Review of advances in glycan analysis on exosomes, cancer cells, and circulating cancer-derived glycoproteins with an emphasis on electrochemistry

Glycosylation, the intricate process of adding carbohydrate motifs to proteins, lipids, and exosomes on the cell surface, is crucial for both physiological and pathological mechanisms. Alterations in glycans significantly affect cancer cell metastasis by mediating cell-cell and cell-matrix interactions. The subtle changes in glycosylation during malignant transformations highlight the importance of analyzing cell and exosome surface glycosylation for prognostic and early treatment strategies in cancer. This review focuses on recent advancements in sensors for detecting surface glycans on cancer cells, exosomes, and circulating cancer-derived glycoproteins. Among various methods, electrochemical biosensors stand out as a promising tool, offering rapid and cost-effective glycan detection. These devices detect glycan interactions by measuring changes in electrical signals resulting from specific binding events. Techniques such as differential pulse voltammetry, impedance spectroscopy, and chrono amperometry are commonly employed for glycan detection using electrochemical biosensors. Researchers are exploring novel electrode materials and surface functionalization strategies to enhance sensor performance. Notably, selective binding probes such as lectins, aptamers, antibodies, and boronic acids are discussed, with lectins being the most prevalent for specific glycan analysis. By highlighting the significance of electrochemical techniques, emphasizing the role of selective binding probes, integrating microfluidics and miniaturized devices could lead to point-of-care applications for cancer diagnosis and monitoring. This review aims to provide valuable insights for researchers and clinicians working in the field of cancer glycomics.

Surface-enhanced Raman spectroscopy as effective tool for detection of sialic acid as cancer biomarker

Sialic acid, a negatively charged nine-carbon monosaccharide, is mainly located at the terminal end of glycan chains on glycoproteins and glycolipids of cell surface and most secreted proteins. Elevated levels of sialylated glycans have been known as a hallmark in numerous cancers. As a result, sialic acid acts as a useful and accessible cancer biomarker for early cancer detection and monitoring the disease development during cancer treatment which is crucial in elevating the survival rate. The detection of sialic acid has been done by many tools including surface-enhanced Raman spectroscopy (SERS) which gained incredible attention due to its high selectivity and sensitivity. However, currently, comprehensive reviews of sialic acid detection and imaging as a cancer biomarker using SERS are still lacking. Here, we present the significant breakthroughs in SERS-based detection of sialic acid levels on cells, tissues, and body fluids due to the presence of cancer, different cancer metastasis stages, and in response to the external stimuli. This review covers the SERS substrate and novel SERS strategies, using lectin, boronic acid, metabolic glycan labelling and label-free methods, for sialic acid detection as cancer biomarker. The remaining challenges to detect sialic acid and prospect of future development of SERS for other carbohydrate-based cancer biomarker, for instance fucose, are also discussed.

Designing SERS nanotags for profiling overexpressed surface markers on single cancer cells: A review

This review focuses on the chemical design and the use of Surface-Enhanced Raman Scattering (SERS)-active nanotags for measuring surface markers that can be overexpressed at the surface of single cancer cells. Indeed, providing analytical tools with true single-cell measurements capabilities is capital, especially since cancer research is increasingly leaning toward single-cell analysis, either to guide treatment decisions or to understand complex tumor behaviour including the single-cell heterogeneity and the appearance of treatment resistance. Over the past two decades, SERS nanotags have triggered significant interest in the scientific community owing their advantages over fluorescent tags, mainly because SERS nanotags resist photobleaching and exhibit sharper signal bands, which reduces possible spectral overlap and enables the discrimination between the SERS signals and the autofluorescence background from the sample itself. The extensive efforts invested in harnessing SERS nanotags for biomedical purposes, particularly in cancer research, highlight their potential as the next generation of optical labels for single-cell studies. The review unfolds in two main parts. The first part focuses on the structure of SERS nanotags, detailing their chemical composition and the role of each building block of the tags. The second part explores applications in measuring overexpressed surface markers on single-cells. The latter encompasses studies using single nanotags, multiplexed measurements, quantitative information extraction, monitoring treatment responses, and integrating phenotype measurements with SERS nanotags on single cells isolated from complex biological matrices. This comprehensive review anticipates SERS nanotags to persist as a pivotal technology in advancing single-cell analytical methods, particularly in the context of cancer research and personalized medicine.

