Engineering State-of-the-Art Plasmonic Nanomaterials for SERS-Based Clinical Liquid Biopsy Applications

Exosomal Proteins and miRNAs as Mediators of Amyotrophic Lateral Sclerosis

Recent advances in the neurobiology and neurogenerative diseases have attracted growing interest in exosomes and their ability to carry and propagate active biomolecules as a means to reprogram recipient cells. Alterations in exosomal protein content and nucleic acid profiles found in human biological fluids have been correlated with various diseases including amyotrophic lateral sclerosis (ALS). In ALS pathogenesis, these lipid-bound nanoscale vesicles have emerged as valuable candidates for diagnostic biomarkers. Moreover, their capacity to spread misfolded proteins and functional non-coding RNAs to interconnected neuronal cells make them putative mediators for the progressive motor degeneration found remarkably apparent in ALS. This review outlines current knowledge concerning the biogenesis, heterogeneity, and function of exosomes in the brain as well as a comprehensive probe of currently available literature on ALS-related exosomal proteins and microRNAs. Lastly, with the rapid development of employing nanoparticles for drug delivery, we explore the therapeutic potentials of exosomes as well as underlying limitations in current isolation and detection methodologies.

Characterizing the Heterogeneity of Small Extracellular Vesicle Populations in Multiple Cancer Types via an Ultrasensitive Chip

Identifying small extracellular vesicle (sEV) subpopulations based on their different molecular signatures could potentially reveal the functional roles in physiology and pathology. However, it is a challenge to achieve this aim due to the nano-sized dimensions of sEVs, low quantities of biological cargo each sEV carries, and our incomplete knowledge of identifying features capable of separating heterogeneous sEV subpopulations. Here, a sensitive, multiplexed, and nano-mixing-enhanced sEV subpopulation characterization platform (ESCP) is proposed to precisely determine the sEV phenotypic heterogeneity and understand the role of sEV heterogeneity in cancer progression and metastasis. The ESCP utilizes spatially patterned anti-tetraspanin-functionalized micro-arrays for sEV subpopulation sorting and nanobarcode-based surface-enhanced Raman spectroscopy for multiplexed read-outs. An ESCP has been used for investigating sEV phenotypic heterogeneity in terms of canonical sEV tetraspanin molecules and cancer-associated protein biomarkers in both cancer cell line models and cancer patient samples. Our data explicitly demonstrate the selective enrichment of tetraspanins and cancer-associated protein biomarkers, in particular sEV subpopulations. Therefore, it is believed that the ESCP could enable the evaluation and broader application of sEV subpopulations as potential diagnostic disease biomarkers.

SERS monitoring of local pH in encapsulated therapeutic cells

Microencapsulation of therapeutic cells has widely advanced toward the development of treatments for various diseases, in particular seeking the protection of cell transplants from immune rejection. However, several challenges in cell therapy remain due to the lack of suitable methods to monitor in vivo microcapsule tracking, microcapsule stability and/or altered cell viability and proliferation upon transplantation. We propose in this work the incorporation of contrast agents in microcapsules, which can be easily visualized by SERS imaging. By placing SERS probes in the alginate extracellular layer, a high contrast can be obtained with negligible toxicity. Specifically, we used a pH-sensitive SERS tracking probe consisting of gold nanostars encoded with a pH-sensitive Raman-active molecule, and protected by a layer of biocompatible polymer coating, grafted on the nanoparticles via electrostatic interactions. This nanomaterial is highly sensitive within the biologically relevant pH range, 5.5-7.8. We demonstrate that this SERS-based pH sensor can provide information about cell death of microencapsulated cells, in a non-invasive manner. As a result, we expect that this approach should provide a general strategy to study biological interactions at the microcapsule level.

Highly specific detection of KRAS single nucleotide polymorphism by asymmetric PCR/SERS assay

The molecular diagnosis of KRAS mutations has become crucial for clinical decision-making in colorectal cancer (CRC) treatments. Currently, the common methods for detecting mutations are based on quantitative PCR, DNA sequencing and droplet digital PCR (ddPCR), which require expensive specialized equipment and testing reagents. Herein, we propose a simple and specific strategy by integrating asymmetric PCR with surface-enhanced Raman spectroscopy (Asy-PCR/SERS) for the detection of KRAS G12V mutation, one of the most common driver mutations in CRC. To discriminate mutant targets from non-targets, Asy-PCR was applied to obtain single-stranded DNA (ssDNA) with unequal amounts of forward and reverse primers, subsequently, detection of the target mutant ssDNA amplicons was attempted by hybridization with Raman reporter-coded and allele-specific oligonucleotide-functionalized gold nanoparticles (SERS nanotags). The oligo encoding of the KRAS G12V mutant sequence could be identified by using a portable Raman spectrometer where the characteristic spectra of SERS nanotags indicate the presence of mutant targets. The Asy-PCR/SERS method showed high specificity and sensitivity for identifying as few as 0.1% mutant alleles of KRAS G12V mutation from non-target sequences. Using colorectal polyp biopsies, we demonstrated that Asy-PCR/SERS assay could distinguish KRAS G12V (c.35G > T) and KRAS G12D (c.35G > A) which occur at the same nucleotide location. As KRAS G12V is a driver oncogene in other cancers including lung, pancreatic, ovarian and endometrial cancers, the proposed assay shows great potential for application in additional tumor streams.

