Selective Surface Enhanced Raman Scattering for Quantitative Detection of Lung Cancer Biomarkers in Superparticle@MOF Structure

Macroscopic two-dimensional monolayer films of gold nanoparticles: fabrication strategies, surface engineering and functional applications

In the last few decades, two-dimensional monolayer films of gold nanoparticles (2D MFGS) have attracted increasing attention in various fields, due to their superior attributes of macroscopic size and accessible fabrication, controllable electromagnetic enhancement, distinctive optical harvesting and electron transport capabilities. This review will focus on the recent progress of 2D monolayer films of gold nanoparticles in construction approaches, surface engineering strategies and functional applications in the optical and electric fields. The research challenges and prospective directions of 2D MFGS are also discussed. This review would promote a better understanding of 2D MFGS and establish a necessary bridge among the multidisciplinary research fields.

Surface-enhanced Raman spectroscopy: benefits, trade-offs and future developments

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique with sensitivity down to the single molecule level that provides fine molecular fingerprints, allowing for direct identification of target analytes. Extensive theoretical and experimental research, together with continuous development of nanotechnology, has significantly broadened the scope of SERS and made it a hot research field in chemistry, physics, materials, biomedicine, and so on. However, SERS has not been developed into a routine analytical technique, and continuous efforts have been made to address the problems preventing its real-world application. The present minireview focuses on analyzing current and potential strategies to tackle problems and realize the SERS performance necessary for translation to practical applications.

Cross-Linked Surface Engineering to Improve Iron Porphyrin Catalytic Activity

Quasi-two-dimensional (QTD) structural heterogeneous catalysts have attracted a broad interest in multidisciplinary research due to their unique structure, preeminent surface properties and outstanding catalytic performance. Herein, a HZIF@TCPP-Fe/Fe heterogeneous catalyst based on cross-linked surface engineering is constructed by supporting QTD TCPP-Fe/Fe ultra-thin metallized film (≈2 nm) on hollow skeleton of zeolite imidazolate frameworks. The designed QTD structure exhibits high efficiency for the catalytic oxidative dehydrogenation of aromatic hydrazides reactions which is the key technology in various industrial processes. Taking advantage of QTD structure with excellent accessibility, the metallized film with irregular defects not only enhances electron transfer during the reaction but also exposes more surface-active sites. Furthermore, the prepared HZIF@TCPP-Fe/Fe heterogeneous catalyst can be recycled and reused, which is of great significance in the field of green chemistry.

Spectroscopic insights into the effect of pH, temperature, and stabilizer on erlotinib adsorption behavior onto Ag nanosurface

In this study, surface - enhanced Raman spectroscopy (SERS) was applied at the first time for estimation of how pH, temperature, and nanoparticle (NP) stabilizer affect an adsorption behavior of erlotinib (drug approved in a non-small cell lung cancer therapy) onto citrate-stabilized silver nanoparticles (AgNPs). Novel approach to improve cancer therapy assumes application of NPs as an efficient drug delivery system. This strategy requires designing stable drug/nanocarrier conjugates that can effectively interact in the target site. It is also important to perform deeply characterization of a drug orientation on the potential carrier surface and estimation how stable the appeared interaction is. Performed analysis, indicates that pH, temperature, presence of NP stabilizers, and time of incubation have an influence on the occurring adsorption geometry of the drug. However, the observed erlotinib/AgNP interaction remains stable regardless of the applied conditions. These considerations were supported by insightful physicochemical characteristics of the AgNPs and the erlotinib/AgNP conjugates by conducting transmission electron microscopy (TEM) imaging, determination of colloid stability conducted with the use of dynamic light scattering technique (DLS) and measurements of electrophoretic mobility. Such complex approach allows a better understanding of the stability of the erlotinib/AgNP conjugates and provides information how the investigated interaction is affected by the induced perturbations.

Metal-Organic Frameworks for Biomedical Applications

Metal-organic frameworks (MOFs) are an interesting and useful class of coordination polymers, constructed from metal ion/cluster nodes and functional organic ligands through coordination bonds, and have attracted extensive research interest during the past decades. Due to the unique features of diverse compositions, facile synthesis, easy surface functionalization, high surface areas, adjustable porosity, and tunable biocompatibility, MOFs have been widely used in hydrogen/methane storage, catalysis, biological imaging and sensing, drug delivery, desalination, gas separation, magnetic and electronic devices, nonlinear optics, water vapor capture, etc. Notably, with the rapid development of synthetic methods and surface functionalization strategies, smart MOF-based nanocomposites with advanced bio-related properties have been designed and fabricated to meet the growing demands of MOF materials for biomedical applications. This work outlines the synthesis and functionalization and the recent advances of MOFs in biomedical fields, including cargo (drugs, nucleic acids, proteins, and dyes) delivery for cancer therapy, bioimaging, antimicrobial, biosensing, and biocatalysis. The prospects and challenges in the field of MOF-based biomedical materials are also discussed.

