FeMo2Ox(OH)y-based mineral hydrogels as a novel POD nanozyme for sensitive and selective detection of aromatic amines contaminants via a colorimetric sensor array.

Developing convenient pathways to discriminate and identify multiple aromatic amines (AAs) remains fascinating and critical. Here, a novel three-channel colorimetric sensor array based on FeMo2Ox(OH)y-based mineral (FM) hydrogels is successfully constructed to monitor AAs in tap water. Benefiting from the substantial oxygen vacancies (VO), FM nanozymes exhibit extraordinary peroxidase (POD)-like activities with Km of 0.133 mM and Vmax of 2.518 × 10-2 mM·s-1 toward 3,3',5,5'-tetramethylbenzidine (TMB), which are much better than horseradish peroxidase and most of POD mimics. This reveals that doping Cu and Co into FM (FM-Cu and FM-Co) can change POD activity. Based on various POD activities, TMB and H2O2 are used to generate fingerprint colorimetry signals from the colorimetry sensor array. The analytes can accurately discriminate through linear discriminant analysis, with a detection limit as low as 2.12 × 10-2-0.14 µM. The sensor array can effectively identify and discriminate AA contaminants and their mixtures and has performed well in real sample tests.

Catechol oxidase nanozyme based colorimetric sensors array for highly selective distinction among multiple catecholamines.

In order to effectively monitor multiple catecholamine (CA) neurotransmitters with extreme similar structures, a rapid, sensitive and selective detection strategy has become an urgent problem to be solved. In this paper, a novel colorimetric sensors array based on CuNCs protected by various ligands such as tannic acid, ascorbic acid and polymethylacrylic acid (CuNCs@TA, CuNCs@AA and CuNCs@PMAA) was constructed. All of these CuNCs could mimic catechol oxidase to selective catalyze catechol-type analogues (such as CAs) to corresponding quinones along with color changes. Furthermore, experiments and theory calculations demonstrated that Cr6+-modification on the surface of CuNCs facilitated the steady-state kinetics of enzymatic activity. Based on these CuNCs as sensing probes, this sensors array can quickly detect different CAs (such as epinephrine (EP), including dopamine (DA), norepinephrine (NE) and l-dopa) with similar structures. When those analogues were added to the CuNC-based colorimetric array sensors, different absorbance changes were produced at 485 nm. Linear discriminant analysis (LDA) showed that the tri-probe colorimetric array sensors could recognize and distinguish these analogues, and corresponding binary and ternary mixtures could be well categorized. The value of Factor 1 of an array with varied CA concentrations had a good linear correlation, and the detection limit (LOD) was as low as 10-8∼10-9 mol/L. Four CA analogues in real samples were identified by CuNCs-based colorimetric array sensors. This work provides a fast and convenient experimental basis for monitoring the complex structure CAs neurotransmitters.

NH2-MIL-101(Fe) nanozyme-based dual-modality sensor for determination of alendronate sodium and study of two-dimensional correlation spectroscopy.

We developed a dual-modality sensing platform for ratiometric fluorescence and colorimetric determination of alendronate sodium (ALDS). This platform was performed by using a NH2- MIL-101(Fe) as a peroxidase mimic. Since preferential complexing between Fe3+ (active site for peroxidase) and ALDS, the production of 2,3-diaminophenazine (DAP, oxidized product of OPD) has been inhibited in the presence of H2O2. As a result, the ratiometric fluorescence value of F556/F456 and absorbance at 450 nm exhibited significant changes, which could be used as the dual-modality sensing platform. In addition, Two-dimensional correlation spectroscopy (2D-COS) analysis on Fourier-transform infrared (FTIR), ultraviolet visible and ratiometric fluorescence spectra were applied to investigate the binding features. Synchronous and asynchronous maps of these spectra confirmed our above hypothesis, in which Fe3+-ALDS complex was the critical factor that regulated dual-modality signals. To our knowledge, the 2D-COS method was applied to study the catalytic and sensing mechanism of nanozyme as NH2- MIL-101(Fe) for the first time. This technique was helpful to understand interaction of substrates on nanozyme and develop more sensitive sensors for assaying.

