Aggregation Of AgNPs Research Articles

Phytofabrication of silver nanoparticles by using Cucurbita maxima leaf extract and its potential anticancer activity and pesticide degradation

ABSTRACT Global cancer mortality is rising yearly due to various factors. Silver nanoparticles (AgNPs) are widely utilized for their low cost and antibacterial properties compared to other noble metals. Here, AgNPs were synthesized using Cucurbita maxima leaf extract, which was analyzed by various analytical instruments. UV-visible spectra showed an absorbance peak in the 410-420 nm range, while the Fourier transform infrared exhibited bands at 653 cm−1, 1629, 2276, and 3786 cm−1. X-ray diffraction showed major intensity peaks at 38.1º two theta value with an average crystallite size of 18.34 nm. The transmission electron microscope showed the aggregation of the spherical-shaped AgNPs, the size of which was 10-90 nm. The MTT assay of the AgNPs showed that it is highly effective against SiHa cervical cancer cells with a much lower IC50 value (~8 µg/mL) and capable of pesticide removal with the highest efficiency at pH 9.

Synthesis and potent antibacterial activity of nano-CuFe2O4/MoS2@Ag composite under visible light

With antibiotic resistance on the rise due to misuse, the urgent need for new antibacterial materials has become paramount in global health. Herein, a CuFe2O4/MoS2 (CFM) composite with a large specific surface area was synthesized through a simple hydrothermal method and physical adsorption, and the subsequent loading of silver nanoparticles (Ag NPs) onto its surface yielded the nanocomposite CuFe2O4/MoS2@Ag (CFMA) with a rough defect-rich surface. The nanocomposite demonstrates remarkable antibacterial activity against Escherichia coli, Staphylococcus aureus, and drug-resistant Salmonella (T-Salmonella) by releasing metal ions that alter the electrical potential of bacterial cell membranes, compromise the integrity of cell membranes, and produce reactive oxygen species that lead to oxidative stress. It thus achieves an antibacterial rate of 96 % against the three tested bacterial strains within just 20 min at a concentration of 200 μg/mL. The composite exhibits a broad-spectrum antibacterial effect against Gram-negative and Gram-positive bacteria, as well as drug-resistant bacteria. Moreover, CFM acts as a carrier that effectively prevents the aggregation of Ag NPs, and the magnetism of CuFe2O4 facilitates the recovery of the antibacterial agent. This work provides new ideas and methods for the development of highly efficient, cost-effective, and biocompatible antibacterial materials.

One-step construction of silver nanoparticles immersed hydrogels by triple-helix β-glucans and the application in infectious wound healing

Hydrogels composed of polysaccharides and silver nanoparticles (AgNPs) are widely recognized for their applications in wound dressings, particularly for healing wounds prone to infection. Traditional methods for preparing AgNPs immersed hydrogels are often complex, costly, and may lead to sustained cytotoxicity. To address these challenges, we developed a biocompatible, one-step green reduction strategy to generate AgNPs within hydrogels using a triple-helix β-glucan (PCPA) derived from Poria cocos, a renowned Chinese traditional herb. PCPA serves as a reducing agent, converting silver ions into AgNPs while its triple-helix conformation prevents AgNPs aggregation. The resulting hydrogel (PAg-G) is injectable and contains uniformly distributed AgNPs. PAg-G exhibits broad-spectrum antimicrobial activity and enhanced bioactivity. The in vivo study on S.aureus-infected SD rats demonstrated that PAg-G can accelerate wound healing within 12 days by down-regulating inflammatory factors such as IL-6 and TNF-α, and up-regulating VEGF and CD31 expression, promoting neovascularization in wound tissues. This innovative one-step construction of AgNPs immersed hydrogels offers a promising approach for the development of antimicrobial hydrogels, especially for treating bacterial-infected wounds.

