Silver Probe Research Articles

Colorimetric Silver Ion Detection Based on Silver Metallization of Gold Nanorods

AbstractDespite the use of silver in various industries, this heavy metal can pose serious risks to living organisms and the environment. Therefore, the development of simple measurement strategies for detection of silver ions (Ag+) with high sensitivity is of great importance. In this research, gold nanorods (AuNRs) have been used as indicator element in colorimetric sensor, which provides the possibility of facile and visual detection of silver by forming gold@silver core‐shell nanostructures (Au@Ag NRs). The basis of this sensor is the metallization of silver on AuNRs through ascorbic acid (AA) as a reducing agent, which forms Au@Ag NRs. During this mechanism, Ag+ is converted to silver atom (Ago) in the presence of AA and the surface of AuNRs is coated by inducing metallization. Any changes in composition and dimensions of AuNRs will cause color changes in the detection solution and subsequently spectral changes. The obtained results showed a good correlation between silver concentration and probe response (λo–λ) in the range of 2.5 to 30.0 μmol L−1 with a detection limit of 1.3 μmol L−1. In addition, the evaluation of the sensor in water and soil samples showed that it has acceptable accuracy in detecting silver ions in real conditions.

Tuning the Probe-Bilayer Architecture of Silver Nanoneedle-based Ion Channel Probes.

Ion channel probes, as one of the ion channel platforms, provide an appealing opportunity to perform localized detection with a high precision level. These probes come basically in two classes: glass and metal. While the glass-based probes showed the potential to be employed for molecular sensing and chemical imaging, these probes still suffer from limited resolution and lack of control over protein insertion. On the other hand, metal-based nanoneedle probes (gold and silver) have been recently developed to allow reducing probe dimensions to the nanoscale geometry. More specifically, silver probes are preferable owing to their ability to mitigate the channel current decay observed with gold probes and provide a stable DC channel current. However, there are still some challenges related to the probe design and bilayer curvature that render such probes insensitive to small changes in the tip-substrate distance. Herein, we introduce two main pathways to control the probe-bilayer architecture; the first is by altering the probe shape and geometry during the fabrication process of silver probes. The second pathway is by altering the surface characteristics of the silver probe via an electrophoretic deposition process. Our findings reveal that varying the electrochemical etching parameters results in different probe geometries and producing sharper tips with a 2-fold diameter reduction. In addition, the electrophoretic deposition of a cathodic paint on the silver nanoneedle surface led to a miniaturized exposed silver tip that enables the formation of a confined bilayer. We further investigated the characteristics of bilayers supported on both the sharper nanoneedles and the HSR-coated silver probes produced by controlling the etching conditions and electrodeposition process, respectively. We believe this work paves the way to rationally design silver nanoneedle ion channel probes, which are well suited for localized molecular sensing and chemical imaging.

A selective colorimetric and efficient removal strategy for mercury(II) in aquatic systems using mesoporous Fe3O4-loaded silver probes.

Mesoporous Fe3O4-loaded silver nanocomposites (Fe3O4@Ag) were simply fabricated as bi-functional nanozymes for the catalysis-based detection and removal of Hg2+ ions. It was found that the as-prepared magnetic Fe3O4@Ag could display peroxidase-like catalysis activity that could be rationally enhanced in the presence of Hg2+ ions. To our surprise, the shell of the Ag element may decrease the catalysis of the Fe3O4 to some degree. However, the Ag particles could serve as the probes for specifically recognizing Hg2+ ions and trigger increased catalysis through the formation of Ag-Hg alloys, with a decreased signal background. A high-throughput colorimetric analytical method was thereby developed based on the Fe3O4@Ag catalysis for probing Hg2+ ions in the muscles of fish by using 96-well plates, at linear Hg2+ concentrations ranging from 0.010 to 2.5 mg kg-1. Moreover, the developed colorimetric analytical method was applied to evaluate Hg2+ levels in muscle samples of different kinds of fish. Unexpectedly, an obvious difference of Hg2+ levels in muscles of four kinds of fish was discovered, with the order of snakehead (Ophicephalus argus) > largemouth bass (Micropterus salmoides) > crucian carp (Carassius auratus) > silver carp (Hypophthalmichthys molitrix), where the carnivorous fish showed higher Hg2+ levels than the omnivorous or plant-based ones. Moreover, the as-fabricated Fe3O4@Ag adsorbents with their large specific surface area and high environmental robustness could exhibit efficient Hg2+ adsorption with capacities of up to 397.60 mg g-1. A removal efficiency of 99.40% can also be expected for Hg2+ ions from wastewater, with the magnet-aided recycling of Fe3O4@Ag adsorbents. Such an Fe3O4@Ag-based colorimetric analysis and removal strategy for Hg2+ ions should find wide applications in the fields of aquatic food safety, environmental monitoring, and clinical diagnostics of Hg-poisoning diseases.

