Robust but ultrasensitive biosensors with a capability of detecting low abundance biomarkers could revolutionize clinical diagnostics and enable early detection of cancer, neurological diseases, and ...infections. We utilized a combination of localized surface plasmon resonance (LSPR) refractive index sensing and the well-known enzyme-linked immunosorbent assay to develop a simple colorimetric biosensing methodology with single molecule sensitivity. The technique is based on spectral imaging of a large number of isolated gold nanoparticles. Each particle binds a variable number of horseradish peroxidase (HRP) enzyme molecules that catalyze a localized precipitation reaction at the particle surface. The enzymatic reaction dramatically amplifies the shift of the LSPR scattering maximum, λmax, and makes it possible to detect the presence of only one or a few HRP molecules per particle.
This perspective presents recent developments in the application of surface-enhanced Raman spectroscopy (SERS) to biosensing, with a focus on in vivo diagnostics. We describe the concepts and ...methodologies developed to date and the target analytes that can be detected. We also discuss how SERS has evolved from a “point-and-shoot” stand-alone technique in an analytical chemistry laboratory to an integrated quantitative analytical tool for multimodal imaging diagnostics. Finally, we offer a guide to the future of SERS in the context of clinical diagnostics.
Molecule–surface interactions and processes are at the heart of many technologies, including heterogeneous catalysis, organic photovoltaics, and nanoelectronics, yet they are rarely well understood ...at the molecular level. Given the inhomogeneous nature of surfaces, molecular properties often vary among individual surface sites, information that is lost in ensemble-averaged techniques. In order to access such site-resolved behavior, a technique must possess lateral resolution comparable to the size of surface sites under study, analytical power capable of examining chemical properties, and single-molecule sensitivity. Tip-enhanced Raman spectroscopy (TERS), wherein light is confined and amplified at the apex of a nanoscale plasmonic probe, meets these criteria. In ultrahigh vacuum (UHV), TERS can be performed in pristine environments, allowing for molecular-resolution imaging, low-temperature operation, minimized tip and molecular degradation, and improved stability in the presence of ultrafast irradiation. The aim of this review is to give an overview of TERS experiments performed in UHV environments and to discuss how recent reports will guide future endeavors. The advances made in the field thus far demonstrate the utility of TERS as an approach to interrogate single-molecule properties, reactions, and dynamics with spatial resolution below 1 nm.
Hair is one of the most common types of physical evidence found at a crime scene. Forensic examination may suggest a connection between a suspect and a crime scene or victim, or it may demonstrate an ...absence of such associations. Therefore, forensic analysis of hair evidence is invaluable to criminal investigations. Current hair forensic examinations are primarily based on a subjective microscopic comparison of hair found at the crime scene with a sample of suspect’s hair. Since this is often inconclusive, the development of alternative and more-accurate hair analysis techniques is critical. In this study, we utilized surface-enhanced Raman spectroscopy (SERS) to demonstrate that artificial dyes can be directly detected on hair. This spectroscopic technique is capable of a confirmatory identification of analytes with single molecule resolution, requires minimal sample, and has the advantage of fluorescence quenching. Our study reveals that SERS can (1) identify whether hair was artificially dyed or not, (2) determine if a permanent or semipermanent colorants were used, and (3) distinguish the commercial brands that are utilized to dye hair. Such analysis is rapid, minimally destructive, and can be performed directly at the crime scene. This study provides a novel perspective of forensic investigations of hair evidence.
We describe the fabrication of optimized plasmonic substrates in the form of immobilized nanorod assemblies (INRA) for surface-enhanced Raman spectroscopy (SERS). Included are high-resolution ...scanning electron micrograph (SEM) images of the surface structures, along with a mechanistic description of their growth. It is shown that, by varying the size of support microspheres, the surface plasmon resonance is tuned between 330 and 1840 nm. Notably, there are predicted optimal microsphere sizes for each of the commonly used SERS laser wavelengths of 532, 633, 785, and 1064 nm.