CoFe2O4@HNTs/AuNPs Substrate for Rapid Magnetic Solid-Phase Extraction and Efficient SERS Detection of Complex Samples All-in-One

Fast and accurate practical sample detection is a great challenge in on-site detection. Herein, we developed a CoFe₂O₄@HNTs/AuNPs substrate for rapid and efficient magnetic solid-phase extraction (MSPE) surface-enhanced Raman scattering (SERS) detection of aromatic amines and nitrofuran in real samples all-in-one. Magnetic CoFe₂O₄ beads filled inside halloysite nanotubes (HNTs) can avoid aggregation of particles, endow the substrate with the rapid magnetic separation ability to simplify the pretreatment procedure, and reduce complex matrix interference. Meanwhile, outer surface AuNPs can generate electromagnetic enhancement and hot spots to amplify Raman signals of target molecules enriched/concentrated by HNTs. The CoFe₂O₄@HNTs/AuNPs substrate exhibited excellent SERS activity (high sensitivity, good reproducibility, and repeatability), pH stability (3.0-11.0), and good MSPE ability (fast magnetic enrichment/separation ability within 5 min). The CoFe₂O₄@HNTs/AuNPs MSPE SERS substrate can be applied for the determination of 4,4'-thioaniline and nitrofurantoin with a linear range of 0.054-21.7 mg/L and 0.05-1.0 mg/L, and the limits of detection were down to 0.026 mg/L and 0.014 mg/L, respectively. Furthermore, the enhancement factor (EF) of the substrate to 4,4'-thioaniline is up to 2.7 × 10⁷. Besides, the substrate can realize practical SERS determination of trace 4,4-thioaniline in cosmetics and nitrofurantoin in fish feed and aquatic samples. The recoveries were varied from 71.6% to 103.6% for 4,4-thioaniline in hair dyes and 81.9% to 116.3% for nitrofurantoin in fish feed and aquatic samples, respectively. Such a robust and efficient MSPE SERS substrate possesses great potential in rapid detection (within 15 min) for a practical sample, and it also provides a methodology for the preparation of other HNTs-based composites.

A split-type structure of Ag nanoparticles and Al2O3@Ag@Si nanocone arrays: an ingenious strategy for SERS-based detection

Herein, we report a facile strategy of combined SERS measurements based on a split-type SERS substrate, which exhibits excellent SERS activity, detection signal reproducibility and chemical stability. The SERS substrate consists of an ordered Al2O3@Ag@Si nanocone array and Ag nanoparticles (Ag-NPs), both of which are fabricated individually. The Al2O3@Ag@Si nanocone array is obtained by ion-sputtering Ag on an Si nanocone array and then coating an ultrathin (∼2 nm) Al2O3 dielectric layer via atomic layer deposition (ALD). Ag-NPs are synthesized via the liquid phase method and then immersed in an organic solvent for liquid seal. For the SERS measurement, Ag-NPs are dispersed in a liquid containing the probe molecules and then, they self-assemble on the surface of the Al2O3@Ag@Si nanocones. Subsequently, the ultrathin Al2O3 dielectric layer separates Ag-NPs from the Ag@Si nanocones, forming massive gap-introduced hot spots. This substrate is sensitive to 1 pM Rhodamine R6G with an average enhancement factor of up to 109, exhibiting excellent SERS activity. Moreover, due to the protection of the Al2O3 dielectric layer and the organic solvent for the Ag@Si nanocones and Ag-NPs against oxidation, the split-type SERS substrate achieves an SERS signal with almost no attenuation after five months, indicating its good chemical stability.

Core-shell nanostructures introduce multiple potential barriers to enhance energy filtering for the improvement of the thermoelectric properties of SnTe

Using dispersed nanostructures to induce an energy filtering effect is an easy and effective mechanism to optimize the performance of bulk thermoelectric materials. Compared with other nanostructures, core-shell nanostructures possess more interfaces and multiple potential barriers, which would lead to a significant impact on the thermal and electrical properties of materials. In this paper, after BiCuSeO alloy doping into SnTe, SnO2 layers were formed at the interfaces and the BiCuSeO nanoparticles were wrapped in the SnO2 shell during the following high temperature solid state reaction. The formation of SnO2 layers could be observed and confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). BiCuSeO@SnO2 core-shell nanostructures can introduce multiple potential barriers to enhance the energy filtering effect. Once the BiCuSeO doping concentration was over 3%, the carrier concentration could decrease to about 10% while the mobility increases to 350% compared to the values of the undoped sample at room temperature. Meanwhile, the Seebeck coefficients were improved to 176.05 μV K-1 at 835 K. Additionally, due to the scattering of core-shell nanostructures for the phonons, a lower thermal conductivity is achieved with a value of 1.04 W m-1 K-1 at 835 K in Sn1.03Te-5% BiCuSeO. Combined with the improvement of thermal and electrical properties by the BiCuSeO@SnO2 core-shell, a high ZT value of ∼1.21 was achieved for Sn1.03Te-5% BiCuSeO at 835 K, which was enhanced by 190% compared to pristine SnTe.

