Silver Nanoislands Research Articles

Stable random laser of perovskite quantum dots based on SiO2-QDs-SiO2 composite nanostructure

In recent years, metal halide perovskite has gradually become a hotspot in the field of optoelectronics. However, the inherent instability of CsPbX3 quantum dots (QDs) seriously affects the amplified spontaneous emission (ASE) or lasing performance. Herein, the highly stable CsPbBr3 random laser is realized in SiO2-QDs-SiO2 (SQS) composite nanostructure doped with Ag nanoislands. The strong scattering generated by SQS composite nanostructure and the localized surface plasmon resonance (LSPR) of metal silver nanoislands provide optical feedback for the formation of random laser. Then a coherent random laser with low threshold (∼2.2 mJ/cm2) is obtained. SiO2 microspheres anchor QDs to avoid photoinduced regeneration and fluorescence quenching caused by QDs clusters. The inner QDs of SQS are effectively protected from water erosion, thus resulting that the samples have higher water resistance. The luminescence intensity still maintains 70 % of the original intensity after 40 days with the addition of pure water. Our research provides an effective method for improving the water stability of perovskite QDs. The highly stable random laser based on perovskite quantum dot film has a wide application prospect in integrated optoelectronics, display imaging and sensing measurement.

Comparing silver and gold nanoislands’ surface plasmon resonance for bisacodyl and its metabolite quantification in human plasma

Gold and silver nanoparticles have witnessed increased scientific interest due to their colourful colloidal solutions and exceptional applications. Comparing the localized surface plasmon resonance (LSPR) of gold and silver nanoparticles is crucial for understanding and optimizing their optical properties. This comparison informs the design of highly sensitive plasmonic sensors, aids in selecting the most suitable nanoparticles for applications like surface-enhanced infrared spectroscopy (SEIRA) and biomedical imaging, and guides the choice between gold and silver nanoparticles based on their catalytic and photothermal properties. Ultimately, the study of LSPR facilitates the tailored use of these nanoparticles in diverse scientific and technological applications. Two SEIRA methods combined with partial least squares regression (PLSR) chemometric tools were developed. This development is based on the synthesis of homogeneous, high-dense deposited metal nanoparticle islands over the surface of glass substrates to be used as lab-on-chip SEIRA sensors for the determination of bisacodyl (BIS) and its active metabolite in plasma. SEM micrographs revealed the formation of metallic islands of colloidal citrate-capped gold and silver nanoparticles of average sizes of 29.7 and 15 nm, respectively. BIS and its active metabolite were placed on the nanoparticles’ coated substrates to be directly measured, then PLSR chemometric modelling was used for the quantitative determinations. Plasmonic citrate-capped gold nanoparticle substrates showed better performance than those prepared using citrate-capped silver nanoparticles in terms of preparation time, enhancement factor, PLSR model prediction, and quantitative results. This study offers a way to determine BIS and its active metabolite in the concentration range 15–240 ng/mL in human plasma using inexpensive disposable glass-coated substrates that can be prepared in 1 h to get results in seconds with good recovery between 98.77 and 100.64%. The sensors provided fast, simple, selective, molecular-specific and inexpensive procedures to determine molecules in their pure form and biological fluid.

Low-temperature iodinated plasmonically tuned Ag@AgI core-shell nanostructured thin films for highly specific ascorbic acid SERS detection at ultra-low concentrations

