be identified from each other by their own colorimetric response patterns. Moreover, the complex mixtures of oxidizing anions could be well discriminated. Most importantly, the sensor array was successfully applied to the discrimination of oxidizing anions in river water and tap water samples.

Comparative study of serum sample preparation methods in aggregation-based plasmonic sensing

The use of nanoparticle-based colorimetric methods has received considerable attention for clinical analysis in biofluids. Sample preparation methods are surveyed here to minimize the impact of the sample matrix on the performance of a nanoparticle aggregation assay.

Noble Metal Nanoparticles-Based Colorimetric Biosensor for Visual Quantification: A Mini Review

Nobel metal can be used to form a category of nanoparticles, termed noble metal nanoparticles (NMNPs), which are inert (resistant to oxidation/corrosion) and have unique physical and optical properties. NMNPs, particularly gold and silver nanoparticles (AuNPs and AgNPs), are highly accurate and sensitive visual biosensors for the analytical detection of a wide range of inorganic and organic compounds. The interaction between noble metal nanoparticles (NMNPs) and inorganic/organic molecules produces colorimetric shifts that enable the accurate and sensitive detection of toxins, heavy metal ions, nucleic acids, lipids, proteins, antibodies, and other molecules. Hydrogen bonding, electrostatic interactions, and steric effects of inorganic/organic molecules with NMNPs surface can react or displacing capping agents, inducing crosslinking and non-crosslinking, broadening, or shifting local surface plasmon resonance absorption. NMNPs-based biosensors have been widely applied to a series of simple, rapid, and low-cost diagnostic products using colorimetric readout or simple visual assessment. In this mini review, we introduce the concepts and properties of NMNPs with chemical reduction synthesis, tunable optical property, and surface modification technique that benefit the development of NMNPs-based colorimetric biosensors, especially for the visual quantification. The “aggregation strategy” based detection principle of NMNPs colorimetric biosensors with the mechanism of crosslinking and non-crosslinking have been discussed, particularly, the critical coagulation concentration-based salt titration methodology have been exhibited by derived equations to explain non-crosslinking strategy be applied to NMNPs based visual quantification. Among the broad categories of NMNPs based biosensor detection analyses, we typically focused on four types of molecules (melamine, single/double strand DNA, mercury ions, and proteins) with discussion from the standpoint of the interaction between NMNPs surface with molecules, and DNA engineered NMNPs-based biosensor applications. Taken together, NMNPs-based colorimetric biosensors have the potential to serve as a simple yet reliable technique to enable visual quantification.

A colorimetric sensor array for detection and discrimination of antioxidants based on Ag nanoshell deposition on gold nanoparticle surfaces

There is growing interest in developing a high-performance sensor array for detection and discrimination of antioxidants owing to their widespread use and essential role in the human body. The present work unveils a novel colorimetric sensor array for colorimetric discrimination of antioxidants based on the red, green, and blue alteration (ΔRGB) pattern recognition. In this sensor array, three concentrations of AgNO3 were used as sensing elements, and gold nanoparticles (AuNPs) were employed as a colorimetric probe. In the presence of antioxidants, the sensor array produces unique colorimetric response patterns for the discrimination of these antioxidants due to different reactivities between three different concentrations of AgNO3 and each antioxidant, leading to deposition of different quantities of Ag nanoshells on the surface of AuNPs, enabling an excellent discrimination of six antioxidants (catechin, epigallocatechin 3-gallate, epicatechin, epigallocatechin, epicatechin 3-gallate, and gallocatechin) at a 20 nM level, when linear discriminant analysis (LDA), hierarchical cluster analysis (HCA), centroid diagram, spidergram, and color contour profiles were smartly combined. Furthermore, different concentrations of antioxidants and binary antioxidant mixtures, even ternary mixtures, could also be discriminated with this sensor array. Finally, the sensor array was successfully used for the discrimination of antioxidants in serum samples, demonstrating its potential applications in the diagnosis of antioxidant-related diseases.

