Synthesis of Au@Ag core-shell nanorods with tunable optical properties.

The synthesis of noble metal nanostructures with adjustable optical properties is essential due to their potential applications in various fields such as imaging, (bio) sensors, and catalysis. In this study, Au@Ag core-shell nanorods were synthesized with tunable optical properties. The synthesis process includes a two-stage approach: first, gold nanorods were synthesized through seed-mediated growth, and in the second stage, these gold nanorods were used as seeds to synthesize Au@Ag core-shell nanorods through the silver deposition process. Tunable core-shell nanorods were produced by changing the concentration of silver ions, reducing agent, stabilizing agent, seeds, and buffer as well as pH and the reaction time. Transmission electron microscopy (TEM) images demonstrated the formation of the Au@Ag core-shell nanorod structure. In addition, UV-visible spectroscopy revealed the peak height and its shift towards shorter wavelengths, demonstrating the tunable optical properties of the synthesized nanorods. Overall, in this study, we demonstrated the synthesis of Au@Ag core-shell nanorods with adjustable plasmonic optical properties that could be changed by precisely controlling the thickness of the silver shell on the surface of the gold core. .

Machine Learning-Assisted Colorimetric Assay Based on Au@Ag Nanorods for Chromium Speciation.

The oxidation state of an element significantly controls its toxicological impacts on biological ecosystems. Therefore, design of robust sensing strategies for multiplex detection of species with respect to their oxidation states or bonding conditions, i.e., chemical speciation, is quite consequential. Chromium (Cr) species are known as the most abundant inorganic groundwater pollutants and can be quite harmful to human health depending on their oxidation states. In the present study, a multicolorimetric probe based on silver-deposition-induced color variations of gold nanorods (AuNRs) was designed for identification and quantification of Cr species including Cr (III) and Cr (VI) (i.e., CrO42- and Cr2O72-) in water samples. In fact, the presence of Cr species leads to inhibition of the silver metallization of AuNRs to various degrees depending on the concentration and identity of the analyte. This process is accompanied by the blue shift of the longitudinal peak which results in sharp-contrast rainbow-like color variations, thereby providing great opportunity for highly accurate visual detection. The gathered dataset was then statistically analyzed using two pattern recognition and regression machine learning techniques. In particular, linear discriminant analysis was used as a classification method to discriminate the unicomponent and mixture samples of Cr species with 100% accuracy. Then, a well-known multivariate calibration technique called partial least-squares regression was employed for quantitative analysis of Cr species. Responses were linearly related to Cr species concentrations over a wide range of 10.0-1000.0, 1.0-200.0, and 1.0-200.0 µmol L-1 with detection limits of 37.7, 8.7, and 2.9 µmol L-1 for Cr3+, CrO42-, and Cr2O72-, respectively. The practical applicability of the multicolorimetric probe was successfully evaluated by analyzing Cr species in several water specimens comprising tap water, mineral water, river water, and seawater. Above all, the vivid rainbow color tonality of the proposed assay further improves the accuracy of the naked eye detection, making it a practical platform for on-site monitoring of Cr contamination.

Analyte-restrained silver coating of gold nanostructures: an efficient strategy to advance multicolorimetric probes.

Visual detection based on gold nanorods (AuNRs) has gained tremendous attention in sensing applications owing to the potential for simple, inexpensive, instrument-free, and on-site detection. The proper selection of the mechanism involved in the interaction between the analyte and the nanostructure plays a significant role in designing a selective and multicolorimetric probe for visual purposes. A winning mechanism to develop multicolorimetric probes is the silver metalization of AuNRs. Herein, an unprecedented idea is presented to expand the variety of multicolorimetric sensors relying on the mechanism of silver deposition. We introduce the anti-silver deposition mechanism in which the analyte directly or indirectly restrains the silver coating of AuNRs. To ascertain the anti-silver deposition mechanism, we have exploited the proposed idea for the direct detection of nitrate. The presence of nitrate (as restrainer agent), which was firstly treated with ascorbic acid (as reducing agent), induced a decrease in the spectral blueshift of AuNRs along with diverse sharp color transitions from reddish-orange (blank) to maroon, wine, berry/purple, dark blue, teal, green, seafoam, and mint. The difference in the spectrum area of the probe in the absent (So) and presence (S) of nitrate were linearly proportional to nitrate concentration in the range of 0.5-5.5 mmol l-1and the limit of detection was calculated to be 465µmol l-1. Furthermore, the practicability of the multicolor probe was assessed by the determination of nitrate in complex environmental samples.

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.

Formation of plasmonic core/shell nanorods through ammonia-mediated dissolution of silver(i)oxide for ammonia monitoring.