Highly dispersed nanocomposite based on magnesium ion modified and silver nanoparticles loaded graphene oxide for enhanced antibacterial activity of silicone coatings

Silver nanoparticles (Ag NPs) possess excellent antibacterial properties and have received widespread attention. However, the poor dispersion and easy aggregation of Ag NPs can severely diminish their antibacterial efficacy, limiting their practical applications. In this work, we report a simple method for preparing graphene oxide (GO) nanocomposites (Mg-GO/Ag NPs), in which GO is modified by Mg2+ and uniformly loaded with Ag NPs. The Ag NPs have an average diameter of approximately 11.14 nm, and uniformly are deposited on the surface of the GO. Compared with GO, the dispersion of Mg-GO/Ag NPs in deionized water (DW) and N, N-dimethylformamide (DMF) is significantly improved. The reaction principle of preparing Mg-GO/Ag NPs was revealed by gas chromatography–mass spectrometry (GC–MS). Additionally, we studied the antibacterial properties of Mg-GO/Ag NPs coatings against marine bacteria and Navicula tenera. This study introduces a novel approach for the preparation of high-efficiency silver-based antifouling coatings, with promising potential for a wide range of marine antifouling applications.

Structural Characterization of DNA from Allium Leaves and E. coli by Surface-Enhanced Raman Spectroscopy (SERS)

The label-free detection of biological molecules was demonstrated for different types of DNA. Surface-enhanced Raman spectroscopy (SERS) investigation on nucleic acids extracted from leaves of different Allium cepa cultivars (cvs.) De Buzău, Aurie de Buzău, Rubiniu, Roşie de Arieş as well as taxa A. ursinum, A. senescens subsp. montanum, A. schoenoprasum, A. obliquum, and A. fistulosum was performed using 532-nm laser excitation. Main SERS vibrations of these nucleic acids have been characterized, highlighting those at 658, 704, 1089, and 1125 cm−1 attributed to dG and dA phosphodiester groups as well as deoxyribose, specific constituents of DNA. The mild basic pH conditions of the samples can induce a partial breaking of the hydrogen bonds from the dsDNA, which affects the A = T/T = A as well as C≡G/G≡C base pairs and causes the aggregation of AgNPs mixed with DNA of the Allium cultivars and species. Also, SERS profiles of genomic DNA from E. coli 1559 were analyzed at decreasing pHs from 7 to 4. Protonation of the nitrogen N3 of the aromatic six-membered ring of both deoxyadenosine and deoxyguanosine, respectively, induces the decrease of the peak’s intensity at 1588 cm-1. Furthermore, SERS characteristics of plasmidic DNA from E. coli 7832 and of chromosomal DNA from E. coli MG 1655 are provided, with specific SERS modes indicated and new SERS bands found upon nucleic acids in vitro aging. Principal component analysis (PCA) in the full SERS spectrum range of bacterial DNA was performed.

Bactericidal behavior of silver nanoparticle decorated nano-sized magnetic hydroxyapatite.

Methicillin-resistant Staphylococcus aureus (MRSA) is the most common cause of acute bacterial arthritis. Due to the increase in antibiotic resistance in these bacteria, the discovery of new antibacterial agents has become one of the hot topics in the scientific community. Here, we prepared a nano-sized porous biocompatible magnetic hydroxyapatite through a solvothermal method. Then, we adopted a post-synthesis modification strategy to modify its surface for the stabilization of Ag NPs through a green reduction by the euphorbia plant extract. Moreover, the results show that the prepared composite perfectly prevents the aggregation of Ag NPs. This composite was used as a bactericidal and antibiofilm agent against MRSA bacteria in an in vitro environment, which showed excellent results. Also, the cell viability assay indicates that the prepared composite has low cytotoxicity, making it a perfect antibacterial agent for in vivo experiments.

