Real-time imaging reveal anisotropic dissolution behaviors of silver nanorods.

The morphology and size control of anisotropic nanocrystals are critical for tuning shape-dependent physicochemical properties. Although the anisotropic dissolution process is considered to be an effective means to precisely control the size and morphology of nanocrystals, the anisotropic dissolution mechanism remains poorly understood. Here, usingin situliquid cell transmission electron microscopy, we investigate the anisotropic etching dissolution behaviors of polyvinylpyrrolidone (PVP)-stabilized Ag nanorods in NaCl solution. Results show that etching dissolution occurs only in the longitudinal direction of the nanorod at low chloride concentration (0.2 mM), whereas at high chloride concentration (1 M), the lateral and longitudinal directions of the nanorods are dissolved. First-principles calculations demonstrate that PVP is selectively adsorbed on the {100} crystal plane of silver nanorods, making the tips of nanorods the only reaction sites in the anisotropic etching process. When the chemical potential difference of the Cl-concentration is higher than the diffusion barrier (0.196 eV) of Cl-in the PVP molecule, Cl-penetrates the PVP molecular layer of {100} facets on the side of the Ag nanorods. These findings provide an in-depth insight into the anisotropic etching mechanisms and lay foundations for the controlled preparation and rational design of nanostructures.

3D SERS Substrate of Z-Shaped Ag Nanorod Array for Thiabendazole Detection.

Ag nanoparticles sputtered on silicon wafer are used as masks for the fabrication of silicon columns by ion etching, which induces the growth of the inclined Ag nanorod by inclined Ag sputtering. V-shaped and Z-shaped Ag nanorods can be obtained by varying incline angles and deposition times. SERS detection and FDTD simulation are used to compare and investigate the enhanced electromagnetic coupling of incline nanorod arrays with different shapes in three-dimensional space, which indicates that Z-shaped nanorods show good SERS properties. The Z-shaped Ag nanorod array is used as a SERS substrate for the detection of thiabendazole with a concentration down to 10-11 M.

High-Performance Au@Ag Nanorods Substrate for SERS Detection of Malachite Green in Aquatic Products.

In order to improve the detection performance of surface-enhanced Raman scattering (SERS), a low-cost Au@Ag nanorods (Au@Ag NRs) substrate with a good SERS enhancement effect was developed and applied to the detection of malachite green (MG) in aquaculture water and crayfish. By comparing the SERS signal enhancement effect of five kinds of Au@Ag NRs substrates with different silver layer thickness on 4-mercaptobenzoic acid (4-MBA) solution, it was found that the substrate prepared with 100 µL AgNO3 had the smallest aspect ratio (3.27) and the thickest Ag layer (4.1 nm). However, it showed a good signal enhancement effect, and achieved a detection of 4-MBA as low as 1 × 10-11 M, which was 8.7 times higher than that of the AuNRs substrate. In addition, the Au@Ag NRs substrate developed in this study was used for SRES detection of MG in crayfish; its detection limit was 1.58 × 10-9 M. The developed Au@Ag NRs sensor had the advantages of stable SERS signal, uniform size and low cost, which provided a new tool for SERS signal enhancement and highly sensitive SERS detection method development.

Atomic layer deposition assisted fabrication of large-scale metal nanogaps for surface enhanced Raman scattering.

Metal nanogaps can confine electromagnetic field into extremely small volumes, exhibiting strong surface plasmon resonance effect. Therefore, metal nanogaps show great prospects in enhancing light-matter interaction. However, it is still challenging to fabricate large-scale (centimeter scale) nanogaps with precise control of gap size at nanoscale, limiting the practical applications of metal nanogaps. In this work, we proposed a facile and economic strategy to fabricate large-scale sub-10 nm Ag nanogaps by the combination of atomic layer deposition (ALD) and mechanical rolling. The plasmonic nanogaps can be formed in the compacted Ag film by the sacrificial Al2O3deposited via ALD. The size of nanogaps are determined by the twice thickness of Al2O3with nanometric control. Raman results show that SERS activity depends closely on the nanogap size, and 4 nm Ag nanogaps exhibit the best SERS activity. By combining with other porous metal substrates, various sub-10 nm metal nanogaps can be fabricated over large scale. Therefore, this strategy will have significant implications for the preparation of nanogaps and enhanced spectroscopy.

