Effective reduction of nitrophenols and colorimetric detection of Pb(ii) ions by Siraitia grosvenorii fruit extract capped gold nanoparticles

Ecofriendly ratiometric colorimetric determination of mercury(II) ion in environmental water samples using gallic acid-capped gold nanoparticles

Today, the monitoring and determination of heavy metal pollutants in the environment is an essential requirement for the environmental and research communities. Mercury ion is one of the most hazardous heavy metals, and scientists are trying to develop new methods for its detection. In this study, a new colorimetric sensor based on aggregation gallic acid-capped gold nanoparticles (GA-AuNPs) for the determination of mercury ions in environmental water samples was presented. The green synthesized GA-AuNPs exhibited a sharp surface plasmon resonance peak at 515 nm. The addition of mercury ions changed the surface properties of GA-AuNPs, resulting in the formation of a new peak near 670 nm due to the aggregation of GA-AuNPs, and an obvious color change from red to purple occurred. Thus, mercury ions were detected based on the change in the absorbance ratio (A670/A515). The developed sensor can determine the mercury ions in the concentration range of 78.0 nM to 8.3 µM with a detection limit of 5.5 nM. Based on the Environmental Protection Agency (EPA) and the World Health Organization (WHO) reports, the amount of Hg2+ ions in fresh water should be between 10.0 and 30.0 nM. The results indicate that the developed sensor can detect and determine trace amounts of Hg2+ ions in environmental water samples.

Biosynthesis, Characterization, and Biomedical Applications of Gold Nanoparticles with Cucurbita moschata Duchesne Ex Poiret Peel Aqueous Extracts

In this study, AuNPs were biosynthesized from Cucurbita moschata fruit peel extracts. Biosynthesized AuNPs exhibited maximum absorbance at a 555 nm wavelength, and XRD analysis indicated that the CM-AuNPs had a particle size of less than 100 nm and a cubic crystal structure. TEM scans revealed that the gold particles exhibited a spherical morphology, with an average size of 18.10 nm. FTIR analysis revealed strong peaks indicating the presence of functional groups involved in the reduction reactions. The surface charge of the biosynthesized AuNPs was determined to be -19.7 mV. The antibacterial and antifungal activities of AuNPs against pathogen strains were assessed by the minimum inhibitory concentration (MIC) method. The cytotoxic effects of CM-AuNPs on cancer cell lines (Sk-Ov-3, CaCo2, and A549) and healthy cell lines (HUVEC) were investigated using the MTT method. The findings indicated that AuNPs biosynthesized by the green synthesis method using C. moschata peel aqueous extract had high inhibition on the growth of pathogenic microorganisms and effective cytotoxic activity against cancerous cell lines at low doses. As a result, it can be concluded that CM-AuNPs will be eminently effective in the production of antibacterial and/or anticancer drugs in the pharmaceutical, food, and cosmetic industries.

Localized surface plasmon resonance shift of biosynthesized and functionalized quasi-spherical gold nanoparticle systems

Rapid and more environment-friendly means of gold nanoparticle synthesis is necessary in many applications, as in ion detection. Leaf extracts have become effective and economical reducing agents for gold nanoparticle formation, however, effects of extract combinations have not been thoroughly investigated. With the exploitation of combined extract effects, gold nanoparticles were synthesized then functionalized and investigated to produce selected nanoparticle systems which are capable of detecting aqueous lead(ii) ions with minimum detection limits of 10-11 ppm. The measured localized surface plasmon resonance absorption peaks of the gold nanoparticles were 541-800 nm for the synthesis and 549 nm for the functionalization. The diameters of different gold nanoparticle systems were 17-37 nm. These were mostly quasi-spherical in morphology with some rod-, triangular-, and hexagonal plate-like particles. The biosynthesis used polyphenols and acids present in the extracts in the reduction of gold ions into gold nanoparticles, and in the nanoparticle capping and stabilization. Functionalization replaced the capping compounds with alliin, S-allylcysteine, allicin, and ajoene. Gold nanoparticle stability in aqueous systems was verified for two weeks up to five months. The investigations concluded the practicability of the gold nanoparticles in lead(ii) ion detection with selectivity initially verified for other divalent cations.