A simple low temperature iodination route was developed to controllably iodinate silver nanoislands film (Ag) into silver@silver iodide core-shell nanoparticles film (Ag@AgI) as a chemically stable, near infrared active surface enhanced Raman scattering (SERS) substrate. The localised surface plasmon resonance (LSPR) of the core-shell film exhibits a huge red-shift of 100 nm. The formation of Ag core and a complete ultra-thin AgI shell layer on top of the core is confirmed by transmission electron microscope. Selected area electron diffraction reveals the amorphous nature of AgI shell layer. These results are further substantiated by Raman and x-ray diffraction measurements. The enhancement factor of Ag@AgI film estimated with methylene blue is 5 × 106, an order of magnitude higher compared to that of Ag film. It demonstrated excellent chemical stability and unwavering SERS performance for two months since fabrication. The Ag@AgI film fielded as a label-free SERS substrate exhibited a lowest limit-of-detection of 1 × 10−12 M for ascorbic acid and a linear detection range of 1 × 10−6 to 1 × 10−12 M. The ascorbic acid selective signal enhancement of Ag@AgI film at low concentration region offers a practical sample dilution strategy to suppress interference from non-target molecules in biofluids.

Thermal-effect dominated plasmonic catalysis on silver nanoislands.

Plasmonic metal nanostructures with the intrinsic property of localized surface plasmon resonance can effectively promote energy conversion in many applications such as photocatalysis, photothermal therapy, seawater desalinization, etc. It is known that not only are plasmonically excited hot electrons generated from metal nanostructures under light irradiation, which can effectively trigger chemical reactions, but also plasmonically induced heating simultaneously occurs. Although plasmonic catalysis has been widely explored in recent years, the underlying mechanisms for distinguishing the contribution of hot electrons from thermal effects are not fully understood. Here, a simple and efficient self-assembly system using silver nanoislands as plasmonic substrates is designed to investigate the photo-induced azo coupling reaction of nitro- and amino-groups at various temperatures. In the experiments, surface-enhanced Raman spectroscopy is employed to monitor the time and temperature dependence of plasmon-induced catalytic reactions. It was found that a combination of hot electrons and thermal effects contribute to the reactivity. The thermal effects play the dominant role in the plasmon-induced azo coupling reaction of nitro-groups, which suggests that the localized temperature must be considered in the development of photonic applications based on plasmonic nanomaterials.

Ag nanoisland functionalized hollow carbon nanofibers as a non-invasive, label-free SERS salivary biosensor platform for salivary nitrite detection for pre-diagnosis of oral cancer.

A highly selective, label-free, surface-enhanced Raman spectroscopy (SERS) based sensor platform employing hollow carbon nanofibers functionalized with silver nanoparticles (Ag@HCNFs) has been developed to monitor anomalous concentrations of potential biomarkers, such as salivary nitrite facilitating pre-diagnosis of oral cancer. Co-axial electrospinning was used for the fabrication of the nanofibrous Ag@HCNFs followed by thermal treatment of PAN/PVP core-shell nanofibers and chemical reduction of silver nanoislands. The developed plasmonic Ag@HCNFs was structurally and morphologically characterized using X-Ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy, which clearly demonstrated the successful anchoring of silver nanoparticles on hollow carbon nanofibers. The properties of Ag@HCNFs showed significant SERS enhancement of the order of 107 with a detection limit of 10-11 M with R6G, demonstrating its efficacy to investigate real-time salivary samples, particularly towards the detection of salivary nitrite within the clinically relevant range (50 μM-300 μM) towards the pre-diagnosis of oral cancer. The proposed SERS-based salivary platform has the potential to be used as a low-cost, non-invasive pre-diagnostic tool for early diagnosis and mass screening of oral cancer.

Nanoisland SERS-Substrates for Specific Detection and Quantification of Influenza A Virus.

Surface-enhanced Raman spectroscopy (SERS)-based aptasensors for virus determination have attracted a lot of interest recently. This approach provides both specificity due to an aptamer component and a low limit of detection due to signal enhancement by a SERS substrate. The most successful SERS-based aptasensors have a limit of detection (LoD) of 10-100 viral particles per mL (VP/mL) that is advantageous compared to polymerase chain reactions. These characteristics of the sensors require the use of complex substrates. Previously, we described silver nanoisland SERS-substrate with a reproducible and uniform surface, demonstrating high potency for industrial production and a suboptimal LoD of 4 × 105 VP/mL of influenza A virus. Here we describe a study of the sensor morphology, revealing an unexpected mechanism of signal enhancement through the distortion of the nanoisland layer. A novel modification of the aptasensor was proposed with chromium-enhanced adhesion of silver nanoparticles to the surface as well as elimination of the buffer-dependent distortion-triggering steps. As a result, the LoD of the Influenza A virus was decreased to 190 VP/mL, placing the nanoisland SERS-based aptasensors in the rank of the most powerful sensors for viral detection.

