Single-atom Pd catalysts as oxidase mimics with maximum atom utilization for colorimetric analysis

Pd-based nanomaterials have shown great promise as potential mimic enzymes,but conventional catalysts use only a small fraction of the Pd content that located on the catalyst's surface.Herein,we demonstrated that maximum atom utilization could be achieved by using single-atom Pd catalysts as oxidase mimic.The single-atom Pd nanozymes exhibit significantly enhanced catalytic efficiency,with a catalytic rate constant(Kcat)and the catalytic efficiency(Kcat/Km)values more than 625 and 4,837 times higher than those of horseradish peroxidase,respectively.A combined experimental and theoretical calculation reveals reactive oxygen species involved catalytic mechanism which endows single-atom Pd catalysts with excellent colorimetric analysis performance.Benefiting from the maximum atom utilization efficiency and well-defined structural features,the single-atom Pd nanozymes could be successfully applied for the total antioxidant capacity of fruit,determining the serum acid phosphatase activity as well as constructing NAND logic gate.This finding not only provides an effective strategy to maximize the noble-metal atom utilization efficiency as enzyme mimics,but also provides a new idea for extending their possible applications.

Pyrrole and Pyrimidine Derivatives as Possible Electron Donors for Colored Charge-Transfer Complexes with a Weakly Electrophilic Energetic Material,FOX-7:A Theoretical Study

A number of electron-rich heterocycles are studied as potential reagents for visual colorimetric detection of FOX-7 due to colored charge-transfer complexes formation.The obtained results suggest that pyrrole and pyrimidine derivatives can form such complexes playing the role of electron donors despite a low electrophilicity of FOX-7.Density functional theory calculations,as well as quantum theory of atoms in molecules analysis,suggest stacking binding mode as the most preferable one with the binding energy of about 21-36 kJ/mol.All the complexes demonstrate a clear single charge-transfer absorption band in the visible region and the expected colors of the complexes are varying from violet and blue to red and orange.The calculations of the crystalline state of the studied complexes indicate high lattice energies,which are higher than that of pure FOX-7 and are close to the recently reported hydrogen-bonded complex of FOX-7 with 1,10-phenanthroline.Additional analysis of the studied charge-transfer complexes using properties based on density difference grids clearly suggests the acceptor role of FOX-7 in the complexes.This analysis can be effectively applied to identify the nature of other possible complexes of FOX-7,in which its role is unclear because of the specific reactivity,namely,both weak electrophilic and nucleophilic properties at the same time.

Improvement of hybridization signals of gold label silver stain gene detection

The factors that influence the colorimetric gene detection of gold label silver stain and improve the detection signals were studied. The influence of amino DNA probes and thiol DNA modified gold nanoparticles was investigated based on a sandwich hybridization system. An increase in amino probe concentration brought about an increase in hybridization signal which reached a threshold corresponding to the saturated concentration of amino probes bounded onto a glass slide surface. Since the steric hindrance effect of nanoparticles was dominant over the influence of a surface area, the bigger gold nanoparticles led to weaker hybridization signals. The hybridization efficiency enhanced significantly with the increase of the thiol DNA modified nanoparticle concentrations. Experimental results showed that 125 μmol/L of the amino DNA probe concentration, 15 nm of the gold nanoparticle diameter, and 4.07 nmol/L of the thiol DNA modified gold nanoparticle concentration were optimal for the detection system. The hybridization signals can be improved remarkably by choosing optimal hybridization conditions.

Influence of Blueberry and Jaboticaba Agroindustrial Residue Particle Size on Color Change of Corn Starch Based Films Submitted to Different pH Values Solutions

Corn starch,glycerol and agroindustrial residues were used to produce films by casting.By-products from juice processing,blueberry and jaboticaba in powder with different particle sizes were added in the filmogenic matrix to evaluate its potential as a colorimetric indicator.Blueberry and jaboticaba peels are commonly discarded although contain high amount of important compounds as anthocyanins.These compounds have the ability to color change after immersion in different pH values,demonstrating its potential for the intelligent packaging development.Analyses were performed in a colorimeter after films immersion in different buffer solutions.Visual color changes were perceived;reddish and bluish color in acidic and basic pH values,respectively.Independently of the particle size,theΔE* values were greater than 5,showing visually perceptible change to the human eye.The results indicate the potential of use of these residues as a pH indicator for the development of renewable and biodegradable sensor of food deterioration.

