In situ synthesis of gold nanoparticles on novel nanocomposite lactose/alginate: Recyclable catalysis and colorimetric detection of Fe(III)

Microflow injection analysis based on modular 3D platforms and colorimetric detection for Fe(III) monitoring in a wide concentration range

A modular microflow injection analysis (microFIA) system for the determination of Fe(III) in a bioleaching reactor has been designed, developed and validated. The different modules of the analyzer (mixer, diluter, disperser and detector) were 3D-printed. Fe(III) quantification is due by measuring the color intensity of the chelate formed between Fe(III) and salicylic acid at 525 nm. The device has been designed to dilute, disperse and detect high Fe(III) concentrations in the form of an inexpensive multi-step photometric flow cell that uses an light-emitting diode (LED) as a light source and an light-dependent resistor (LDR) as a light intensity detector. This microFIA system has been shown to be suitable for automatic and continuous determination of Fe(III) in the operation of a bioreactor for the oxidation of Fe(II). The device has a good repeatability (less than 5% of coefficient of variation in the whole range of concentrations) and accuracy of around 100%. The analyzer features an exceptional wide linear range, between 25 and 6000 mg·L-1. The device was successfully applied to the determination of Fe(III) in real samples. The obtained results proved that the method is applicable for accurate, precise, rapid, and low-cost colorimetric analysis and didn't show significant differences with a conventional UV-Vis method.

Surface plasmon-assisted catalytic reduction of p-nitrothiophenol for the detection of Fe2+ by surface-enhanced Raman spectroscopy

Herein, we developed a concise, time-efficient, and high selective assay for detecting Fe2+ through its triggered surface plasmon-assisted reduction reaction of p-nitrothiophenol (PNTP) to p,p'-dimercaptoazobenzene (DMAB) on the surface of gold nanoparticles (AuNPs) based on surface-enhanced Raman scattering (SERS) spectroscopy. When Fe2+ was added to the PNTP-AuNPs system, the appearance of three characteristic peaks at 1142, 1392, and 1440 cm-1 attributed to DMAB demonstrated that Fe2+ induced the catalytic coupling reaction of PNTP. The Raman intensity ratio of the peak at 1142 cm-1 to the peak at 1336 cm-1 and the concentration of Fe2+ presented a good linear response from 10 to 100 μM with a limit of detection (LOD) of 0.35 μM. More importantly, the entire detection process can be completed within 2 min and further successfully used for the detection of Fe2+ in river water.

Silver nanoparticles loaded on lactose/alginate: in situ synthesis, catalytic degradation, and pH-dependent antibacterial activity

We present the in situ synthesis of silver nanoparticles (AgNPs) through ionotropic gelation utilizing the biodegradable saccharides lactose (Lac) and alginate (Alg). The lactose reduced silver ions to form AgNPs. The crystallite structure of the nanocomposite AgNPs@Lac/Alg, with a mean size of 4-6 nm, was confirmed by analytical techniques. The nanocomposite exhibited high catalytic performance in degrading the pollutants methyl orange and rhodamine B. The antibacterial activity of the nanocomposite is pH-dependent, related to the alterations in surface properties of the nanocomposite at different pH values. At pH 6, the nanocomposite demonstrated the highest antibacterial activity. These findings suggest that this nanocomposite has the potential to be tailored for specific applications in environmental and medicinal treatments, making it a highly promising material.

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.

Colorimetric and naked-eye detection of arsenic(iii) using a paper-based microfluidic device decorated with silver nanoparticles

Arsenic (As) as a metal ion has long-term toxicity and its presence in water poses a serious threat to the environment and human health. So, rapid and accurate recognition of traces of As is of particular importance in environmental and natural resources. In this study, a fast and sensitive colorimetric method was developed using silver nano prisms (Ag NPrs), cysteine-capped Ag NPrs, and methionine-capped Ag NPrs for accurate detection of arsenic-based on transforming the morphology of silver nanoparticles (AgNPs). The generated Ag atoms from the redox reaction of silver nitrate and As(iii) were deposited on the surface of Ag NPrs and their morphology changed to a circle. The morphological changes resulted in a change in the color of the nanoparticles from blue to purple, which was detectable by the naked eye. The rate of change was proportional to the concentration of arsenic. The changes were also confirmed using UV-Vis absorption spectra and showed a linear relationship between the change in adsorption peak and the concentration of arsenic in the range of 0.0005 to 1 ppm with a lower limit of quantification (LLOQ) of 0.0005 ppm. The proposed probes were successfully used to determine the amount of As(iii) in human urine samples. In addition, modified microfluidic substrates were fabricated with Ag NPrs, Cys-capped Ag NPrs, and methionine-capped Ag NPrs nanoparticles that are capable of arsenic detection in the long-time and can be used in the development of on-site As(iii) detection kits. In addition, silver nanowires (AgNWs) were used as a probe to detect arsenic, but good results were not obtained in human urine specimens and paper microfluidic platforms. In this study, for the first time, AgNPs were developed for optical colorimetric detection of arsenic using paper-based microfluidics. Ag NPrs performed best in both optical and colorimetric techniques. Therefore, they can be a promising option for the development of sensitive, inexpensive, and portable tools in the environmental and biomedical diagnosis of As(iii).