Array-Assisted SERS Microfluidic Chips for Highly Sensitive and Multiplex Gas Sensing

A novel kind of array-assisted surface-enhanced Raman spectroscopy (SERS) microfluidic chip (ArraySERS chip) is demonstrated for gas sensing, which has the advantages of both ultrahigh sensitivity and multiplex sensing ability. On the one hand, the introduction of a microstructured triangular array can greatly increase the multiple collision probability between gas molecules and sensing interfaces in the channel. Compared with traditional gas sensors using sealed boxes, where gaseous molecules move only by diffusion, the ArraySERS chip exhibits significantly improved sensitivity. On the other hand, a composite nanoparticle is fabricated as a SERS probe for reading out the fingerprint spectral data, which consists of metal-organic framework (MOF) materials [Zeolitic Imidazolate framework-8 (ZIF-8)] and Au@Ag nanocubes, as well as cysteamine (CA) that serves as the gas-capturing agent. The experimental results show that such a structure of the SERS probe can further increase the sensing ability because of better adsorption of ZIF-8 for gas and the lower SERS background of CA itself. In addition, the simultaneous detection of multiplex gases was easily performed according to their own intrinsic SERS signals. Taking aldehyde gas as a model of a typical air pollutant, trace and multicomponent detection was realized using the ArraySERS chip. The limit of detection value was as low as 1 ppb, which is 2 magnitudes lower than that obtained by traditional methods. This strategy can be well extended for the detection of universal gases and help unleash the potential of existing gas sensors, especially for samples at low concentrations in air.

Tetrahedron Probes for Ultrasensitive In Situ Detection of Telomerase and Surface Glycoprotein Activity in Living Cells

In the present study, a tetrahedron probe with encoded internal reference nanoparticles (NPs) was self-assembled by a complementary nucleic acid aptamer for simultaneous ratiometric detection of telomerase (TE) and epithelial cell-adhesion molecule (EpCAM) in living cells. In the presence of a target, the dissociation of gold (Au) NPs, which was modified with corresponding tags, resulted in decreased surface-enhanced Raman scattering (SERS) signals. In addition, the ratios of Raman intensity at 1346 cm^-1/1096 cm^-1 (TE) and 1614 cm^-1/1096 cm^-1 (EpCAM) compared with the internal reference were demonstrated to quantify the level of TE and EpCAM, respectively, and can eliminate certain background noise. A good linear relationship was observed between them, and the linear range of TE and EpCAM in HeLa cells was 0.7 × 10^-12 to 37.5 × 10^-12 IU and 1.24 to 75.48 pg/mL with a limit of detection (LOD) of 7.6 × 10^-16 IU and 0.53 pg/mL, respectively, which were consistent with the results of Raman confocal imaging. Meanwhile, the versatility and specificity of the developed probes were confirmed in cell lines. These results provide a reliable and ultrasensitive strategy for the in situ detection of biomarkers and a new method for SERS-based tetrahedrons in the early diagnosis of cancer.

Spectroscopy, microscopy, diffraction and scattering of archetypal MOFs: formation, metal sites in catalysis and thin films

A comprehensive overview of characterization tools for the analysis of well-known metal–organic frameworks and physico-chemical phenomena associated to their applications.

Enhanced chemical sensing for Cu2+ based on composites of ZIF-8 with small molecules

Two organic molecules, pyridoxal hydrazide (PAH) and salicylaldehyde based Rhodamine B hydrazone (RBS) were integrated into zeolitic imidazolate framework-8 (ZIF-8) to give composites, namely PAH/ZIF-8 and RBS/ZIF-8. The organic molecules and ZIF-8 are proposed to be assembled via hydrogen bonds and π–π stacking in the composites. The mass fraction of PAH and RBS in the composites was calculated to be 21.86% and 29.3%. The fluorescence of PAH/ZIF-8 is quenched regularly by Cu²⁺. The detection limit for Cu²⁺ was calculated to be 1.42 nM for PAH/ZIF-8, which is one order of magnitude lower than that of PAH. The detection limit for Cu²⁺ was determined to be 0.8 μM for RBS/ZIF-8, which is three times lower than that of RBS. The two composites both display high selectivity to Cu²⁺ over competing metal ions. The PAH/ZIF-8 fluorescent sensor was successfully applied to Cu²⁺ determination in environmental water. PAH/ZIF-8 exhibits excellent cell membrane permeability and low cytotoxicity in cellular imaging. The enhanced chemical sensor was designed by introducing small molecules into ZIF-8 for the specific recognition of Cu²⁺.

An enhanced chemical sensor was designed by introducing small molecules into ZIF-8 for the specific recognition of Cu²⁺.

Porous materials applied to biomarker sensing in exhaled breath for monitoring and detecting non-invasive pathologies

Overview of the use of porous materials for gas sensing to analyze the exhaled breath of patients for disease identification.