Due to the expansion of the aquaculture industry in the world and the importance of controlling ammonia in fish breeding water, high levels of which impose significant damage to fish farming, it is crucial to develop affordable, rapid, and on-site methods for timely and accurate detection of ammonia. In this study, a colorimetric sensor based on the formation of gold/silver core/shell nanorods (NRs) was developed for the rapid detection of ammonia. The sensor functioned by the specific dissolution of silver(i) oxide by ammonia, which triggered the activation of silver ions and the subsequent formation of gold/silver core/shell NRs in the presence of a reducing agent (i.e., ascorbic acid (AA)). This led to changes in the surface composition, size, and aspect ratio of the NRs, which was accompanied by a vivid color change from green to red/orange in less than a minute. The colorimetric sensor was optimized by adjusting the effective parameters, including ascorbic acid, silver ion, and sodium hydroxide concentration as well as pH and reaction time. After the optimization process, the sensor was found to have a linear range from 50 to 800 µmol L-1 (0.85-13.6 ppm). In addition, the application of the sensor was validated by measuring the ammonia content in water samples from rearing ponds for rainbow trout, sturgeon, and tilapia before and after feeding. The sensor's label-free, rapid, user-friendly, naked-eye, and cost-effective operation makes it an attractive option for on-site environmental monitoring of ammonia.

Fabrication and evaluation of optical nanobiosensor based on localized surface plasmon resonance (LSPR) of gold nanorod for detection of CRP.

C-reactive protein (CRP) is a plasma protein that is one of the most expressed proteins in acute phase inflammation cases. It is a well-known biomarker for inflammatory disorders. There is a significant correlation between increasing CRP concentration and the risk of being exposed to cardiovascular diseases (CVD) and sepsis; thus, monitoring and quantifying CRP levels in a simple, inexpensive, and quick manner can improve clinical diagnostics and help prevent major inflammatory conditions. Here a nanobiosensor was developed, benefiting from the LSPR property of gold-nanorod (GNR) to measure CRP concentration. Nanorods were fabricated using One-pot synthesis by trimethyl ammonium bromide (CTAB) as a surfactant. This method provides the advantage of both step and time reduction in synthesis and decreases the contamination probability of nanorods as the products. The nanorods were characterized using TEM with an average size of (24 ± 1 nm) × (5 ± 1 nm) and a typical aspect ratio of ∼4.9. The surface of the rods was modified with a specific aptamer for the target protein, and the LSPR shifts due to the gold nanorod's refractive index change as the result of protein interaction with the biosensor investigated using a 100-900 nm UV absorption device. The results indicated that the nanobiosensor could respond to different CRP concentrations within 30 min. The selectivity test has shown nonresponsive results of nanobiosensor to BSA and TNF-α proteins which are used to evaluate the biosensor behavior in non-target proteins. The detection limit was evaluated at 2 nM, and the sensor's linear response ranged between 2 - 20 nM.

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.

Thiol-mediated etching of gold nanorods as a neoteric strategy for room-temperature and multicolor detection of nitrite and nitrate.

The excessive presence of nitrite and nitrate in environmental matrixes has raised concerns among the scientific communities due to their negative impacts on human health and living organisms. Considering the necessity of regular monitoring and rapid evaluation of nitrite and nitrate, it is of great interest to develop methods capable of on-site detection of these compounds. This study presents a non-aggregation colorimetric method based on etching gold nanorods (AuNRs) for visual detection of nitrite and nitrate. Instead of temperature, we propose using thiourea as a sulfur-containing compound to accelerate the rate of AuNR etching. Thiourea forms stable cationic species with Au+ ions and consequently speeds up the etching process by reducing the redox potential of Au+/Au. In the presence of thiourea, the AuNRs are etched by nitrite resulting in wide obvious color changes from brown to light brown, green, blue, purple, pink, and colorless. In addition to nitrite, the developed method is capable of nitrate determination by reducing nitrate to nitrite through acid-washed zinc powder and is the first report of colorful detection of nitrate. Under optimized conditions, a good linear relationship was found between nitrite/nitrate concentration and the colorimetric response in the range of 8.0 to 100 µmol L-1 and 0.5 to 3.0 mmol L-1 with a limit of detection (LOD) as low as 1.3 µmol L-1 and 173.3 µmol L-1 for nitrite and nitrate, respectively. Furthermore, the practical application of our developed probe was confirmed by accurate determination of nitrite and nitrate in various complex media including water samples, soil extracts, and food products such as salami and sausage.

Plasmonic nanoparticles for colorimetric detection of nitrite and nitrate.

Irregular and unknowingly use of chemical compounds is a serious threat to the environment, human health, and other living organisms attributable and intensified by the growing population and increasing demand for food. Nitrite and nitrate are among those compounds that are widely used in agricultural and industrial products. Therefore on-site, rapid, simple, and accurate monitoring of nitrite/nitrate is highly desirable. In this review, while emphasizing the importance of nitrite and nitrate in food chain safety and health of living organisms, their measurement methods, in particular, nanoplasmonic colorimetric sensors are comprehensively discussed based on the researches in this field. Nanoplasmonic-based sensors have proved to be successful in comparison with traditional methods due to their low cost, biocompatibility, high sensitivity and selectivity, and most importantly, the ability to visually detect and be used on-site to measure nitrite and nitrate. The design principle of nanoplasmonic sensors will be presented into two categories of aggregation- and etching-based detection followed by their applications in nitrite detection. The nitrate measurement will be discussed based on either direct detection of nitrate or indirect strategy in which nitrate is reduced to nitrite by enzymes or metals. Finally, the remaining challenges and prospects in this topic will be described and outlined.

