Sol-gel-derived silver-nanoparticle-embedded thin film for mass spectrometry-based biosensing

A single atom cobalt anchored MXene bifunctional platform for rapid, label-free and high-throughput biomarker analysis and tissue imaging

Few of single-atom materials have been served as platform to analyze small molecules for surface assisted laser desorption/ionization mass spectrometry (SALDI-MS). Herein, a novel single Co atom-anchored MXene (Co-N-Ti3C2) is prepared to achieve enhanced SALDI-MS and mass spectrometry imaging (MSI) performance for the first time. The Co-N-Ti3C2 films were prepared by a simple in situ self-assembly strategy to generate an efficient SALDI-MS platform. Compared to typical inorganic/organic matrices, Co-N-Ti3C2 films exhibit superior performance in small molecules detection with ultra-high sensitivity (LOD at amol level), excellent repeatability (CV <4%), clean background and wide analyte coverage, enabling accurate quantitative analysis of various low-concentration metabolites from 1 μL biofluid in seconds. Its usage efficiently enhanced SALDI-MS detection of various small-molecule biomarkers such as amino acids, succinic acid, itaconic acid, arachidonic acid, citrulline, prostaglandin E2, creatinine, uric acid, glutamine, D-mannose, cholesterol and inositol in positive ion mode. The blood glucose level in humans was successfully determined from a linearity concentration range (0.25-10 mM). Notably, the Co-N-Ti3C2 assisted SALDI-MSI enables study the spatial distribution of small molecules covering the range central to metabolomics at a high resolution on a tissue section. Furthermore, Co-N-Ti3C2 platform revealed a specific peak profile that distinguishes osteoarthritis (OA) from rheumatoid arthritis (RA) tissue. Density functional theory theoretical investigation revealed that single Co atoms anchored on Ti3C2 could highly enhanced the ionization ability of metabolites, resulting in high-sensitivity and heterogeneous metabolome coverage.

Use of Nanoparticle Decorated Surface-Enhanced Raman Scattering Active Sol-Gel Substrates for SALDI-MS Analysis

Spectroscopy and mass spectrometry techniques are sometimes combined into the same analytical workflow to leverage each technique's analytical benefits. This combined workflow is especially useful in forensic and medical contexts where samples are often precious in nature. Here, we adopt metal nanoparticle (NP) doped sol-gel substrates, initially developed for surface-enhanced Raman scattering (SERS) analysis, as surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) substrates. Using dried blood and sample protocols previously developed for SERS analysis, we observe heme-related spectral features on both silver and gold NP substrates by SALDI-MS, demonstrating dual functionality for these orthogonal techniques. Modifying the dried blood extraction procedures also allows for the observation of blood triacylglycerols by SALDI-MS. This is the first demonstration of a SERS/SALDI-MS substrate based on a sol-gel scaffold and the first demonstration of a gold NP sol-gel substrate for SALDI-MS which features lower substrate-related SALDI-MS background compared to the silver substrate.

Study on Biogenic Spindle-Shaped Iron-Oxide Nanoparticles by Pseudostaurosira trainorii in Field of Laser Desorption/Ionization Applications

Nanostructures-assisted laser desorption/ionization mass spectrometry (NALDI-MS) is gaining attention for the analysis of a wide range of molecules. In this present investigation, Pseudostaurosira trainorii mediated biosynthesized iron-oxide nanoparticles (IONPs) have been utilized as nanostructures assisting ionization and desorption for laser desorption/ionization mass spectrometry (LDI-MS). The chain forming diatom, P. trainorii showed efficiency in the production of IONPs against 0.01 M Fe+3 (pH 2) aqueous solution at the intracellular and extracellular level. The whole biomass and external media turned dark orange in color after 3 days of reaction with Fe3+ solution. Scanning electron microscopic (SEM) images illustrated that the surface of Fe3+ exposed frustules of P. trainorii were entirely covered by synthesized nanostructures contrasting with the natural surface ornamentation of control cells. The IONPs loaded frustules also exhibited catalytic properties by decolorizing yellow colored nitrophenol after 3 h of reaction. Transmission electron microscopic (TEM) images confirmed that the produced particles are spindle-shaped with ~50–70 nm length and ~10–30 nm width. The biogenic IONPs were utilized as an inorganic matrix in LDI-MS and showed high sensitivity towards small molecules as glucose, alanine and triacylglycerols at nano- and picomolar level per spot, respectively. The presented biocompatible technique offers new perspectives in nanobiotechnology for the production of spindle-shaped IONPs that can be applied in future for the preparation of NALDI plates.