X-Ray Activatable Au/Ag Nanorods for Tumor Radioimmunotherapy Sensitization and Monitoring of the Therapeutic Response Using NIR-II Photoacoustic Imaging.

Radioimmunotherapy (RIT) is an advanced physical therapy used to kill primary cancer cells and inhibit the growth of distant metastatic cancer cells. However, challenges remain because RIT generally has low efficacy and serious side effects, and its effects are difficult to monitor in vivo. This work reports that Au/Ag nanorods (NRs) enhance the effectiveness of RIT against cancer while allowing the therapeutic response to be monitored using activatable photoacoustic (PA) imaging in the second near-infrared region (NIR-II, 1000-1700 nm). The Au/Ag NRs can be etched using high-energy X-ray to release silver ions (Ag+ ), which promotes dendritic cell (DC) maturation, enhances T-cell activation and infiltration, and effectively inhibits primary and distant metastatic tumor growth. The survival time of metastatic tumor-bearing mice treated with Au/Ag NR-enhanced RIT is 39 days compared with 23 days in the PBS control group. Furthermore, the surface plasmon absorption intensity at 1040 nm increases fourfold after Ag+ are released from the Au/Ag NRs, allowing X-ray activatable NIR-II PA imaging to monitor the RIT response with a high signal-to-background ratio of 24.4. Au/Ag NR-based RIT has minimal side effects and shows great promise for precise cancer RIT.

A SERS based clinical study on HIV-1 viral load quantification and determination of disease prognosis.

In resource limited settings, a cost-effective point-of-care diagnostic testing possessing the characteristics of detecting the minimum viral load of a malady like human immunodeficiency virus (HIV) acquired immune deficiency syndrome (AIDS) is a pressing priority. The present work describes a novel, rapid and field-deployable method using surface enhanced Raman spectroscopy (SERS) for detection and prognosis of HIV positive clinical samples, in seven different viral load ranges varying between 200 and 1 million copies/ml. A relationship between the increasing and decreasing intensity peaks of HIV-1 was also established for quantitation efficacy of the handheld tool. Three different types of SERS substrates: single arm Ag nanorods, double arm Ag nanorods and Au sputtered single arm Ag nanorods were used and the obtained data was compared for the three substrates. It was demonstrated that maximum enhancement was obtained for Au sputtered Ag nanorods. Rigorous coupled wave analysis (RCWA) simulations were performed to study the 'hotspots' in three different SERS substrates. Further, to explore the utility of our platform and to differentiate between the clade specific X4 and R5 tropism, their corresponding SERS spectra were studied using HIV-1 strains belonging to four different HIV-1 subtypes (A, B, C and D) which showed a clear distinction, implying the usefulness of the platform in understanding the disease prognosis. Statistical analysis of the obtained SERS spectra using principal component analysis (PCA) showed good agreement with the experimental results, confirming the ability of SERS platform to quantitate HIV-1 viral load and distinguish HIV-1 strains on the basis of their SERS spectra.

Effects of Thermal Annealing on Optical and Microscopic Ferromagnetic Properties in InZnP:Ag Nano-Rods.

InZnP:Ag nano-rods fabricated by the ion milling method were thermally annealed in the 250~350 °C temperature range and investigated the optimum thermal annealing conditions to further understand the mutual correlation between the optical properties and the microscopic magnetic properties. The formation of InZnP:Ag nano-rods was determined from transmission electron microscopy (TEM), total reflectivity and Raman scattering analyses. The downward shifts of peak position for LO and TO modes in the Raman spectrum are indicative of the production of Ag ion-induced strain during the annealing process of the InZnP:Ag nano-rod samples. The appearance of two emission peaks of both (A0 X) and (e, Ag) in the PL spectrum indicated that acceptor states by Ag diffusion are visible due to the effective incorporation of Ag-creating acceptor states. The binding energy between the acceptor and the exciton measured as a function of temperature was found to be 21.2 meV for the sample annealed at 300 °C. The noticeable MFM image contrast and the clear change in the MFM phase with the scanning distance indicate the formation of the ferromagnetic spin coupling interaction on the surface of InZnP:Ag nano-rods by Ag diffusion. This study suggests that the InZnP:Ag nano-rods should be a potential candidate for the application of spintronic devices.