Identification of Arceuthobium globosum using unmanned aerial vehicle images in a high mountain forest of central Mexico

The identification of forests infested by parasitic plants is important for the design of appropriate control and prevention strategies.Satellite images and geographic information systems are commonly used to analyze the presence of pest and parasitic plants in the forests.However there is a need for finer resolution.In the last decade,the use of unmanned aerial vehicles has become increasingly common for capturing aerial images(<10 cm per pixel).The objective of the study was to obtain RGB values(Red,Green and Blue)through the colorimetric ranges for use in identification of Yellow Dwarf Mistletoe(YDM)(Arceuthobium globosum)in aerial images taken in a forest of central Mexico via a programmed algorithm.Three tonalities of YDM were classified according to its phenological stages,viz.green(young stage),yellow(adult stage),and brown(senescence stage),considering two light intensities,sunny and cloudy.Non-parametric tests were used in statistical analyses.The Spearman test showed significant negative correlation(p<0.001)between phenological stage and colour,indicating that lower RGB values were associated with greater age.The differences between groups were analysed using Kruskal–Wallis(p<0.01)and Mann–Whitney tests(p<0.01).The applied algorithm identified the presence and predominant colours of YDM according to its phenological stage.

A cellphone-based colorimetric multi-channel sensor for water environmental monitoring

The development of colorimetric analysis technologies for the commercial cellphone platform has attracted great attention in environmental monitoring due to the low cost,high versatility,easy miniaturization,and widespread ownership of cellphones.This work demonstrates a cellphone-based colorimetric multi-channel sensor for quantifying multiple environmental contaminants simultaneously with high sensitivity and stability.To improve the sensitivity of the sensor,a delicate optical path system was created by using a diffraction grating to split six white beams transmitting through the multiple colored samples,which allows the cellphone CMOS camera to capture the diffracted light for image analysis.The proposed sensor is a universal colorimetric detection platform for a variety of environmental contaminants with the colorimetry assay in the range of 400–700 nm.By introducing the diffraction grating for splitting light,the sensitivity was improved by over six folds compared with a system that directly photographed transmitted light.As a successful proof-of-concept,the sensor was used to detect turbidity,orthophosphate,ammonia nitrogen and three heavy metals simultaneously with high sensitivity(turbidity:detection limit of 1.3 NTU,linear range of 5–400 NTU;ammonia nitrogen:0.014 mg/L,0.05–5 mg/L;orthophosphate:0.028 mg/L,0.1–10 mg/L;Cr(VI):0.0069 mg/L,0.01–0.5 mg/L;Fe:0.025 mg/L,0.1–2 mg/L;Zn:0.032 mg/L,0.05–2 mg/L)and reliability(relative standard deviations of six parallel measurements of 0.37%–1.60%and recoveries of 95.5%–106.0%in surface water).The miniature sensor demonstrated in-field sensing ability in environmental monitoring,which can be extended to point-of-care diagnosis and food safety control.

Pyrophosphate-Mediated On-Off-On Oxidase-Like Activity Switching of Nanosized MnFe_(2)O_(4) for Alkaline Phosphatase Sensing

Developing reliable and facile approaches for alkaline phosphatase(ALP)sensing is important due to its role as a clinical biomarker for many diseases.In this study,we proposed a new and convenient colorimetric assay based on the pyrophosphate(PPi)-mediated oxidase-mimicking activity switching of nanosized MnFe_(2)O_(4) for the detection of ALP.The synthesized MnFe_(2)O_(4) exhibited high oxidase-like activity to catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine(TMB)to its blue product TMBox in the presence of dissolved O2,leading to a color reaction rapidly and remarkably;PPi could significantly inhibit the activity of the MnFe_(2)O_(4) nanozyme via the strong interaction between PPi and the Fe(III)species in MnFe_(2)O_(4),resulting in the suppression of the TMB color reaction;when ALP was added,it hydrolyzed the PPi substrate to phosphate(Pi)that had no obvious effect on the MnFe_(2)O_(4) activity,and such that the TMB color reaction catalyzed by the nanozyme could be observed again.With the above principle,linear colorimetric determination of ALP in the scope of 0.6-55 U L−1 was achieved,giving the limit of detection down to 0.27 U L−1.Besides,the developed assay could provide selective response toward ALP against other co-existing biological species.Furthermore,reliable detection of ALP in human serum samples was verified by our assay,revealing its great promise as an effective and facile tool for ALP monitoring in clinical practice.