Flexible silver ring SERS substrate array fabrication by vortex evaporation method and its application for high sensitive detection of sulfonamides residues in water

Flexible surface-enhanced Raman scattering (SERS) substrates have driven much attention in Raman detection of environmental pollutants due to their unique advantage of sensitivity, low-cost and fast sampling. However, it is still a high challenge for fabricating flexible SERS substrate with high reproducibility and sensitivity. In this study, we developed a novel silver nanoparticle assembly method based on vortex evaporation method to batch assemble multiple silver ring (SR) SERS substrate array on a parafilm. The flexible SR SERS substrates were uniformly covered with active silver nano-islands, which significantly improved the Raman signal intensity of the targets by 126 folds and showed 5 times Raman enhancement compared with the common SERS substrate by direct evaporation method, and also represented the unique bending response properties of flexible substrate. The Raman detection for sulfonamide residues in water with SR SERS substrate represented high sensitivity, which limits of detection for Sulfapyridine and Sulfacloropyridazine were 9.46 and 9.3 × 10−8 mol/L, respectively. The quantitative relationships were obtained in wide linear range of 4 orders with good accuracy and stability. The flexible SR SERS substrate array can be large-scale prepared with good repeatability, stability, and low-cost, which has promising applications for trace contaminants detection in water environment.

Rapid SERS Detection of Botulinum Neurotoxin Type A.

Surface-enhanced Raman scattering (SERS) is a powerful technique for decoding of 2-5-component mixes of analytes. Low concentrations of analytes and complex biological media are usually non-decodable with SERS. Recognition molecules, such as antibodies and aptamers, provide an opportunity for a specific binding of ultra-low contents of analyte dissolved in complex biological media. Different approaches have been proposed to provide changes in SERS intensity of an external label upon binding of ultra-low contents of the analytes. In this paper, we propose a SERS-based sensor for the rapid and sensitive detection of botulinum toxin type A. The silver nanoisland SERS substrate was functionalized using an aptamer conjugated with a Raman label. The binding of the target affects the orientation of the label, providing changes in an analytical signal. This trick allowed detecting botulinum toxin type A in a one-stage manner without additional staining with a monotonous dose dependence and a limit of detection of 2.4 ng/mL. The proposed sensor architecture is consistent with the multiarray detection systems for multiplex analyses.

Rapid and sensitive detection of nucleoprotein SARS-CoV-2 virus: SERS vs ELISA

The recent pandemic calls for a rapid and cheap diagnosis of COVID-19 to impede the virus from spreading. The main clinically used techniques for diagnostics of virus diseases are PCR and ELISA, whereas it is well known that optical methods such as FTIR, Raman spectroscopy, and SERS are extremely precise, perspective, and also rapid. Here, we provide a comparative study of SERS and ELISA methods for the detection of SARS-CoV-2 nucleoproteins revealing and discussing the advantages and disadvantages of both these methods. We show that the standard ELISA method demonstrates the detection limit of about 50–100 pg/ml vs 1 pg/ml demonstrated by SERS with using silver nanoisland substrates. The detection time for ELISA is about 2 h being mainly defined by the requirements of incubation and washing, while SERS measurements take several seconds. We show that the SERS spectra allow distinguishing the features of antigens, antibodies, and even the features showing the bonding between them. We believe that the obtained results and the comparative analysis will be useful for developing cheap and rapid point-of-care diagnostics.