Multifunctionality of gold nanoparticles: Plausible and convincing properties

In a couple of decades, nanotechnology has become a trending area in science due to it covers all subject that combines diverse range of fields including but not limited to chemistry, physics and medicine. Various metal and metal oxide nanomaterials have been developed for wide range applications. However, the application of gold nanostructures and nanoparticles has been received more attention in various biomedical applications. The unique property of gold nanoparticles (AuNPs) is surface plasmon resonance (SPR) that determine the size, shape and stability. The wide surface area of AuNPs eases the proteins, peptides, oligonucleotides, and many other compounds to tether and enhance the biological activity of AuNPs. AuNPs have multifunctionality including antimicrobial, anticancer, drug and gene delivery, sensing applications and imaging. This state-of-the-art review is focused on the role of unique properties of AuNPs in multifunctionality and its various applications.

Diversely positive-charged gold nanoparticles based biosensor: A label-free and sensitive tool for foodborne pathogen detection

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A label-free, non-paired antibodies dependent biosensor was constructed.

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(+) AuNPs were employed to generate signal and capture bacteria in the new LFS.

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This work possesses a desirable universality for other pathogens.

Gold nanoparticles (AuNPs)-based lateral flow strip (LFS) enables a quick screening of foodborne bacteria in point-of-care (POC) diagnostics but suffers from the cumbersome labeling of antibodies and poor sensitive performance. Here, we innovated a label-free immunoassay to detect pathogenic bacteria by introducing diversely positive charges functionalized AuNPs ((+) AuNPs). The (+) AuNPs can be loaded on negatively charged bacteria via electrostatic interaction, leading to a color labeling to target bacteria. Afterward, the (+) AuNPs-bacteria complex can be specifically captured by monoclonal antibody (McAb) immobilized on test (T)-line. Under optimum conditions, the proposed LFS exhibited a lowest detectable concentration of 10³ CFU/mL for Salmonella enteritidis (S. enteritidis) and could be well applied in drinking water, lettuce and pork samples. Moreover, this novel (+) AuNPs-LFS possessed a universal applicability, which could also be used for detecting Escherichia coli O157 (E. coli O157) with a superior sensitivity (10⁴ CFU/mL) and specificity.

ThThnated Development of a pH assisted AgNP-based colorimetric sensor Array for simultaneous identification of phosalone and azinphosmethyl pesticides

Development of simple and rapid methods for identification of pesticides, due to their broad usage and harmful effects on mammals, has been known as a critical demand. Herein, we have introduced a silver nanoparticle (AgNP) based colorimetric sensor array for simultaneous identification of Azinphosmethyl (AM) and Phosalone (PS) pesticides. In the presence of the target pesticides, unmodified AgNPs at various pHs (4.5, 5.5 and 9.5) showed different aggregation behaviors. As a result of aggregation, the color and UV-Vis spectra of AgNPs changed differentially, leading to distinct response patterns for AM and PS. The aggregation induced spectral changes of AgNPs, were used to identify AM and PS with the help of linear discriminant analysis (LDA). The applicability of the proposed sensor array was then evaluated by identifying the target pesticides in apple samples. Altogether, the developed AgNPs based colorimetric sensor array can be potentially exploited as an efficient discrimination tool in the near future for agrichemical applications.

A pH-based sensor array for the detection and identification of proteins using CdSe/ZnS quantum dots as an indicator

A novel and simple fluorescence sensor array was developed for the detection and identification of proteins using pH buffer solutions as sensing elements.

Metal Nanoparticles for Diagnosis and Therapy of Bacterial Infection

Infectious diseases caused by pathogenic bacteria, especially multidrug-resistant bacteria, and their global spreading have become serious public health concerns. Early diagnosis and effective therapy can efficiently prevent deterioration and further spreading of the infections. There is an urgent need for sensitive, selective, and facile diagnosis as well as therapeutically potent treatment. The emergence of nanotechnology has provided more options for diagnosis and treatments of bacterial infections. Metal nanoparticles and metal oxide nanoparticles have drawn intense attention owing to their unique optical, magnetic, and electrical properties. These versatile metal-based nanoparticles have great potential for selective detection of bacteria and/or therapy. This review gives an overview of recent efforts on developing various metal-based nanoparticles for bacterial detection and infection therapy. It begins with an introduction of fundamental concepts and mechanisms in designing diagnostic and therapeutic strategies. Representative achievements are selected to illustrate the proof-of-concept in vitro and in vivo applications. A brief discussion of challenges and perspective outlook in this field is provided at the end of this review.