Providing Multicolor Plasmonic Patterns with Au@Ag Core-Shell Nanostructures for Visual Discrimination of Biogenic Amines.

Biogenic amines (BAs) are known as substantial indicators of the quality and safety of food. Developing rapid and visual detection methods capable of simultaneously monitoring BAs is highly desired due to their harmful effects on human health. In the present study, we have designed a multicolor sensor array consisting of two types of gold nanostructures (i.e., gold nanorods (AuNRs) and gold nanospheres (AuNSs)) for the discrimination and determination of critical BAs (i.e., spermine (SM), tryptamine (TT), ethylenediamine (EA), tyramine (TR), spermidine (SD), and histamine (HT)). The design principle of the probe was based on the metallization of silver ions on the surface of AuNRs and AuNSs in the presence of BAs, forming Au@Ag core-shell nanoparticles. Changes in the surface composition, size, and aspect ratio of AuNSs and AuNRs induced a blue shift in the plasmonic band, which was accompanied by sharp and rainbowlike color variations in the solution. The collected data were visually assessed and statistically analyzed by various data visualization and pattern recognition methods. Namely, linear discriminant analysis (LDA) and partial least squares (PLS) regression were employed for the qualitative and quantitative determination of BAs. The responses were linearly correlated to the concentrations of BAs in a wide range of 10-800, 20-800, 40-800, 40-800, 60-800, and 80-800 µmol L-1 with the limit of detections of 2.46, 4.79, 8.58, 14.26, 10.03, and 27.29 µmol L-1 for SD, SM, TT, HT, EA, and TR, respectively. Finally, the practical applicability of the sensor array was investigated by the determination of BAs in meat and fish samples by which the potential of the probe for on-site determination of food freshness/spoilage was successfully verified.

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.

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.

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.

Impact of plasma concentration of transferrin on targeting capacity of nanoparticles.

It is becoming increasingly accepted that various diseases have a capacity to alter the composition of plasma proteins. This alteration in protein composition may consequently change the targeting capacity of nanoparticles (NPs). In this study, the impact of a model targeting ligand's (i.e., Transferrin; Tf) concentration in human plasma on the targeting capacity of gold NPs (Au NPs), pre-conjugated with Tf, is investigated. Our findings demonstrate that the protein corona formation by both healthy and Tf depleted human plasma diminishes the targeting efficacy of Au NPs within human cancer cells despite a preservation of targeting ability by plasma with excess Tf (10-fold). Moreover, the plasma samples obtained from patients with various Tf levels (e.g., thalassemia major, sickle cell anemia, aplastic anemia, and iron deficiency anemia) have affected the accessibility of the targeting Tf in the corona layer and subsequently affected their targeting ability, which emphasizes the critical role of disease-specific protein corona on the efficacy of Au NPs. Ultimately, variations of protein concentration (e.g., due to disease occurrence and progress) in plasma affect its recruiting in corona formation, and in turn, affect the targeting and therapeutic efficacies of Au NPs.

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.

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.

Impact of Gold Nanoparticles on Amyloid ß-Induced Alzheimer's Disease in a Rat Animal Model: Involvement of STIM Proteins.

Alzheimer's disease (AD) is the most common type of neurodegenerative amyloid disorder causing progressive cognitive decline and memory loss. A considerable number of therapies for AD rely on inhibition/delay/dissociation of amyloid beta (Aß) oligomers and fibrils. In this case, nanoparticles (NPs) demonstrated substantial effects on the Aß fibrillation process; however, their effects on progressive cognitive decline and memory have been poorly investigated in vivo. In this study, acquisition and retention of spatial learning and memory are studied in a rat animal model of AD after intrahippocampal (IH) and intraperitoneal (IP) injections of a model NP, i.e., gold NPs (AuNPs). The outcomes revealed that the AuNPs could improve the acquisition and retention of spatial learning and memory in Aß treated rats as indicated by decreased time (Aß: 39.60 ± 3.23 s vs Aß+AuNPs: 25.78 ± 2.80 s) and distance (Aß: 917.98 ± 50.81 cm vs Aß+AuNPs: 589.09 ± 65.96 cm) of finding the hidden platform during training days and by increased time spent in the target quadrant (Aß: 19.40 ± 0.98 s vs Aß+AuNPs: 29.36 ± 1.14 s) in the probe test in Morris water maze (MWM). Expression of brain-derived neurotrophic factor, BDNF, cAMP response element binding protein, CREB, and stromal interaction molecules, e.g., STIM1 and STIM2 was also increased, supporting improved neural survival. Our outcomes may pave a way for mechanistic insights toward the role of NPs on retrieval of the deteriorated behavioral functions in brain tissue after AD outbreak.

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.

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 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.