Chrono-colorimetric sensor array for detection and discrimination of halide ions using an all-in-one plasmonic sensor element.

Most nanoparticle based colorimetric sensor array utilize several sensor elements and static response for discrimination of target analytes. This approach can be complicated and costly to synthesize or functionalize different nanoparticles for providing wide color variation. Herein, triangular silver nanoparticles (TSNPs) were used to develop a colorimetric sensor array by time-dimension responses. The principle of this sensor array is based on the diverse etching process of TSNPs in the presence of three halide ions, including bromide (Br-), iodide (I-) and chloride (Cl-). Various etchings of TSNPs induced color changes at different reaction time intervals, which produced a colorimetric pattern for each ion. Therefore, using time dependent etching responses of TSNPs as a single sensing component can produce a wide color variation which can be distinguished by naked eyes. The colorimetric responses of TSNPs upon the addition of different concentrations of halide ions have been analyzed by PLS regression (PLS-R) and PLS discriminant analysis (PLS-DA). The analytical figures of merit confirmed that the developed chrono-colorimetric TSNPs -based sensor array is successful in both the discrimination and quantitative detection of halide ions. At the final step, the three halide ions were accurately determined in a real water sample, which verified the potential of the developed sensor in a real sample.

Paper-based optical nanosensors - A review.

Paper-based analytical devices (PADs) have shown great promise for point-of-care testing and on-site detection of analytes with chemical, biochemical, and environmental importance owing to their low cost, convenience, scalability, portability, and biocompatibility. The World Health Organization stated that sensors should meet the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverable). Paper-based optical sensors meet most of these criteria, making them in high demand and applicable in remote areas. Optical PADs outputs are obtained by different means, such as dyes, nanostructures, redox agents, and pH indicators. The outstanding physical and chemical characteristics of nanostructures, their intense signals, and tunable optical properties make them ideal for many sensing platforms, including paper-based ones. This review focuses primarily on paper-based nanosensors using various nanostructures to fabricate and produce optical signals for visualization. We describe the fundamentals and state of the art of PADs and comprehensively explain the following topics: paper types as the substrate of PADs, PAD fabrication approaches, nanostructure stabilization on PADs, signal acquisition, data handling, interpretation of results, sensing mechanisms, and application areas. We also discuss future trends and strategies to enable PADs to reach their full potential and increase their commercialization opportunities.

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.

Nanoplasmonic sensor array for the detection and discrimination of pesticide residues in citrus fruits.

Great attention has been directed towards developing rapid and straightforward methods for the identification of various pesticides that are usually used simultaneously in citrus fruits. The extensive use of diverse classes of pesticides in citrus fruits and their high toxicity may cause serious diseases in the human body. In the current study, a non-enzymatic sensor array has been developed for the identification and discrimination of five different pesticides belonging to diverse classes, including organophosphate, carbamate, and bipyridylium. For this aim, two gold nanoparticles (AuNPs) with different capping agents, citrate and borohydride, were used as sensing elements. The aggregation-induced spectra alterations of AuNPs were utilized to identify the pesticides in a wide range of concentrations (20-5000 ng mL-1). We have employed data visualization methods (i.e., heat maps, bar plots, and color difference maps), a supervised pattern recognition method (i.e., linear discrimination analysis), and partial least squares regression to qualitatively and quantitatively determine the pesticides. Finally, the practical applicability of the developed sensor array was evaluated for the identification of target pesticides in lime peel. The outcomes revealed that the probe could accurately verify the absence or presence of the pesticides in lime fruit.

Optical nanoprobes for chiral discrimination.

Chiral discrimination has always been a hot topic in chemical, food and pharmaceutical industries, especially when dealing with chiral drugs. Enantiomeric recognition not only leads to better understanding of the mechanism of molecular recognition in biological systems, but may further assist in developing useful molecular devices in biochemical and pharmaceutical studies. By emerging nanotechnology and exploiting nanomaterials in sensing applications, a great deal of attention has been given to the design of optical nanoprobes that are able to discriminate enantiomers of chiral analytes. This review explains how engineering nanoparticles (NPs) with desired physicochemical properties allows developing novel optical nanoprobes for chiral recognition. Fundamental concepts related to the origin of chirality in NPs have been briefly presented. Colorimetric and fluorimetric assays in which different types of chiral NPs are used for enantioselective recognition, have been comprehensively described. The main types of nanomaterials described in this review consist of luminescent quantum dots (QDs), carbon dots (CDs), silicon NPs and metal nanoclusters (NCs), as well as plasmonic nanostructures. The mechanisms of sensing in these NP-based optical chiral assays along with relevant examples have been also discussed. Finally, the remaining challenges and future directions have been provided for researchers interested in this topic.

