Red-emissive carbon nanostructure-anchored molecularly imprinted Er-BTC MOF: a biosensor for visual anthrax monitoring.

Investigating effective fluorescence strategies for real-time monitoring of dipicolinic acid (DPA) is of paramount importance in safeguarding human health. Herein, we present the design of a desirable red-emissive carbon nanostructure anchoring a molecularly imprinted Er-BTC MOF as a fluorescence biosensor for the visual determination of DPA. DPA is a biomarker of Bacillus anthracis, a subcategory of serious infectious diseases and bioweapons. We introduce a paper test strip sensitized with the aforementioned nanostructure, which is integrated with online UV excitation and smartphone digital imaging, resulting in a DPA signal-off sensing platform. The proposed fluorometric visual paper-based biosensor demonstrates wide linear ranges for DPA (10-125 µM) with a LOQ and LOD of 4.32 and 1.28 µM, respectively. The designed platform exhibits impressive emission properties and adaptable surface functional groups, which confirm its desirable selective sensing capabilities against other biological molecules and DPA isomers. As a proof of concept, DPA monitoring is successfully applied to real samples of tap water and urine. This integrated selective paper-based nano-biosensor, coupled with smartphone signal recording, holds great promise for state-of-the-art practical applications including fluorometric/colorimetric detection in healthcare and environmental monitoring, food safety analysis, and point-of-care testing.

Ruthenium-Encapsulated Porphyrinic Organic Polymer as a Photoresponsive Oxidoreductase Mimetic Nanozyme for Colorimetric Sensing.

The advantages of porosity and stable unpaired electrons of porphyrinic organic polymers (POPs) with free radicals are exclusive and potentially practical functionalities and combining the semiconductor-like characteristics of these materials and metal ions has been an effective way to assemble an efficient photocatalytic system. Herein, a new ruthenium (Ru) ion-encapsulated porphyrinic organic polymer (POP/Ru) is facilely synthesized as a proper photoresponsive nanozyme with unique photo-oxidase properties. Surprisingly, the proposed POP/Ru revealed outstanding photoresponsive oxidase-mimicking activity due to the synergetic effect of the integration of Ru and π-electrons of POP, which boosts charge separation and transport. POP/Ru was applied to the oxidation of o-phenylenediamine (o-PDA) as a chromogenic probe for producing a colorimetric signal. The kinetic study reveals that these photo-oxidase mimics have a significant affinity for the o-PDA chromogenic agent owing to a lower Km and superior Vmax. Further findings demonstrate that the presence of the l-arginine (l-Arg) target causes an inhibition effect on the photo-nanozymatic colorimetry of POP/Ru. This research develops the applications of the comprehensive colorimetric strategy for ultrasensitive l-Arg monitoring with a limit of detection (LOD) of 15.2 nM in the dynamic range of 4.0 nM-340 µM and illuminates that the proposed photo-oxidase nanozyme as a visual strategy is feasible in l-Arg environmentally friendly colorimetric detection in juice samples.

Photo-responsive oxidase-like nanozyme based on a vanadium-docked porphyrinic covalent organic framework for colorimetric L-Arginine sensing.

This study reports the development of a vanadium-docked porphyrinic covalent organic framework as a novel class of highly polar photoactive materials. Thanks to its extended π-electron conjugation and high chemical stabilities, this framework can serve as an oxidase-Like photo-nanozyme for photocatalytic oxidation of o-phenylenediamine (o-PDA) and a colorimetric substrate for the production of the yellow-colored oxidized o-PDA (o-PDAox). The physicochemical properties of the as-prepared photo-nanozyme were characterized by several analytical techniques. Its enhanced light harvesting and charge separation and transfer were also verified by electrochemical and spectroscopic analysis. This photo-nonenzymatic colorimetric assay was applied for the sensitive L-Arginine (L-Arg) detection as a typical amino acid in the linear range of 8.1 nM-330 µM with a limit of detection (LOD) of 3.5 nM. The findings of this research confirmed the safety and feasibility of the proposed photo-nonenzymatic colorimetric sensing strategy for the detection of L-Arg and other similar biomolecules in food samples. Kinetic investigation revealed that the photo-responsive oxidase mimic exhibits satisfactory Km (0.47 mM) and Vmax (42.0 µM/s) values. This work broadened our insight into the development of modified porphyrinic-COF-based visible light-responsive oxidase-like photo-nanozyme for environmentally friendly colorimetric biosensing.

Development of peptide impregnated V/Fe bimetal Prussian blue analogue as Robust nanozyme for colorimetric fish freshness assessment.

Colorimetric sensing is a low-cost and visual method for food freshness monitoring. We prepared a Vanadium-Iron Prussian blue analogue (V1/5Fe(CN)6 PBA) impregnated with insulin (INS), as a peroxidase-like mimetic probe toward 3,3'5,5'-tetramethylbenzidine (TMB) oxidation and colorimetric monitoring of fish freshness. A specific chemical reaction between putrescine as spoilage marker and the Vanadium-Iron V1/5Fe(CN)6PBA impregnated with insulin (V1/5Fe(CN)6PBA/INS) induces a decreasing peroxidase-like activity of the V1/5Fe(CN)6PBA/INS, generating lower amounts of oxidized products of TMB. The proposed bio-strategy achieved highly sensitive responses in the range of 30 nM to 12 µM toward putrescine with a detection limit of 9.0 nM and outstanding stability, reproducibility, and selectivity. The freshness of five different types of fish samples determined and produces a noticeable color change consistent with the stale fish around the 10 µM, which can warn the oldness of the fish. This new strategy of integration between peptide and multi-metal PBA with intensified enzyme-like mimetics activity may be highly meaningful for thoroughly monitoring the amount of fish freshness.

