Nanoglassified, optically-active monolayer films of gold nanoparticles for in situ orthogonal detection by localized surface plasmon resonance and surface-assisted laser desorption/ionization-MS

Efficient Mass Spectrometric Dissection of Glycans via Gold Nanoparticle-Assisted in-Source Cation Adduction Dissociation

Structural identification of glycans is important but remains challenging, for which tandem mass spectrometry has evolved as an indispensable tool. However, it requires additional complex hardware and extra time for ion extraction. Herein, we report a straightforward approach called gold nanoparticles (AuNPs)-assisted in-source cation adduction dissociation (isCAD) for efficient mass spectrometry (MS) dissection of glycans. Although AuNPs have been employed as an inorganic matrix for MALDI MS, this is the first report of AuNP-induced fragmentation. In this approach, AuNPs were employed as an energy absorber for laser ionization as well as a trigger for fragmentation, while residual or deliberately added sodium ions acted as a cationizing agent. The addition of sodium ions induced intensive fragmentation, but the addition of protons suppressed the fragmentation, allowing for facile tuning of the degree of fragmentation. In addition, it was found that larger oligosaccharides and glycans were much easier to fragment as compared with their smaller counterparts, and the use of high-concentration AuNPs effectively suppressed the degree of fragmentation and thereby provided abundant molecular ions. Without any extra hardware and ion extraction, this approach provides a straightforward, cost-efficient and tunable fragmentation for efficient MS dissection of saccharides, including monosaccharides, oligosaccharides, and glycans. Thus, it opens new access to efficient MS dissection of glycans.

Nanoplasmonic sensors for biointerfacial science

In recent years, nanoplasmonic sensors have become widely used for the label-free detection of biomolecules across medical, biotechnology, and environmental science applications. To date, many nanoplasmonic sensing strategies have been developed with outstanding measurement capabilities, enabling detection down to the single-molecule level. One of the most promising directions has been surface-based nanoplasmonic sensors, and the potential of such technologies is still emerging. Going beyond detection, surface-based nanoplasmonic sensors open the door to enhanced, quantitative measurement capabilities across the biointerfacial sciences by taking advantage of high surface sensitivity that pairs well with the size of medically important biomacromolecules and biological particulates such as viruses and exosomes. The goal of this review is to introduce the latest advances in nanoplasmonic sensors for the biointerfacial sciences, including ongoing development of nanoparticle and nanohole arrays for exploring different classes of biomacromolecules interacting at solid-liquid interfaces. The measurement principles for nanoplasmonic sensors based on utilizing the localized surface plasmon resonance (LSPR) and extraordinary optical transmission (EOT) phenomena are first introduced. The following sections are then categorized around different themes within the biointerfacial sciences, specifically protein binding and conformational changes, lipid membrane fabrication, membrane-protein interactions, exosome and virus detection and analysis, and probing nucleic acid conformations and binding interactions. Across these themes, we discuss the growing trend to utilize nanoplasmonic sensors for advanced measurement capabilities, including positional sensing, biomacromolecular conformation analysis, and real-time kinetic monitoring of complex biological interactions. Altogether, these advances highlight the rich potential of nanoplasmonic sensors and the future growth prospects of the community as a whole. With ongoing development of commercial nanoplasmonic sensors and analytical models to interpret corresponding measurement data in the context of biologically relevant interactions, there is significant opportunity to utilize nanoplasmonic sensing strategies for not only fundamental biointerfacial science, but also translational science applications related to clinical medicine and pharmaceutical drug development among countless possibilities.

Plasmonic nanodisc arrays on calcinated titania for multimodal analysis of phosphorylated peptides

A hybrid material of gold nanodiscs on a calcinated titania nanofilm that allows for selective quantitative and qualitative characterization of surface-enriched phosphopeptides has been designed and reported. Fabrication was realized through a combination of layer-by-layer deposition and high temperature calcination for the titania, and hole-mask colloidal lithography for the plasmonic nanostructures. The morphology of the resulting titania material was rigorously characterized, exhibiting substantially decreased surface roughness, which allows for lithographic fabrication of plasmonic nanostructures. Moreover, high specificity in adsorption and enrichment of phosphopeptides was exhibited, which was verified by LSPR shifts and matching peaks under mass spectrometric analysis. The construction of these biochips should inform other combinatorial nanofabrication techniques, in addition to allowing future phosphoproteomic analyses to be performed in a time and resource-efficient manner.

Chemoselective ligation reaction of N-acetylglucosamine (NAG) with hydrazide functional probes to determine galactosyltransferase activity by MALDI mass spectrometry

A perfluorocarbon-modified gold surface is used to immobilize PF-β-NAG and allows quantification of β-GT enzymatic activity with MALDI-TOF/MS.