Double-Tetrahedral DNA Probe Functionalized Ag Nanorod Biointerface for Effective Capture, Highly Sensitive Detection, and Nondestructive Release of Circulating Tumor Cells.

Circulating tumor cells (CTCs) are indicative of tumorigenesis, metastasis, and recurrence; however, it is still a great challenge to efficiently analyze the extremely rare CTCs in peripheral blood. Herein, a novel nanobiointerface integrating high affinities of arrayed silver nanorods (Ag NRs) and double-tetrahedral DNA (DTDN) probes by a clever strategy is proposed for the efficient capture, highly sensitive detection, and nondestructive release of CTCs. Under the optimal conditions, the DTDN-probe-functionalized Ag NRs nanobiointerface can capture 90.2% of SGC-7901 cells in PBS, and the capture efficiency is 2.8 times and 50 times those of a DTDN-probe-functionalized Ag film and unfunctionalized Ag NRs, respectively, benefiting from the nanorough interface of the Ag NRs array and multivalent recognition of the DTDN probe. In addition, 93.4% of cells was released via Zn2+-assisted DNAzyme cleavage, and the viability of the postreleased CTCs is about 98.0%. The potential practicality of the nanobiointerface for testing CTCs in blood was further characterized by spiking SGC-7901 cells in leukocytes collected from human blood, and the results show that 83.8% capture efficiency, 91.2% release efficiency, and single-cell detection limit were achieved, which indicates that the nanobiointerface has great potential in clinical applications for reliable CTC analyses.

Target-manipulated drawstring DNAzyme for ultrasensitive detection of UDG using Au@Ag NRs indicator.

Uracil-DNA glycosylase (UDG) is a common glycosylase that can expressly recognize and remove damaged uracil bases, and the ultrasensitive detection of which is significant to maintain genomic stability and early clinical diagnosis of disease. Herein, we proposed a sensitive colorimetric sensing platform to detect UDG. Combined with target-manipulated drawstring DNAzyme and Au@Ag nanorods (Au@Ag NRs) indicator, we achieved in naked-eyes observation and ultrasensitive detection of UDG. Briefly, when the UDG exists, the dynamic reaction of rope pulling will occur generating the active conformation of DNAzyme. The cutting effect will be further produced when we add Mg2+, thus the generated trigger chain can mediate the occurrence of CHA reaction, followed by generating amount of ·OH which can etch Au@Ag NRs causing the shifted of localized surface plasmon resonance (LSPR) peak. By contrast, there is no obvious shift of LSPR peak. This strategy shows extraordinary specificity and sensitivity toward UDG providing a detection limit of 4.6 × 10-5 U mL-1. By using of this method, we detected UDG specifically in complex samples, proving that it's potential applications in biomedical research and clinical diagnosis are fantastic.

SERS and Indicator Paper Sensing of Hydrogen Peroxide Using Au@Ag Nanorods.

The detection of hydrogen peroxide and the control of its concentration are important tasks in the biological and chemical sciences. In this paper, we developed a simple and quantitative method for the non-enzymatic detection of H2O2 based on the selective etching of Au@Ag nanorods with embedded Raman active molecules. The transfer of electrons between silver atoms and hydrogen peroxide enhances the oxidation reaction, and the Ag shell around the Au nanorod gradually dissolves. This leads to a change in the color of the nanoparticle colloid, a shift in LSPR, and a decrease in the SERS response from molecules embedded between the Au core and Ag shell. In our study, we compared the sensitivity of these readouts for nanoparticles with different Ag shell morphology. We found that triangle core-shell nanoparticles exhibited the highest sensitivity, with a detection limit of 10-4 M, and the SERS detection range of 1 × 10-4 to 2 × 10-2 M. In addition, a colorimetric strategy was applied to fabricate a simple indicator paper sensor for fast detection of hydrogen peroxide in liquids. In this case, the concentration of hydrogen peroxide was qualitatively determined by the change in the color of the nanoparticles deposited on the nitrocellulose membrane.