An asymmetric Schiff base-functionalized gold nanoparticle-based colorimetric sensor for Hg2+ ion determination: experimental and DFT studies.

We report a colorimetric sensor for the detection of Hg2+ ions utilizing surface-modified gold nanoparticles. Gold nanoparticles (GNPs) were synthesized by direct reduction and were subsequently functionalized using Schiff base ligands. Schiff base ligands as electron transfer agents have been frequently used for the determination of heavy metal ions. From the spectroscopic analysis, it was found that the mechanism could be defined as coordination between azomethine nitrogen and the carbonyl oxygen of the ligand with Hg2+ ions. The affinity of Hg2+ ions towards the bidentate Schiff base on the GNPs result from their self-aggregation and investigated to be a powerful asset for the development of Hg2+ ion-selective sensors, which is accompanied by a visible color change from pink to purple or can be detect by UV-Vis spectroscopy. The optimized structures and binding mechanisms were supported with a high correlation and agreement via spectroscopy and DFT calculations. These simple colorimetric tests can be extended for the rapid pre-screening of a wide variety of heavy metal ions for onsite detection and mitigation.

Electrostatically controlled plasmonic effects of gold nanoparticles with indigo-carmine functionation for rapid and straightforward colorimetric detection of Cu2+ ions.

A colorimetric sensor is fabricated for effective on-site monitoring of Cu2+ ions content based on the distance-dependent optical properties of gold nanoparticles-polyvinyl alcohol-citrate (Au-NPs-PVA-Cy) which plasmonic effect electrostatically was controlled by PVA-Cy stabilizing indigo-carmine (IC) functionalizing. The surface-modified gold nanoparticles were extremely stable with a strong affinity toward Cu2+ ions. Citrate ion was employed as a cross-linking agent for pairs of Au-NPs-PVA-Cy and IC for stabilizing coordination between Cu2+ ion and IC. The active materials were characterized by UV-Vis, SEM, DLS, XRD, FT-IR, and EDS analyses. The sensor response toward Cu2+ ion was found to be linear in the range of 0.0974 to 3.27 µM with the limit of detection and quantification values of 0.021 and 0.07 µM, respectively. The sensor represents good sensitivity and stability, promisingly suggesting this device for the accurate and repeatable determination of Cu2+ in real water samples. The effect of different foreign ions on the selectivity of the sensor was checked. The sensor has a long shelf life in comparison to other similar colorimetric sensors. Also, it shows a repeatable response with RSD% of 2.02%. Thus, the sensing of Cu2+ ions based on the electrostatically control plasmonic of Au-NPs-PVA-Cy was developed with proper signaling based on the color change from dark blue to light blue as readily seen by the naked eye. Furthermore, the efficient environmental applicability of this simple and rapid determination of the Cu2+ sensor is proved.

Colorimetric determination of F-, Br- and I- ions by Ehrlich's bio-reagent oxidation over enzyme mimic like gold nanoparticles: Peroxidase-like activity and multivariate optimization.

Citrate and polyvinyl alcohol capped gold nanoparticles (PVA-GNPs) were synthesized via chemical reduction technique and fully characterized by DLS, SEM, EDS, XRD, UV-Vis and FT-IR analysis. A simple and practical colorimetric sensor based on red-ox reaction of p-dimethylaminobenzaldehyde (DABA) as ehrlich's bio-reagent and Au(III) with H2O2 on PVA-GNPs mimic catalyst with enzyme-like activity, has been fabricated for determination of F-, Br- and I- halide anions. Prepared PVA-GNPs, can simultaneously catalyze the disintegration of H2O2, that used to reduce Au(III) ions into co-doped Au-NPs and oxidation of p-dimethylaminobenzaldehyde ehrlich's bio-reagent while in the presence of halide ions Au-X complex can be formed and improved sensor selectivity. Halide ions (F-, Br- and I-) effectively diminishes the catalytic activity of GNPs to disintegrate oxygenated water by the interaction among Au+ and Au0 and suppressing oxidation of p-dimethylaminobenzaldehyde ehrlich's bio-reagent. In this system which contains PVA-GNPs, H2O2, p-dimethylaminobenzaldehyde ehrlich's bio-reagent, and Au(III), increasing the halide ions (F-, Br- and I-) concentration show color changes from deep green to red. In view of this rule, in this work, a novel colorimetric technique for sensitive determination of F-, Br- and I- was developed. This method has the detection limits of 2.60 × 10-6 M, 6.64 × 10-8 M and 9.93 × 10-9 M and linear ranges between 1.98 × 10-5-1.22 × 10-3 M, 1.99 × 10-6-2.0 × 10-4 M and 1.07 × 10-7- 2.86 × 10-5 M for F-, Br- and I-, respectively. Assays are highly selective over other ions. They effectively applied to detection of halide ions in real water samples.