Metal Carbonyl-Gold Nanoparticle Conjugates for Live-Cell SERS Imaging

IRTIDP: A simple integrated real-time isolation and detection platform for small extracellular vesicles Glypican-1 in pancreatic cancer patients

Glypican-1 (GPC-1) protein-positive small extracellular vesicles (GPC-1+-sEV) have been proposed as potential biomarkers for early diagnosis of pancreatic cancer. In this study, we present an integrated real-time isolation and detection platform (IRTIDP) to capture and analyze GPC-1+-sEV directly from sera of pancreatic cancer patients. First, CD63 antibody-modified metal-organic framework (MOF) materials were utilized to enrich sEVs with a capture efficiency of 93.93 %. Second, a SERS probe was constructed by Raman reporter 4-MBA and GPC-1 antibody modified SERS active silver nanoparticles (AgNPs), which formed a sandwich complex structure of "MOFs@GPC-1+-sEV@AgNPs-4-MBA" with MOFs-enriched sEVs. The IRTSDP can complete the capture and detection process within 35 min, with a detection limit for 1 GPC-1+-sEV/μL, and linear range between 105∼109 GPC-1+-sEV/mL. Furthermore, this approach has been applied to quantify serum sEV GPC-1 in clinical pancreatic cancer patients. Based on the SERS intensity analysis, pancreatic cancer patients can be distinguished from pancreatic cystadenoma patients and healthy individuals effectively using this innovative platform that provides highly specific and sensitive means for early diagnosis of pancreatic cancer as well as other tumor types.

Advancing SERS as a quantitative technique: challenges, considerations, and correlative approaches to aid validation

Surface-enhanced Raman scattering (SERS) remains a significant area of research since it's discovery 50 years ago. The surface-based technique has been used in a wide variety of fields, most prominently in chemical detection, cellular imaging and medical diagnostics, offering high sensitivity and specificity when probing and quantifying a chosen analyte or monitoring nanoparticle uptake and accumulation. However, despite its promise, SERS is mostly confined to academic laboratories and is not recognised as a gold standard analytical technique. This is due to the variations that are observed in SERS measurements, mainly caused by poorly characterised SERS substrates, lack of universal calibration methods and uncorrelated results. To convince the wider scientific community that SERS should be a routinely used analytical technique, the field is now focusing on methods that will increase the reproducibility of the SERS signals and how to validate the results with more well-established techniques. This review explores the difficulties experienced by SERS users, the methods adopted to reduce variation and suggestions of best practices and strategies that should be adopted if one is to achieve absolute quantification.

Biomedical applications, perspectives and tag design concepts in the cell - silent Raman window

Spectroscopic studies increasingly employ Raman tags exhibiting a signal in the cell - silent region of the Raman spectrum (1800-2800 cm-1), where bands arising from biological molecules are inherently absent. Raman tags bearing functional groups which contain a triple bond, such as alkyne and nitrile or a carbon-deuterium bond, have a distinct vibrational frequency in this region. Due to the lack of spectral background and cell-associated bands in the specific area, the implementation of those tags can help overcome the inherently poor signal-to-noise ratio and presence of overlapping Raman bands in measurements of biological samples. The cell - silent Raman tags allow for bioorthogonal imaging of biomolecules with improved chemical contrast and they have found application in analyte detection and monitoring, biomarker profiling and live cell imaging. This review focuses on the potential of the cell - silent Raman region, reporting on the tags employed for biomedical applications using variants of Raman spectroscopy.

Acoustofluidic lysis of cancer cells and Raman spectrum profiling

The lysis of cancer cells inside a sessile droplet was performed using traveling surface acoustic waves (SAWs) without any chemical reagents. Raman spectrum profiling was then carried out to explore detailed cell-derived data. The Rayleigh waves formed by an interdigital transducer were made to propagate along the surface of an LiNbO3 substrate. Polystyrene microparticles (PSMPs) were used to establish mechanical cell lysis effectively, and gold nanoparticles (AuNPs) were added to enhance the Raman signals from the lysed cells by SAWs. The lysis efficiency was evaluated according to the size and concentration of the PSMPs in experiments where the frequency was varied. Lysis occurred mainly by mechanical collision using PSMPs in a high-frequency domain, and the lysis efficiency was improved by increasing the application time and the energy density of the SAWs. Raman signals from the lysed cells were greatly enhanced by nanogaps formed by the AuNPs, which were evenly distributed irrespective of the SAWs through the frequency-independent behavior of the AuNPs. Finally, detailed Raman spectra of MDA-MB-231, malignant breast cancer cells, were acquired, and various organic matter-derived peaks were observed. The 95% confidence region for cells subjected to lysis was more widely distributed than that of cells not subjected to lysis. The proposed SAW platform is expected to facilitate the detection of small quantities and to be applied in biomedical applications.