A colorimetric sensing probe for chromium (III) ion based on domino like reaction.

In this work, a gold nanobipyramid@Ag nanorod (AuNBP@Ag NR)-based sensor platform was developed for the quantitative, visual, and sensitive detection of Cr3+ ions in aqueous solutions. This assay provides quantitative detection of Cr3+, which relies on the absorbance change of AuNBP@Ag NRs due to morphological change of the AuNBP@Ag NRs induced by Cr3+. When AuNBP@Ag NRs and Cr3+ mix, the coordination reaction of the carboxyl groups of citrate and Cr3+ occurs, which leads to the collapse of Ag shell nanorods, similar to the domino effect, and obvious color changes from yellow to pink can be observed by the naked eye. When combined with UV-vis spectrophotometer-based colorimetric detection, a detection limit of 8.7 nM for Cr3+ in ultrapure water was achieved. With the advantages of high sensitivity, selectivity, and performance, we anticipate that the sensor will be helpful for the on-site, quantitative detection of Cr3+ ions in water samples.

Corn-like Au/Ag nanorod-mediated NIR-II photothermal/photodynamic therapy potentiates immune checkpoint antibody efficacy by reprogramming the cold tumor microenvironment.

Immune checkpoint blocking (ICB) antibodies have shown great success in the clinic, but their low response rate in patients with immunosuppressive cold tumors remains a huge challenge. Inspired by the capability of immunogenic cell death (ICD) to convert tumors from cold to hot, we developed a corn-like Au/Ag nanorod (NR) that can induce the ICD of tumor cells under 1064-nm light irradiation. The corn-like Au/Ag NRs plus NIR-II light irradiation strikingly increased the tumor infiltration of T cells and provoked a systemic immune response to reprogram the immunosuppressive cold tumor microenvironment; these NRs synergized with ICB antibodies to efficiently inhibit distant tumor growth. Encouragingly, the combination of aCTLA4 and Au/Ag NRs plus 1064-nm light irradiation elicited a strong immunological memory effect that protected against tumor recurrence.

Lab-On-Capillary Platform for On-Site Quantitative SERS Analysis of Surface Contaminants Based on Au@4-MBA@Ag Core-Shell Nanorods.

A portable and highly reproducible lab-on-capillary surface-enhanced Raman scattering (SERS) platform was developed using a specially designed homemade device for rapid on-site SERS measurement. In particular, this platform was composed of a capillary with a tiny orifice, which allows an effective and lossless sample extraction, resulting in high SERS performance. The capillary-based plasmonic substrate was prepared by compactly assembling Au@Ag core-shell nanorods (NRs) embedded with the 4-mercaptobenzoic acid (4-MBA) molecule as an internal standard onto the inner wall of a capillary tube. The fabrication process is facile and convenient with no requirement for complicated procedures. The exclusively prepared nanoparticles were able to significantly improve the signal consistency and overcome the limitations of reliable quantitative SERS analysis compared with conventional methods. Importantly, it was found that this capillary-based substrate with higher sensitivity was essentially attributed to more valid nanoparticles in the effective laser excitation region derived from the unique structure of the capillary. Furthermore, the applicability of the Au@4-MBA@Ag nanorod-decorated capillary for the quantitative identification of fungicides (malachite green and crystal violet) on the shell was demonstrated. As a result, this proposed lab-on-capillary sensor holds promising practical potential for rapid on-site analysis, especially for various contaminants on an uneven surface.

Multi-plasmon resonances enhanced two-photon coherent anti-Stokes Raman scattering by nanorods.