High-performance surface-enhanced Raman spectroscopy chip integrated with a micro-optical system for the rapid detection of creatinine in serum

To improve the sensitivity of disease biomarker detection, we proposed a high-performance surface-enhanced Raman spectroscopy (SERS) chip integrated with a micro-optical system (MOS). The MOS, which is based on the micro-reflecting cavity and the micro-lens, optimizes the optical matching characteristics of the SERS substrate and the Raman detection system, and greatly improves the SERS detection sensitivity by improving the collection efficiency of the Raman scattering signal. A uniform single layer of silver nanoparticles on a gold film was prepared as the SERS substrate using a liquid-liquid interface self-assembly method. The micro-reflecting cavity and micro-lens were prepared using micro-processing technology. The SERS chip was constructed based on the MOS and the Au film-based SERS substrate, and experimental results showed an EF of 1.46×10⁸, which is about 22.4 times higher than that of the Si-based SERS substrate. The chip was used for the detection of creatinine and the detection limit of creatinine in aqueous solution was 1 µM while the detection limit in serum was 5 µM. In addition, SERS testing was conducted on serum samples from normal people and patients with chronic renal impairment. Principal component analysis and linear discriminant analysis were used for modeling and identification, and the results showed a 90% accuracy of blind sample detection. These results demonstrate the value of this SERS chip for both research and practical applications in the fields of disease diagnosis and screening.

Enhancement of refractive index sensing for an infrared plasmonic metamaterial absorber with a nanogap

An infrared plasmonic metamaterial absorber with a nanogap was numerically and experimentally investigated as a refractive index sensor. We experimentally demonstrated large enhancements of both sensitivity (approximately 1091 nm/refractive index unit) and figure of merit (FOM*; approximately 273) owing to the nanogap formation in the metamaterial absorber to achieve perfect absorption (99%). The refractive index sensing platform was fabricated by producible nanoimprint lithography and isotropic dry etching processes to have a large area and low cost while providing a practical solution for high-performance plasmonic biosensors.

Biophotonics for diagnostic detection of extracellular vesicles

Extracellular Vesicles (EVs) are versatile carriers for biomarkers involved in the pathogenesis of multiple human disorders. Despite the increasing scientific and commercial interest in EV application in diagnostics, traditional biomolecular techniques usually require consistent sample amount, rely on operator-dependent and time- consuming procedures and cannot cope with the nano-size range of EVs, limiting both sensitivity and reproducibility of results. The application of biophotonics, i.e. light-based methods, for the diagnostic detection of EVs has brought to the development of innovative platforms with excellent sensitivity. In this review, we propose an overview of the most promising and emerging technologies used in the field of EV-related biomarker discovery. When tested on clinical samples, the reported biophotonic approaches in most cases have managed to discriminate between nanovesicles and contaminants, achieved much higher resolution compared to traditional procedures, and reached moderate to excellent diagnostic accuracy, thus demonstrating great potentialities for their clinical translation.

Separation of distinct exosome subpopulations: isolation and characterization approaches and their associated challenges

Exosomes are nano-sized extracellular vesicles that serve as a communications system between cells and have shown tremendous promise as liquid biopsy biomarkers in diagnostic, prognostic, and even therapeutic use in different human diseases. Due to the natural heterogeneity of exosomes, there is a need to separate exosomes into distinct biophysical and/or biochemical subpopulations to enable full interrogation of exosome biology and function prior to the possibility of clinical translation. Currently, there exists a multitude of different exosome isolation and characterization approaches which can, in limited capacity, separate exosomes based on biophysical and/or biochemical characteristics. While notable reviews in recent years have reviewed these approaches for bulk exosome sorting, we herein present a comprehensive overview of various conventional technologies and modern microfluidic and nanotechnological advancements towards isolation and characterization of exosome subpopulations. The benefits and limitations of these different technologies to improve their use for distinct exosome subpopulations in clinical practices are also discussed. Furthermore, an overview of the most commonly encountered technical and biological challenges for effective separation of exosome subpopulations is presented.