Metasurface-Enhanced Raman Spectroscopy (mSERS) for Oriented Molecular Sensing

Surface-enhanced Raman spectroscopy (SERS) is a widely used sensing technique for ultrasensitivity chemical sensing, biomedical detection, and environmental analysis. Because SERS signal is proportional to the fourth power of the local electric field, several SERS applications have focused on the design of plasmonic nanogaps to take advantage of the extremely strong near-field enhancement that results from plasmonic coupling, but few designs have focused on how SERS detection is affected by molecular orientation within these nanogaps. Here, we demonstrate a nanoparticle-on-metal metasurface designed for near-perfect optical absorption as a platform for Raman detection of highly oriented molecular analytes, including two-dimensional materials and aromatic molecules. This metasurface platform overcomes challenges in nanoparticle aggregation, which commonly leads to low or fluctuating Raman signals in other colloidal nanoparticle platforms. Our metasurface-enhanced Raman spectroscopy (mSERS) platform is based on a colloidal Langmuir-Schaefer deposition, with up to 32% surface coverage density of nanogaps across an entire sensor chip. In this work, we perform both simulations of the local electric field and experimental characterization of the mSERS signal obtained for oriented molecular layers. We then demonstrate this mSERS platform for the quantitative detection of the drinking-water toxin polybrominated diphenyl ether (BDE-15), with a limit of detection of 0.25 μM under 530 μW excitation. This detection limit is comparable to other SERS-based sensors operating at laser powers over 3 orders of magnitude higher, indicating the promise of our mSERS platform for nondestructive and low-level analyte detection.

Experimental and computational investigation of the bond energy of thorium dicarbonyl cation and theoretical elucidation of its isomerization mechanism to the thermodynamically most stable isomer, thorium oxide ketenylidene cation, OTh+CCO

Collision-induced dissociation (CID) of [Th,2C,2O]⁺ with Xe is performed using a guided ion beam tandem mass spectrometer (GIBMS). The only products observed are ThCO⁺ and Th⁺ by sequential loss of CO ligands. The experimental findings and theoretical calculations support that the structure of [Th,2C,2O]⁺ is the bent homoleptic thorium dicarbonyl cation, Th⁺(CO)₂, having quartet spin, which is both thermodynamically and kinetically stable enough in the gas phase to be observed in our GIBMS instrument. Analysis of the kinetic energy-dependent cross sections for this CID reaction yields the first experimental determination of the bond dissociation energy (BDE) of (CO)Th⁺-CO at 0 K as 1.05 ± 0.09 eV. A theoretical BDE calculated at the CCSD(T) level with cc-pVXZ (X = T and Q) basis sets and a complete basis set (CBS) extrapolation is in very good agreement with the experimental result. Although the doublet spin bent thorium oxide ketenylidene cation, OTh⁺CCO, is calculated to be the most thermodynamically stable structure, it is not observed in our experiment where [Th,2C,2O]⁺ is formed by association of Th⁺ and CO in a direct current discharge flow tube (DC/FT) ion source. Potential energy profiles of both quartet and doublet spin are constructed to elucidate the isomerization mechanism of Th⁺(CO)₂ to OTh⁺CCO. The failure to observe OTh⁺CCO is attributed to a barrier associated with C-C bond formation, which makes OTh⁺CCO kinetically inaccessible under our experimental conditions. Chemical bonding patterns in low-lying states of linear and bent Th⁺(CO)₂ and OTh⁺CCO isomers are also investigated.

Comparative Study of In Situ Techniques to Enlarge Gold Nanoparticles for Highly Sensitive Lateral Flow Immunoassay of SARS-CoV-2

Three techniques were compared for lowering the limit of detection (LOD) of the lateral flow immunoassay (LFIA) of the receptor-binding domain of severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) based on the post-assay in situ enlargement of Au nanoparticles (Au NPs) on a test strip. Silver enhancement (growth of a silver layer over Au NPs-Au@Ag NPs) and gold enhancement (growth of a gold layer over Au NPs) techniques and the novel technique of galvanic replacement of Ag by Au in Au@Ag NPs causing the formation of Au@Ag-Au NPs were performed. All the enhancements were performed on-site after completion of the conventional LFIA and maintained equipment-free assay. The assays demonstrated lowering of LODs in the following rows: 488 pg/mL (conventional LFIA with Au NPs), 61 pg/mL (silver enhancement), 8 pg/mL (galvanic replacement), and 1 pg/mL (gold enhancement). Using gold enhancement as the optimal technique, the maximal dilution of inactivated SARS-CoV-2-containing samples increased 500 times. The developed LFIA provided highly sensitive and rapid (8 min) point-of-need testing.