Selective colorimetric detection of pentaerythritol tetranitrate (PETN) using arginine-mediated aggregation of gold nanoparticles.

Detection of pentaerythritol tetranitrate (PETN) as an explosive has been of great interest because of public safety and military concerns. Here, we have presented a simple, selective and sensitive colorimetric method for direct detection of PETN. The gold nanoparticles (AuNPs) were first exposed to arginine which has primary amines in its structure. Electron deficient -NH2 groups from arginine could strongly interact with -NO2 groups of PETN as electron donors. Hydrogen bonding happens between the -NO2 group of PETN and -NH2 group of arginine molecules. Therefore, selective aggregation of AuNPs happened because of the donor-acceptor and hydrogen bonding interactions. Due to the aggregation, the color of reddish AuNPs turned to blue or purple depend on PETN concentration. A good linear relationship was achieved between the aggregation signal (absorbance ratio of A650/A520) of the probe and the concentration of PETN with a limit of detection of 0.169 µmol L-1. Furthermore, we have found that the developed probe can detect PETN in complex matrices of groundwater and soil samples.

Identification of Catecholamine Neurotransmitters Using a Fluorescent Electronic Tongue.

Catecholamine neurotransmitters, specifically, dopamine (DA), epinephrine (EP), and norepinephrine (NE), are known as substantial indicators of various neurological diseases. Developing rapid detection methods capable of simultaneously screening their concentrations is highly desired for early clinical diagnosis of such diseases. To this aim, we have designed an optical sensor array using three fluorescent dyes with distinct emission bands and have monitored variations in their emission profiles upon the addition of DA, EP, and NE in the presence of gold ions. Because of the different reducing power of catecholamines, differently sized gold nanoparticles (GNPs) with different levels of aggregation were generated, resulting in different amounts of spectral overlap between the absorption band of the in situ generated plasmonic GNPs and the emission bands of the fluorescent dyes. These energy-transfer-based fingerprint profiles were used to discriminate the neurotransmitters by applying pattern recognition methods including linear discriminant analysis (LDA) and artificial neural networks (ANN) and to determine their concentration using multiple linear regression (MLR). Our proposed array also showed a good performance in the discrimination of DA, EP, and NE in complex biological media such as human urine.

Ratiometric fluorescent nanoprobes for visual detection: Design principles and recent advances - A review.

Signal generation techniques for visual detection of analytes have received a great deal of attention in various sensing fields. These approaches are considered to be advantageous when instrumentation cannot be employed, such as for on-site assays, point-of-care tests, and he althcare diagnostics in resource-constrained areas. Amongst various visual detection approaches explored for non-invasive quantitative measurements, ratiometric fluorescence sensing has received particular attention as a potential method to overcome the limitations of intensity-based probes. This technique relies on changes in the intensity of two or more emission bands (induced by an analyte), resulting in an effective internal referencing which improves the sensitivity of the detection. The self-calibration, together with the unique optophysical properties of nanoparticles (NPs) have made the ratiometric fluorescent nanoprobes more sensitive and reliable, which in turn, can result in more precise visual detection of the analytes. Over the past few years, a vast number of ratiometric sensing probes using nanostructured fluorophores have been designed and reported for a wide variety of sensing, imaging, and biomedical applications. In this work, a review on the NP-based ratiometric fluorescent sensors has been presented to meticulously elucidate their development, advances and challenges. With a special emphasis on visual detection, the most important steps in the design of fluorescent ratiometric nanoprobes have been given and based on different classes of analytes, recent applications of fluorescent ratiometric nanoprobes have been summarized. The challenges for the future use of the technique investigated in this review have been also discussed.