Bioinspired Assemblies and Plasmonic Interfaces for Electrochemical Biosensing

Electrochemical biosensing represents a collection of techniques that may be utilized for capture and detection of biomolecules in both simple and complex media. While the instrumentation and technological aspects play important roles in detection capabilities, the interfacial design aspects are of equal importance, and often, those inspired by nature produce the best results. This review highlights recent material designs, recognition schemes, and method developments as they relate to targeted electrochemical analysis for biological systems. This includes the design of electrodes functionalized with peptides, proteins, nucleic acids, and lipid membranes, along with nanoparticle mediated signal amplification mechanisms. The topic of hyphenated surface plasmon resonance assays is also discussed, as this technique may be performed concurrently with complementary and/or confirmatory measurements. Together, smart materials and experimental designs will continue to pave the way for complete biomolecular analyses of complex and technically challenging systems.

Classical Characterization Techniques to Reveal the Structural Model of Nanocomposites with Bimetallic Monolayers of Porphyrins

Nanocomposites with bimetallic monolayers of porphyrins were prepared. The well-ordered metalloporphyrin monolayers covalently linked to the gold surface produce an important increase of the B band (∼400 nm) shifted 20 nm relative to that of the related high-spin iron(III) complexes in solution. The position of the B band in the bimetallic architectures is highly dependent on the relative amount of the two porphyrins, showing the most significant shift for the SiO2/APTES/AuNp/Fe-TPyP&M-TPyP (1:1) (30 nm, M = Ni(II) or Cu(II)). Resonance Raman based on the oxidation state marker bands (1553, 1354, and 390 cm(-1)) indicates that Fe-TPyP attached on gold nanoparticles adopts a low-spin Fe(II) conformation, which changes to Fe(II) intermediate spin or a low-spin Fe(III) in the presence of Cu-TPyP or Ni-TPyP. Surface-enhanced Raman scattering studies confirmed the hypothesis. MALDI-TOF analysis of the composites on gold nanoparticles was very useful in the detection of oxygenated forms of the metal complexes.

Calcinated gold nanoparticle arrays for on-chip, multiplexed and matrix-free mass spectrometric analysis of peptides and small molecules

A patterned gold nanoparticle microarray, functionalized with a nanoscale silicate coating, has been developed for on-chip, high-throughput mass spectrometric analyses of biomolecules with minimal sample preparation and reagent costs. Fabrication was realized by the combination of layer-by-layer functionalization of the nanoparticles with suitable polyelectrolytes, followed by fluidic patterning of the glass microarray support and calcination for permanent fixation of the nano-coating. Performance of the microarray was evaluated for surface-assisted laser-desorption/ionization mass spectrometry (SALDI-MS), where the nano-silicate coating was found to enhance SALDI efficiency, resulting in comparable performance to some common organic matrices for small and medium sized molecules. Performance contributing factors of this material have been discussed; heat confinement and interband transition/plasmonic resonance may play important roles. Taking the accessibility of fabrication, performance, and reusability of this substrate together, the material developed here provides a new tool for multiplexed and chip-based mass spectrometric analysis.

On-Demand Formation of Supported Lipid Membrane Arrays by Trehalose-Assisted Vesicle Delivery for SPR Imaging

The fabrication of large-scale, solid-supported lipid bilayer (SLB) arrays has traditionally been an arduous and complex task, primarily due to the need to maintain SLBs within an aqueous environment. In this work, we demonstrate the use of trehalose vitrified phospholipid vesicles that facilitate on-demand generation of microarrays, allowing each element a unique composition, for the label-free and high-throughput analysis of biomolecular interactions by SPR imaging (SPRi). Small, unilamellar vesicles (SUVs) are suspended in trehalose, deposited in a spatially defined manner, with the trehalose vitrifying on either hydrophilic or hydrophobic SPR substrates. SLBs are subsequently spontaneously formed on-demand simply by in situ hydration of the array in the SPR instrument flow cell. The resulting SLBs exhibit high lateral mobility, characteristic of fluidic cellular lipid membranes, and preserve the biological function of embedded cell membrane receptors, as indicated by SPR affinity measurements. Independent fluorescence and SPR imaging studies show that the individual SLBs stay localized at the area of deposition, without any encapsulating matrix, confining coral, or boundaries. The introduced methodology allows individually addressable SLB arrays to be analyzed with excellent label-free sensitivity in a real-time, high-throughput manner. Various protein-ganglioside interactions have been selected as a model system to illustrate discrimination of strong and weak binding responses in SPRi sensorgrams. This methodology has been applied toward generating hybrid bilayer membranes on hydrophobic SPR substrates, demonstrating its versatility toward a range of surfaces and membrane geometries. The stability of the fabricated arrays, over medium to long storage periods, was evaluated and found to be good. The highly efficient and easily scalable nature of the method has the potential to be applied to a variety of label-free sensing platforms requiring lipid membranes for high-throughput analysis of their properties and constituents.