Recent Trends in Nanomaterials-Based Colorimetric Detection of Pathogenic Bacteria and Viruses

Rapid, sensitive, selective, convenient, and cost-effective pathogen diagnosis is important to prevent further spread of pandemic diseases, minimize social and economic losses, and to facilitate right clinical therapy. Over the past few years, various sensor-based diagnostic systems outperforming conventional pathogenic diagnostic assays have been developed. Among them, colorimetric biosensors detecting target molecules by the naked eye have attracted much attention due to their simplicity, practicality, and cost-effectiveness. Recently, nanomaterials have been adopted as a versatile signal transduction and amplification tool for rapid and sensitive detection of pathogenic bacteria and viruses. Here, recent trends and advances are reviewed in detecting and diagnosing pathogenic bacteria and viruses using colorimetric biosensors employing various nanomaterials. In addition, it is discussed how nanomaterials and bioreceptors can be better integrated together to develop rapid and sensitive colorimetric detection system in the future.

Highly selective and sensitive determination of dopamine in biological samples via tuning the particle size of label-free gold nanoparticles

Herein, a rapid, sensitive and selective approach for the colorimetric detection of dopamine (DA) was developed utilizing unmodified gold nanoparticles (AuNPs). This assay relied upon the size-dependent aggregation behavior of DA and three other structurally similar catecholamines (CAs), offering highly specific and accurate detection of DA. By means of this study, we attempted to overcome the tedious procedures of surface premodifications and achieve selectivity through tuning the particle size of AuNPs. DA could induce the aggregation of the AuNPs via hydrogen-bonding interactions, resulting in a color change from pink to blue which can be monitored by spectrophotometry or even the naked-eye. The proposed colorimetric probe works over the 0.1 to 4μM DA concentration range, with a lower detection limit (LOD) of 22nM, which is much lower than the therapeutic lowest abnormal concentrations of DA in urine (0.57μM) and blood (16μM) samples. Furthermore, the selectivity and potential applicability of the developed method in spiked actual biological (human plasma and urine) specimens were investigated, suggesting that the present assay could satisfy the requirements for clinical diagnostics and biosensors.

Gold Nanorod-Based Chrono-Colorimetric Sensor Arrays: A Promising Platform for Chemical Discrimination Applications

Most array-based sensing platforms, to date, utilize static response patterns for discrimination of a wide variety of analytes, but only a few studies have focused on the important task of quantitatively resolving structural isomers, which are nowadays important because of their broad usage in medicines and industries. A possible way of accomplishing this feat is to combine kinetic (rather than static) sensor response profiles with the chemical tongue strategy to allow the development of array-based sensors for isomeric discrimination. Here, by adding the time dimension, a simple and novel gold nanorod (AuNR)-based chrono-colorimetric sensor array is proposed for chemical discrimination applications. Because of their similar structure but different redox potentials, dihydroxybenzene (DHB) structural isomers have been chosen, as models, to evaluate the applicability of the proposed array. The principle of the array relies on various growth rates of silver shells on AuNRs at different silver ion/AuNR concentration ratios owing to the different kinetic behaviors of DHBs, which can be used as fingerprints to identify DHBs with the help of multivariate analysis methods. The combinatorial colorimetric response of AuNRs upon DHB addition has been analyzed by linear discriminant analysis and hierarchical cluster analysis. Finally, identification of individual DHBs or their mixtures in real samples confirms the potential application of the proposed array.