Supramolecule self-assembly synthesis of amyloid phenylalanine-Cu fibrils with laccase-like activity and their application for dopamine determination.

Laccases are multicopper proteins for dioxygen-involved oxidation of a broad spectrum of organic compounds. I Novel amyloid-like phenylalanine-Cu (F-Cu(II)) fibrils were developed, which were obtained via supramolecular self-assembly of Cu2+ and phenylalanine (F) under basic condition. The obtained amyloid-like fibrils represented highly periodic structure, of which the lattice unit was constructed via alternating hydrophobic (aromatic environment) and hydrophilic (both hydrogen bonding and Cu(II) coordination) interactions. Relative to natural laccases, the amyloid-like F-Cu(II) architecture exhibited comparable substrate affinity (Michaelis constant, Km = 0.75 mM) and higher catalytic efficiency (kcat/Km = 773.33 × 10-3 g-1 min-1L). Moreover, it exhibited remarkable tolerances in pH (4 ~ 10), temperature (room temperature ~ 200 ℃), organic solvent, and long-term storage (> 15 days). These stabilities were superior among the reported nature and artificial laccases, presenting a more promising candidate in various chemo- or bio-applications. In addition, F-Cu(II) fibrils could catalyze the oxidation of dopamine (DA) to a brown product, in which a new absorption band at 470 nm was observed. Based on this, a simple colorimetric assay for the detection of DA could be performed. We reported a novel amyloid-like phenylalanine-Cu fibrils, in which F-Cu+ complex can mimick the T1 site of natural laccase to oxidize the substrates. Then electrons transferred to F-Cu2+ complex via N-H···O=C hydrogen binding pathway. Finally, the dioxygen was transformed to water though radical reaction.

A novel ratiometric fluorescence probe for highly sensitive and specific detection of chlorotetracycline among tetracycline antibiotics.

It is of great importance to detect chlorotetracycline (CTC) in a highly sensitive and specific way because of its wide distribution in aquaculture and animal husbandry. Herein, we propose a novel ratiometric fluorescence strategy to assay CTC by using bovine serum albumin stabilized gold nanoclusters (BSA-AuNCs). The BSA-AuNCs consisting of 25 gold atoms (Au25NCs) display a red emission at 640 nm (λex = 370 nm). In the presence of CTC, a new blue emission at 425 nm is emerged and its intensity dramatically increases with the addition of more the analyte; meanwhile the red emission at 640 nm shows a linear decrease reversely. However, at identical conditions neither the analogues of CTC as tetracycline (TC), oxytetracycline (OTC) or doxycycline (DC) induces similar response of BSA-AuNCs. Such interesting phenomenon is proven related to the conversion from large Au25NCs to smaller nanoclusters composing 8 gold atoms (Au8NCs), which intrinsically originate from the interaction between CTC and the ligand BSA. Therefore, a ratiometric probe is established to sensitively detect CTC in the wide range (0.2-10 µM) with a low limit of detection (LOD) at 65 nM. In addition, this strategy can also be applied to assay CTC in human serum, showing great promise for practical applications in future.

Nitrogen-terminated silicon nanoparticles obtained via chemical etching and passivation are specific fluorescent probes for creatinine.

A method is described here to prepare water-dispersible nitrogen-functionalized silicon nanoparticles (N-SiNPs). It consists of two steps, viz. etching of the oxidized shell of SiNPs and nitrogen-passivation of the exposed silicon. The resulting N-SiNPs have an average diameter of 2.6±0.7 nm and show blue fluorescence (with excitation/emission peaks at 340/420 nm). The fluorescence quantum yield is 23% and the decay time is in the nanosecond regime. Compared to etching methods using a plasma or hydrofluoric acid, the process described here (etching and passivation) is mild, continuous, fast, and air-compatible. The N-SiNPs modified with chlorotetracycline are shown to be a viable fluorescent probe for creatinine. Fluorescence drops in the 0 to 20 µM creatinine concentration range, and the limit of detection is 0.14 µM.