Determination and identification of nitroaromatic explosives by a double-emitter sensor array.

Detection of nitroaromatic explosives is of strong concern because of human health, public safety, environment, and military issues. In this study, we present a ratiometric sensor array for detection and discrimination of widely-used nitroaromatics (i.e., 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol (TNP), and 2,4-dinitrotoluene (DNT)). In the design of sensor elements (SE) we employ blue emissive carbon dots (BCDs) in combination with yellow (SE-A) and red (SE-B) emissive cadmium telluride quantum dots (CdTe QDs). The fluorescence intensity of BCDs, YQDs, and RQDs is quenched by TNT, DNT, and TNP in various degrees. Both TNT and TNP cause the quenching and spectral shift of BCDs (TNT causes a blueshift and TNP causes a redshift). However, DNT has no effect on CDs emission. The developed double-emitter sensor array is capable of discriminating nitroaromatics in the concentration range of 5.0-200.0 µmol L-1 with a limit of quantification as low as 5.0 µmol L-1. In addition, the sensor array demonstrates a promising capacity to detect structurally similar nitroaromatics in mixtures and complex media of soil and groundwater samples.

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 wide-color-varying ratiometric nanoprobe for detection of norepinephrine in urine samples.

Owing to its dual role as a hormone and neurotransmitter, norepinephrine (NE) detection is of great significance to biomedical diagnosis. In the present work, we have explored intense green fluorescence of poly (norepinephrine) (PNE) nanoparticles synthesized by oxidizing NE in alkaline condition, in combination with red fluorescent bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) for naked-eye detection of NE. The effect of sodium hydroxide on the emission behavior of NE was studied. The surface morphology and optical properties of PNE nanoparticles were characterized by UV-Vis, fluorescence, FTIR, Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) techniques. For ratiometric sensing of NE, red fluorescent BSA-AuNCs were served as an internal reference while NE delivered a new emission peak at 527 nm, resulting in a wide distinguishable color change from strong red into red, pink, orange, and green under a UV lamp. The ratiometric approach was demonstrated to be highly sensitive and selective for NE detection against even structurally similar biomolecules with a detection limit of 49 nmol L-1. Furthermore, the proposed method was successfully applied to determine NE in urine samples.

Nanoparticle-based Chemiluminescence for Chiral Discrimination of Thiol-Containing Amino Acids.

The ability to recognize the molecular chirality of enantiomers is extremely important owing to their critical role in drug development and biochemistry. Convenient discrimination of enantiomers has remained a challenge due to lack of unsophisticated methods. In this work, we have reported a simple strategy for chiral recognition of thiol-containing amino acids including penicillamine (PA), and cysteine (Cys). We have successfully designed a nanoparticle-based chemiluminescence (CL) system based on the reaction between cadmium telluride quantum dots (CdTe QDs) and the enantiomers. The different interactions of CdTe QDs with PA enantiomers or Cys enantiomers led to different CL intensities, resulting in the chiral recognition of these enantiomers. The developed method showed the ability for determination of enantiomeric excess of PA and Cys. It has also obtained an enantioselective concentration range from 1.15 to 9.2 mM for PA. To demonstrate the potential application of this method, the designed platform was applied for the quantification of PA in urine and tablet samples. For the first time, we presented a novel practical application of nanoparticle-based CL system for chiral discrimination.