The development of new structures allows two-photon coherent anti-Stokes Raman scattering (TPCARS) to be strongly enhanced by multiple surface plasmon resonances (MSPRs). In this paper, plasmonic structure consisting of two Ag nanorods is designed and the enhancement of TPCARS is investigated. By properly selecting designing structure parameters, strong MSPRs peaks at 1020 nm and 505 nm are obtained, which can enhance the TPCARS signal based on the frequency match of the fundamental frequency and frequency doubling. The enhancement factor of TPCARS can reach as high as 3.66 × 1028 with significant electric field enhancements under appropriate selection of system parameters. Furthermore, the two-photon process can be controlled at different optical frequencies by changing the geometric parameters of Ag nanorods. The new scheme advanced in this work can help to achieve single molecule level of CARS, and may have a potential to increase the intensity and resolution of nonlinear optical imaging.

Gelsolin Encountering Ag Nanorods/Triangles: An Aggregation-Based Colorimetric Sensor Array for in Vivo Monitoring the Cerebrospinal Aß42% as an Indicator of Cd2+ Exposure-Related Alzheimer's Disease Pathogenesis.

Nowadays, the environmental risk factors for Alzheimer's disease (AD) have received widespread attention. Two major amyloid-ß peptide (Aß) variants, Aß42 and Aß40, play a pivotal role in the etiology of AD and the concentration ratio of which (i.e., Aß42%) has been suggested to be the superior biomarker for AD. In this study, an "aggregation-based colorimetric sensor array" for the simultaneous identification and detection of Aß40 and Aß42 with structural similarity was established based on gelsolin-modified silver nanotriangles (Ag NTs) and silver nanorods (Ag NRs). Different aggregation behaviors of gelsolin-modified Ag NTs and Ag NRs in the presence of Aß42 and Aß40 resulted in different color and spectral changes, which could be quantitatively analyzed in terms of unique spectral patterns by principal component analysis. With the colorimetric sensor array employed here, the fluctuation of Aß42% in different brain regions of rats exposed to Cd2+ could be directly monitored. The downward trend of Aß42% accompanied by variations of other biochemical indicators suggested that subchronic Cd2+ exposure possibly triggered the onset of AD through the intervention of lipid peroxidation pathway. Furthermore, in vivo monitoring the downtrend of Aß42% in cerebrospinal fluid (CSF) could also be realized, which offers a great opportunity for early diagnosis and treatment of AD that may be induced by environmental factors with CSF Aß42% as a reliable indicator.

Biocompatible Au@Ag nanorod@ZIF-8 core-shell nanoparticles for surface-enhanced Raman scattering imaging and drug delivery.

A surface-enhanced Raman scattering (SERS) imaging probe and drug carrier based on zeolitic imidazolate framework (ZIF-8)-coated Au@Ag core-shell nanorod has been developed. Strong Raman signal is generated by a reporter molecule of 4-aminothiophenol (4-ATP) adsorbed on Au@Ag core-shell nanorod, endowing the probe with function of SERS imaging. Further coating of ZIF-8 on Au@Ag core-shell nanorod offered high loading capacity for anti-cancer drugs, doxorubicin (DOX), as well as improved the stability and biocompatibility of the SERS tag due to the protection of ZIF-8 shell. After immobilization of folic acid onto the Au@Ag NRs4-ATP@ZIF-8, the SERS probes were successfully applied to the targeted SERS imaging of HeLa, MCF-7, LNCaP, QGY-7703, HCT116 and MDA-MB-231 cells with low cytotoxicity, and further applied to the image of tumor tissue of human colon cancer. In vitro cell cytotoxicity confirmed that DOX-loaded SERS probes had potential therapeutic effect compared with the free drug. All of these original results contribute to develop potential biocompatible nanosystem integrating diagnosis and therapy.

Localized Surface Plasmon Resonance-Mediated Charge Trapping/Detrapping for Core-Shell Nanorod-Based Optical Memory Cells.