Development of a colorimetric sensor for selective manganese detection using green-synthesized silver nanoparticles from Withania somnifera

This study reports the green synthesis of silver nanoparticles (AgNPs) using the fruit extract of Withania somnifera and their application as a colorimetric sensor for selective manganese (Mn2+) ion detection. The synthesis of AgNPs was optimized by varying pH, reaction time, and concentrations of fruit extract and AgNO3. UV–visible spectroscopy revealed that the highest absorbance of AgNPs occurred at pH 11, indicating optimal conditions for NPs formation. The absorbance behavior over time demonstrated the nucleation and stabilization processes, with optimal stability achieved after 1800 min. Increasing concentrations of fruit extract and AgNO3 enhanced NPs synthesis, reaching a plateau at 1.0 mL of extract and 1.0 mM AgNO3, respectively. Transmission electron microscopy (TEM) confirmed the formation of spherical AgNPs of 43–85 nm. Fourier-transform infrared spectroscopy (FTIR) indicated the involvement of functional groups such as O-H and C=O in the reduction and stabilization of AgNPs. The green-synthesized AgNPs exhibited notable antioxidant activity, with moderate free radical scavenging abilities compared to ascorbic acid. The colorimetric detection of Mn2+ was achieved through the aggregation of AgNPs, leading to a visible color change. UV–vis absorption spectra showed a prominent peak at 412 nm, with a linear relationship between absorbance change and Mn2+ concentration, demonstrating high sensitivity and selectivity. Comparative studies with other metal ions (Co2+, Cr3+, Ni2+) confirmed the specificity of AgNPs towards Mn2+. In conclusion, the green-synthesized AgNPs from W. somnifera offer a cost-effective and environmentally friendly approach for Mn2+ detection, with significant potential for environmental monitoring and biomedical applications.

Case study of freezing-induced loading of silver nanoparticles into vaterite microcrystals

Hybrid materials composed of porous vaterite CaCO3 microcrystals loaded with functional inorganic nanoparticles are actively studied with respect to various practical applications. Recently, freezing-induced loading method was demonstrated as a versatile and effective approach for preparation of vaterite-based functional hybrid microparticles. However, despite of its high efficiency, the effect of nanoparticle concentration on the freezing-induced loading process and the structural properties of the resulted hybrids were not studied previously. Herein, for the first time, we have evaluated the feasibility of the conventional adsorption models to describe the freezing-induced loading of citrate-capped silver nanoparticles (AgNPs). The fitting of the dependence of the loading capacity of vaterite crystals on the residual concentration of AgNPs to two- or three-parameter models revealed that the best fit was obtained with the Freundlich model (R2 = 0.969), suggesting non-uniform deposition of AgNPs and interparticle agglomeration (Freundlich n > 1). This was confirmed with electron microscopy and elemental analysis demonstrating the formation and growth of AgNP aggregates on the CaCO3 surface with increasing initial nanoparticle concentration. Overall, the reported findings are valuable for a better understanding of the freezing-induced loading process and for further optimization of the preparation of vaterite-based functional hybrid microparticles.

Synergistic effect of Silver-Nanodiamond composite as an efficient antibacterial agent against E. coli and S. aureus

Bacterial antimicrobial resistance (BAMR) seems to pose the greatest threat to public health, food safety, and agriculture in this century. The development of novel efficient antimicrobial agents to combat bacterial infections has become a global issue. Silver nanoparticles (Ag NPs) appeared as a feasible alternative to antibiotics. However, Ag NPs face cost, toxicity, and aggregation issues which limit their antibacterial activity. This work aims to stabilize Ag NPs with enhanced antimicrobial activity at comparatively lower Ag concentrations to prevent bacterial infections. For this purpose, the Ag core was covered with nanodiamonds (NDs). Ag-NDs composite have been synthesized by microplasma technique. TEM analysis confirmed the presence of both Ag and NDs in the Ag-NDs composite. A particle size (∼19 nm) was reported for Ag-NDs at the highest concentration as compared to Ag NPs (∼3 nm). The conduction band of the diamond acted as an extremely strong reducing agent for Ag NPs. The large surface area of NDs stabilized the Ag NPs. A redshift (∼400 nm–406 nm) in UV–visible spectra of the Ag-NDs composite indicated the formation of bigger-sized Ag NPs after incorporating NDs. XRD and LIBS analysis verified the increase in intensity of Ag-NPs by increasing ND concentration. The presence of functional groups including OH, CH, and Ag/Ag2O was confirmed by FTIR. Bacterial inhibition growth appeared to be a dose-dependent process. The minimum inhibition concentration value of Ag-NDs composite at the highest NDs concentration against E. coli (∼ 0.69 μg/ml) and S. aureus (∼44 μg/ml). This is the first study to report the smallest MIC for E. coli (<1 μg/ml). Ag-ND composites emerged to be more efficient than Ag NPs and preferred to be used against BAMR. The enhanced antibacterial activity of the Ag-NDs composite makes it a potential candidate for antibiotics, food products, and pesticides.