Nanomaterial-based gas sensors used for breath diagnosis

Gas-sensing applications commonly use nanomaterials (NMs) because of their unique physicochemical properties, including a high surface-to-volume ratio, enormous number of active sites, controllable morphology, and potential for miniaturisation.

Raman-tag labelled Au@ZIF-8 for cell metabolism monitoring in vitro

 Cell metabolism decides the state of cells in division, differentiation and growth, maintaining intracellular balance. Monitoring the metabolic behavior of cells is of great significance to study the development of diseases in cell levels. Surface-enhanced Raman spectroscopy (SERS) is a powerful technique to detect and quantify analytes in extremely low concentration. Combined with SRES technology, we can monitor the concentration of metabolites in live cells and thus study the biological behavior of cells. In this work, Raman-tag labelled Au@ZIF-8 nanoparticles were used to monitor the distribution of reactive oxygen species (ROS) in SKOV3 cells. With the help of the ultrasensitive Raman enhancement material, the distribution of ROS in SKOV3 cells was mapped, the results were further confirmed in the fluorescent images. The SERS platform provides an ultrasensitive monitoring method of ROS distribution, which may offer an opportunity for real-time monitoring the cell metabolism in the cell biology applications.

Metal–organic frameworks: a future toolbox for biomedicine?

The present review focuses on the use of Metal–Organic Frameworks, (MOFs) highlighting the most recent developments in the biological field and as bio-sensors.

Surface-enhanced Raman scattering-based detection of hazardous chemicals in various phases and matrices with plasmonic nanostructures

Surface-enhanced Raman scattering (SERS)-based sensors utilize the electromagnetic-field enhancement of plasmonic substrates with the chemical specificity of vibrational Raman spectroscopy to identify trace amounts of a wide variety of different target analytes while being minimally affected by photobleaching. However, despite many advantageous features of this method, SERS sensors, particularly for detecting hazardous chemicals, suffer from several limitations such as requirement of gigantic signal enhancement that is often poorly controllable, subtle change and degradation of the SERS substrate, consecutive fluctuation of the signal, the lack of reliable receptors for capturing targets of interest and the absence of general principles for detecting various chemicals in different phases and matrices. To overcome these limitations and for SERS sensors to find practical use, one must (1) acknowledge the characteristics of the matrices of target systems, (2) finely engineer and tune the receptors of the SERS sensor to properly extract the target analyte from the phase, and (3) implement additional mechanistic modifications to enhance the plasmonic signal. This minireview underlines the difficulties associated with different phases and a wide range of target analytes, and introduces the practical measures undertaken to overcome the respective difficulties in SERS-based detection of hazardous chemicals.

Dynamic covalent chemistry steers synchronizing nanoparticle self-assembly with interfacial polymerization

Precise organization of matter across multiple length scales is of particular interest because of its great potential with advanced functions and properties. Here we demonstrate a simple yet versatile strategy that enables the organization of hydrophobic nanoparticles within the covalent organic framework (COF) in an emulsion droplet. The interfacial polymerization takes place upon the addition of Lewis acid in the aqueous phase, which allows the formation of COF after a crystallization process. Meanwhile, the interaction between nanoparticles and COF is realized by the use of amine-aldehyde reactions in the nearest loci of the nanoparticles. Importantly, the competition between the nanoparticle self-assembly and interfacial polymerization allows control over the spatial distribution of nanoparticles within COF. As a general strategy, a wide variety of COF-wrapped nanoparticle assemblies can be synthesized and these hybridized nanomaterials could find applications in optoelectronics, heterogeneous catalysis and energy chemistry.

Manipulating "Hot Spots" from Nanometer to Angstrom: Toward Understanding Integrated Contributions of Molecule Number and Gap Size for Ultrasensitive Surface-Enhanced Raman Scattering Detection

Narrower gaps between metal nanoparticles (so-called "hot spots") in surface-enhanced Raman scattering (SERS) substrates contribute to stronger electromagnetic (EM) enhancement; however, the accompanying steric effect hinders analyte molecules entering hot spots to access the benefit. To comprehensively understand integrated contributions of the gap size and molecule number accommodated in hot spots and then optimize design of SERS substrates, the thermal shrinking method was employed to manipulate hot spots and the "hottest zone" was defined to evaluate the integrated contributions to SERS intensity of the two factors. In the conventional shrink-adsorption mode, the contributions of the molecule number and gap size are competitive when the gap width is comparable with the target molecule size, which leads to oscillating behavior of SERS intensity versus gap size, and it is analyte molecule size dependent. This result suggests that engineering hot spots should be target molecule directed to achieve ultrasensitive detection. In the proposed adsorption-shrink mode, the contributions of the molecule number and gap size are synergistic, which makes the detection ability of the adsorption-shrink mode attains a single-molecule (SM) level. Excellent performance of the adsorption-shrink SERS strategy benefits detection of trace level pollutants in complex environments. Detection ranges for contaminants with different metal affinity, such as thiram, malachite green (MG), and formaldehyde, are as low as parts per billion, even down to parts per trillion.