A novel approach for rapid and sensitive detection of Zika virus utilizing silver nanoislands as SERS platform

To control the spread of the disease, the Zika virus (ZIKV), a flavivirus infection spread by mosquitoes and common in across the world, needs to be accurately and promptly diagnosed. This endeavour gets challenging when early-stage illnesses have low viral loads. As a result, we have created a biosensor based on surface-enhanced Raman scattering (SERS) for the quick, accurate, and timely diagnosis of the Zika virus. In this study, a glass coverslip was coated with silver nanoislands, which were then utilized as the surface for creating the sensing platform. Silver nanoislands exhibit strong plasmonic activity and good conductive characteristics. It enhances the Raman signals as a result and gives the SERS platform an appropriate surface. The created platform has been applied to Zika virus detection. With a limit of detection (LOD) of 0.11 ng/mL, the constructed sensor exhibits a linear range from 5 ng/mL to 1000 ng/mL. Hence, even at the nanogram scale, this technique may be a major improvement over clinical diagnosis approaches for making proper, precise, and accurate Zika virus detection.

A fluorescent sensor based on the cascade signal amplification strategy for ultra-sensitive detection of Cu2.

Copper is an essential element in the human body, participating in various physiological activities in the bodies of organisms. However, an excessive load of Cu2+ is associated with several neurodegenerative diseases and prion diseases, also identified as a symptom of Wilson's disease (WD). A straightforward, rapid, sensitive, and specific copper sensor is highly required but remains a challenge. In this study, guided by the simulation, we developed a chemical sensor using a cascade signal amplification strategy based on the Cu-catalyzed click reaction, combined with a fluorescence-enhanced substrate with gold nanorods coupled with silver nanoislands. The sensor can selectively detect Cu2+ as low as 3.87 nM within 10 min. We have demonstrated that this method can be directly employed for WD diagnosis in urine samples. In addition, using antibiotic susceptibility testing (AST) as an example, we verify whether this assay can be adapted to other targets where Cu is designed as an indirect indicator.

A Novel Approach for Rapid and Sensitive Detection of Zika Virus Utilizing Silver Nanoislands as SERS Platform

A Novel Approach for Rapid and Sensitive Detection of Zika Virus Utilizing Silver Nanoislands as SERS Platform

Remote plasmonic-enhanced Raman spectroscopy with the plasmon-molecule coupling in distance over 100 nm

We propose remote plasmonic-enhanced Raman scattering (RPERS) spectroscopy for molecular sensing and imaging applications. RPERS requires no contact between analyte molecules and metallic nanostructures, which overcomes the limitations of surface-enhanced Raman scattering (SERS). We constructed RPERS substrates consisting of silver nanoislands and columnar silica structures, which demonstrated a 2×107 enhancement in Raman scattering for Rhodamine 6G molecules, even when the metal nanostructures and analyte molecules were over 100 nm apart. The RPERS substrate also exhibited improved reproducibility (<15% RSD), long-term stability (>1 month), and sensitivity (>10 times) compared to conventional SERS substrates. We also confirmed the feasibility of RPERS for biophotonic analysis, i.e., enhancing Raman histological imaging of oesophagus tissues with oesophageal adventitia of a Wistar rat attached atop the columnar silica structure layer. Our demonstration is a promising advancement in the field of enhanced spectroscopy using plasmon and offers a solution to the challenges faced by conventional SERS spectroscopy. It has the potential to pave the way for future developments in remote plasmonic-enhanced spectroscopy.

Flexible PDMS-Based SERS Substrates Replicated from Beetle Wings for Water Pollutant Detection