The incorporation of tetraoxolene radical bridging ligands into a microporous magnetic solid is demonstrated. Metalation of the redox-active bridging ligand ...2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (LH2) with FeII affords the solid (Me2NH2)2Fe2L3·2H2O·6DMF. Analysis of X-ray diffraction, Raman spectra, and Mössbauer spectra confirm the presence of FeIII centers with mixed-valence ligands of the form (L3)8– that result from a spontaneous electron transfer from FeII to L2–. Upon removal of DMF and H2O solvent molecules, the compound undergoes a slight structural distortion to give the desolvated phase (Me2NH2)2Fe2L3, and a fit to N2 adsorption data of this activated compound gives a BET surface area of 885(105) m2/g. Dc magnetic susceptibility measurements reveal a spontaneous magnetization below 80 and 26 K for the solvated and the activated solids, respectively, with magnetic hysteresis up to 60 and 20 K. These results highlight the ability of redox-active tetraoxolene ligands to support the formation of a microporous magnet and provide the first example of a structurally characterized extended solid that contains tetraoxolene radical ligands.
Nanoparticle encapsulation inside zirconium-based metal–organic frameworks (NP@MOF) is hard to control, and the resulting materials often have nonuniform morphologies with NPs on the external surface ...of MOFs and NP aggregates inside the MOFs. In this work, we report the controlled encapsulation of gold nanorods (AuNRs) by a scu-topology Zr-MOF, via a room-temperature MOF assembly. This is achieved by functionalizing the AuNRs with poly(ethylene glycol) surface ligands, allowing them to retain colloidal stability in the precursor solution and to seed the MOF growth. Using this approach, we achieve core–shell yields exceeding 99%, tuning the MOF particle size via the solution concentration of AuNRs. The functionality of AuNR@MOFs is demonstrated by using the AuNRs as embedded probes for selective surface-enhanced Raman spectroscopy (SERS). The AuNR@MOFs are able to both take-up or block molecules from the pores, thereby facilitating highly selective sensing at the AuNR ends. This proof-of-principle study serves to present both the outstanding level of control in the synthesis and the high potential for AuNR@Zr-MOF composites for SERS.
Electrochemical tip-enhanced Raman spectroscopy (EC-TERS) has been implemented to investigate the structure and activity of iron(II) phthalocyanine (FePc)a model catalyst for the oxygen reduction ...reaction (ORR). Using EC-TERS, both reversible change and irreversible degradation to FePc have been observed during ORR. The reversible change in the Raman spectrum of FePc can be related to the FePc molecules that adapt a nonplanar geometry during catalysis. In contrast, the irreversible degradation of FePc is a consequence of FePc demetalation, leading to the subsequent formation of free base phthalocyanine. This observation affirms that FePc demetalation during ORR proceeds via a direct loss of Fe2+ and that carbon corrosion is not the operative mechanism. Importantly, the FePc demetalation process can be correlated with a loss of ORR activity suggesting that Fe-containing sites are essential for FePc to achieve high catalytic activity. This study establishes EC-TERS as a promising technique for the operando characterization of electrocatalytic reactions at the molecular scale.
Amyloid fibrils are β-sheet rich protein aggregates that are strongly associated with various neurodegenerative diseases. Raman spectroscopy has been broadly utilized to investigate protein ...aggregation and amyloid fibril formation and has been shown to be capable of revealing changes in secondary and tertiary structures at all stages of fibrillation. When coupled with atomic force (AFM) and scanning electron (SEM) microscopies, Raman spectroscopy becomes a powerful spectroscopic approach that can investigate the structural organization of amyloid fibril polymorphs. In this review, we discuss the applications of Raman spectroscopy, a unique, label-free and non-destructive technique for the structural characterization of amyloidogenic proteins, prefibrilar oligomers, and mature fibrils.
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