Using single-vesicle technologies to unravel the heterogeneity of extracellular vesicles

Extracellular vesicles (EVs) are heterogeneous lipid containers with a complex molecular cargo comprising several populations with unique roles in biological processes. These vesicles are closely associated with specific physiological features, which makes them invaluable in the detection and monitoring of various diseases. EVs play a key role in pathophysiological processes by actively triggering genetic or metabolic responses. However, the heterogeneity of their structure and composition hinders their application in medical diagnosis and therapies. This diversity makes it difficult to establish their exact physiological roles, and the functions and composition of different EV (sub)populations. Ensemble averaging approaches currently employed for EV characterization, such as western blotting or 'omics' technologies, tend to obscure rather than reveal these heterogeneities. Recent developments in single-vesicle analysis have made it possible to overcome these limitations and have facilitated the development of practical clinical applications. In this review, we discuss the benefits and challenges inherent to the current methods for the analysis of single vesicles and review the contribution of these approaches to the understanding of EV biology. We describe the contributions of these recent technological advances to the characterization and phenotyping of EVs, examination of the role of EVs in cell-to-cell communication pathways and the identification and validation of EVs as disease biomarkers. Finally, we discuss the potential of innovative single-vesicle imaging and analysis methodologies using microfluidic devices, which promise to deliver rapid and effective basic and practical applications for minimally invasive prognosis systems.

Surface-Enhanced Raman Scattering-Active Plasmonic Metal Nanoparticle-Persistent Luminescence Material Composite Films for Multiple Illegal Dye Detection

Uniform two-dimensional plasmonic nanoparticle (NP)-semiconductor composite films could retard the attenuation of electromagnetic evanescent wave and show intensive Raman activity for the multiplex monitoring of hazards in a practical food matrix. Here, an efficient Raman platform is developed by employing a plasmonic nanoparticle (NP)-persistent luminescence material (PLM) composite film. PLM show upconversion photoluminescence (UCPL) properties. The emitted photons are absorbed by plasmonic NPs, which further boost the surface plasmon resonance for the generation of high polarizability and induce strong electromagnetic strength for surface-enhanced Raman scattering (SERS) enhancement. A UCPL-assisted SERS-enhanced mechanism is proposed and verified. A plasmonic NP-PLM film with superior SERS activity and detection capability becomes an alternative candidate for the sensitive and multiple detection of illegal addition of dyes in a food matrix. The proposed UCPL-assisted SERS-enhanced mechanism provides promising future directions to this end to design a next-generation SERS-active plasmonic NP-PLM composite film for the specific detection in complex samples.

Updates on Clinical Use of Liquid Biopsy in Colorectal Cancer Screening, Diagnosis, Follow-Up, and Treatment Guidance

Colorectal cancer (CRC) is one of the most common cancers worldwide, being the third most diagnosed in the world and the second deadliest. Solid biopsy provides an essential guide for the clinical management of patients with colorectal cancer; however, this method presents several limitations, in particular invasiveness, and cannot be used repeatedly. Recently, clinical research directed toward the use of liquid biopsy, as an alternative tool to solid biopsy, showed significant promise in several CRC clinical applications, as (1) detect CRC patients at early stage, (2) make treatment decision, (3) monitor treatment response, (4) predict relapses and metastases, (5) unravel tumor heterogeneity, and (6) detect minimal residual disease. The purpose of this short review is to describe the concept, the characteristics, the genetic components, and the technologies used in liquid biopsy in the context of the management of colorectal cancer, and finally we reviewed gene alterations, recently described in the literature, as promising potential biomarkers that may be specifically used in liquid biopsy tests.

Nanotechnology in emerging liquid biopsy applications

Liquid biopsy is considered as the most attractive alternative to traditional tissue biopsies. The major advantages of this approach lie in the non-invasive procedure, the rapidness of sample collection and the potential for early cancer diagnosis and real-time monitoring of the disease and the treatment response. Nanotechnology has dynamically emerged in a wide range of applications in the field of liquid biopsy. The benefits of using nanomaterials for biosensing include high sensitivity and detectability, simplicity in many cases, rapid analysis, the low cost of the analysis and the potential for portability and personalized medicine. The present paper reports on the nanomaterial-based methods and biosensors that have been developed for liquid biopsy applications. Most of the nanomaterials used exhibit great analytical performance; moreover, extremely low limits of detection have been achieved for all studied targets. This review will provide scientists with a comprehensive overview of all the nanomaterials and techniques that have been developed for liquid biopsy applications. A comparison of the developed methods in terms of detectability, dynamic range, time-length of the analysis and multiplicity, is also provided.