Can Metal-Organic Frameworks Be Used for Cannabis Breathalyzers?

Δ⁹-Tetrahydrocannabinol (THC) is the principal psychoactive component of cannabis, and there is an urgent need to build low-cost and portable devices that can detect its presence from breath. Similarly to alcohol detectors, these tools can be used by law enforcement to determine driver intoxication and enforce safer and more regulated use of cannabis. In this work, we propose to use a class of microporous crystals, metal-organic frameworks (MOFs), to selectively adsorb THC that can be later detected using optical, electrochemical, or fluorescence-based sensing methods. We computationally screened more than 5000 MOFs, highlighting the materials that have the largest affinity with THC, as well as the highest selectivity against water, showing that it is thermodynamically feasible for MOFs to adsorb THC from humid breath. We propose and compare different models for THC and different computational protocols to rank the promising materials, also presenting a novel approach to assess the permeability of a porous framework to nonspherical molecules. We identified three adsorption motifs in MOFs with high affinity to THC, which we refer to as "narrow channels", "thick walls", and "parking spots". Therefore, we expect our protocols and our findings to be generalizable for different classes of microporous materials and also for investigating the adsorption properties of other large molecules that, like THC, have a nonspherical shape.

Signal-Off Electrogenerated Chemiluminescence Biosensing Platform Based on the Quenching Effect between Ferrocene and Ru(bpy)32+-Functionalized Metal-Organic Frameworks for the Detection of Methylated RNA

N⁶-methyladenine (m⁶A), one of the most common chemical modifications of eukaryotic RNA, participates in many important biological processes. An effective strategy for the quantitative determination of m⁶A is of great significance. Herein, we used methylated microRNA-21 (miRNA21) as the model target to propose a simple and sensitive electrogenerated chemiluminescence (ECL) biosensing platform to detect a specific m⁶A RNA sequence. This strategy is based on the fact that the anti-m⁶A-antibody can specifically recognize and bind to the m⁶A site in the RNA sequence, resulting in a quenching effect between Ru(bpy)₃²⁺-functionalized metal-organic frameworks and ferrocene. Luminescent metal-organic frameworks (Ru@MOFs) not only act as ECL indicators but also serve as nanoreactors for the relative ECL reactions owing to their porous or multichannel structure, which overcomes the fact that Ru(bpy)₃²⁺ is easily released when used for aqueous-phase detection, thus enhancing the ECL efficiency. Moreover, the ECL method has fewer modification steps and uses only one antibody to recognize the target RNA sequence, which simplifies the operation process and reduces the detection time, presenting a wide linear range (0.001-10 nM) for m⁶A RNA determination with a low detection limit (0.0003 nM). Additionally, this developed strategy was validated for m⁶A RNA detection in human serum. Thus, the ECL biosensing method provides a new method for m⁶A RNA determination that is simple, highly specific, and sensitive.

Optical Diagnostic Based on Functionalized Gold Nanoparticles

Au nanoparticles (NPs) possess unique physicochemical and optical properties, showing great potential in biomedical applications. Diagnostic spectroscopy utilizing varied Au NPs has become a precision tool of in vitro and in vivo diagnostic for cancer and other specific diseases. In this review, we tried to comprehensively introduce the remarkable optical properties of Au NPs, including localized surfaces plasmon resonance (LSPR), surface-enhanced Raman scattering (SERS), and metal-enhanced fluorescence (MEF). Then, we highlighted the excellent works using Au NPs for optical diagnostic applications. Ultimately, the challenges and future perspective of using Au NPs for optical diagnostic were discussed.

Electrochemical biosensors for the detection of lung cancer biomarkers: A review

Cancer is one of the most widespread challenges and important diseases, which has the highest mortality rate. Lung cancer is the most common type of cancer, so that about 25% of all cancer deaths are related to the lung cancer. The lung cancer is classified as two different types with different treatment methodology: the small cell lung carcinoma and nonsmall cell lung carcinoma are two categories of the lung cancer. Since the lung cancer is often in the latent period in its early stages, therefore, early diagnosis of lung cancer has many challenges. Hence, there is a need for sensitive and reliable tools for preclinical diagnosis of lung cancer. Therefore, many detection methods have been employed for early detection of lung cancer. As lung cancer tumors growth in the body, the cancerous cells release numerous DNA, proteins, and metabolites as special biomarkers of the lung cancer. The levels of these biomarkers show the stages of the lung cancer. Therefore, detection of the biomarkers can be used for screening and clinical diagnosis of the lung cancer. There are numerous biomarkers for the lung cancer such as EGFR, CEA, CYFRA 21-1, ENO1, NSE, CA 19-9, CA 125 and VEGF. Nowadays, electrochemical methods are very attractive and useful in the lung cancer detections. So, in this paper, the recent advances and improvements (2010-2018) in the electrochemical detection of the lung cancer biomarkers have been reviewed.