Maintaining Single-Channel Recordings on a Silver Nanoneedle through Probe Design and Feedback Tip Positioning Control.

Ion channel proteins showed great promise in the field of nanopore sensing and molecular flux imaging applications due to the atomic-level precision of the pore size and a high signal-to-noise ratio. More specifically, ion channel probes, where the protein channels are integrated at the end of a solid probe, can achieve highly localized detection. Metal probe materials such as gold and silver have been developed to support lipid bilayers and enable the use of smaller probes, or nanoneedles, compared to more traditional glass micropipette ion channel probes. Silver probes are preferable because they support sustained DC stable channel current due to the AgCl layer formed around the tip during the fabrication process. However, one of the current challenges in ion channel measurements is maintaining a single-channel recording. Multiple protein insertions complicate data analysis and destabilize the bilayer. Herein, we combine the promising probe material (Ag/AgCl) with an approach based on current feedback-controlled tip positioning to maintain long-term single-channel recordings for up to 3 h. We develop a hybrid positioning control system, where the channel current is used as feedback to control the vertical movement of the silver tip and, subsequently, control the number of protein channels inserted in the lipid membrane. Our findings reveal that the area of the lipid bilayer decreases with moving the silver tip up (i.e., decreasing the displacement in the z-direction). By reducing the bilayer area around the fine silver tip, we minimize the probability of multiple insertions and remove unwanted proteins. In addition, we characterize the effect of lipid properties such as fluidity on the lipid membrane area. We believe that the use of silver nanoneedles, which enables DC stable channel current, coupled with the developed tip displacement mechanism will offer more opportunities to employ these probes for chemical imaging and mapping different surfaces.

Activity Measurement of Iodine Fission Products in 2LiF-BeF2 Salt and Its Application in Redox Potential Surveillance for a Thorium Molten Salt Reactor.

The activities of 131I, 132I, 133I, and 135I produced by neutron-induced fission of 235U in 2LiF-BeF2 (FLiBe) eutectic salt and their dependence on the redox potential were studied. The dependence observed experimentally suggested that the activity ratio for 131I to 132I could be used as an indicator of the redox potential for FLiBe salt. Relying on the selective adsorption of iodine ions on the activated silver probe by ion exchange, a novel method for activity distribution measurement of the iodine isotopes in FLiBe salt was founded. The method is simple, fast, and easy to operate and would be suitable particularly to in situ monitor the redox potential of a thorium molten salt reactor, where the redox potential should keep at a high level to avoid possible safety risk induced by 233Pa deposition in the reactor.

SERS-Based Immunoassay Enhanced with Silver Probe for Selective Separation and Detection of Alzheimer's Disease Biomarkers.

PurposeDeveloping a sensitive SERS-based method to quantitatively detect serum biomarkers (Aβ1-42 and P-Tau-181) for the early diagnosis of Alzheimer’s disease (AD).MethodsIn this study, a novel SERS-based sandwich immunoassay, which consists of tannin-capped silver nanoparticles and magnetic graphene oxide (Fe3O4@GOs), was developed. We firstly applied this method for the detection of protein standards in buffer solution, obtaining the regression equation. Then, its potential value on real serum samples of AD was further explored.ResultsThe detection linear range of Aβ1-42 and P-Tau-181 protein standards were observed to range from 100 pg mL−1 to 10 fg mL−1, 100 pg mL−1 to 1 fg mL−1 respectively. We finally explored clinical application of the proposed method in 63 serum samples. As a result, P-tau-181 differentiated AD from non-AD dementia patients (AUC = 0.770), with a more favored ROC than Aβ1-42 (AUC = 0.383).ConclusionThe developed SERS-based immunoassay is successfully applied to the determination of Aβ1-42 and P-Tau-181 in human serum specimens, which provides a promising tool for the early diagnosis of AD.