Surface-Enhanced Raman Scattering (SERS) Spectroscopy for Sensing and Characterization of Exosomes in Cancer Diagnosis

Simple Summary

The distinct molecular and biological properties of exosomes, together with their abundance and stability, make them an ideal target in liquid biopsies for early diagnosis and disease monitoring. On the other hand, in recent years, nanomaterial-based optical biosensors have been extensively investigated as novel, rapid and sensitive tools for exosome detection and discrimination. The scope of this review is to summarize and coherently discussed the diverse applications, challenges and limitations of nanosensors based on surface-enhanced Raman spectroscopy (SERS) as the optosensing technique.

Abstract

Exosomes are emerging as one of the most intriguing cancer biomarkers in modern oncology for early cancer diagnosis, prognosis and treatment monitoring. Concurrently, several nanoplasmonic methods have been applied and developed to tackle the challenging task of enabling the rapid, sensitive, affordable analysis of exosomes. In this review, we specifically focus our attention on the application of plasmonic devices exploiting surface-enhanced Raman spectroscopy (SERS) as the optosensing technique for the structural interrogation and characterization of the heterogeneous nature of exosomes. We summarized the current state-of-art of this field while illustrating the main strategic approaches and discuss their advantages and limitations.

Liquid biopsy genotyping by a simple lateral flow strip assay with visual detection

Liquid biopsy, as a minimally invasive method that allows real-time monitoring of the tumor genome, represents a competing approach for cancer diagnosis, prognosis and therapy decision making. Liquid biopsy in cancer patients mainly includes analysis of circulating tumor cells (CTC) and cell-free circulating tumor DNA (ctDNA). ctDNA is the tumor-derived fraction of the cell-free DNA present in the blood. ctDNA is detected based on cancer-specific genomic aberrations (mainly mutations) and represents a challenging analyte due to high fragmentation and low concentration. Several methodologies have been developed for ctDNA analysis in cancer patients but many of these technologies are too time-intensive, complicated and expensive for implementation in diagnostic testing. Herein, we developed a novel lateral flow strip assay for mutational analysis of ctDNA in blood samples and visual detection that is based on gold nanoparticles as reporters. As a model, common single-point mutations of the KRAS gene, related to colorectal cancer (CRC), have been selected for method development. The proposed DNA biosensor has been successfully applied for the detection of three KRAS mutations (KRAS G12D/A/V), along with the wild-type KRAS gene in synthetic DNA targets, cancer cell lines and cfDNA from blood samples of healthy individuals and CRC patients. The main advantages of the proposed lateral flow assay are simplicity, rapid analysis time (∼10 min) and visual detection without the requirement of special instrumentation. The assay is also cost-effective with high detectability, specificity and reproducibility and has the potential to be used as a portable and universal device. In conclusion, the proposed assay offers a rapid diagnostic strip test for visual genotyping, as an alternative approach for liquid biopsy applications.

Interfacial interactions of SERS-active noble metal nanostructures with functional ligands for diagnostic analysis of protein cancer markers

Noble metal nanostructures with designed hot spots have been widely investigated as surface-enhanced Raman spectroscopy (SERS)-active substrates, particularly for selective and sensitive detection of protein cancer markers. For specific target recognition and efficient signal amplification, SERS probe design requires a choice of SERS-active nanostructures as well as their controlled functionalization with Raman dyes and target recognition entities such as antibodies. However, the chemical conjugation of antibodies and Raman dyes to SERS substrates has rarely been discussed to date, despite their substantial roles in detection schemes. The interfacial interactions of metal nanostructures with functional ligands during conjugation are known to be strongly influenced by the various chemical and physical properties of the ligands, such as size, molecular weight, surface charge, 3-dimensional structures, and hydrophilicity/hydrophobicity. In this review, we discuss recent developments in the design of SERS probes over the last 4 years, focusing on their conjugation chemistry for functionalization. A strong preference for covalent bonding is observed with Raman dyes having simpler molecular structures, whereas more complicated ones are non-covalently adsorbed. Antibodies are both covalently and non-covalently bonded to nanostructures, depending on their activity in the SERS probes. Considering that ligand conjugation is highly important for chemical stability, biocompatibility, and functionality of SERS probes, this review is expected to expand the understanding of their interfacial design, leading to SERS as one of the most promising spectroscopic analytical tools for the early detection of protein cancer markers.