Detection of Sialic Acid to Differentiate Cervical Cancer Cell Lines Using a Sambucus nigra Lectin Biosensor

Pap smear screening is a widespread technique used to detect premalignant lesions of cervical cancer (CC); however, it lacks sensitivity, leading to identifying biomarkers that improve early diagnosis sensitivity. A characteristic of cancer is the aberrant sialylation that involves the abnormal expression of α2,6 sialic acid, a specific carbohydrate linked to glycoproteins and glycolipids on the cell surface, which has been reported in premalignant CC lesions. This work aimed to develop a method to differentiate CC cell lines and primary fibroblasts using a novel lectin-based biosensor to detect α2,6 sialic acid based on attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and chemometric. The biosensor was developed by conjugating gold nanoparticles (AuNPs) with 5 µg of Sambucus nigra (SNA) lectin as the biorecognition element. Sialic acid detection was associated with the signal amplification in the 1500-1350 cm-1 region observed by the surface-enhanced infrared absorption spectroscopy (SEIRA) effect from ATR-FTIR results. This region was further analyzed for the clustering of samples by applying principal component analysis (PCA) and confidence ellipses at a 95% interval. This work demonstrates the feasibility of employing SNA biosensors to discriminate between tumoral and non-tumoral cells, that have the potential for the early detection of premalignant lesions of CC.

Surface-enhanced Raman scattering sensing for detection and mapping of key cellular biomarkers

Cellular biomarkers mainly contain proteins, nucleic acids, glycans and many small molecules including small biomolecule metabolites, reactive oxygen species and other cellular chemical entities. The detection and mapping of the key cellular biomarkers can effectively help us to understand important cellular mechanisms associated with physiological and pathological processes, which greatly promote the development of clinical diagnosis and disease treatment. Surface-enhanced Raman scattering (SERS) possesses high sensitivity and is free from the influence of strong self-fluorescence in living systems as well as the photobleaching of the dyes. It exhibits rich and narrow chemical fingerprint spectra for multiplexed detection, and has become a powerful tool to detect and map cellular biomarkers. In this review, we present an overview of recent advances in the detection and mapping of different classes of cellular biomarkers based on SERS sensing. These advances fully confirm that the SERS-based sensors and sensing methods have great potential for the exploration of biological mechanisms and clinical applications. Additionally, we also discuss the limitations of present research and the future developments of the SERS technology in this field.

An intelligent alkyne-tag for Raman imaging of living cells: graphdiyne-encapsulated Au nanospheres

A new graphdiyne-encapsulated Au nanosphere (Au@GDY) material was fabricated, which possessed an amplified Raman signal of acetylene linkage and produced bright, stable, and distinct signals in the cellular Raman-silent region. Its signal repeatability is far superior to that of alkyne-containing molecules. This work provides promise as an alkyne-tag for Raman imaging of living cells.

In situ evaluation of in vivo sialylation with a dual-color imaging strategy

This work designs a functional dendrimer probe to conveniently identify newly generated sialic acid groups in vivo with a dual-color imaging strategy, which achieves in situ semiquantitative evaluation of the sialylation difference between tumor and normal tissues to reveal sialylation-related biological events and promote clinical tumor diagnosis.