Slanted Ag-Al alloy nanorods arrays for highly active and stable surface-enhanced Raman scattering substrates

Aluminum has been established as an earth-abundant and low-cost alternative to gold and silver for plasmonic applications. Particularly, aluminum largely tends to combines with oxygen compared with silver. Here, a simple glancing angle deposition technique is presented to prepare Ag-Al alloy nanorods (NRs) with a small amount of aluminum. The effect of aluminum is to combine oxygen or corroded substances under certain conditions, such as in the air and in etchants. Beside this, owing to the large diffusion coefficient of aluminum in a Si wafer, the aluminum diffuses easily into a Si wafer, so the bonding force between the Ag-Al alloy NRs and Si wafer can be improved accordingly. In this work, 3.5 at% Al alloy NRs are optimal to exhibit high surface-enhanced Raman scattering (SERS) sensitivity, long-time stability as well as strong bonding force with a Si wafer. Ag-Al alloy NRs make a metal-metal alloy a promising material platform to develop pretty sensitive as well as stable SERS substrates.

A Generalized Methodology of Designing 3D SERS Probes with Superior Detection Limit and Uniformity by Maximizing Multiple Coupling Effects

Accurate design of high-performance 3D surface-enhanced Raman scattering (SERS) probes is the desired target, which is possibly implemented with a prerequisite of quantifying formidable multiple coupling effects involved. Herein, by combining theory and experiments on 3D periodic Au/SiO2 nanogrid models, a generalized methodology of accurately designing high performance 3D SERS probes is developed. Structural symmetry, dimensions, Au roughness, and polarization are successfully correlated quantitatively to intrinsic localized electromagnetic field (EMF) enhancements by calculating surface plasmon polariton (SPP), localized surface plasmon resonance (LSPR), optical standing wave effects, and their couplings theoretically, which is experimentally verified. The hexagonal SERS probes optimized by this methodology realize over two orders of magnitudes (405 times) improvement of detection limit for Rhodamine 6G model molecules (2.17 × 10-11 m) compared to the unoptimized probes with the same number density of hot spots, an enhancement factor of 3.4 × 108, a uniformity of 5.52%, and are successfully applied to the detection of 5 × 10-11 m Hg ions in water. This unambiguously results from the Au roughness-independent extra 144% contribution of LSPR effects excited by SPP interference waves as secondary sources, which is very unusual to be beyond the conventional recognition.

Porous zeolite imidazole framework-wrapped urchin-like Au-Ag nanocrystals for SERS detection of trace hexachlorocyclohexane pesticides via efficient enrichment

A core-shell configuration of the zeolite imidazole framework (ZIF-8) wrapped urchin-like Au-Ag alloyed nanocrystals (UAANs) were designed and fabricated via adding the pre-formed plasmonic nanoparticles into the ZIF-8 precursor solution with hexadecyltrimethyl ammonium bromide (CTAB). The UAANs are about 100 nm in size with high-density tips. The ZIF-8 shell layer is nanoporous and can be controlled in thickness from 10 nm to 40 nm by the CTAB concentration. Importantly, such ZIF-8 wrapped UAANs can be used as the highly efficient surface enhanced Raman scattering (SERS) substrates for detection of the trace hexachlorocyclohexane (HCH) molecules. The ZIF-8 shell layer with an appropriate thickness (-∼20 nm) can evidently increase the SERS performance of the UAANs to the trace γ-HCH and α-HCH. Such wrapping-enhanced SERS effect significantly increases, by a power function, with the decreasing HCH concentration, especially in the concentration below 10^-6 M, which is attributed to the ever-increasing enrichment effect to the HCH molecules. The detection limit is down below 1.5 ppb. This work presents a highly efficient substrate for the SERS-based detection of the trace HCH, and also displays the potential application in the SERS detection of volatile small molecules.

Metal-organic framework (MOF-5) coated SERS active gold gratings: A platform for the selective detection of organic contaminants in soil

In this work, we proposed the functionalization of a surface plasmon-polariton (SPP)-supported gold grating surface with the metal-organic framework (MOF-5) for sensitive, selective and reproducible surface-enhanced Raman scattering (SERS) detection of organophosphorus pesticides. Homogeneous distribution of plasmon intensity along the Au grating surface ensures the high reproducibility of SERS results (deviation of Raman peak intensity does not exceed the 4% along the sample). The surface-assisted growth of thin MOF-5 film was accomplished in two steps procedure: (i) covalent grafting by 4-carboxyphenyl groups and (ii) the immersion of samples in the mother liquid of MOF-5. Proposed SERS chip proved itself to be a perfect analytical probe for the detection of organophosphorus pesticides with high reliability and low detection limit up to 10^-12 M. Moreover, selective detection and recognition of several relevant organic contaminants (azo-dye, mycotoxin, and pesticide) from the simulated soil was successfully demonstrated. All SERS measurements were performed using portable Raman spectrometer and can easily be expanded to environmental conditions. Our work combines the high affinity of organic contaminants to the MOF-5 with excellent plasmonic excitation on the surface plasmon-polariton supported structure and shows the way to the realization of closed-to-ideal analytical SERS chip.