New Evidences which Support Existence of the Forced Heat Exchange Phenomenon

In the paper the forced heat exchange phenomenon is validated based on experimental data shown by different authors in different countries and published in respected scientific journals. Software IQLab and regular thermal condition theory were used for solving inverse problems. The data of silver and copper spherical probes quenching in electrolytes were used. As in previous publication, it was established in the paper that heat transfer coefficients (HTCs) increase versus time during quenching of silver and copper probes in electrolytes. As noted early, all of this contradicts the theory of transient nucleate boiling processes. The problem is solved by periodical replacement of film boiling by shock boiling with the high frequency that takes place during quenching. The new idea can be used in practice for designing new and original quenching technology to save materials, increase service life of machine components and also provide an environmentally friendly solution. The importance of new technologies is widely discussed in the paper.

Evaporation-induced self-assembly of silver nanospheres and gold nanorods on a super-hydrophobic substrate for SERS applications

Surface-enhanced Raman scattering (SERS) has drawn attention for broad applications. We successfully fabricated highly effective SERS structures via evaporation-induced self-assembly of blend nanoparticles containing sliver nanospheres (Ag NSs) and gold nanorods (Au NRs) on a super-hydrophobic (SH) substrate. On the SH substrate, the droplets of the mixed aqueous solution of silver nanospheres (Ag NSs), gold nanorods (Au NRs), and probe molecules can preserve their spherical shape during the evaporation process, and the probe molecules (R6G) are confined into extremely small areas after solvent removal due to hydrophobicity-enhanced concentration effects. The Raman enhancement effect of the blend nanoparticles with 40 vol% Ag NSs is far higher than that of the other samples. The structure of the aggregated Ag NSs on the film-like Au NRs greatly enhances the SERS effect of Ag NSs, which is optimal for the blend system with 40 vol% Ag NSs. The SERS structure also displays excellent signal reproducibility (RSD < 10%) and low detection limits (0.5 nM). Thus, this work offers a simple and efficient strategy to fabricate a highly effective SERS structure with broad applications in environmental science, analytical chemistry, etc.

Analysis of CMOS Extended-Gate Field-Effect Transistor With On-Chip Window Based on Uricase/RuO2 Sensing Film

In this study, the extended-gate field-effect transistor (EGFET) with an on-chip sensing window under the TSMC 0.18μm 1P6M (one poly and six metals) CMOS process technology was fabricated as a biosensor. The sensing window was composed of six metal layers and functionalized with the ruthenium dioxide (RuO2) thin film and uricase for uric acid detection. The RuO2 thin film was deposited on the top metal layer of the sensing window using the radio frequency (RF) sputtering system. The silver probe was employed as a reference electrode to provide a voltage to the test solution with a micro-volume of 0.5 μL. The properties of the EGFET for uric acid detection were investigated through the semiconductor parameter analyzer. The EGFET had a voltage and the current sensitivity of 8.63 mV/(mg/dL) and 0.17 (μA)1/2/(mg/dL), respectively. The device worked with a supply voltage lower than 1.8V. Based on the results, the fabrication of the miniaturized biosensor device was a success. Due to its advantages such as the use of low voltage and its simple fabrication process, it could help realize the development of a wearable biosensor.

Unusual Phenomenon of Forced Heat Exchange Taking Place during Quenching Silver Probe in Cold Electrolyte

It is shown in the paper that forced heat transfer exchange during quenching silver probes in cold electrolytes is explained by periodical replacement of short film boiling process by shock boiling. The frequency of such process is very high that increases cardinally heat transfer exchange. This phenomenon doesn’t fit contemporary theory concerning nucleate boiling processes and needs further careful investigations. The reason for existing periodical process is a double boundary electrical layer where are acting increased electrical forces during quenching in electrolytes. In contrast of quenching steel, silver generates higher heat flux density during quenching; however full film boiling cannot be developed due to presence of high electrical forces in a double electrical layer caused by increased electrical conductivity of silver. The discovered phenomenon can be used in the practice in the future after its careful investigation to force heat transfer exchange by external electrical forces to eliminate any film boiling process during batch quenching.

