Colorimetric captopril assay based on oxidative etching-directed morphology control of silver nanoprisms

A portable intelligent hydrogel platform for multicolor visual detection of HAase

Hyaluronidase (HAase) is an important endoglycosidase involved in numerous physiological and pathological processes, such as apoptosis, senescence, and cancer progression. Simple, convenient, and sensitive detection of HAase is important for clinical diagnosis. Herein, an easy-to-operate multicolor visual sensing strategy was developed for HAase determination. The proposed sensor was composed of an enzyme-responsive hydrogel and a nanochromogenic system (gold nanobipyramids (AuNBPs)). The enzyme-responsive hydrogel, formed by polyethyleneimine-hyaluronic acid (PEI-HA), was specifically hydrolyzed with HAase, leading to the release of platinum nanoparticles (PtNPs). Subsequently, PtNPs catalyzed the mixed system of 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 to produce TMB2+ under acidic conditions. Then, TMB2+ effectively etched the AuNBPs and resulted in morphological changes in the AuNBPs, accompanied by a blueshift in the localized surface plasmon resonance peak and vibrant colors. Therefore, HAase can be semiquantitatively determined by directly observing the color change of AuNBPs with the naked eye. On the basis of this, the method has a linear detection range of HAase concentrations between 0.6 and 40 U/mL, with a detection limit of 0.3 U/mL. In addition, our designed multicolor biosensor successfully detected the concentration of HAase in human serum samples. The results showed no obvious difference between this method and enzyme-linked immunosorbent assay, indicating the good accuracy and usability of the suggested method.

Plasmonic nanoparticle etching-based optical sensors: current status and future prospects

Plasmonic nanoparticles are an emerging tool for developing label-free multicolorimetric sensors for biosensing and chemosensing applications. The color absorbed by nanoparticles from visible light is influenced by their size, shape, orientation, and interparticle distance. Differently sized and shaped gold and silver nanoparticles exhibit a wide range of colors, aiding in the development of label-free sensors. Etching is the process of oxidizing nanoparticles, which alters their aspect ratio, shape, plasmonic peak, and outward appearance. It is typically used to create sensitive sensing platforms. Through etching, analytes could be detected in a simple, sensitive, and selective manner. The multicolor readout of nanoparticle etching-based multicolorimetric sensors can overcome the limitations of conventional colorimetric assays and improve the accuracy of visual inspection. This review discusses different approaches for target sensing using nanoparticle etching strategies like direct etching, enzyme-mediated etching, chemical reaction-driven etching, and anti-etching-based sensors and their mechanisms. In the future, etching strategies could be modified into portable sensing devices to detect a variety of analytes, which will aid in the development of on-time, in situ, and point-of-care sensing systems.

Rapid and sensitive determination of ascorbic acid based on label-free silver triangular nanoplates

In this study, a new method for the detection of ascorbic acid (AA) was proposed. It was based on the protective effect of AA on silver triangular nanoplates (Ag TNPs) against Cl- induced etching reactions. Cl- can attack the corners of Ag TNPs and etch them, causing a morphological shift from triangular nanoplates to nanodiscs. As a result, the solution changes color from blue to yellow. However, in the presence of AA, the corners of Ag TNPs can be protected from Cl- etching, and the blue color of the solution remains unchanged. Using this effect, a selective sensor was designed to detect AA in the range of 0-40.00 μM with a detection limit of 2.17 μM. As the concentration of AA varies in this range, color changes from yellow to blue can be easily observed, so the designed sensor can be used for colorimetric detection. This method can be used to analyze fruit juice samples.