Precise Encoding of Triple-Bond Raman Scattering of Single Polymer Nanoparticles for Multiplexed Imaging Application

Stimulated Raman scattering (SRS) microscopy in combination with innovative tagging strategies offers great potential as a universal high-throughput biomedical imaging tool. Here, we report rationally tailored small molecular monomers containing triple-bond units with large Raman scattering cross-sections, which can be polymerized at the nanoscale for enhancement of SRS contrast with smaller but brighter optical nanotags with artificial fingerprint output. From this, a class of triple-bond rich polymer nanoparticles (NPs) was engineered by regulating the relative dosages of three chemically different triple-bond monomers in co-polymerization. The bonding strategy allowed for 15 spectrally distinguishable triple-bond combinations. These accurately structured nano molecular aggregates, rather than long-chain macromolecules, could establish a universal method for generating small-sized biological SRS imaging tags with high sensitivity for high-throughput multi-color biomedical imaging.

Geometrically encoded SERS nanobarcodes for the logical detection of nasopharyngeal carcinoma-related progression biomarkers

The limited availability of nasopharyngeal carcinoma-related progression biomarker array kits that offer physicians comprehensive information is disadvantageous for monitoring cancer progression. To develop a biomarker array kit, systematic identification and differentiation of a large number of distinct molecular surface-enhanced Raman scattering (SERS) reporters with high spectral temporal resolution is a major challenge. To address this unmet need, we use the chemistry of metal carbonyls to construct a series of unique SERS reporters with the potential to provide logical and highly multiplex information during testing. In this study, we report that geometric control over metal carbonyls on nanotags can produce 14 distinct barcodes that can be decoded unambiguously using commercial Raman spectroscopy. These metal carbonyl nanobarcodes are tested on human blood samples and show strong sensitivity (0.07 ng/mL limit of detection, average CV of 6.1% and >92% degree of recovery) and multiplexing capabilities for MMPs.

Fine synthesis of Prussian-blue analogue coated gold nanoparticles (Au@PBA NPs) for sorting specific cancer cell subtypes

Multiplex surface-enhanced Raman scattering (SERS) detection of markers without background in tumor biosystems has its superiority over other optical methods. Herein, we reported a strategy of quantitative discrimination of two breast cancer cell subtypes. Based on our previous studies, two kinds of Prussian blue analogue coated gold nanoparticles (Au@PBA NPs) were designed and synthesized by the replacement of Fe²⁺ with Pb²⁺ or Cu²⁺. Therefore, two distinct SERS emissions of C≡N bonds at 2122 cm^-1 and 2176 cm^-1 have been acquired. When modified with aptamers of epithelial cell adhesion molecule (EpCAM) and epidermal growth factor receptor (EGFR), which are both expressed in MCF-7 and MDA-MB-231 cell lines but in different levels, the SERS nanoprobes simultaneously identified the relative expression of these biomarkers on the cell surface, providing a good example for ratiometric detection in biosystems without any interference. Each surface marker of tumor cells corresponds to a single SERS emission. Thus, each subtype could be described in a molecular profiling way through duplex C≡N bonds-based SERS emission, which is more advanced than traditional flow cytometry method.

Integrated SERS Platform for Reliable Detection and Photothermal Elimination of Bacteria in Whole Blood Samples

Herein, an interference-free surface-enhanced Raman scattering (SERS) platform with a "sandwich" structure has been developed for reliable detection and photothermal killing of bacteria with whole blood as the real sample. The multifunctional platform comprised a plasmonic gold film (pAu) functionalized with bacteria-capturing units of 4-mercaptophenylboronic acid and internal reference of 4-mercaptobenzonitrile as the SERS substrate and vancomycin-modified core (gold)-shell (Prussian blue) nanoparticles (Au@PB@Van NPs) as the SERS tag. The detected SERS signals were from the Raman-silent region where no background signals occurred from biological sources, eliminating the interference and improving the detection sensitivity and accuracy. As a proof-of-concept, model bacterial strain, Staphylococcus aureus, was captured and detected in the whole blood samples. Furthermore, high antibacterial efficiency of approximately 100% was reached under the synergistic photothermal effect from pAu and Au@PB@Van NPs. This study provides a new avenue for bacteria detection in real samples and their subsequent in situ elimination.

Regulating Tumor N6 -Methyladenosine Methylation Landscape using Hypoxia-Modulating OsSx Nanoparticles

The epigenetic dysregulation and hypoxia are two important factors that drive tumor malignancy, and N⁶ -methyladenosine (m⁶ A) in mRNA is involved in the regulation of gene expression. Herein, a nanocatalyst OsS_x -PEG (PEG = poly(ethylene glycol)) nanoparticles (NPs) as O₂ modulator is developed to improve tumor hypoxia. OsS_x -PEG NPs can significantly downregulate genes involved in hypoxia pathway. Interestingly, OsS_x -PEG NPs elevate RNA m⁶ A methylation levels to cause the m⁶ A-dependent mRNA degradation of the hypoxia-related genes. Moreover, OsS_x -PEG NPs can regulate the expression of RNA m⁶ A methyltransferases and demethylases. Finally, DOX@OsS_x -PEG (DOX = doxorubicin; utilized as a model drug) NPs modulate tumor hypoxia and regulate mRNA m⁶ A methylation of hypoxia-related genes in vivo. As the first report about relationship between catalytic nanomaterials and RNA modifications, the research opens a new avenue for unveiling the underlying action mechanisms of hypoxia-modulating nanomaterials and shows potential of regulating RNA modification to overcome chemoresistance.