Green synthesis of fluorescent carbon nanospheres from chrysanthemum as a multifunctional sensor for permanganate, Hg(II), and captopril

A simple and green method for the synthesis of fluorescent carbon nanospheres (CNs) was proposed using chrysanthemum as a natural precursor and ethylenediamine as the co-reagent. The prepared CNs show strong blue fluorescence in water with quantum yield of 13.7 %, and distinguished fluorescent stability against photobleaching and ion strength. Meanwhile, the fluorescence signal of CNs is reversible and sensitive to temperature in the range of 20-80 °C, which makes CNs useful as a temperature sensor. More importantly, the CNs can serve as excellent fluorescent sensors for detecting MnO₄^- and Hg²⁺ with the detection limit of 0.72 and 0.26 μM, respectively. MnO₄^- quenches the fluorescence of CNs through inner filter effect and static quenching mechanism, while Hg²⁺ forms a stable complex with the amino group on the surface of CNs, resulting in the fluorescence quenching of CNs. However, the stronger affinity between Hg²⁺ and captopril (Cap) results in the fluorescence quenched by Hg²⁺ recovery after the addition of Cap. Thus, the CNs-Hg²⁺ system is employed as a novel sensitive and selective fluorescence "turn-on" sensor for Cap in the range of 0-75 μM. Inspired by the sensing results, the developed sensors were successfully used for the determination of MnO₄^-, Hg²⁺ in river water samples and Cap in the pharmaceutical and urine samples.

A Simple Yet Effective Preanalytical Strategy Enabling the Application of Aptamer-Conjugated Gold Nanoparticles for the Colorimetric Detection of Antibiotic Residues in Raw Milk

The misuse of antibiotics in the cattle sector can lead to milk contamination, with concomitant effects on the dairy industry and human health. Biosensors can be applied in this field; however, the influence of the milk matrix on their activity has been poorly studied in light of the preanalytical process. Herein, aptamer-conjugated gold nanoparticles (nanoaptasensors) were investigated for the colorimetric detection in raw milk of four antibiotics used in cattle. The effect of milk components on the colorimetric response of the nanoaptasensors was analyzed by following the selective aggregation of the nanoparticles, using the absorption ratio A₅₂₀/A₇₂₀. A preanalytical strategy was developed to apply the nanoaptasensors to antibiotic-contaminated raw milk samples, which involves a clarification step with Carrez reagents followed by the removal of cations through dilution, chelation (EDTA) or precipitation (NaHCO₃). The colorimetric signals were detected in spiked samples at concentrations of antibiotics as low as 0.25-fold the maximum residue limits (MRLs) for kanamycin (37.5 μg/L), oxytetracycline (25 μg/L), sulfadimethoxine (6.25 μg/L) and ampicillin (1 μg/L), according to European and Chilean legislation. Overall, we conclude that this methodology holds potential for the semiquantitative analysis of antibiotic residues in raw milk obtained directly from dairy farms.

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.

Mercaptosuccinic-Acid-Functionalized Gold Nanoparticles for Highly Sensitive Colorimetric Sensing of Fe(III) Ions

The development of reliable and highly sensitive methods for heavy metal detection is a critical task for protecting the environment and human health. In this study, a qualitative colorimetric sensor that used mercaptosuccinic-acid-functionalized gold nanoparticles (MSA-AuNPs) to detect trace amounts of Fe(III) ions was developed. MSA-AuNPs were prepared using a one-step reaction, where mercaptosuccinic acid (MSA) was used for both stabilization, which was provided by the presence of two carboxyl groups, and functionalization of the gold nanoparticle (AuNP) surface. The chelating properties of MSA in the presence of Fe(III) ions and the concentration-dependent aggregation of AuNPs showed the effectiveness of MSA-AuNPs as a sensing probe with the use of an absorbance ratio of A530/A650 as an analytical signal in the developed qualitative assay. Furthermore, the obvious Fe(III)-dependent change in the color of the MSA-AuNP solution from red to gray-blue made it possible to visually assess the metal content in a concentration above the detection limit with an assay time of less than 1 min. The detection limit that was achieved (23 ng/mL) using the proposed colorimetric sensor is more than 10 times lower than the maximum allowable concentration for drinking water defined by the World Health Organization (WHO). The MSA-AuNPs were successfully applied for Fe(III) determination in tap, spring, and drinking water, with a recovery range from 89.6 to 126%. Thus, the practicality of the MSA-AuNP-based sensor and its potential for detecting Fe(III) in real water samples were confirmed by the rapidity of testing and its high sensitivity and selectivity in the presence of competing metal ions.