Multiple fluorescence quenching effects mediated fluorescent sensing of captopril Based on amino Acids-Derivative carbon nanodots

Carbon nanodots (CNDs) were facilely synthesized through a pyrolysis procedure with histamine, an amino acid rich in element carbon and nitrogen, being the precursor. Taking advantage of the favorable fluorescence performance of CNDs, a multiple fluorescence quenching effects mediated fluorescent sensor was established for captopril (CAP) detection. MnO₂ NPs were firstly combined with CNDs via electrostatic attraction and subsequently quenched the fluorescence. The quenching mechanisms were concluded to be the combined effects of fluorescence resonance energy transfer (FRET) and inner filtration effect (IFE). Subsequently CAP triggered a unique redox reaction and decomposed the quencher so that renewed the fluorescence. Hence, the sensitive and selective detection of CAP was achieved through the indication of fluorescence recovery efficiency. A proportional range of 0.4 ∼ 60 μmol L^-1 with the LOD of 0.31 μmol L^-1 was obtained. The sensor was further applied to the real sample detection and the satisfactory results revealed the practical value of CNDs. The facile synthesis of CNDs and brand-new sensing mechanism made it a novel fluorescent method and could improve the analysis of CAP.

A dual colorimetric and fluorometric sensor based on N, P-CDs and shape transformation of AgNPrs for the determination of 6-mercaptopurine

In this study, we designed a dual colorimetric and fluorometric sensor by using nitrogen and phosphor doped carbon dots (N, P-CDs) and Ag nanoprisms (AgNPrs) to detect 6-mercaptopurine (6-MP). For this purpose, we applied the AgNPrs/I^- mixture to establish a shape transformation based colorimetric method for the detection of 6-MP. The assay mechanism of colorimetric method was based on etching and protecting effect of I^- and 6-MP on the AgNPrs. In the presence of I^-, as an etching agent, the solution color altered from blue to purple and the position of AgNPrs' local surface plasmon resonance (LSPR) peak shifted to the blue wavelengths. This phenomenon was assigned to the morphological change of AgNPrs. In the presence of 6-MP, AgNPrs were protected from etching by I^-, so the LSPR peak position and solution color of AgNPrs remained unchangeable. Furthermore, the fluorescence intensity of N, P-CDs decreased with adding AgNPrs/I^- due to the spectral overlap between etched AgNPrs and N, P-CDs. The CDs' quenched fluorescence was restored in the presence of 6-MP, as a result of the protecting effect of 6-MP on the AgNPrs. These facts have been applied to develop a dual sensor for the determination of 6-MP at the range of 10-500 nM and 30-500 nM by colorimetric and fluorometric detection methods. The detection limits were obtained 10 and 4 nM for fluorometric and colorimetric methods, respectively. The developed sensor was utilized for dual signal analysis of 6-MP in human serum samples with satisfactory results.

Gold and Silver Nanoparticle-Based Colorimetric Sensors: New Trends and Applications

Gold and Silver nanoparticles (AuNPs and AgNPs) are perfect platforms for developing sensing colorimetric devices thanks to their high surface to volume ratio and distinctive optical properties, particularly sensitive to changes in the surrounding environment. These characteristics ensure high sensitivity in colorimetric devices. Au and Ag nanoparticles can be capped with suitable molecules that can act as specific analyte receptors, so highly selective sensors can be obtained. This review aims to highlight the principal strategies developed during the last decade concerning the preparation of Au and Ag nanoparticle-based colorimetric sensors, with particular attention to environmental and health monitoring applications.

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

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

Rapid and simple colorimetric detection of hydrogen sulfide using an etching-resistant effect on silver nanoprisms

A fast and sensitive colorimetric paper sensor has been developed using silver nanoprisms (Ag NPRs) with an edge length of ~50 nm for the detection of free H₂S gas. We prepared two types of Ag NPRs-coated H₂S sensing papers: a multi-zone patterned paper for passive (diffusion mode), and a single-zone patterned paper for pumped mode of H₂S gas. The change in color intensity was quantitatively analyzed of Ag NPRs-coated paper after KCl treatment depending on the concentration of H₂S gas, from yellow to purplish brown. As a result, Ag NPRs-coated H₂S sensing paper showed good sensitivity with a linear range of 1.03 to 32.9 μM H₂S, high selectivity, and good reproducibility and stability, together with a fast response time of 1 min. The developed H₂S sensing paper was applied to detect the free H₂S gas released from three types of garlic including crushed, peeled, and fresh garlic. Therefore, it can be utilized as a simple, fast, and reliable tool for on-site colorimetric detection of free H₂S gas for quality control of dietary supplements and exhaled breath analysis.Graphical abstract.