In vitro Label Free Raman Microspectroscopic Analysis to Monitor the Uptake, Fate and Impacts of Nanoparticle Based Materials

The continued emergence of nanoscale materials for nanoparticle-based therapy, sensing and imaging, as well as their more general adoption in a broad range of industrial applications, has placed increasing demands on the ability to assess their interactions and impacts at a cellular and subcellular level, both in terms of potentially beneficial and detrimental effects. Notably, however, many such materials have been shown to interfere with conventional in vitro cellular assays that record only a single colorimetric end-point, challenging the ability to rapidly screen cytological responses. As an alternative, Raman microspectroscopy can spatially profile the biochemical content of cells, and any changes to it as a result of exogenous agents, such as toxicants or therapeutic agents, in a label free manner. In the confocal mode, analysis can be performed at a subcellular level. The technique has been employed to confirm the cellular uptake and subcellular localization of polystyrene nanoparticles (PSNPs), graphene and molybdenum disulfide micro/nano plates (MoS₂), based on their respective characteristic spectroscopic signatures. In the case of PSNPs it was further employed to identify their local subcellular environment in endosomes, lysosomes and endoplasmic reticulum, while for MoS₂ particles, it was employed to monitor subcellular degradation as a function of time. For amine functionalized PSNPs, the potential of Raman microspectroscopy to quantitatively characterize the dose and time dependent toxic responses has been explored, in a number of cell lines. Comparing the responses to those of poly (amidoamine) nanoscale polymeric dendrimers, differentiation of apoptotic and necrotic pathways based on the cellular spectroscopic responses was demonstrated. Drawing in particular from the experience of the authors, this paper details the progress to date in the development of applications of Raman microspectroscopy for in vitro, label free analysis of the uptake, fate and impacts of nanoparticle based materials, in vitro, and the prospects for the development of a routine, label free high content spectroscopic analysis technique.

Reversible detection of phosphorylation and dephosphorylation by tip-enhanced Raman spectroscopy using a cyclopentadienyl ruthenium nanotag functionalized tip

The detection of cancer invasion is crucial for diagnosis. In this report, we employed a TERS tip and SERS nanotags to create a cell signaling based nano-sensing system. This system is capable of creating a reversible phosphorylation/de-phosphorylation cycle for TERS measurement. The reversible TERS sensing is then paired with a downstream binding domain, Src homology region 2 (SH2), which is associated with the cell signaling for cancer cell invasion. Such a system offers the advantages of convenient detection of nanotags and high sensitivity as validated in a cell model.

From single cells to complex tissues in applications of surface-enhanced Raman scattering

This tutorial review explores how three of the most common methods for introducing nanoparticles to single cells for surface-enhanced Raman scattering measurements can be adapted for experiments with complex tissues.

Operando characterization of chemical reactions in single living cells using SERS

Operando probing of chemical reactions for the delivery of gaseous signaling molecules in living cells that is critical for understanding the physiological metabolic processes.

Multicolor Raman Beads for Multiplexed Tumor Cell and Tissue Imaging and in Vivo Tumor Spectral Detection

Developing new nanomaterials with strong and distinctive Raman vibrations in the biological Raman-silent region (1800-2800 cm^-1) were highly desirable for Raman hyperspectral detection and imaging in living cells and animals. Herein, polymeric nanoparticles with monomers containing alkyne, cyanide, azide, and carbon-deuterate were prepared as Raman-active nanomaterials (Raman beads) for bioimaging applications. Intense Raman signals were obtained due to the high density of alkyne, cyanide, azide, and carbon-deuterate in single nanoparticles, in absence of metal (such as Au or Ag) as Raman enhancers. We have developed a library of Raman beads for frequency multiplexing through the end-capping substitutions of monomers and demonstrated five-color SRS imaging of mixed nanoparticles with distinct Raman frequencies. In addition, with further surface functionalization of targeting moieties (such as nucleic acid aptamers and targeting peptides), targetable Raman beads were successfully used as probes for tumor targeting and Raman spectroscopic detection, including multicolor SRS imaging in living tumor cells and tissues with high specificity. Further in vivo studies indicated that Raman beads anchored with targeting moieties were successfully employed to target tumors in living mice after tail intravenous injection, and Raman spectral detection of tumor in live mice was achieved only through spontaneous Raman signal at the biological Raman-silent region without any signal enhancement due to a high density of Raman reporters in Raman beads. With further copolymerization of these monomers, Raman beads with supermultiplex barcoding could be readily achieved.