Methods to fabricate and recycle plasmonic probes for ultrahigh vacuum scanning tunneling microscopy‐based tip‐enhanced Raman spectroscopy

AbstractScanning tunneling microscopy‐based tip‐enhanced Raman spectroscopy (TERS) is a powerful analytical technique for surface characterization, providing both topological and chemical information with sub‐nm spatial resolution, well below the diffraction limit of light. In order to take advantage of plasmonic activity, it is necessary to use silver (Ag) probes due to their plasmonic range in the visible region. However, the Ag probe fabrication process remains challenging and is not yet standardized in practice, leading to inconsistent enhancements even for two similar types of tips prepared consecutively. In this work, we demonstrate an alternative way to reuse and recycle a plasmonic tip for distinct molecular systems inside an ultrahigh vacuum (UHV). We provide evidence of the ability to recycle tips without compromising the TERS experimental results. A long‐term preservation (&gt;2 months) of plasmonically active probes inside UHV is demonstrated.

Probe-induced resistive switching memory based on organic-inorganic lead halide perovskite materials

Abstract In this paper we demonstrate a resistive storage device with CH3NH3PbI3−xClx/FTO structure which stores information in two levels of resistance states induced by electrical probe excitation. The perovskite layer is formed on a FTO coated glass by a single-step solution spin coating method in the air. We study the effects of different probe materials on the memory cell behavior including silver epoxy, copper and graphite. The device with silver probe shows a bipolar resistive switching behavior with 106 on/off resistance ratio in the forming process. The fabricated probe-based memory cell shows a minimum endurance of 104 cycles and a minimum retention time of 2 × 103 s. These experimental results confirm that organic-inorganic lead halide perovskite (OILHP) materials are a potential candidate to be used as a storage medium for probe based storage memories. This study provides a better understanding of resistive switching mechanism in organic-inorganic lead halide perovskites thin films that can be useful for understanding of the future probe-based beyond Moore's law memory devices.

Clinical Study to Evaluate Efficacy of Agnikarma (Locally) and Ashwagandha Ghanavati (Internally ) in the Management of Manyagata Vata w.s.r Cervical Spondylosis

Cervical Spondylosis is described as degenerative condition of the cervical spine. It is found most commonly in individuals aged 40-60 years, leads to symptoms like pain, restricted movement stiffness and tingling-numbness at neck region. In Ayurveda, it can be correlated with Manyagata Vata which is managed with various Panchkarma such as Basti, Raktamokshan ,Nasya, Agnikarma etc. Adjuvant to Vata-Kaphashamak and Asthi Dhatuvardhan palliative drugs. The Agnikarma though effective tool for pain management has varied results due to fluctuation in temperature from intermittent heating of shalaka (metallic probe).To overcome this, conventional Agnikarma device is modified with temperature controlling unit (produces constant temperature) and Raupya Shalaka (specially designed silver probe having micro rods)which helped in minimizing the pain as heat is delivered once at desire site. Adjuvantly, Ashwagandha Ghanavati (internally) was given, which acts as Rasayan to Asthi Dhatu (rejuvenating bone tissue). The combination treatment showed statistically significant results in relieving symptoms such as pain, stiffness, flexion, extension, lateral movement of neck and tingling numbness. Out of 50 patients, 92% patients got complete relief from cervical pain, 98 % patients got relieved from Stiffness whereas restricted movements of neck and tingling numbness present was relieved in 96% patients. The device helps in keeping the temperature constant (60o C) throughout the procedure &amp; desired heat is delivered by keeping the probe in contact for 10seconds at affected site. In this study,Agnikarma with modified device and AshwagandhaGhanavatirevealed their efficacy in relieving symptoms of Manyagatavata. Further, the Agnikarm with modified deviceproved user friendly, safe (without iatrogenic effects) and made procedure swift.&#x0D;

Comparison and Evaluation of Silver Probe Preparation Techniques for Tip-Enhanced Raman Spectroscopy

In this work, the different procedures for the fabrication of Ag probes for tip-enhanced Raman spectroscopy (TERS) in a top illumination/detection setup are proposed and tested. We focus on technologically simple methods allowing Si tips coated with plasmonic silver nanostructures and bulk metal Ag tips with good shape reproducibility to be produced for atomic force microscopy (AFM) feedback setup. The preparation of Ag TERS probes was based on chemical deposition and vacuum sputtering of Ag on the tips of commercially available Si cantilevers. A straightforward technique for the fabrication of bulk metal Ag probes by the electrochemical etching of Ag microwires was also proposed. Chemically coated, sputtered, and electrochemically etched TERS tips were characterized by scanning electron microscopy (SEM). The produced tips were tested for TERS measurements using graphene oxide (GO) as the target analyte in a top illumination setup. A comparative analysis of enhancement factors (EF) for the different types of tips (probes) is presented in this work.