Infrared pulsed fiber laser-produced silver-109-nanoparticles for laser desorption/ionization mass spectrometry of amino acids

Application of monoisotopic cationic 109Ag nanoparticles (109AgNPs) obtained by pulsed fiber laser (PFL) 2D galvo-scanner (GS) laser generated nanomaterial (LGN) for both high resolution laser desorption/ionization mass spectrometry and mass spectrometry imaging of amino acids is presented. Four amino acids, alanine, isoleucine, lysine, and phenylalanine were used as test compounds for quantification with matrix-assisted laser desorption/ionization mas (MALDI)-type mass spectrometer. Comparison of commonly made manual measurements with semiautomatic mass spectrometry imaging (MSI) was performed providing very interesting findings. Amino acids were directly tested in 1 000 000-fold concentration change conditions ranging from 1 mg/ml to 1 ng/ml, which equates to 500 ng to 500 fg of amino acid per measurement spot. Methods were also tested on samples of human blood plasma for quantification of endogenous amino acids.

Hybrid Surface Design of Organosilica Films for Laser Desorption/Ionization Mass Spectrometry: Low Free Energy Surface with Interactive Sites

Laser desorption/ionization mass spectrometry (LDI-MS) assisted by solid substrates is useful for the facile and rapid analysis of low-molecular-weight compounds. The LDI performance of solid substrates depends on not only a surface morphology but also the surface functionalities dominating the surface-analyte interactions. In this study, we propose a hybrid surface design for LDI substrates, realizing both weak surface-analyte interaction and homogeneous distribution of analytes. The hybrid surface consisted of a mixture of fluoroalkylsilane (FAS), SiO₂, and TiO₂ and was formed on organosilica substrates containing UV-laser-absorbing naphthalimide moieties. To investigate the surface interactions, the hybrid surface as well as conventional hydrophobic surfaces treated with FAS only were prepared on flat organosilica films. Contact angle measurements and surface free energy analysis showed that the hybrid surface exhibited the highest hydrophobicity, while the contribution of the polar and hydrogen bonding terms in the surface free energy was clearly observed. The organosilica film with the hybrid surface demonstrated significant LDI performance for the detection of biorelated compounds (e.g., peptides, phospholipids, and medicines), and a high detection ability was particularly observed for peptides. The substrate surface promoted the desorption/ionization of analytes through a low surface free energy and uniform distribution of the analytes due to the interactive sites. The hybrid surface design was then applied to a nanostructured organosilica substrate consisting of a base film and a nanoparticle layer. The signal intensity of a peptide was further improved approximately 3-fold owing to the increased surface area of the nanostructured substrate, and the limit of detection reached the subfemtomole order. Our hybrid surface design is expected to improve the LDI performance of various nanostructured solid substrates.

Complementarity of Matrix- and Nanostructure-Assisted Laser Desorption/Ionization Approaches

In recent years, matrix-assisted laser desorption/ionization (MALDI) has become the main tool for the study of biological macromolecules, such as protein nano-machines, especially in the determination of their molecular masses, structure, and post-translational modifications. A key role in the classical process of desorption and ionization of the sample is played by a matrix, usually a low-molecular weight weak organic acid. Unfortunately, the interpretation of mass spectra in the mass range of below m/z 500 is difficult, and hence the analysis of low molecular weight compounds in a matrix-assisted system is an analytical challenge. Replacing the classical matrix with nanomaterials, e.g., silver nanoparticles, allows improvement of the selectivity and sensitivity of spectrometric measurement of biologically important small molecules. Nowadays, the nanostructure-assisted laser desorption/ionization (NALDI) approach complements the classic MALDI in the field of modern bioanalytics. In particular, the aim of this work is to review the recent advances in MALDI and NALDI approaches.

