Experimental (FT-IR, FT-Raman and UV-Vis) spectra and theoretical DFT investigations of 2,3-diaminophenazine

Bifunctional ratiometric sensor based on highly fluorescent nitrogen and sulfur biomass-derived carbon nanodots fabricated from manufactured dairy product as a precursor

Novel biomass-derived carbon dots co-doped with nitrogen and sulfur were fabricated through facile and simple synthetic method from manufactured milk powder and methionine as precursors. The as-fabricated platform was used for ratiometric fluorescence sensing of Cu (II) and bisphosphonate drug risedronate sodium. The sensing platform is based on oxidation of o-phenylenediamine by Cu (II) to form 2, 3-diaminophenazine (oxidized product) with an emission peak at 557 nm. The resultant product quenched the fluorescence emission of as-fabricated carbon dots at 470 nm through Förster resonance energy transfer (FRET) and inner-filter effect (IFE). Upon addition of risedronate sodium, the formation of 2, 3-diaminophenazine was decreased as a result of Cu (II) chelation with risedronate sodium, recovering the fluorescence emission of carbon dots. The ratio of fluorescence at 470 nm and 557 nm was measured as a function of Cu (II) and risedronate sodium concentrations. The proposed sensing platform sensitively detected Cu (II) and risedronate sodium in the range of 0.01-55 μM and 5.02-883 µM with LODs (S/N = 3) of 0.003 μM and 1.48 µM, respectively. The sensing platform exhibited a good selectivity towards Cu (II) and risedronate sodium. The sensing system was used to determine Cu (II) and risedronate sodium in different sample matrices with recoveries % in the range of 99-103 % and 97.4-103.8 %, and RSDs % in the range of 1.5-3.0 % and 1.8-3.6 %, respectively.

In Situ Formation of o-Phenylenediamine Cascade Polymers Mediated by Metal-Organic Framework Nanozymes for Fluorescent and Photothermal Dual-Mode Assay of Acetylcholinesterase Activity

A fluorescent and photothermal dual-mode assay method was established for the detection of acetylcholinesterase (AChE) activity based on in situ formation of o-phenylenediamine (oPD) cascade polymers. First, copper metal-organic frameworks of benzenetricarboxylic acid (Cu-BTC) were screened out as nanozymes with excellent oxidase-like activity and confinement catalysis effect. Then, an ingenious oPD cascade polymerization strategy was proposed. That is, oPD was oxidized by Cu-BTC to oPD oligomers with strong yellow fluorescence, and oPD oligomers were further catalyzed to generate J-aggregation, which promotes the formation of oPD polymer nanoparticles with a high photothermal effect. By utilizing thiocholine (enzymolysis product of acetylthiocholine) to inhibit the Cu-BTC catalytic effect, AChE activity was detected through the fluorescence-photothermal dual-signal change of oPD oligomers and polymer nanoparticles. Both assay modes have low detection limitation (0.03 U L^-1 for fluorescence and 0.05 U L^-1 for photothermal) and can accurately detect the AChE activity of human serum (recovery 85.0-111.3%). The detection results of real serum samples by fluorescent and photothermal dual modes are consistent with each other (relative error ≤ 5.2%). It is worth emphasizing that this is the first time to report the high photothermal effect of oPD polymers and the fluorescence-photothermal dual-mode assay of enzyme activity.

Spectrofluorimetric determination of Cr(VI) and Cr(III) by quenching effect of Cr(III) based on the Cu-CDs with peroxidase-mimicking activity