Metal-Modified Montmorillonite as Plasmonic Microstructure for Direct Protein Detection

Thanks to its negative surface charge and high swelling behavior, montmorillonite (MMT) has been widely used to design hybrid materials for applications in metal ion adsorption, drug delivery, or antibacterial substrates. The changes in photophysical and photochemical properties observed when fluorophores interact with MMT make these hybrid materials attractive for designing novel optical sensors. Sensor technology is making huge strides forward, achieving high sensitivity and selectivity, but the fabrication of the sensing platform is often time-consuming and requires expensive chemicals and facilities. Here, we synthesized metal-modified MMT particles suitable for the bio-sensing of self-fluorescent biomolecules. The fluorescent enhancement achieved by combining clay minerals and plasmonic effect was exploited to improve the sensitivity of the fluorescence-based detection mechanism. As proof of concept, we showed that the signal of fluorescein isothiocyanate can be harvested by a factor of 60 using silver-modified MMT, while bovine serum albumin was successfully detected at 1.9 µg/mL. Furthermore, we demonstrated the versatility of the proposed hybrid materials by exploiting their plasmonic properties to develop liquid label-free detection systems. Our results on the signal enhancement achieved using metal-modified MMT will allow the development of highly sensitive, easily fabricated, and cost-efficient fluorescent- and plasmonic-based detection methods for biomolecules.

An efficient strategy for circulating tumor cell detection: surface-enhanced Raman spectroscopy

Circulating tumor cells (CTCs) are circulating cancer cells that shed from tumor tissue into blood vessels and circulate in the blood to invade other organs, which results in fatal metastases. The CTCs in human peripheral blood are the main cause of death in most cancer patients. The detection of CTCs is of great scientific significance and clinical application value for early diagnosis, rapid evaluation of the treatment effect, in vivo drug resistance testing, individualized treatment, tumor recurrence detection and survival time judgment, etc. The surface-enhanced Raman scattering (SERS) method possesses the features of remarkable detection sensitivity, a non-destructive nature, label-free detection, a quick spectrum response and a molecular fingerprint spectrum, which give it great potential in the detection field. In the past decade, SERS technology serving as a bioprobe has been increasingly applied to detect and analyze biological components due to its unique detection advantages. Here, we present an overview of SERS biosensing substrates and recent achievements in detecting CTCs using high-sensitivity SERS platforms, and provide a unique perspective on the design and application of high-performance SERS platforms for CTC detection, especially using non-metal materials.

On-tissue polysulfide visualization by surface-enhanced Raman spectroscopy benefits patients with ovarian cancer to predict post-operative chemosensitivity

Chemosensitivity to cisplatin derivatives varies among individual patients with intractable malignancies including ovarian cancer, while how to unlock the resistance remain unknown. Ovarian cancer tissues were collected the debulking surgery in discovery- (n = 135) and validation- (n = 47) cohorts, to be analyzed with high-throughput automated immunohistochemistry which identified cystathionine γ-lyase (CSE) as an independent marker distinguishing non-responders from responders to post-operative platinum-based chemotherapy. We aimed to identify CSE-derived metabolites responsible for chemoresistant mechanisms: gold-nanoparticle (AuN)-based surface-enhanced Raman spectroscopy (SERS) was used to enhance electromagnetic fields which enabled to visualize multiple sulfur-containing metabolites through detecting scattering light from Au-S vibration two-dimensionally. Clear cell carcinoma (CCC) who turned out less sensitive to cisplatin than serous adenocarcinoma was classified into two groups by the intensities of SERS intensities at 480 cm^-1; patients with greater intensities displayed the shorter overall survival after the debulking surgery. The SERS signals were eliminated by topically applied monobromobimane that breaks sulfane-sulfur bonds of polysulfides to result in formation of sulfodibimane which was detected at 580 cm^-1, manifesting the presence of polysulfides in cancer tissues. CCC-derived cancer cell lines in culture were resistant against cisplatin, but treatment with ambroxol, an expectorant degrading polysulfides, renders the cells CDDP-susceptible. Co-administration of ambroxol with cisplatin significantly suppressed growth of cancer xenografts in nude mice. Furthermore, polysulfides, but neither glutathione nor hypotaurine, attenuated cisplatin-induced disturbance of DNA supercoiling. Polysulfide detection by on-tissue SERS thus enables to predict prognosis of cisplatin-based chemotherapy. The current findings suggest polysulfide degradation as a stratagem unlocking cisplatin chemoresistance.