Tumor identification via in vivo portable Raman detection of sialic acid with a dual gold nanoprobe system

A dual gold nanoprobe system was designed for in vivo portable Raman detection of sialic acid (SA) for tumor identification. The dual gold nanoprobe system contained two gold nanoprobes, Au10-DTTC/PEG-PBA and Au40-PEG-SA. Au10-DTTC/PEG-PBA was constructed on a 10 nm gold nanoparticle modified with 3,3'-diethylthia tricarbocyanine iodide (DTTCI) as the Raman reporter and 3-aminophenylboronic acid (APBA) through a thiol PEG succinimidyl carboxymethyl ester (HS-PEG-NHS) linker for specific recognition of SA. Au40-PEG-SA was constructed on a 40 nm gold nanoparticle modified with SA through HS-PEG-NHS. For in vivo detection of SA, Au10-DTTC/PEG-PBA and Au40-PEG-SA were subsequently injected into tumor xenografted mice with optimal interval and retention times. Through the specific recognition between PBA and SA, the conjugates of Au10-DTTC/PEG-PBA and Au40-PEG-SA formed in the tumor region emitted strong SERS signals of DTTC, which could be detected by a portable Raman detector. This work provides a convenient and portable method to detect SA in tumor xenografted mice, which is useful for family-stay identification and clinical cleavage of tumors.

Chemical Strategies for Dendritic Magneto-plasmonic Nanostructures Applied to Surface-Enhanced Raman Spectroscopy

Chemical analyses in the field using surface-enhanced Raman scattering (SERS) protocols are expected to be part of several analytical procedures applied to water quality monitoring. To date, these endeavors have been supported by developments in SERS substrate nanofabrication, instrumentation portability, and the internet of things. Here, we report distinct chemical strategies for preparing magneto-plasmonic (Fe3 O4  : Au) colloids, which are relevant in the context of trace-level detection of water contaminants due to their inherent multifunctionality. The main objective of this research is to investigate the role of poly(amidoamine) dendrimers (PAMAMs) in the preparation of SERS substrates integrating both functionalities into single nanostructures. Three chemical routes were investigated to design magneto-plasmonic nanostructures that translate into different ways for assessing SERS detection by using distinct interfaces. Hence, a series of magneto-plasmonic colloids have been characterized and then assessed for their SERS activity by using a model pesticide (thiram) dissolved in aqueous samples.

Toward Sensitive and Reliable Surface-Enhanced Raman Scattering Imaging: From Rational Design to Biomedical Applications

Early specific detection through indicative biomarkers and precise visualization of lesion sites are urgent requirements for clinical disease diagnosis. However, current detection and optical imaging methods are insufficient for these demands. Molecular imaging technologies are being intensely studied for reliable medical diagnosis. In the past several decades, molecular imaging with surface-enhanced Raman scattering (SERS) has significant advances from analytical chemistry to medical science. SERS is the inelastic scattering generated from the interaction between photons and substances, presenting molecular structure information. The outstanding SERS virtues of high sensitivity, high specificity, and resistance to biointerference are highly advantageous for biomarker detection in a complex biological matrix. In this work, we review recent progress on the applications of SERS imaging in clinical diagnostics. With the assistance of SERS imaging, the detection of disease-related proteins, nucleic acids, small molecules, and pH of the cellular microenvironment can be implemented for adjuvant medical diagnosis. Moreover, multimodal imaging integrates the high penetration and high speed of other imaging modalities and imaging precision of SERS imaging, resulting in final complete and accurate imaging outcomes and exhibiting robust potential in the discrimination of pathological tissues and surgical navigation. As a promising molecular imaging technology, SERS imaging has achieved remarkable performance in clinical diagnostics and the biomedical realm. It is expected that this review will provide insights for further development of SERS imaging and promote the rapid progress and successful translation of advanced molecular imaging with clinical diagnostics.