Nanopatterned Polymer Molds Using Anodized Aluminum Templates for Anti-Reflective Coatings

This work introduces a facile geometry-controlled method for the fabrication of embossed and engraved polymeric moth-eye-inspired nanostructures in imprinting molds using anodic aluminum oxide (AAO) templates, resulting in a novel anti-reflective transparent coating. The moth-eye nanostructures are prepared directly on the surface of a flexible polyethylene terephthalate (PET) substrate. As a prerequisite procedure, a UV-curable polyurethane acrylate resin is spun on the PET. The shape of the moth-eye nanostructures can then be adjusted by controlling the size and shape of the nanopores in the AAO templates. Both embossed and concaved polymer moth-eye nanostructures were successfully mounted on a PET substrate. Embossed polymer replica molds were prepared using the AAO master templates in combination with an imprinting process. As revealed by field-emission electron microscope (FE-SEM) images, conical nanopatterns in the AAO template with a diameter of ~90 nm and a depth of ~100 nm, create a homogeneous embossed morphology in the polymer moth-eye nanostructure. The polymeric molds with the depths of 300 and 500 nm revealed the amalgamated structures in their apexes. In addition, a dip-imprinting process of the polymeric layers was implemented to yield a concaved mold by assembly on the surface of the 100 nm embossed polymer mold substrate. Considering that the embossed structures may be crumbled due to their protuberant shapes, the concaved geometries can have an advantage of stability in a certain application concerning physical degradation along with a higher transmission by ~2%, despite somewhat nonuniform structure. The experimental and theoretical results of this study indicate that this polymer layer has the potential for use in anti-reflective coating applications in transparent films.

Quantifying instant water cleaning efficiency using zinc oxide decorated complex 3D printed porous architectures

Industrialization harms the quality of water; therefore, cleaning and monitoring water sources are essential for sustainable human health and aquatic life. An increase in active surface area and porosity can result in quick and efficient cleaning activity. 3D printing can build porous architecture with controlled porosity and active surface area. Here, catalytically active ZnO nanosheets were grown on the surface of 3D printed architecture (Schwarzites and Weissmuller) with different porosity and surface area. The Weissmuller structure along with ZnO, has shown better catalytic performance due to its higher porosity (~69%) and high active surface area, compared to Schwarzites structure. Synergistic effect of adsorption and photodegradation has resulted in ~95% removal efficiency of mixed dye within 10 min by Weissmuller structure. The dye degradation efficiency was determined using colorimetric measurements with a regular smartphone for real-time quantitative investigation of dye removal efficiency. Most importantly, decorated 3D printed structures exhibit high structural stability without residuals (ZnO nanosheets) in water after performing the recycling experiment. Therefore, the decorated 3D printing structures and colorimetric detection method will offer a user-friendly versatile technique for analysis of removal efficiency of toxic components in different polluted water sources without using high-end sophisticated instruments and complicated procedures.

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

This study presents a simple and green approach for the synthesis of Siraitia grosvenorii fruit extract capped gold nanoparticles (SG-AuNPs). The SG-AuNPs samples prepared under the optimized conditions were characterized by various techniques (UV-Vis, XRD, FTIR, HR-TEM, EDX, DLS). The biosynthesized nanoparticles were then studied for the reduction of 2-nitrophenol (2-NP) and 3-nitrophenols (3-NP) and for colorimetric detection of Pb2+ ions. The characterization results revealed that the crystals of SG-AuNPs were spherical with an average size of 7.5 nm. The FTIR and DLS analyses proved the presence of the biomolecule layer around AuNPs, which played an important role in stabilizing the nanoparticles. The SG-AuNPs showed excellent catalytic activity in the reduction of 3-NP and 2-NP, achieving complete conversion within 14 min. The catalytic process was endothermic and followed pseudo-first-order kinetics. The activation energy was determined to be 10.64 and 26.53 kJ mol-1 for 2-NP and 3-NP, respectively. SG-AuNPs maintained high catalytic performance after five recycles. The fabricated material was also found to be highly sensitive and selective to Pb2+ ions with the detection limit of 0.018 μM in a linear range of 0-1000 μM. The practicality of the material was validated through the analyses of Pb2+ in mimic pond water samples. The developed nanoparticles could find tremendous applications in environmental monitoring.

Shape recoverable, Au nanoparticles loaded nanocellulose foams as a recyclable catalyst for the dynamic and batch discoloration of dyes

An environmental benign in-situ formation and growth of gold nanoparticles (AuNPs) on TEMPO-oxidized cellulose nanofibrils (TOCNF) is reported here. With the active functional groups (aldehyde and carboxyl), TOCNF served as a synchronized reducing and supporting agent for the formation of AuNPs. The entire synthesis process was completed within 30 s under microwave irradiation and regarded as ultra-fast. As obtained AuNPs@TOCNF nanohybrid suspension was freeze-dried to form strong water-activated shape recovery 3D foam. Internal morphology and porosity of the foam were studied by SEM and BET. AuNPs@TOCNF foams exhibited excellent catalytic activity for the discoloration of cationic and anionic dyes in batch and dynamic column processes. The spent foams can be easily recovered and reused up to five cycles with more than 98 % efficiency. During the catalytic processes, no obvious deterioration of the foam structure was observed. Practical applicability of the nanocatalyst was evaluated by treating spiked sea water sample.