UV‐Induced Oxidation Preparation of Multi‐Functional Lignin‐Based AgNPs and its Application for Conductive Coating, Antibacterial Enhancement, and Product Separation

AbstractThis study presents a novel approach for regulating the properties of lignin‐based silver nanoparticles (AgNPs), which was UV‐induced Tetrahydrofuran (THF) to form peroxide for the etching of these nanoparticles. The lignin coating was first degraded by oxidation, and the properties of the exposed AgNPs changed under etching. Notably, water can greatly regulate the oxidation capacity of the THF medium, thereby controlling the degradation degree of lignin coating and obtaining dissolution, aggregation, precipitation, and color‐variable phenomena of AgNPs under the synergistic effect of UV irradiation and peroxide etching. By adjusting UV irradiation time, various functional products of silver nanowires (AgNWs), color‐variable AgNPs, lignin‐based AgNPs aggregates, and composite solution of Ag particles and Ag+ were obtained. The transformation of these product properties is closely related to the oxidation capacity of H2O/THF medium. In addition, Multi‐functional Lignin‐based AgNPs show excellent application potential in conductive coating, antibacterial enhancement, and product separation, providing a promising avenue for the targeted utilization of lignin‐based AgNPs.

UiO-66/AgNPs Coating for Dental Implants in Preventing Bacterial Infections

Titanium (Ti)–based biomaterials lack inherent antimicrobial activities, and the dental plaque formed on the implant surface is one of the main risk factors for implant infections. Construction of an antibacterial surface can effectively prevent implant infections and enhance implant success. Silver nanoparticles (AgNPs) exhibit broad antibacterial activity and a low tendency to induce drug resistance, but AgNPs easily self-aggregate in the aqueous environment, which significantly impairs their antibacterial activity. In this study, UiO-66/AgNP (U/A) nanocomposite was prepared, where zirconium metal–organic frameworks (UiO-66) were employed as the confinement matrix to control the particle size and prevent aggregation of AgNPs. The bactericidal activity of U/A against methicillin-resistant Staphylococcus aureus and Escherichia coli increased nearly 75.51 and 484.50 times compared with individually synthesized Ag. The antibacterial mechanism can be attributed to the enhanced membrane rupture caused by the ultrafine AgNPs on UiO-66, leading to protein leakage and generation of intracellular reactive oxygen species. Then, U/A was loaded onto Ti substrates (Ti-U/A) by using self-assembly deposition methods to construct an antibacterial surface coating. Ti-U/A exhibited excellent antibacterial activities and desired biocompatibility both in vitro and in vivo. The U/A nanocomposite coating technique is thus expected to be used as a promising surface modification strategy for Ti-based dental implants for preventing dental implant infections.

Improving the sensing sensitivity of silver nanoparticle-based colorimetric biosensors from the point of salt.

The sensing sensitivity was improved for silver nanoparticles (AgNPs)-based colorimetric biosensors by using the most suitable salt to induce AgNPs aggregation. As for the salt composed of low-affinity anion and monovalent cation, the cation-dependent charge screening effect was the driving force for AgNPs aggregation. Apart from the charge screening effect, both the bridging of multivalent cation to the surface ligand of AgNP and the interaction between anion and Ag contributed to inducing AgNPs aggregation. Considering the higher aggregation efficiency of AgNPs resulted in a narrower sensing range, salt composed of low-affinity anion and monovalent cation was recommended for AgNPs-based colorimetric analysis, which was confirmed by fourfold higher sensitivity of DNA-21 detection using NaF than NaCl. This work inspires further thinking on improving the sensing performanceof metal nanomaterials-based sensors from the point of colloidal surface science.