The study presents a spectrofluorimetric method for the determination of Cr(III) based on 2,3-diaminophenazine (DAP) as fluorescent nano sensor. With the peroxidase-mimicking activity of copper-doped carbon dots (Cu-CDs), colorless o-phenylenediamine (OPD) was oxidized to fluorescent DAP in the presence of H₂O₂ via generation of hydroxyl radicals. The Cr(III) was found to decrease the fluorescent intensity of the Cu-CDs-mediated OPD oxidation system. Cr(VI) species were reduced to Cr(III) by employing 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the reductant, and a novel spectrofluorimetric method for the highly sensitive detection of speciation Cr(VI) and Cr(III) was developed. The Cu-CDs nanozyme was prepared from ethylenediaminetetraacetic acid copper disodium salt (Na₂[Cu (EDTA)]) by one-step pyrolysis method. Under optimal conditions, the fluorescence intensity of DAP is linearly proportional to the Cr(III) ion concentration in the range of 5 × 10^-6 to 1.5 × 10^-4 mol L^-1 and the detection limit is 1.2 × 10^-7 mol L^-1. The method has a good anti-interference performance against some metal ions, such as, Hg²⁺, Co²⁺, Cu²⁺, Mg²⁺, Ba²⁺, K⁺, Mn²⁺, Ni²⁺, Al³⁺, and Fe³⁺. The proposed method was successfully applied in the determination of Cr(VI) and Cr(III) in water samples.

Integration of a Thermoelectric Heating Unit with Ionic Wind-Induced Droplet Centrifugation Chip to Develop Miniaturized Concentration Device for Rapid Determination of Salmonella on Food Samples Using Antibody-Functionalized SERS Tags

When a centrifugation-enriched sample of 100 μL containing the surface-enhanced Raman scattering (SERS) tag-bound bacteria (Salmonella in this study) is siphoned onto a glass slide next to an embedded thermoelectric heating chip, such a sessile droplet is quickly evaporated. As the size of the sample droplet is significantly reduced during the heating process, ionic wind streams from a corona discharge needle, stationed above the sample, sweep across the liquid surface to produce centrifugal vortex flow. Tag-bound Salmonella in the sample are then dragged and trapped at the center of droplet bottom. Finally, when the sample is dried, unlike the "coffee ring" effect, the SERS tag-bound Salmonella is concentrated in one small spot to allow sensitive detection of a Raman signal. Compared with our previous electrohydrodynamic concentration device containing only a corona discharge needle, this thermoelectric evaporation-assisted device is more time-effective, with the time of concentrating and drying about 100 μL sample reduced from 2 h to 30 min. Hence, sample throughput can be accelerated with this device for practical use. It is also more sensitive, with SERS detection of a few cells of Salmonella in neat samples achievable. We also evaluated the feasibility of using this device to detect Salmonella in food samples without performing the culturing procedures. Having spiked a few Salmonella cells into ice cubes and lettuce leaves, we use filtration and ultracentrifugation steps to obtain enriched tag-bound Salmonella samples of 200 μL. After loading an aliquot of 100 μL of sample onto this concentration device, the SERS tag signals from samples of 100 g ice cubes containing two Salmonella cells and 20 g lettuce leaf containing 5 Salmonella cells can be successfully detected.

Safranin-O dye in the ground state. A study by density functional theory, Raman, SERS and infrared spectroscopy

The analysis of ground state structural and vibrational properties of Safranin-O is presented. The experimental results, obtained by FTIR, Raman and SERS spectroscopy, are discussed in comparison to the results of DFT calculations carried out at the B3LYP/6-311+G(d,p) level of theory. The calculated spectra reproduce quite satisfactorily the experimental data. The calculated Safranin-O equilibrium structure and the assignment of the vibrational spectra are reported as well. From the changes between Raman and SERS spectra a model is presented for the interaction of Safranin-O with silver nanoparticles.

Highly sensitive SERS sensor for mercury ions based on the catalytic reaction of mercury ion decorated Ag nanoparticles

Schematic diagram of the SERS sensing mechanism for mercury ions by a catalytic oxidation reaction.

Experimental and computational studies on 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methoxy]phthalonitrile and synthesis and spectroscopic characterization of its novel phthalocyanine magnesium(II) and tin(II) metal complexes

The molecular structure of the substituted phthalonitrile was analyzed crystallographically and compared with optimized geometric structure. The structural properties of the compound such as energy, vibrational frequency, ground state transitions, (1)H and (13)C NMR chemical shifts, NBO analysis and hyperpolarizability were computed by DFT (Density Functional Theory) method and compared with experimental results. The novel Mg(II) and Sn(II) phthalocyanines synthesized from the substituted phthalonitrile and their aggregation behaviors were investigated in different solvents and at different concentrations in DMSO.