The flexible surface-enhanced Raman scattering (SERS) sensor, which has the bionic 3D nanoarray structure of a beetle-wing substrate (BWS), was successfully prepared by replicated technology and thermal evaporation. The bionic structure was replicated with polydimethylsiloxane (PDMS) and then silver (Ag) nanoisland thin films were deposited by thermal evaporation. The deposition times and thicknesses (25-40 nm) of the Ag thin films were manipulated to find the optimal SERS detection capability. The Ag nanoisland arrays on the surface of the bionic replicated PDMS were observed by scanning electron microscope (SEM), X-ray diffraction (XRD), and contact angle, which can generate strong and reproducible three-dimensional hotspots (3D hotspots) to enhance Raman signals. The water pollutant, rhodamine 6G (R6G), was used as a model molecule for SERS detection. The results show that 35 nm Ag deposited on a PDMS-BWS SERS substrate displays the strongest SERS intensity, which is 10 times higher than that of the pristine BWS with 35 nm Ag coating, due to the excellent 3D bionic structure. Our results demonstrate that bionic 3D SERS sensors have the potential to be applied in wearable devices and sensors to detect biomolecules and environmental pollutants, such as industrial wastewater, in the future.

Silica Nanospheres Coated Silver Islands as an Effective Opto-Plasmonic SERS Active Platform for Rapid and Sensitive Detection of Prostate Cancer Biomarkers.

The in vitro diagnostics of cancer are not represented well yet, but the need for early-stage detection is undeniable. In recent decades, surface-enhanced Raman spectroscopy (SERS) has emerged as an efficient, adaptable, and unique technique for the detection of cancer molecules in their early stages. Herein, we demonstrate an opto-plasmonic hybrid structure for sensitive detection of the prostate cancer biomarker sarcosine using silica nanospheres coated silver nano-islands as a facile and efficient SERS active substrate. The SERS active platform has been developed via thin (5-15 nm) deposition of silver islands using a simple and cost-effective Radio Frequency (RF) sputtering technique followed by the synthesis and decoration of silica nanospheres (~500 nm) synthesized via Stober's method. It is anticipated that the coupling of Whispering Gallery Modes and photonic nano-jets in SiO2 nanospheres induce Localized Surface Plasmon Resonance (LSPR) in Ag nano-islands, which is responsible for the SERS enhancement. The as-fabricated SERS active platform shows a linear response in the physiological range (10 nM to 100 μM) and an extremely low limit of detection (LOD) of 1.76 nM with a correlation coefficient of 0.98 and enhancement factor ~2 × 107. The findings suggest that our fabricated SERS platform could be potentially used for the rapid detection of bio-chemical traces with high sensitivity.

TiO2/Ag nanostructured coatings as recyclable platforms for surface-enhanced Raman scattering detection

The surface-enhanced Raman scattering (SERS) has become irreplaceable for the direct detection of organic chemicals and biomolecules. However, the SERS-active platforms need to meet certain requirements for routine use. Among them, the most important are low detection limit, spectra reproducibility, and the possibility of being re-used. In this study, we investigate and compare the SERS performance of Ag/TiO2 coatings with three different architectures - planar, tubular and nanoparticle-based – prepared by means of plasma-assisted techniques. In all three cases, the nanoislands, made of plasmonic Ag, enhance the SERS signal, while the TiO2 provides degradation of surface contaminants after UV irradiation. The latter relates to the natural photoactivity of titania, which enables the recycling of the substrates. As shown, nanopatterning of surfaces offers a good compromise between the high detection limit and re-cyclability of those nanostructured Ag/TiO2 coatings with larger active surface area; here, namely TiO2 nanoparticle films decorated with silver nanoislands behave promisingly. Such nanostructured Ag/TiO2 films allow not only the detection of methylene blue (MB) at concentrations down to 5 × 10−9 M, but also may be easily cleaned by UV radiation in a reasonable time scale.