Immobilization of ultrafine Ag nanoparticles on well-designed hierarchically porous silica for high-performance catalysis

Catalyst immobilization is of much significance not only for maintaining the high activity of the ultrafine catalyst, but also for the separation of catalyst during the practical application. Herein, a novel support material, three-dimensional hierarchically porous silica (HPS) with interconnected micro-meso-macro pores and high specific surface area was successfully fabricated though a freeze-drying technique in the presence of poly(vinyl alcohol) (PVA) and subsequent calcination process. A series of characterizations revealed that the specific surface area of HPS can be well adjusted by changing the addition of PVA. The specific surface area of HPS was as high as 360 m² g^-1, which was 211-fold higher than HPS-0 (silica prepared without using PVA). To demonstrate the potential application of such novel support material, highly dispersed silver nanoparticles (AgNPs) were immobilized on the surfaces of HPS and HPS-0 through in-situ reduction. By contrast, the catalytic activity of AgNPs anchored on HPS (531 s^-1 g^-1) was about 42-fold higher than that of AgNPs anchored on HPS-0 (12.67 s^-1 g^-1). The significantly enhanced catalytic activity of AgNPs/HPS was believed to be related to their high specific surface area and interconnected macroporous scaffolds, which could provide numerous reactive sites and mass transfer routes for the reactants.

Highly oriented Langmuir-Blodgett film of silver cuboctahedra as an effective matrix-free sample plate for surface-assisted laser desorption/ionization mass spectrometry

The design of a homogeneous sample plate to solve the sweet heating spot issues is the key step to expand the applicability of surface-assisted laser desorption/ionization mass spectrometry (SALDI MS). Herein, large-scale and highly oriented Langmuir-Blodgett (LB) films of uniform silver nanocrystals have been fabricated as a highly efficient and matrix-free sample plate for SALDI MS. Three individual silver nanocrystals (cubes, cuboctahedra and octahedra) assembled LB films have been applied as the sample plates for glucose detection by SALDI MS without an additional matrix. The results show that the signal intensity, background noise, signal-to-noise ratio and reproducibility have been significantly improved using LB films as the sample plate in comparison with commercial matrixes of CHCA and DHB. In particular, a relative signal of 5.7% was obtained for LB films of silver cuboctahedra. The significant improvement in the SALDI MS measurement could be attributed to the homogenous dissipation of laser irradiation energy to create a large area of the sweet heating spot on well-oriented silver cuboctahedra-based LB film. This ready-to-use sample plate has the potential for widespread commercial applications in SALDI MS.

Synthesis, characterization and antibacterial activity of Ag incorporated ZnO–graphene nanocomposites

One pot low temperature synthesis of silver incorporated ZnO–chemically converted graphene nanocomposites is reported. An optimum of 10% Ag incorporated sample at 6.25 μg ml⁻¹ dose shows an excellent antibacterial activity on E. coli and S. aureus.

Multi-mode photocatalytic degradation and photocatalytic hydrogen evolution of honeycomb-like three-dimensionally ordered macroporous composite Ag/ZrO2

Honeycomb-like 3DOM Ag/ZrO₂was prepared by using PS as template and combined with one-step method of vacuum impregnation, which had both good photocatalytic degradation under multi-modes and ability on photocatalytic hydrogen evolution.

Green synthesis of silver nanoparticles using Andean blackberry fruit extract

Green synthesis of nanoparticles using various plant materials opens a new scope for the phytochemist and discourages the use of toxic chemicals. In this article, we report an eco-friendly and low-cost method for the synthesis of silver nanoparticles (AgNPs) using Andean blackberry fruit extracts as both a reducing and capping agent. The green synthesized AgNPs were characterized by various analytical instruments like UV–visible, transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The formation of AgNPs was analyzed by UV–vis spectroscopy at λ_max = 435 nm. TEM analysis of AgNPs showed the formation of a crystalline, spherical shape and 12–50 nm size, whereas XRD peaks at 38.04°, 44.06°, 64.34° and 77.17° confirmed the crystalline nature of AgNPs. FTIR analysis was done to identify the functional groups responsible for the synthesis of the AgNPs. Furthermore, it was found that the AgNPs showed good antioxidant efficacy (>78%, 0.1 mM) against 1,1-diphenyl-2-picrylhydrazyl. The process of synthesis is environmentally compatible and the synthesized AgNPs could be a promising candidate for many biomedical applications.