In Situ Determination of Sialic Acid on Cell Surface with a pH-Regulated Polymer Enzyme Nanoreactor

Sialic acid (SA) is an important monosaccharide that is involved in incurable cancer immunotherapy. However, it is difficult to detect SA in situ using the existing strategy based on the SA-terminated glycopeptide extraction from the cell lysate. The countermeasures of the bottleneck caused by cell disruption and peptide extraction should be designed based on a "cell-surface attachment and controlled enzymolysis" protocol. Herein, a poly(styrene-co-maleic anhydride-acrylic acid-concanavalin A) (PSM-PAA-ConA) was synthesized and developed as a pH-regulated enzyme nanoreactor after being loaded with sialidase and myoglobin. The nanoreactor showed controllable biocatalysis induced by a cascade enzyme reaction and applied for the in situ detection of SA on a living cell surface. The addition of an acidic solution resulted in a decrease in the size of the nanoreactor and enhancement of its permeability, triggering an "on" state of the SA catalysis. Subsequent pH increase led to increased hydrophilicity of the nanoreactor, increasing its size and resulting in the catalytic "off" state. ConA assisted the cell-surface attachment of the enzyme reactor. Furthermore, SA on the surface of living cancer cells was successfully monitored by the pH-regulated enzyme nanoreactor, demonstrating the feasibility of high specificity in situ analysis for SA. This pH-induced catalytic efficiency control by the enzyme nanoreactor provides a potential platform for functional stimuli-responsive catalytic systems as well as a strategy for in situ analysis of biomolecules on the cell surface.

Cell surface-localized imaging and sensing

Systematically dissecting the molecular basis of the cell surface as well as its related biological activities is considered as one of the most cutting-edge fields in fundamental sciences. The advent of various advanced cell imaging techniques allows us to gain a glimpse of how the cell surface is structured and coordinated with other cellular components to respond to intracellular signals and environmental stimuli. Nowadays, cell surface-related studies have entered a new era featured by a redirected aim of not just understanding but artificially manipulating/remodeling the cell surface properties. To meet this goal, biologists and chemists are intensely engaged in developing more maneuverable cell surface labeling strategies by exploiting the cell's intrinsic biosynthetic machinery or direct chemical/physical binding methods for imaging, sensing, and biomedical applications. In this review, we summarize the recent advances that focus on the visualization of various cell surface structures/dynamics and accurate monitoring of the microenvironment of the cell surface. Future challenges and opportunities in these fields are discussed, and the importance of cell surface-based studies is highlighted.

Multiplex micro-SERS imaging of cancer-related markers in cells and tissues using poly(allylamine)-coated Au@Ag nanoprobes

Surface-enhanced Raman scattering (SERS) nanoprobes based on Au@Ag core@shell nanoparticles coated with poly(allylamine) were functionalized with small targeting molecules to evaluate simultaneously the level of expression of two cancer-related markers, both in cells and in tissues. The Au@Ag nanoparticles provide a high SERS signal enhancement in the visible range when combined with resonant Raman-active molecules. The poly(allylamine) coating plays a dual key role in (i) protecting the metal surface against the complex biological medium, leading to a stable signal of the Raman-active molecules, and (ii) enabling specific biofunctionalization through its amine functions. Using small targeting molecules linked to the polymer coating, two different nanoprobes (duplex approach) were designed. Each was able to specifically target a particular cancer-related marker: folate receptors (FRs) and sialic acid (SA). We demonstrate that the level of expression of these targeted markers can be evaluated following the SERS signal of the probes incubated on cells or tissues. The potential overexpression of folate receptors and of sialic acid was evaluated and measured in breast and ovarian cancerous tissue sections. In addition, FR and/or SA overexpression in the tumor region can be visualized with high contrast with respect to the healthy region and with high spatial accuracy consistent with histology by SERS imaging of the nanoprobe signal. Owing to the unique spectral signature of the designed nanoprobes, this approach offers an efficient tool for the spatially resolved, in situ measurement of the expression level of several cancer-related markers in tumors at the same time.Graphical abstract.