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.

Organometallic-Constructed Tip-Based Dual Chemical Sensing by Tip-Enhanced Raman Spectroscopy for Diabetes Detection

Tip-enhanced Raman spectroscopy (TERS) is capable of probing specific molecular information with high sensitivity, but dual chemical sensing remains a challenge. Another major hindrance to TERS chemical detection in biosamples such as blood is the interference from the strong absorptions of biomolecules. Herein, we report the preparation of an organometallic-conjugated TERS tip. We demonstrate that organometallic chemistry can be perfectly coupled with TERS for dual-molecule sensing. The unique Raman signals generated by the organometallic compound circumvent signal interference from the biomolecules in blood, allowing the rapid analysis of two important molecules (glucose and thiol) in ultralow volume (50 nL) samples. This enabled a correlation between the thiol and glucose levels in the blood of nondiabetic and diabetic patients to be drawn.

Label-Free SERS Quantum Semiconductor Probe for Molecular-Level and in Vitro Cellular Detection: A Noble-Metal-Free Methodology

Accurate in vitro molecular-level analysis is an essential step prior to in vivo and clinical application for early diagnosis and cancer treatment. Among the diagnostic techniques, surface-enhanced Raman scattering (SERS) biosensing has shown growing potential due to its noninvasive and real-time characterization of the biomolecules. However, the application of SERS biosensing is mostly limited to the plasmonic noble metals, in the form of either nanoparticles or tips and substrates (fixed probe), on which surface plasmon resonance (SPR) is the prominent enhancement principle. The semiconductor quantum particles have been explored in several optoelectronics applications, but have never been reported to be exploited as a means of surface-enhanced Raman scattering (SERS) for molecular-level and intracellular sensing. Here, we report on the new generation of noble-metal-free SERS probe; Si@SiO₂ quantum probe (Si@SiO₂ Q-probe) whose affinity to functional groups not only imitates a self-driven labeling attribution that enables charge transfer (CT) as an augmented enhancement principle but also its mobile nature in miniaturized scale facilitates endocytosis for in situ live cell biosensing. Moreover, a significant enhancement factor of 10⁶ of rhodamine 6G (R6G) and 10⁷ of glutathione (GSH) at ∼5 × 10^-12 pM concentration has been achieved that is comparable to inherently plasmonic noble metals. Our results showed a capability of the Si@SiO₂ Q-probe to unveil the "biochemical fingerprint" of substantial components of mammalian and cancerous cervical cells, which leads to diagnosis of cervical cancer. These unique attributions of the Si@SiO₂ Q-probe can provide better insight into cell mutation and malignancy.

Exploring the margins of SERS in practical domain: An emerging diagnostic modality for modern biomedical applications

Excellent multiplexing capability, molecular specificity, high sensitivity and the potential of resolving complex molecular level biological compositions augmented the diagnostic modality of surface-enhanced Raman scattering (SERS) in biology and medicine. While maintaining all the merits of classical Raman spectroscopy, SERS provides a more sensitive and selective detection and quantification platform. Non-invasive, chemically specific and spatially resolved analysis facilitates the exploration of SERS-based nano probes in diagnostic and theranostic applications with improved clinical outcomes compared to the currently available so called state-of-art technologies. Adequate knowledge on the mechanism and properties of SERS based nano probes are inevitable in utilizing the full potential of this modality for biomedical applications. The safety and efficiency of metal nanoparticles and Raman reporters have to be critically evaluated for the successful translation of SERS in to clinics. In this context, the present review attempts to give a comprehensive overview about the selected medical, biomedical and allied applications of SERS while highlighting recent and relevant outcomes ranging from simple detection platforms to complicated clinical applications.

Surface-enhanced Raman spectroscopic identification in fingerprints based on adhesive Au nanofilm

The visualization and acquisition of information on substances within fingerprints have attracted considerable interest owing to their practical application in forensic science. There are still some challenges in the transfer and imaging of fingerprints and the extraction of residues. Here, a facile approach was successfully developed for transferring and recovering the pattern of fingerprints, which is based on surface-enhanced Raman spectroscopy (SERS) and an adhesive Au nanofilm (ANF). The reproducibility of SERS effects and the adhesive quality of the ANF enabled the transfer, recovery of the pattern and extraction of chemical residues from living/latent fingerprints. The results demonstrated that the pattern of living fingerprints, including ridges, furrows and sweat pores, was recovered on the basis of SERS mapping of the vibrational band of amino acids from endogenous protein substances. The dye rhodamine 6G (R6G) was employed as a developing agent to enhance the visualization of fingerprints by SERS mapping of the band at 1360 cm-1. Moreover, exogenous residues, such as cotinine (COT) and methylene blue (MB), were also detected by SERS. Their distribution in fingerprints was also determined, although it was not associated with the pattern of fingerprints. This indicated that the extraction process based on the adhesive ANF could be applied to transfer fingerprints from a crime scene to the laboratory for precise identification via structural information on chemical residues and the pattern image of fingerprints. It is anticipated that the adhesive ANF when combined with an ultrahigh-sensitivity SERS technique could be developed as a promising tool for the visualization of fingerprints and monitoring of trace chemical residues for crime tracking in forensic science.