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

Considering the crucial role of biothiols in many biological processes, which turns them into highly valuable biomarkers for the early diagnosis of various diseases, the development of an affordable, sensitive and portable probe for the identification and discrimination of these compounds is of great importance. Herein, we developed a ratiometric fluorescent (RF) sensor array with a wide color emissive variation, on a bacterial cellulose (BC) nanopaper substrate for the visual discrimination of biothiols. To this aim, RF sensing elements including N-acetyl l-cysteine capped green CdTe quantum dots-rhodamine B (GQDs-RhB) and red CdTe QDs-carbon dots (RQDs-CDs) at two different NaOH concentrations (0 and 5 mM) were utilized as sensor elements for the discrimination of biothiols. Owing to the high affinity of the thiol group (SH) to the surface of CdTe QDs and the aggregation of the QDs, the fluorescence (FL) emission of the QDs changed while the emission of the CDs and rhodamine B remained almost unchanged upon the addition of biothiols. Accordingly, characteristic rainbow-like FL fingerprint patterns were created for each biothiol which were then distinguished both visually and spectroscopically. Hierarchical cluster analysis (HCA) and linear discriminant analysis (LDA) pattern recognition techniques were employed for the identification and discrimination of biothiols. Based on the designed RF sensor array, convenient test strips were fabricated on BC nanopaper for the visual discrimination of biothiols. It has been shown that this probe can successfully identify biothiols in human plasma as well. Altogether, the developed nanopaper-based sensor array offers an efficient biothiol discrimination tool that can be potentially exploited in the near future in theranostic and point-of-care applications.

Label-free detection of ß-amyloid peptides (Aß40 and Aß42): a colorimetric sensor array for plasma monitoring of Alzheimer's disease.

Monitoring the ratio of 40- and 42-residue amyloid ß peptides (i.e., Aß40 and Aß42) in human plasma is considered one of the hallmarks of detection of the early stage of Alzheimer's disease (AD). Therefore, development of a specific, yet non-antibody-based method for simultaneous detection of Aß40 and Aß42 may have considerable clinical applications. Here, we developed a 'nanoparticle-based colorimetric sensor array' utilizing label-free gold and silver nanoparticles for visual detection of Aß42 and Aß40. Different aggregation behaviors of nanoparticles through their conjugation with Aß42 and Aß40 followed by the coordination of Aß42 and Aß40 with Cu(ii) led to diverse spectral and color changes. The spectral changes were quantitatively differentiated by a supervised pattern recognition approach, linear discriminant analysis (LDA). The proposed sensor array was able to discriminate among Aß42, Aß40, and HSA in different concentrations (50 nmol L-1 to 500 nmol L-1) and their mixtures. Moreover, the sensor array had the capability to identify structurally similar Aß peptides in human plasma samples. The developed sensor array technology might pave the way for a cheap and rapid, yet robust, platform for high-throughput screening of human plasma for defining the at-risk population for AD.

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.

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.

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.

Colorimetric Fingerprints of Gold Nanorods for Discriminating Catecholamine Neurotransmitters in Urine Samples.

Catecholamine neurotransmitters, generally including dopamine (DA), epinephrine (EP) and norepinephrine (NE) are known as substantial indicators of various neurological diseases. Simultaneous detection of these compounds and their metabolites is highly recommended in early clinical diagnosis. To this aim, in the present contribution, a high performance colorimetric sensor array has been proposed for the detection and discrimination of catecholamines based on their reducing ability to deposit silver on the surface of gold nanorods (AuNRs). The amassed silver nanoshell led to a blue shift in the longitudinal localized surface plasmon resonance (LSPR) peak of AuNRs, creating a unique pattern for each of the neurotransmitters. Hierarchical cluster analysis (HCA) and linear discriminate analysis (LDA) pattern recognition techniques were employed to identify DA, EP and NE. The proposed colorimetric array is able to differentiate among individual neurotransmitters as well as their mixtures, successfully. Finally, it was shown that the sensor array can identify these neurotransmitters in human urine samples.

Aggregation-based colorimetric sensor for determination of prothioconazole fungicide using colloidal silver nanoparticles (AgNPs).

There is a growing interest in developing high-performance sensors monitoring fungicides, due to their broadly usage and their adverse effects on humans and wildlife. In the present study, a colorimetric probe has been proposed for detection of prothioconazole based on aggregation of unmodified silver nanoparticles (AgNPs). Under optimized condition, linear relationships between the concentration of prothioconazole and the absorbance ratio of A500/A395 were found over the range of 0.01µg·mL-1 to 0.4µg·mL-1 with quantification limit as low as 1.7ng·mL-1. Furthermore, AgNPs color change from yellow to pink-orange in presence of prothioconazole, indicates highly sensitive naked-eye colorimetric assay for quantifying prothioconazole in real applications. The proposed approach was successfully used for the determination of prothioconazole in wheat flour and paddy water sample.