Etching-controlled suppression of fluorescence resonance energy transfer between nitrogen-doped carbon dots and Ag nanoprisms for glucose assay and diabetes diagnosis

Numerous methods have been developed for glucose detection, only few cases can be really applied in clinical diagnosis. Herein, we report a new approach to achieve the detection of glucose in clinical samples and distinguishing the diabetic patients with healthy ones. Specifically, a fluorescence resonance energy transfer (FRET) system is established first, where nitrogen-doped carbon dots (N-CDs) and Ag nanoprisms (AgNPRs) with good spectral overlap act as energy donor and acceptor, respectively. Then, the FRET can be inhibited through oxidative etching of the energy acceptor in the presence of glucose and glucose oxidase, where hydrogen peroxide is generated to transform AgNPRs into Ag⁺ ions. Based on the turn-on fluorescent signal versus glucose concentration, a new method for quantitative detection of glucose is developed. This etching-induced analytical method is simple, reliable, robust and cost-effective, which is promising to assist the doctors to clinically diagnose diabetes and other diseases related to metabolic disorders.

Label-free silver triangular nanoplates for spectrophotometric determination of catecholamines and their metabolites

A novel method towards spectrophotometric determination of catecholamines and their metabolites differing in their functional groups has been developed. This method is based on a change in morphology of silver triangular nanoplates upon the action of cateсholamines and their metabolites, which is manifested by the decrease of the nanoparticle local surface plasmon resonance (LSPR) band intensity or its shift to the short-wavelength region of the spectrum. The shift value of the LSPR band or the change of its intensity increases with increasing concentration of catecholamines or their metabolites, which is proposed for their spectrophotometric determination. The limits of detection of catecholamines and their metabolites under selected conditions increase in the series homovanillic acid < vanillylmandelic acid < L-epinephrine < L-norepinephrine < dopamine and are 0.25, 1.2, 3.0, 64, and 130 μmol L^-1, respectively. The selectivity of the proposed method was assessed using vanillylmandelic acid as example. It was found that the determination of vanillylmandelic acid does is not interfered in the presence of 4000-fold excess of Na⁺, K⁺, CH₃COO^-, and 1000-fold excess of Mg²⁺, Ca²⁺, Al³⁺, NO₃^-. The method also allows for the selective determination of vanillylmandelic acid in the presence of a 1000-fold excess of structurally related substances that do not contain either a catechol fragment or an electron donor substituent. The proposed approach was successfully applied to the determination of catecholamines in pharmaceuticals and artificial urine. Graphical abstract.

Manipulating Bimetallic Nanostructures With Tunable Localized Surface Plasmon Resonance and Their Applications for Sensing

Metal nanocrystals with well-controlled shape and unique localized surface plasmon resonance (LSPR) properties have attracted tremendous attention in both fundamental studies and applications. Compared with monometallic counterparts, bimetallic nanocrystals endow scientists with more opportunities to precisely tailor their LSPR and thus achieve excellent performances for various purposes. The aim of this mini review is to present the recent process in manipulating bimetallic nanostructures with tunable LSPR and their applications for sensing. We first highlight several significant strategies in controlling the elemental ratio and spatial arrangement of bimetallic nanocrystals, followed by discussing on the relationship between their composition/morphology and LSPR properties. We then focus on the plasmonic sensors based on the LSPR peak shift, which can be well-controlled by seed-mediated growth and selective etching. This review provides insights of understanding the “rules” involving in the formation of bimetallic nanocrystals with different structures and desired LSPR properties, and also forecasts the development directions of plasmonic sensors in the future.