Metal Carbonyls for the Biointerference-Free Ratiometric Surface-Enhanced Raman Spectroscopy-Based Assay for Cell-Free Circulating DNA of Epstein-Barr Virus in Blood

By taking advantage of the spectral properties of metal carbonyls, we have designed a surface-enhanced Raman spectroscopy (SERS) ratiometric assay for measuring cell-free circulating DNA (cfDNA) from Epstein-Barr virus in blood for nasopharyngeal carcinoma (NPC). This assay consists of a rhenium carbonyl (Re-CO) to serve as a DNA probe, an osmium carbonyl (Os-CO) embedded within the SERS-active substrate as an internal reference, and a streptavidin layer on the surface of the substrate. Hybridization of cfDNA with biotinylated-capture sequence leads to immobilization of cfDNA on the substrate. The binding of Re-CO via daunorubicin (DNR) to cfDNA is accompanied by an appearance of a strong symmetry stretching vibrations peak at 2113 cm^-1, which has spectral overlap with Os-CO (2025 cm^-1). This results in an increase in the I₂₁₁₃/ I₂₀₂₅ ratio and quantitatively correlates with cfDNA. This SERS assay can be readily used to detect cfDNA in blood samples from patients due to the intensity ratio of I₂₁₁₃/ I₂₀₂₅ lying in a silent region (1780-2200 cm^-1) in the SERS spectrum of the biomolecules.

Surface-Enhanced Raman Spectroscopy for Bioanalysis: Reliability and Challenges

Surface-enhanced Raman spectroscopy (SERS) inherits the rich chemical fingerprint information on Raman spectroscopy and gains sensitivity by plasmon-enhanced excitation and scattering. In particular, most Raman peaks have a narrow width suitable for multiplex analysis, and the measurements can be conveniently made under ambient and aqueous conditions. These merits make SERS a very promising technique for studying complex biological systems, and SERS has attracted increasing interest in biorelated analysis. However, there are still great challenges that need to be addressed until it can be widely accepted by the biorelated communities, answer interesting biological questions, and solve fatal clinical problems. SERS applications in bioanalysis involve the complex interactions of plasmonic nanomaterials with biological systems and their environments. The reliability becomes the key issue of bioanalytical SERS in order to extract meaningful information from SERS data. This review provides a comprehensive overview of bioanalytical SERS with the main focus on the reliability issue. We first introduce the mechanism of SERS to guide the design of reliable SERS experiments with high detection sensitivity. We then introduce the current understanding of the interaction of nanomaterials with biological systems, mainly living cells, to guide the design of functionalized SERS nanoparticles for target detection. We further introduce the current status of label-free (direct) and labeled (indirect) SERS detections, for systems from biomolecules, to pathogens, to living cells, and we discuss the potential interferences from experimental design, measurement conditions, and data analysis. In the end, we give an outlook of the key challenges in bioanalytical SERS, including reproducibility, sensitivity, and spatial and time resolution.

Water soluble derivatives of platinum carbonyl Chini clusters: synthesis, molecular structures and cytotoxicity of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2-

The reactions of [Pt3n(CO)6n]2- (n = 2-5) homoleptic Chini-type clusters with increasing amounts of 1,3,5-triaza-7-phosphaadamantane (PTA) result in the stepwise substitution of one terminal CO ligand per Pt3 triangular unit up to the formation of [Pt3n(CO)5n(PTA)n]2- (n = 2-5). Competition between the nonredox substitution with retention of the nuclearity and the redox fragmentation to afford lower nuclearity heteroleptic Chini-type clusters is observed as a function of the amount of PTA and the nuclearity of the starting cluster. Because of this, [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- are more conveniently obtained via the oxidation of [Pt9(CO)15(PTA)3]2-. All the new species were spectroscopically characterized, and the structures of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- were determined by single-crystal X-ray diffraction. These clusters may be viewed as heteroleptic Chini-type clusters composed of stacks of four and five Pt3(μ-CO)3(CO)2(PTA) units, respectively. The solubility in water of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- has been determined and their cytotoxicity towards human ovarian (A2780) cancer cells and their cisplatin-resistant strain (A2780cisR) has been evaluated.