Stable biogenic silver nanoparticles from Syzygium nervosum bud extract for enhanced catalytic, antibacterial and antifungal properties

In the present study, the biosynthesis of stable silver nanoparticles (BioAgNPs) was accomplished successfully for the first time by using an aqueous extract derived from the buds of Syzygium nervosum (SN) as both a reducing and a stabilizing agent. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM) investigations revealed that the biosynthesized BioAgNPs were predominantly spherical with an average size of 10-30 nm. It was found that the outstanding stability of the BioAgNPs colloidal solution was assigned to the additive effect of the surrounding protective organic layer and the highly negatively charged surface of the nanoparticles. Consequently, good antibacterial activity was demonstrated by the colloidal BioAgNPs solution against four distinct bacterial strains, including Gram-positive S. aureus and B. subtilis as well as Gram-negative E. coli and S. typhi. Interestingly, the biosynthesized BioAgNPs displayed greater antibacterial activity even when tested at low doses against Gram-negative S. typhi. In addition, the biogenic AgNPs demonstrated a significant level of catalytic activity in the process of converting 2-NP, 3-NP, and 4-NP into aminophenols within 15 min, with reaction rate constants of 9.0 × 10-4, 10 × 10-4, and 9.0 × 10-4 s-1, respectively. BioAgNPs formulations were assessed against anthracnose disease in tea plants and were found to be as effective as the positive control at a dose of 20-fold dilution, but less effective at a dose of 30-fold dilution. Both doses of BioAgNPs formulations significantly suppressed Colletotrichum camelliae (anthracnose disease) without affecting the growth of the tea plants.

Highly sensitive and selective colorimetric detection of Pb(ii) ions using Michelia tonkinensis seed extract capped gold nanoparticles

In this study, gold nanoparticles (AuNPs) were synthesized via a green and environmentally-friendly approach and applied as a colorimetric probe for detecting Pb2+ ions in aqueous solution. Instead of toxic chemicals, Michelia tonkinensis (MT) seed extract was used for reducing Au3+ and stabilizing the formed AuNPs. The synthesis conditions, including temperature, reaction time, and Au3+ ion concentration, were optimized at 90 °C, 40 min, and 1.25 mM, respectively. The physicochemical properties of the produced MT-AuNPs were assessed by means of transmission electron microscopy, X-ray diffraction, field emission scanning electron microscopy, dynamic light scattering, and Fourier-transform infrared spectroscopy. The characterization results revealed that the MT-AuNPs exhibited a spherical shape with a size of about 15 nm capped by an organic layer. The colorimetric assay based on MT-AuNPs showed excellent sensitivity and selectivity toward Pb2+ ions with the limit of detection value of 0.03 μM and the limit of quantification of 0.09 μM in the linear range of 50-500 μM. The recoveries of inter-day and intra-day tests were 97.84-102.08% and 98.78-102.34%, respectively. The MT-AuNPs probe also demonstrated good and reproducible recoveries (98.71-101.01%) in analyzing Pb2+ in drinking water samples, indicating satisfactory practicability and operability of the proposed method.

Novel biogenic gold nanoparticles stabilized on poly(styrene-co-maleic anhydride) as an effective material for reduction of nitrophenols and colorimetric detection of Pb(II)

Biogenic gold nanoparticles (AuNPs) have been extensively studied for the catalytic conversion of nitrophenols (NP) into aminophenols and the colorimetric quantification of heavy metal ions in aqueous solutions. However, the high self-agglomeration ability of colloidal nanoparticles is one of the major obstacles hindering their application. In the present study, we offered novel biogenic AuNPs synthesized by a green approach using Cistanche deserticola (CD) extract as a bioreducing agent and stabilized on poly(styrene-co-maleic anhydride) (PSMA). The prepared Au@PSMA nanoparticles were characterized by various techniques (HR-TEM, SEAD, FE-SEM, DLS, TGA, XRD, and FTIR) and studied for two applications: the catalytic reduction of 3-NP by NaBH₄ and the sensing detection of Pb²⁺ ions. The optimal conditions for the synthesis of AuNPs were investigated and established at 60 °C, 20 min, pH of 9, and 0.5 mM Au³⁺. Morphological studies showed that AuNPs synthesized by CD extract were mostly spherical with a mean diameter of 25 nm, while the size of polymer-integrated AuNPs was more than two-fold larger. Since PSMA acted as a matrix keeping the nanoparticles from coagulation and maintaining the optimal surface area, AuNPs integrated with PSMA showed higher catalytic efficiency with a faster reaction rate and lower activation energy than conventional nanoparticles. Au@PSMA could completely reduce 3-NP within 10 min with a rate constant of 0.127 min^-1 and activation energy of 9.96 kJ/mol. The presence of PSMA also improved the stability and recyclability of AuNPs. Used as a sensor, Au@PSMA exhibited excellent sensitivity and selectivity for Pb²⁺ ions with a limit of detection of 0.03 μM in the linear range of 0-100 μM. The study results suggested that Au@PSMA could be used as a promising catalyst for the reduction of NP and the colorimetric sensor for detection of Pb²⁺ ions in aqueous environmental samples.