Template-Assisted Plasmonic Nanogap Shells for Highly Enhanced Detection of Cancer Biomarkers

We present a template-assisted method for synthesizing nanogap shell structures for biomolecular detections based on surface-enhanced Raman scattering. The interior nanogap-containing a silver shell structure, referred to as a silver nanogap shell (Ag NGS), was fabricated on silver nanoparticles (Ag NPs)-coated silica, by adsorbing small aromatic thiol molecules on the Ag NPs. The Ag NGSs showed a high enhancement factor and good signal uniformity, using 785-nm excitation. We performed in vitro immunoassays using a prostate-specific antigen as a model cancer biomarker with a detection limit of 2 pg/mL. To demonstrate the versatility of Ag NGS nanoprobes, extracellular duplex surface-enhanced Raman scattering (SERS) imaging was also performed to evaluate the co-expression of cancer biomarkers, human epidermal growth factor-2 (HER2) and epidermal growth factor receptor (EGFR), in a non-small cell lung cancer cell line (H522). Developing highly sensitive Ag NGS nanoprobes that enable multiplex biomolecular detection and imaging can open up new possibilities for point-of-care diagnostics and provide appropriate treatment options and prognosis.

Effect of Cetuximab-Conjugated Gold Nanoparticles on the Cytotoxicity and Phenotypic Evolution of Colorectal Cancer Cells

Epidermal growth factor receptor (EGFR) is estimated to be overexpressed in 60~80% of colorectal cancer (CRC), which is associated with a poor prognosis. Anti-EGFR targeted monoclonal antibodies (cetuximab and panitumumab) have played an important role in the treatment of metastatic CRC. However, the therapeutic response of anti-EGFR monoclonal antibodies is limited due to multiple resistance mechanisms. With the discovery of new functions for gold nanoparticles (AuNPs), we hypothesize that cetuximab-conjugated AuNPs (cetuximab-AuNPs) will not only improve the cytotoxicity for cancer cells, but also introduce expression change of the related biomarkers on cancer cell surface. In this contribution, we investigated the size-dependent cytotoxicity of cetuximab-AuNPs to CRC cell line (HT-29), while also monitored the expression of cell surface biomarkers in response to treatment with cetuximab and cetuximab-AuNPs. AuNPs with the size of 60 nm showed the highest impact for cell cytotoxicity, which was tested by cell counting kit-8 (CCK-8) assay. Three cell surface biomarkers including epithelial cell adhesion molecule (EpCAM), melanoma cell adhesion molecule (MCAM), and human epidermal growth factor receptor-3 (HER-3) were found to be expressed at higher heterogeneity when cetuximab was conjugated to AuNPs. Both surface-enhanced Raman scattering/spectroscopy (SERS) and flow cytometry demonstrated the correlation of cell surface biomarkers in response to the drug treatment. We thus believe this study provides powerful potential for drug-conjugated AuNPs to enhance cancer prognosis and therapy.

Self-Concentrated Surface-Enhanced Raman Scattering-Active Droplet Sensor with Three-Dimensional Hot Spots for Highly Sensitive Molecular Detection in Complex Liquid Environments

In this work, a surface-enhanced Raman scattering (SERS)-active droplet with three-dimensional (3D) hot spots prepared from a superhydrophobic SERS substrate, which is inspired by the nut wizard strategy, was developed for ultrasensitive detection in complex liquid environments. The SERS substrate was composed of silver-capped parylene C-coated carbon nanoparticles (Ag-PC@CNPs). Such a SERS substrate was prepared by candle-soot deposition to provide a porous carbon nanoparticle layer followed by deposition of a parylene C film to protect the CNPs and then sputtering of silver nanoparticles. Similar to a nut wizard, a droplet rolling on the Ag-PC@CNP-coated substrate picked up the Ag-PC@CNPs. In this way, a self-concentrated and extremely sensitive SERS-active droplet sensor with 3D hot spots was formed. The sensor did not require precise laser focusing and showed relatively high repeatability and much higher sensitivity than those of a corresponding SERS substrate with two-dimensional hot spots. The sensor also achieved high sensitivity and specificity in complex liquid environments; in addition, bovine serum albumin with a concentration as low as 1 pM can be achieved. Consequently, an extremely simple, flexible, and highly sensitive SERS detection technique applicable to liquid biopsy analysis is anticipated.

Large-Scale Flexible Surface-Enhanced Raman Scattering (SERS) Sensors with High Stability and Signal Homogeneity