One-step method to prepare coccinellaseptempunctate-like silver nanoparticles for high sensitivity SERS detection

The surface morphology of metal particles can be adjusted by the annealing process to enhance the activity of Raman substrate and achieve an ultra-low concentration detection limitation. In this study, a surface-enhanced Raman scattering (SERS) substrate of coccinellaseptempunctate-like silver nanospheres coated with a silver nanoisland structure (Ag NI@Ag NSs) was prepared using a simple annealing process. Numerous silver nanospheres were dispersed on the surface of the silver nanoislands, which exhibited a single crystal plane (111) orientation. The SERS substrate had an enhancement factor of 108 for Rhodamine B (Rh B) and was highly sensitive to phosphoethanolamine (PETA). The SERS response toward PETA showed excellent correlation during the range of 5 × 10−7 - 1 × 10−5 mol/L with the detection limitation as low as 5 × 10−7 mol/L, and the correlation coefficient is 0.9918. The simulated high-pressure test showed that the SERS response could be still observed at 1100 m sub ocean pressure even with a PETA concentration of 1 mM. The test results of selectivity, reproducibility, and accuracy indicated that the Ag NI@Ag NS sensor possessed potential applications in the deep-sea analytical and other related fields.

Identification of milk quality and adulteration by surface-enhanced infrared absorption spectroscopy coupled to artificial neural networks using citrate-capped silver nanoislands

Milk is one of the most important multicomponent superfoods owing to its rich macronutrient composition. It requires quality control at all the production stages from the farm to the finished products. A localized surface plasmon resonance optical sensor based on a citrate-capped silver nanoparticle (Cit-AgNP)–coated glass substrate was developed. The fabrication of such sensors involved a single-step synthesis of Cit-AgNPs followed by surface modification of glass slides to be coated with the nanoparticles. The scanning electron microscope micrographs demonstrated that the nanoparticles formed monolayer islands on glass slides. The developed surface-enhanced infrared absorption spectroscopy (SEIRA) sensor was coupled to artificial neural networking (ANN) for the qualitative differentiation between cow, camel, goat, buffalo, and infants’ formula powdered milk types. Moreover, it can be used for the quantitative determination of the main milk components such as fat, casein, urea, and lactose in each milk type. The qualitative results showed that the obtained FTIR spectra of cow and buffalo milk have high similarity, whereas camel milk resembled infant formula powdered milk. The most difference in FTIR characteristics was evidenced in the case of goat milk. The developed sensor adds several advantages over the traditional techniques of milk analysis using MilkoScan™ such as less generated waste, elimination of pre-treatment steps, minimal sample volume, low operation time, and on-site analysis.Graphical abstract

Raman Scattering Study of Amino Acids Adsorbed on a Silver Nanoisland Film.

We studied the surface-enhanced Raman spectra of amino acids D-alanine and DL-serine and their mixture on silver nanoisland films (SNF) immersed in phosphate-buffered saline (PBS) solution at millimolar amino acid concentrations. It is shown that the spectra from the amino acid solutions differ from the reference spectra for microcrystallites due to the electrostatic orientation of amino acid zwitterions by the metal nanoisland film. Moreover, non-additive peaks are observed in the spectrum of the mixture of amino acids adsorbed on SNF, which means that intermolecular interactions between adsorbed amino acids are very significant. The results indicate the need for a thorough analysis of the Raman spectra from amino acid solutions, particularly, in PBS, in the presence of a nanostructured silver surface, and may also be of interest for studying molecular properties and intermolecular interactions.

Thermally-Driven Micro-Walled Nano-Composite Microfluidic Platform for Controlled Localized Surface Plasmonic Detection of Bovine Growth Hormones

A novel method of integration of a silver-polydimethylsiloxane (PDMS) nanocomposite in a microfluidic channel for the realization of a lab-on-a-chip is reported in this work. By using a silver nitrate aqueous precursor solution, silver nanostructures are formed on, and under the surface of PDMS, by in situ reduction. The silver aggregates formed by reduction have a wide absorbance plasmon band in the UV–Visible range. Separated silver nano-islands, having narrow absorbance bands are formed by using the post-reduction annealing process. The plasmonic property of the silver nanostructures is used for the detection of bovine growth hormone. Subsequently, the nanocomposite was integrated into a specially fabricated micro-wall in the channel which is the actual sensing area in the microfluidic environment. The experiments confirmed that the nanocomposite can be integrated into the microfluidic device in order to enhance the detection sensitivity.