Nanoscale Vertical Arrays of Gold Nanorods by Self-Assembly: Physical Mechanism and Application

The unique photonic effect of self-assembled metal nanoparticles is widely used in many applications. In this article, we prepared self-assembled gold nanorod (GNR) vertical arrays substrate by an evaporation method and found that the morphology of the substrate can be effectively regulated by changing the immersion time in the target molecules solution to obtain different Raman enhancement effects. We separately calculated the local electromagnetic field of the GNR vertical arrays and disorder substrate by the finite element method (FEM), which was consistent with the experimental results. Based on optimal soaking time, the sensitivity, reproducibility, and stability of substrates were separately studied. The experimental results show that the GNR vertical arrays can detect Rhodamine 6G (Rh6G) at concentrations as low as 10-11 M and exhibit good reproducibility and stability due to local electromagnetic (EM) field enhancement caused by the coupling of adjacent nanorods. Thus, our work can demonstrate that the substrate has excellent surface-enhanced Raman scattering (SERS) activity and the obtained GNR vertical arrays have great potential for biosensor and biodetection.

Enhancing Disease Diagnosis: Biomedical Applications of Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) has recently gained increasing attention for the detection of trace quantities of biomolecules due to its excellent molecular specificity, ultrasensitivity, and quantitative multiplex ability. Specific single or multiple biomarkers in complex biological environments generate strong and distinct SERS spectral signals when they are in the vicinity of optically active nanoparticles (NPs). When multivariate chemometrics are applied to decipher underlying biomarker patterns, SERS provides qualitative and quantitative information on the inherent biochemical composition and properties that may be indicative of healthy or diseased states. Moreover, SERS allows for differentiation among many closely-related causative agents of diseases exhibiting similar symptoms to guide early prescription of appropriate, targeted and individualised therapeutics. This review provides an overview of recent progress made by the application of SERS in the diagnosis of cancers, microbial and respiratory infections. It is envisaged that recent technology development will help realise full benefits of SERS to gain deeper insights into the pathological pathways for various diseases at the molecular level.

Designing surface-enhanced Raman scattering (SERS) platforms beyond hotspot engineering: emerging opportunities in analyte manipulations and hybrid materials

Surface-enhanced Raman scattering (SERS) is a molecule-specific spectroscopic technique with diverse applications in (bio)chemistry, clinical diagnosis and toxin sensing. While hotspot engineering has expedited SERS development, it is still challenging to detect molecules with no specific affinity to plasmonic surfaces. With the aim of improving detection performances, we venture beyond hotspot engineering in this tutorial review and focus on emerging material design strategies to capture and confine analytes near SERS-active surfaces as well as various promising hybrid SERS platforms. We outline five major approaches to enhance SERS performance: (1) enlarging Raman scattering cross-sections of non-resonant molecules via chemical coupling reactions; (2) targeted chemical capturing of analytes through surface-grafted agents to localize them on plasmonic surfaces; (3) physically confining liquid analytes on non-wetting SERS-active surfaces and (4) confining gaseous analytes using porous materials over SERS hotspots; (5) synergizing conventional metal-based SERS platforms with functional materials such as graphene, semiconducting materials, and piezoelectric polymers. These approaches can be integrated with engineered hotspots as a multifaceted strategy to further boost SERS sensitivities that are unachievable using hotspot engineering alone. Finally, we highlight current challenges in this research area and suggest new research directions towards efficient SERS designs critical for real-world applications.

Metal-Organic Frameworks as Surface Enhanced Raman Scattering Substrates with High Tailorability

Surface enhanced Raman scattering (SERS) is a widely used analytical technique for detecting trace-level molecules based on an indispensable SERS substrate. SERS substrates with high tailorability are assumed to be attractive and desirable for SERS detection, because the substrates match the need for the selective detection of different species. Nevertheless, the rational design of such SERS substrates is rather challenging for both noble-metal and semiconductor substrates. Herein, expanding beyond conventional SERS substrates, we demonstrate that metal-organic framework (MOF) materials can serve as a type of SERS substrate with molecular selectivity, which are rarely realized for SERS detection without any special pretreatment. A salient structural characteristic of MOF-based SERS substrates benefiting the SERS selectivity is their high tailorability. By controlling the metal centers, organic ligands, and framework topologies of our MOF-based SERS substrates, we show that the electronic band structures of MOF-based SERS substrate can be purposively manipulated to match those of the target analytes, thus resulting in different detectable species. Going further, the SERS enhancement factors (EFs) of the MOF-based SERS substrates can be greatly enhanced to as high as 10⁶ with a low detection limit of 10^-8 M by pore-structure optimization and surface modification, which is comparable to the EFs of noble metals without "hot spots" and recently reported semiconductors. This selective enhancement is interpreted as being due to the controllable combination of several resonances, such as the charge-transfer, interband and molecule resonances, together with the ground-state charge-transfer interactions. Our study opens a new venue for the development of SERS substrates with high-design flexibility, which is especially important for selective SERS detection toward specific analytes.