Flexible surface-enhanced Raman scattering (SERS) sensors have attracted great attention as a portable and low-cost device for chemical and bio-detection. However, flexible SERS sensors tend to suffer low signal spatial homogeneity due to the uneven distribution of active plasmonic nanostructures (hot spots) and quick degradation of their sensitivity due to low adhesion of hot spots and flexible substrates during fast sampling. Herein, a large-area (20 × 20 cm²) polyimide (PI)-based SERS sensor is exploited for trace detection with high signal homogeneity and stability. The SERS sensor is constructed from PI through in situ growth of silver and gold core-shell nanoparticles (Ag@Au NPs) based on chemical reduction and galvanic replacement processes. Benefiting from the abundant carboxyl groups on the surface-cleaved PI, densely and uniformly distributed Ag@Au NPs are successfully prepared on the film under ambient conditions. The high Raman enhancement factor (EF) (up to 1.07 × 10⁷) and detection capability with low nanomolar (10^-9 M) detection limits are obtained for this flexible SERS sensor. The uniform Raman signals in the random region show good signal homogeneity with a low variation of 8.7%. Moreover, the flexible SERS sensor exhibited superior efficiency and durability after storage for 30 days even after 500 cycles of mechanical stimuli (bending or torsion). The residue of pesticide thiram (tetramethylthiuram disulfide, TMTD) has been rapidly traced by direct sampling from the apple surface, and a sensitivity of 10 ng/cm² for TMTD was achieved. These findings show that the PI-based SERS sensor is a very strong candidate for broad and simple utilization of flexible SERS for both laboratory and commercial applications in chemical and biomolecule detections.

Attomolar Sensing Based on Liquid Interface-Assisted Surface-Enhanced Raman Scattering in Microfluidic Chip by Femtosecond Laser Processing

Surface-enhanced Raman scattering (SERS) is a multidisciplinary trace analysis technique based on plasmonic effects. The development of SERS microfluidic chips has been exploited extensively in recent times impacting on applications in diverse fields. However, despite much progress, the excitation of label-free molecules is extremely challenging when analyte concentrations are lower than 1 nM because of the blinking SERS effect. In this paper, a novel analytical strategy which can achieve detection limits at an attomolar level is proposed. This performance improvement is due to the use of a glass microfluidic chip that features an analyte air-solution interface which forms on the SERS substrate in the microfluidic channel, whereby the analyte molecules aggregate locally at the interface during the measurement, hence the term liquid interface-assisted SERS (LI-SERS). The microfluidic chips are fabricated using hybrid femtosecond (fs) laser processing consisting of fs laser-assisted chemical etching, selective metallization, and metal surface nanostructuring. The novel LI-SERS technique can achieve an analytical enhancement factor of 1.5 × 10¹⁴, providing a detection limit below 10^-17 M (<10 aM). The mechanism for the extraordinary enhancement afforded by LI-SERS is attributed to Marangoni convection induced by the photothermal effect.

Multiplex detection of ctDNA mutations in plasma of colorectal cancer patients by PCR/SERS assay

Molecular diagnostic testing of KRAS and BRAF mutations has become critical in the management of colorectal cancer (CRC) patients. Some progress has been made in liquid biopsy detection of mutations in circulating tumor DNA (ctDNA), which is a fraction of circulating cell-free DNA (cfDNA), but slow analysis for DNA sequencing methods has limited rapid diagnostics. Other methods such as quantitative PCR and more recently, droplet digital PCR (ddPCR), have limitations in multiplexed capacity and the need for expensive specialized equipment. Hence, a robust, rapid and facile strategy is needed for detecting multiple ctDNA mutations to improve the management of CRC patients. To address this significant problem, herein, we propose a new application of multiplex PCR/SERS (surface-enhanced Raman scattering) assay for the detection of ctDNA in CRC, in a fast and non-invasive manner to diagnose and stratify patients for effective treatment.

Methods: To discriminate ctDNA mutations from wild-type cfDNA, allele-specific primers were designed for the amplification of three clinically important DNA point mutations in CRC including KRAS G12V, KRAS G13D and BRAF V600E. Surface-enhanced Raman scattering (SERS) nanotags were labelled with a short and specific sequence of oligonucleotide, which can hybridize with the corresponding PCR amplicons. The PCR/SERS assay was implemented by firstly amplifying the multiple mutations, followed by binding with multicolor SERS nanotags specific to each mutation, and subsequent enrichment with magnetic beads. The mutation status was evaluated using a portable Raman spectrometer where the fingerprint spectral peaks of the corresponding SERS nanotags indicate the presence of the mutant targets. The method was then applied to detect ctDNA from CRC patients under a blinded test, the results were further validated by ddPCR.

Results: The PCR/SERS strategy showed high specificity and sensitivity for genotyping CRC cell lines and plasma ctDNA, where as few as 0.1% mutant alleles could be detected from a background of abundant wild-type cfDNA. The blinded test using 9 samples from advanced CRC patients by PCR/SERS assay was validated with ddPCR and showed good consistency with pathology testing results.

Conclusions: With ddPCR-like sensitivity yet at the convenience of standard PCR, the proposed assay shows great potential in sensitive detection of multiple ctDNA mutations for clinical decision-making.

