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There is an increasing demand for monitoring ammonia in livestock farming, which can prevent livestock products from being contaminated by bacteria and viruses. As a prospective material for resistive sensors, polypyrrole (PPy) still suffers from low sensitivity and poor selectivity. Herein, zinc-tetra(p-sulfonylphenyl) porphyrin (Zntpp) particles are anchored on the PPy network by a one-step mild electrodeposition route to form a resistive sensor with the wrinkle-like nanostructure. The optimal PPy/Zntpp (Pzt) sensor demonstrates an outstanding response value of 104.3 % toward ammonia with a response/recovery time of 42/223 s, compared with that of PPy (7.2 % in response and 47/230 s). The durability and stabilities have been explored, and the limit of detection for Pzt is calculated to be ∼8.63 ppm, which enables trace ammonia in livestock farming. Additionally, the sensing mechanism can be attributed to the p-n heterojunction. Furthermore, a wireless sensor device that consists of a Pzt sensory unit, a microcomputer, and a Bluetooth module is assembled, and the concentration information can be read precisely in real-time by a smartphone, indicating the great application prospects in the field of livestock farming. [Display omitted] • Constructure of polypyrrole/zinc-porphyrin for ammonia resistive sensor. • Outstanding sensitivity and selectivity of PPy/Zntpp toward NH 3. • Fabrication of a wireless sensor that display NH 3 concentration on a smartphone. • Great potential application prospects in the field livestock farming. [ABSTRACT FROM AUTHOR]

It is an important task to real-time monitor biogenic amines (BAs) released from perishable seafood for predicting their freshness. To this endeavor, herein we developed a simple and effective strategy for visual determination of BAs by dual-emissive metal-organic framework (MOF) probes and color-transition hydrogels. Through situ encapsulating Ru(bpy) 3 2+ into UiO-OH, the functionalized Ru@UiO-OH was solvothermally prepared. At a single excitation wavelength, the fluorescence intensity of Ru@UiO-OH at 537 and 600 nm showed different changes in the case of trimethylamine (TMA), leading to a ratiometric platform with apparent color variation from orange red to bright yellow. The achieved turn-on yellow emission resulted from the inhibition of LMCT and ESIPT process caused by MOF skeleton damage and deprotonation. Intelligently, Ru@UiO-OH was loaded into hydrogels that acted as "sniffing" trademarks to detect volatile TMA vapor, which was further integrated with a smartphone-based readout to quantify. Meanwhile, the practical applicability of fluorescent sensory hydrogels was confirmed via depicting the spoilage degree of shrimp and fish at 4 and 20 ℃, the results were good consistent with standard method for detection of total volatile basic nitrogen (TVB-N). The current creation holds great significance for precise guidance of sensing seafood freshness with straightforward manner. [Display omitted] • Dual-emitting Ru@UiO-OH has been solvothermally prepared by situ encapsulation. • The red-emission acted as a reference, overcoming the interference of environment. • Hydrogel-based "sniffing" sensing platform with color transition was constructed. • The hydrogel label successfully described the spoilage degree of shrimp and fish. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple and portable photothermal method for biothiols was designed. • The polydopamine nanoparticles with photothermal effects were formed on the surface of ZIF-67. • Biothiols could "weaken" the photothermal signal through decomposition of ZIF-67. • The proposed sensor possessed high sensitivity and specificity for biothiols. • Satisfactory analytical results in fetal bovine serum suggests the sensor's applicability. Abnormal levels of biothiols such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) are associated with many pathological diseases. The demand for bulky and costly apparatuses represents a big impediment for point-of-care testing of biothiols. Herein, we developed a novel photothermal sensor for biothiols based on the formation of polydopamine nanoparticles (PDA NPs) using a thermometer as readout. A zeolitic imidazolate framework (ZIF-67) was first fabricated through a facile one-pot strategy. Then dopamine (DA) was immediately polymerized into PDA NPs with excellent photothermal effects (PETs) in the presence of the ZIF-67. Biothiols could disintegrate ZIF-67 by substituting ligands, causing the reaction between biothiols and cobalt ions to form complexes, and release 2-methylimidazole (2MIM) that can slowly oxidize DA, thereby "weakening" the PETs signal, which enabled us to convert biological signals into temperature signals. Therefore, the quantitative detection of Cys, Hcy and GSH can be achieved by recording temperature changes, with detection limits as low as 0.158 μM, 0.181 μM and 0.207 μM, respectively. Furthermore, the photothermal sensor has been applied in detection of biothiols in fetal bovine serum with satisfactory recovery rates, correlating well with the results by standard Ellman method, signifying its promising potential in integrated biological detection system. [ABSTRACT FROM AUTHOR]

[Display omitted] • The novel Ru@V 2 O 4 nanocomposite were synthesized successfully by facile hydrothermal approach. • With the introduction of Ru, the Ru@V 2 O 4 nanocomposite exhibited enhanced catalytic performance. • The synthesized Ru@V 2 O 4 nanowires possessed superior tetra-enzyme-like activities. • A very low limit of detection of 0.788/0.139 μM was obtained for H 2 O 2 /Cys detection, respectively. • This prominent technique could be applied in water samples and human serum samples. In the last decades, nanozymes have drawn significant attention because of their higher stability and lower preparation cost than natural enzymes. In this report, the novel Ru@V 2 O 4 nanocomposite with multi-enzyme-like activities has been synthesized via one-step hydrothermal method and simple stirring. It was proved that the prepared Ru@V 2 O 4 nanowires presented magnificent tetra-enzyme-like activities, comprising oxidase-like (OD-like), peroxidase-like (POD-like), catalase-like (CAT-like) and superoxide dismutase-like (SOD-like) activity. Firstly, the kinetic investigation validated the OD and POD-mimics behaviors of Ru@V 2 O 4 nanowires, which were in conformity with the Michaelis-Menten kinetics. Then a bifunctional colorimetric sensing platform was constructed for the sensitive detection of H 2 O 2 and cysteine (Cys) on the basis of POD-like and OD-like enzyme activities of Ru@V 2 O 4 nanowires. H 2 O 2 could be detected by Ru@V 2 O 4 nanowires over a range of 1–500 μM and the response limit was 0.788 μM. Under optimal conditions, the degree of discoloration was linearly proportional to the concentration of Cys in the range of 3–50 μM with a low detect limit of 0.139 μM. Besides, Ru@V 2 O 4 nanowires can detect H 2 O 2 in water samples and Cys in serum samples. Therefore, this research significantly expands the application of the tetra-enzyme mimetic Ru@V 2 O 4 nanowires in the fields of biosensing, biocatalysis, environmental monitoring and medical diagnosis. [ABSTRACT FROM AUTHOR]