Cysteine is one of the important amino acids that is involved in various physiological processes, food industries, pharmaceuticals, and personal care. It also serves as a biomarker for some diseases. ...The large use of cysteine necessitates rapid, cheap, and accurate determination of cysteine in a range of samples. Although many techniques have been employed for the detection of cysteine, they suffer from limitations that make them unsuitable for routine analysis. Here we report on a cheap colorimetric method using biosynthesized silver nanoparticles (AgNPs) as nanozymes. The AgNPs were characterized by UV/visible spectrophotometry, scanning electron microscopy (SEM), and surface-enhanced Raman spectroscopy (SERS). The AgNPs exhibit peroxidase-like activity using
o
-phenylenediamine (OPD) as a chromogenic reagent. The low
K
m
values observed for OPD and H
2
O
2
(0.9133 and 61.56 mM respectively) show strong affinity of the substrates to AgNPs. The peroxidase-like activity of AgNPs, however, was inhibited on the addition of cysteine. The results show that the absorption intensity of the oxidized OPD decreased linearly with the concentration of cysteine in the range of 0.520 μM. The limit of detection (LOD) in this linear range was found to be as low as 90.4 nM. The recovery from urine sample (spiked with cysteine) analyses demonstrated the feasibility of the method in real sample application. From our findings, we anticipate that our method can be applied for the analysis of cysteine in various samples.
The peroxidase-like activity of the biosynthesized AgNPs was inhibited on addition of cysteine. This enables us to develop a colorimetric method for cysteine detection.
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•Oxidation of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) is initiated by chromium (VI) in the presence of CuO.•The method avoids utilization of the unstable and environmental unfriendly ...H2O2 as oxidizing agent.•Non-expensive and stable material was used for detection of chromium (VI) in contrast to expensive plasmonic nanostructures.
Extensive use of chromium makes it one of the major pollutants of water resources. Chromium (VI) in particular is toxic and has detrimental health effects. Because of its high toxicity a tolerable concentration limit of chromium (VI) in drinking water has been recommended. Here we report a colorimetric method for determination of chromium (VI) in water based on the oxidase-like activity of solvothermal synthesized copper oxide. The particles have been characterized by X- ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Using 3, 3′, 5, 5′- tetramethylbenzidine (TMB) as a chromogenic substrate, CuO exhibited a pronounced oxidase-like activity in the presence of chromium (VI). This method enables successful colorimetric detection of chromium (VI). It demonstrated excellent selectivity for detection of chromium (VI) ions against potentially interfering ions. The method’s feasibility to real sample analysis has been proven by testing tap water. Hence, we anticipate that the method can be successfully applied for analysis of chromium (VI) in environmental samples.
In this study, vesicular basalt volcanic rock was taken and its application for adsorption of chromium (VI) from aqueous solution was investigated. Different physical and chemical properties of the ...powdered rock was studied using Fourier transform infrared spectroscopy (FT-IR), Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). A series of batch experiments were carried out to study the effect of various experimental parameters (pH, ionic strength and contact time) on chromium (VI) adsorption. It was found that the removal efficiency of chromium (VI) decreased with increasing pH and ionic strength. The adsorption process was optimal at pH 2. The maximum adsorption capacity was 79.20 mg kg−1 at an initial concentration of 5.0 mg L−1 and adsorbent dosage of 50 g L−1. In individual adsorption tests, Pseudo-second-order kinetic and Freundlich isotherm models could better describe chromium (VI) adsorption on the vesicular basalt. This study indicated that vesicular basalt, which is inexpensive, has the potential to remove chromium (VI) from polluted water.
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•ZnO assisted the formation of gold nanoparticles using ethylene glycol as a reducing agent at low temperature.•Sensitive colorimetric determination of mercury (II) ions was achieved ...by enhancing the peroxidase-like activity of the gold-loaded ZnO/Fe3O4.•The peroxidase-like activity of the nanozyme was enhanced selectively in the presence of mercury (II) ions.•The AuNPs/ZnO/Fe3O4 nanozymes were employed repeatedly for seven consecutive cycles for the detection of mercury (II) ions.