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

Profiling DNA mutation patterns by SERS fingerprinting for supervised cancer classification

Profiling DNA mutation patterns for cancer classification plays an essential role in precision and personalized medicine. Conventional PCR-based mutation assay is limited by the extensive labour on target amplification. We herein create an amplification-free surface enhanced Raman spectroscopy (SERS) biochip which enables direct and simultaneous identification of multiple point mutations in tumor cells. Without pre-amplifying the target sequences, the SERS assay reads out the presence of cellular mutations through the interpretation of Raman fingerprints. The SERS sensor is integrated into a microfluidic chip, achieving one-step multiplex analysis within 40 min. Importantly, by combining SERS spectra encoding technique with supervised learning algorithm, a panel of nucleotide mixtures can be well distinguished according to their mutation profiles. We initially demonstrate an excellent levels of classification in samples from colorectal cancer and melanoma cell lines. For final clinical validation, the system performance is verified by classifying cancer patient samples, which shows an accuracy above 90%. Due to the simplicity and rapidness, the SERS biosensor is expected to become a promising tool for clinical point-of-care diagnosis towards precision medicine.

Surface-Enhanced Raman Spectroscopy for Cancer Immunotherapy Applications: Opportunities, Challenges, and Current Progress in Nanomaterial Strategies

Cancer immunotherapy encompasses a variety of approaches which target or use a patient's immune system components to eliminate cancer. Notably, the current use of immune checkpoint inhibitors to target immune checkpoint receptors such as CTLA-4 or PD-1 has led to remarkable treatment responses in a variety of cancers. To predict cancer patients' immunotherapy responses effectively and efficiently, multiplexed immunoassays have been shown to be advantageous in sensing multiple immunomarkers of the tumor microenvironment simultaneously for patient stratification. Surface-enhanced Raman spectroscopy (SERS) is well-regarded for its capabilities in multiplexed bioassays and has been increasingly demonstrated in cancer immunotherapy applications in recent years. This review focuses on SERS-active nanomaterials in the modern literature which have shown promise for enabling cancer patient-tailored immunotherapies, including multiplexed in vitro and in vivo immunomarker sensing and imaging, as well as immunotherapy drug screening and delivery.

Quantification of cyclic DNA polymerization with lanthanide coordination nanomaterials for liquid biopsy

Quantification of circulating tumor DNA (ctDNA) is of great importance in liquid biopsy but difficult due to its low amount in bodily fluids. To meet this high demand, a novel method for ctDNA detection is established by quantifying cyclic DNA polymerization using lanthanide coordination polymers (Ln-CPs). Relying on the coordination between the pyrophosphate ion (PPi) and trivalent cerium ion (Ce3+), organic ligand-free PPi-Ce coordination polymer networks (PPi-Ce CPNs) with enhanced fluorescence are prepared for the first time. By surveying the optical properties of PPi-Ce CPNs, it is found that PPi regulates electric-dipole transition of Ce3+ to the lowest excited state, thus facilitating the emission of fluorescence. Therefore, fluorescence enhancement of PPi-Ce CPNs originates from the ligand field effect rather than the normal antenna effect. Moreover, a new strategy to quantify DNA polymerization is developed based on PPi-Ce CPNs. By introducing multifold cyclic DNA polymerization, a small amount of ctDNA triggers the exponential generation of PPi to form plenty of PPi-Ce CPNs. Accordingly, a biosensor is constructed for sensitive ctDNA detection by measuring the intense fluorescence of PPi-Ce CPNs. The biosensor is capable of sensing ctDNA at the sub-femtomolar level, which is far better than the analytical performances of commercial dyes. Besides, the analytical method is able to detect single nucleotide polymorphism and determine ctDNA in real samples. Considering that DNA polymerization is widely used in bio-recognition, bio-assembly and biomineralization, the work provides a versatile quantitative strategy of making relevant processes precise and controllable.

MiRNA-Based Inspired Approach in Diagnosis of Prostate Cancer

Prostate cancer is one of the most encountered cancer diseases in men worldwide and in consequence it requires the improvement of therapeutic strategies. For the clinical diagnosis, the standard approach is represented by solid biopsy. From a surgical point of view, this technique represents an invasive procedure that may imply several postoperative complications. To overcome these impediments, many trends are focusing on developing liquid biopsy assays and on implementing them in clinical practice. Liquid samples (blood, urine) are rich in analytes, especially in transcriptomic information provided by genetic markers. Additionally, molecular characterization regarding microRNAs content reveals outstanding prospects in understanding cancer progression mechanisms. Moreover, these analytes have great potential for prostate cancer early detection, more accurate prostate cancer staging and also for decision making respecting therapy schemes. However, there are still questionable topics and more research is needed to standardize liquid biopsy-based techniques.

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.