A crossover study of antimicrobial capacity and biotoxicity of silver nanoparticles

Silver nanoparticles (AgNPs) have a primordial role in the nanotechnology industry since they have great antimicrobial effects against diverse pathogens. AgNP production, use, and discard have been increasing; still, there is debate about the consequences of exposure to AgNPs for animals and humans. The bioaccumulation and toxicity of AgNPs depend on several factors, including AgNP concentration, physicochemical characteristics, and aggregation. So, complete activity and toxicity profiles for each silver nanoparticle synthesized must be performed. The present work aimed to characterize the behavior of specific AgNPs, then crossover of their antimicrobial capacity against Pseudomonas aeruginosa and Staphylococcus aureus with their potential in vitro cytotoxic effects in murine fibroblasts (3T3) and human keratinocytes (HaCat) cell lines, and in vivo general and organ‐specific toxicity in zebrafish embryos and larvae. A high susceptibility of P. aeruginosa and S. aureus to low concentrations of AgNPs was observed, yet a cytotoxic effect was also detected in 3T3 and HaCat cells. Moreover, these concentrations delayed embryonic development in zebrafish embryos and presented morphological abnormalities, neurotoxicity, and cardiotoxicity in zebrafish larvae. The results highlight the importance of jointly evaluating the antimicrobial activity and the toxicological profile of each nanoparticle manufactured; this study presents a suitable platform for such crossover assessment.

A green approach to nanoplastic detection: SERS with untreated filter paper for polystyrene nanoplastics.

Plastic pollution at the nanoscale continues to pose adverse effects on environmental sustainability and human health. However, the detection of nanoplastics (NPLs) remains challenging due to limitations in methodology and instrumentation. Herein, a "green approach" for surface-enhanced Raman spectroscopy (SERS) was exploited to detect polystyrene nanospheres (PSNSs) in water, employing untreated filter paper and a simple syringe-filtration set-up. This SERS protocol not only enabled the filtration of nano-sized PSNSs, which are smaller than the pore size of the ordinary filter paper, but also offered SERS enhancement by utilizing quasi-spherical-shaped silver nanoparticles (AgNPs) as the SERS-active substrate. The filtering of NPLs was accomplished by adding an aggregating agent to the nanoparticle mixture, which caused the aggregation of NPLs and AgNPs, resulting in a larger cluster and more hot spots for SERS detection. The optimal aggregating agent and its concentration, as well as the volume ratio between the AgNPs and NPLs, were also optimized. This SERS method successfully detected and quantified PSNSs of various sizes (i.e., 100, 300, 460, 600, and 800 nm) down to a limit of detection (LOD) of about 0.31 μg mL-1. The method was also validated against the presence of several interferents (i.e., salts, sugars, amino acids, and surfactants) and was proven practical, as evidenced by the detection of 800nm PSNSs in drinking and tap water (LODs of 1.47 and 1.55 μg mL-1, respectively).

Ultrasensitive colorimetric detection of creatinine via its dual binding affinity for silver nanoparticles and silver ions.

Creatinine is an important biomarker for the diagnosis of chronic kidney disease (CKD). Recently, it has been reported that the concentration of salivary creatinine correlates well with the concentration of serum creatinine, which makes the former useful for the development of non-invasive and point-of-care (POC) detection for CKD diagnosis. However, there exists a technical challenge in the rapid detection of salivary creatinine at low concentrations of 3-18 μM when using the current kidney function test strips as well as the traditional methods employed in hospitals. Herein, we demonstrate a simple, sensitive colorimetric assay for the detection of creatinine with a limit-of-detection (LOD) down to the nanomolar level. Our approach utilises the dual binding affinity of creatinine for citrate-capped silver nanoparticles (Ag NPs) and Ag(i) ions, which can trigger the aggregation of Ag NPs and thus lead to the colour change of a sample. The quantitative detection of creatinine was achieved using UV-Vis spectroscopy with a LOD of 6.9 nM in artificial saliva and a linear dynamic range of 0.01-0.06 μM. This method holds promise to be further developed into a POC platform for the CKD diagnosis.