Mercury is one of the heavy metal ions that are released to the environment through various means including anthropogenic pollution. A very low dose of mercury in environmental systems such as water can lead to debilitating effects on the health of humans and animals, if consumed untreated. To reduce this effect, it is critical to develop a simple, non-expensive, and non-sophisticated detection and monitoring system of mercury. Here, we report a simple colorimetric method based on the peroxidase-like activity of AuNPs/ZnO/Fe3O4. Different characterization techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and surface-enhanced Raman spectroscopy (SERS) were used to investigate the successful formation of these composites. The formation of AuNPs was assisted by ZnO. The low Km value (0.7368 mM) obtained from the kinetic study of the catalytic oxidation of 3, 3′, 5, 5′ − Tetramethylbenzidine (TMB) showed strong affinity of TMB to AgNPs/ZnO/Fe3O4. The peroxidase-like activity of AgNPs/ZnO/Fe3O4, was further enhanced in the presence of mercury (II). The absorption intensities of the resulting oxidized TMB (oxTMB) increased linearly in a concentration range of 0.05 – 20 µM. The method also exhibited high selectivity to mercury (II) ions. The limit of detection (LOD) in this linear range was found to be 28.1 nM. The feasibility of the method in determination of mercury (II) ions from real samples was confirmed from high recovery rates in tap water samples. The method shows a great potential for determination of mercury (II) ions in environmental samples.
Magnetic microspheres decorated with gold nanoparticles (AuNPs) were prepared and used for the determination of adenine by surface-enhanced Raman scattering (SERS). Magnetic particles were first ...synthesized by coprecipitation of solutions containing iron(II) and iron(III) ions with ammonium hydroxide. Subsequently, the magnetic particles were suspended into a solution of poly(divinylbenzene-co-methyl methacrylate) to yield polymer-stabilized magnetic microspheres. These were further decorated with AuNPs via a new photochemical reduction method. The magnetic microspheres were characterized by XRD patterns and SEM images. They are shown to represent highly SERS-active substrates by giving an enhancement by almost 7 orders of magnitude compared to conventional Raman spectroscopy. Several factors that affect the photochemical reduction to form the AuNPs were examined. It is found that the concentration of gold ion, UV irradiation time, and citrate concentration have more impact on the reaction rate than on the morphologies of the AuNPs. The gold-decorated magnetic microspheres are highly stable in aqueous solution and capable of concentrating nucleobases. A linear response of the SERS signal to adenine in concentrations up to 10 μM is found, with a linear regression coefficient of 0.997. The detection limit is estimated to a few hundreds of nM (at an SNR of 3). Based on its specific Raman peak at 734 cm
−1
, adenine can be selectively determined without interference by other nucleobases, and a recovery higher than 95 % could be obtained.
Graphical Abstract
Magnetic microspheres decorated with gold nanoparticles were prepared and used for the determination of adenine by surface-enhanced Raman scattering. Based on its specific Raman peak at 734 cm
−1
, adenine can be selectively determined without interference by other nucleobases, and the recovery is higher than 95 %
The utilization of nitrophenols as raw materials for the synthesis of dyes, explosives, pesticides, and pharmaceuticals has increased the presence of nitrophenols as pollutants in industrial and ...agricultural wastewater. Similarly, the wide application range of rhodamine 6G and methylene blue enable their potential as pollutants of surface and ground waters. Both classes of chemicals can change water ecosystems dangerously. In this study, filter paper-based silver nanoparticles are prepared as catalysts for reduction of 4-nitrophenol to 4-aminophenol and for degradation of rhodamine 6G and methylene blue. This method avoids utilization of toxic reagents and is simple and inexpensive. The formation of the silver nanoparticles on filter paper was characterized using different techniques, such as scanning electron microscopy, X-ray diffraction, and surface-enhanced Raman spectroscopy. In the presence of sodium borohydride, the silver nanoparticles coated filter paper was able to reduce 4-nitophenol to 4-aminophenol within a short period of time. It has been found that, the nanocatalyst can be recycled and recovered from the reaction solutions easily without losing its high efficiency. Additionally, we demonstrated the potential of the substrate to study the in situ reduction reaction via surface-enhanced Raman spectroscopy.
In this study, silver nanostructures decorated magnetic nanoparticles for surface-enhanced Raman scattering (SERS) measurements were prepared via photoreduction utilizing the catalytic activity of ...ZnO nanostructure. The ZnO/Fe3O4 composite was first prepared by dispersing pre-formed magnetic nanoparticles into alkaline zinc nitrate solutions. After annealing of the precipitates, the formed ZnO/Fe3O4 composites were successfully decorated with silver nanostructures by soaking the composites into silver nitrate/ethylene glycol solution following UV irradiations. To find the optimal condition when preparing Ag@ZnO/Fe3O4 composites for SERS measurements, factors such as the reaction conditions, photoreduction time, concentration of zinc nitrate and silver nitrate were studied. Results indicated that the photoreduction efficiency was significantly improved with the assistance of ZnO but the amount of ZnO in the composite is not critical. The concentration of silver nitrate and UV irradiation time affected the morphologies of the formed composites and optimal condition in preparation of the composites for SERS measurement was found using 20mM of silver nitrate with an irradiation time of 90min. Under the optimized condition, the obtained SERS intensities were highly reproducible with a SERS enhancement factor in the order of 7. Quantitative analyses showed that a linear range up to 1µM with a detection limit lower than 0.1µM in the detection of creatinine in aqueous solution could be obtained. Successful applying of these prepared composites to determine creatinine in urine sample was obtained.