Flexible Modulation of CO-Release Using Various Nuclearity of Metal Carbonyl Clusters on Graphene Oxide for Stroke Remediation

Utilizing the size-dependent adsorption properties of ruthenium carbonyl clusters (Ru-carbon monoxide (CO)) onto graphene oxide (GO), a facile CO-release platform for in situ vasodilation as a treatment for stroke-related vascular diseases is developed. The rate and amount of formation of the CO-release-active Ru^II (CO)₂ species can be modulated by a simple mixing procedure at room temperature. The subsequent thermally induced oxidation of Ru^II (CO)₂ to RuO₂ on the GO surface results in the release of CO. Further modulation of thermal and CO-release properties can be achieved via a hybridization of medium- and high-nuclearity of Ru-CO clusters that produces a RuO₂ /Ru^II (CO)₂ /⁶ Ru-CO-GO composite, where ⁶ Ru-CO-GO provides a photothermally activated reservoir of Ru^II (CO)₂ species and the combined infrared absorption properties of GO and RuO₂ provides photothermal response for in situ CO-release. The RuO₂ /Ru^II (CO)₂ /⁶ Ru-CO-GO composite does not produce any cytotoxicity and the efficacy of the composite is further demonstrated in a cortical photothrombotic ischemia rat model.

Structure and dynamics of heterometallic clusters derived from addition of metal carbonyl fragments to the unsaturated hydride [W2Cp2(μ-H)(μ-PPh2)(NO)2]

The title complex reacted with [Fe₂(CO)₉] to give the trinuclear derivative [FeW₂Cp₂(μ-H)(μ-PPh₂)(CO)₄(NO)₂] (W-W = 3.044(1) Å) as a result of full insertion of the 16-electron Fe(CO)₄ fragment into the tricentric W-H-W bond of the parent substrate. In contrast, the reactions with the THF adducts [M(CO)₅(THF)] (M = W, Mo) and [MnCp'(CO)₂(THF)] (Cp' = C₅H₄Me) yielded the μ₃-hydride derivatives [MW₂Cp₂(μ₃-H)(μ-PPh₂)(CO)₅(NO)₂] (W-W = 3.006(1) to 3.164(1) Å for the W₃ compound) and [MnW₂Cp₂Cp'(μ₃-H)(μ-PPh₂)(CO)₂(NO)₂] respectively, all of them resulting from addition (rather than insertion) of the corresponding 16-electron fragment to the W₂H moiety of the parent compound. Density Functional Theory calculations revealed that edge- and face-bridged hydride clusters were of similar energy in the W₂Fe system, while the face-bridged structure was significantly more stable (by more than ca. 40 kJ mol^-1) for the W₃ system. Both clusters displayed fast rearrangement in solution involving a flapping movement of the puckered PW₂M core of these molecules. This was combined, in the W₂Fe cluster, with fast exchange between the almost isoenergetic edge- and face-bridged hydride isomers. The reactions of the title compound with several carbonyl dimers were also examined as an additional synthetic approach to the rational synthesis of heterometallic clusters, but were unsuccessful except in the case of [Co₂(CO)₈], which reacted at 253 K in the dark to give a mixture of the binuclear complex [CoWCp(μ-PPh₂)(CO)₄(NO)] (Co-W = 2.8623(6) Å) and the trinuclear cluster [CoW₂Cp₂(μ-PPh₂)(CO)₄(NO)₂] (W-W = 3.1654(4) Å; W-Co = 2.638(1), 2.829(1) Å), the latter resulting from formal replacement of the hydride ligand with the 17-electron fragment Co(CO)₄, which displayed an asymmetric binding to the W₂ centre.

Metal carbonyl-gold nanoparticle conjugates for highly sensitive SERS detection of organophosphorus pesticides

The binding of organometallic osmium carbonyl clusters onto the surface of gold nanoparticles (10OsCO-Au NPs) greatly enhanced the CO stretching vibration signal at ~2100cm-1, which is relatively free from interference due to the absorbance of biomolecules. By utilizing the acetylcholinesterase (AChE) mediated hydrolysis of acetylthiocholine to thiocholine where the activity of AChE is inhibited by the presence of organophosphate pesticides (OPPs), the subsequent thiocholine-induced aggregation of 10OsCO-Au NPs can be monitored by the change in color of the NPs solution and the variation in intensity of the SERS CO signal. The change in color offers a fast pre-screening method, whereas monitoring via SERS is used for greater accuracy and lower limit of detection (0.1 ppb) for quantitative detection. Its potential as a quick and accurate method of OPPs monitoring in consumer products was demonstrated in the detection of OPPs in real spiked samples such as beer.

Large-Scale Nanofabrication of Designed Nanostructures Using Angled Nanospherical-Lens Lithography for Surface Enhanced Infrared Absorption Spectroscopy

Nanophotonics has been a focused research discipline for the past decade and has resulted in many novel concepts that promise to change human life. However, the actual penetration of this research into real products is severely limited mostly due to the slow development of economic nanofabrication. In this study, we have demonstrated a versatile and low-cost nanofabrication method referred to as "angled nanospherical-lens lithography (A-NLL)", which is able to produce large-scale and periodic nanopatterns. The nanopatterns designed within a two-dimensional polar chart can be carefully fabricated on the substrate. The fabricated patterns easily cover an area larger than 1 cm², which is beneficial as platforms for surface enhanced infrared absorption (SEIRA) where an expensive and bulky IR microscope is not required. We believe that the proposed A-NLL method is ideal for industrialization of future nanophotonic applications.