Simultaneous ionic cobalt sensing and toxic Congo red dye removal: a circular economic approach involving silver-enhanced fluorescence.

A highly fluorescent quinone-capped silver hydrosol (AgOSA) was obtained using salicylaldehyde and an ionic silver solution. Such metal-enhanced fluorescence was efficiently quenched with Congo red dye (CR), producing CRAgOSA, due to the strong silver-sulfur interaction, replacing the capping of quinone (oxidized salicylaldehyde). The introduction of cobalt ions restored the fluorescence by engaging CR (CoCRAgOSA). Cobalt-induced fluorescence enhancement was 8.3 times higher than that of AgOSA due to the freeing of CR and the release of self-quenching of excess quinone molecules in CoCRAgOSA. The mammoth and selective fluorescence enhancement with ionic cobalt assisted in designing a turn-on ionic cobalt sensor with a limit of detection (LOD) of 9.4 × 10-11 M and a linear detection range (5 × 10-5 to 10-9 M). Moreover, toxic CR dye was eliminated by quinone-capped silver nanoparticles and Co2+ due to chemisorption. Not only the fluorimetric sensing of ionic cobalt but also the colorimetric sensing of Hg2+ was designed due to the simultaneous aggregation of AgNPs and complexation with CR induced by Hg2+ (LOD 1.36 × 10-5 M and linear detection range from 1.00 × 10-4 to 5 × 10-7 M). We applied our sensing method to estimate ionic cobalt and mercury in natural samples. The experiment was a unique case of circular economy, where a toxic dye was used for making a nanosensor.

Pilot SERS Monitoring Study of Two Natural Hypersaline Lake Waters from a Balneary Resort during Winter-Months Period.

Water samples from two naturally hypersaline lakes, renowned for their balneotherapeutic properties, were investigated through a pilot SERS monitoring program. Nanotechnology-based techniques were employed to periodically measure the ultra-sensitive SERS molecular characteristics of the raw water-bearing microbial community and the inorganic content. Employing the Pearson correlation coefficient revealed a robust linear relationship between electrical conductivity and pH and Raman and SERS spectral data of water samples, highlighting the interplay complexity of Raman/SERS signals and physicochemical parameters within each lake. The SERS data obtained from raw waters with AgNPs exhibited a dominant, reproducible SERS feature resembling adsorbed β-carotene at submicromole concentration, which could be related to the cyanobacteria-AgNPs interface and supported by TEM analyses. Notably, spurious SERS sampling cases showed molecular traces attributed to additional metabolites, suggesting multiplexed SERS signatures. The conducted PCA demonstrated observable differences in the β-carotene SERS band intensities between the two lakes, signifying potential variations in picoplankton abundance and composition or environmental influences. Moreover, the study examined variations in the SERS intensity ratio I245/I1512, related to the balance between inorganic (Cl--induced AgNPs aggregation) and organic (cyanobacteria population) balance, in correlation with the electrical conductivity. These findings signify the potential of SERS data for monitoring variations in microorganism concentration, clearly dependent on ion concentration and nutrient dynamics in raw, hypersaline water bodies.

Inhibitive determination of organophosphate pesticides using acetylcholinesterase and silver nanoparticle as colorimetric probe

Accurate and real-time detection of pesticides is needed to ensure food safety and ecosystem protection. A biosensor was developed to determine organophosphate pesticides using acetylcholinesterase (AChE) and silver nanoparticle (AgNP) immobilized on the alginate-chitosan film matrix. The sensing principle is based on organophosphate pesticides (OP) inhibiting AChE activity. AChE hydrolyzes acetylthiocoline (ATCh) to thiocholine (TCh) and acetic acid (AA). The -SH group on TCh induces AgNP aggregation, resulting in fading of the film's brownish-yellow color. The presence of OP in the sample inhibited AChE activity, leading to a decrease in TCh and color fading. The biosensor response is determined by measuring the Red Green Blue (RGB) value of the film. The biosensor offers rapid detection directly in-situ and real time without the use of sophisticated instruments, with optimal measurement conditions of pH 7, incubation time of 1 minute, and concentrations of AgNP, ATCh, and tris-HCl buffer of 10 μg/mL, 50, and 7 mM, respectively. Biosensors have excellent sensitivity, reproducibility, and selectivity. Measurement of OP levels in nine vegetable samples revealed that the proposed colorimetric probe's results agreed well with the GC result as the reference method. Therefore, this method can be applied in monitoring food and environment OP levels.