Superficial-Layer-Enhanced Raman Scattering (SLERS) for Depth Detection of Noncontact Molecules

Although the strength of Raman signals can be increased by many orders of magnitude on noble metal nanoparticles, this enhancement is confined to an extremely short distance from the Raman-active surface. The key to the development of Raman spectroscopy for applications in diagnosis and detection of cancer and inflammatory diseases, and in pharmacology, relies on the capability of detecting analytes that are noninteractive with Raman-active surfaces. Here, a new Raman enhancement system is constructed, superficial-layer-enhanced Raman scattering (SLERS), by covering elongated tetrahexahedral gold nanoparticle arrays with a superficial perovskite (CH₃ NH₃ PbBr₃ ) film. Plasmonic decay is depressed along the vertical direction away from the noble metal surface and the penetration depth is increased in the perovskite media. The vertical penetration of SLERS is verified by the spatial distribution of the analytes via Raman imaging in layer-scanning mode.

Antibodies@MOFs: An In Vitro Protective Coating for Preparation and Storage of Biopharmaceuticals

Antibodies have emerged as a fast-growing category of biopharmaceuticals that have been widely applied in scientific research, medical diagnosis, and disease treatment. However, many antibodies and other biopharmaceuticals display inferior biophysical properties, such as low stability and a propensity to undergo aggregation. Enhancing the stability of biopharmaceuticals is essential for their wide applications. Here, a facile in vitro protective coating strategy based on metal-organic frameworks (MOFs) is proposed to efficiently protect antibodies against perturbation environments and quickly recover them from the MOFs before usage, which avoids introducing protective additives into the body, which may cause biosafety risks. The protected antibodies exhibit extraordinary thermal, chemical, and mechanical stabilities, and they can survive for long-term storage (>3 weeks) under severe temperature variation (4 ↔ 50 °C) at a fast ramp rate (25 °C min^-1 ). More importantly, the encapsulated antibodies can be easily released as quickly as 10 s with high efficiency (≈100%) to completely remove the MOFs before use. This study paves a new avenue for the facile preparation and storage of biopharmaceuticals represented by antibodies under ambient or perturbation conditions, which may greatly broaden and promote the applications of both MOFs and biopharmaceuticals.

Fabrication and simulation of V-shaped Ag nanorods as high-performance SERS substrates

Bending straight Ag nanorods (AgNRs) into V-shaped structures can generate a higher surface-enhanced Raman scattering (SERS) performance. Numerical simulations showed that V-shaped AgNRs with a total length between 300 nm and 800 nm were more sensitive than equal-length straight AgNRs under a 785 nm laser in most cases. It was found that at a laser wavelength between 500 nm and 1000 nm, the Raman enhancement factor (EF) of a V-shaped AgNR's 3rd plasmon mode was not only optimal among the other major plasmon modes, but also outperformed the plasmon modes of straight AgNRs. Besides, a linear relationship between the resonance wavelength of the V-shaped AgNR's 3rd mode and its length was observed both numerically and experimentally, which was beneficial for the optimization of SERS substrates. Under 785 nm laser excitation, V-shaped AgNR substrates with a single arm length between 330 nm and 340 nm possessed the highest SERS efficiency. This work took AgNR array substrates one step closer to practical applications.

[Research Progress of Raman Spectroscopy in the Diagnosis of Early Lung Cancer]

Lung cancer (LC) is the most common cancer and the leading cause of cancer-related death worldwide. The 5-year survival rate for LC remains low at 18% and is 5% for patients with metastatic disease, while the 5-year overall survival rate of patients with stage I NSCLC can reach 77.9%, hence early diagnosis and treatment of LC is the key to improve the prognosis. As a non-invasive detection technique, Raman spectroscopy can realize the non-destructive detection of the differences in molecular level structure between cancerous tissues and normal tissues, which can be used for the early diagnosis of lung cancer. The aim of this review is to summarize the progress of Raman spectroscopycombined with different tissue or body fluid samplesin the diagnosis of early LC.
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In Vitro and In Vivo SERS Biosensing for Disease Diagnosis

For many disease states, positive outcomes are directly linked to early diagnosis, where therapeutic intervention would be most effective. Recently, trends in disease diagnosis have focused on the development of label-free sensing techniques that are sensitive to low analyte concentrations found in the physiological environment. Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy that allows for label-free, highly sensitive, and selective detection of analytes through the amplification of localized electric fields on the surface of a plasmonic material when excited with monochromatic light. This results in enhancement of the Raman scattering signal, which allows for the detection of low concentration analytes, giving rise to the use of SERS as a diagnostic tool for disease. Here, we present a review of recent developments in the field of in vivo and in vitro SERS biosensing for a range of disease states including neurological disease, diabetes, cardiovascular disease, cancer, and viral disease.