For following the trend of miniaturization as per Moore's law, increasing efforts have been made to develop single devices with versatile functionalities for Internet of Things (IoT). In this work, organic optical memory devices with excellent dual optoelectronic functionality including light sensing and data storage have been proposed. The Au@Ag core-shell nanorods (NRs)-based memory device exhibits large memory window up to 19.7 V due to the well-controlled morphology of Au@Ag NRs with optimum size and concentration. Furthermore, since the extinction intensity of Au@Ag NRs gradually enhance with the increase in Ag shell thickness, the phototunable behaviors of memory device were systematically studied by varying the thickness of Ag shell. Multilevel data storage can be achieved with the light assistant. Finally, the simulation results demonstrate that the phototunable memory property is originated from the multimode localized surface plasmon resonance (LSPR) of Au@Ag NRs, which is in consistent with the experimental results. The Au@Ag core-shell NRs-based memories may open up a new strategy toward developing high-performance optoelectronic devices.

Ag Nanorods-Oxide Hybrid Array Substrates: Synthesis, Characterization, and Applications in Surface-Enhanced Raman Scattering.

Over the last few decades, benefitting from the sufficient sensitivity, high specificity, nondestructive, and rapid detection capability of the surface-enhanced Raman scattering (SERS) technique, numerous nanostructures have been elaborately designed and successfully synthesized as high-performance SERS substrates, which have been extensively exploited for the identification of chemical and biological analytes. Among these, Ag nanorods coated with thin metal oxide layers (AgNRs-oxide hybrid array substrates) featuring many outstanding advantages have been proposed as fascinating SERS substrates, and are of particular research interest. The present review provides a systematic overview towards the representative achievements of AgNRs-oxide hybrid array substrates for SERS applications from diverse perspectives, so as to promote the realization of real-world SERS sensors. First, various fabrication approaches of AgNRs-oxide nanostructures are introduced, which are followed by a discussion on the novel merits of AgNRs-oxide arrays, such as superior SERS sensitivity and reproducibility, high thermal stability, long-term activity in air, corrosion resistivity, and intense chemisorption of target molecules. Next, we present recent advances of AgNRs-oxide substrates in terms of practical applications. Intriguingly, the recyclability, qualitative and quantitative analyses, as well as vapor-phase molecule sensing have been achieved on these nanocomposites. We further discuss the major challenges and prospects of AgNRs-oxide substrates for future SERS developments, aiming to expand the versatility of SERS technique.

Non-invasive detection of hepatocellular carcinoma serum metabolic profile through surface-enhanced Raman spectroscopy.

The present study aims to identify distinctive Raman spectrum metabolic peaks to predict hepatocellular carcinoma (HCC). We performed a label-free, non-invasive surface-enhanced Raman spectroscopy (SERS) test on 230 serum samples including 47 HCC, 60 normal controls (NC), 68 breast cancer (BC) and 55 lung cancer (LC) by mixing Au@AgNRs with serum directly. Based on the observed SERS spectra, discriminative metabolites including tryptophan, phenylalanine, and etc. were found in HCC, when compared with BC, LC, and NC (P<0.05 in all). Common metabolites-proline, valine, adenine and thymine were found in HCC, BC and LC with compared to NC group (P<0.05). Importantly, Raman spectra of HCC serum biomarker AFP were firstly detected to analyze the HCC prominent peak. Orthogonal partial least squares discriminant analysis was adopted to assess the diagnostic accuracy; area under curve value of HCC is 0.991. This study provides new insights into the HCC metabolites detection through Raman spectroscopy.

Formation of core-shell Au@Ag nanorods induced by catecholamines: A comparative study and an analytical application.

Gold nanorods (AuNRs) stabilized by cetyltrimethylammonium bromide (CTAB) were synthesized and an interaction of catecholamines (CAs) with silver ions in the presence of the obtained AuNRs was studied. The reaction results into formation of core-shell Au@Ag nanorods (Au@AgNRs) and leads to a hypsochromic shift of the long-wave surface plasmon resonance (SPR) band in the absorption spectrum of AuNRs. The influence of a CA structure, excess of CTAB, interaction time, pH, concentration of AuNRs, silver ions and CAs on this interaction was studied. Based on correlation of the NRs spectral characteristics with the concentration of CAs, a method for spectrophotometric determination of dobutamine, epinephrine, norepinephrine and dopamine with detection limits 27, 18, 16 and 13 µg L(-1), respectively, has been developed. The method can be applied to the analysis of medicines.