Aggregation of Ag nanoparticle based on surface acoustic wave for surface-enhanced Raman spectroscopy detection of dopamine

BackgroundDopamine (DA), a vital neurotransmitter, plays a critical role in the human brain and relates to neuropsychiatric disorders such as Parkinson's disease and schizophrenia. Numerous studies have explored detection of such biomarkers through surface-enhanced Raman spectroscopy (SERS). However, most of the studies focused on SERS detection face significant challenges with plasmonic nanostructure development. Such challenges often include time-consuming processes, complex fabrication, specialized chemical labeling, poor reproducibility, and random hotspot generation. Therefore, the need for simple and rapid nanostructure development is evident in SERS. ResultsWe propose an innovative SERS-active sensing technique for 50 nm silver nanoparticle (AgNP) clustering based on surface acoustic wave (SAW). When a 1 μL droplet of AgNP colloid is dispensed onto the SAW-propagation zone, the AgNP cluster is deposited after the droplet completely evaporates, developing plasmonic nanogaps for SERS hotspot caused by spherical AgNP aggregation. By optimizing the SAW system through the hydrophobic treatment and modulation of the operational power, the SAW-induced AgNP clustering showed densely packed AgNP within a dot-like configuration (∼2200 AgNP μm−2), effectively preventing particle welding. The characterization of 4-mercaptobenzoic acid as a probe analyte revealed that concentrations as low as 1.14 pM was detected using our SAW-SERS system under 785 nm laser excitation. Moreover, DA was detected up to 4.28 nM with a determination of 0.99 (R2). SignificanceThis technique for AgNP clustering induced by SAW provides a rapid, in situ, label-free SERS sensing method with outstanding sensitivity and linearity. A mere act of dropping can create extensive plasmonic hotspots featuring nanogap of ∼1.5 nm. The SAW-induced AgNP clustering can serve as an ultrasensitive SERS-active substrate for diverse molecular detections, including neurotransmitter detection.

Sunlight-Mediated Synthesis of Metallic Silver Nanoparticles with Coffee (&lt;i&gt;Robusta/Arabica&lt;/i&gt;) Pulp Aqueous Extract for Hg&lt;sup&gt;2+&lt;/sup&gt; Ion Detection

On-site and portable detection of heavy metals, especially in water, is critical for public health safety. Mercury is a toxic heavy metal and poses environmental and health hazard concerns causing neurological and behavioral disorders. Metallic nanoparticles possess unique optical properties, which can be used for heavy metal sensing applications. In this study, a colorimetric method for detecting mercury using silver nanoparticles was developed. The reduction of Ag+ to AgNP was initiated using sunlight with coffee pulp aqueous extract as a reducing agent. The UV-Vis spectrum of the as-prepared AgNP solution shows a maximum absorption peak at 433 nm due to the metal’s localized surface plasmon resonance (LSPR). The SEM analysis of the dried sample shows an aggregate of AgNPs with spherical morphology with diameters less than 100 nm. The dynamic light scattering distribution curve shows a bimodal peak with a mean hydrodynamic radius of 12.73 nm and 145 nm, respectively. The large hydrodynamic radius of more than 100 nm may be attributed to the presence of AgNP aggregates in the solution. The synthesized AgNP was shown to selectively detect Hg2+ ions in solution colorimetrically. A linear calibration curve was obtained for the Hg2+ solution between 0.04 mM and 0.2 mM with R2 equal to 0.9934. This proposed method can potentially be used in the analysis of actual water samples.