Biochemical reprogramming of tumors for active modulation of receptor-mediated nanomaterial delivery

Here we report that reactive oxygen species (ROS) can reprogram cancer cells to increase the expression of specific receptors and modulate the delivery of nanomaterials. Gold and γ-polyglutamic acid (γ-PGA) hybrid nanoparticles (PGANP) were prepared via a facile single-step process. Gold nanoclusters in PGANP were dispersed within the tangled γ-PGA matrix of the nanoparticles. The condensed assembly of gold nanoclusters in γ-PGA matrix enabled the interparticle plasmon coupling effect, which lacks in single gold nanoparticles. Compared with gold nanoparticles of the similar sizes, PGANP showed significantly higher absorbance at near infrared (NIR) wavelength and light-to-heat converting ratios, resulting in greater temperature increase upon NIR light irradiation. Pretreatment of HeLa cancer cells with methylene blue (MB) generated reactive oxygen species. The ROS reprogrammed the cancer cells to express higher cell membrane levels of gamma glutamyl transferase (GGT), which is known to bind to γ-PGA of PGANP. MB pretreatment significantly enhanced delivery of PGANP to cancer cells. Cancer cells internalized PGANP to a greater extent and, were highly susceptible to irradiation with NIR light, which reduced cell viability to near zero. In vivo, MB pretreatment of HeLa xenograft mice increased the expression of GGT in tumor tissues. In mice pretreated with MB and exposed to NIR irradiation, PGANP treatment resulted in complete tumor ablation. The strategy of actively reprogramming tumor membrane levels of target receptors could be widely applied to overcome the heterogeneity of cancer cells. Although we used interparticle plasmon coupling effect-based PGANP for proving the concept of receptor-modulated delivery, this strategy could be broadly applicable to the active modulation of the receptor-mediated delivery of anticancer nanomaterials.

Rolling "wool-balls": rapid live-cell mapping of membrane sialic acids via poly-p-benzoquinone/ethylenediamine nanoclusters

Here, we report a convenient, fast labeling strategy for the imaging of cell surface sialic acids (SAs, nine-carbon monosaccharides located at the terminals of cell surface sugar chains). This strategy is based on the synthesis of sticky, furry and fluorescent "wool-balls", which are wound into nanoclusters from p-benzoquinone/ethylenediamine polymer "wires". With abundant amino groups at the surface, the wool-balls can easily stick to the C-7 aldehyde group generated at the ends of periodate treated SAs in less than 30 min.

A dual signal amplification nanosensor based on SERS technology for detection of tumor-related DNA

A dual signal amplification method based on surface-enhanced Raman scattering (SERS) is developed by photo-triggered release of SERS probes from mesoporous silica-coated Au nanorods (SiO2@Au) and the use of a specially-designed SERS substrate with an internal reference. Two metal carbonyl (metal-CO) labels (Os-SCO and Re-SCO) are proposed here as novel interference-free labels. Results demonstrate that tumor-related DNA can be quantitatively detected by this reliable and ultra-sensitive SERS platform.

Potentiometric analysis of sialic acid with a flexible carbon cloth based on boronate affinity and molecularly imprinted polymers

A potentiometric sensor for sialic acid detection was designed based on a boronic acid-containing MIP modified carbon cloth electrode.

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.

Identification of breast cancer through spectroscopic analysis of cell-membrane sialic acid expression