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•Ag nanostructure-decorated magnetic composites were successfully prepared.•Photochemical decoration of Ag nanostructure is feasible using ZnO.•Prepared magnetic composites exhibit large SERS enhancement.•Easy in concentration Ag-decorated magnetic composites for SERS detection.•Composites were successfully applied in the detection of creatinine by SERS.
The authors present a fast and sensitive surface-enhanced Raman spectroscopy (SERS) method for the determination of
Mycobacterium smegmatis
. It is based on the formation of silver nanoparticles ...(AgNPs) directly on the surface of bacteria via the silver mirror reaction. To achieve this, the bacteria are mixed with silver nitrate, treated with NaOH, and then with ammonium hydroxide until all silver oxide precipitate is completely dissolved. Treatment of the reaction mixture with glucose at 55 °C results in the formation of AgNPs on the surface of the bacteria. The detection of
M. smegmatis
by SERS is simple and straightforward in that 4 μL of a suspension of Ag-coated
M. smegmatis
are pipetted onto a polypropylene surface and SERS spectra are acquired. Quantitative evaluation is done best by using the distinct vibrational band at 731 cm
−1
. Routine detection and identification of
M. smegmatis
thereafter required ~1000 bacilli per laser spot area and a limit of detection below 100 bacilli, using a cheap, dispersive Raman spectrometer. Our method was also applied to detect
M. bovis
BCG,
M. tuberculosis
,
Staphylococcus aureus
,
S. epidermis
,
Bacillus cereus
and two laboratory strains of
Escherichia coli
, thus demonstrating the wider applicability of this approach.
Graphical abstract
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•A simple method based on the oxidoreductase-like activity of Fe3O4 for colorimetric determination of Cr6+ is developed.•The rate of oxidation of 3, 3′, 5, 5′-tetramethylbenzidine ...(TMB) increases with increasing concentration of Cr6+.•The method exhibits high selectivity, low limit of detection and a wide linear range for determination of Cr6+.
Chromium (VI) is a highly toxic metal ion that is usually emitted to the environment through different activities like metal plating, leather tanning, wood preservatives treatment, pigment production and mining. Therefore, rapid and simple routine method of detection is highly demanding. Here, we develop a simple method based on the oxidoreductase-like activity of Fe3O4 for colorimetric determination of Cr6+. Simple co-precipitation method was employed to produce Fe3O4. The colorless 3, 3′, 5, 5′-tetramethylbenzidine (TMB) solution can be oxidized to deep blue colored oxTMB in the presence of Fe3O4, and Cr6+ rapidly. On account of this we determine Cr6+ using Fe3O4 as oxidoreductase catalyst. The method avoids utilization of H2O2 which can compromise the repeatability of measurements due to its instability. The method can detect Cr6+ with a wide linear range of concentration and low limit of detection as small as 34.65 nM that enables determination of the minimum allowable concentration of Cr6+ in drinking water. The assay shows excellent selectivity against potentially interfering metal ions and anions. The method has also employed for quantification of Cr6+ in borehole water samples.
Nanozymes are nanomaterials that possess intrinsic enzyme mimicking activity. In this study, the application of silver nanoparticles coated filter paper (AgNPs/FP) that exhibits a peroxidase-like ...catalytic activity as a potential sensor is reported. A simple chemical reduction method was used to produce AgNPs/FP. The formation of the particles on filter paper were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and surface-enhanced Raman spectroscopy (SERS). In the presence of hydrogen peroxide, AgNPs/FP oxidized the colorless o-phenylenediamine (OPD) and 3,3′,5,5′-tetramethylbenzidine (TMB) solutions to a yellow colored 2,3-diaminophenazine (DAP) and deep blue colored oxidized TMB (oxTMB), respectively. In the presence of thiocyanate, however, the peroxidase-like activity was inhibited in a concentration dependent manner. This makes the AgNPs/FP a promising catalyst and employed for colorimetric detection of thiocyanate via inhibition of the peroxidase-like activity. The application can be further extended to other environmentally and biologically important analytes.
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