Novel biogenic silver and gold nanoparticles for multifunctional applications: Green synthesis, catalytic and antibacterial activity, and colorimetric detection of Fe(III) ions

In this study, novel biogenic silver (AgNPs) and gold nanoparticles (AuNPs) were developed using a green approach with Ganoderma lucidum (GL) extract. The optimization of synthesis conditions for the best outcomes was conducted. The prepared materials were characterized and their applicability in catalysis, antibacterial and chemical sensing was comprehensively evaluated. The GL-AgNPs crystals were formed in a spherical shape with an average diameter of 50 nm, while GL-AuNPs exhibited multi-shaped structures with sizes ranging from 15 to 40 nm. As a catalyst, the synthesized nanoparticles showed excellent catalytic activity (>98% in 9 min) and reusability (>95% after five recycles) in converting 4-nitrophenol to 4-aminophenol. As an antimicrobial agent, GL-AuNPs were low effective in inhibiting the growth of bacteria, while GL-AgNPs expressed strong antibacterial activity against all the tested strains. The highest growth inhibition activity of GL-AgNPs was observed against B. subtilis (14.58 ± 0.35 mm), followed by B. cereus (13.8 ± 0.52 mm), P. aeruginosa (12.38 ± 0.64 mm), E. coli (11.3 ± 0.72 mm), and S. aureus (10.41 ± 0.31 mm). Besides, GL-AgNPs also demonstrated high selectivity and sensitivity in the colorimetric detection of Fe³⁺ in aqueous solution with a detection limit of 1.85 nM. Due to the suitable thickness of the protective organic layer and the appropriate particle size, GL-AgNPs validated the triple role as a high-performance catalyst, antimicrobial agent, and nanosensor for environmental monitoring and remediation.

Efficient and fast degradation of 4-nitrophenol and detection of Fe(III) ions by Poria cocos extract stabilized silver nanoparticles

In this study, a simple and environment-friendly method has been successfully applied for the production of silver nanoparticles (AgNPs) using Poria cocos extract. The reaction time of 60 min, the temperature of 90 °C, and silver ion concentration of 2.0 mM were identified as the best condition for the PC-AgNPs fabrication. The XRD analysis confirmed a highly crystalline face-centered cubic structure of the biosynthesized material. The PC-AgNPs were presented separately in a spherical shape with an average crystal size of 20 nm, as endorsed by the TEM and FE-SEM measurements. The presence and crucial role of biomolecules in stabilizing the nanoparticles were elucidated by FTIR, EDX, and DLS techniques. The prepared biogenic nanoparticles were further applied for the reduction of 4-nitrophenol (4-NP) and colorimetric detection of Fe³⁺ ions. The study results proved that PC-AgNPs exhibited superior catalytic activity and reusability in the conversion of 4-NP by NaBH₄. The complete reduction of 4-NP could be achieved in 10 min with the pseudo-first-order rate constant of 0.466 min^-1, and no significant performance loss was found when the material was reused five times. The colorimetric probe based on PC-AgNPs displayed outstanding sensitivity and selectivity towards Fe³⁺ ions with a detection limit of 1.5 μM in a linear range of 0-250 μM. Additionally, the applicability of the developed assay was explored for testing Fe³⁺ ions in tap water. PC-AgNPs have a great potential for further applications as a promising catalyst for reducing nitrophenols and biosensors for the routine monitoring of Fe³⁺ in water.