Microwave-Assisted Synthesis of a Series of Ag/ZnO Nanocomposites and Evaluation of Their Photocatalytic Activities under Multi-Mode Photodegradation

A series of Ag/ZnO nanocomposites were prepared under microwave irradiation of different powers (100, 200, and 300 W). The crystal structure, morphology, and surface physicochemical properties of the as-synthesized samples were characterized by X-ray diffraction, UV–visible diffuse reflectance spectroscopy, scanning electron microscopy, and nitrogen adsorption–desorption analyses. Compared with the Ag/ZnO prepared by conventional sedimentation process, the crystal structures of Ag and ZnO did not exhibit any transformation after microwave irradiation; however, slight increases or decreases were observed in their absorption spectra and the specific surface areas. Moreover, the morphologies of all Ag/ZnO samples were changed dramatically by microwave irradiation, showing morphologies such as octagonal nano-pyramidal and multi-angled nano-pyramidal. The multi-mode photocatalytic degradation studies showed that the photocatalytic activities of the Ag/ZnO nanocomposites prepared under microwave irradiation of different powers were enhanced to different extents and were much higher than that of P25, ZnO, and Ag/ZnO prepared in the absence of microwave irradiation.

The synthesis of controlled shape nanoplasmonic silver-silica structures by combining sol-gel technique and direct silver reduction

In this work, we have obtained nanoplasmonic silver structures deposited on the glass substrates by combining sol-gel technology and direct silver ion reduction on the film surfaces. The key point of the work was the usage of polyethylene glycol 400 (PEG 400) both as the pore former and reducing agent for silver ions. We have investigated the influence of PEG 400 amount on the formation of silver nanoparticles on the film surface. It was found that control of PEG 400 amount in the sols allows the creation of porous films with specific organized silver nanoparticles or clusters on the surface. Optical, morphological and structural characteristics of the structures were measured and studied. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used for nanostructure size and shape characterization. We were able to form a 40- to 200-nm-diameter ring-type, spherical and self-assembled nanoparticles on the film surface. The results of UV-vis absorbance spectra have shown the high quality of plasmonic structures with plasmon resonance wavelength in the region between 470 and 480 nm. The synthesized silica films decorated with silver nanoparticles were tested as substrates for the surface-enhanced Raman spectroscopy (SERS) and showed an enhancement relative to micro-Raman of more than 200 times.

Graphene oxide embedded sol–gel (GOSG) film as a SALDI MS substrate for robust metabolite fingerprinting

A graphene oxide embedded sol–gel (GOSG) film was utilized as a substrate for surface-assisted laser desorption/ionization mass spectrometry (SALDI MS).

Silver nanostructures in laser desorption/ionization mass spectrometry and mass spectrometry imaging

Silver nanoparticles have been successfully applied as a matrix replacement for the laser desorption/ionization time-of-flight mass spectrometry (LDI-ToF-MS).

Metal nanotubes and nanowires with rhombohedral cross-section electrolessly deposited in mica templates

Electroless plating is a facile wet-chemical process for the creation of metal thin films on arbitrary substrates, which can be used to produce intricate nanomaterials. In this study, we demonstrate how nanotubes and nanowires can be electrolessly deposited in the rhombohedral pores of ion-track etched muscovite mica templates. Mutual optimization of the activation and plating reactions proved to be essential for the fabrication of well-defined nanostructures of an aspect ratio (length-to-diameter) of up to approximately 70. By repeating the activation procedure utilizing the redox couple Sn(II) and Ag(I), a high density of Ag nanoparticle seeds could be deposited on the template surface, which was required to initiate metal film nucleation with nanoscale homogeneity. Furthermore, it was necessary to adapt the plating reaction to ensure sufficient diffusion of the reagents into the depth of the template pores. To prove the flexibility of the process and to evaluate the effect of the intrinsic film morphology on the shape of the resulting nanostructures, three different plating reactions were applied (Ag, Au, Pt). If the size of the deposited metal particles approached the dimension of the template pores, only wire-like structures of moderate shape conformity were obtained. Electroless plating protocols which yield homogeneous deposits consisting of small nanoparticles allowed exact replication of the pore shape. Under consideration of the above-mentioned requirements, electroless plating displays an effective and versatile route toward the fabrication of parallel arrays of angular metal nanotubes and nanowires in the chemically and thermally robust mica templates. By simply immersing the templates in aqueous plating solutions for an appropriate time, well-defined metal nanomaterials for application in, for example, plasmonics, catalysis, or molecular separation are obtained.