Identification of specific and reliable biomarkers or unique characteristics is significant for cancer molecular diagnosis and cancer therapeutic assessment. As a biomarker, sialic acid expression in human biofluid or on cell surface is one of interest to determine the tumor malignancy and metastasis since it involves in many crucial metabolic processes. In this work, we aimed to develop a molecular diagnosis method to make it possible to distinguish human breast cancer and normal tissues by capturing rich spectral features of phenyboronic acid-based nanoprobe (MPBA@AgNP) when it binds to sialic acid on cell surface. We analyzed and found that the marker bands at 1074 and 1570 cm^-1 recorded by Surface-enhanced Raman spectroscopy (SERS) displayed discernible spectral differences in vitro cell lines. Density functional theory (DFT) was further used to explore and support the detailed changes of vibrational modes affected by sialic acid. This method is generally applicable by testing three types of in vitro cell lines (HepG2, Hela, BNL.CL2) and one pair of the tissue sections (cancer tissue and normal tissue) from the human breast regions. Besides, the area under receiver operating characteristic (ROC) curves for 1074 and 1572 cm^-1 are 0.9419 and 0.9023, confirming determination of the specific molecular expression by the spectral features holds potential promise for improving cancer detection accuracy. Furthermore, sialic acid expression and distribution acquired of breast tissues by confocal SERS mapping further indicated our method is possible for cancer early diagnosis and toward to real-time in vivo study.

In Situ Cellular Glycan Analysis

Glycan decorates all mammalian cell surfaces through glycosylation, which is one of the most important post-modifications of proteins. Glycans mediate a wide variety of biological processes, including cell growth and differentiation, cell-cell communication, immune response, pathogen interaction, and intracellular signaling events. Besides, tumor cells aberrantly express distinct sets of glycans, which can indicate different tumor onsets and progression processes. Thus, analysis of cellular glycans may contribute to understanding of glycan-related biological processes and correlation of glycan patterns with disease states for clinical diagnosis and treatment. Although proteomics and glycomics have included great efforts for in vitro study of glycan structures and functions using lysis samples of cells or tissues, they cannot offer real-time qualitative or quantitative information, especially spatial distribution, of glycans on/in intact cells, which is important to the revelation of glycan-related biological events. Moreover, the complex lysis and separation procedures may bring unpredictable loss of glycan information. Focusing on the great urgency for in situ analysis of cellular glycans, our group developed a series of methods for in situ analysis of cellular glycans in the past 10 years. By construction of electrochemical glycan-recognizable probes, glycans on the cell surface can be quantified by direct or competitive electrochemical detection. Using multichannel electrodes or encoded lectin probes, multiple glycans on the cell surface can be dynamically monitored simultaneously. Through design of functional nanoprobes, the cell surface protein-specific glycans and intracellular glycan-related enzymes can be visualized by fluorescence or Raman imaging. Besides, some biological enzymes-based methods have been developed for remodeling or imaging of protein-specific glycans and other types of glycoconjugates, such as gangliosides. Through tracing the changes of glycan expression induced by drugs or gene interference, some glycan-related biological processes have been deduced or proved, demonstrating the reliability and practicability of the developed methods. This Account surveys the key technologies developed in this area, along with the discussion on the shortages of current methodology as well as the possible strategies to overcome those shortages. The future trend in this topic is also discussed. It is expected that this Account can provide a versatile arsenal for chemical and biological researchers to unravel the complex mechanisms involved in glycan-related biological processes and light new beacons in tumor diagnosis and treatment.

Recent progress in surface-enhanced Raman spectroscopy for biological and biomedical applications: from cells to clinics

The application of surface-enhanced Raman spectroscopy (SERS) in biological and biomedical detection schemes is feasible due to its excellent molecular specificity and high sensitivity as well as the capability of SERS to be performed in complex biological compositions. SERS-based investigation of cells, which are the basic structure and functional unit of organisms, represents the starting point of this review. It is demonstrated that SERS provides a deep understanding of living cells as well as their microenvironment which is needed to assess the development of diseases. The clinical relevance of SERS is proved by its application for the detection of cancer cells and tumour margins under in vivo conditions and examples for theranostic approaches are discussed. This review article provides a comprehensive overview of the recent progress within the last 3 years.

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.

Branched Ag nanoplates: synthesis dictated by suppressing surface diffusion and catalytic activity for nitrophenol reduction

Highly branched Ag nanoplates were achieved at extremely low Ag atoms surface diffusion rate, fulfilledviathe Cu under potential deposition.