A nanopaper-based artificial tongue: a ratiometric fluorescent sensor array on bacterial nanocellulose for chemical discrimination applications

In the present study, a ratiometric fluorescent sensor array as an artificial tongue has been developed on a nanopaper platform for chemical discrimination applications. The bacterial cellulose (BC) nanopaper was utilized for the first time as a novel, flexible, and transparent substrate in the optical sensor arrays for developing high-performance artificial tongues. To fabricate this platform, the hydrophobic walls on the BC nanopaper substrates were successfully created using a laser printing technology. In addition, we have used the interesting photoluminescence (PL) properties of an immobilized ratiometric probe (carbon dot-Rhodamine B (CD-RhB) nanohybrids) on the nanopaper platform to improve the visual discrimination analysis. Heavy metal ions were utilized as model analytes to verify the applicability of the fabricated nanopaper-based ratiometric fluorescent sensor array (NRFSA). Using the color variation of the NRFSA platform upon the addition of heavy metal ions, which have been obtained by a smartphone (under an UV irradiation), five heavy metal ions (i.e., Hg(ii), Pb(ii), Cd(ii), Fe(iii), and Cu(ii)) have been well-distinguished through the RGB analysis via production of the characteristic PL fingerprint-like response patterns for each of them. Moreover, the developed optical sensor array was successfully exploited to identify the heavy metal ions in the water and fish samples. We have also found that the PL spectra, which have been obtained by a spectrofluorometer, of the developed NRFSA can be exploited for discrimination applications. We believe that the nanopaper-based artificial tongues will provide innovative insights into the development of optical sensor arrays towards advanced (bio)chemical discrimination applications and can revolutionize the conventional optical sensor array technology.

A rainbow ratiometric fluorescent sensor array on bacterial nanocellulose for visual discrimination of biothiols

The crucial role of biothiols in many biological processes, which turns them into important biomarkers for the early diagnosis of various diseases, the development of an affordable, sensitive and portable probe for the detection and discrimination of these compounds is of great importance.

Nanoparticle-based optical sensor arrays

As in many other methods that have integrated nanoparticles (NPs), the chemical nose/tongue strategy has also progressed greatly since the entrance of NPs into this field. The fascinating tunable physicochemical properties of NPs have made them powerful candidates for array-based sensing platforms and have enabled the development of real-time, sensitive and portable systems that are able to target complex mixtures of analytes. In particular, the unique optical properties of NPs have a key role in providing promising array-based sensing approaches. This review will describe the main aspects and processes of most common NP-based optical sensor arrays. The fundamental steps in the design of a sensor array together with details of each step would be provided. The review begins with the principles of optical sensor arrays and presents the concept of cross-reactivity as the main criterion in the selection of sensing elements. Changes in the absorption and emission properties of the assembled sensing elements are categorized into two main classes of optical signals (colorimetric and fluorometric). Popular chemometric methods used for analyzing the data acquired by a sensor array have also been briefly introduced. On the basis of the objective and the desired application, different types of plasmonic and fluorescent NP that possess unique opto-physical properties have been presented as available choices in the design of sensing elements. The vast number of applications of NP-based optical sensor arrays published throughout the literature have then been reviewed according to their mechanism of interaction and the type of optical signal. Finally, the remaining challenges and future directions in this topic have been highlighted.

Perylene dye-functionalized silver nanoparticles serving as pH-dependent metal sensor systems

Lysine-functionalized perylene was used to modify nanoparticles. Due to the benefits from a synergetic effect that originated between the perylene and silver nanoparticles, color-based metal sensor systems were established.

A smartphone readable colorimetric sensing platform for rapid multiple protein detection

We have developed a very simple colorimetric sensor array by using only unmodified gold nanoparticles and NaCl salt for discrimination of multiple proteins. The inexpensive and convenient sensor array and the ubiquitous smartphone are coupled to achieve an immediate point-of-care diagnosis without additional devices.

A rapid SERS method for label-free bacteria detection using polyethylenimine-modified Au-coated magnetic microspheres and Au@Ag nanoparticles

A rapid and efficient method for label-free SERS detection of bacteria in solution.

A nanoplasmonic probe as a triple channel colorimetric sensor array for protein discrimination

The salt-induced aggregation, nanoparticle regrowth and self-assembly behaviors of gold nanoparticles (AuNPs) and DNA conjugates could be changed after interaction with different proteins, generating various color changes and a unique fingerprint pattern for each protein.