High-Precision Profiling of Sialic Acid Expression in Cancer Cells and Tissues Using Background-Free Surface-Enhanced Raman Scattering Tags

Precise profiling of the sialic acid (SA) expression on the membrane of cancer cells is critical for early identification of cancers and assessment of cancer metastasis. However, the complex physiological environments often result in false positives with currently available imaging technologies. Herein, we have established a background-free surface-enhanced Raman scattering (SERS) imaging platform that allows high-precision profiling of SA expression in cancer cells and differentiation of clinically relevant cancer tissues with various metastasis degrees. Three-dimensional Raman imaging technique provided a deeper insight into visualizing the probe distribution and thus the SA expression at the single-cell level, without destructing the cells. This noninvasive, high-precision imaging technique could favor early diagnosis, staging, and monitoring therapeutic responses of cancers that are highly essential in clinical settings.

Building Electromagnetic Hot Spots in Living Cells via Target-Triggered Nanoparticle Dimerization

Electromagnetic hot spots of surface-enhanced Raman scattering have been extensively employed for bioanalysis in solution or on a substrate, but building hot spots in living systems for probing targets of interest has not been achieved yet because of the complex and dynamic physiological environment. Herein, we show that a target-programmed nanoparticle dimerization can be combined with the background-free Raman reporters (alkyne, C≡C; nitrile, C≡N) for multiplexed imaging of microRNAs (miRNAs) in living cells. The in situ formation of plasmonic dimers results in an intense hot spot, thus dramatically enhancing the Raman signals of the reporters residing in the hot spot. More significantly, the reporters exhibit single nonoverlapping peaks in the cellular Raman-silent region (1800-2800 cm^-1), thus eliminating spectral unmixing and background interference. A 3D Raman mapping technique was harnessed to monitor the spatial distribution of the dimers and thus the multiple miRNAs in cells. This approach could be extended to probe other biomarkers of interest for monitoring specific pathophysiological events at the live-cell level.

Interference-Free Surface-Enhanced Raman Scattering Tags for Single-Cell Molecular Imaging with a High Signal-to-Background Ratio

An interference-free surface-enhanced Raman scattering tag is constructed to profile the expression of cancer biomarkers at the single-cell level. The Raman tags present a strong and sharp peak in the cellular Raman-silent region, significantly diminishing the background interference. Moreover, the reporters are embedded in the layered gold nanoparticles, avoiding desorption and enzymatic degradation in physiological conditions.

Optical Interference-Free Surface-Enhanced Raman Scattering CO-Nanotags for Logical Multiplex Detection of Vascular Disease-Related Biomarkers

Matrix metalloproteinases (MMPs), specifically MMP-2, MMP-7, and MMP-9, have been discovered to be linked to many forms of vascular diseases such as stroke, and their detection is crucial to facilitate clinical diagnosis. In this work, we prepared a class of optical interference-free SERS nanotags (CO-nanotags) that can be used for the purpose of multiplex sensing of different MMPs. Multiplex detection with the absence of cross-talk was achieved by using CO-nanotags with individual tunable intrinsic Raman shifts of CO in the 1800-2200 cm^-1 region determined by the metal core and ligands of the metal carbonyl complex. Boolean logic was used as well to simultaneously probe for two proteolytic inputs. Such nanotags offer the advantages of convenient detection of target nanotags and high sensitivity as validated in the ischemia rat model.

A promising magnetic SERS immunosensor for sensitive detection of avian influenza virus

Avian influenza viruses infect a great number of global populations every year and can lead to severe epidemics with high morbidity and mortality. Facile, rapid and sensitive detection of viruses is very crucial to control the viral spread at its early stage. In this work, we developed a novel magnetic immunosensor based on surface enhanced Raman scattering (SERS) spectroscopy to detect intact but inactivated influenza virus H3N2 (A/Shanghai/4084T/2012) by constructing a sandwich complex consisting of SERS tags, target influenza viruses and highly SERS-active magnetic supporting substrates. The procedure of sample pretreatment could be significantly simplified since the magnetic supporting substrates allowed the enrichment and separation of viruses from a complex matrix. With a portable Raman spectrometer, the immunosensor could detect H3N2 down to 10²TCID₅₀/mL (TCID₅₀ refers to tissue culture infection dose at 50% end point), with a good linear relationship from 10² to 5×10³ TCID₅₀/mL. Considering its time efficiency, portability and sensitivity, the proposed SERS-based magnetic immunoassay is very promising for a point-of-care (POC) test in clinical and diagnostic praxis.