Apertureless Near-Field Scanning Probes Based on Graphene Plasmonics

We present a novel approach in designing high-throughput high-resolution apertureless near-field scanning probes with enhanced nanofocusing based on graphene plasmonics. Extremely localized plasmons on graphene are mingled with nanofocusing of surface plasmon polaritons to confine and steer the plasmon waves into the apex of a near-field scanning optical microscopy tip. The Fermi level, localized emission sites on graphene, and the angle of excitation play a critical role in exciting graphene surface plasmons on the lateral walls of the designed conical probes. The optimized probes feature full-width at half-maximum (FWHM) around 25 nm, which is at least two times smaller than conventional metallic plasmonic tips. The near-field electromagnetic properties of the designed probes are characterized in detail and compared to the conventional single-aperture and typical apertureless metallic plasmonic (silver and gold) probes. Over three orders of magnitude electric field enhancement compared to metallic probes on SiO 2 substrate has been achieved.

Novel Applications of Micro/Nanostructured Volcanic Ash for Water Purification and Surface-Enhanced Raman Spectroscopy

ABSTRACTVolcanic ash is frequently referenced as natural particles, yet few applications for wastewater purification and surface-enhanced Raman scattering (SERS) have been reported. Here, a unique micro/nanostructured nozzle-shaped volcanic ash was characterized. The natural volcanic ash had an ordered porous structure with an average diameter of 20 µm. Macropores with 200-nm pore size and 3–5-nm mesopores were homogeneously distributed on the surface of the volcanic ash. The volcanic ash provided an efficient water purification for simulated dye and livestock wastewater. The volcanic ash/silver nanoparticle hybrid also exhibited strong SERS. Moreover, the differing adsorption sequence of silver nanoparticles and probes on the surface of volcanic ash created distinctive enhancements. The micro/nanostructured volcanic ash was shown to be a promising water purifying agent and platform for SERS in environmental monitoring.

Darkfield microspectroscopy of nanostructures on silver tip-enhanced Raman scattering probes

We report an evaluation method employing darkfield microspectroscopy for silver probes used in tip-enhanced Raman scattering (TERS). By adjusting the darkfield illumination, the diffracted light from the probe outlines disappears and the diffracted light from the surface nanostructures and tips of the probes appears as colorful spots. Scanning electron microscopy reveals that the spectral variations in these spots reflect the shapes of the surface nanostructures. The tip curvatures correlate to the spectral maxima of their spots. Temporal color changes in the spots indicate the deterioration due to the oxidation of the silver surfaces. These results show that the proposed method is useful for in situ evaluation of plasmonic properties of TERS probes.

Development of a New Method for Testing Cooling Power Using a Silver Probe and a New Reference Quenching Fluid

Abstract Cooling curve tests have been the most useful means of testing the cooling power of liquid quenchants such as oils and polymer quenchants. The JIS method for evaluating the cooling power of oils (JIS K 2242) was established in 1965. A cylindrical silver probe was adopted for the JIS method because of the following advantages: measurement results will not be affected by phase transformations or surface oxidation, and the probe has high sensitivity and excellent reproducibility. In the JIS method, 80°C di-2-ethylhexyl phthalate (DOP) is used as a reference quenching fluid for initial calibration and for periodic calibration checks of the probe and the overall system. However, it has been pointed out that DOP may be an environmental pollutant. Therefore, the JIS Technical Committee on heat treating fluids looked at new reference quenching fluids that could replace DOP. Through a series of round-robin tests, mineral oil having a flash point within a prescribed range and a viscosity of ISO VG22 was selected as the new reference quenching fluid. This mineral oil is specified as the reference quenching fluid in the revised standard for heat treating fluids, JIS K 2242:2012.

Fluorescent chemodosimeter based on NHC complex for selective recognition of cyanide ions in aqueous medium

Novel N-heterocyclic carbene based mono and di-nuclear silver probes having the anthracene chromophore act as chemodosimeters for selective and sensitive detection of cyanide ions in the aqueous medium and signal the event through visible enhancement in fluorescence intensity.

A new mode to light up an adjacent DNA-scaffolded silver probe pair and its application for specific DNA detection.

By fluorescence enhancement of a proximity-dependent DNA-scaffolded silver nanocluster probe pair and exonuclease III-mediated signal amplification, we present a new fluorescence turn-on mode and its application for specific DNA detection.